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doi: 10.3878/j.issn.1006-9895.2010.20110
Abstract:
As global warming intensifies, the growing season changes correspondingly across China. Earlier, pertinent studies of the growing season have only covered short-term periods, used low-resolution horizontal data, and focused on limited regions. Based on these premises, the authors investigated the climatological trends of the start of the growing season (GSS), end of the growing season (GSE), and growing season length (GSL) across China during 1961–2018. The authors used daily mean temperature data from a high-resolution horizontal gridded dataset CN05.1 (0.25°×0.25°). The relationship between the changes in the growing season and seasonal average temperature was also analyzed. The results indicated that the national average GSS and GSE were 31 March and 29 October, respectively, and GSL was 212 d across China during 1961–2018. Spatially, annual average GSS was delayed from southeast to northwest, whereas, GSE showed the opposite trend; GSL decreased from southeast to northwest. In generally, the trends in the national average growing season displayed an early start [−1.3 d (10 a)−1], a late end [0.9 d (10 a)−1 ], and a long length [2.2 d (10 a)−1] across China from 1961 to 2018. Finally, both the advance of the national average GSS and extension of the GSL were mainly related to increased spring temperatures, whereas, the delay in the GSE originated from increased autumn temperatures.
As global warming intensifies, the growing season changes correspondingly across China. Earlier, pertinent studies of the growing season have only covered short-term periods, used low-resolution horizontal data, and focused on limited regions. Based on these premises, the authors investigated the climatological trends of the start of the growing season (GSS), end of the growing season (GSE), and growing season length (GSL) across China during 1961–2018. The authors used daily mean temperature data from a high-resolution horizontal gridded dataset CN05.1 (0.25°×0.25°). The relationship between the changes in the growing season and seasonal average temperature was also analyzed. The results indicated that the national average GSS and GSE were 31 March and 29 October, respectively, and GSL was 212 d across China during 1961–2018. Spatially, annual average GSS was delayed from southeast to northwest, whereas, GSE showed the opposite trend; GSL decreased from southeast to northwest. In generally, the trends in the national average growing season displayed an early start [−1.3 d (10 a)−1], a late end [0.9 d (10 a)−1 ], and a long length [2.2 d (10 a)−1] across China from 1961 to 2018. Finally, both the advance of the national average GSS and extension of the GSL were mainly related to increased spring temperatures, whereas, the delay in the GSE originated from increased autumn temperatures.
2021 Issue 1
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2021, 45(1): 1-20.
doi: 10.3878/j.issn.1006-9895.2003.19204
Abstract:
Western Pacific subtropical high (WPSH) is a large-scale circulation system that affects climate change in China. It is of great significance to study the influence of the subseasonal WPSH east–west movement on the precipitation anomalies in Southwest China. In this study, the WPSH east–west displacement index is first defined according to the main activity region of the WPSH in early and late summers. The index has a significant period of 10–30 d and can well indicate the WPSH zonal movement. A total of 195 east and west WPSH events (1374 d) are chosen based on the standardization index. The results show that the subseasonal WPSH zonal movement is closely related to the precipitation in Southwest China. During the west (east) events, the WPSH moves gradually as follows: east→west→east (west→east→west), and the rainfall in most of Southwest China changes as follows: less→more→less (more→less→more). The precipitation variation in Southwest China is closed related to the anomalous water vapor and atmospheric vertical movement in the northern side and main WPSH area. Furthermore, the results show that the precipitation anomalies in Guizhou and Chongqing are well coincident, which demonstrates the significant characteristics of the regional difference in Yunnan and Sichuan during the subseasonal WPSH movement, especially in Yunnan. In early summer, the precipitation anomalies in Yunnan are contrary to those in most of Southwest China, especially in Guizhou and Chongqing. For example, when the WPSH moves westward (eastward), the precipitation is less (more) in most of Yunnan; on the contrary, the precipitation in most regions of Southwest China is more (less). In the late summer, except the central and northern Yunnan, the precipitation anomalies in most of Southwest China are basically accordant.
Western Pacific subtropical high (WPSH) is a large-scale circulation system that affects climate change in China. It is of great significance to study the influence of the subseasonal WPSH east–west movement on the precipitation anomalies in Southwest China. In this study, the WPSH east–west displacement index is first defined according to the main activity region of the WPSH in early and late summers. The index has a significant period of 10–30 d and can well indicate the WPSH zonal movement. A total of 195 east and west WPSH events (1374 d) are chosen based on the standardization index. The results show that the subseasonal WPSH zonal movement is closely related to the precipitation in Southwest China. During the west (east) events, the WPSH moves gradually as follows: east→west→east (west→east→west), and the rainfall in most of Southwest China changes as follows: less→more→less (more→less→more). The precipitation variation in Southwest China is closed related to the anomalous water vapor and atmospheric vertical movement in the northern side and main WPSH area. Furthermore, the results show that the precipitation anomalies in Guizhou and Chongqing are well coincident, which demonstrates the significant characteristics of the regional difference in Yunnan and Sichuan during the subseasonal WPSH movement, especially in Yunnan. In early summer, the precipitation anomalies in Yunnan are contrary to those in most of Southwest China, especially in Guizhou and Chongqing. For example, when the WPSH moves westward (eastward), the precipitation is less (more) in most of Yunnan; on the contrary, the precipitation in most regions of Southwest China is more (less). In the late summer, except the central and northern Yunnan, the precipitation anomalies in most of Southwest China are basically accordant.
2021, 45(1): 21-36.
doi: 10.3878/j.issn.1006-9895.2007.19208
Abstract:
Basing from observational data, this study analyzed the variations in ISO (intraseasonal oscillation) of the daily temperatures and its relationships to the low temperature in December–February of 1979/1980–2017/2018 over the lower reaches of the Yangtze River (LYR). The daily temperatures over the LYR in December–February are mainly of periodic oscillations of 15–25 d, 25–40 d, and 50–70 d, and the interannual variation in the intensity of its 25–40-day oscillation has a strong positive correlation with the number of low-temperature days in December–February. The real-time low-frequency components of daily temperature in the LYR and the principal components of 850-hPa low-frequency temperature in eastern Asia from 2001 to 2018 were used to establish the time-varying extended complex autoregressive (ECAR) model on an extended-range forecast of the 25–40-day low-frequency temperature over the LYR in winter. Real-time SSA (singular spectrum analysis) filtering with the T-EOF (temporal empirical orthogonal functions) extension can effectively inhibit the end effects of the traditional SSA and enhance the real-time signal of ISO. A 17-year independent real-time extended-range forecast was conducted on the extended-range forecast of the low-frequency component of the temperature over the LYR in December–February of 2001/2002–2017/2018. Experimental results show that the data-driven ECAR model has a good forecast skill at the lead time of approximately 26 days, and its forecast ability is superior to that of the traditional autoregressive model. Hence, the development and variation of the leading 25–40-day modes for the low-frequency temperatures at 850 hPa in eastern Asia and temporal evolutions of their relationships to the low-frequency components of the temperature over the LYR in winter supplied the valuable predicting background to determine the extended-range weather process in the persistent low temperature over the LYR at the 3–4-week leads.
Basing from observational data, this study analyzed the variations in ISO (intraseasonal oscillation) of the daily temperatures and its relationships to the low temperature in December–February of 1979/1980–2017/2018 over the lower reaches of the Yangtze River (LYR). The daily temperatures over the LYR in December–February are mainly of periodic oscillations of 15–25 d, 25–40 d, and 50–70 d, and the interannual variation in the intensity of its 25–40-day oscillation has a strong positive correlation with the number of low-temperature days in December–February. The real-time low-frequency components of daily temperature in the LYR and the principal components of 850-hPa low-frequency temperature in eastern Asia from 2001 to 2018 were used to establish the time-varying extended complex autoregressive (ECAR) model on an extended-range forecast of the 25–40-day low-frequency temperature over the LYR in winter. Real-time SSA (singular spectrum analysis) filtering with the T-EOF (temporal empirical orthogonal functions) extension can effectively inhibit the end effects of the traditional SSA and enhance the real-time signal of ISO. A 17-year independent real-time extended-range forecast was conducted on the extended-range forecast of the low-frequency component of the temperature over the LYR in December–February of 2001/2002–2017/2018. Experimental results show that the data-driven ECAR model has a good forecast skill at the lead time of approximately 26 days, and its forecast ability is superior to that of the traditional autoregressive model. Hence, the development and variation of the leading 25–40-day modes for the low-frequency temperatures at 850 hPa in eastern Asia and temporal evolutions of their relationships to the low-frequency components of the temperature over the LYR in winter supplied the valuable predicting background to determine the extended-range weather process in the persistent low temperature over the LYR at the 3–4-week leads.
2021, 45(1): 37-57.
doi: 10.3878/j.issn.1006-9895.2005.19209
Abstract:
Stratiform cloud systems are important for the exploitation and utilization of cloud water resources. Precipitation enhancement requires scientific and feasible operational technical indicators to guide the implementation of actual operations, and a reasonable and accurate assessment of operation effects is an important issue that needs to be solved. One of the necessary ways to establishing and improving operation technologies is to simulate the seeding operation process reasonably through a numerical model and study the changes and mechanisms of a series of macro and micro characteristics of cloud and precipitation after seeding operations. Evaluating the effect of realistic precipitation enhancement is also an effective method through a seeding model simulation. An aircraft seeding operation during the stratiform cloud precipitation in Hebei province on April 15, 2014 was simulated in accordance with a real operation process by a 3D mesoscale cold cloud seeding model. The actual operation process was reasonably simulated by the numerical model. The diffusion and transmission characteristics of AgI particles seeded by aircraft in the atmosphere were studied, the seeding influence on the macro and micro characteristics of clouds and precipitation was analyzed, and the precipitation enhancement effect of the aircraft seeding operation was evaluated. Results show that the horizontal scale of AgI plume can extend to more than tens of kilometers, and most AgI particles in the vertical direction are concentrated within the range of approximately 1 km above and below the seeding layer. Moreover, the upward transport of AgI particles is significantly stronger than the downward transport. The outstanding increase in ice crystals and snow particles in clouds after seeding leads to the inhibition of graupel growth in the early simulation stage. However, the enhancement of the graupel collection snow process and ice phase particle riming processes near the zero layer gradually increases the total mass of graupel after some time. After the aircraft seeding operation, radar reflectivity is enhanced; in addition, it shows different structural characteristics with time. Precipitation decreases first and then increases with time due to seeding. Three hours after seeding, the operation influence area extends to more than 100 km to the downstream of the operation area, showing the distribution characteristics of rainfall-reducing area first and then rainfall-increasing area in general. The model evaluation indicates that the net rainfall increases by 3.6×107 kg in the entire evaluation area, with an average rainfall-increasing rate of 1.1%; furthermore, the increase in the concentration and size of graupel particles in the warm layer is the main reason for rainfall increase. Given the weak seeding operation conditions in the target cloud area, the AgI seeding amount of this operation is relatively high, resulting in a low effect of precipitation enhancement.
Stratiform cloud systems are important for the exploitation and utilization of cloud water resources. Precipitation enhancement requires scientific and feasible operational technical indicators to guide the implementation of actual operations, and a reasonable and accurate assessment of operation effects is an important issue that needs to be solved. One of the necessary ways to establishing and improving operation technologies is to simulate the seeding operation process reasonably through a numerical model and study the changes and mechanisms of a series of macro and micro characteristics of cloud and precipitation after seeding operations. Evaluating the effect of realistic precipitation enhancement is also an effective method through a seeding model simulation. An aircraft seeding operation during the stratiform cloud precipitation in Hebei province on April 15, 2014 was simulated in accordance with a real operation process by a 3D mesoscale cold cloud seeding model. The actual operation process was reasonably simulated by the numerical model. The diffusion and transmission characteristics of AgI particles seeded by aircraft in the atmosphere were studied, the seeding influence on the macro and micro characteristics of clouds and precipitation was analyzed, and the precipitation enhancement effect of the aircraft seeding operation was evaluated. Results show that the horizontal scale of AgI plume can extend to more than tens of kilometers, and most AgI particles in the vertical direction are concentrated within the range of approximately 1 km above and below the seeding layer. Moreover, the upward transport of AgI particles is significantly stronger than the downward transport. The outstanding increase in ice crystals and snow particles in clouds after seeding leads to the inhibition of graupel growth in the early simulation stage. However, the enhancement of the graupel collection snow process and ice phase particle riming processes near the zero layer gradually increases the total mass of graupel after some time. After the aircraft seeding operation, radar reflectivity is enhanced; in addition, it shows different structural characteristics with time. Precipitation decreases first and then increases with time due to seeding. Three hours after seeding, the operation influence area extends to more than 100 km to the downstream of the operation area, showing the distribution characteristics of rainfall-reducing area first and then rainfall-increasing area in general. The model evaluation indicates that the net rainfall increases by 3.6×107 kg in the entire evaluation area, with an average rainfall-increasing rate of 1.1%; furthermore, the increase in the concentration and size of graupel particles in the warm layer is the main reason for rainfall increase. Given the weak seeding operation conditions in the target cloud area, the AgI seeding amount of this operation is relatively high, resulting in a low effect of precipitation enhancement.
2021, 45(1): 58-72.
doi: 10.3878/j.issn.1006-9895.2005.19171
Abstract:
Five planetary boundary layer (PBL) parameterization schemes [Yonsei University (YSU), Mellor–Yamada–Janjic (MYJ), Mellor–Yamada–Nakanishi–Niino Level 2.5 (MYNN2), Shin-Hong (SH), and the asymmetric convective model, version 2 (ACM2)] in the Weather Research and Forecast model (WRF v4.0), were used to simulate all well-developed Southwest China vortex (SWCV) processes in the eastern Sichuan basin in 2016. Each level of precipitation prediction was verified, and the L-band radiosonde data with temporal resolution of 1 s were used to reveal the fine structure of the PBL during a midday. The differences between the observation and simulation are assessed, and the reasons are discussed based on the characteristics of the turbulence algorithm used in each scheme. Finally, the parameter of turbulence intensity was adjusted for the ACM2 scheme to improve the structure of the PBL that influences the simulation of the precipitation in the eastern Sichuan basin. The results show that the ACM2 and YSU schemes show a relatively better TS performance. Compared with other schemes, ACM2 has fewer false alarms. The attribute of ACM2 that can modify local or nonlocal algorithms according to the stability of the surrounding environment seems to be more suitable for the Sichuan basin precipitation simulation than the other schemes. However, all PBL schemes show a high false-alarm rate in the prediction of the SWCV precipitation, especially when the precipitation is heavy. The sounding data with 1 s temporal and 3 m spatial resolution further show that all the PBL schemes predict a higher PBL height compared with that of the observations, which means that the simulation has a stronger mixing intensity compared with that of the real atmosphere. By parameter adjustment, using the ACM2 scheme with reduced mixing intensity, the potential temperature and humidity structure in PBL are more aligned with the observations. Further, the potential temperature of the low PBL is low, humidity is high, and false alarm reports of heavy precipitation are reduced, which leads to an improvement regarding the precipitation simulation in the Sichuan basin. The different characters of the PBL schemes that are used in the simulation of the SWCV mainly lead to different positions of the vortex and precipitation intensity. Essentially, these characters are derived from a local or nonlocal attribute and the intensity of vertical mixing. A selection based on regional features of a research object is the key to the accurate simulation of a PBL structure and precipitation process.
Five planetary boundary layer (PBL) parameterization schemes [Yonsei University (YSU), Mellor–Yamada–Janjic (MYJ), Mellor–Yamada–Nakanishi–Niino Level 2.5 (MYNN2), Shin-Hong (SH), and the asymmetric convective model, version 2 (ACM2)] in the Weather Research and Forecast model (WRF v4.0), were used to simulate all well-developed Southwest China vortex (SWCV) processes in the eastern Sichuan basin in 2016. Each level of precipitation prediction was verified, and the L-band radiosonde data with temporal resolution of 1 s were used to reveal the fine structure of the PBL during a midday. The differences between the observation and simulation are assessed, and the reasons are discussed based on the characteristics of the turbulence algorithm used in each scheme. Finally, the parameter of turbulence intensity was adjusted for the ACM2 scheme to improve the structure of the PBL that influences the simulation of the precipitation in the eastern Sichuan basin. The results show that the ACM2 and YSU schemes show a relatively better TS performance. Compared with other schemes, ACM2 has fewer false alarms. The attribute of ACM2 that can modify local or nonlocal algorithms according to the stability of the surrounding environment seems to be more suitable for the Sichuan basin precipitation simulation than the other schemes. However, all PBL schemes show a high false-alarm rate in the prediction of the SWCV precipitation, especially when the precipitation is heavy. The sounding data with 1 s temporal and 3 m spatial resolution further show that all the PBL schemes predict a higher PBL height compared with that of the observations, which means that the simulation has a stronger mixing intensity compared with that of the real atmosphere. By parameter adjustment, using the ACM2 scheme with reduced mixing intensity, the potential temperature and humidity structure in PBL are more aligned with the observations. Further, the potential temperature of the low PBL is low, humidity is high, and false alarm reports of heavy precipitation are reduced, which leads to an improvement regarding the precipitation simulation in the Sichuan basin. The different characters of the PBL schemes that are used in the simulation of the SWCV mainly lead to different positions of the vortex and precipitation intensity. Essentially, these characters are derived from a local or nonlocal attribute and the intensity of vertical mixing. A selection based on regional features of a research object is the key to the accurate simulation of a PBL structure and precipitation process.
2021, 45(1): 73-87.
doi: 10.3878/j.issn.1006-9895.2001.19184
Abstract:
With regard to tropical cyclone formation, few studies focus on the transition from a tropical disturbance to a tropical depression, which is accompanied by the formation, merger, and development of the mesoscale convective system (MCS). In this study, the Final Operational Global Analysis (FNL) data and high-resolution numerical model are used to simulate typhoon Dujuan (No. 1521) three days before its formation, and the development and evolution characteristics of MCS in the formation process of Dujuan are preliminarily explored. During the formation of Dujuan, the tropical upper tropospheric trough (TUTT) was located farther east of it, and Dujuan migrated northwestward from the southeastern edge of the monsoon gyre (MG). The decreased vertical wind shear and MG-related low-level convergence are conducive to the formation of Dujuan. In the early stage of the formation of Dujuan, more MCSs are generated, which is favorable for the development of Dujuan from tropical disturbance to a tropical depression. In the later stage of the formation of Dujuan, with the occurrence of convective bursts, the MCSs merge, reducing its number and becoming more compact and the largest MCS shrinks towards the core region of the tropical disturbance. As a result, the formation of Dujuan is accelerated. The comparison of the characteristics of stratiform and convective precipitation in the MCSs indicates that the coverage of stratiform precipitation is the larger than that of convective precipitation, whereas the precipitation rate of convective precipitation is larger than that of stratiform precipitation and the variation of the coverage of convective precipitation is more significant than that of stratiform precipitation. The increased percentage of stratiform precipitation is closely related to the intensification of Dujuan, and the increase in the convective precipitation rate is beneficial to the intensification of the MCS. Their combined effect promotes the formation of Dujuan.
With regard to tropical cyclone formation, few studies focus on the transition from a tropical disturbance to a tropical depression, which is accompanied by the formation, merger, and development of the mesoscale convective system (MCS). In this study, the Final Operational Global Analysis (FNL) data and high-resolution numerical model are used to simulate typhoon Dujuan (No. 1521) three days before its formation, and the development and evolution characteristics of MCS in the formation process of Dujuan are preliminarily explored. During the formation of Dujuan, the tropical upper tropospheric trough (TUTT) was located farther east of it, and Dujuan migrated northwestward from the southeastern edge of the monsoon gyre (MG). The decreased vertical wind shear and MG-related low-level convergence are conducive to the formation of Dujuan. In the early stage of the formation of Dujuan, more MCSs are generated, which is favorable for the development of Dujuan from tropical disturbance to a tropical depression. In the later stage of the formation of Dujuan, with the occurrence of convective bursts, the MCSs merge, reducing its number and becoming more compact and the largest MCS shrinks towards the core region of the tropical disturbance. As a result, the formation of Dujuan is accelerated. The comparison of the characteristics of stratiform and convective precipitation in the MCSs indicates that the coverage of stratiform precipitation is the larger than that of convective precipitation, whereas the precipitation rate of convective precipitation is larger than that of stratiform precipitation and the variation of the coverage of convective precipitation is more significant than that of stratiform precipitation. The increased percentage of stratiform precipitation is closely related to the intensification of Dujuan, and the increase in the convective precipitation rate is beneficial to the intensification of the MCS. Their combined effect promotes the formation of Dujuan.
2021, 45(1): 88-106.
doi: 10.3878/j.issn.1006-9895.2004.19202
Abstract:
Based on the observation data obtained by the “Rainfall Enhancement and Hail Suppression Project on the Eastern Side of Taihang Mountains” in this paper, we analyze the microphysical characteristics of the stratiform cloud induced by the upper-level westerly trough on May 21, 2018. The results indicate that the supercooled liquid water content in the −5°C layer is less than 0.05 g m−3, and the concentrations of supercooled cloud droplets range from 10–102 L−1. Needle-like and columnar ice crystals are often observed in regions with high number concentrations of ice crystals, which may be related to ice crystal fragments produced by the Hallett–Mossop mechanism and other mechanisms, which are then deposited under super-saturated ice conditions. Ice crystal habits are predominantly planar and dendritic in regions with low ice-crystal number concentrations. Ice and snow crystals mainly grow via deposition and coalescence processes, with a weak rimming process. The liquid water content accounts for more than 70% in regions with a peak cloud water content near the 0°C layer. These particles are mainly cloud droplets with diameters ranging from 10 μm to 50 μm, accompanied by a few aggregates. The supercooled water content is about 0.05 g m−3 in other regions near the 0°C layer, with the ice crystal habits being predominantly aggregates, rimed snow, and graupel. Most of the particles are spherical droplets and melting ice crystals in the liquid water layer. Vertical observations indicate that the ice- and snow-crystal number concentrations increase with height above the 0°C layer. The supercooled-liquid-water content of the mixed layer is much lower in a stable stratiform cloud. Most particles mainly grow by deposition and coalescence, and the degree of ice crystallization is much higher. The existence of liquid droplets indicates that the transformation between the liquid and ice phases is not sufficient in strongly developed stratiform cloud regions where supercooled liquid water is relatively abundant. The particle size distributions at different temperature levels indicate that the average number concentration of ice particles in regions with an abundant supercooled-liquid-water content is higher than those with a low supercooled-liquid-water content. However, the average diameter of ice particles in regions with low supercooled-liquid-water content is larger.
Based on the observation data obtained by the “Rainfall Enhancement and Hail Suppression Project on the Eastern Side of Taihang Mountains” in this paper, we analyze the microphysical characteristics of the stratiform cloud induced by the upper-level westerly trough on May 21, 2018. The results indicate that the supercooled liquid water content in the −5°C layer is less than 0.05 g m−3, and the concentrations of supercooled cloud droplets range from 10–102 L−1. Needle-like and columnar ice crystals are often observed in regions with high number concentrations of ice crystals, which may be related to ice crystal fragments produced by the Hallett–Mossop mechanism and other mechanisms, which are then deposited under super-saturated ice conditions. Ice crystal habits are predominantly planar and dendritic in regions with low ice-crystal number concentrations. Ice and snow crystals mainly grow via deposition and coalescence processes, with a weak rimming process. The liquid water content accounts for more than 70% in regions with a peak cloud water content near the 0°C layer. These particles are mainly cloud droplets with diameters ranging from 10 μm to 50 μm, accompanied by a few aggregates. The supercooled water content is about 0.05 g m−3 in other regions near the 0°C layer, with the ice crystal habits being predominantly aggregates, rimed snow, and graupel. Most of the particles are spherical droplets and melting ice crystals in the liquid water layer. Vertical observations indicate that the ice- and snow-crystal number concentrations increase with height above the 0°C layer. The supercooled-liquid-water content of the mixed layer is much lower in a stable stratiform cloud. Most particles mainly grow by deposition and coalescence, and the degree of ice crystallization is much higher. The existence of liquid droplets indicates that the transformation between the liquid and ice phases is not sufficient in strongly developed stratiform cloud regions where supercooled liquid water is relatively abundant. The particle size distributions at different temperature levels indicate that the average number concentration of ice particles in regions with an abundant supercooled-liquid-water content is higher than those with a low supercooled-liquid-water content. However, the average diameter of ice particles in regions with low supercooled-liquid-water content is larger.
2021, 45(1): 107-122.
doi: 10.3878/j.issn.1006-9895.2005.19214
Abstract:
The weather research and forecasting model with a spectral-bin microphysical scheme (WRF-SBM) was used to simulate a hailstorm that occurred in Xinjiang during a summer. The effects of aerosol concentration on the microphysical characteristics and precipitation of the hailstorm and hail formation mechanism were studied via sensitivity tests. The results show that the convection of the hailstorm increases in strength with increasing aerosol concentration. At the development stage of the hailstorm, the liquid water content increases with increasing aerosol concentration, and the ice water content is the highest under moderate pollution conditions. With the increase in aerosol concentration, the hail mixing ratio first increases and then decreases. Under moderate pollution conditions, the cloud droplet size is appropriate, and the amount of supercooled water is relatively sufficient, which are favorable conditions for the transformation of water from the liquid to ice phase, thus contributing to hail growth. Hail is initially formed by the riming of supercooled liquid water by ice crystals, but this process is rapidly weakened after the hailstorm development. Further, the freezing of droplets becomes the main source of hail formation for a short while. However, once the hails are formed, they grow rapidly by collecting the supercooled water, which becomes the dominant process of the hail growth. The severe pollution condition will delay the start of hail formation processes. With enhanced aerosol loading, the surface accumulated liquid precipitation increases, whereas, the ice-phase precipitation first increases and then reduces. The moderate aerosol concentration leads to a large amount of hail mixing ratio and a high percentage of hail in the ice-phase precipitation. However, with further increase in aerosol concentration, both values are reduced. Therefore, we propose “optimal aerosol concentration,” which is the most suitable condition for hail growth.
The weather research and forecasting model with a spectral-bin microphysical scheme (WRF-SBM) was used to simulate a hailstorm that occurred in Xinjiang during a summer. The effects of aerosol concentration on the microphysical characteristics and precipitation of the hailstorm and hail formation mechanism were studied via sensitivity tests. The results show that the convection of the hailstorm increases in strength with increasing aerosol concentration. At the development stage of the hailstorm, the liquid water content increases with increasing aerosol concentration, and the ice water content is the highest under moderate pollution conditions. With the increase in aerosol concentration, the hail mixing ratio first increases and then decreases. Under moderate pollution conditions, the cloud droplet size is appropriate, and the amount of supercooled water is relatively sufficient, which are favorable conditions for the transformation of water from the liquid to ice phase, thus contributing to hail growth. Hail is initially formed by the riming of supercooled liquid water by ice crystals, but this process is rapidly weakened after the hailstorm development. Further, the freezing of droplets becomes the main source of hail formation for a short while. However, once the hails are formed, they grow rapidly by collecting the supercooled water, which becomes the dominant process of the hail growth. The severe pollution condition will delay the start of hail formation processes. With enhanced aerosol loading, the surface accumulated liquid precipitation increases, whereas, the ice-phase precipitation first increases and then reduces. The moderate aerosol concentration leads to a large amount of hail mixing ratio and a high percentage of hail in the ice-phase precipitation. However, with further increase in aerosol concentration, both values are reduced. Therefore, we propose “optimal aerosol concentration,” which is the most suitable condition for hail growth.
2021, 45(1): 123-147.
doi: 10.3878/j.issn.1006-9895.2004.19216
Abstract:
With the 0.5°×0.5° analysis fields of the National Centers for Environmental Prediction/Global Forecast System (NCEP/GFS) as the numerical forecast background and using surface precipitation data aimed at data assimilation, in this study, we first analyzed the quality of wind products from 12 L-band wind-profiler radars in Fujian Province, including three CFL-03 radars and nine CFL-06 radars obtained at 0000 UTC, 0600 UTC, 1200 UTC, and 1800 UTC from January to December 2017. Then, we considered different quality control (QC) schemes and their effects. The results indicate that: (1) Winds detected by CFL-06 radars are obviously better than those by CFL-03 radars with respect to the maximum detection height, effective data availability, and horizontal wind quality at low levels. (2) Great differences exist in the horizontal winds detected by different wind-profiler radars in same series, including data availability, effective detection height, and the vertical distributions of the standard deviation, correlation coefficients, and bias. These differences have no direct relationship with the geographical locations of the wind-profiler radars, i.e., coastal area or inland, or their heights above sea level. (3) Wind-profiler radar products have obvious systematic negative biases relative to the GFS u-wind field, that is, the u winds detected by wind-profiler radars are lower than the GFS background field. This does not meet the no-bias requirement for data assimilation, so bias corrections are necessary in the data assimilation process. In contrast, the v-wind data are relatively better than u-wind data. (4) Precipitation has a great impact on the detection capability of wind-profiler radars. On precipitation days, the data availability is decreased in the middle-low levels but greatly enhanced in the middle-high levels. The standard deviations of u and v winds both increase in the middle-low levels, whereas the standard deviation of the v winds increase and those of u winds greatly decrease in the middle-high levels. (5) Two QC schemes, i.e., a scheme using different high-confidence ranges and a scheme using different effective detection heights are introduced to different wind-profiler radars to compare their results with those of the fixed effective detection height scheme. The results show that the two QC schemes both have obvious advantages. The QC effect of the different high-confidence range scheme is much more obvious, with the horizontal wind data of different radars more fully and effectively identified. This scheme reduces unnecessary loss of radar data, eliminates poor quality data, and achieves good results regarding the precipitation conditions.
With the 0.5°×0.5° analysis fields of the National Centers for Environmental Prediction/Global Forecast System (NCEP/GFS) as the numerical forecast background and using surface precipitation data aimed at data assimilation, in this study, we first analyzed the quality of wind products from 12 L-band wind-profiler radars in Fujian Province, including three CFL-03 radars and nine CFL-06 radars obtained at 0000 UTC, 0600 UTC, 1200 UTC, and 1800 UTC from January to December 2017. Then, we considered different quality control (QC) schemes and their effects. The results indicate that: (1) Winds detected by CFL-06 radars are obviously better than those by CFL-03 radars with respect to the maximum detection height, effective data availability, and horizontal wind quality at low levels. (2) Great differences exist in the horizontal winds detected by different wind-profiler radars in same series, including data availability, effective detection height, and the vertical distributions of the standard deviation, correlation coefficients, and bias. These differences have no direct relationship with the geographical locations of the wind-profiler radars, i.e., coastal area or inland, or their heights above sea level. (3) Wind-profiler radar products have obvious systematic negative biases relative to the GFS u-wind field, that is, the u winds detected by wind-profiler radars are lower than the GFS background field. This does not meet the no-bias requirement for data assimilation, so bias corrections are necessary in the data assimilation process. In contrast, the v-wind data are relatively better than u-wind data. (4) Precipitation has a great impact on the detection capability of wind-profiler radars. On precipitation days, the data availability is decreased in the middle-low levels but greatly enhanced in the middle-high levels. The standard deviations of u and v winds both increase in the middle-low levels, whereas the standard deviation of the v winds increase and those of u winds greatly decrease in the middle-high levels. (5) Two QC schemes, i.e., a scheme using different high-confidence ranges and a scheme using different effective detection heights are introduced to different wind-profiler radars to compare their results with those of the fixed effective detection height scheme. The results show that the two QC schemes both have obvious advantages. The QC effect of the different high-confidence range scheme is much more obvious, with the horizontal wind data of different radars more fully and effectively identified. This scheme reduces unnecessary loss of radar data, eliminates poor quality data, and achieves good results regarding the precipitation conditions.
2021, 45(1): 148-164.
doi: 10.3878/j.issn.1006-9895.1912.19219
Abstract:
Taking a torrential rainfall that occurred in the Ili Valley of Xinjiang on June 26, 2015 as an example, this study analyzes the circulation background and unstable conditions of the rainstorm process by using observation data and the high-resolution numerical simulation results of WRF. Some results are as follows: (1) Precipitation occurs under the background of synoptic circulation with the “two-ridges-and-one-trough” pattern over the middle and high latitudes in the middle troposphere and the “double highs” pattern of the South Asian High in the upper troposphere. Under the effect of the terrain of the Ili Valley (i.e., trumpet shaped topography with an opening to the west), the Central Asian vortex located in Kazakhstan causes westerly winds in the lower layer of the Ili Valley, whereas that located in the Tarim Basin causes easterly winds in the middle layer of the Ili Valley. The vertical shear of horizontal winds in the Ili Valley is enhanced by the interaction of two Central Asian vortexes. In the Ili Valley, affected by the topography and the Central Asian vortexes, the low-layer convergence line is formed and coupled with a divergence area caused by the upper jet, which enhances the upward motion. The low-layer westerly wind transports water vapor into the Ili Valley, and the water vapor accumulates in the valley. The enhancement of the upward motion lifts the water vapor in the Ili Valley. (2) The simulation results of WRF can reproduce the location, intensity, and evolution process of precipitation during this weather process and provide data with high spatial and temporal resolution for analyzing the evolution of the rainstorm process. The analysis of the simulation results shows that the divergence distribution, water vapor, the vertical shear of horizontal wind, and thermal stratification distribution over the precipitation area have important contributions to the generation of precipitation. The analysis of the vertical and horizontal components of moist potential vorticity reveals that the convective instability affected by thermal stratification influences the generation of precipitation, and the symmetric instability affected by the vertical shear of the horizontal wind influences the enhancement and maintenance of precipitation. The analysis of potential divergence further indicates that the convective instability in the lower layer of the entire precipitation area is mainly caused by the vertical shear part of potential divergence, whereas the divergence part of the potential divergence can strengthen the convective instability in the leeward slope of the small terrain. These results show that the dynamic and thermodynamic factors are coupled with each other in the entire precipitation evolution process, thus affecting the precipitation intensity and area.
Taking a torrential rainfall that occurred in the Ili Valley of Xinjiang on June 26, 2015 as an example, this study analyzes the circulation background and unstable conditions of the rainstorm process by using observation data and the high-resolution numerical simulation results of WRF. Some results are as follows: (1) Precipitation occurs under the background of synoptic circulation with the “two-ridges-and-one-trough” pattern over the middle and high latitudes in the middle troposphere and the “double highs” pattern of the South Asian High in the upper troposphere. Under the effect of the terrain of the Ili Valley (i.e., trumpet shaped topography with an opening to the west), the Central Asian vortex located in Kazakhstan causes westerly winds in the lower layer of the Ili Valley, whereas that located in the Tarim Basin causes easterly winds in the middle layer of the Ili Valley. The vertical shear of horizontal winds in the Ili Valley is enhanced by the interaction of two Central Asian vortexes. In the Ili Valley, affected by the topography and the Central Asian vortexes, the low-layer convergence line is formed and coupled with a divergence area caused by the upper jet, which enhances the upward motion. The low-layer westerly wind transports water vapor into the Ili Valley, and the water vapor accumulates in the valley. The enhancement of the upward motion lifts the water vapor in the Ili Valley. (2) The simulation results of WRF can reproduce the location, intensity, and evolution process of precipitation during this weather process and provide data with high spatial and temporal resolution for analyzing the evolution of the rainstorm process. The analysis of the simulation results shows that the divergence distribution, water vapor, the vertical shear of horizontal wind, and thermal stratification distribution over the precipitation area have important contributions to the generation of precipitation. The analysis of the vertical and horizontal components of moist potential vorticity reveals that the convective instability affected by thermal stratification influences the generation of precipitation, and the symmetric instability affected by the vertical shear of the horizontal wind influences the enhancement and maintenance of precipitation. The analysis of potential divergence further indicates that the convective instability in the lower layer of the entire precipitation area is mainly caused by the vertical shear part of potential divergence, whereas the divergence part of the potential divergence can strengthen the convective instability in the leeward slope of the small terrain. These results show that the dynamic and thermodynamic factors are coupled with each other in the entire precipitation evolution process, thus affecting the precipitation intensity and area.
2021, 45(1): 165-180.
doi: 10.3878/j.issn.1006-9895.2004.19226
Abstract:
A series of persistently extreme hot days, which broke the historical record for length, was experienced by Yunnan province from April to June 2019 and induced a severe local drought. Based on the daily in-situ surface air temperature in China, JRA-55 reanalysis datasets, and outputs from the Community Earth System Model Large Ensemble (CESM-LE) Project, we investigate the general circulation regime related to the hot weather in Yunnan and discuss the possible causes of these persistently hot days in 2019. Our results indicate that lower- and upper-level strong anticyclonic circulation anomalies directly result in the local hot weather, which induces adiabatic warming in a descending motion and enhances solar radiation heating at the surface. The anticyclonic anomaly is a node of high and mid-latitude eastward-propagating wave trains originating from the North Atlantic. The 2019 April–June mean temperature and associated anticyclonic anomalies were the highest recorded since 1961. The anthropogenic contribution to the magnitude of this 2019 temperature anomaly was approximately 37.51% and the occurrence probability of extreme-high-temperature events analogous to or higher than those of 2019 is 56.32%, with an important impact of internal variability. The negative phase of the Arctic Oscillation (AO) and warm phase of El Niño and the Southern Oscillation (ENSO) are important external forcing factors responsible for the persistent anticyclonic anomalies over Yunnan from April to June 2019. The negative phase of the AO causes a southward shift of the positive geopotential height anomalies over the Arctic at the longitudes of Eastern Europe, and favors a high-latitude wave train and an anticyclonic anomaly over Yunnan. The warm phase of ENSO enhances the western North Pacific anticyclone and favors its westward shift, which leads to the persistence of the anomalous anticyclonic circulation over Yunnan. Under the recent global warming conditions, the negative phase of the AO and the warm phase of ENSO jointly reinforce the intensity and duration of the anomalous anticyclonic circulation over Yunnan, which result in frequent and persistent occurrences of the record-breaking extremely high temperatures and the severe drought event in 2019.
A series of persistently extreme hot days, which broke the historical record for length, was experienced by Yunnan province from April to June 2019 and induced a severe local drought. Based on the daily in-situ surface air temperature in China, JRA-55 reanalysis datasets, and outputs from the Community Earth System Model Large Ensemble (CESM-LE) Project, we investigate the general circulation regime related to the hot weather in Yunnan and discuss the possible causes of these persistently hot days in 2019. Our results indicate that lower- and upper-level strong anticyclonic circulation anomalies directly result in the local hot weather, which induces adiabatic warming in a descending motion and enhances solar radiation heating at the surface. The anticyclonic anomaly is a node of high and mid-latitude eastward-propagating wave trains originating from the North Atlantic. The 2019 April–June mean temperature and associated anticyclonic anomalies were the highest recorded since 1961. The anthropogenic contribution to the magnitude of this 2019 temperature anomaly was approximately 37.51% and the occurrence probability of extreme-high-temperature events analogous to or higher than those of 2019 is 56.32%, with an important impact of internal variability. The negative phase of the Arctic Oscillation (AO) and warm phase of El Niño and the Southern Oscillation (ENSO) are important external forcing factors responsible for the persistent anticyclonic anomalies over Yunnan from April to June 2019. The negative phase of the AO causes a southward shift of the positive geopotential height anomalies over the Arctic at the longitudes of Eastern Europe, and favors a high-latitude wave train and an anticyclonic anomaly over Yunnan. The warm phase of ENSO enhances the western North Pacific anticyclone and favors its westward shift, which leads to the persistence of the anomalous anticyclonic circulation over Yunnan. Under the recent global warming conditions, the negative phase of the AO and the warm phase of ENSO jointly reinforce the intensity and duration of the anomalous anticyclonic circulation over Yunnan, which result in frequent and persistent occurrences of the record-breaking extremely high temperatures and the severe drought event in 2019.
2021, 45(1): 181-194.
doi: 10.3878/j.issn.1006-9895.2001.19230
Abstract:
In this study, the performances of the median-resolution (about 110 km) climate system model (BCC-CSM2-MR) and atmospheric model (BCC-AGCM3-MR) developed at the National Climate Center are evaluated using three reanalysis datasets (ERA5, JRA55, and NCEP/NCAR). The results show that a high blocking tendency can be distinguished over the “North Atlantic–Western Europe” and “Central North Pacific”. The winter and spring blocking frequency is almost twice of that in summer and autumn. The blocking frequency in the ERA5 dataset is higher than that in the JRA55 and NCEP/NCAR datasets, especially over the North Pacific. Model evaluations show that the atmospheric model reproduces the main features of the Northern Hemisphere blocking frequency, spatial structures, and seasonal variations very well. The main biases of the model are overestimation over Europe–Asia in winter and spring, especially over the Ural Mountains, and underestimations over the North Atlantic. These biases are attributed to the climatological biases in geopotential heights at 500 hPa. The overall performances of the BCC-CSM2-MR model are similar to those of the BCC-AGCM3-MR model. However, the winter and spring blocking over Europe–Asia and especially over the Ural Mountains, is improved. Spring blocking and the double-peak blocking structure in summer over the North Pacific are also better reproduced in the coupled model. Therefore, air–sea coupling may help to improve the reproduction of blocking frequency over Europe–Asia and the North Pacific. The internal variability of the climate system has a great impact on the variation of the blocking frequency, which also affects the capability of the model to predict blocking highs.
In this study, the performances of the median-resolution (about 110 km) climate system model (BCC-CSM2-MR) and atmospheric model (BCC-AGCM3-MR) developed at the National Climate Center are evaluated using three reanalysis datasets (ERA5, JRA55, and NCEP/NCAR). The results show that a high blocking tendency can be distinguished over the “North Atlantic–Western Europe” and “Central North Pacific”. The winter and spring blocking frequency is almost twice of that in summer and autumn. The blocking frequency in the ERA5 dataset is higher than that in the JRA55 and NCEP/NCAR datasets, especially over the North Pacific. Model evaluations show that the atmospheric model reproduces the main features of the Northern Hemisphere blocking frequency, spatial structures, and seasonal variations very well. The main biases of the model are overestimation over Europe–Asia in winter and spring, especially over the Ural Mountains, and underestimations over the North Atlantic. These biases are attributed to the climatological biases in geopotential heights at 500 hPa. The overall performances of the BCC-CSM2-MR model are similar to those of the BCC-AGCM3-MR model. However, the winter and spring blocking over Europe–Asia and especially over the Ural Mountains, is improved. Spring blocking and the double-peak blocking structure in summer over the North Pacific are also better reproduced in the coupled model. Therefore, air–sea coupling may help to improve the reproduction of blocking frequency over Europe–Asia and the North Pacific. The internal variability of the climate system has a great impact on the variation of the blocking frequency, which also affects the capability of the model to predict blocking highs.
2021, 45(1): 195-204.
doi: 10.3878/j.issn.1006-9895.2010.19237
Abstract:
Using the short-lead-time forecast bias and target-lead-time latitude forecast (i.e., the lead time required to be corrected) of numerically forecasted typhoon tracks as the predictors, a track forecast bias prediction equation is established by multiple linear regression. The equation permits typhoon track forecast correction in real time. In this paper, 12 h is taken as the short lead time, and the European Center for Medium-Range Weather Forecasts deterministic prediction system (ECMWF-IFS) and ensemble prediction system (ECMWF-EPS) for typhoon track forecasts are applied. The modeled forecast results from 2018 show that the mean track error of the corrected typhoon tracks forecasted by ECMWF-IFS at 24 h, 36 h, 48 h, 60 h, 72 h, and 84 h is reduced by 7.3 km, 9.3 km, 8.9 km, 6.5 km, 6.9 km, and 2.6 km, respectively, compared with those of uncorrected typhoon tracks. In general, the corrective effect is better for strong typhoons (observed intensity at 12 h≥32.7 m s−1). First, the typhoon track forecast of each ensemble forecast member from ECMWF-EPS is corrected; the integrated forecast is then obtained. The typhoon track forecasts obtained by the following five methods are compared: “corrected deterministic prediction,” “ensemble mean of all ensemble forecast members,” “ensemble mean of selective ensemble forecast members,” “ensemble mean of all corrected ensemble forecast members,” and “ensemble mean of corrected selective ensemble forecast members.” The modeled forecast results from 2018 show that “ensemble mean of corrected selective ensemble forecast members,” “ensemble mean of all corrected ensemble forecast members,” and “ensemble mean of selective ensemble forecast members” yield the lowest track error at 24 h and 36 h, 48 h and 60 h, and 72 h and 84 h, respectively. When applied in a targeted manner in operational application, an objective comprehensive forecast result for typhoon tracks with excellent performance for each lead time is expected. At 24 h, 36 h, 48 h, and 72 h, the mean track error of “ensemble mean of corrected selective ensemble forecast members” is reduced by 13.3 km, 11.7 km, 10.0 km and 7.6 km, respectively, compared with those of “ensemble mean of all ensemble forecast members” and by 0.7 km, 2.0 km, 3.9 km, and 2.4 km, respectively, compared with those of the Central Meteorological Office official track forecast (with corresponding lead times of 12 h, 24 h, 36 h, and 48 h, respectively).
Using the short-lead-time forecast bias and target-lead-time latitude forecast (i.e., the lead time required to be corrected) of numerically forecasted typhoon tracks as the predictors, a track forecast bias prediction equation is established by multiple linear regression. The equation permits typhoon track forecast correction in real time. In this paper, 12 h is taken as the short lead time, and the European Center for Medium-Range Weather Forecasts deterministic prediction system (ECMWF-IFS) and ensemble prediction system (ECMWF-EPS) for typhoon track forecasts are applied. The modeled forecast results from 2018 show that the mean track error of the corrected typhoon tracks forecasted by ECMWF-IFS at 24 h, 36 h, 48 h, 60 h, 72 h, and 84 h is reduced by 7.3 km, 9.3 km, 8.9 km, 6.5 km, 6.9 km, and 2.6 km, respectively, compared with those of uncorrected typhoon tracks. In general, the corrective effect is better for strong typhoons (observed intensity at 12 h≥32.7 m s−1). First, the typhoon track forecast of each ensemble forecast member from ECMWF-EPS is corrected; the integrated forecast is then obtained. The typhoon track forecasts obtained by the following five methods are compared: “corrected deterministic prediction,” “ensemble mean of all ensemble forecast members,” “ensemble mean of selective ensemble forecast members,” “ensemble mean of all corrected ensemble forecast members,” and “ensemble mean of corrected selective ensemble forecast members.” The modeled forecast results from 2018 show that “ensemble mean of corrected selective ensemble forecast members,” “ensemble mean of all corrected ensemble forecast members,” and “ensemble mean of selective ensemble forecast members” yield the lowest track error at 24 h and 36 h, 48 h and 60 h, and 72 h and 84 h, respectively. When applied in a targeted manner in operational application, an objective comprehensive forecast result for typhoon tracks with excellent performance for each lead time is expected. At 24 h, 36 h, 48 h, and 72 h, the mean track error of “ensemble mean of corrected selective ensemble forecast members” is reduced by 13.3 km, 11.7 km, 10.0 km and 7.6 km, respectively, compared with those of “ensemble mean of all ensemble forecast members” and by 0.7 km, 2.0 km, 3.9 km, and 2.4 km, respectively, compared with those of the Central Meteorological Office official track forecast (with corresponding lead times of 12 h, 24 h, 36 h, and 48 h, respectively).
2021, 45(1): 205-216.
doi: 10.3878/j.issn.1006-9895.2004.19251
Abstract:
The forest canopy, as an active interface between vegetation and the environment, transmits energy by reflecting, absorbing, and transmitting solar radiation through its leaves. The radiation levels above, within, and beneath the forest canopy are considerably important factors that affect the energy balance and water and carbon cycles. The variation of radiation with the seasons and the distribution of radiation among the forest canopies of the Huainan area have rarely been studied. Using total radiation data obtained by the Huainan forest observation station from July 1, 2018 to June 30, 2019, we investigated the temporal changes in solar radiation above the Sawtooth Oak canopy, analyzed the spatial distribution and transfer of solar radiation through the canopy, and determined the albedo, transmittance, and absorbance of the canopy. The results show the following. (1) The downward shortwave radiation above the Sawtooth Oak canopy increases from spring to summer and then decreases gradually toward winter. Unlike that above the canopy, the downward shortwave radiation within and under the canopy demonstrate a different trend with smaller values that decrease from early spring and increase from autumn to winter. Concerning the upward shortwave radiation, the seasonal variation pattern is the same as the downward pattern, whether above, within, or under the canopy, but the values are much smaller. (2) The downward longwave radiation above, within, and under the canopy gradually increases from spring to summer, then decreases gradually, and reaches a minimum in winter. In terms of spatial change, the radiation longwave values within and under the canopy are higher than that above the canopy, enhancing the longwave radiation by as much as 1.3 times under clear skies. (3) The annual average albedo above the canopy in the Huainan forest area is 0.14, which is 0.01 lower than that in the temperate monsoon climate area (mainly mixed forest) in northern China (35°N), which indicates that the forest is denser in Huainan. (4) The shortwave radiation transmittance values of the upper part and the whole canopy are mainly affected by the leaves. In summer, the average shortwave transmittance of the whole canopy is 0.1, whereas in winter, as the leaves fall, the transmittance increases and tends to a stable fluctuation. The absorbance of shortwave radiation in the canopy is highest in summer, decreases gradually in autumn, and then decreases rapidly in winter as the leaves fall, tending to a constant value. These results are useful for validating layered-radiative-transfer and photosynthesis models as well as for further investigations of the energy, water, and carbon cycles of forest ecosystems.
The forest canopy, as an active interface between vegetation and the environment, transmits energy by reflecting, absorbing, and transmitting solar radiation through its leaves. The radiation levels above, within, and beneath the forest canopy are considerably important factors that affect the energy balance and water and carbon cycles. The variation of radiation with the seasons and the distribution of radiation among the forest canopies of the Huainan area have rarely been studied. Using total radiation data obtained by the Huainan forest observation station from July 1, 2018 to June 30, 2019, we investigated the temporal changes in solar radiation above the Sawtooth Oak canopy, analyzed the spatial distribution and transfer of solar radiation through the canopy, and determined the albedo, transmittance, and absorbance of the canopy. The results show the following. (1) The downward shortwave radiation above the Sawtooth Oak canopy increases from spring to summer and then decreases gradually toward winter. Unlike that above the canopy, the downward shortwave radiation within and under the canopy demonstrate a different trend with smaller values that decrease from early spring and increase from autumn to winter. Concerning the upward shortwave radiation, the seasonal variation pattern is the same as the downward pattern, whether above, within, or under the canopy, but the values are much smaller. (2) The downward longwave radiation above, within, and under the canopy gradually increases from spring to summer, then decreases gradually, and reaches a minimum in winter. In terms of spatial change, the radiation longwave values within and under the canopy are higher than that above the canopy, enhancing the longwave radiation by as much as 1.3 times under clear skies. (3) The annual average albedo above the canopy in the Huainan forest area is 0.14, which is 0.01 lower than that in the temperate monsoon climate area (mainly mixed forest) in northern China (35°N), which indicates that the forest is denser in Huainan. (4) The shortwave radiation transmittance values of the upper part and the whole canopy are mainly affected by the leaves. In summer, the average shortwave transmittance of the whole canopy is 0.1, whereas in winter, as the leaves fall, the transmittance increases and tends to a stable fluctuation. The absorbance of shortwave radiation in the canopy is highest in summer, decreases gradually in autumn, and then decreases rapidly in winter as the leaves fall, tending to a constant value. These results are useful for validating layered-radiative-transfer and photosynthesis models as well as for further investigations of the energy, water, and carbon cycles of forest ecosystems.
2021, 45(1): 217-228.
doi: 10.3878/j.issn.1006-9895.2009.20139
Abstract:
Based on the WRF (Weather Research and Forecasting) model and GSI (Gridpoint Statistical Interpolation analysis system) three-dimensional variational assimilation system, regional assimilation and prediction experiments for China’s autonomic Yunhai-2 occultation data were performed for the first time in May 2019. The results of the experiments demonstrated that after assimilating Yunhai-2 occultation data, the improvement for the wind and temperature fields is mainly reflected in the middle and later stages of the forecast, while the improvement for the humidity field is witnessed through the entire forecast period. The results also showed that the improvement degree of the wind, temperature, and humidity fields tends to be consistent with the extension of forecast time. It was found that the improvement for the wind and temperature fields is mainly reflected in the middle layer of the model, while the improvement for the water vapor mixing ratio is mainly reflected in the middle and lower layers of the model. Thus, assimilating Yunhai-2 occultation data can reasonably adjust the potential height, humidity, temperature, and wind fields in the model, thereby improving the precipitation forecast results.
Based on the WRF (Weather Research and Forecasting) model and GSI (Gridpoint Statistical Interpolation analysis system) three-dimensional variational assimilation system, regional assimilation and prediction experiments for China’s autonomic Yunhai-2 occultation data were performed for the first time in May 2019. The results of the experiments demonstrated that after assimilating Yunhai-2 occultation data, the improvement for the wind and temperature fields is mainly reflected in the middle and later stages of the forecast, while the improvement for the humidity field is witnessed through the entire forecast period. The results also showed that the improvement degree of the wind, temperature, and humidity fields tends to be consistent with the extension of forecast time. It was found that the improvement for the wind and temperature fields is mainly reflected in the middle layer of the model, while the improvement for the water vapor mixing ratio is mainly reflected in the middle and lower layers of the model. Thus, assimilating Yunhai-2 occultation data can reasonably adjust the potential height, humidity, temperature, and wind fields in the model, thereby improving the precipitation forecast results.
2021, 45(1): 229-244.
doi: 10.3878/j.issn.1006-9895.2010.20107
Abstract:
The background error correlation function in data assimilation systems is important because it determines the spread distance of observed data in the grid space and the analyzed increments on different scales in the spectral space. Herein, the features in the time-space domain and the spectral space domain are compared among Gaussian function (Gauss), second-order auto-regressive function (Soar), and superposition of Gaussian components (Supergauss). The three correlation functions are then applied in the Global/Regional Assimilation and Prediction System, three-dimensional variational data assimilation (GRAPES-3DVar), and their impacts on the analysis increments are analyzed through a single observation test. Research has demonstrated that the Gaussian correlation function contributes to the insufficiency of meso- and small-scale analysis increments. This leads to a larger negative correlation, which is the inverse of the wind field observation according to the correlation among the dynamic field variables when the stream function and unbalanced velocity potential function are used as the control variables. The Soar correlation function can increase the meso- and small-scale analysis increments. However, the less accuracy of a one-order recursive filtering scheme in the 3DVar system causes an abnormal analysis increment of the wind field. Application of the Supergauss correlation function can not only mitigate the inappropriate negative analysis increments of wind observation but also increase the meso- and small-scale power spectrum in analysis increments. Moreover, the analysis increment structure of isotropy with the Supergauss correlation function can be obtained through recursive filter implementation. Thus, the Supergauss correlation function is the most suitable one to describe the background error correlation among the three functions, which is beneficial for the meso- and small-scale analysis in the high-resolution 3DVAR system.
The background error correlation function in data assimilation systems is important because it determines the spread distance of observed data in the grid space and the analyzed increments on different scales in the spectral space. Herein, the features in the time-space domain and the spectral space domain are compared among Gaussian function (Gauss), second-order auto-regressive function (Soar), and superposition of Gaussian components (Supergauss). The three correlation functions are then applied in the Global/Regional Assimilation and Prediction System, three-dimensional variational data assimilation (GRAPES-3DVar), and their impacts on the analysis increments are analyzed through a single observation test. Research has demonstrated that the Gaussian correlation function contributes to the insufficiency of meso- and small-scale analysis increments. This leads to a larger negative correlation, which is the inverse of the wind field observation according to the correlation among the dynamic field variables when the stream function and unbalanced velocity potential function are used as the control variables. The Soar correlation function can increase the meso- and small-scale analysis increments. However, the less accuracy of a one-order recursive filtering scheme in the 3DVar system causes an abnormal analysis increment of the wind field. Application of the Supergauss correlation function can not only mitigate the inappropriate negative analysis increments of wind observation but also increase the meso- and small-scale power spectrum in analysis increments. Moreover, the analysis increment structure of isotropy with the Supergauss correlation function can be obtained through recursive filter implementation. Thus, the Supergauss correlation function is the most suitable one to describe the background error correlation among the three functions, which is beneficial for the meso- and small-scale analysis in the high-resolution 3DVAR system.
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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