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doi: 10.3878/j.issn.1006-9895.2106.21047
Abstract:
Using the National Centers for Environmental Prediction/Department of Energy reanalysis 2 and the National Oceanic and Atmospheric Administration sea surface temperatures (SSTs) during the 1985–2015 period, eight warm events in the North Pacific are selected based on the definition of large-scale SST anomalies. The dynamic composite method, following the SST anomaly center, is used to study the large-scale SST warm anomalies with a lifespan of 50 days over the wintertime North Pacific and associated characteristics of the air–sea interaction on submonthly timescales before and after their peak stages. The results show the following: (1) the early stage of the large-scale SST warm anomalies are mainly characterized by the forcing of the atmosphere on the ocean, whereas the late stage is dominated by the forcing of the ocean on the atmosphere. (2) The atmospheric structure associated with the SST warm anomalies changes significantly from the early to late stages. The early stage shows an equivalent barotropic dipole pattern of pressure anomalies above the warmer SSTs, with an anomalous high in the northeast and an anomalous low in the southwest, corresponding to the anomalous easterly wind over SST anomalies. At the late stage, an equivalent barotropic anomalous cyclone is located to the north of warmer SSTs, with a weak anomalous anticyclone to the south, corresponding to the anomalous westerly wind over SST anomalies. (3) The cyclonic circulation anomaly occurs at the late stage mainly due to the high-frequency transient eddy vorticity feedback forcing, which acts as the major contributing factor. (4) The structure of the ocean current is also different between the early and late stages. At the early stage, the ocean dynamic process is not conducive to maintaining the SST warm anomalies. At the late stage, both anomalous warm advection and anomalous downwelling act to maintain the SST warming and thus its influence on the atmosphere.
Using the National Centers for Environmental Prediction/Department of Energy reanalysis 2 and the National Oceanic and Atmospheric Administration sea surface temperatures (SSTs) during the 1985–2015 period, eight warm events in the North Pacific are selected based on the definition of large-scale SST anomalies. The dynamic composite method, following the SST anomaly center, is used to study the large-scale SST warm anomalies with a lifespan of 50 days over the wintertime North Pacific and associated characteristics of the air–sea interaction on submonthly timescales before and after their peak stages. The results show the following: (1) the early stage of the large-scale SST warm anomalies are mainly characterized by the forcing of the atmosphere on the ocean, whereas the late stage is dominated by the forcing of the ocean on the atmosphere. (2) The atmospheric structure associated with the SST warm anomalies changes significantly from the early to late stages. The early stage shows an equivalent barotropic dipole pattern of pressure anomalies above the warmer SSTs, with an anomalous high in the northeast and an anomalous low in the southwest, corresponding to the anomalous easterly wind over SST anomalies. At the late stage, an equivalent barotropic anomalous cyclone is located to the north of warmer SSTs, with a weak anomalous anticyclone to the south, corresponding to the anomalous westerly wind over SST anomalies. (3) The cyclonic circulation anomaly occurs at the late stage mainly due to the high-frequency transient eddy vorticity feedback forcing, which acts as the major contributing factor. (4) The structure of the ocean current is also different between the early and late stages. At the early stage, the ocean dynamic process is not conducive to maintaining the SST warm anomalies. At the late stage, both anomalous warm advection and anomalous downwelling act to maintain the SST warming and thus its influence on the atmosphere.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2008.20157
Abstract:
Using the analyses and leading 35-day predictions with the Global and Regional Assimilation Prediction System-Global Forecast System (GRAPES-GFS) during the period from September 2018 to August 2019, we diagnosed the prediction errors and evaluated the extended forecast capability to provide a numerical weather guidance for the prediction at a sub-seasonal timescale. Results showed that, GRAPES-GFS could capture the spatial distribution characteristics of 2-m temperatures and 500 hPa geopotential heights during the winter in 2018 and summer in 2019, however there existed large system bias related to 2-m temperature analysis in the desert plateau areas where there was significant thermal forcing effect, especially in arid areas of Africa. Related to the 2-m temperature, the Root-Mean-Square Errors (RMSE) of the leading 1- to 3-week predictions approximated to the linear growth. GRAPES-GFS possessed a high prediction skill in the East Asia and Austria but had relatively low prediction skills in the ocean areas compared with that of the land areas. For the leading 1- to 3-week predictions related to the 500 hPa geopotential height, the prediction skills were higher at the low latitudes than at the high latitudes of East Asia. Also, the prediction skills for the tropics were much lower than for the other regions, of which the northern hemisphere was higher than that of the southern hemisphere. Regarding to the related Madden-Julian Oscillation (MJO), it is found that GRAPES-GFS could reproduce the propagation characteristics of spatial-temporal variations related to the upper and lower zonal wind and could capture the location of strong convective activity signals. However, the positive anomaly of the Outgoing Long Wave Radiation (OLR) was much weaker and the negative anomaly was much stronger. GRAPES-GFS could skillfully forecast MJO with 11 leading days from the view of Anomaly Correlation Coefficient (ACC), which was about the same level as the results from other forecasting models. For the selected two strong MJO cases, GRAPES-GFS could describe the MJO propagation process exactly but had a stronger signal during the MJO developing and decaying periods.
Using the analyses and leading 35-day predictions with the Global and Regional Assimilation Prediction System-Global Forecast System (GRAPES-GFS) during the period from September 2018 to August 2019, we diagnosed the prediction errors and evaluated the extended forecast capability to provide a numerical weather guidance for the prediction at a sub-seasonal timescale. Results showed that, GRAPES-GFS could capture the spatial distribution characteristics of 2-m temperatures and 500 hPa geopotential heights during the winter in 2018 and summer in 2019, however there existed large system bias related to 2-m temperature analysis in the desert plateau areas where there was significant thermal forcing effect, especially in arid areas of Africa. Related to the 2-m temperature, the Root-Mean-Square Errors (RMSE) of the leading 1- to 3-week predictions approximated to the linear growth. GRAPES-GFS possessed a high prediction skill in the East Asia and Austria but had relatively low prediction skills in the ocean areas compared with that of the land areas. For the leading 1- to 3-week predictions related to the 500 hPa geopotential height, the prediction skills were higher at the low latitudes than at the high latitudes of East Asia. Also, the prediction skills for the tropics were much lower than for the other regions, of which the northern hemisphere was higher than that of the southern hemisphere. Regarding to the related Madden-Julian Oscillation (MJO), it is found that GRAPES-GFS could reproduce the propagation characteristics of spatial-temporal variations related to the upper and lower zonal wind and could capture the location of strong convective activity signals. However, the positive anomaly of the Outgoing Long Wave Radiation (OLR) was much weaker and the negative anomaly was much stronger. GRAPES-GFS could skillfully forecast MJO with 11 leading days from the view of Anomaly Correlation Coefficient (ACC), which was about the same level as the results from other forecasting models. For the selected two strong MJO cases, GRAPES-GFS could describe the MJO propagation process exactly but had a stronger signal during the MJO developing and decaying periods.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2103.21021
Abstract:
With the construction of about 70,000 automatic weather stations across China, a comprehensively automatic meteorological observation has been realized. However, the real application of this kind of observation always suffers from their low quality. A large number of error data seriously affects the practical application of observation. Therefore, it is a particularly important task to repair these abnormal observations. Using a total of 168 times of hourly surface temperature observations of automatic weather station during December 1–7, 2019, which is provided by the Jiangsu meteorological bureau, a restoration method based on the empirical orthogonal function method is proposed. The accuracy analysis of ideal restoration experiments shows that the new restoration method can well repair wrong observations with an error of about 0.48 degrees centigrade. The methods based on the Cressman interpolation, which relies on a single point observation information, are more vulnerable to small-scale signal interferences and introduce unnatural observation information, with the surface temperature repair error reaching up to 1.55 degrees centigrade. The analysis of the actual repair results also proves that the new repair method makes full use of the time-space separation and modal orthogonality of the EOF analysis method and gradually eliminates the influence of wrong data through an iterative method to obtain better space-time continuity repair results with the surrounding observation data.
With the construction of about 70,000 automatic weather stations across China, a comprehensively automatic meteorological observation has been realized. However, the real application of this kind of observation always suffers from their low quality. A large number of error data seriously affects the practical application of observation. Therefore, it is a particularly important task to repair these abnormal observations. Using a total of 168 times of hourly surface temperature observations of automatic weather station during December 1–7, 2019, which is provided by the Jiangsu meteorological bureau, a restoration method based on the empirical orthogonal function method is proposed. The accuracy analysis of ideal restoration experiments shows that the new restoration method can well repair wrong observations with an error of about 0.48 degrees centigrade. The methods based on the Cressman interpolation, which relies on a single point observation information, are more vulnerable to small-scale signal interferences and introduce unnatural observation information, with the surface temperature repair error reaching up to 1.55 degrees centigrade. The analysis of the actual repair results also proves that the new repair method makes full use of the time-space separation and modal orthogonality of the EOF analysis method and gradually eliminates the influence of wrong data through an iterative method to obtain better space-time continuity repair results with the surrounding observation data.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2102.20173
Abstract:
This paper mainly focuses on resolving the numerical weather prediction problem in the steep orographic region of China. The stepped terrain vertical coordinate (known as Eta) is introduced into the dynamic core of the weather research and forecasting (WRF) model to improve numerical forecasting in the complex orographic region. We designed the atmospheric column mass transformation scheme to give the Eta WRF core the same model equation system formulation as the Sigma WRF core, which can facilitate discretization and programming. The design of the stepped terrain follows the computational scheme of the advanced regional Eta-coordinate model (AREM), including the introduction of the reference atmosphere, the adoption of mesh description indicators, and the representation of stepped mountains. We performed 2D idealized mountain wave simulations and 3D real-case experiments to test the correctness and robustness of the new dynamic frame. Inherent isolation of the stepped topography can result in airflow separation, which accounts for inadequate simulation of the mountain wave with a coarse vertical layering using the new Eta WRF core. In this case, the mountain wave simulation will improve using the new dynamic frame either because of the fine vertical resolution or the long simulation time, which is considered alleviation on the airflow isolation in stepped mountains.
This paper mainly focuses on resolving the numerical weather prediction problem in the steep orographic region of China. The stepped terrain vertical coordinate (known as Eta) is introduced into the dynamic core of the weather research and forecasting (WRF) model to improve numerical forecasting in the complex orographic region. We designed the atmospheric column mass transformation scheme to give the Eta WRF core the same model equation system formulation as the Sigma WRF core, which can facilitate discretization and programming. The design of the stepped terrain follows the computational scheme of the advanced regional Eta-coordinate model (AREM), including the introduction of the reference atmosphere, the adoption of mesh description indicators, and the representation of stepped mountains. We performed 2D idealized mountain wave simulations and 3D real-case experiments to test the correctness and robustness of the new dynamic frame. Inherent isolation of the stepped topography can result in airflow separation, which accounts for inadequate simulation of the mountain wave with a coarse vertical layering using the new Eta WRF core. In this case, the mountain wave simulation will improve using the new dynamic frame either because of the fine vertical resolution or the long simulation time, which is considered alleviation on the airflow isolation in stepped mountains.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2106.21041
Abstract:
This review summarizes the research progresses on tropical synoptic systems and mesoscale convective processes during the warm season (May–October) over the South China Sea in recent decades. The basic characteristics of tropical atmospheric circulation and summer monsoon related to mesoscale convective processes are briefly reviewed. Furthermore, the activity regularities, structural features, and formation mechanisms of mesoscale convective systems are emphatically summarized. Opportunities and challenges involving mesoscale convective processes currently occurring over the South China Sea are identified, and future research directions in this field are highlighted.
This review summarizes the research progresses on tropical synoptic systems and mesoscale convective processes during the warm season (May–October) over the South China Sea in recent decades. The basic characteristics of tropical atmospheric circulation and summer monsoon related to mesoscale convective processes are briefly reviewed. Furthermore, the activity regularities, structural features, and formation mechanisms of mesoscale convective systems are emphatically summarized. Opportunities and challenges involving mesoscale convective processes currently occurring over the South China Sea are identified, and future research directions in this field are highlighted.
, Available online ,
doi: 10.3878/j.issn.1006-9895.2105.21002
Abstract:
This paper analyzes the anomalous characteristics of precipitation in the east of southwestern China (ESWC) during June–July 2020 and the related large-scale characteristics of water vapor transport, water vapor budget, and water vapor source using correlation, regression, clustering, hybrid single-particle Lagrangian integrated trajectory (HYSPLITv5.0) model simulation, and other statistical methods based on the daily precipitation data of 118 stations and other reanalysis data. Some indexes of the water vapor intensity in key areas are defined, and the relationship between the water vapor intensity in key areas and sea temperature is investigated. Results show that the average precipitation in the ESWC during June–July 2020 is 50% more than that in the normal year, which is the highest since 1961. Precipitation in most areas is obviously higher than that in the normal year, except for some areas in central Guizhou and northeastern Sichuan. The configuration of the tropospheric atmospheric circulation field during June–July 2020 is a typical rainy circulation situation in the ESWC. At 200 hPa, the position of the upper jet stream leans to the south, and the ESWC is located just south of the jet axis with a strong divergence outflow from the upper layer and a strong convergence inflow from the lower layer, providing favorable dynamic conditions for precipitation. In addition, the western Pacific subtropical high (WPSH) obviously extends westward, and the warm and humid airflow in the southwest side of the WPSH is transported to the ESWC, which is conducive to more precipitation in this region. The quantitative water vapor trajectory tracking results calculated by the Lagrange method show that there are 70.5% of the water vapor paths associated with precipitation in the ESWC during June–July 2020 from the southern routes such as the Bay of Bengal, the South China Sea, and the Arabian Sea, while 17.6% and 11.9% comes from the northern route and the local area, respectively. In the previous winter, the SST (Surface Sea Temperature) of the equatorial Middle East Pacific and the Indian Ocean was relatively high, the WPSH is obviously strong and westward, resulting in the east wind anomaly in the Bay of Bengal and the South China Sea, which is favorable for the westward water vapor transport in the South China Sea but unfavorable for the eastward water vapor transport in the Bay of Bengal. Meanwhile, the anomalous anticyclone from the Philippines to the South China Sea makes the south wind anomaly in the northern part of the Indo-China peninsula, which is conducive to the strong northward water vapor transport in this area. These together resulted in more precipitation in the ESWC.
This paper analyzes the anomalous characteristics of precipitation in the east of southwestern China (ESWC) during June–July 2020 and the related large-scale characteristics of water vapor transport, water vapor budget, and water vapor source using correlation, regression, clustering, hybrid single-particle Lagrangian integrated trajectory (HYSPLITv5.0) model simulation, and other statistical methods based on the daily precipitation data of 118 stations and other reanalysis data. Some indexes of the water vapor intensity in key areas are defined, and the relationship between the water vapor intensity in key areas and sea temperature is investigated. Results show that the average precipitation in the ESWC during June–July 2020 is 50% more than that in the normal year, which is the highest since 1961. Precipitation in most areas is obviously higher than that in the normal year, except for some areas in central Guizhou and northeastern Sichuan. The configuration of the tropospheric atmospheric circulation field during June–July 2020 is a typical rainy circulation situation in the ESWC. At 200 hPa, the position of the upper jet stream leans to the south, and the ESWC is located just south of the jet axis with a strong divergence outflow from the upper layer and a strong convergence inflow from the lower layer, providing favorable dynamic conditions for precipitation. In addition, the western Pacific subtropical high (WPSH) obviously extends westward, and the warm and humid airflow in the southwest side of the WPSH is transported to the ESWC, which is conducive to more precipitation in this region. The quantitative water vapor trajectory tracking results calculated by the Lagrange method show that there are 70.5% of the water vapor paths associated with precipitation in the ESWC during June–July 2020 from the southern routes such as the Bay of Bengal, the South China Sea, and the Arabian Sea, while 17.6% and 11.9% comes from the northern route and the local area, respectively. In the previous winter, the SST (Surface Sea Temperature) of the equatorial Middle East Pacific and the Indian Ocean was relatively high, the WPSH is obviously strong and westward, resulting in the east wind anomaly in the Bay of Bengal and the South China Sea, which is favorable for the westward water vapor transport in the South China Sea but unfavorable for the eastward water vapor transport in the Bay of Bengal. Meanwhile, the anomalous anticyclone from the Philippines to the South China Sea makes the south wind anomaly in the northern part of the Indo-China peninsula, which is conducive to the strong northward water vapor transport in this area. These together resulted in more precipitation in the ESWC.
2022 Issue 1
Display Method:
2022, 46(1): 1-14.
doi: 10.3878/j.issn.1006-9895.2107.20217
Abstract:
Based on quality control of the hourly rain gauge dataset in 39 years (1981–2019) from 51 meteorological stations provided by the Meteorological Information Center of Jilin Province, the spatial and temporal distribution characteristics of precipitation during the northeast cold vortex process in the warm season were analyzed. Results showed that: (1) Overall, precipitation in Jilin Province exhibited a clear diurnal variation. The peaks of diurnal precipitation and frequency occurred during 1600–1800 BJT (Beijing time). Frequency of 0.1–5 mm h−1 precipitation (P＜5 mm h−1) exhibited a large value in the mountainous area in eastern Jilin Province. However, the high-value center moved to the south–central part of Jilin Province, whereas the precipitation was larger than 5 mm h−1 (P＞5 mm h−1). (2) Only a slight difference in the spatial distribution of the contribution of P＜5 mm h−1 to warm-season precipitation in Jilin Province during the daytime was observed. However, the value center was detected more clearly in the mountainous area in eastern Jilin Province at night. The contribution of the gauge record between 5 mm h−1 and 10 mm h−1 (5 mm h−1＜P＜10 mm h−1) was greater in central Jilin Province. Moreover, the contribution was greater during the daytime than at night. By contrast, for P＞10 mm h−1, the high-value center moved to the mid-west of Jilin Province. Similarly, the contribution was greater during the daytime than at night. (3) The rainfall amount of P＜5 mm h−1 accounted for 61% of total precipitation, and the rainfall amounts of 5 mm h−1＜P＜10 mm h−1 and P＞10 mm h−1 accounted for about 20% of total precipitation. The contribution of P＜5 mm h−1 exhibited a decreasing trend in recent years. By contrast, the contribution of P＞10 mm h−1 exhibited an increasing trend.
Based on quality control of the hourly rain gauge dataset in 39 years (1981–2019) from 51 meteorological stations provided by the Meteorological Information Center of Jilin Province, the spatial and temporal distribution characteristics of precipitation during the northeast cold vortex process in the warm season were analyzed. Results showed that: (1) Overall, precipitation in Jilin Province exhibited a clear diurnal variation. The peaks of diurnal precipitation and frequency occurred during 1600–1800 BJT (Beijing time). Frequency of 0.1–5 mm h−1 precipitation (P＜5 mm h−1) exhibited a large value in the mountainous area in eastern Jilin Province. However, the high-value center moved to the south–central part of Jilin Province, whereas the precipitation was larger than 5 mm h−1 (P＞5 mm h−1). (2) Only a slight difference in the spatial distribution of the contribution of P＜5 mm h−1 to warm-season precipitation in Jilin Province during the daytime was observed. However, the value center was detected more clearly in the mountainous area in eastern Jilin Province at night. The contribution of the gauge record between 5 mm h−1 and 10 mm h−1 (5 mm h−1＜P＜10 mm h−1) was greater in central Jilin Province. Moreover, the contribution was greater during the daytime than at night. By contrast, for P＞10 mm h−1, the high-value center moved to the mid-west of Jilin Province. Similarly, the contribution was greater during the daytime than at night. (3) The rainfall amount of P＜5 mm h−1 accounted for 61% of total precipitation, and the rainfall amounts of 5 mm h−1＜P＜10 mm h−1 and P＞10 mm h−1 accounted for about 20% of total precipitation. The contribution of P＜5 mm h−1 exhibited a decreasing trend in recent years. By contrast, the contribution of P＞10 mm h−1 exhibited an increasing trend.
2022, 46(1): 15-26.
doi: 10.3878/j.issn.1006-9895.2108.20226
Abstract:
Based on the NCEP/NCAR reanalysis and the datasets of daily basic meteorological elements from China’s national meteorological stations, this study investigates the statistical characteristics of the regional daily precipitation extreme events (RDPEs) in the Yangtze–Huaihe rivers (YHR) region in eastern China from 1979 to 2016 and their relationships with Rossby wave activities. The results show that in the summer seasons (June–July) of 1979–2016, the 95th percentile threshold of the regional extreme daily precipitation in the YHR region is 33.95 mm d−1. There have been a total of 63 RDPEs in the past 38 years. The occurrence of RDPEs in the YHR region is controlled by an anomalous cyclonic circulation in the middle and lower troposphere and an anomalous anticyclonic circulation in the upper troposphere. The water vapor from the Bay of Bengal and the South China Sea has a strong concentration in the YHR region. The baroclinic circulation and sufficient water vapor are conducive to the occurrence and development of RDPEs. The eddy enstrophy in the upper troposphere over the YHR region reaches its maximum on the day before RDPEs occur and rapidly decreases thereafter. Meanwhile, the eddy enstrophy in the middle and lower troposphere reaches its maximum when RDPEs occur. This is dominated by processes including the advection term of the time average flow to the disturbed vorticity and the horizontal divergence term of the disturbed flow. Moreover, Rossby waves originate near the Caspian and Black Seas, and clearly disperse downstream. It takes approximately 3–5 days to move to the YHR region, providing disturbance energy for the formation of RDPEs in this region. Overall, these results have deepened the understanding of the reasons for the occurrence of RDPEs in the YHR region and could provide clues for effective predictions.
Based on the NCEP/NCAR reanalysis and the datasets of daily basic meteorological elements from China’s national meteorological stations, this study investigates the statistical characteristics of the regional daily precipitation extreme events (RDPEs) in the Yangtze–Huaihe rivers (YHR) region in eastern China from 1979 to 2016 and their relationships with Rossby wave activities. The results show that in the summer seasons (June–July) of 1979–2016, the 95th percentile threshold of the regional extreme daily precipitation in the YHR region is 33.95 mm d−1. There have been a total of 63 RDPEs in the past 38 years. The occurrence of RDPEs in the YHR region is controlled by an anomalous cyclonic circulation in the middle and lower troposphere and an anomalous anticyclonic circulation in the upper troposphere. The water vapor from the Bay of Bengal and the South China Sea has a strong concentration in the YHR region. The baroclinic circulation and sufficient water vapor are conducive to the occurrence and development of RDPEs. The eddy enstrophy in the upper troposphere over the YHR region reaches its maximum on the day before RDPEs occur and rapidly decreases thereafter. Meanwhile, the eddy enstrophy in the middle and lower troposphere reaches its maximum when RDPEs occur. This is dominated by processes including the advection term of the time average flow to the disturbed vorticity and the horizontal divergence term of the disturbed flow. Moreover, Rossby waves originate near the Caspian and Black Seas, and clearly disperse downstream. It takes approximately 3–5 days to move to the YHR region, providing disturbance energy for the formation of RDPEs in this region. Overall, these results have deepened the understanding of the reasons for the occurrence of RDPEs in the YHR region and could provide clues for effective predictions.
2022, 46(1): 27-39.
doi: 10.3878/j.issn.1006-9895.2102.20233
Abstract:
Vegetation coverage is extremely sensitive to climate change. North China is located in the semiarid and subhumid transitional region of China. Meteorological factors have an important impact on the vegetation coverage in this area. However, effective mathematical models to quantitatively describe the influences of meteorological elements on vegetation are lacking. Therefore, based on the vegetation coverage data of the Moderate Resolution Imaging Spectroradiometer and main meteorological element data in North China from 2000 to 2018, the authors analyzed the influence of multiple meteorological elements on vegetation coverage and initially established the relationship between the summer vegetation coverage and meteorological elements in North China. The main study conclusions are summarized as follows: (1) A trend toward warm and dry climate conditions in North China is observed, and summer vegetation coverage is positively correlated with precipitation and relative humidity and negatively correlated with temperature, sunshine hours, and ground temperature. (2) The most important meteorological element affecting the vegetation coverage in North China is relative humidity, which reflects the combined effect of temperature and precipitation. (3) The multiple regression and least squares methods can quantitatively describe the possible impact of the changes in meteorological elements on vegetation coverage. Therefore, the five-variable combination of meteorological elements can better simulate the change in vegetation coverage. Results elucidate how meteorological elements affect vegetation ecosystem and provide a theoretical reference for constructing national ecological civilization.
Vegetation coverage is extremely sensitive to climate change. North China is located in the semiarid and subhumid transitional region of China. Meteorological factors have an important impact on the vegetation coverage in this area. However, effective mathematical models to quantitatively describe the influences of meteorological elements on vegetation are lacking. Therefore, based on the vegetation coverage data of the Moderate Resolution Imaging Spectroradiometer and main meteorological element data in North China from 2000 to 2018, the authors analyzed the influence of multiple meteorological elements on vegetation coverage and initially established the relationship between the summer vegetation coverage and meteorological elements in North China. The main study conclusions are summarized as follows: (1) A trend toward warm and dry climate conditions in North China is observed, and summer vegetation coverage is positively correlated with precipitation and relative humidity and negatively correlated with temperature, sunshine hours, and ground temperature. (2) The most important meteorological element affecting the vegetation coverage in North China is relative humidity, which reflects the combined effect of temperature and precipitation. (3) The multiple regression and least squares methods can quantitatively describe the possible impact of the changes in meteorological elements on vegetation coverage. Therefore, the five-variable combination of meteorological elements can better simulate the change in vegetation coverage. Results elucidate how meteorological elements affect vegetation ecosystem and provide a theoretical reference for constructing national ecological civilization.
2022, 46(1): 40-54.
doi: 10.3878/j.issn.1006-9895.2104.20241
Abstract:
This study focuses on the bias of the multimodel ensemble mean in the precipitation simulated using models of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) compared with the precipitation data using Climatic Research Unit Timeseries version 4.0 (CRU TS v4.0). Three bias correction methods are tested, and a precipitation projection with the correction is made for the coming 30 years (2021–2050) based on the selected 20 CMIP5 models. Results show that the precipitation in the CMIP5 historical simulation is overestimated in northern Asia and underestimated in the south for 1960–2005 with 30%–40% more precipitation than that observed in the Tibetan Plateau, Inner Mongolia, and Mongolia; 20%–30% less in the South China Coast and Vietnam; and 30%–40% less in South Asia than that of the observation. The bias pattern of the projected precipitation for 2006–2015 under the Representative Concentration Pathway (RCP) 4.5 scenario is found to be similar to that from the CMIP5 historical climate simulation, implying that the bias pattern is almost stationary and should belong to the model climate drift that can be removed using the difference between the period-mean projection and historical simulation. However, this bias correction leads to a much small magnitude of the precipitation anomaly, although it has a good anomaly rate compared with the observation. The bias correction test confirms that the performance of the bias correction using logarithm regression (LR) is better in northern Asia compared with the year-to-year increment regression (YYIR) during the warm season (May–October). Meanwhile, the YYIR is better than the LR in southern Asia in this season. Nevertheless, the LR is better in the south, and YYIR is better in the north during the cold season (November throughout next April). Therefore, combining the two regression methods can form a regional combination bias correction. The regional combination method is applied in the bias correction for the 2021–2050 precipitation projection of the Asian continent under the RCP4.5 scenario, in which an additional bias correction of climate drift removal is added in the blind areas in the two bias corrections. The projection for the warm season shows more or less changes in the precipitation pattern compared with that of 1976–2005, such as the 10%–20% decrease in precipitation in the Southern China, the northeastern part of South Asia, south part of Central Asia, and northeastern Arabian Peninsula. The projected precipitation would increase to approximately 20% in the belt from the Three-River-Source area throughout the Huaihe delta area, 10% increase in the southern part of Northeast China, 10% and 20% increase in northern and southern Xinjiang, respectively, 10% or 20% decrease in North China and most of Northeast China, and 10% increase in northern Indo–China Peninsula, in addition to a minor increase in precipitation in the high latitude of Asia. In the cold season, the projected precipitation would increase in the north and decrease in the south of Asia, such as the 10% decrease in South Asia, 5% decrease in Southwest China, 20%–40% increase in West China, 5% increase in North and Northeast China, and 10%–40% increase in the high latitude of Asia. Consequently, there would be more precipitation with potential floods in the upper reaches of the Yangtze River and Yellow River over the next 30 years, whereas the drought would possibly continue in Southwest China as it has experienced for the last decade. These will provide suggestions for the relevant department of the local government to take advance measures concerning the risks of flood and drought in the context of climate warming.
This study focuses on the bias of the multimodel ensemble mean in the precipitation simulated using models of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) compared with the precipitation data using Climatic Research Unit Timeseries version 4.0 (CRU TS v4.0). Three bias correction methods are tested, and a precipitation projection with the correction is made for the coming 30 years (2021–2050) based on the selected 20 CMIP5 models. Results show that the precipitation in the CMIP5 historical simulation is overestimated in northern Asia and underestimated in the south for 1960–2005 with 30%–40% more precipitation than that observed in the Tibetan Plateau, Inner Mongolia, and Mongolia; 20%–30% less in the South China Coast and Vietnam; and 30%–40% less in South Asia than that of the observation. The bias pattern of the projected precipitation for 2006–2015 under the Representative Concentration Pathway (RCP) 4.5 scenario is found to be similar to that from the CMIP5 historical climate simulation, implying that the bias pattern is almost stationary and should belong to the model climate drift that can be removed using the difference between the period-mean projection and historical simulation. However, this bias correction leads to a much small magnitude of the precipitation anomaly, although it has a good anomaly rate compared with the observation. The bias correction test confirms that the performance of the bias correction using logarithm regression (LR) is better in northern Asia compared with the year-to-year increment regression (YYIR) during the warm season (May–October). Meanwhile, the YYIR is better than the LR in southern Asia in this season. Nevertheless, the LR is better in the south, and YYIR is better in the north during the cold season (November throughout next April). Therefore, combining the two regression methods can form a regional combination bias correction. The regional combination method is applied in the bias correction for the 2021–2050 precipitation projection of the Asian continent under the RCP4.5 scenario, in which an additional bias correction of climate drift removal is added in the blind areas in the two bias corrections. The projection for the warm season shows more or less changes in the precipitation pattern compared with that of 1976–2005, such as the 10%–20% decrease in precipitation in the Southern China, the northeastern part of South Asia, south part of Central Asia, and northeastern Arabian Peninsula. The projected precipitation would increase to approximately 20% in the belt from the Three-River-Source area throughout the Huaihe delta area, 10% increase in the southern part of Northeast China, 10% and 20% increase in northern and southern Xinjiang, respectively, 10% or 20% decrease in North China and most of Northeast China, and 10% increase in northern Indo–China Peninsula, in addition to a minor increase in precipitation in the high latitude of Asia. In the cold season, the projected precipitation would increase in the north and decrease in the south of Asia, such as the 10% decrease in South Asia, 5% decrease in Southwest China, 20%–40% increase in West China, 5% increase in North and Northeast China, and 10%–40% increase in the high latitude of Asia. Consequently, there would be more precipitation with potential floods in the upper reaches of the Yangtze River and Yellow River over the next 30 years, whereas the drought would possibly continue in Southwest China as it has experienced for the last decade. These will provide suggestions for the relevant department of the local government to take advance measures concerning the risks of flood and drought in the context of climate warming.
2022, 46(1): 55-69.
doi: 10.3878/j.issn.1006-9895.2102.20246
Abstract:
Using the ERA-Interim reanalysis data and daily precipitation observation from 756 stations over China, the extreme winter precipitation over South China during 1979–2015 are identified and classified into five groups according to their spatial distribution via K-means clustering method, i.e., extreme precipitation occurs over the Yangtze River valley, central South China, southeastern South China, Huaihe River valley, and Southwest China. To disclose the causes of the widespread extreme winter precipitation over South China, the extreme precipitation with an eastward migration from Southwest China to coastal Southeast China has been further analyzed by comparing with that occurring locally over Southwest China. Results show that the main differences in the trigger and maintenance mechanisms of the extreme winter precipitation between the local and eastward migrating cases are the conflict between the warm and moist advection by the India–Burma trough and the intensity of cold air activity. For local cases, the active cold air activity inhibits the development of the India–Burma trough, resulting in the constraint of extreme precipitation over Southwest China. On the contrary, the warm and moist advection by the India–Burma trough moves eastward continuously in the eastward migration cases along with the weak cold air activity. The cooperation of the high-latitude wave train and South Asian jet wave train is crucial to the conflict between cold air activity and warm advection. When these two wave trains develop synchronously, the cold air activity over South China will be strong, and the warm advection from the Bay of Bengal will be confined over Southwest China, so does the resulting precipitation. However, when the high-latitude wave train developed ahead of the South Asian jet wave train and the cold air activity is weak when the India–Burma trough is enhanced by the South Asian jet wave train, the warm advection from the Bay of Bengal could move eastward continuously, resulting in the eastward migration of precipitation from Southwest China to coastal Southeast China.
Using the ERA-Interim reanalysis data and daily precipitation observation from 756 stations over China, the extreme winter precipitation over South China during 1979–2015 are identified and classified into five groups according to their spatial distribution via K-means clustering method, i.e., extreme precipitation occurs over the Yangtze River valley, central South China, southeastern South China, Huaihe River valley, and Southwest China. To disclose the causes of the widespread extreme winter precipitation over South China, the extreme precipitation with an eastward migration from Southwest China to coastal Southeast China has been further analyzed by comparing with that occurring locally over Southwest China. Results show that the main differences in the trigger and maintenance mechanisms of the extreme winter precipitation between the local and eastward migrating cases are the conflict between the warm and moist advection by the India–Burma trough and the intensity of cold air activity. For local cases, the active cold air activity inhibits the development of the India–Burma trough, resulting in the constraint of extreme precipitation over Southwest China. On the contrary, the warm and moist advection by the India–Burma trough moves eastward continuously in the eastward migration cases along with the weak cold air activity. The cooperation of the high-latitude wave train and South Asian jet wave train is crucial to the conflict between cold air activity and warm advection. When these two wave trains develop synchronously, the cold air activity over South China will be strong, and the warm advection from the Bay of Bengal will be confined over Southwest China, so does the resulting precipitation. However, when the high-latitude wave train developed ahead of the South Asian jet wave train and the cold air activity is weak when the India–Burma trough is enhanced by the South Asian jet wave train, the warm advection from the Bay of Bengal could move eastward continuously, resulting in the eastward migration of precipitation from Southwest China to coastal Southeast China.
2022, 46(1): 70-82.
doi: 10.3878/j.issn.1006-9895.2103.20254
Abstract:
The sea level pressure in the East Asia–Northwest Pacific region directly reflects the circulation characteristics of the lower atmosphere, and its dynamical characteristics have considerable effects on the atmospheric circulation situation, the evolution of the pressure system, and the development of weather and climate systems. Therefore, an in-depth analysis of the spatial and temporal evolution characteristics of the sea level pressure field in the East Asia–Northwest Pacific region is of great significance to improve the weather and climate forecasting in China. To investigate the dynamical characteristics of the daily sea level pressure field from the viewpoint of nonlinear dynamics, a new method is used to quantitatively estimate two instantaneous indicators of the sea level pressure attractor: (1) The instantaneous dimension and (2) the instantaneous stability. The instantaneous dimension characterizes the dispersion of the attractor orbit in local space, and the instantaneous stability characterizes the stability of the orbit in local time, which together characterize the instantaneous (daily) dynamical properties of the sea level baroclinic attractor. This paper studies the different spatial and temporal characteristics of the sea level pressure field in the East Asia–Northwest Pacific region by the correspondence between the indicator values of different sizes and the daily sea level pressure circulation field. The main conclusions are as follows: (1) When both indicators of the sea level pressure attractor are low, the spatial characteristics of the corresponding circulation field exhibit a single pressure structure, usually with several strong high- and low-pressure centers facing each other at the east–west direction, while the time characteristics show that the circulation mode can be stable for approximately 10 days. (2) Whereas, when both the indicators are high, the spatial characteristics of the circulation field show the simultaneous existence of multiple weak pressure centers with a chaotic spatial structure. As for the temporal characteristics, the circulation field is extremely unstable and the duration is approximately only one day. (3) In addition, the instantaneous dimension and instantaneous stability were found to have consistent interdecadal trends, both showing a clear downward trend from the 1970s to the 1990s, a rapidly rising trend in the late 1990s, and fluctuating changes after the year 2000.
The sea level pressure in the East Asia–Northwest Pacific region directly reflects the circulation characteristics of the lower atmosphere, and its dynamical characteristics have considerable effects on the atmospheric circulation situation, the evolution of the pressure system, and the development of weather and climate systems. Therefore, an in-depth analysis of the spatial and temporal evolution characteristics of the sea level pressure field in the East Asia–Northwest Pacific region is of great significance to improve the weather and climate forecasting in China. To investigate the dynamical characteristics of the daily sea level pressure field from the viewpoint of nonlinear dynamics, a new method is used to quantitatively estimate two instantaneous indicators of the sea level pressure attractor: (1) The instantaneous dimension and (2) the instantaneous stability. The instantaneous dimension characterizes the dispersion of the attractor orbit in local space, and the instantaneous stability characterizes the stability of the orbit in local time, which together characterize the instantaneous (daily) dynamical properties of the sea level baroclinic attractor. This paper studies the different spatial and temporal characteristics of the sea level pressure field in the East Asia–Northwest Pacific region by the correspondence between the indicator values of different sizes and the daily sea level pressure circulation field. The main conclusions are as follows: (1) When both indicators of the sea level pressure attractor are low, the spatial characteristics of the corresponding circulation field exhibit a single pressure structure, usually with several strong high- and low-pressure centers facing each other at the east–west direction, while the time characteristics show that the circulation mode can be stable for approximately 10 days. (2) Whereas, when both the indicators are high, the spatial characteristics of the circulation field show the simultaneous existence of multiple weak pressure centers with a chaotic spatial structure. As for the temporal characteristics, the circulation field is extremely unstable and the duration is approximately only one day. (3) In addition, the instantaneous dimension and instantaneous stability were found to have consistent interdecadal trends, both showing a clear downward trend from the 1970s to the 1990s, a rapidly rising trend in the late 1990s, and fluctuating changes after the year 2000.
2022, 46(1): 83-97.
doi: 10.3878/j.issn.1006-9895.2103.20256
Abstract:
According to the Nonlinear forcing singular vector type (NFSV-type) sea surface temperature (SST) forcing errors of 12 tropical cyclones (TCs), the optimal target observation deployment of the sea surface temperature is identified through the observing system simulation experiments (OSSEs). The sensitive area of NFSV-type SST forcing errors occurs along the track of TCs and during the intensification phase of TCs. Results of OSSEs show that the additional observations deployed in the sensitive area with intervals of 90 km effectively improve the simulation of the TC intensity. Compared with the observations deployed in nonsensitive areas, the target observations in the sensitive areas of NFSV-type SST forcing errors can more effectively improve the simulation of the TC intensity. When the local target observation area in the nonsensitive area reaches the sensitive area, the additional observations will gradually improve the simulation of the TC intensity. In particular, further experiments show that the simulation of the TC intensity improves more significantly when the target observations deployed during the intensification phase correspond to the periods of the occurrence of the large-value region of NFSV. Therefore, the additional observations in the target area identified using NFSV-type SST forcing errors can improve the simulation of the TC intensity most effectively, and the suitable deployment of observations in the sensitive area during the sensitive periods is the most economical observation strategy.
According to the Nonlinear forcing singular vector type (NFSV-type) sea surface temperature (SST) forcing errors of 12 tropical cyclones (TCs), the optimal target observation deployment of the sea surface temperature is identified through the observing system simulation experiments (OSSEs). The sensitive area of NFSV-type SST forcing errors occurs along the track of TCs and during the intensification phase of TCs. Results of OSSEs show that the additional observations deployed in the sensitive area with intervals of 90 km effectively improve the simulation of the TC intensity. Compared with the observations deployed in nonsensitive areas, the target observations in the sensitive areas of NFSV-type SST forcing errors can more effectively improve the simulation of the TC intensity. When the local target observation area in the nonsensitive area reaches the sensitive area, the additional observations will gradually improve the simulation of the TC intensity. In particular, further experiments show that the simulation of the TC intensity improves more significantly when the target observations deployed during the intensification phase correspond to the periods of the occurrence of the large-value region of NFSV. Therefore, the additional observations in the target area identified using NFSV-type SST forcing errors can improve the simulation of the TC intensity most effectively, and the suitable deployment of observations in the sensitive area during the sensitive periods is the most economical observation strategy.
2022, 46(1): 98-110.
doi: 10.3878/j.issn.1006-9895.2104.21010
Abstract:
Meteorological satellites have provided useful information for improving weather forecasting, environmental monitoring, and short-term climate prediction. In the field of the weather forecast, satellites provide a powerful means for the forecast of typhoons, rainstorms, hail, sandstorms, and other severe weather conditions. In this study, the microstructure of hail clouds was analyzed by satellite observation data based on nearly a decade of hail event records of Shaanxi, Shandong, Guizhou, and Xinjiang. The comparison between the hail cloud and deep convective precipitation cloud characteristics retrieved by polar orbit satellites showed different cloud properties such as cloud top temperature/effective radius and cloud glaciation temperatures. Based on distinct cloud properties between hail clouds and convective clouds, this work summarized the characteristics and further applied them to the FY-4A geostationary satellite, which captures the hail cycle, which occurred on August 16, 2019, in the Shandong area. Results showed that the satellite has the potential to capture a hail cloud during its developing stage and use it as an application of early warning. The hail cloud shows the following characteristics: (1) There are considerable differences in the cloud’s physical characteristics between hail clouds and deep convective precipitation clouds. Microphysical characteristics of hail clouds observed by satellites are shown in three aspects: Glaciation temperature（Tg）is cooler with an average value of −33°C. The hail cloud reaches the glaciation temperature with a smaller effective radius (<40 μm) with an average of 36.9 μm when the clouds are fully glaciated. It also shows that the smaller the reg (effective radius corresponding to glaciation temperature), the stronger the hail cloud. Additionally, hail cloud tops often have a reduction zone of re with increasing height. (2) All the studied areas have consistent cloud properties such as a lower Tg, smaller reg, and a decreased re compared to those of adjacent convective clouds. However, it still showed regional variabilities that indicate the need to establish different indicators for identifying hail clouds for early warning purposes. (3) The case study of the FY-4A geostationary satellite shows that the geostationary satellite can track the evolution of hail clouds. By tracking the hail cloud, the geostationary satellite has a response consistent with that of the polar orbit satellite, providing a method for monitoring and early warning service of hail weather. The geostationary satellite can be used to track the development and evolution of the cloud cluster at any time when the satellite detects a strong hail signal because of the high time resolution. Combining the satellite’s early warning with radar observation, the location of hail occurrence can be determined precisely. (4) Combining the indicators summarized by polar orbit satellites with the FY-4A to track the hail cloud evolution. Four hail storms that occurred in Shaanxi and Shandong were applied for early warnings. Ground observations reported 24 hail events in the two regions, of which the satellite successfully warned 22 times in advance and missed two times. The average early warning time is about two hours before the hail disaster. All of these suggest that the automatic warning of hail by the FY-4A satellite has important practical significance for timely and effective organization and implementation of operational hail mitigation.
Meteorological satellites have provided useful information for improving weather forecasting, environmental monitoring, and short-term climate prediction. In the field of the weather forecast, satellites provide a powerful means for the forecast of typhoons, rainstorms, hail, sandstorms, and other severe weather conditions. In this study, the microstructure of hail clouds was analyzed by satellite observation data based on nearly a decade of hail event records of Shaanxi, Shandong, Guizhou, and Xinjiang. The comparison between the hail cloud and deep convective precipitation cloud characteristics retrieved by polar orbit satellites showed different cloud properties such as cloud top temperature/effective radius and cloud glaciation temperatures. Based on distinct cloud properties between hail clouds and convective clouds, this work summarized the characteristics and further applied them to the FY-4A geostationary satellite, which captures the hail cycle, which occurred on August 16, 2019, in the Shandong area. Results showed that the satellite has the potential to capture a hail cloud during its developing stage and use it as an application of early warning. The hail cloud shows the following characteristics: (1) There are considerable differences in the cloud’s physical characteristics between hail clouds and deep convective precipitation clouds. Microphysical characteristics of hail clouds observed by satellites are shown in three aspects: Glaciation temperature（Tg）is cooler with an average value of −33°C. The hail cloud reaches the glaciation temperature with a smaller effective radius (<40 μm) with an average of 36.9 μm when the clouds are fully glaciated. It also shows that the smaller the reg (effective radius corresponding to glaciation temperature), the stronger the hail cloud. Additionally, hail cloud tops often have a reduction zone of re with increasing height. (2) All the studied areas have consistent cloud properties such as a lower Tg, smaller reg, and a decreased re compared to those of adjacent convective clouds. However, it still showed regional variabilities that indicate the need to establish different indicators for identifying hail clouds for early warning purposes. (3) The case study of the FY-4A geostationary satellite shows that the geostationary satellite can track the evolution of hail clouds. By tracking the hail cloud, the geostationary satellite has a response consistent with that of the polar orbit satellite, providing a method for monitoring and early warning service of hail weather. The geostationary satellite can be used to track the development and evolution of the cloud cluster at any time when the satellite detects a strong hail signal because of the high time resolution. Combining the satellite’s early warning with radar observation, the location of hail occurrence can be determined precisely. (4) Combining the indicators summarized by polar orbit satellites with the FY-4A to track the hail cloud evolution. Four hail storms that occurred in Shaanxi and Shandong were applied for early warnings. Ground observations reported 24 hail events in the two regions, of which the satellite successfully warned 22 times in advance and missed two times. The average early warning time is about two hours before the hail disaster. All of these suggest that the automatic warning of hail by the FY-4A satellite has important practical significance for timely and effective organization and implementation of operational hail mitigation.
2022, 46(1): 111-132.
doi: 10.3878/j.issn.1006-9895.2104.21007
Abstract:
In this paper, the two torrential rain processes in Beijing on July 21, 2012 (hereinafter referred to as “7.21”) and July 20, 2016 (hereinafter referred to as “7.20”) are analyzed to compare and reveal their differences from multiple perspectives using multisource observation and reanalysis data combined with various analysis methods. The results show that the total amount of precipitation for the two processes is similar, but the precipitation duration and hourly rainfall intensity are different, indicating that the duration of “7.21” is shorter and the rainfall intensity is stronger, which corresponds to the dominant weather system and evolution, convective system evolution and local sounding conditions of the two processes. The convective effective potential energy is significant in “7.21” main precipitation period resulting in the dominant convective heavy precipitation in a warm area, whereas the convective effective potential energy is small in “ 7.20” main precipitation period and is dominated by low vortex systematic precipitation. Therefore, significant differences are observed in the statistics of hourly rainfall intensity and short-duration rainfall events between the two processes. The proportion of medium intensity hourly rainfall stations of “7.20” is significant, whereas the proportion of short-duration heavy rainfall stations “7.21” is obvious. The differences in accumulated rainfall, duration, 5 min, and 1 h maximum rainfall between the two short-duration precipitation events are significant. The “7.21” short-duration heavy rainfall events (the short-duration extremely heavy rainfall events with an hourly rainfall of more than 50 mm accounted for a significant proportion) exceeded half, as well as the maximum 5 min and 1 h precipitation were 20.4 and 103.6 mm, respectively. While the short-duration medium intensity precipitation events of “7.20” accounted for the largest proportion, the maximum 5 min and 1 h precipitation of only 10.7 and 59.3 mm. Compared with “7.20”, “7.21” is more disastrous. The contribution of water vapor from central and eastern China as well as coastal areas is the largest in both processes, with “7.21” being more pronounced. However, the contributions of the Indian Peninsula–Bay of Bengal–Central South Peninsula, South China Sea, Northwest Pacific, and the Sea of Japan are also obvious in the “7.20”. The above conclusions contribute to understanding the reasons for the different disasters of the two torrential rain processes.
In this paper, the two torrential rain processes in Beijing on July 21, 2012 (hereinafter referred to as “7.21”) and July 20, 2016 (hereinafter referred to as “7.20”) are analyzed to compare and reveal their differences from multiple perspectives using multisource observation and reanalysis data combined with various analysis methods. The results show that the total amount of precipitation for the two processes is similar, but the precipitation duration and hourly rainfall intensity are different, indicating that the duration of “7.21” is shorter and the rainfall intensity is stronger, which corresponds to the dominant weather system and evolution, convective system evolution and local sounding conditions of the two processes. The convective effective potential energy is significant in “7.21” main precipitation period resulting in the dominant convective heavy precipitation in a warm area, whereas the convective effective potential energy is small in “ 7.20” main precipitation period and is dominated by low vortex systematic precipitation. Therefore, significant differences are observed in the statistics of hourly rainfall intensity and short-duration rainfall events between the two processes. The proportion of medium intensity hourly rainfall stations of “7.20” is significant, whereas the proportion of short-duration heavy rainfall stations “7.21” is obvious. The differences in accumulated rainfall, duration, 5 min, and 1 h maximum rainfall between the two short-duration precipitation events are significant. The “7.21” short-duration heavy rainfall events (the short-duration extremely heavy rainfall events with an hourly rainfall of more than 50 mm accounted for a significant proportion) exceeded half, as well as the maximum 5 min and 1 h precipitation were 20.4 and 103.6 mm, respectively. While the short-duration medium intensity precipitation events of “7.20” accounted for the largest proportion, the maximum 5 min and 1 h precipitation of only 10.7 and 59.3 mm. Compared with “7.20”, “7.21” is more disastrous. The contribution of water vapor from central and eastern China as well as coastal areas is the largest in both processes, with “7.21” being more pronounced. However, the contributions of the Indian Peninsula–Bay of Bengal–Central South Peninsula, South China Sea, Northwest Pacific, and the Sea of Japan are also obvious in the “7.20”. The above conclusions contribute to understanding the reasons for the different disasters of the two torrential rain processes.
2022, 46(1): 133-150.
doi: 10.3878/j.issn.1006-9895.2105.21026
Abstract:
This paper employed the piecewise linear fitting model (PLFIM) to analyze the seasonal differences of Surface Sensible Heat (SSH) trend evolution characteristics at 70 meteorological stations on the central and eastern part of Tibetan Plateau (TP) during 1982–2018. The key meteorological factors influencing the changes of SSH in different seasons were quantitatively evaluated using the linear tendency estimation and variance method analysis. Results show that: (1) the seasonal average SSH fluxes on the central and eastern TP have a trend turning feature in all four seasons. As a whole, the trend turning time of autumn and winter is earlier (1999) and that of spring and summer is later (2000). In terms of region, the turning time is earliest in Zone II (Eastern part of TP) and then expands to Zone IV (Southeastern part of TP) and Zone I (Northern part of TP), while the turning time is latest in Zone III (Southwestern part of TP). Before the trend turning time, the weakening of the SSH is most prominent in summer, followed by spring and autumn, and weakest in winter. After the trend turning time, the enhancement of SSH is strongest in winter and the enhancement trend is similar in other seasons. In winter and spring, the key areas for the trend turning of SSH are in the eastern and southern part of TP, respectively, while the key areas are mainly in Zone II and III in summer and autumn. (2) Before the trend turning time, the decrease in the surface wind speed has an important contribution to the decreasing trend of the SSH in four seasons; however, after the trend turning time, the key meteorological factors affecting the trend of SSH have significant differences in the four seasons, i.e., the change of surface wind speed is still dominant in summer, whereas winter and autumn are affected by both the variations of the ground-air temperature difference and surface wind speed. The increase of ground-air temperature difference in spring is the main reason for the trend strengthening of SSH. Additionally, in the interannual variability of SSH, the effect of the ground-air temperature difference is more prominent than that of the surface wind speed, particularly in autumn and winter. The ground-air temperature difference is always the dominant factor affecting its interannual variation. The eastern part of TP is primarily affected by the ground-air temperature difference in spring. Before the trend turning time, the interannual variability of the SSH in summer is affected by both the variations of ground-air temperature difference and surface wind speed. After the trend turning time, the influence of ground-air temperature difference on the SSH is more prominent.
This paper employed the piecewise linear fitting model (PLFIM) to analyze the seasonal differences of Surface Sensible Heat (SSH) trend evolution characteristics at 70 meteorological stations on the central and eastern part of Tibetan Plateau (TP) during 1982–2018. The key meteorological factors influencing the changes of SSH in different seasons were quantitatively evaluated using the linear tendency estimation and variance method analysis. Results show that: (1) the seasonal average SSH fluxes on the central and eastern TP have a trend turning feature in all four seasons. As a whole, the trend turning time of autumn and winter is earlier (1999) and that of spring and summer is later (2000). In terms of region, the turning time is earliest in Zone II (Eastern part of TP) and then expands to Zone IV (Southeastern part of TP) and Zone I (Northern part of TP), while the turning time is latest in Zone III (Southwestern part of TP). Before the trend turning time, the weakening of the SSH is most prominent in summer, followed by spring and autumn, and weakest in winter. After the trend turning time, the enhancement of SSH is strongest in winter and the enhancement trend is similar in other seasons. In winter and spring, the key areas for the trend turning of SSH are in the eastern and southern part of TP, respectively, while the key areas are mainly in Zone II and III in summer and autumn. (2) Before the trend turning time, the decrease in the surface wind speed has an important contribution to the decreasing trend of the SSH in four seasons; however, after the trend turning time, the key meteorological factors affecting the trend of SSH have significant differences in the four seasons, i.e., the change of surface wind speed is still dominant in summer, whereas winter and autumn are affected by both the variations of the ground-air temperature difference and surface wind speed. The increase of ground-air temperature difference in spring is the main reason for the trend strengthening of SSH. Additionally, in the interannual variability of SSH, the effect of the ground-air temperature difference is more prominent than that of the surface wind speed, particularly in autumn and winter. The ground-air temperature difference is always the dominant factor affecting its interannual variation. The eastern part of TP is primarily affected by the ground-air temperature difference in spring. Before the trend turning time, the interannual variability of the SSH in summer is affected by both the variations of ground-air temperature difference and surface wind speed. After the trend turning time, the influence of ground-air temperature difference on the SSH is more prominent.
2022, 46(1): 151-167.
doi: 10.3878/j.issn.1006-9895.2104.21028
Abstract:
The spring-to-summer seasonal transition over mid- and high-latitude Asia (MHASST) is an important part of several spring-to-summer seasonal transitions in different regions of the Asian continent. It provides the necessary circulation conditions in the mid- and high-latitudes for the establishment of the Meiyu rainfall in the Yangtze and Huaihe River basins. However, so far, there is no systematic summary of its uniqueness and key characteristics. This paper analyzes and summarizes the key characteristics of the MHASST process based on the daily data of NCEP/NCAR reanalysis data I. The MHASST is symbolized by the establishment of the Northeast Asian ridge at 500 hPa and the “double blocking” circulation pattern. The formation of the Northeast Asian ridge and its related land-sea temperature difference is mainly attributed to the snow melting process and consequently the local strong warming process in Northeast Asia. The establishment of the northern East Asian low (850 hPa) is another important sign of the MHASST. When the MHASST occurs, the 200-hPa Asian jet axis over the Tibetan Plateau jumps northward from 35°N to 37°N, while the Asian temperate jet disappears completely. With the seasonal change, the meridional gradient of the near-surface temperature in the mid- and high-latitude Asia weakens, thus causing the attenuation of high-frequency transient baroclinic disturbances. In contrast, low-frequency weather systems, including the Asian blocking high and the Northeast China cold vortex system, become the dominant weather systems in the same region. From the perspective of the early and late timing of the MHASST, this paper also discusses the evolution features of the circulation and weather system over the mid- and high-latitude Asia. The obtained results further supplement the key information of the climatic MHASST.
The spring-to-summer seasonal transition over mid- and high-latitude Asia (MHASST) is an important part of several spring-to-summer seasonal transitions in different regions of the Asian continent. It provides the necessary circulation conditions in the mid- and high-latitudes for the establishment of the Meiyu rainfall in the Yangtze and Huaihe River basins. However, so far, there is no systematic summary of its uniqueness and key characteristics. This paper analyzes and summarizes the key characteristics of the MHASST process based on the daily data of NCEP/NCAR reanalysis data I. The MHASST is symbolized by the establishment of the Northeast Asian ridge at 500 hPa and the “double blocking” circulation pattern. The formation of the Northeast Asian ridge and its related land-sea temperature difference is mainly attributed to the snow melting process and consequently the local strong warming process in Northeast Asia. The establishment of the northern East Asian low (850 hPa) is another important sign of the MHASST. When the MHASST occurs, the 200-hPa Asian jet axis over the Tibetan Plateau jumps northward from 35°N to 37°N, while the Asian temperate jet disappears completely. With the seasonal change, the meridional gradient of the near-surface temperature in the mid- and high-latitude Asia weakens, thus causing the attenuation of high-frequency transient baroclinic disturbances. In contrast, low-frequency weather systems, including the Asian blocking high and the Northeast China cold vortex system, become the dominant weather systems in the same region. From the perspective of the early and late timing of the MHASST, this paper also discusses the evolution features of the circulation and weather system over the mid- and high-latitude Asia. The obtained results further supplement the key information of the climatic MHASST.
2022, 46(1): 168-180.
doi: 10.3878/j.issn.1006-9895.2103.21031
Abstract:
Nocturnal warming is a frequent weather phenomenon in the Hebei Winter Olympic Games area, and its accurate simulation and forecast are very important for the construction of the competition area and guarantee of the competition. By introducing the higher resolution terrain data, the mesoscale regional numerical model WRFv4.1.5 was used to reproduce the nocturnal warming process, and the meteorological characteristics and causes of the process were explored. Results show that: (1) the process is affected by the northeast cold vortex, (2) the cold advection is significant at the middle and upper levels, (3) the wind shear is strong at the high and low levels, and (4) there are obvious advection differences. At the same time, the variation characteristics of meteorological elements near the surface are obvious, including the decrease in relative humidity, increase in wind speed, decrease in sea level pressure, and enhancement of surface heat flux and long-wave radiation. In addition, the strong wind shear and advection difference between the upper and lower levels easily produces vertical mixing. The isentropic surface fluctuation is obvious and the turbulence is strengthened, which further strengthens the turbulent vertical mixing movement, enhances the moving heat flux transport, and produces the abnormal increase of night temperature.
Nocturnal warming is a frequent weather phenomenon in the Hebei Winter Olympic Games area, and its accurate simulation and forecast are very important for the construction of the competition area and guarantee of the competition. By introducing the higher resolution terrain data, the mesoscale regional numerical model WRFv4.1.5 was used to reproduce the nocturnal warming process, and the meteorological characteristics and causes of the process were explored. Results show that: (1) the process is affected by the northeast cold vortex, (2) the cold advection is significant at the middle and upper levels, (3) the wind shear is strong at the high and low levels, and (4) there are obvious advection differences. At the same time, the variation characteristics of meteorological elements near the surface are obvious, including the decrease in relative humidity, increase in wind speed, decrease in sea level pressure, and enhancement of surface heat flux and long-wave radiation. In addition, the strong wind shear and advection difference between the upper and lower levels easily produces vertical mixing. The isentropic surface fluctuation is obvious and the turbulence is strengthened, which further strengthens the turbulent vertical mixing movement, enhances the moving heat flux transport, and produces the abnormal increase of night temperature.
2022, 46(1): 181-190.
doi: 10.3878/j.issn.1006-9895.2106.21055
Abstract:
Affected by the special geographical environment, winter snowfall in Beijing is often accompanied by the easterly wind in the boundary layer. The water vapor transport and dynamic convergence effect caused by the easterly wind in the boundary layer are of great significance to the occurrence and development of snowfall. This paper is based on the topographic characteristics of the Yanqing zone of the 2022 Winter Olympic Games and is different from the existing snowfall studies on the easterly wind of boundary layer in plain areas. The paper compared the easterly wind mechanism in the boundary layer with various thermal and humidity properties and development heights on snowfall under similar weather conditions. The results show that: (1) A longer route through the Bohai Bay is beneficial to the obvious humidification of the boundary layer easterly wind and vice versa. (2) The “dry and cold” easterly wind can form a cold pad to lift the warm and humid air in the Beijing plain area. When the easterly wind develops deep in the vertical direction (over 600 m), it can overturn the Jundu mountain with lower altitudes in eastern Yanqing and form a around-flow confluence on leeward slopes. At the same time, the easterly wind is blocked by the Haituo mountain with higher altitudes in the west, forming the forced uplift of the windward slope. The two effects together lead to the convergence of the strong east and the weak west, which causes more snowfall distribution in the east than in the west. (3) The “warm and humid” boundary-layered easterly wind cannot cross the Jundu mountain westward because of its lower vertical development height, which has little effect on snow in Yanqing. (4) When the air gets affected by the northwest airflow of 500 hPa, closer to the terrain, the saturation area near the 700 hPa height and the lifting movement make the high-altitude mountainous area of Yanqing experience the obvious snowfall.
Affected by the special geographical environment, winter snowfall in Beijing is often accompanied by the easterly wind in the boundary layer. The water vapor transport and dynamic convergence effect caused by the easterly wind in the boundary layer are of great significance to the occurrence and development of snowfall. This paper is based on the topographic characteristics of the Yanqing zone of the 2022 Winter Olympic Games and is different from the existing snowfall studies on the easterly wind of boundary layer in plain areas. The paper compared the easterly wind mechanism in the boundary layer with various thermal and humidity properties and development heights on snowfall under similar weather conditions. The results show that: (1) A longer route through the Bohai Bay is beneficial to the obvious humidification of the boundary layer easterly wind and vice versa. (2) The “dry and cold” easterly wind can form a cold pad to lift the warm and humid air in the Beijing plain area. When the easterly wind develops deep in the vertical direction (over 600 m), it can overturn the Jundu mountain with lower altitudes in eastern Yanqing and form a around-flow confluence on leeward slopes. At the same time, the easterly wind is blocked by the Haituo mountain with higher altitudes in the west, forming the forced uplift of the windward slope. The two effects together lead to the convergence of the strong east and the weak west, which causes more snowfall distribution in the east than in the west. (3) The “warm and humid” boundary-layered easterly wind cannot cross the Jundu mountain westward because of its lower vertical development height, which has little effect on snow in Yanqing. (4) When the air gets affected by the northwest airflow of 500 hPa, closer to the terrain, the saturation area near the 700 hPa height and the lifting movement make the high-altitude mountainous area of Yanqing experience the obvious snowfall.
2022, 46(1): 191-205.
doi: 10.3878/j.issn.1006-9895.2107.21057
Abstract:
Based on the observed data from automated weather stations during November 2018–March 2019 and November 2019–March 2020 at the Yunding Winter Olympic Stadium in Chongli, Hebei Province, nocturnal warming events at the stadium are statistically analyzed in this paper. Several possible formation mechanisms for these events are then discussed based on microwave radiometer, three-dimensional laser radar and the wind profiler data, and reanalysis data from NCEP/NACR. The results show that the occurrence probability of nocturnal warming events in Yunding Stadium reaches 76.9% from November to the following March, indicating that such warming events are a common phenomenon there. The frequency and amplitude of the warming decrease with increasing altitude. The triggering mechanisms of nocturnal warming events at Yunding Stadium can be classified into four categories: (1) mixed warming in the inversion layer caused by vertical wind shears, (2) Foehn-type warming, (3) whole-layer subsidence warming, and (4) warm advection in the mid and low levels. During the warming process of the second through fourth types, the warming amplitude at the bottom of the valley may be significantly larger than that at the top of the mountain when there is an initial temperature inversion in the valley. In this scenario, warming amplitude decreases with increasing altitude. The warming at the top of the mountain is only affected by the third and fourth types of formation mechanisms, while all four types can trigger warming events in the valley. This explains why the occurrence frequency of warming events decreases with increasing altitude.
Based on the observed data from automated weather stations during November 2018–March 2019 and November 2019–March 2020 at the Yunding Winter Olympic Stadium in Chongli, Hebei Province, nocturnal warming events at the stadium are statistically analyzed in this paper. Several possible formation mechanisms for these events are then discussed based on microwave radiometer, three-dimensional laser radar and the wind profiler data, and reanalysis data from NCEP/NACR. The results show that the occurrence probability of nocturnal warming events in Yunding Stadium reaches 76.9% from November to the following March, indicating that such warming events are a common phenomenon there. The frequency and amplitude of the warming decrease with increasing altitude. The triggering mechanisms of nocturnal warming events at Yunding Stadium can be classified into four categories: (1) mixed warming in the inversion layer caused by vertical wind shears, (2) Foehn-type warming, (3) whole-layer subsidence warming, and (4) warm advection in the mid and low levels. During the warming process of the second through fourth types, the warming amplitude at the bottom of the valley may be significantly larger than that at the top of the mountain when there is an initial temperature inversion in the valley. In this scenario, warming amplitude decreases with increasing altitude. The warming at the top of the mountain is only affected by the third and fourth types of formation mechanisms, while all four types can trigger warming events in the valley. This explains why the occurrence frequency of warming events decreases with increasing altitude.
2022, 46(1): 206-224.
doi: 10.3878/j.issn.1006-9895.2109.21070
Abstract:
Based on the mesoscale regional numerical model (WRF) and a spectral nudging method, this study simulates a cold air pool (CAP) process during the 2021 Winter Olympics test competition. The vertical change in the wind and temperature fields during this process has been analyzed, and the specific reasons for the formation and dissipation of the CAP have been demonstrated. The results show that the stationary synoptic situation formed the general background for the maintenance and development of the CAP. During the development of the CAP, a temperature inversion layer was rapidly established from top to bottom, and a southeast cold air flow appeared at the bottom of the valley. Affected by the downward gravitational wind, the cold air accumulated at the bottom of the valley, and the CAP deepened. After sunrise, the mesoscale winds over the mountain were reestablished. The temperature inversion layer was eroded from the bottom, and the structure of the CAP was destroyed. Strong nocturnal radiation cooling was the main reason for the formation of the CAP. Differences in the intensity of radiation cooling cause differences in the cooling range of the CAP. Sudden enhancement of radiational cooling after midnight created favorable conditions for the maintenance and development of the CAP in the middle and later periods. Through analysis of the evolution of the potential temperature profile, friction velocity, and boundary layer height during the process, it can be confirmed that the development of turbulent activity is an important factor in influencing the dissipation of the temperature inversion and the destruction of the CAP structure.
Based on the mesoscale regional numerical model (WRF) and a spectral nudging method, this study simulates a cold air pool (CAP) process during the 2021 Winter Olympics test competition. The vertical change in the wind and temperature fields during this process has been analyzed, and the specific reasons for the formation and dissipation of the CAP have been demonstrated. The results show that the stationary synoptic situation formed the general background for the maintenance and development of the CAP. During the development of the CAP, a temperature inversion layer was rapidly established from top to bottom, and a southeast cold air flow appeared at the bottom of the valley. Affected by the downward gravitational wind, the cold air accumulated at the bottom of the valley, and the CAP deepened. After sunrise, the mesoscale winds over the mountain were reestablished. The temperature inversion layer was eroded from the bottom, and the structure of the CAP was destroyed. Strong nocturnal radiation cooling was the main reason for the formation of the CAP. Differences in the intensity of radiation cooling cause differences in the cooling range of the CAP. Sudden enhancement of radiational cooling after midnight created favorable conditions for the maintenance and development of the CAP in the middle and later periods. Through analysis of the evolution of the potential temperature profile, friction velocity, and boundary layer height during the process, it can be confirmed that the development of turbulent activity is an important factor in influencing the dissipation of the temperature inversion and the destruction of the CAP structure.
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doi: 10.3878/j.issn.1006-9895.2111.21187
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doi: 10.3878/j.issn.1006-9895.2201.21095
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doi: 10.3878/j.issn.1006-9895.2111.21034
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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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doi: 10.3878/j.issn.1006-9895.2111.21178
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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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