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, Available online ,
doi: 10.3878/j.issn.1006-9895.2106.21061
Abstract:
The diurnal variation of cloud macro parameters over the Tibetan Plateau is affected by the combined effects of large-scale circulation, local solar radiation and surface processes, while it also remarkably affects the radiation budget and transmission and the distribution of sensible and latent heat. Due to the lack of continuous quantitative observation, the understanding of the diurnal variation characteristics of the cloud macro parameters in various weather systems is still quite insufficient. Ka-band cloud radar of atmospheric profiling synthetic observation system (APSOS) is the first radar to realize long-term cloud observation in the Tibetan Plateau. In this paper, using statistical and Fast Fourier Transform methods, the data of the APSOS Ka-band cloud radar in 2019 are used to study the time- and frequency-domain diurnal variation characteristics of cloud frequency, single-layer cloud top height, cloud bottom height, and cloud thickness under the influence of westerly trough, shear line, and vortex system. The major conclusions are as follows: (1) The daily mean cloud frequency is 56.9% for the westerly trough system, 50.8% for the shear line system, and 73% for the vortex system. (2) Although the origins of the westerly trough and shear line system are different, the diurnal variation trend and main harmonic period of the cloud macro parameters of the two systems are similar: the diurnal variation trend is sinusoidal; the minimum value appears before sunrise, and the maximum value appears before sunset. The main harmonics of cloud frequency are diurnal (24 h) and semidiurnal (12 h), and the diurnal harmonics have the largest amplitude among the main harmonics of cloud top height, bottom height, and thickness. (3) The diurnal variation characteristics of cloud macro parameters in a vortex system are different from that in the first two systems. The diurnal variation of cloud parameters in the vortex system is multipeak type. Although the harmonic amplitude of the diurnal period is the largest among the main harmonics of the cloud frequency, single-layer cloud top height, and cloud bottom height, the spectrum distribution is discrete, and the maximum harmonic period of cloud thickness amplitude is 4.8 h. (4) The statistical regression equations of the diurnal variation of the cloud frequency, single-layer cloud top height, cloud bottom height, and cloud thickness are provided.
The diurnal variation of cloud macro parameters over the Tibetan Plateau is affected by the combined effects of large-scale circulation, local solar radiation and surface processes, while it also remarkably affects the radiation budget and transmission and the distribution of sensible and latent heat. Due to the lack of continuous quantitative observation, the understanding of the diurnal variation characteristics of the cloud macro parameters in various weather systems is still quite insufficient. Ka-band cloud radar of atmospheric profiling synthetic observation system (APSOS) is the first radar to realize long-term cloud observation in the Tibetan Plateau. In this paper, using statistical and Fast Fourier Transform methods, the data of the APSOS Ka-band cloud radar in 2019 are used to study the time- and frequency-domain diurnal variation characteristics of cloud frequency, single-layer cloud top height, cloud bottom height, and cloud thickness under the influence of westerly trough, shear line, and vortex system. The major conclusions are as follows: (1) The daily mean cloud frequency is 56.9% for the westerly trough system, 50.8% for the shear line system, and 73% for the vortex system. (2) Although the origins of the westerly trough and shear line system are different, the diurnal variation trend and main harmonic period of the cloud macro parameters of the two systems are similar: the diurnal variation trend is sinusoidal; the minimum value appears before sunrise, and the maximum value appears before sunset. The main harmonics of cloud frequency are diurnal (24 h) and semidiurnal (12 h), and the diurnal harmonics have the largest amplitude among the main harmonics of cloud top height, bottom height, and thickness. (3) The diurnal variation characteristics of cloud macro parameters in a vortex system are different from that in the first two systems. The diurnal variation of cloud parameters in the vortex system is multipeak type. Although the harmonic amplitude of the diurnal period is the largest among the main harmonics of the cloud frequency, single-layer cloud top height, and cloud bottom height, the spectrum distribution is discrete, and the maximum harmonic period of cloud thickness amplitude is 4.8 h. (4) The statistical regression equations of the diurnal variation of the cloud frequency, single-layer cloud top height, cloud bottom height, and cloud thickness are provided.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2107.21043
Abstract:
Based on the ground-based microrain radar and cloud radar, combined with aircraft observation, stratiform precipitation with embedded convection is analyzed to accurately study the cloud precipitation’s microphysical structure. Results show that: (1) The selected precipitation process is divided into stratified cloud and convective cloud. Above the zero-degree layer, especially at the height of 5–6 km, the Doppler velocity and the spectrum width of convective precipitation are greater than those of stratiform cloud precipitation. This indicates that the vertical wind of the environment and the size range of the particle occurring in convective precipitation are greater than those of stratiform precipitation. (2) At the period of convective precipitation, there is a “V” glyph gap caused by the attenuation in the radar reflectivity of the cloud and microrain radars in the time and height profiles. The attenuation of the cloud radar is greater than that of the microrain radar. The higher the height, the greater is the attenuation. (3) At the period of stratiform precipitation, near the bright band, the leap increase height of the radar reflectivity factor is 80 m higher than that of the Doppler velocity, and the leap increase height of the Doppler velocity is 20 m higher than that of the spectral width. (4) The precipitation mechanism near the 0°C layer is complex. When the negative temperature is close to 0°C, the particle morphology includes radiated dendritic ice crystals, acicular ice crystals, and cloud droplets. The Doppler velocity and the spectral width of convective cloud precipitation are greater than those of stratiform precipitation above the 0°C layer, especially at altitudes of 5 and 6 km. The vertical airflow and the scale range of small and large particles in convective precipitation are greater than those of stratiform cloud precipitation.
Based on the ground-based microrain radar and cloud radar, combined with aircraft observation, stratiform precipitation with embedded convection is analyzed to accurately study the cloud precipitation’s microphysical structure. Results show that: (1) The selected precipitation process is divided into stratified cloud and convective cloud. Above the zero-degree layer, especially at the height of 5–6 km, the Doppler velocity and the spectrum width of convective precipitation are greater than those of stratiform cloud precipitation. This indicates that the vertical wind of the environment and the size range of the particle occurring in convective precipitation are greater than those of stratiform precipitation. (2) At the period of convective precipitation, there is a “V” glyph gap caused by the attenuation in the radar reflectivity of the cloud and microrain radars in the time and height profiles. The attenuation of the cloud radar is greater than that of the microrain radar. The higher the height, the greater is the attenuation. (3) At the period of stratiform precipitation, near the bright band, the leap increase height of the radar reflectivity factor is 80 m higher than that of the Doppler velocity, and the leap increase height of the Doppler velocity is 20 m higher than that of the spectral width. (4) The precipitation mechanism near the 0°C layer is complex. When the negative temperature is close to 0°C, the particle morphology includes radiated dendritic ice crystals, acicular ice crystals, and cloud droplets. The Doppler velocity and the spectral width of convective cloud precipitation are greater than those of stratiform precipitation above the 0°C layer, especially at altitudes of 5 and 6 km. The vertical airflow and the scale range of small and large particles in convective precipitation are greater than those of stratiform cloud precipitation.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2107.20222
Abstract:
Many assimilated observations can effectively improve the results of a model forecast. However, there are significant differences in the effects of various observations on the forecast. It is one of the most challenging diagnostics in numerical models to reasonably evaluate the observation contribution to the forecast. In this paper, the weather research and forecasting model’s data assimilation (WRFDA) and forecast sensitivity to observation (FSO) system was constructed in WRFDA by the method of adjoint-based FSO. Based on wind profile radar (WPR) and ground-based microwave radiometer (MWR) data obtained by the mega city project in Beijing in September 2019, the experiments on the impact of observations on the 12 h forecast of the WRF model are carried out using the WRFDA-FSO system. The contribution of wind, temperature, and humidity observations to the forecast is analyzed. The results show the following: (1) In general, the assimilated observations (MWR, WPR, Sound, Synop, and Geoamv) reduce the 12 h forecast error of the WRF model and make a positive contribution to the forecast. Among these, MWR observations have the greatest impact on the forecast, and the improvement of WPR observations on the forecast is better than that of wind field observations of sound. (2) Among the U and V observations of WPR and temperature and specific humidity observations of MWR, the positive contribution value of V observations and temperature observations to the forecast is higher, and the effect of improving the forecast is better. (3) The WPR and MWR observations, at most levels, reduce the forecast error and are a positive contribution to the forecast. The positive contribution of temperature observations is mainly below 800 hPa near the ground.
Many assimilated observations can effectively improve the results of a model forecast. However, there are significant differences in the effects of various observations on the forecast. It is one of the most challenging diagnostics in numerical models to reasonably evaluate the observation contribution to the forecast. In this paper, the weather research and forecasting model’s data assimilation (WRFDA) and forecast sensitivity to observation (FSO) system was constructed in WRFDA by the method of adjoint-based FSO. Based on wind profile radar (WPR) and ground-based microwave radiometer (MWR) data obtained by the mega city project in Beijing in September 2019, the experiments on the impact of observations on the 12 h forecast of the WRF model are carried out using the WRFDA-FSO system. The contribution of wind, temperature, and humidity observations to the forecast is analyzed. The results show the following: (1) In general, the assimilated observations (MWR, WPR, Sound, Synop, and Geoamv) reduce the 12 h forecast error of the WRF model and make a positive contribution to the forecast. Among these, MWR observations have the greatest impact on the forecast, and the improvement of WPR observations on the forecast is better than that of wind field observations of sound. (2) Among the U and V observations of WPR and temperature and specific humidity observations of MWR, the positive contribution value of V observations and temperature observations to the forecast is higher, and the effect of improving the forecast is better. (3) The WPR and MWR observations, at most levels, reduce the forecast error and are a positive contribution to the forecast. The positive contribution of temperature observations is mainly below 800 hPa near the ground.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2104.20225
Abstract:
In recent years, deep learning models have been increasingly used in solving nowcasting problems that largely affect disaster prevention and mitigation. In this study, we take nowcasting as a spatio-temporal sequence prediction task and use the radar reflectivity factor as the test object. We use the two-stream attention generative adversarial network (TAGAN) deep learning model based on the Generative Adversarial Network frame to predict the radar echo image of the future 1 h and compare it with the Rover optical flow method and the 3D U-Net model based on the convolutional neural network. The radar echo data set of the 2018 Global Weather AI Challenge is selected for training and testing. The test results show that the TAGAN model has advances by multiple scores, including hit rate, false alarm rate, critical success index, and correlation coefficient. The TAGAN model performs well in these test scores and increases with the prediction time compared to the traditional optical flow method and the comparative deep learning model. Moreover, compared with that of the traditional optical flow model, the improvement effect of the TAGAN model is more significant. The results may shed some light on the expansion and improvement of the application of deep learning models in near-weather forecasting.
In recent years, deep learning models have been increasingly used in solving nowcasting problems that largely affect disaster prevention and mitigation. In this study, we take nowcasting as a spatio-temporal sequence prediction task and use the radar reflectivity factor as the test object. We use the two-stream attention generative adversarial network (TAGAN) deep learning model based on the Generative Adversarial Network frame to predict the radar echo image of the future 1 h and compare it with the Rover optical flow method and the 3D U-Net model based on the convolutional neural network. The radar echo data set of the 2018 Global Weather AI Challenge is selected for training and testing. The test results show that the TAGAN model has advances by multiple scores, including hit rate, false alarm rate, critical success index, and correlation coefficient. The TAGAN model performs well in these test scores and increases with the prediction time compared to the traditional optical flow method and the comparative deep learning model. Moreover, compared with that of the traditional optical flow model, the improvement effect of the TAGAN model is more significant. The results may shed some light on the expansion and improvement of the application of deep learning models in near-weather forecasting.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2109.21003
Abstract:
We analyzed the climatic characteristics of early and late years of spring soaking rain (SSR) in Northeast China (NEC) and the relationship with sea surface temperature (SST) especially the tropical Indian Ocean SST forcing from the interannual time scale on the basis of the daily precipitation data from 1961 to 2019 at stations in NEC, monthly mean data of the National Centers for Environmental Prediction/ National Center for Atmospheric Research (NCEP/NCAR) reanalysis, sea surface temperature (SST) data reconstructed using NOAA, and outgoing longwave radiation (OLR) data using statistical diagnostic methods such as causal analysis, correlation analysis and regression analysis. Results showed that the onset date of SSR and April precipitation were considerably consistent. The onset date of typical SSR was concentrated in mid–late April during the early years (1964, 1968, 1969, 1979, 1983, 1988, 1990, 1991, 1999, 2002, 2005, 2010, 2013, 2015, 2016) and in mid–late May during late years (1965, 1970, 1971, 1972, 1985, 1986, 1989, 1993, 1994, 1997, 2001, 2003, 2006, 2014, 2017, 2019). If 500-hPa geopotential height fields over Northeast Asia in April showed a “− +” anomalous circulation distribution from west to east with southerly winds and cyclonic circulation dominating in Northeast Asia, which were conducive to water vapor transport, SSR started early, and vice versa. The warm sea surface temperature anomaly (SSTA) in the tropical Indian Ocean during February–March was one of the important sources of stable influence in the early years of the SSR in NEC. The possible impact mechanism was that the Indian Ocean Basin warming (IOBW) in a positive phase was favorable to the anomalous anticyclone in Northwest Pacific during April and the 500-hPa atmospheric circulation anomaly over Northeast Asia was similar to that of the early years of SSR. The NEC was situated in the right of the 200-hPa westerly jet stream exit area with an enhanced vertical upward motion, resulting in increased precipitation.
We analyzed the climatic characteristics of early and late years of spring soaking rain (SSR) in Northeast China (NEC) and the relationship with sea surface temperature (SST) especially the tropical Indian Ocean SST forcing from the interannual time scale on the basis of the daily precipitation data from 1961 to 2019 at stations in NEC, monthly mean data of the National Centers for Environmental Prediction/ National Center for Atmospheric Research (NCEP/NCAR) reanalysis, sea surface temperature (SST) data reconstructed using NOAA, and outgoing longwave radiation (OLR) data using statistical diagnostic methods such as causal analysis, correlation analysis and regression analysis. Results showed that the onset date of SSR and April precipitation were considerably consistent. The onset date of typical SSR was concentrated in mid–late April during the early years (1964, 1968, 1969, 1979, 1983, 1988, 1990, 1991, 1999, 2002, 2005, 2010, 2013, 2015, 2016) and in mid–late May during late years (1965, 1970, 1971, 1972, 1985, 1986, 1989, 1993, 1994, 1997, 2001, 2003, 2006, 2014, 2017, 2019). If 500-hPa geopotential height fields over Northeast Asia in April showed a “− +” anomalous circulation distribution from west to east with southerly winds and cyclonic circulation dominating in Northeast Asia, which were conducive to water vapor transport, SSR started early, and vice versa. The warm sea surface temperature anomaly (SSTA) in the tropical Indian Ocean during February–March was one of the important sources of stable influence in the early years of the SSR in NEC. The possible impact mechanism was that the Indian Ocean Basin warming (IOBW) in a positive phase was favorable to the anomalous anticyclone in Northwest Pacific during April and the 500-hPa atmospheric circulation anomaly over Northeast Asia was similar to that of the early years of SSR. The NEC was situated in the right of the 200-hPa westerly jet stream exit area with an enhanced vertical upward motion, resulting in increased precipitation.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2105.21062
Abstract:
This paper uses the coupling Noah/Single-layer Urban Canopy scheme coupled with WRF (V3.9.1) model is used as a Control experiment to investigate the effects of land-use type (Md04 experiment), land surface process (NoUCM experiment), and lake (Nolake experiment) on the intensity of urban heat island, and the horizontal and vertical spatial distribution characteristics of urban meteorological elements in Kunming. The following are the main findings: (1) In all four experiments, the average daily variation trend of urban heat island intensity is almost similar. The urban heat island (UHI) intensity is low during the daytime and high at night, peaking at around 2000 BJT (Beijing time). The average daily maximum difference for Control-NoUCM (Nolake) is −0.79°C (+1.07°C). (2) The difference of the sensible heat (latent heat) flux is +46.18 (−79.71) W m−2 based on the energy balance equation analysis of the Control-Md04 experiment, and the release of latent heat flux is greater than the absolute value of the sensible heat flux. In the Control-NoUCM experiment, the sensible heat (latent heat) flux difference is −40.88 (+29.60) W m−2. The NoUCM experiment does not take into account the heat storage and shielding of geometric buildings. The land surface absorbs the majority of solar radiation, resulting in a large absolute value of the sensible heat flux. (3) The boundary layer height reaches its maximum (minimum) value at 1500 (0700) BJT in all four experiments. The height of the urban boundary layer decreased by approximately 103 m (32 m) in NoUCM (Nolake), while it increased by approximately 102 m in Md04 experiment. (4) The numerical simulation results of the influence of the lake (Dianchi lake) on the circulation of urban heat islands show that the vertical movement over the lake is weak, but the horizontal lake-land breeze is strong. The breeze’s circulation benefits from the transportation of water vapor to the city center, which increases the humidity of dry air and enlarges the water vapor content. Furthermore, it increases the release of latent heat flux and reduces the sensible heat flux and the temperature gradient.
This paper uses the coupling Noah/Single-layer Urban Canopy scheme coupled with WRF (V3.9.1) model is used as a Control experiment to investigate the effects of land-use type (Md04 experiment), land surface process (NoUCM experiment), and lake (Nolake experiment) on the intensity of urban heat island, and the horizontal and vertical spatial distribution characteristics of urban meteorological elements in Kunming. The following are the main findings: (1) In all four experiments, the average daily variation trend of urban heat island intensity is almost similar. The urban heat island (UHI) intensity is low during the daytime and high at night, peaking at around 2000 BJT (Beijing time). The average daily maximum difference for Control-NoUCM (Nolake) is −0.79°C (+1.07°C). (2) The difference of the sensible heat (latent heat) flux is +46.18 (−79.71) W m−2 based on the energy balance equation analysis of the Control-Md04 experiment, and the release of latent heat flux is greater than the absolute value of the sensible heat flux. In the Control-NoUCM experiment, the sensible heat (latent heat) flux difference is −40.88 (+29.60) W m−2. The NoUCM experiment does not take into account the heat storage and shielding of geometric buildings. The land surface absorbs the majority of solar radiation, resulting in a large absolute value of the sensible heat flux. (3) The boundary layer height reaches its maximum (minimum) value at 1500 (0700) BJT in all four experiments. The height of the urban boundary layer decreased by approximately 103 m (32 m) in NoUCM (Nolake), while it increased by approximately 102 m in Md04 experiment. (4) The numerical simulation results of the influence of the lake (Dianchi lake) on the circulation of urban heat islands show that the vertical movement over the lake is weak, but the horizontal lake-land breeze is strong. The breeze’s circulation benefits from the transportation of water vapor to the city center, which increases the humidity of dry air and enlarges the water vapor content. Furthermore, it increases the release of latent heat flux and reduces the sensible heat flux and the temperature gradient.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2110.21078
Abstract:
This study sets up a long-term (2013–2017) dynamically and thermodynamically consistent atmospheric dataset over the Tibetan Plateau-Naqu analysis region that is derived by a constrained variational objective analysis with ground-based, sounding, and satellite measurements as well as ERA-Interim reanalysis data. Annual evolutions of atmospheric basic environments, cloud precipitation, and large-scale dynamic and thermal structures in the Naqu analysis region are analyzed using averaged results from the five-year dataset. Results show that: (1) The seasonal variation of the wind speed above 350 hPa is significant with a maximum (＞50 m s−1) from November to February in the next year. The vertical variation of the wind speed is the weakest, while that of the temperature is the strongest from July to August. The high-humidity area is located at 350–550 hPa in summer and autumn but at 300–400 hPa in winter and spring. (2) There is rich precipitation in the analysis region from June to early July. The 300–400 hPa layer (as the junction of atmospheric ascending and descending motion) is the cloud concentration area in spring, autumn, and winter. However, the enhanced atmospheric ascending convection and water vapor in summer lead to an increase of high clouds and total clouds and a decrease of medium and low clouds. (3) The surface latent heat flux and the total air-column latent heat are the strongest, whereas the air-column net radiative cooling is the weakest in summer. The strong surface sensible heating in the plateau results in the horizontal warm advection below 500 hPa, while the strong westerly and radiative cooling cause the cold advection above 500 hPa. In addition, the analysis region is characterized by dry advection in the whole year. However, there is a weak moist advection in summer. (4) The apparent heat source Q1 has obvious vertical stratification characteristics, i.e., showing diabatic cooling below 500 hPa and diabatic heating in 300–500 hPa and 100–150 hPa in the whole year. Meanwhile, the 150–300 hPa layer has diabatic cooling in the dry seasons (winter and spring) and diabatic heating in the wet seasons (from the end of spring to autumn). In summer, the entire air column is almost dominated by the diabatic heating because of the enhanced ascending motion, net latent heating, transport of sensible heat by rising turbulence, and existence of high clouds.
This study sets up a long-term (2013–2017) dynamically and thermodynamically consistent atmospheric dataset over the Tibetan Plateau-Naqu analysis region that is derived by a constrained variational objective analysis with ground-based, sounding, and satellite measurements as well as ERA-Interim reanalysis data. Annual evolutions of atmospheric basic environments, cloud precipitation, and large-scale dynamic and thermal structures in the Naqu analysis region are analyzed using averaged results from the five-year dataset. Results show that: (1) The seasonal variation of the wind speed above 350 hPa is significant with a maximum (＞50 m s−1) from November to February in the next year. The vertical variation of the wind speed is the weakest, while that of the temperature is the strongest from July to August. The high-humidity area is located at 350–550 hPa in summer and autumn but at 300–400 hPa in winter and spring. (2) There is rich precipitation in the analysis region from June to early July. The 300–400 hPa layer (as the junction of atmospheric ascending and descending motion) is the cloud concentration area in spring, autumn, and winter. However, the enhanced atmospheric ascending convection and water vapor in summer lead to an increase of high clouds and total clouds and a decrease of medium and low clouds. (3) The surface latent heat flux and the total air-column latent heat are the strongest, whereas the air-column net radiative cooling is the weakest in summer. The strong surface sensible heating in the plateau results in the horizontal warm advection below 500 hPa, while the strong westerly and radiative cooling cause the cold advection above 500 hPa. In addition, the analysis region is characterized by dry advection in the whole year. However, there is a weak moist advection in summer. (4) The apparent heat source Q1 has obvious vertical stratification characteristics, i.e., showing diabatic cooling below 500 hPa and diabatic heating in 300–500 hPa and 100–150 hPa in the whole year. Meanwhile, the 150–300 hPa layer has diabatic cooling in the dry seasons (winter and spring) and diabatic heating in the wet seasons (from the end of spring to autumn). In summer, the entire air column is almost dominated by the diabatic heating because of the enhanced ascending motion, net latent heating, transport of sensible heat by rising turbulence, and existence of high clouds.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2107.21012
Abstract:
This study explores the characteristics of interannual and interdecadal air–sea interactions related to the Pacific Decadal Oscillation (PDO) over the different regions of the North Pacific based on the relationship between turbulent heat flux and sea surface temperature (SST) anomalies during 1958–2018. The results show that the atmosphere directly drives SST anomalies over the Kuroshio–Oyashio Extension and the SST anomalies force atmospheric circulation over the equatorial central and eastern Pacific on the interannual scale. On the interdecadal scale, SST anomalies are mainly driven via atmospheric circulation over the north center of PDO. However, the ocean is very important in forming SST anomalies off the California coast. Further analysis shows that the area off the California coast is one of the key areas of quasi-12-year oscillation in the North Pacific. The period is similar to the decadal oscillation of PDO. The anticyclone (cyclone) circulation off the California coast may be forced via the cold (warm) SST anomalies off the California coast. The other two important parts in the quasi-12-year oscillation in the North Pacific are the upwelling of the equatorial central Pacific and meridional wind stress anomalies in the subtropical eastern North Pacific.
This study explores the characteristics of interannual and interdecadal air–sea interactions related to the Pacific Decadal Oscillation (PDO) over the different regions of the North Pacific based on the relationship between turbulent heat flux and sea surface temperature (SST) anomalies during 1958–2018. The results show that the atmosphere directly drives SST anomalies over the Kuroshio–Oyashio Extension and the SST anomalies force atmospheric circulation over the equatorial central and eastern Pacific on the interannual scale. On the interdecadal scale, SST anomalies are mainly driven via atmospheric circulation over the north center of PDO. However, the ocean is very important in forming SST anomalies off the California coast. Further analysis shows that the area off the California coast is one of the key areas of quasi-12-year oscillation in the North Pacific. The period is similar to the decadal oscillation of PDO. The anticyclone (cyclone) circulation off the California coast may be forced via the cold (warm) SST anomalies off the California coast. The other two important parts in the quasi-12-year oscillation in the North Pacific are the upwelling of the equatorial central Pacific and meridional wind stress anomalies in the subtropical eastern North Pacific.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2204.21260
Abstract:
Tibetan Plateau (TP) is regarded as the “Chinese Water Tower.” Interaction between the westerly and monsoon flows around the TP has an important impact on the Asian climate. Based on the atmospheric reanalysis dataset during 1981–2020, we extracted the coupling modes of the seasonal cycle component of westerly wind and monsoon flow over the TP via the empirical orthogonal function (EOF) method, and discussed their seasonal variation characteristics. The first mode accounts for 78.39% of the total variances, mainly reflecting the seasonal cycle characteristics of the East Asian monsoon, South Asian monsoon, and midlatitude westerly wind, as well as their interannual variation in each season. In summers, easterly winds prevail on the TP and the southern side of TP at the upper troposphere, ranging from 5° to 35°N. Simultaneously, the lower troposphere is characterized by a typical cyclonic monsoon circulation around the TP, and the tropical and subtropical areas are controlled by the southwest monsoon. Notably, the circulation structure is opposite in the winter. The transit timing of this mode from winter (summer) to summer (winter) is consistent with the onset (ending) of East Asian and South Asian summer monsoon. On the interannual timescale, the enhancement of the coupling mode is correlated with the intensity of East Asian and South Asian monsoons, as well as the northward movement of westerly in each season. For a weak coupling mode, the monsoon and westerly display opposite characteristics. El Niño–Southern Oscillation is the key external force affecting the interannual variation of the westerly monsoon coupling mode. Its impact is strengthened in summer, autumn, and the following summer, while weakened in winter and the following spring of the La Niña event. The second coupling mode of westerly monsoon is characterized by the coordinated variation of easterly wind over the TP and westerly wind in the south of the TP in the upper troposphere, and the southwesterly in the South Asian monsoon region and anticyclone in the Northwest Pacific at the lower troposphere. The variance contribution rate of this mode is 4.68%, showing the interannual variation with a significant long-term weakening trend, especially in winter.
Tibetan Plateau (TP) is regarded as the “Chinese Water Tower.” Interaction between the westerly and monsoon flows around the TP has an important impact on the Asian climate. Based on the atmospheric reanalysis dataset during 1981–2020, we extracted the coupling modes of the seasonal cycle component of westerly wind and monsoon flow over the TP via the empirical orthogonal function (EOF) method, and discussed their seasonal variation characteristics. The first mode accounts for 78.39% of the total variances, mainly reflecting the seasonal cycle characteristics of the East Asian monsoon, South Asian monsoon, and midlatitude westerly wind, as well as their interannual variation in each season. In summers, easterly winds prevail on the TP and the southern side of TP at the upper troposphere, ranging from 5° to 35°N. Simultaneously, the lower troposphere is characterized by a typical cyclonic monsoon circulation around the TP, and the tropical and subtropical areas are controlled by the southwest monsoon. Notably, the circulation structure is opposite in the winter. The transit timing of this mode from winter (summer) to summer (winter) is consistent with the onset (ending) of East Asian and South Asian summer monsoon. On the interannual timescale, the enhancement of the coupling mode is correlated with the intensity of East Asian and South Asian monsoons, as well as the northward movement of westerly in each season. For a weak coupling mode, the monsoon and westerly display opposite characteristics. El Niño–Southern Oscillation is the key external force affecting the interannual variation of the westerly monsoon coupling mode. Its impact is strengthened in summer, autumn, and the following summer, while weakened in winter and the following spring of the La Niña event. The second coupling mode of westerly monsoon is characterized by the coordinated variation of easterly wind over the TP and westerly wind in the south of the TP in the upper troposphere, and the southwesterly in the South Asian monsoon region and anticyclone in the Northwest Pacific at the lower troposphere. The variance contribution rate of this mode is 4.68%, showing the interannual variation with a significant long-term weakening trend, especially in winter.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2108.21052
Abstract:
Combined disaster events refer to the combination of several simultaneously occurring weather disasters. In this paper, the daily mean temperature, precipitation, and glaze data of 206 stations over southern China in winter from 1961 to 2013 are integrated to establish an objective method for identifying combined disaster events of extensive and persistent low temperatures, rain/snow, and freezing weather in winter, and the key features of these kinds of combined disaster events are discussed. First, the identification methods for extensive and persistent low temperatures and rain/snow and freezing events are proposed according to the thresholds of their intensities and impact areas. The three most prominent combined disaster events, namely cold-rain/snow (C-RS), cold-freezing (C-F), and C-RS-freezing (C-RS-F) disaster events, are identified. These combined disaster events often occur from early January to mid-February. Although they have similar low temperatures and precipitation levels, their formation conditions are significantly different. Abundant water vapor supply and large-scale strong water vapor convergence are key conditions for the occurrence of C-RS and C-RS-F disaster events, while an inversion layer and cold pad are necessary conditions for the occurrence of C-F and C-RS-F disaster events. The large-scale tilted ridge in mid- and high-latitude Asia is the key circulation feature of C-F and C-RS-F disaster events. It provides favorable circulation conditions for strong cold air activities. During C-RS disaster events, wavy circulation prevails in mid- and high-latitude Asia, which is conducive to moderate cold air activities. The water vapor supply and inversion layer formation associated with the three kinds of combined disaster events are controlled by different subtropical anomalous circulation systems. The southern branch trough over the Bay of Bengal and the anomalous anticyclone over the South China Sea are key subtropical circulation systems for the formation of C-RS and C-F disaster events, respectively, while the combination of the southern branch trough over the Bay of Bengal and anomalous anticyclone over Northwestern Pacific is the key circulation system for the formation of C-RS-F disaster events.
Combined disaster events refer to the combination of several simultaneously occurring weather disasters. In this paper, the daily mean temperature, precipitation, and glaze data of 206 stations over southern China in winter from 1961 to 2013 are integrated to establish an objective method for identifying combined disaster events of extensive and persistent low temperatures, rain/snow, and freezing weather in winter, and the key features of these kinds of combined disaster events are discussed. First, the identification methods for extensive and persistent low temperatures and rain/snow and freezing events are proposed according to the thresholds of their intensities and impact areas. The three most prominent combined disaster events, namely cold-rain/snow (C-RS), cold-freezing (C-F), and C-RS-freezing (C-RS-F) disaster events, are identified. These combined disaster events often occur from early January to mid-February. Although they have similar low temperatures and precipitation levels, their formation conditions are significantly different. Abundant water vapor supply and large-scale strong water vapor convergence are key conditions for the occurrence of C-RS and C-RS-F disaster events, while an inversion layer and cold pad are necessary conditions for the occurrence of C-F and C-RS-F disaster events. The large-scale tilted ridge in mid- and high-latitude Asia is the key circulation feature of C-F and C-RS-F disaster events. It provides favorable circulation conditions for strong cold air activities. During C-RS disaster events, wavy circulation prevails in mid- and high-latitude Asia, which is conducive to moderate cold air activities. The water vapor supply and inversion layer formation associated with the three kinds of combined disaster events are controlled by different subtropical anomalous circulation systems. The southern branch trough over the Bay of Bengal and the anomalous anticyclone over the South China Sea are key subtropical circulation systems for the formation of C-RS and C-F disaster events, respectively, while the combination of the southern branch trough over the Bay of Bengal and anomalous anticyclone over Northwestern Pacific is the key circulation system for the formation of C-RS-F disaster events.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21237
Abstract:
In this study, we investigated the raindrop size distribution (DSD) characteristics of an extreme rainstorm event on July 20, 2021, in Zhengzhou using disdrometer observation data. The performance of many radar quantitative precipitation estimation (QPE) approaches was then examined using polarimetric radar data. The results show that during the peak rain rate period, the DSD indicated a high number concentration and large mean particle size. During this event, the normalized intercept parameter was similar to those observed in other regions of China, but the mass-weighted diameter was significantly higher. The DSD experienced significant changes before the peak rain rate period. The number concentration increased as the mass-weighted diameter increased, resulting in a quick increase in the rain rate. Polarimetric radar data were used to calculate the hourly QPE rainfall during 0800 UTC–0900 UTC, July 20, 2021, based on several QPE approaches and parameters, and then the performances of each approach were examined against the gauge observation. The result showed that the cap of reflectivity-based estimator (R(ZH) )should be removed or raised; otherwise, the rainfall would be significantly underestimated. The estimator was sensitive to the QPE parameters; however, the specific differential phase-based estimator (R(Kdp)) was relatively insensitive to the QPE parameters, and the accuracy of the specific differential phase was responsible for its performance. The best R(Kdp) estimator reached over 70% of the observational hourly rainfall and outperformed the best R(ZH) estimator during this extreme rainstorm event.
In this study, we investigated the raindrop size distribution (DSD) characteristics of an extreme rainstorm event on July 20, 2021, in Zhengzhou using disdrometer observation data. The performance of many radar quantitative precipitation estimation (QPE) approaches was then examined using polarimetric radar data. The results show that during the peak rain rate period, the DSD indicated a high number concentration and large mean particle size. During this event, the normalized intercept parameter was similar to those observed in other regions of China, but the mass-weighted diameter was significantly higher. The DSD experienced significant changes before the peak rain rate period. The number concentration increased as the mass-weighted diameter increased, resulting in a quick increase in the rain rate. Polarimetric radar data were used to calculate the hourly QPE rainfall during 0800 UTC–0900 UTC, July 20, 2021, based on several QPE approaches and parameters, and then the performances of each approach were examined against the gauge observation. The result showed that the cap of reflectivity-based estimator (R(ZH) )should be removed or raised; otherwise, the rainfall would be significantly underestimated. The estimator was sensitive to the QPE parameters; however, the specific differential phase-based estimator (R(Kdp)) was relatively insensitive to the QPE parameters, and the accuracy of the specific differential phase was responsible for its performance. The best R(Kdp) estimator reached over 70% of the observational hourly rainfall and outperformed the best R(ZH) estimator during this extreme rainstorm event.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2107.21059
Abstract:
We calculated the rainy season precipitation in North China (RSPNC) and the onset/ending dates through a new monitoring method based on the homogenized daily precipitation in North China and 1961–2018 ERA5 reanalysis data and a new monitoring standard that considers precipitation and the position of the Western Pacific subtropical high ridge. Moreover, we analyzed the climatic characteristics of water vapor transport and associated interdecadal variations in precipitation and moisture budget. The temporal and spatial variations in water vapor transport and the associated impact on RSPNC were further investigated. The main results can be summarized as follows: (1) The onset/ending dates of the rainy season in North China are distinct each year; therefore, the periods of the rainy season and the intraseasonal variation are also distinct. (2) Precipitation is determined by large-scale atmospheric moisture transport and the associated convergence. The critical four water vapor pathways, including Indian monsoon, East Asian monsoon, transequatorial airflow between 110°E and 120°E, and mid-latitude westerlies near 40°N, maintained the RSPNC. (3) The RSPNC and water vapor budget exhibits similar interdecadal variations, and abrupt climate changes occurred in 1977, 1987, and 1999, featuring a “reduction–increase–reduction” phase. The RSPNC is strongly correlated with the net water vapor budget within the North China domain. (4) The intensity of water vapor flux and the arriving time significantly affect the precipitation amount. The distribution patterns of water vapor flux anomalies in rainy decades and rainless decades are distinct: In the rainy decades, anomalous anticyclonic circulation dominates the Northwest Pacific, and the northward water vapor transport is strong, which converges with the eastward water vapor transport over mid to high latitude westerlies in North China, and the water vapor diverges more strongly than that in normal years. In terms of intraseasonal processes, water vapor fluxes are stronger in amplitude, reach North China earlier, weaken later, converge stronger, and last longer. In the rainless decades, anomalous cyclonic circulation dominates Northeast China, the Korean Peninsula, and the area around the Sea of Japan, and it turns into a weaker-than-usual northward water vapor transport, and the water vapor divergence is considerably strengthened. The intraseasonal process shows the opposite characteristics. (5) Considering the four boundaries of water vapor transport, the southern and western boundary water vapor inputs are the largest and the second-largest, respectively. Their interdecadal variations are critical for the interdecadal variation of the RSPNC. In rainy decades, there are stronger inputs of water vapor from the southern and western boundaries but strong output from the north boundary; however, in rainless decades, water vapor inputs are weak from the southern and western boundaries, and the output switches to input from the northern boundary, which is essentially distinct from the case in the rainy decades.
We calculated the rainy season precipitation in North China (RSPNC) and the onset/ending dates through a new monitoring method based on the homogenized daily precipitation in North China and 1961–2018 ERA5 reanalysis data and a new monitoring standard that considers precipitation and the position of the Western Pacific subtropical high ridge. Moreover, we analyzed the climatic characteristics of water vapor transport and associated interdecadal variations in precipitation and moisture budget. The temporal and spatial variations in water vapor transport and the associated impact on RSPNC were further investigated. The main results can be summarized as follows: (1) The onset/ending dates of the rainy season in North China are distinct each year; therefore, the periods of the rainy season and the intraseasonal variation are also distinct. (2) Precipitation is determined by large-scale atmospheric moisture transport and the associated convergence. The critical four water vapor pathways, including Indian monsoon, East Asian monsoon, transequatorial airflow between 110°E and 120°E, and mid-latitude westerlies near 40°N, maintained the RSPNC. (3) The RSPNC and water vapor budget exhibits similar interdecadal variations, and abrupt climate changes occurred in 1977, 1987, and 1999, featuring a “reduction–increase–reduction” phase. The RSPNC is strongly correlated with the net water vapor budget within the North China domain. (4) The intensity of water vapor flux and the arriving time significantly affect the precipitation amount. The distribution patterns of water vapor flux anomalies in rainy decades and rainless decades are distinct: In the rainy decades, anomalous anticyclonic circulation dominates the Northwest Pacific, and the northward water vapor transport is strong, which converges with the eastward water vapor transport over mid to high latitude westerlies in North China, and the water vapor diverges more strongly than that in normal years. In terms of intraseasonal processes, water vapor fluxes are stronger in amplitude, reach North China earlier, weaken later, converge stronger, and last longer. In the rainless decades, anomalous cyclonic circulation dominates Northeast China, the Korean Peninsula, and the area around the Sea of Japan, and it turns into a weaker-than-usual northward water vapor transport, and the water vapor divergence is considerably strengthened. The intraseasonal process shows the opposite characteristics. (5) Considering the four boundaries of water vapor transport, the southern and western boundary water vapor inputs are the largest and the second-largest, respectively. Their interdecadal variations are critical for the interdecadal variation of the RSPNC. In rainy decades, there are stronger inputs of water vapor from the southern and western boundaries but strong output from the north boundary; however, in rainless decades, water vapor inputs are weak from the southern and western boundaries, and the output switches to input from the northern boundary, which is essentially distinct from the case in the rainy decades.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2112.21191
Abstract:
Traditional urban flood forecasting mostly adopts the urban hydrodynamic model with a single rainfall product, making it difficult to solve the uncertainty due to rainfall measurements or numerical modeling. Comprehensive utilization of multisource precipitation (radar, rain gage, and distrometer) and surface ponding observation will help improve the forecasting accuracy of waterlogging and the spatial description of risk. Therefore, to cope with the threat of extreme storms in a better manner, this study proposes a warning system of urban waterlogging based on comprehensive observations to further strengthen the ability of flood forecasting. Moreover, the authors have conducted the preliminary practice and validation in the Qing River basin of Beijing. The system contains six modules, integrates emerging observation technologies of both rainfall and waterlogging, introduces a mainstream method of rainfall nowcasting, and adopts well-established simulation methods of urban flooding. It can provide real-time water depth for road traffic and early warning products for urban emergency management.
Traditional urban flood forecasting mostly adopts the urban hydrodynamic model with a single rainfall product, making it difficult to solve the uncertainty due to rainfall measurements or numerical modeling. Comprehensive utilization of multisource precipitation (radar, rain gage, and distrometer) and surface ponding observation will help improve the forecasting accuracy of waterlogging and the spatial description of risk. Therefore, to cope with the threat of extreme storms in a better manner, this study proposes a warning system of urban waterlogging based on comprehensive observations to further strengthen the ability of flood forecasting. Moreover, the authors have conducted the preliminary practice and validation in the Qing River basin of Beijing. The system contains six modules, integrates emerging observation technologies of both rainfall and waterlogging, introduces a mainstream method of rainfall nowcasting, and adopts well-established simulation methods of urban flooding. It can provide real-time water depth for road traffic and early warning products for urban emergency management.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2101.20243
Abstract:
The relationships between the lightning activities and the radar reflectivity intensities of seven severe squall lines, which occurred in Beijing from 2015 to 2017, were analyzed. The analysis was done based on three-dimensional lightning location data from Beijing Broadband Lightning Network (BLNet) and the S-band Doppler radar. The results show that lightning flashes are mainly located in the convective leading line and centered in the strong echo region, with reflectivity greater than 30 dBZ, and a small part of lightning flashes distributed in the trailing stratiform region. Based on the three-dimensional lightning structure, the lightning flashes are mostly concentrated in the range of 6–11 km height layer. Using the radar echo volume with reflectivity >30 dBZ (V30dBZ) between the 0 and −30℃ level, as a strong convection index to reflect both the depth and area of strong convection, we found that of all seven squall lines, the trend of the lightning frequency and V30dBZ evolution showed some relationship. For five squall lines, the lightning frequency peak is the same or earlier than that of V30dBZ, the lagged correlation coefficient is higher than 0.61, and the lightning frequency is earlier than V30dBZ, with a leading time from 0 to 96 min. For the other two cases, the lightning frequency peak lags V30dBZ at 30 and 60 min, respectively. The results are significant for understanding lightning activity and convection intensification and provide a scientific basis for lightning data assimilation in numerical weather prediction.
The relationships between the lightning activities and the radar reflectivity intensities of seven severe squall lines, which occurred in Beijing from 2015 to 2017, were analyzed. The analysis was done based on three-dimensional lightning location data from Beijing Broadband Lightning Network (BLNet) and the S-band Doppler radar. The results show that lightning flashes are mainly located in the convective leading line and centered in the strong echo region, with reflectivity greater than 30 dBZ, and a small part of lightning flashes distributed in the trailing stratiform region. Based on the three-dimensional lightning structure, the lightning flashes are mostly concentrated in the range of 6–11 km height layer. Using the radar echo volume with reflectivity >30 dBZ (V30dBZ) between the 0 and −30℃ level, as a strong convection index to reflect both the depth and area of strong convection, we found that of all seven squall lines, the trend of the lightning frequency and V30dBZ evolution showed some relationship. For five squall lines, the lightning frequency peak is the same or earlier than that of V30dBZ, the lagged correlation coefficient is higher than 0.61, and the lightning frequency is earlier than V30dBZ, with a leading time from 0 to 96 min. For the other two cases, the lightning frequency peak lags V30dBZ at 30 and 60 min, respectively. The results are significant for understanding lightning activity and convection intensification and provide a scientific basis for lightning data assimilation in numerical weather prediction.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2106.21006
Abstract:
Abnormal heavy precipitation in the middle and lower reaches of the Yangtze River during the 2020 Meiyu period (June–July) resulted in enormous loss of lives and property. Moreover, the length and intensity of precipitation during this period far exceed the historical average. Using daily National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data and the Climate Prediction Center global daily precipitation data, this study investigated the features of heavy precipitation and their relationship with baroclinic Rossby wave in the upper troposphere. The results showed that the total precipitation and precipitation anomalies in the middle and lower reaches of the Yangtze River were located in the southern part of Anhui Province, and that there were seven consecutive precipitation processes. The middle and lower reaches of the Yangtze River featured a convergence, while the upper troposphere featured a dispersion, and a strong anomalous upward motion occurred over the region, which favored the development of anomalous heavy precipitation. Moreover, water vapor was transported from the Bay of Bengal and the South China Sea to the middle and lower reaches of the Yangtze River, which provided sufficient water vapor for heavy precipitation. Wavelet-based analysis of the standardized time series of daily precipitation in this region revealed significant cycles of 2–4 days and 6–14 days. The Rossby fluctuations shown by high-frequency (2–14 days) perturbations exhibited a downstream dispersion in the upper troposphere, with fluctuations originating near Lake Baikal. The propagation process of the fluctuations downstream, shown by the wave disturbance energy and flux, was more consistent with that of the wave packet. The wave disturbances originating near the Mediterranean Sea and Lake Baikal could disperse eastward or southeastward to the middle and lower reaches of the Yangtze River. The energy transmitted to the middle and lower reaches of the river favored the intensification of the disturbance in this region and thus the occurrence and continuation of heavy precipitation. The results of this study further clarify the causes of the 2020 super-long “violent Meiyu” and may help scientists effectively predict similar events.
Abnormal heavy precipitation in the middle and lower reaches of the Yangtze River during the 2020 Meiyu period (June–July) resulted in enormous loss of lives and property. Moreover, the length and intensity of precipitation during this period far exceed the historical average. Using daily National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data and the Climate Prediction Center global daily precipitation data, this study investigated the features of heavy precipitation and their relationship with baroclinic Rossby wave in the upper troposphere. The results showed that the total precipitation and precipitation anomalies in the middle and lower reaches of the Yangtze River were located in the southern part of Anhui Province, and that there were seven consecutive precipitation processes. The middle and lower reaches of the Yangtze River featured a convergence, while the upper troposphere featured a dispersion, and a strong anomalous upward motion occurred over the region, which favored the development of anomalous heavy precipitation. Moreover, water vapor was transported from the Bay of Bengal and the South China Sea to the middle and lower reaches of the Yangtze River, which provided sufficient water vapor for heavy precipitation. Wavelet-based analysis of the standardized time series of daily precipitation in this region revealed significant cycles of 2–4 days and 6–14 days. The Rossby fluctuations shown by high-frequency (2–14 days) perturbations exhibited a downstream dispersion in the upper troposphere, with fluctuations originating near Lake Baikal. The propagation process of the fluctuations downstream, shown by the wave disturbance energy and flux, was more consistent with that of the wave packet. The wave disturbances originating near the Mediterranean Sea and Lake Baikal could disperse eastward or southeastward to the middle and lower reaches of the Yangtze River. The energy transmitted to the middle and lower reaches of the river favored the intensification of the disturbance in this region and thus the occurrence and continuation of heavy precipitation. The results of this study further clarify the causes of the 2020 super-long “violent Meiyu” and may help scientists effectively predict similar events.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2107.21013
Abstract:
Taking aerosol field measurement experiments conducted in the summer of 2016 at Xingtai (XT) siteand the 2016 and 2017 winters at Beijing (BJ) site as examples, the effects of typical new particle formation (NPF) events on aerosol hygroscopicity and cloud condensation nuclei (CCN) activity were investigated. BJ and XT are respectively located in a northern megalopolis area and a central–southern industrial area in the North China Plain. The formation mechanisms of new particles in different seasons at the two sites were different, and the corresponding condensation sink, growth rate, and aerosol chemical composition were also different. Organics and sulfate were the dominant chemical species formed during NPF events at the BJ and XT sites, respectively. Furthermore, the XT site exhibited significantly stronger aerosol hygroscopicity and CCN activity than the BJ site, especially for the nucleation mode particles. The results of this study indicate that the difference in aerosol hygroscopicity and activation ability should be fully considered in the estimation of the influence of NPF on CCN number concentration.
Taking aerosol field measurement experiments conducted in the summer of 2016 at Xingtai (XT) siteand the 2016 and 2017 winters at Beijing (BJ) site as examples, the effects of typical new particle formation (NPF) events on aerosol hygroscopicity and cloud condensation nuclei (CCN) activity were investigated. BJ and XT are respectively located in a northern megalopolis area and a central–southern industrial area in the North China Plain. The formation mechanisms of new particles in different seasons at the two sites were different, and the corresponding condensation sink, growth rate, and aerosol chemical composition were also different. Organics and sulfate were the dominant chemical species formed during NPF events at the BJ and XT sites, respectively. Furthermore, the XT site exhibited significantly stronger aerosol hygroscopicity and CCN activity than the BJ site, especially for the nucleation mode particles. The results of this study indicate that the difference in aerosol hygroscopicity and activation ability should be fully considered in the estimation of the influence of NPF on CCN number concentration.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2110.20252
Abstract:
The round-trip horizontal drift observation is a new type of observation method studied and implemented in China. It can effectively improve the observation efficiency and economic benefits and is of great significance to overcome the defects of the conventional radiosonde observation and improve the quality of numerical prediction. In this paper, according to the characteristics of thermal and dynamic processes and their main influencing factors in the rising and horizontal drift stages of sounding, a theoretical model of the thermodynamics of a horizontal drift on a sounding system is established. The reliability of the theoretical model is further analyzed and verified by combining it with the actual observation test. Research results have important theoretical support and practical value for designing and improving the round-trip drift sounding system.
The round-trip horizontal drift observation is a new type of observation method studied and implemented in China. It can effectively improve the observation efficiency and economic benefits and is of great significance to overcome the defects of the conventional radiosonde observation and improve the quality of numerical prediction. In this paper, according to the characteristics of thermal and dynamic processes and their main influencing factors in the rising and horizontal drift stages of sounding, a theoretical model of the thermodynamics of a horizontal drift on a sounding system is established. The reliability of the theoretical model is further analyzed and verified by combining it with the actual observation test. Research results have important theoretical support and practical value for designing and improving the round-trip drift sounding system.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2105.20237
Abstract:
For a physical inspection of the artificial precipitation enhancement effect based on multi-source detection data, this study established the similarity measurement coefficient, APC (Analogy Deviation-Pearson Correlation Coefficient), of a contrast area selection and the dimensionless PIDI (Physical Inspection Dimensionless Index) index method for a physical inspection of the artificial precipitation enhancement effect. The results revealed the following: (1) The PIDI index method of a physical inspection for the artificial precipitation enhancement effect can minimize the variable influence of a seeding cloud body and precipitation with the similarity coefficient APC. In addition, a variety of dimensionless cloud physical detection parameters can be synthesized using a dimensionless method. Finally, the percentage change rate was used to measure the overall variations and the degree of various cloud physical parameters. (2) The PIDI index method was applied to inspect the precipitation enhancement effect of 24 aircraft from 2014 to 2019. The average change rate of seven indices (cloud top temperature, effective particle radius, optical thickness, liquid water path, combined reflectivity, ≥30 dBZ echo area, and vertical cumulative liquid water content) caused by artificial precipitation enhancement was 3.4%–19.6%. The change rate of hourly precipitation of 18 operations was 0–58.3%; the change rate of 6 operations was −37.5% to 0. The changes in the cloud physical parameters caused by most precipitation-increasing operations are smaller than the changes in precipitation. (3) For the 18 operations with a positive effect of precipitation enhancement, the cloud top temperature, combined reflectivity, and the vertical cumulative liquid water content for most operations were increased due to the artificial catalysis, effective particle radius, and optical thickness. Moreover, the liquid water path for most operations was decreased by artificial catalysis. (4) The PIDI index and K-value methods were compared using an aircraft precipitation enhancement operation. For the test of precipitation variation trend, the two methods were consistent. The main difference was that the PIDI index method could reflect the average change rate of all inspection indices caused by artificial catalysis.
For a physical inspection of the artificial precipitation enhancement effect based on multi-source detection data, this study established the similarity measurement coefficient, APC (Analogy Deviation-Pearson Correlation Coefficient), of a contrast area selection and the dimensionless PIDI (Physical Inspection Dimensionless Index) index method for a physical inspection of the artificial precipitation enhancement effect. The results revealed the following: (1) The PIDI index method of a physical inspection for the artificial precipitation enhancement effect can minimize the variable influence of a seeding cloud body and precipitation with the similarity coefficient APC. In addition, a variety of dimensionless cloud physical detection parameters can be synthesized using a dimensionless method. Finally, the percentage change rate was used to measure the overall variations and the degree of various cloud physical parameters. (2) The PIDI index method was applied to inspect the precipitation enhancement effect of 24 aircraft from 2014 to 2019. The average change rate of seven indices (cloud top temperature, effective particle radius, optical thickness, liquid water path, combined reflectivity, ≥30 dBZ echo area, and vertical cumulative liquid water content) caused by artificial precipitation enhancement was 3.4%–19.6%. The change rate of hourly precipitation of 18 operations was 0–58.3%; the change rate of 6 operations was −37.5% to 0. The changes in the cloud physical parameters caused by most precipitation-increasing operations are smaller than the changes in precipitation. (3) For the 18 operations with a positive effect of precipitation enhancement, the cloud top temperature, combined reflectivity, and the vertical cumulative liquid water content for most operations were increased due to the artificial catalysis, effective particle radius, and optical thickness. Moreover, the liquid water path for most operations was decreased by artificial catalysis. (4) The PIDI index and K-value methods were compared using an aircraft precipitation enhancement operation. For the test of precipitation variation trend, the two methods were consistent. The main difference was that the PIDI index method could reflect the average change rate of all inspection indices caused by artificial catalysis.
2022 Issue 3
Display Method:
2022, 46(3): 507-519.
doi: 10.3878/j.issn.1006-9895.2110.20212
Abstract:
There are abundant cloud water resources for development and utilization in the snowfall cloud system in winter in Beijing. For the needs of artificial snow enhancement research and full development of cloud water resources, the first annual snowfall in Beijing was observed on November 29, 2019. Data are analyzed, and numerical simulation is carried out. The macro-observation characteristics of the snowfall process are studied, and the atmospheric hydrometeor transportation characteristics and microphysical mechanism of the snowfall are also analyzed through the simulation results. The results show that the stable stratified cold cloud system affects the snowfall in Beijing. Water vapor and water condensate are mainly transported into the region from the western and southern boundaries of the Beijing area and flow out from the eastern and northern boundaries. The cloud hydrometeor transport channel for the snowfall cloud system accompanies a westward and southward component of the moist airflow. The water condensate in the snowfall cloud comprises ice crystals, snow, and a small amount of cloud water. The entire layer of the cloud system contains rich water vapor and runs through the entire snowfall period. In an ice-saturated environment, deposition of snow (Prds) are the main source of the snow, followed by the automatic conversion of cloud ice to snow (Prci) and the accretion of cloud ice by snow (Prai).
There are abundant cloud water resources for development and utilization in the snowfall cloud system in winter in Beijing. For the needs of artificial snow enhancement research and full development of cloud water resources, the first annual snowfall in Beijing was observed on November 29, 2019. Data are analyzed, and numerical simulation is carried out. The macro-observation characteristics of the snowfall process are studied, and the atmospheric hydrometeor transportation characteristics and microphysical mechanism of the snowfall are also analyzed through the simulation results. The results show that the stable stratified cold cloud system affects the snowfall in Beijing. Water vapor and water condensate are mainly transported into the region from the western and southern boundaries of the Beijing area and flow out from the eastern and northern boundaries. The cloud hydrometeor transport channel for the snowfall cloud system accompanies a westward and southward component of the moist airflow. The water condensate in the snowfall cloud comprises ice crystals, snow, and a small amount of cloud water. The entire layer of the cloud system contains rich water vapor and runs through the entire snowfall period. In an ice-saturated environment, deposition of snow (Prds) are the main source of the snow, followed by the automatic conversion of cloud ice to snow (Prci) and the accretion of cloud ice by snow (Prai).
2022, 46(3): 520-540.
doi: 10.3878/j.issn.1006-9895.2106.20213
Abstract:
The slow feature analysis (SFA) can extract slowly varying external forcing information from non-stationary time series. In recent years, the SFA method has been applied to the climate change field to explore the potential driving forces of climate change and related dynamic mechanisms. This study extracts the slowly varying external forcing information of the global land surface air temperature (LSAT) based on the SFA method. It investigates the spatial structure characteristics of the global LSAT slow varying driving force and the main driving factors of low-frequency variability. The LSAT slowly varying driving force extracted by the SFA method has a significant correlation with global radiative forcing (GRF) and the main modes of the global sea surface temperature (SST) (i.e., Atlantic Multidecadal Oscillation, tropical Pacific El Niño–Southern Oscillation variability, and Interdecadal Pacific Oscillation), indicating that the LSAT variability in most parts of the world is significantly affected by GRF and the three SST modes. The influence of GRF on the LSAT variability has global consistency, while that of the three SST modes on the LSAT variability has obvious regional characteristics. In addition, the interpretation variance of the LSAT variability of the GRF and SST modes significantly improved because the SFA method can effectively reduce the explanatory random noise in the original LSAT sequence, further showing that the GRF and SST modes are the main driving factors of the global LSAT low-frequency variability. Finally, the results of the historical sea surface temperature-driven Atmospheric General Circulation Model test, which is also known as the Atmospheric Model Intercomparison Project (AMIP)test, verify the significant influence of the three SST modes on the regional LSAT variability.
The slow feature analysis (SFA) can extract slowly varying external forcing information from non-stationary time series. In recent years, the SFA method has been applied to the climate change field to explore the potential driving forces of climate change and related dynamic mechanisms. This study extracts the slowly varying external forcing information of the global land surface air temperature (LSAT) based on the SFA method. It investigates the spatial structure characteristics of the global LSAT slow varying driving force and the main driving factors of low-frequency variability. The LSAT slowly varying driving force extracted by the SFA method has a significant correlation with global radiative forcing (GRF) and the main modes of the global sea surface temperature (SST) (i.e., Atlantic Multidecadal Oscillation, tropical Pacific El Niño–Southern Oscillation variability, and Interdecadal Pacific Oscillation), indicating that the LSAT variability in most parts of the world is significantly affected by GRF and the three SST modes. The influence of GRF on the LSAT variability has global consistency, while that of the three SST modes on the LSAT variability has obvious regional characteristics. In addition, the interpretation variance of the LSAT variability of the GRF and SST modes significantly improved because the SFA method can effectively reduce the explanatory random noise in the original LSAT sequence, further showing that the GRF and SST modes are the main driving factors of the global LSAT low-frequency variability. Finally, the results of the historical sea surface temperature-driven Atmospheric General Circulation Model test, which is also known as the Atmospheric Model Intercomparison Project (AMIP)test, verify the significant influence of the three SST modes on the regional LSAT variability.
2022, 46(3): 541-556.
doi: 10.3878/j.issn.1006-9895.2105.20215
Abstract:
Existing studies have shown that radiation has a significant effect on the occurrence and development of a tropical cyclone (TC). A Tibetan Plateau vortex (TPV) and a TC have a similar structure, the same as that of a warm-hearted and low-pressure structure, so the roles of radiation in the occurrence and development of the TPV is also worth discussing. In this study, the influence of the diurnal cycle of radiation on TPV development was examined using the Advanced Research Weather Research and Forecasting model. The results showed that solar shortwave radiation has a significant effect on the occurrence and development of the TPV. The control run (CTL; with the diurnal cycle of solar shortwave radiation) well reproduced the development process of the TPV. In the experiment with turning off the shortwave radiation (All_night), the TPV developed much faster at the early stage, whereas in the daytime experiment (All_day), the shortwave radiation suppressed the TPV development. The diagnostic analysis indicated that the longwave radiation cooling steepened the tropospheric lapse rate, thus weakening the atmospheric static stability. Additionally, the temperature reduction increased the relative humidity at night, which was conducive to potential instability in the lower troposphere and thus promoted TPV formation and development. Conversely, solar shortwave radiation warmed the upper troposphere and strengthened the static stability, which inhibited the convection development. The convergence at the lower layer is stronger at night than at day, which is beneficial to the ascending motion enhancement and the TPV formation. The unbalanced term indicated that the center of the TPV corresponded to the positive area of the unbalanced term and the outer edge of the TPV with the negative area of the unbalanced term. Numerical results showed that the TPV development bears many similarities to tropical cyclogenesis in terms of dynamics and thermodynamics.
Existing studies have shown that radiation has a significant effect on the occurrence and development of a tropical cyclone (TC). A Tibetan Plateau vortex (TPV) and a TC have a similar structure, the same as that of a warm-hearted and low-pressure structure, so the roles of radiation in the occurrence and development of the TPV is also worth discussing. In this study, the influence of the diurnal cycle of radiation on TPV development was examined using the Advanced Research Weather Research and Forecasting model. The results showed that solar shortwave radiation has a significant effect on the occurrence and development of the TPV. The control run (CTL; with the diurnal cycle of solar shortwave radiation) well reproduced the development process of the TPV. In the experiment with turning off the shortwave radiation (All_night), the TPV developed much faster at the early stage, whereas in the daytime experiment (All_day), the shortwave radiation suppressed the TPV development. The diagnostic analysis indicated that the longwave radiation cooling steepened the tropospheric lapse rate, thus weakening the atmospheric static stability. Additionally, the temperature reduction increased the relative humidity at night, which was conducive to potential instability in the lower troposphere and thus promoted TPV formation and development. Conversely, solar shortwave radiation warmed the upper troposphere and strengthened the static stability, which inhibited the convection development. The convergence at the lower layer is stronger at night than at day, which is beneficial to the ascending motion enhancement and the TPV formation. The unbalanced term indicated that the center of the TPV corresponded to the positive area of the unbalanced term and the outer edge of the TPV with the negative area of the unbalanced term. Numerical results showed that the TPV development bears many similarities to tropical cyclogenesis in terms of dynamics and thermodynamics.
2022, 46(3): 557-572.
doi: 10.3878/j.issn.1006-9895.2106.21030
Abstract:
This study evaluates the performances of 19 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating the water cycle over East China based on observations and reanalysis data using the Brubaker model. Sources of model bias are also investigated. Results reveal that the CMIP6 multi-model ensemble (MME) can reasonably simulate the climatic distribution and annual cycle of precipitation and evaporation with a pattern correlation coefficient of 0.92 and 0.87, respectively. Compared with observations, MME overestimates the precipitation (0.55 mm d−1) in North China but underestimates the precipitation (−0.3 mm d−1) in coastal areas of South China. All 19 models overestimate the evaporation with biases of 0.03–0.98 mm d−1. Thus, differences between the simulated precipitation and evaporation by most models are smaller than those of the observation and reanalysis data. The MME can well simulate the annual cycle of the contribution of each moisture source to the precipitation but underestimates the contribution of remote moisture via the southern boundary, resulting in a dry bias over the study region. It is found that the southerly wind speed over the southern boundary determines the difference in the water vapor transport among CMIP6 models. The stronger the southerly wind speed is in the model, the higher the water vapor flux incomes via the southern boundary, and the more precipitation the model simulates. The position of the convergence zone over the Northwest Pacific is one of the important systems affecting the southerly wind speed over the southern boundary. The eastward shift of the convergence position in the model results in weaker southerly winds, leading to a weaker moisture transport to the study region and less precipitation, and vice versa. This study systematically evaluates the performance of CMIP6 in reproducing the East Asian water cycle and demonstrates the limitation of the models in simulating the convergence zone over the Northwest Pacific and its impact on the East Asian water cycle.
This study evaluates the performances of 19 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating the water cycle over East China based on observations and reanalysis data using the Brubaker model. Sources of model bias are also investigated. Results reveal that the CMIP6 multi-model ensemble (MME) can reasonably simulate the climatic distribution and annual cycle of precipitation and evaporation with a pattern correlation coefficient of 0.92 and 0.87, respectively. Compared with observations, MME overestimates the precipitation (0.55 mm d−1) in North China but underestimates the precipitation (−0.3 mm d−1) in coastal areas of South China. All 19 models overestimate the evaporation with biases of 0.03–0.98 mm d−1. Thus, differences between the simulated precipitation and evaporation by most models are smaller than those of the observation and reanalysis data. The MME can well simulate the annual cycle of the contribution of each moisture source to the precipitation but underestimates the contribution of remote moisture via the southern boundary, resulting in a dry bias over the study region. It is found that the southerly wind speed over the southern boundary determines the difference in the water vapor transport among CMIP6 models. The stronger the southerly wind speed is in the model, the higher the water vapor flux incomes via the southern boundary, and the more precipitation the model simulates. The position of the convergence zone over the Northwest Pacific is one of the important systems affecting the southerly wind speed over the southern boundary. The eastward shift of the convergence position in the model results in weaker southerly winds, leading to a weaker moisture transport to the study region and less precipitation, and vice versa. This study systematically evaluates the performance of CMIP6 in reproducing the East Asian water cycle and demonstrates the limitation of the models in simulating the convergence zone over the Northwest Pacific and its impact on the East Asian water cycle.
2022, 46(3): 573-589.
doi: 10.3878/j.issn.1006-9895.2110.21027
Abstract:
This study investigates the intraseasonal variation characteristics of winter temperature in China and related atmospheric circulation anomalies under two different interdecadal time scale stages, classified as before and after 1986, using observed temperature data in China from 1951 to 2020, NCEP/NCAR reanalysis dataset, and statistical methods. The proportion of anti-phase years of temperature in early winter (December) and late winter (January–February) is higher in each stage than in the same phase years. Furthermore, the season-reliant empirical orthogonal function (S-EOF) method was used to obtain the dominant modes of the interseasonal variation in winter under two interdecadal time scale periods. Before 1986, the dominant spatial mode in winter showed that the national cold (warm) in early winter was likely to change to the warm (cold) in southern China in late winter, implying that the intraseasonal variability in the southern region was greater than that in the northern region. After 1986, the dominant spatial mode is more likely to demonstrate that the cold (warm) in northern China in early winter changed to the obvious warm (cold) in the entire country in late winter, indicating that the intraseasonal variability in the northern region is greater than that in the southern region. The interseasonal variation of winter temperature is significantly affected by the interseasonal variation of the key circulation of the East Asia winter monsoon system. Before 1986, the tropospheric circulation anomaly signal in the middle and high latitudes of Eurasia weakened significantly from early winter to late winter, correlating to the positive phase anomaly years of the dominant mode. The circulation adjustment in the middle and upper troposphere was more prominent in the Northwest Pacific, the subtropical height field was enhanced, and the tropical easterly jet expanded northward. The circulation adjustment in winter is conducive to the country-wide cold in early winter, while warm in southern China in late winter, resulting in strong intraseasonal variability in the southern region. After 1986, the circulation anomalies in the high, middle, and low latitudes of Eurasia increased significantly from the early winter to the late winter, and the circulation in the middle and high latitudes of Eurasia adjusted significantly, while the circulation in the low latitudes changed little. The northern region of China was cold in the early winter, warm in the late winter, and the intraseasonal variability was greater than in the southern region. The subtropical circulation and the mid-high latitude circulation play major roles in the intraseasonal variability of southern and northern China in the two interdecadal scale stages (before and after 1986), respectively.
This study investigates the intraseasonal variation characteristics of winter temperature in China and related atmospheric circulation anomalies under two different interdecadal time scale stages, classified as before and after 1986, using observed temperature data in China from 1951 to 2020, NCEP/NCAR reanalysis dataset, and statistical methods. The proportion of anti-phase years of temperature in early winter (December) and late winter (January–February) is higher in each stage than in the same phase years. Furthermore, the season-reliant empirical orthogonal function (S-EOF) method was used to obtain the dominant modes of the interseasonal variation in winter under two interdecadal time scale periods. Before 1986, the dominant spatial mode in winter showed that the national cold (warm) in early winter was likely to change to the warm (cold) in southern China in late winter, implying that the intraseasonal variability in the southern region was greater than that in the northern region. After 1986, the dominant spatial mode is more likely to demonstrate that the cold (warm) in northern China in early winter changed to the obvious warm (cold) in the entire country in late winter, indicating that the intraseasonal variability in the northern region is greater than that in the southern region. The interseasonal variation of winter temperature is significantly affected by the interseasonal variation of the key circulation of the East Asia winter monsoon system. Before 1986, the tropospheric circulation anomaly signal in the middle and high latitudes of Eurasia weakened significantly from early winter to late winter, correlating to the positive phase anomaly years of the dominant mode. The circulation adjustment in the middle and upper troposphere was more prominent in the Northwest Pacific, the subtropical height field was enhanced, and the tropical easterly jet expanded northward. The circulation adjustment in winter is conducive to the country-wide cold in early winter, while warm in southern China in late winter, resulting in strong intraseasonal variability in the southern region. After 1986, the circulation anomalies in the high, middle, and low latitudes of Eurasia increased significantly from the early winter to the late winter, and the circulation in the middle and high latitudes of Eurasia adjusted significantly, while the circulation in the low latitudes changed little. The northern region of China was cold in the early winter, warm in the late winter, and the intraseasonal variability was greater than in the southern region. The subtropical circulation and the mid-high latitude circulation play major roles in the intraseasonal variability of southern and northern China in the two interdecadal scale stages (before and after 1986), respectively.
2022, 46(3): 590-598.
doi: 10.3878/j.issn.1006-9895.2105.21048
Abstract:
In autumn, the Indian Ocean Dipole (IOD) has the strongest interannual variability in the tropical Indian Ocean. It will influence the climate in many parts of the world due to atmospheric teleconnection. The current coupled climate model has very limited IOD forecasting skills, which are far inferior to those of El Niño events in the tropical Pacific. The authors used the convolutional neural network (CNN) of the deep learning and the multi-layer perceptron (MLP) of the artificial neural network, respectively, to perform IOD prediction due to the super capability of deep learning in processing data. In order to explore the forecasting capabilities of CNN, this article only uses three initial conditions in the boreal spring with low prediction skill to forecast the Indian Ocean Dipole Mode Index (DMI), East Pole Index (EIOI), and West Pole Index (WIOI) for the next seven months. The results show that the CNN model can make useful predictions for the DMI, EIOI, and WIOI at least six months in advance. When compared with the current state-of-the-art general coupled model, the CNN model significantly improves the prediction skills of the DMI and EIOI while only slightly improving WIOI prediction skills. The CNN model could predict the strong IOD events in 1994, 1997, and 2019 well for the lead time longer than seven months. In general, CNN outperforms the traditional neural network MLP for the IOD prediction due to its strong capability to capture the spatial structure characteristics of the Indian Ocean SST.
In autumn, the Indian Ocean Dipole (IOD) has the strongest interannual variability in the tropical Indian Ocean. It will influence the climate in many parts of the world due to atmospheric teleconnection. The current coupled climate model has very limited IOD forecasting skills, which are far inferior to those of El Niño events in the tropical Pacific. The authors used the convolutional neural network (CNN) of the deep learning and the multi-layer perceptron (MLP) of the artificial neural network, respectively, to perform IOD prediction due to the super capability of deep learning in processing data. In order to explore the forecasting capabilities of CNN, this article only uses three initial conditions in the boreal spring with low prediction skill to forecast the Indian Ocean Dipole Mode Index (DMI), East Pole Index (EIOI), and West Pole Index (WIOI) for the next seven months. The results show that the CNN model can make useful predictions for the DMI, EIOI, and WIOI at least six months in advance. When compared with the current state-of-the-art general coupled model, the CNN model significantly improves the prediction skills of the DMI and EIOI while only slightly improving WIOI prediction skills. The CNN model could predict the strong IOD events in 1994, 1997, and 2019 well for the lead time longer than seven months. In general, CNN outperforms the traditional neural network MLP for the IOD prediction due to its strong capability to capture the spatial structure characteristics of the Indian Ocean SST.
2022, 46(3): 599-620.
doi: 10.3878/j.issn.1006-9895.2107.21064
Abstract:
Using ERA5 reanalysis data as the initial field, the WRF model was used to conduct a numerical simulation study of a large-scale snowstorm event from April 19–20, 2020. This work adopted different microphysical parameterization schemes for sensitivity experiments, and the capability of the model for simulation was evaluated based on observation data (precipitation data collected at automatic weather stations, radar base data). Temporal and spatial evolution characteristics of precipitation, radar reflectance, dynamic thermodynamics, and water condensate in heavy snow weather were also analyzed. Results reveal that the Morrison scheme can better simulate the snowstorm weather event, which shows that the simulated radar echo intensity, range, and shape are more consistent with the observation data, and the correlation coefficient and root mean square error of the simulated precipitation are better than other schemes. The detailed microphysical structure of the proposed scheme is characterized by a strong ascending motion and long-term maintenance of positive vorticity in the lower layer, more ice crystals in the upper layer above 7 km, and less graupel and rain particles in the middle and lower layers. From the perspective of the thermal dynamic field, there is an obvious vorticity wave train below the height of 600 hPa in the bin scheme. This is mainly because the bin scheme grades the particle swarm, does not bind different particle types to move, and can describe the sinking and dragging effect of different particles in a more detailed way. Cloud microphysical characteristics show that the specific masses of snow, graupel, cloud water, and rain particles simulated by different schemes are close to each other. However, the simulation of the specific mass of ice crystals has great differences in both magnitude and distribution range, which determine the difference in the magnitude and the phase state simulation of the radar echo and precipitation by different microphysics schemes.
Using ERA5 reanalysis data as the initial field, the WRF model was used to conduct a numerical simulation study of a large-scale snowstorm event from April 19–20, 2020. This work adopted different microphysical parameterization schemes for sensitivity experiments, and the capability of the model for simulation was evaluated based on observation data (precipitation data collected at automatic weather stations, radar base data). Temporal and spatial evolution characteristics of precipitation, radar reflectance, dynamic thermodynamics, and water condensate in heavy snow weather were also analyzed. Results reveal that the Morrison scheme can better simulate the snowstorm weather event, which shows that the simulated radar echo intensity, range, and shape are more consistent with the observation data, and the correlation coefficient and root mean square error of the simulated precipitation are better than other schemes. The detailed microphysical structure of the proposed scheme is characterized by a strong ascending motion and long-term maintenance of positive vorticity in the lower layer, more ice crystals in the upper layer above 7 km, and less graupel and rain particles in the middle and lower layers. From the perspective of the thermal dynamic field, there is an obvious vorticity wave train below the height of 600 hPa in the bin scheme. This is mainly because the bin scheme grades the particle swarm, does not bind different particle types to move, and can describe the sinking and dragging effect of different particles in a more detailed way. Cloud microphysical characteristics show that the specific masses of snow, graupel, cloud water, and rain particles simulated by different schemes are close to each other. However, the simulation of the specific mass of ice crystals has great differences in both magnitude and distribution range, which determine the difference in the magnitude and the phase state simulation of the radar echo and precipitation by different microphysics schemes.
2022, 46(3): 621-644.
doi: 10.3878/j.issn.1006-9895.2106.21068
Abstract:
A physically consistent atmospheric objective analysis model, based on the constrained variational analysis method, was applied to the Tibetan Plateau for large-scale atmospheric structure analysis. This objective analysis model can deal with multisource measurements with different spatial and temporal resolutions, and satisfy the conservation of column-integrated mass, heat, moisture, and momentum using surface precipitation and flux data at the surface and top of the atmosphere to constrain the sounding measurements. An experiment during August 2014 around Naqu in the Tibetan Plateau shows that those state variables generated by the model can retain observational characteristics. The analyzed large-scale derivatives, such as vertical velocity, divergence, temperature and water vapor advection, apparent heat source, and apparent moisture sink, obtained by the objective analysis model, can reasonably demonstrate dynamic, thermal, and moisture structures during the analysis period, which is conducive to precipitation process studies. It also shows that the layer of 350–400 hPa is an important change center of dynamics, heat, and water vapor in the analysis region during August 2014. Different sources of measurements have different impacts on the final analysis fields in this model. The sounding measurement significantly impacts the upper-level wind, but the amplitude of this impact is small, within 1 m/s. Precipitation and flux measurements mainly affect the large-scale derivatives, such as vertical velocity, in which precipitation mainly affects the upward movement during precipitation periods, and flux data mainly affect the downward movement during light rain/no-rain periods. Generally, the physically consistent atmospheric variational objective analysis model has high stability and strong validity.
A physically consistent atmospheric objective analysis model, based on the constrained variational analysis method, was applied to the Tibetan Plateau for large-scale atmospheric structure analysis. This objective analysis model can deal with multisource measurements with different spatial and temporal resolutions, and satisfy the conservation of column-integrated mass, heat, moisture, and momentum using surface precipitation and flux data at the surface and top of the atmosphere to constrain the sounding measurements. An experiment during August 2014 around Naqu in the Tibetan Plateau shows that those state variables generated by the model can retain observational characteristics. The analyzed large-scale derivatives, such as vertical velocity, divergence, temperature and water vapor advection, apparent heat source, and apparent moisture sink, obtained by the objective analysis model, can reasonably demonstrate dynamic, thermal, and moisture structures during the analysis period, which is conducive to precipitation process studies. It also shows that the layer of 350–400 hPa is an important change center of dynamics, heat, and water vapor in the analysis region during August 2014. Different sources of measurements have different impacts on the final analysis fields in this model. The sounding measurement significantly impacts the upper-level wind, but the amplitude of this impact is small, within 1 m/s. Precipitation and flux measurements mainly affect the large-scale derivatives, such as vertical velocity, in which precipitation mainly affects the upward movement during precipitation periods, and flux data mainly affect the downward movement during light rain/no-rain periods. Generally, the physically consistent atmospheric variational objective analysis model has high stability and strong validity.
2022, 46(3): 645-652.
doi: 10.3878/j.issn.1006-9895.2108.21069
Abstract:
Spectra measured using an atmospheric carbon dioxide grating spectrometer (ACGS) by the Chinese global carbon dioxide monitoring scientific experimental satellite (TanSat) in the bands of 0.76, 1.61, and 2.06 μm can be used for retrieving carbon dioxide (CO2) concentrations by fitting observations and simulations using an optimal estimation algorithm. Accurately detecting the change in the center wavelength is important because of its very high spectral resolution and accuracy requirement for product retrieval. Variations in the center wavelength for all the three bands of ACGS have been calculated at the locations of the Fraunhofer lines by comparing solar-viewing measurements and a high-resolution solar reference spectrum. Variations in magnitudes less than 10% of the spectral resolution for each band have been detected. Changes are probably caused by the vibration and instrument status difference between the ground and space, especially the temperature variation in the orbit. The scheme described herein can be used not only for monitoring spectral stability but also to gain spectral knowledge prior to the level-2 product processing. These minor temporal changes in the wavelength in the orbit should be corrected during the product retrieval.
Spectra measured using an atmospheric carbon dioxide grating spectrometer (ACGS) by the Chinese global carbon dioxide monitoring scientific experimental satellite (TanSat) in the bands of 0.76, 1.61, and 2.06 μm can be used for retrieving carbon dioxide (CO2) concentrations by fitting observations and simulations using an optimal estimation algorithm. Accurately detecting the change in the center wavelength is important because of its very high spectral resolution and accuracy requirement for product retrieval. Variations in the center wavelength for all the three bands of ACGS have been calculated at the locations of the Fraunhofer lines by comparing solar-viewing measurements and a high-resolution solar reference spectrum. Variations in magnitudes less than 10% of the spectral resolution for each band have been detected. Changes are probably caused by the vibration and instrument status difference between the ground and space, especially the temperature variation in the orbit. The scheme described herein can be used not only for monitoring spectral stability but also to gain spectral knowledge prior to the level-2 product processing. These minor temporal changes in the wavelength in the orbit should be corrected during the product retrieval.
2022, 46(3): 653-665.
doi: 10.3878/j.issn.1006-9895.2203.21193
Abstract:
The lidar ratio (LR) is an important parameter and impact factor for the retrieval of aerosol optical properties using micro-pulse lidar. We analyze the vertical LR retrieved by the method of correcting micro-pulse lidar with aircraft observation using multiple-observation equipment during one clean case (December 10, 2016) and two pollution cases (November 15–18, December 16–19, 2016) in Beijing. PM2.5 concentration was lower than 40 μg m−3,while PM2.5 concentration was higher than 150 μg m−3, and visibility was lower than 5 km during the severe-pollution period. The first pollution case was characterized via high-altitude transportation. The vertical extinction coefficient profiles and aerosol optical depth (AOD) obtained by the iterative algorithm using the LR values were closer to the in-situ observation than those obtained by the single column average value. LR obtained from this method primarily varied between 19 and 76 sr in different periods. The results showed a small LR value and insignificant differences in vertical distribution during the cleaning period, and LR increased in height from 19 to 45 sr in the boundary layer during the first pollution case. During the second pollution case, LR presented little variation during the pollution-development period and later decreased in height from 70 to 20 sr at the boundary layer under the severe-pollution period, while there were slight fluctuations above the boundary layer. The vertical distribution of LR along the boundary layer is related to the source of aerosols, especially the regional transportation in the high layer, and regional dust transportation may significantly increase the LR. LR fluctuates due to the influence of large particles or strong absorbing particles above the boundary layer. The results showed that LR increased with the increase in the extinction coefficient at the boundary layer as well as relative humidity (RH) when RH was higher than 40%.
The lidar ratio (LR) is an important parameter and impact factor for the retrieval of aerosol optical properties using micro-pulse lidar. We analyze the vertical LR retrieved by the method of correcting micro-pulse lidar with aircraft observation using multiple-observation equipment during one clean case (December 10, 2016) and two pollution cases (November 15–18, December 16–19, 2016) in Beijing. PM2.5 concentration was lower than 40 μg m−3,while PM2.5 concentration was higher than 150 μg m−3, and visibility was lower than 5 km during the severe-pollution period. The first pollution case was characterized via high-altitude transportation. The vertical extinction coefficient profiles and aerosol optical depth (AOD) obtained by the iterative algorithm using the LR values were closer to the in-situ observation than those obtained by the single column average value. LR obtained from this method primarily varied between 19 and 76 sr in different periods. The results showed a small LR value and insignificant differences in vertical distribution during the cleaning period, and LR increased in height from 19 to 45 sr in the boundary layer during the first pollution case. During the second pollution case, LR presented little variation during the pollution-development period and later decreased in height from 70 to 20 sr at the boundary layer under the severe-pollution period, while there were slight fluctuations above the boundary layer. The vertical distribution of LR along the boundary layer is related to the source of aerosols, especially the regional transportation in the high layer, and regional dust transportation may significantly increase the LR. LR fluctuates due to the influence of large particles or strong absorbing particles above the boundary layer. The results showed that LR increased with the increase in the extinction coefficient at the boundary layer as well as relative humidity (RH) when RH was higher than 40%.
2022, 46(3): 666-676.
doi: 10.3878/j.issn.1006-9895.2112.21214
Abstract:
To determine regional transport and local contribution, vertical gradient observation of air pollutants is required. Based on this, the number concentrations of aerosols in the particle size range of 0.13–3.39 μm were recorded with an optical particle counter POPS (the Printed Optical Particle Spectrometer) at ground level and in a tethered airboat in Lhasa in August 2020. The results demonstrate that (1) near-ground aerosol number concentrations in Lhasa range from 16 cm−3 to 870 cm−3, which is 2–3 orders of magnitude lower than those in northern China and the Yangtze River Delta. (2) The daily variation structure of the aerosol number concentration display two peaks and valleys. The peaks, which correlate to morning and evening peaks [1000 BJT (Beijing time) and 2100 LT, respectively], are usually dominated by small particles of 0.13–0.4 μm. (3) Furthermore, the vertical distribution of the aerosol number concentration is closely related to the evolution of the boundary layer. The aerosol in the stable boundary layer decreases with height, and the particle number concentration is 194± 94 cm−3. Conversely, the aerosols in the convective boundary and residual layers are uniformly distributed with the number concentrations of 165±99 cm−3 and 123±95 cm−3, respectively, which are significantly lower than that in the stable boundary layer. According to the above research results, local motor vehicle emissions are the main sources of pollution in Lhasa. Therefore, motor vehicles must be controlled and emissions must be reduced to build a highland ecotourism city.
To determine regional transport and local contribution, vertical gradient observation of air pollutants is required. Based on this, the number concentrations of aerosols in the particle size range of 0.13–3.39 μm were recorded with an optical particle counter POPS (the Printed Optical Particle Spectrometer) at ground level and in a tethered airboat in Lhasa in August 2020. The results demonstrate that (1) near-ground aerosol number concentrations in Lhasa range from 16 cm−3 to 870 cm−3, which is 2–3 orders of magnitude lower than those in northern China and the Yangtze River Delta. (2) The daily variation structure of the aerosol number concentration display two peaks and valleys. The peaks, which correlate to morning and evening peaks [1000 BJT (Beijing time) and 2100 LT, respectively], are usually dominated by small particles of 0.13–0.4 μm. (3) Furthermore, the vertical distribution of the aerosol number concentration is closely related to the evolution of the boundary layer. The aerosol in the stable boundary layer decreases with height, and the particle number concentration is 194± 94 cm−3. Conversely, the aerosols in the convective boundary and residual layers are uniformly distributed with the number concentrations of 165±99 cm−3 and 123±95 cm−3, respectively, which are significantly lower than that in the stable boundary layer. According to the above research results, local motor vehicle emissions are the main sources of pollution in Lhasa. Therefore, motor vehicles must be controlled and emissions must be reduced to build a highland ecotourism city.
2022, 46(3): 677-690.
doi: 10.3878/j.issn.1006-9895.2202.22008
Abstract:
By analyzing how adjoint sensitivity (ADS), leading singular vector (LSV), and conditional nonlinear optimal perturbation (CNOP) methods are used to identify sensitive areas for target observation, the authors developed the concept of nonlinear degree. Moreover, the authors investigated the nonlinear degrees of straight and recurved types of typhoons. Subsequently, the sensitive areas identified using the three methods indicated earlier under different nonlinear degrees, together with the sensitive areas for straight and recurved types of typhoons, were analyzed. Finally, the sensitivity of the forecast to the initial values in the sensitive areas under different nonlinear degrees and for straight and recurved types of typhoons was explored. The results showed that the nonlinear degrees of recurved typhoons were quite different, either particularly strong or particularly weak, whereas negligible differences were observed among the nonlinear degrees of straight typhoons. For typhoons with weak nonlinearity, the sensitive areas identified using the three methods were similar, whereas for typhoons with strong nonlinearity, the sensitive areas identified by the LSV and ADS methods were similar, but they were quite different from those identified by the CNOP method. For recurved typhoons, the sensitive area was mainly located at the right front of its travel path, whereas for straight typhoons, the sensitive area was mainly located behind its travel path. The sensitivity test showed that the development of random perturbation in CNOP sensitive areas was the largest, regardless of whether the typhoon was strong nonlinear or not. In addition, the development of perturbation for weak nonlinear typhoons was greater than that for strong nonlinear typhoons. These results imply that the prediction for weak nonlinear typhoons is more sensitive to the initial uncertainty; thus, targeted observations for this kind of typhoon may be more effective.
By analyzing how adjoint sensitivity (ADS), leading singular vector (LSV), and conditional nonlinear optimal perturbation (CNOP) methods are used to identify sensitive areas for target observation, the authors developed the concept of nonlinear degree. Moreover, the authors investigated the nonlinear degrees of straight and recurved types of typhoons. Subsequently, the sensitive areas identified using the three methods indicated earlier under different nonlinear degrees, together with the sensitive areas for straight and recurved types of typhoons, were analyzed. Finally, the sensitivity of the forecast to the initial values in the sensitive areas under different nonlinear degrees and for straight and recurved types of typhoons was explored. The results showed that the nonlinear degrees of recurved typhoons were quite different, either particularly strong or particularly weak, whereas negligible differences were observed among the nonlinear degrees of straight typhoons. For typhoons with weak nonlinearity, the sensitive areas identified using the three methods were similar, whereas for typhoons with strong nonlinearity, the sensitive areas identified by the LSV and ADS methods were similar, but they were quite different from those identified by the CNOP method. For recurved typhoons, the sensitive area was mainly located at the right front of its travel path, whereas for straight typhoons, the sensitive area was mainly located behind its travel path. The sensitivity test showed that the development of random perturbation in CNOP sensitive areas was the largest, regardless of whether the typhoon was strong nonlinear or not. In addition, the development of perturbation for weak nonlinear typhoons was greater than that for strong nonlinear typhoons. These results imply that the prediction for weak nonlinear typhoons is more sensitive to the initial uncertainty; thus, targeted observations for this kind of typhoon may be more effective.
2022, 46(3): 691-706.
doi: 10.3878/j.issn.1006-9895.2201.21145
Abstract:
In present operating systems, indirect assimilation is frequently used to assimilate the radar reflectivity factor to avoid the problems caused by the linearization of the observation operator. Based on a real-time background-dependent radar reflectivity factor indirect assimilation scheme, cycling assimilation and forecasting experiments of four heavy rainfall processes (two convective and two frontal) were carried out. The results show that compared with the traditional temperature-determination scheme, the background-dependent scheme has smaller temperature forecast errors and higher precipitation forecast scores for the severe convective rainfall cases, but the difference in frontal process is not obvious. Further analysis shows that for severe convective rainfall, the background-dependent scheme introduced real-time background information when assimilating the reflectivity factor, allowing the hydrometeor structure of the analysis field to characterize the actual convective characteristics better and be more coordinated with other model variables, thereby improving the thermal, dynamic, and humidity conditions of the model forecast, thus improving precipitation forecasting. For heavy frontal rainfall, the hydrometeor structural difference in the analysis field of the two schemes is not obvious; thus, the difference in precipitation forecast is small.
In present operating systems, indirect assimilation is frequently used to assimilate the radar reflectivity factor to avoid the problems caused by the linearization of the observation operator. Based on a real-time background-dependent radar reflectivity factor indirect assimilation scheme, cycling assimilation and forecasting experiments of four heavy rainfall processes (two convective and two frontal) were carried out. The results show that compared with the traditional temperature-determination scheme, the background-dependent scheme has smaller temperature forecast errors and higher precipitation forecast scores for the severe convective rainfall cases, but the difference in frontal process is not obvious. Further analysis shows that for severe convective rainfall, the background-dependent scheme introduced real-time background information when assimilating the reflectivity factor, allowing the hydrometeor structure of the analysis field to characterize the actual convective characteristics better and be more coordinated with other model variables, thereby improving the thermal, dynamic, and humidity conditions of the model forecast, thus improving precipitation forecasting. For heavy frontal rainfall, the hydrometeor structural difference in the analysis field of the two schemes is not obvious; thus, the difference in precipitation forecast is small.
2022, 46(3): 707-724.
doi: 10.3878/j.issn.1006-9895.2111.21187
Abstract:
As a consequence of global warming, China has experienced increasing extreme precipitation events and secondary disasters such as floods and droughts, which have had significant effects on the ecosystem, production, life, and society. This study uses daily station precipitation records to systematically analyze the long-term trends in precipitation over China and nine river basins from 1961 to 2017. It uses ten precipitation indices specified by the Expert Team on Climate Change Detection and Indices (ETCCDI). In addition, the detectability of the trends in several precipitation characteristics is also examined based on the field significance test. The findings indicate that the extreme precipitation over China shows obvious regional features. The number of stations showing increasing trends in mean precipitation, precipitation intensity, extreme heavy precipitation, and continuous heavy precipitation exceeds the decreasing trends. However, the observed percentage of stations with significant increasing trends differs statistically from the internal climate variability but is influenced by the external forcings. Furthermore, for the majority of the station, the consecutive dry days (CDD) decreases, and the observed percentage of stations with significant decreasing trends is also related to the external forcing. Across the continental river basins, strengthened mean precipitation, precipitation intensity, extreme heavy precipitation, continuous heavy precipitation, and reduced CDD can be observed, which can be attributed to the influence of external forcings. Flood are becoming frequent in the continental. Strengthened mean precipitation and external force-related increase in heavy precipitation can be found across the Yangtze River, Pearl River, and southeastern river basin. The southwestern river basin has experienced an increase of extremely heavy precipitation, but there is a risk of increasing drought as the CDD lengthens for the majority of stations. Several precipitation indices and the area-averaged mean for the Yellow River, Haihe River, Huaihe River, and Songliao River basin. The various responses of precipitation characteristics to global warming suggest that the different river basins will experience a variety of climate disasters.
As a consequence of global warming, China has experienced increasing extreme precipitation events and secondary disasters such as floods and droughts, which have had significant effects on the ecosystem, production, life, and society. This study uses daily station precipitation records to systematically analyze the long-term trends in precipitation over China and nine river basins from 1961 to 2017. It uses ten precipitation indices specified by the Expert Team on Climate Change Detection and Indices (ETCCDI). In addition, the detectability of the trends in several precipitation characteristics is also examined based on the field significance test. The findings indicate that the extreme precipitation over China shows obvious regional features. The number of stations showing increasing trends in mean precipitation, precipitation intensity, extreme heavy precipitation, and continuous heavy precipitation exceeds the decreasing trends. However, the observed percentage of stations with significant increasing trends differs statistically from the internal climate variability but is influenced by the external forcings. Furthermore, for the majority of the station, the consecutive dry days (CDD) decreases, and the observed percentage of stations with significant decreasing trends is also related to the external forcing. Across the continental river basins, strengthened mean precipitation, precipitation intensity, extreme heavy precipitation, continuous heavy precipitation, and reduced CDD can be observed, which can be attributed to the influence of external forcings. Flood are becoming frequent in the continental. Strengthened mean precipitation and external force-related increase in heavy precipitation can be found across the Yangtze River, Pearl River, and southeastern river basin. The southwestern river basin has experienced an increase of extremely heavy precipitation, but there is a risk of increasing drought as the CDD lengthens for the majority of stations. Several precipitation indices and the area-averaged mean for the Yellow River, Haihe River, Huaihe River, and Songliao River basin. The various responses of precipitation characteristics to global warming suggest that the different river basins will experience a variety of climate disasters.
2022, 46(3): 725-744.
doi: 10.3878/j.issn.1006-9895.2202.21226
Abstract:
This study analyzes the water vapor transportation features, water vapor sources, and key synoptic-scale systems of the “7.20” rainstorm in Henan in 2021. Double typhoons “In-fa” and “Cempaka” and the western Pacific subtropical high jointly provided sufficient water vapor conditions for the “7.20” rainstorm in Henan. However, the extreme rainstorm event, which has daily precipitation of 663.9 mm and 1-hour maximum precipitation of 201.9 mm on July 20, can hardly be explained only by the roles of typhoons and western Pacific subtropical high. Results of the water vapor flux analysis and trajectory analysis based on the LAGRANTO model show that a strong northward water vapor flux zone (above 850 hPa) was formed on the southern side of Henan on July 20, 2021. It then converged with the low-level water vapor flux zone facilitated by the typhoon and western Pacific subtropical high near Henan, thus providing the most abundant water vapor conditions for the rainstorm. This work emphasizes that the anticyclonic wave-breaking event that occurred at the tropopause to the west of Henan on July 20 triggered a strong meridional water vapor flux on the southern side of Henan and worked synergistically with typhoons, resulting in this extreme rainstorm.
This study analyzes the water vapor transportation features, water vapor sources, and key synoptic-scale systems of the “7.20” rainstorm in Henan in 2021. Double typhoons “In-fa” and “Cempaka” and the western Pacific subtropical high jointly provided sufficient water vapor conditions for the “7.20” rainstorm in Henan. However, the extreme rainstorm event, which has daily precipitation of 663.9 mm and 1-hour maximum precipitation of 201.9 mm on July 20, can hardly be explained only by the roles of typhoons and western Pacific subtropical high. Results of the water vapor flux analysis and trajectory analysis based on the LAGRANTO model show that a strong northward water vapor flux zone (above 850 hPa) was formed on the southern side of Henan on July 20, 2021. It then converged with the low-level water vapor flux zone facilitated by the typhoon and western Pacific subtropical high near Henan, thus providing the most abundant water vapor conditions for the rainstorm. This work emphasizes that the anticyclonic wave-breaking event that occurred at the tropopause to the west of Henan on July 20 triggered a strong meridional water vapor flux on the southern side of Henan and worked synergistically with typhoons, resulting in this extreme rainstorm.
2022, 46(3): 745-761.
doi: 10.3878/j.issn.1006-9895.2201.21194
Abstract:
Recently, during 15–17 June 2021, an extreme rainstorm occurred on the northern slope of Kunlun mountain in southern Xinjiang, China. After considering the effects of geography on the rainstorm, a terrain-following, nonhydrostatic generalized vertical motion equation was built under Boussinesq approximation and terrain-following governing equations. Diagnostic results indicated that the three main forcing terms stimulating vertical motion development during the rainstorm were meridional pressure gradient force coupled with meridional divergence (first term), vertical pressure gradient force coupled with zonal divergence (second term), and meridional gradient of diabatic heating (third term). The first term reflected that the gradually increased northern flow led to the growth of meridional convergence under the blockage of Kunlun mountain, which activated the ascending motion. The lead forcing process for the convection was the meridional convergence, followed by zonal convergence. Meridional and vertical pressure gradients had an amplification effect on the first two terms in a terrain-following coordinate frame. The meridional gradient of diabatic heating was intensified by the water vapor convergence and diabatic heating processes during the convection development stage, thereby promoting the ascending motion. Westerly winds over the Kunlun mountain exhibited evident wave characteristics in the middle and upper troposphere under the influence of geography. The convection in the Kunlun mountain windward slope was strengthened by the upper divergence induced by a gravity wave. Thus, the rainstorm in southern Xinjiang was caused by the combined effects of meridional and zonal convergences, diabatic heating, and gravity wave activities.
Recently, during 15–17 June 2021, an extreme rainstorm occurred on the northern slope of Kunlun mountain in southern Xinjiang, China. After considering the effects of geography on the rainstorm, a terrain-following, nonhydrostatic generalized vertical motion equation was built under Boussinesq approximation and terrain-following governing equations. Diagnostic results indicated that the three main forcing terms stimulating vertical motion development during the rainstorm were meridional pressure gradient force coupled with meridional divergence (first term), vertical pressure gradient force coupled with zonal divergence (second term), and meridional gradient of diabatic heating (third term). The first term reflected that the gradually increased northern flow led to the growth of meridional convergence under the blockage of Kunlun mountain, which activated the ascending motion. The lead forcing process for the convection was the meridional convergence, followed by zonal convergence. Meridional and vertical pressure gradients had an amplification effect on the first two terms in a terrain-following coordinate frame. The meridional gradient of diabatic heating was intensified by the water vapor convergence and diabatic heating processes during the convection development stage, thereby promoting the ascending motion. Westerly winds over the Kunlun mountain exhibited evident wave characteristics in the middle and upper troposphere under the influence of geography. The convection in the Kunlun mountain windward slope was strengthened by the upper divergence induced by a gravity wave. Thus, the rainstorm in southern Xinjiang was caused by the combined effects of meridional and zonal convergences, diabatic heating, and gravity wave activities.
2022, 46(3): 762-774.
doi: 10.3878/j.issn.1006-9895.2202.21247
Abstract:
Mesoscale vortex usually stimulates local convection, which is an important system for persistent precipitation. The solution to the classical vorticity equation cannot directly describe and quantify the contribution of thermodynamic information to the development of vortices. In this study, the Boussinesq approximation is adopted to rewrite the vorticity equation, and the only forcing term employed is the vertical velocity potential vorticity. The form of this forcing term is similar to that of potential vorticity; however, vertical velocity is used instead of the potential temperature. Furthermore, the indirect effect of the thermodynamic process is introduced in the form of the horizontal pressure gradient to quantitatively describe the contribution of the dynamic and thermodynamic configurations to the vertical velocity potential vorticity equation. A heavy rain event, which occurred in southern Xinjiang on June 15, 2021, was selected as a case to analyze the transfer of low-level thermodynamic forcing to vertical vorticity using high-resolution numerical simulation data. The results showed that the local variation of the vertical velocity potential vorticity mainly originates from the coupling effect of the low-level vertical wind shear and low-level cold pool in the thermodynamic term, which contributed to a wide region of positive values ahead of the rainband. This pattern promotes the growth of vertical velocity potential vorticity in the corresponding region. The distribution and tendency of vertical velocity potential vorticity help maintain the positive vorticity ahead of the rainband, thereby making it conducive to the generation of strong ascending motion and new convection, directly leading to continuous precipitation.
Mesoscale vortex usually stimulates local convection, which is an important system for persistent precipitation. The solution to the classical vorticity equation cannot directly describe and quantify the contribution of thermodynamic information to the development of vortices. In this study, the Boussinesq approximation is adopted to rewrite the vorticity equation, and the only forcing term employed is the vertical velocity potential vorticity. The form of this forcing term is similar to that of potential vorticity; however, vertical velocity is used instead of the potential temperature. Furthermore, the indirect effect of the thermodynamic process is introduced in the form of the horizontal pressure gradient to quantitatively describe the contribution of the dynamic and thermodynamic configurations to the vertical velocity potential vorticity equation. A heavy rain event, which occurred in southern Xinjiang on June 15, 2021, was selected as a case to analyze the transfer of low-level thermodynamic forcing to vertical vorticity using high-resolution numerical simulation data. The results showed that the local variation of the vertical velocity potential vorticity mainly originates from the coupling effect of the low-level vertical wind shear and low-level cold pool in the thermodynamic term, which contributed to a wide region of positive values ahead of the rainband. This pattern promotes the growth of vertical velocity potential vorticity in the corresponding region. The distribution and tendency of vertical velocity potential vorticity help maintain the positive vorticity ahead of the rainband, thereby making it conducive to the generation of strong ascending motion and new convection, directly leading to continuous precipitation.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21097
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21199
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2205.22005
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.22009
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21125
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2204.21208
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21236
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2205.22011
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2205.21205
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2204.22017
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2205.22058B
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doi: 10.3878/j.issn.1006-9895.2205.21023
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doi: 10.3878/j.issn.1006-9895.2202.21103
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2204.21188
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21201
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21227
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Numerical Simulation and Analysis of the Persistent Sea Fog in the Qiongzhou Strait in February 2018
, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21265
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.22004
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doi: 10.3878/j.issn.1006-9895.2204.22034
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doi: 10.3878/j.issn.1006-9895.2204.22037
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2204.21123B
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doi: 10.3878/j.issn.1006-9895.2203.21259
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doi: 10.3878/j.issn.1006-9895.2203.22016
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2112.21154
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2204.21222
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21176
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21085
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21210
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Thermodynamic characteristics over North Asian of the steady warming process before the summer onset
, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21238
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21254
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21229
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21159
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21156
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21252
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2204.21169
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21138
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21180
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2203.21216
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21245
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2112.20247
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.22018
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21096
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21109
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21118
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2112.21112
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2109.21140
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2109.21065
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2112.21105
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21163
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21104
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2112.21120
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21167
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doi: 10.3878/j.issn.1006-9895.2112.21174
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21204
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doi: 10.3878/j.issn.1006-9895.2202.21207
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21186
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21171
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2202.21077
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2111.21184
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21095
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2201.21182
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doi: 10.3878/j.issn.1006-9895.2112.21218
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doi: 10.3878/j.issn.1006-9895.2110.20191
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doi: 10.3878/j.issn.1006-9895.2201.21081
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2111.21051
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doi: 10.3878/j.issn.1006-9895.2110.21101
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doi: 10.3878/j.issn.1006-9895.2108.21102
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doi: 10.3878/j.issn.1006-9895.2112.21127
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2110.21139
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doi: 10.3878/j.issn.1006-9895.2112.21147
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doi: 10.3878/j.issn.1006-9895.2111.21141
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2110.21142
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doi: 10.3878/j.issn.1006-9895.2111.21099
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doi: 10.3878/j.issn.1006-9895.2109.21050
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doi: 10.3878/j.issn.1006-9895.2108.21032
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doi: 10.3878/j.issn.1006-9895.2111.21124
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doi: 10.3878/j.issn.1006-9895.2111.21128
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doi: 10.3878/j.issn.1006-9895.2104.21014
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doi: 10.3878/j.issn.1006-9895.2110.21083
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2111.21143
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doi: 10.3878/j.issn.1006-9895.2108.21045
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Statistical characteristics of tropical cyclone gale and its accompanying weather in southeast China
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doi: 10.3878/j.issn.1006-9895.2110.21136
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2111.21178
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2108.21108
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doi: 10.3878/j.issn.1006-9895.2110.21116
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doi: 10.3878/j.issn.1006-9895.2110.21133
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2110.20220
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doi: 10.3878/j.issn.1006-9895.2110.21054
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doi: 10.3878/j.issn.1006-9895.2107.21049
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doi: 10.3878/j.issn.1006-9895.2105.21063
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2106.21075
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doi: 10.3878/j.issn.1006-9895.2109.21119
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2105.21042
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, Available online ,
doi: 10.3878/j.issn.1006-9895.2108.21071
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Since 1976 Bimonthly
Supervisor: Chinese Academy of Sciences
Sponsors by: Institute of Atmospheric Physics, Chinese Academy of Sciences, Chinese Meteorological Society
Editor: Lu Riyu
Email: dqkx@mail.iap.ac.cn
dqkx@post.iap.ac.cn
ISSN 1006-9895
CN 11-1768/O4
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