ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 50,2024 Issue 10
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- The Future Projections of Extreme Weather, Climate and Water Events and Strategic Responses
- A Review of Downburst Genesis Mechanism and Warning
- The Pattern Structure and Thermodynamic and Dynamic Processes of Severe Storms Associated with Linear Convective Gales
- Analysis on Extremity and Characteristics of the “21·7” Severe Torrential Rain in Henan Province
- Diagnostic Analysis on Water Vapor and Jet Characteristics of the July 2021 Severe Torrential Rain in Henan Province
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2024,50(10):1161-1174, DOI: 10.7519/j.issn.1000-0526.2024.081501
Abstract:
Based on the measured hourly precipitations at 38 meteorological stations in Xizang from 1981 to 2020, the spatio-temporal characteristics of daytime precipitation (Pd) and nighttime precipitation (Pn) and night-precipitation rate (Nr) in recent 40 years are analyzed by the methods of linear trend estimation, Pearson coefficient and Mann-Kendall test. The results show that, in Xizang the multi-year average of annual Pd decreases from east to west, the annual Pn decreases from southeast to northwest, and Pn is larger than Pd. The middle reaches of the Yarlung Zangbo River are the center Nr in Xizang. The correlations between the Pd and Pn and the altitude are most significant in spring, and the correlation coefficients between the Pd and Pn and the longitude are the greatest in summer, autumn and the whole year. In winter, Nr at high latitudes is larger than that at low latitudes. In summer and autumn, Nr at high altitudes is smaller than that at low altitudes. In the past 40 years, the annual Pd and Pn increased at 73.7% of stations in Xizang, while the annual Nr showed a decreasing trend at 57.9% of stations, of which the variation trend of Pn was more obvious than that of Pd at 63.2% of stations. The average annual Pd and Pn increased in Xizang, mainly in spring and summer, and the growth rate of annual Pn was greater than that of Pd. Due to the decreased Nr in winter, spring and autumn, the annual Nr tended to decrease. On the interdecadal scale, the Pd and Pn in the 1980s were the least in Xizang in the past 40 years, with the maxima of annual Pd and Pn appearing in 2010s and in 1990s, respectively. For Nr, the maximum and minimum occurred in the 1980s and in the 2010s, respectively. According to the Mann-Kendall test mutation test, the abrupt changes of climate for the Pd and Pn in spring and Pn in winter occurred in the late 1990s and at the beginning of 21st century, respectively, with the former increasing and the latter decreasing. The years 2004, 2011, and 2009 were the time of mutation for winter, spring, and annual Nr, respectively.
Based on the measured hourly precipitations at 38 meteorological stations in Xizang from 1981 to 2020, the spatio-temporal characteristics of daytime precipitation (Pd) and nighttime precipitation (Pn) and night-precipitation rate (Nr) in recent 40 years are analyzed by the methods of linear trend estimation, Pearson coefficient and Mann-Kendall test. The results show that, in Xizang the multi-year average of annual Pd decreases from east to west, the annual Pn decreases from southeast to northwest, and Pn is larger than Pd. The middle reaches of the Yarlung Zangbo River are the center Nr in Xizang. The correlations between the Pd and Pn and the altitude are most significant in spring, and the correlation coefficients between the Pd and Pn and the longitude are the greatest in summer, autumn and the whole year. In winter, Nr at high latitudes is larger than that at low latitudes. In summer and autumn, Nr at high altitudes is smaller than that at low altitudes. In the past 40 years, the annual Pd and Pn increased at 73.7% of stations in Xizang, while the annual Nr showed a decreasing trend at 57.9% of stations, of which the variation trend of Pn was more obvious than that of Pd at 63.2% of stations. The average annual Pd and Pn increased in Xizang, mainly in spring and summer, and the growth rate of annual Pn was greater than that of Pd. Due to the decreased Nr in winter, spring and autumn, the annual Nr tended to decrease. On the interdecadal scale, the Pd and Pn in the 1980s were the least in Xizang in the past 40 years, with the maxima of annual Pd and Pn appearing in 2010s and in 1990s, respectively. For Nr, the maximum and minimum occurred in the 1980s and in the 2010s, respectively. According to the Mann-Kendall test mutation test, the abrupt changes of climate for the Pd and Pn in spring and Pn in winter occurred in the late 1990s and at the beginning of 21st century, respectively, with the former increasing and the latter decreasing. The years 2004, 2011, and 2009 were the time of mutation for winter, spring, and annual Nr, respectively.
2024,50(10):1175-1186, DOI: 10.7519/j.issn.1000-0526.2024.040801
Abstract:
Hail disaster is one of the main disastrous weather events in Xinjiang, with strong regional characteristics, multiple occurrences, and severe disasters. It is of great significance to conduct research on the microphysical characteristics of hail clouds in different regions of Xinjiang. This article uses severe convective weather processes in Xinjiang from 2015 to 2021 and corresponding NPP/VIIRS satellite data as well as satellite cloud microphysical inversion technology and quantitatively analyzes the microphysical characteristics of hail clouds and deep convective clouds. A comparative study is conducted on the differences in microphysical parameters of hail clouds in northern and southern Xinjiang. The results show that the crystallization temperature of hail cloud (-34.0℃) is lower than that of deep convective cloud (-30.5℃), the height of deep convective cloud top is higher, and the hail cloud top has anvil structure. Hail mostly occurs in June-July in northern Xinjiang, and in May-July in southern Xinjiang. Hail time is mainly distributed from 15:00 BT to 20:00 BT. Hail in southern Xinjiang occurs in the wee hours and morning, with higher frequency than in northern Xinjiang. The mean durations of hail in northern and southern Xinjiang are 12.60 min and 12.27 min, and the mean maximum diameters of hail are 13.53 mm and 12.80 mm, respectively. The hail cloud top in northern Xinjiang is higher, the duration of hail is longer, the diameter of hail is larger, and the freezing temperature is lower than that in southern Xinjiang. The mean cloud bottom temperature and cloud bottom height of hail in northern and southern Xinjiang are 5.15℃, 1.96 km and 4.85℃, 2.19 km, respectively. The cloud bottom temperature in northern Xinjiang is warmer than that in southern Xinjiang, and the cloud bottom height is lower than that in southern Xinjiang. The mean rising speed of cloud base in southern Xinjiang (2.07 m·s-1) is 1.13 times that in northern Xinjiang (1.84 m·s-1), and the average thickness of hail cloud in northern Xinjiang (8.90 km) is 1.25% greater than that in southern Xinjiang (8.79 km). Influenced by human activities, industrial pollution and other factors, the mean concentration of condensation nuclei at the bottom of hail cloud in northern Xinjiang (396 cm-3) is 65% higher than that in southern Xinjiang (240 cm-3) where agriculture is dominant. The mean maximum supersaturations of hail cloud bottom are 0.55% and 0.85%, respectively. Affected by the strong updraft, the growth time of hail cloud particles is short, each growth zone develops slowly, and there is no rain embryo formation zone. Targeted seeding of hygroscopic nuclei in the middle and lower layers of the cloud in advance can promote the formation of precipitation at the bottom of the cloud as soon as possible, and excessive seeding of AgI ice nuclei near the 0℃ layer will compete for the supercooled water in the cloud, which can achieve the goal of increasing rain and preventing hail.
Hail disaster is one of the main disastrous weather events in Xinjiang, with strong regional characteristics, multiple occurrences, and severe disasters. It is of great significance to conduct research on the microphysical characteristics of hail clouds in different regions of Xinjiang. This article uses severe convective weather processes in Xinjiang from 2015 to 2021 and corresponding NPP/VIIRS satellite data as well as satellite cloud microphysical inversion technology and quantitatively analyzes the microphysical characteristics of hail clouds and deep convective clouds. A comparative study is conducted on the differences in microphysical parameters of hail clouds in northern and southern Xinjiang. The results show that the crystallization temperature of hail cloud (-34.0℃) is lower than that of deep convective cloud (-30.5℃), the height of deep convective cloud top is higher, and the hail cloud top has anvil structure. Hail mostly occurs in June-July in northern Xinjiang, and in May-July in southern Xinjiang. Hail time is mainly distributed from 15:00 BT to 20:00 BT. Hail in southern Xinjiang occurs in the wee hours and morning, with higher frequency than in northern Xinjiang. The mean durations of hail in northern and southern Xinjiang are 12.60 min and 12.27 min, and the mean maximum diameters of hail are 13.53 mm and 12.80 mm, respectively. The hail cloud top in northern Xinjiang is higher, the duration of hail is longer, the diameter of hail is larger, and the freezing temperature is lower than that in southern Xinjiang. The mean cloud bottom temperature and cloud bottom height of hail in northern and southern Xinjiang are 5.15℃, 1.96 km and 4.85℃, 2.19 km, respectively. The cloud bottom temperature in northern Xinjiang is warmer than that in southern Xinjiang, and the cloud bottom height is lower than that in southern Xinjiang. The mean rising speed of cloud base in southern Xinjiang (2.07 m·s-1) is 1.13 times that in northern Xinjiang (1.84 m·s-1), and the average thickness of hail cloud in northern Xinjiang (8.90 km) is 1.25% greater than that in southern Xinjiang (8.79 km). Influenced by human activities, industrial pollution and other factors, the mean concentration of condensation nuclei at the bottom of hail cloud in northern Xinjiang (396 cm-3) is 65% higher than that in southern Xinjiang (240 cm-3) where agriculture is dominant. The mean maximum supersaturations of hail cloud bottom are 0.55% and 0.85%, respectively. Affected by the strong updraft, the growth time of hail cloud particles is short, each growth zone develops slowly, and there is no rain embryo formation zone. Targeted seeding of hygroscopic nuclei in the middle and lower layers of the cloud in advance can promote the formation of precipitation at the bottom of the cloud as soon as possible, and excessive seeding of AgI ice nuclei near the 0℃ layer will compete for the supercooled water in the cloud, which can achieve the goal of increasing rain and preventing hail.
2024,50(10):1187-1200, DOI: 10.7519/j.issn.1000-0526.2024.051001
Abstract:
The observation quality of reflectivity of Shenzhen Qiuyutan X-Band Phased-Array Radar is quantitatively evaluated by comparing it to Shenzhen Zhuzilin Disdrometer data and Shenzhen Qiuyutan S-Band Radar data. The results suggest that the reflectivity of X-band phased-array radar is highly consistent with the reflectivity retrieved by disdrometer and observed by S-band radar, with correlation coefficients greater than 0.75 and relative mean biases close to 0, which indicates minimal deviation. The X-band phased-array radar also shows stable performance under different rain intensity periods. However, the deviation of reflectivity of X-band phased-array radar is different under different reflectivity intensities. The reflectivity of X-band phased-array radar is positively biased when reflectivity is under 25 dBz, and negatively biased otherwise. As reflectivity intensifies, the degree of the negative bias gradually increases, and the average bias of reflectivity can reach 8-10 dB when reflectivity exceeds 50 dBz.
The observation quality of reflectivity of Shenzhen Qiuyutan X-Band Phased-Array Radar is quantitatively evaluated by comparing it to Shenzhen Zhuzilin Disdrometer data and Shenzhen Qiuyutan S-Band Radar data. The results suggest that the reflectivity of X-band phased-array radar is highly consistent with the reflectivity retrieved by disdrometer and observed by S-band radar, with correlation coefficients greater than 0.75 and relative mean biases close to 0, which indicates minimal deviation. The X-band phased-array radar also shows stable performance under different rain intensity periods. However, the deviation of reflectivity of X-band phased-array radar is different under different reflectivity intensities. The reflectivity of X-band phased-array radar is positively biased when reflectivity is under 25 dBz, and negatively biased otherwise. As reflectivity intensifies, the degree of the negative bias gradually increases, and the average bias of reflectivity can reach 8-10 dB when reflectivity exceeds 50 dBz.
ZHANG Jing, YAO Wen, SUN Zhaoping, CUI Futao, YUAN Jiusong, WU Yang, SUN Yonglian, LI Yang, YANG Hongqiang
2024,50(10):1201-1215, DOI: 10.7519/j.issn.1000-0526.2024.080101
Abstract:
In order to address the issue of insufficient vertical sampling below 5° elevation angle and the presence of detection gaps in the volume coverage pattern 21D (VCP21D), four new scanning patterns, namely, VCP12D, VCP212D, VCP215D, and VCP35D, were developed based on WSR-88D. These new scanning patterns were tested using the Yingkou Dual-Polarization Weather Radar, and the results are as follow. The sensitivity and data quality of the four new scanning patterns are comparable to the current VCP21D. The capability to suppress ground clutter is also similar, meeting the operational performance requirements. Therefore, these new scanning patterns can be applied in operational settings. The severe convective detection patterns, VCP12D and VCP212D, provide increased vertical resolution in the lower levels compared to VCP11D. They can obtain more detailed detection data beyond 100 km from the radar. Additionally, their scanning time is reduced from 5 min to 4 min, resulting in improved detection performance for the rapidly developing severe convective storms. The non-severe precipitation mode, VCP215D, has 6 more elevation angles added compared to VCP21D. This allows for more continuous vertical detection products and enables a more complete and detailed representation of echo structure characteristics and storm top heights. The detection time of VCP215D is comparable to that of the VCP21D, demonstrating its superiority. The clear sky pattern, VCP35D, has a slightly smaller data coverage range compared to VCP31D, but it offers higher spatio-temporal resolution and exhibits superior detection capabilities. The new scanning modes have increased the maximum non-blur speed. The high-altitude (above 10°) speeds for VCP12D, VCP212D, and VCP215D have been raised to 33.36 m·s-1, the low-altitude (0.5°-1.3°) speeds for VCP212D and VCP215D have been raised to 28.47 m·s-1, while the entire layer speed for VCP35D has been increased to 26.38 m·s-1.
In order to address the issue of insufficient vertical sampling below 5° elevation angle and the presence of detection gaps in the volume coverage pattern 21D (VCP21D), four new scanning patterns, namely, VCP12D, VCP212D, VCP215D, and VCP35D, were developed based on WSR-88D. These new scanning patterns were tested using the Yingkou Dual-Polarization Weather Radar, and the results are as follow. The sensitivity and data quality of the four new scanning patterns are comparable to the current VCP21D. The capability to suppress ground clutter is also similar, meeting the operational performance requirements. Therefore, these new scanning patterns can be applied in operational settings. The severe convective detection patterns, VCP12D and VCP212D, provide increased vertical resolution in the lower levels compared to VCP11D. They can obtain more detailed detection data beyond 100 km from the radar. Additionally, their scanning time is reduced from 5 min to 4 min, resulting in improved detection performance for the rapidly developing severe convective storms. The non-severe precipitation mode, VCP215D, has 6 more elevation angles added compared to VCP21D. This allows for more continuous vertical detection products and enables a more complete and detailed representation of echo structure characteristics and storm top heights. The detection time of VCP215D is comparable to that of the VCP21D, demonstrating its superiority. The clear sky pattern, VCP35D, has a slightly smaller data coverage range compared to VCP31D, but it offers higher spatio-temporal resolution and exhibits superior detection capabilities. The new scanning modes have increased the maximum non-blur speed. The high-altitude (above 10°) speeds for VCP12D, VCP212D, and VCP215D have been raised to 33.36 m·s-1, the low-altitude (0.5°-1.3°) speeds for VCP212D and VCP215D have been raised to 28.47 m·s-1, while the entire layer speed for VCP35D has been increased to 26.38 m·s-1.
2024,50(10):1216-1230, DOI: 10.7519/j.issn.1000-0526.2024.031801
Abstract:
Based on the detection data of S-band dual-polarization Doppler weather radar in Xinle of Shijia-zhuang, Hebei Province, the conventional meteorological observation data and the regional automatic weather station observation data, this article analyzes the evolution characteristics of dual-polarization parameter structure of long-life supercell storm that caused large hail in central Hebei on 25 June 2020. The results show that the supercell storm occurred in an environment of strong thermal instability and strong vertical wind shear. With the process of hail growth, large hails coexisted with severe precipitation in the strong low-level echo center of the supercell storm, and the reflectivity factor exceeded 65 dBz, corresponding to small differential reflectivity factor （ZDR） and correlation coefficient （CC）. Weak rainfall and a small amount of melted hails were located in the strong echo area on the left side of the supercell storm. The reflectivity factor was between 50 dBz and 55 dBz, and ZDR , CC and the specific differential phase （KDP） were larger. The ZDR column, CC low value area and KDP column in the middle layer of the supercell storm were located on the left and right sides of the bounded weak echo area, and the left CC low value area was in the center of the strong echo. The CC was smaller due to the existence of mixed phases of precipitation and the larger structural differences. The right KDP column was stronger and located within bounded weak echo area. The narrow ZDR column in the upper layer was located on the right edge of the strong echo center, and the CC low value area was in the strong echo center. There was a strong updraft in the strong echo center area and the bounded weak echo area in the middle and upper layers. The ZDR hole expanded to the lowest elevation angle and the width increased during the falling process of large hails. This can be used as the criterion for judging the imminent landing of large hail. The low-level ZDR arc intensification indicated that rotation intensifies in the low level. Although the height of the ZDR column and CC low value area in the strong echo center dropped rapidly and the intensity was obviously weakened, they existed all the time, indicating that the stronge updraft was there all the time, which supported the long time maintenance of the supercell.
Based on the detection data of S-band dual-polarization Doppler weather radar in Xinle of Shijia-zhuang, Hebei Province, the conventional meteorological observation data and the regional automatic weather station observation data, this article analyzes the evolution characteristics of dual-polarization parameter structure of long-life supercell storm that caused large hail in central Hebei on 25 June 2020. The results show that the supercell storm occurred in an environment of strong thermal instability and strong vertical wind shear. With the process of hail growth, large hails coexisted with severe precipitation in the strong low-level echo center of the supercell storm, and the reflectivity factor exceeded 65 dBz, corresponding to small differential reflectivity factor （ZDR） and correlation coefficient （CC）. Weak rainfall and a small amount of melted hails were located in the strong echo area on the left side of the supercell storm. The reflectivity factor was between 50 dBz and 55 dBz, and ZDR , CC and the specific differential phase （KDP） were larger. The ZDR column, CC low value area and KDP column in the middle layer of the supercell storm were located on the left and right sides of the bounded weak echo area, and the left CC low value area was in the center of the strong echo. The CC was smaller due to the existence of mixed phases of precipitation and the larger structural differences. The right KDP column was stronger and located within bounded weak echo area. The narrow ZDR column in the upper layer was located on the right edge of the strong echo center, and the CC low value area was in the strong echo center. There was a strong updraft in the strong echo center area and the bounded weak echo area in the middle and upper layers. The ZDR hole expanded to the lowest elevation angle and the width increased during the falling process of large hails. This can be used as the criterion for judging the imminent landing of large hail. The low-level ZDR arc intensification indicated that rotation intensifies in the low level. Although the height of the ZDR column and CC low value area in the strong echo center dropped rapidly and the intensity was obviously weakened, they existed all the time, indicating that the stronge updraft was there all the time, which supported the long time maintenance of the supercell.
2024,50(10):1231-1242, DOI: 10.7519/j.issn.1000-0526.2024.021701
Abstract:
A mesoscale convective progress occurred in Guangdong Province on 16 June 2017, and the system was simulated by WRF model. This article analyzes the impact of the combined assimilation of the lightning and conventional surface observation data on the simulation of mesoscale convective system compared with the single assimilation of one kind of data. The lightning data were continuously assimilated into the model through the WRF-FDDA system with a lightning accumulation window of 15 min, while the conventional observation data were assimilated into the model by the WRFDA-3DVAR system with one hour interval. The results show that the introduction of lightning data in the joint assimilation experiment has improved the accuracy of updrafts, cold pools, and gust fronts in the background fields relative to the assimilation of conventional surface observations only. The introduction of conventional surface observations has reduced the background field errors in temperature, water vapor, and wind fields over a larger area, suppressed the spurious convection in some areas, and overall improved the simulation accuracy of the convective system. The results of prediction skill score show that the combined assimilation of the two kinds of data can also improve the prediction skill score of the assimilation period and the forecast period to some extent.
A mesoscale convective progress occurred in Guangdong Province on 16 June 2017, and the system was simulated by WRF model. This article analyzes the impact of the combined assimilation of the lightning and conventional surface observation data on the simulation of mesoscale convective system compared with the single assimilation of one kind of data. The lightning data were continuously assimilated into the model through the WRF-FDDA system with a lightning accumulation window of 15 min, while the conventional observation data were assimilated into the model by the WRFDA-3DVAR system with one hour interval. The results show that the introduction of lightning data in the joint assimilation experiment has improved the accuracy of updrafts, cold pools, and gust fronts in the background fields relative to the assimilation of conventional surface observations only. The introduction of conventional surface observations has reduced the background field errors in temperature, water vapor, and wind fields over a larger area, suppressed the spurious convection in some areas, and overall improved the simulation accuracy of the convective system. The results of prediction skill score show that the combined assimilation of the two kinds of data can also improve the prediction skill score of the assimilation period and the forecast period to some extent.
2024,50(10):1243-1255, DOI: 10.7519/j.issn.1000-0526.2024.040701
Abstract:
Baihetan Hydroelectric Power Station is located in the canyon area of the lower reaches of the Jinsha River, with frequent northerly strong wind weather in the dry season. Objectively identifying the circulation system that affects the strong winds of the hydroelectric power station is beneficial for revealing the formation mechanism of strong winds in special areas. Based on 139 cases of northerly strong wind weather in the dry season in the canyon area from November to April of 2018-2020, this paper analyzes the circulation situation of strong wind weather, and establishes objective identification conditions with reference to the Lamb-Jenkinson (L-J) method. Moreover, the identification conditions are tested and corrected. The results show that 15 cases of typical northerly strong winds at the hydropower station are selected. According to the analysis of the characteristics of circulation situation, the upper-air circulation affecting strong winds is summarized as southern branch trough, plateau trough and transverse trough. In the 15 cases, the first two types appeared 6 times each and the transverse trough type appeared 3 times. Based on the analysis of circulation characteristic parameters by L-J method, the key areas and preliminary identification conditions of strong wind circulation in dry season are determined. The identification conditions of the southern branch trough and plateau trough types are that the zonal component u of the geostrophic wind in the key area is greater than 10 dagpm/10°longitude-1, and its difference from the meridional component v is greater than 10 dagpm/10°longitude-1. At the same time, the vorticity of the geostrophic wind is greater than 0 dagpm/10°longitude-1. The identification condition of transverse trough type is that the critical area u is less than 20 dagpm/10°longitude-1, and it is required to be greater than u. In addition, 14 cases of strong winds in the dry season of 2021 are selected to test the above circulation identification conditions. It is found that from 11 of the 14 cases, the circulation types are identified accurately. According to the reason that the circulation type is not recognized, the thresholds of u and the difference between u and v are corrected. The results show that the corrected discrimination conditions are accurate and feasible. The objective identification method of circulation situation could provide a reference for strong wind warning at the Baihetan Hydroelectric Power Station.
Baihetan Hydroelectric Power Station is located in the canyon area of the lower reaches of the Jinsha River, with frequent northerly strong wind weather in the dry season. Objectively identifying the circulation system that affects the strong winds of the hydroelectric power station is beneficial for revealing the formation mechanism of strong winds in special areas. Based on 139 cases of northerly strong wind weather in the dry season in the canyon area from November to April of 2018-2020, this paper analyzes the circulation situation of strong wind weather, and establishes objective identification conditions with reference to the Lamb-Jenkinson (L-J) method. Moreover, the identification conditions are tested and corrected. The results show that 15 cases of typical northerly strong winds at the hydropower station are selected. According to the analysis of the characteristics of circulation situation, the upper-air circulation affecting strong winds is summarized as southern branch trough, plateau trough and transverse trough. In the 15 cases, the first two types appeared 6 times each and the transverse trough type appeared 3 times. Based on the analysis of circulation characteristic parameters by L-J method, the key areas and preliminary identification conditions of strong wind circulation in dry season are determined. The identification conditions of the southern branch trough and plateau trough types are that the zonal component u of the geostrophic wind in the key area is greater than 10 dagpm/10°longitude-1, and its difference from the meridional component v is greater than 10 dagpm/10°longitude-1. At the same time, the vorticity of the geostrophic wind is greater than 0 dagpm/10°longitude-1. The identification condition of transverse trough type is that the critical area u is less than 20 dagpm/10°longitude-1, and it is required to be greater than u. In addition, 14 cases of strong winds in the dry season of 2021 are selected to test the above circulation identification conditions. It is found that from 11 of the 14 cases, the circulation types are identified accurately. According to the reason that the circulation type is not recognized, the thresholds of u and the difference between u and v are corrected. The results show that the corrected discrimination conditions are accurate and feasible. The objective identification method of circulation situation could provide a reference for strong wind warning at the Baihetan Hydroelectric Power Station.
2024,50(10):1256-1267, DOI: 10.7519/j.issn.1000-0526.2024.062401
Abstract:
Based on the meteorological data from conventional observation stations, a typical large-scale regional heavy fog process in Henan Province from the night of 11 to the day of 12 March 2021 is analyzed. The study focus is on the analysis of the time characteristics and explosive enhancement characteristics of the heavy fog process. The results show that this heavy fog process had the characteristics of explosive enhancement. The explosive enhancement time at 40 typical heavy fog stations was less than 30 min, with an average of only 9.5 min. The high humidity environment caused by the precipitation ahead of the fog and the clear-sky radiation cooling over night provided important conditions for triggering and strengthening the heavy fog process. Large-scale breeze or even calm wind near the surface was another favorable condition for explosive development of this fog process. In addition, the transport of warm advection near the surface was also an important cause for the explosive development and maintenance of the heavy fog process. According to the variation of visibility, two types of heavy fog explosive enhancement are divided, i.e., jump-burst type and direct burst type, in which wind played different roles. In the former, the effect of wind caused turbulence diffusion and affected the dramatic fluctuation of visibility, while the latter had warm advection transport under the action of wind, which was conducive to the development and persistence of the fog.
Based on the meteorological data from conventional observation stations, a typical large-scale regional heavy fog process in Henan Province from the night of 11 to the day of 12 March 2021 is analyzed. The study focus is on the analysis of the time characteristics and explosive enhancement characteristics of the heavy fog process. The results show that this heavy fog process had the characteristics of explosive enhancement. The explosive enhancement time at 40 typical heavy fog stations was less than 30 min, with an average of only 9.5 min. The high humidity environment caused by the precipitation ahead of the fog and the clear-sky radiation cooling over night provided important conditions for triggering and strengthening the heavy fog process. Large-scale breeze or even calm wind near the surface was another favorable condition for explosive development of this fog process. In addition, the transport of warm advection near the surface was also an important cause for the explosive development and maintenance of the heavy fog process. According to the variation of visibility, two types of heavy fog explosive enhancement are divided, i.e., jump-burst type and direct burst type, in which wind played different roles. In the former, the effect of wind caused turbulence diffusion and affected the dramatic fluctuation of visibility, while the latter had warm advection transport under the action of wind, which was conducive to the development and persistence of the fog.
2024,50(10):1268-1280, DOI: 10.7519/j.issn.1000-0526.2024.081601
Abstract:
In the springtime (March-May, MAM) of 2024, the average precipitation in China was 163 mm, ranking the sixth most precipitation since 1961. During April-May, eastern region of China experienced both severe droughts and floods. South China and most of Jiangnan Region experienced significantly above-average rainfall, with most parts of South China receiving rainfall more than normal by over 50%. Thus, multiple times of torrential rain events led to flood disasters in some areas. Conversely, northern Jianghuai and Huanghuai regions had notably below-average precipitation, which caused the rapid development of drought in later spring. The phenomenon of “floods in South China and droughts in Huanghuai Region” was mainly influenced by atmospheric circulation anomalies in East Asia and their intraseasonal variation. The abnormally strong and southward western North Pacific subtropical high (WPSH) and extremely strong anomalous western North Pacific anticyclone (WNPAC) in April provided favorable conditions for moisture transport, leading to frequent occurrence of intense precipitation events in southern China. The drought over Huanghuai Region was primarily dominated by persistent strong high pressure system near the Korean Peninsula-Japan Sea (Bonin high) in April-May, along with a southward shift of the WPSH. Additionally, the attenuation of El Ni〖AKn~D〗o and abnormally warm sea surface temperature in the tropical Indian Ocean contributed to the activation of abnormally strong WNPAC, which built the important oceanic external forcing background for heavy rainfall in southern China.
In the springtime (March-May, MAM) of 2024, the average precipitation in China was 163 mm, ranking the sixth most precipitation since 1961. During April-May, eastern region of China experienced both severe droughts and floods. South China and most of Jiangnan Region experienced significantly above-average rainfall, with most parts of South China receiving rainfall more than normal by over 50%. Thus, multiple times of torrential rain events led to flood disasters in some areas. Conversely, northern Jianghuai and Huanghuai regions had notably below-average precipitation, which caused the rapid development of drought in later spring. The phenomenon of “floods in South China and droughts in Huanghuai Region” was mainly influenced by atmospheric circulation anomalies in East Asia and their intraseasonal variation. The abnormally strong and southward western North Pacific subtropical high (WPSH) and extremely strong anomalous western North Pacific anticyclone (WNPAC) in April provided favorable conditions for moisture transport, leading to frequent occurrence of intense precipitation events in southern China. The drought over Huanghuai Region was primarily dominated by persistent strong high pressure system near the Korean Peninsula-Japan Sea (Bonin high) in April-May, along with a southward shift of the WPSH. Additionally, the attenuation of El Ni〖AKn~D〗o and abnormally warm sea surface temperature in the tropical Indian Ocean contributed to the activation of abnormally strong WNPAC, which built the important oceanic external forcing background for heavy rainfall in southern China.
2024,50(10):1281-1288, DOI: 10.7519/j.issn.1000-0526.2024.090901
Abstract:
The main characteristics of atmospheric circulation in July 2024 are shown as follows. The polar vortex in the Northern Hemisphere was distributed around the Arctic Pole, which was stronger than normal. The Northwest Pacific subtropical high was stronger than normal, located more westward and northward. The national average precipitation in July was 139.9 mm, 15% more than normal, ranking the third most since 1961. The daily precipitation at 33 national stations reached or surpassed the historical extreme values. There were seven regional rainstorm processes in this month. Influenced by the Super Typhoon Gaemi and the residual circulations, extreme heavy rainstorms occurred in Taiwan, northeastern Fujian, eastern Guangdong, eastern and southern Hunan from 24 to 28 July in order. Two typhoons were generated in total, less than normal in July. The national average temperature (23.2℃) was higher than normal by 1.0℃, being the highest value in July since 1961. The average monthly temperature in most parts of Zhejiang, southern Jiangsu, northwestern Jiangxi and central Hunan was 2-4℃ higher than normal. A continuous high temperature process occurred, during which the daily maximum temperature at 53 national stations in southern China reached or surpassed historical records. High temperature days were obviously more than normal, and the number of high temperature days in the region south of Yangtze River was more than 25 days.
The main characteristics of atmospheric circulation in July 2024 are shown as follows. The polar vortex in the Northern Hemisphere was distributed around the Arctic Pole, which was stronger than normal. The Northwest Pacific subtropical high was stronger than normal, located more westward and northward. The national average precipitation in July was 139.9 mm, 15% more than normal, ranking the third most since 1961. The daily precipitation at 33 national stations reached or surpassed the historical extreme values. There were seven regional rainstorm processes in this month. Influenced by the Super Typhoon Gaemi and the residual circulations, extreme heavy rainstorms occurred in Taiwan, northeastern Fujian, eastern Guangdong, eastern and southern Hunan from 24 to 28 July in order. Two typhoons were generated in total, less than normal in July. The national average temperature (23.2℃) was higher than normal by 1.0℃, being the highest value in July since 1961. The average monthly temperature in most parts of Zhejiang, southern Jiangsu, northwestern Jiangxi and central Hunan was 2-4℃ higher than normal. A continuous high temperature process occurred, during which the daily maximum temperature at 53 national stations in southern China reached or surpassed historical records. High temperature days were obviously more than normal, and the number of high temperature days in the region south of Yangtze River was more than 25 days.
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Available online: October 28, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.093001
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The standard precipitation verificaiton method and the MODE spatial method were applied to evaluate the perfotmance of the CMA-MESO and CMA-SH9 models in predicting precipitation in the eastern region of China in 2021 in this article. The results show that two models have relatively high prediction skills for the second and third quarters, while the predition skills for the first and fourth quarters are relatively low. The regional numetical models have good application potential in warm season precipitation forecasting. Based on the TS and BIAS of the four quarters, the overall precipitation prediction skills of the CMA-MESO model in the third quarter are higher than those of the CMA-SH9 model, while in other seaons, the CMA-SH9 model has relatively higher prediction skills. Both models show a higher BIAS and a higher FAR in each quarter. Improving the shortcomings of these two aspects is an important way to enhance the precipitaiton prediction skills of regional models. The MODE verification results of the ’21.7’ rainstorm in Henan and typhoon ‘Fireworks’ show that CMA-MESO and CMA-SH9 models both have the characteristics of a large range of influence on the prediction of heavy rainfall above heavy rainstorm. CMA-MESO model is slightly better than CMA-SH9 model in forecasting the spatial pattern and influence range of heavy rainstorm precipitation objects.
The standard precipitation verificaiton method and the MODE spatial method were applied to evaluate the perfotmance of the CMA-MESO and CMA-SH9 models in predicting precipitation in the eastern region of China in 2021 in this article. The results show that two models have relatively high prediction skills for the second and third quarters, while the predition skills for the first and fourth quarters are relatively low. The regional numetical models have good application potential in warm season precipitation forecasting. Based on the TS and BIAS of the four quarters, the overall precipitation prediction skills of the CMA-MESO model in the third quarter are higher than those of the CMA-SH9 model, while in other seaons, the CMA-SH9 model has relatively higher prediction skills. Both models show a higher BIAS and a higher FAR in each quarter. Improving the shortcomings of these two aspects is an important way to enhance the precipitaiton prediction skills of regional models. The MODE verification results of the ’21.7’ rainstorm in Henan and typhoon ‘Fireworks’ show that CMA-MESO and CMA-SH9 models both have the characteristics of a large range of influence on the prediction of heavy rainfall above heavy rainstorm. CMA-MESO model is slightly better than CMA-SH9 model in forecasting the spatial pattern and influence range of heavy rainstorm precipitation objects.
Available online: October 28, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.102601
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The atmospheric attenuation characteristics of the FY-3 precipitation measurement radar external calibration test site were analyzed using sounding data from the National High Altitude Meteorological Observatory in Xilinhot (Station No. 54102) throughout 2023. A rapid method for estimating atmospheric attenuation has been established by exploring the relationship between total precipitation water and attenuation. The results indicate that the annual variation of oxygen attenuation is very small, while water vapor attenuation has obvious seasonal characteristics. In addition, the attenuation of water vapor is closely related to the total amount of water vapor. The attenuation of water vapor in Ku band is numerically equivalent to approximately 1/250 of the total amount of water vapor, and the attenuation of water vapor in Ka band is approximately 4 times that of the Ku band. Moreover, there is good consistency between the attenuation estimated by the quick method and the attenuation calculated by the normal method, indicating that the quick method is reasonable and feasible. The calculation and analysis of atmospheric attenuation can lay the foundation for the smooth implementation of precipitation radar external calibration experiments.
The atmospheric attenuation characteristics of the FY-3 precipitation measurement radar external calibration test site were analyzed using sounding data from the National High Altitude Meteorological Observatory in Xilinhot (Station No. 54102) throughout 2023. A rapid method for estimating atmospheric attenuation has been established by exploring the relationship between total precipitation water and attenuation. The results indicate that the annual variation of oxygen attenuation is very small, while water vapor attenuation has obvious seasonal characteristics. In addition, the attenuation of water vapor is closely related to the total amount of water vapor. The attenuation of water vapor in Ku band is numerically equivalent to approximately 1/250 of the total amount of water vapor, and the attenuation of water vapor in Ka band is approximately 4 times that of the Ku band. Moreover, there is good consistency between the attenuation estimated by the quick method and the attenuation calculated by the normal method, indicating that the quick method is reasonable and feasible. The calculation and analysis of atmospheric attenuation can lay the foundation for the smooth implementation of precipitation radar external calibration experiments.
Available online: October 28, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.102301
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The main characteristics of the general atmospheric circulation in August 2024 are as follows: There were two polar vortex centers in the Northern Hemisphere and they were stronger than normal. The circulation at middle-high latitude of the Eurasia showed a two-trough and two-ridge pattern. The location of the western Pacific subtropical high was more westerly and northerly compared to that in normal years. In August, the monthly mean precipitation across China was 96.5mm, 9.8% lower than normal (107.1mm), and the monthly mean temperature was 22.6℃, higher than normal (21.1℃) by 1.5℃. During this month, the number of high temperature days was higher than normal for the same period of the year. The continuous high temperature weather in the south of China is highly extreme, and meteorological drought is developing along the middle and upper reaches of the Yangtze River. There were five heavy precipitation processes occurred in China, and rainstorm processes are frequent in the north of China, with high overlap
The main characteristics of the general atmospheric circulation in August 2024 are as follows: There were two polar vortex centers in the Northern Hemisphere and they were stronger than normal. The circulation at middle-high latitude of the Eurasia showed a two-trough and two-ridge pattern. The location of the western Pacific subtropical high was more westerly and northerly compared to that in normal years. In August, the monthly mean precipitation across China was 96.5mm, 9.8% lower than normal (107.1mm), and the monthly mean temperature was 22.6℃, higher than normal (21.1℃) by 1.5℃. During this month, the number of high temperature days was higher than normal for the same period of the year. The continuous high temperature weather in the south of China is highly extreme, and meteorological drought is developing along the middle and upper reaches of the Yangtze River. There were five heavy precipitation processes occurred in China, and rainstorm processes are frequent in the north of China, with high overlap
Available online: October 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.101501
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The spatio-temporal distribution of thunderstorm high winds (THWs) in Jiangxi are comprehensively analyzed based on hourly automated surface observation data, ground-based flash observations , and the weather radar measurements for the period from 2015 to 2023. ERA5 reanalysis data are further used to investigate the atmospheric environment preceding the onset of THWs. Results show that the THWs occur mainly in spring and summer, with significant seasonal variations between north-central and south. Specifically, the frequency of THWs occurring in spring is only slightly higher than in summer in north-central of Jiangxi, while the frequency of THWs in summer is more than twice as high as in spring in south of Jiangxi. THWs show obvious diurnal variation, the highest frequency of THWs is from 14：00 to 20：00, the frequency of THWs in north-central of Jiangxi from evening to night is much higher than in south of Jiangxi. Thermodynamic and water vapor characteristics of THWs in Jiangxi Province show significant spatio-temporal differences. In the same season the dynamics are generally stronger in north-central of Jiangxi than in south of Jiangxi, while the thermal and water vapor effects are stronger in south of Jiangxi than in north-central of Jiangxi. The thermal and water vapor effects are more favourable in summer than in spring, and the dynamics effects in spring are stronger. The convective instability energy required for THWs varies by time period , but all occur under unstable conditions，with THWs occurring more frequently under low vertical wind shear in the afternoon, and more frequently in the late night under strong vertical wind shear, besides the upper dry and lower wet structure in the daytime is more pronounced than at night. Therefore, it’s crucial to set environmental parameter thresholds by season, by region, and by time period in order to provide the most accurate guidance on THWs forecasts and warnings. The spring in north-central of Jiangxi, if Shear6 is large enough and distributed in the range of 30~33 m·s－１, even if MUCAPE is only in the range of 0~500 J·kg－１and PW is only in the range of 43~48 mm, it’s imperative that we remain vigilant for the advent of THWs. In order to accurately forecast the occurrence of THWs in summer, it is essential to pay attention to the MUCAPE and PW. Espercially in south of Jiangxi, where THWs tend to occur with greater frequency under weak mid-level vertical wind shear.When PW > 60mm and MUCAPE > 1500J·kg－１, even though Shear6 is minimal and confined to a range of 5~8 m·s－１, it is imperative to contemplate the potential for THWs. The increase of water vapour is important for the occurrence of THWs in different regions during different seasons.Therefore, changes in PW should be focused on when forecasting THWs.
The spatio-temporal distribution of thunderstorm high winds (THWs) in Jiangxi are comprehensively analyzed based on hourly automated surface observation data, ground-based flash observations , and the weather radar measurements for the period from 2015 to 2023. ERA5 reanalysis data are further used to investigate the atmospheric environment preceding the onset of THWs. Results show that the THWs occur mainly in spring and summer, with significant seasonal variations between north-central and south. Specifically, the frequency of THWs occurring in spring is only slightly higher than in summer in north-central of Jiangxi, while the frequency of THWs in summer is more than twice as high as in spring in south of Jiangxi. THWs show obvious diurnal variation, the highest frequency of THWs is from 14：00 to 20：00, the frequency of THWs in north-central of Jiangxi from evening to night is much higher than in south of Jiangxi. Thermodynamic and water vapor characteristics of THWs in Jiangxi Province show significant spatio-temporal differences. In the same season the dynamics are generally stronger in north-central of Jiangxi than in south of Jiangxi, while the thermal and water vapor effects are stronger in south of Jiangxi than in north-central of Jiangxi. The thermal and water vapor effects are more favourable in summer than in spring, and the dynamics effects in spring are stronger. The convective instability energy required for THWs varies by time period , but all occur under unstable conditions，with THWs occurring more frequently under low vertical wind shear in the afternoon, and more frequently in the late night under strong vertical wind shear, besides the upper dry and lower wet structure in the daytime is more pronounced than at night. Therefore, it’s crucial to set environmental parameter thresholds by season, by region, and by time period in order to provide the most accurate guidance on THWs forecasts and warnings. The spring in north-central of Jiangxi, if Shear6 is large enough and distributed in the range of 30~33 m·s－１, even if MUCAPE is only in the range of 0~500 J·kg－１and PW is only in the range of 43~48 mm, it’s imperative that we remain vigilant for the advent of THWs. In order to accurately forecast the occurrence of THWs in summer, it is essential to pay attention to the MUCAPE and PW. Espercially in south of Jiangxi, where THWs tend to occur with greater frequency under weak mid-level vertical wind shear.When PW > 60mm and MUCAPE > 1500J·kg－１, even though Shear6 is minimal and confined to a range of 5~8 m·s－１, it is imperative to contemplate the potential for THWs. The increase of water vapour is important for the occurrence of THWs in different regions during different seasons.Therefore, changes in PW should be focused on when forecasting THWs.
Available online: October 16, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.072701
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In view of the increasing global climate change and extreme weather events, the impact of marine thunderstorms on navigation and offshore operations is becoming more and more serious. However, due to the lack of understanding of the characteristics and mechanisms of marine thunderstorms by forecasters, as well as the scarcity of marine observation data, it is difficult to track and forecast marine thunderstorms. In response to the above problems, this article comprehensively summarizes the latest progress in the field of marine thunderstorm research at home and abroad from the perspective of meteorological forecasters, covering marine thunderstorm monitoring methods and technologies, activity characteristics, and formation mechanisms. It aims to sort out and discuss the current status, development trends, and key issues of global marine thunderstorm research. Based on the review, the future research direction of marine thunderstorms in China is discussed, including strengthening the construction of marine observation systems, building marine thunderstorm data sets, deepening the study of the formation mechanisms of marine thunderstorms, and strengthening the application of artificial intelligence to build accurate prediction models. This article aims to provide meteorological forecasters with research results on marine thunderstorms, in order to better serve the safety of navigation and offshore operations, and reduce the adverse effects of marine thunderstorms.
In view of the increasing global climate change and extreme weather events, the impact of marine thunderstorms on navigation and offshore operations is becoming more and more serious. However, due to the lack of understanding of the characteristics and mechanisms of marine thunderstorms by forecasters, as well as the scarcity of marine observation data, it is difficult to track and forecast marine thunderstorms. In response to the above problems, this article comprehensively summarizes the latest progress in the field of marine thunderstorm research at home and abroad from the perspective of meteorological forecasters, covering marine thunderstorm monitoring methods and technologies, activity characteristics, and formation mechanisms. It aims to sort out and discuss the current status, development trends, and key issues of global marine thunderstorm research. Based on the review, the future research direction of marine thunderstorms in China is discussed, including strengthening the construction of marine observation systems, building marine thunderstorm data sets, deepening the study of the formation mechanisms of marine thunderstorms, and strengthening the application of artificial intelligence to build accurate prediction models. This article aims to provide meteorological forecasters with research results on marine thunderstorms, in order to better serve the safety of navigation and offshore operations, and reduce the adverse effects of marine thunderstorms.
Available online: October 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.092701
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The causes and predictability of the high-impact large-scale cryogenic freezing rain and snow weather (CFRSW) in east and central China in February 2024 were investigated using the daily temperature and precipitation data from 2,374 stations, the NCEP/NCAR atmospheric circulation reanalysis data and the HadISST data. The results show that: (1) Two CFRSW processes occurred in China in early and late February 2024, and the overlap of the regions was high. The east and central China suffered the most serious freezing rain and snow disaster. (2) The subtropical and mid-high latitude circulation system configuration that influenced the two CFRSW processes were more consistent, the western north Pacific subtropical high (WNPSH) was strong and westward. Siberian high, the South Branch trough and the western north Pacific anticyclone were strong in the same period, forming a strong synergistic effect. The enhancement of the Siberian high led to cold air southward, and the synchronization of the enhancement of South Branch trough and western north Pacific anticyclone to provide abundant water vapor conditions for the east and central China. (3) A moderate-intensity El Ni?o event occurred in the equatorial east-central Pacific from May 2023 to April 2024. In addition, the tropical Indian Ocean and the tropical North Atlantic were abnormally warm in winter. The abnormal SST of the three oceans jointly led to the continuous strength of the WNPSH. This is conducive to the periodic development and enhancement of the anticyclones in the Northwest Pacific Ocean, and provides abundant water vapor conditions for the two CFRSW processes in February. (4) The predictability of the sub-seasonal model for the two processes is about 1～2 weeks, and the prediction skill within 1 week is relatively high. When advanced by more than 2 weeks, the model is unable to accurately predict the anomalous characteristics of the Eurasian mid-high latitude circulation system, resulting in lower predictive ability for the two processes.
The causes and predictability of the high-impact large-scale cryogenic freezing rain and snow weather (CFRSW) in east and central China in February 2024 were investigated using the daily temperature and precipitation data from 2,374 stations, the NCEP/NCAR atmospheric circulation reanalysis data and the HadISST data. The results show that: (1) Two CFRSW processes occurred in China in early and late February 2024, and the overlap of the regions was high. The east and central China suffered the most serious freezing rain and snow disaster. (2) The subtropical and mid-high latitude circulation system configuration that influenced the two CFRSW processes were more consistent, the western north Pacific subtropical high (WNPSH) was strong and westward. Siberian high, the South Branch trough and the western north Pacific anticyclone were strong in the same period, forming a strong synergistic effect. The enhancement of the Siberian high led to cold air southward, and the synchronization of the enhancement of South Branch trough and western north Pacific anticyclone to provide abundant water vapor conditions for the east and central China. (3) A moderate-intensity El Ni?o event occurred in the equatorial east-central Pacific from May 2023 to April 2024. In addition, the tropical Indian Ocean and the tropical North Atlantic were abnormally warm in winter. The abnormal SST of the three oceans jointly led to the continuous strength of the WNPSH. This is conducive to the periodic development and enhancement of the anticyclones in the Northwest Pacific Ocean, and provides abundant water vapor conditions for the two CFRSW processes in February. (4) The predictability of the sub-seasonal model for the two processes is about 1～2 weeks, and the prediction skill within 1 week is relatively high. When advanced by more than 2 weeks, the model is unable to accurately predict the anomalous characteristics of the Eurasian mid-high latitude circulation system, resulting in lower predictive ability for the two processes.
Available online: October 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.081902
Abstract:
Improving the accuracy of objective classification and spatiotemporal forecasting of severe convective weather has always been a challenge in meteorological forecasting. This paper integrates mesoscale models with machine learning classification algorithms to achieve hourly forecasts of classified severe convection. The specific algorithm is as follows: First, the XGBoost classification algorithm and over 10 years of historical data are used to establish a classification potential forecast model for severe convection. Secondly, by statistically analyzing the optimal spatial neighborhood radius and probability density distribution characteristics of CMA-SH9 model elements, and extracting element thresholds based on the combination of optimal scores, a spatial neighborhood graded element ingredient model is established. Finally, through joint discrimination, the machine learning classification method and the spatial neighborhood element "ingredient method" are integrated to establish hourly forecast models for thunderstorm gales and short-term heavy rainfall. Validation shows that this fusion algorithm significantly outperforms numerical model forecast results and national guidance products. For short-term heavy rainfall forecasts on an hourly basis over 24 hours during 2021-2022, the average hit rate is 0.51, and the TS (Threat Score) is 0.15, representing improvements of 83% and 33% respectively compared to the model. For thunderstorm gale forecasts on an hourly basis over 24 hours, the average hit rate reaches 0.37, and the TS is 0.07, representing improvements of 67% and 130% respectively compared to the model (reflectivity factor Z ≥ 45dBz).Significantly improved the forecast accuracy of thunderstorm gale.
Improving the accuracy of objective classification and spatiotemporal forecasting of severe convective weather has always been a challenge in meteorological forecasting. This paper integrates mesoscale models with machine learning classification algorithms to achieve hourly forecasts of classified severe convection. The specific algorithm is as follows: First, the XGBoost classification algorithm and over 10 years of historical data are used to establish a classification potential forecast model for severe convection. Secondly, by statistically analyzing the optimal spatial neighborhood radius and probability density distribution characteristics of CMA-SH9 model elements, and extracting element thresholds based on the combination of optimal scores, a spatial neighborhood graded element ingredient model is established. Finally, through joint discrimination, the machine learning classification method and the spatial neighborhood element "ingredient method" are integrated to establish hourly forecast models for thunderstorm gales and short-term heavy rainfall. Validation shows that this fusion algorithm significantly outperforms numerical model forecast results and national guidance products. For short-term heavy rainfall forecasts on an hourly basis over 24 hours during 2021-2022, the average hit rate is 0.51, and the TS (Threat Score) is 0.15, representing improvements of 83% and 33% respectively compared to the model. For thunderstorm gale forecasts on an hourly basis over 24 hours, the average hit rate reaches 0.37, and the TS is 0.07, representing improvements of 67% and 130% respectively compared to the model (reflectivity factor Z ≥ 45dBz).Significantly improved the forecast accuracy of thunderstorm gale.
Available online: October 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.101401
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The Huaihe River Basin (HRB), situated in the transitional zone between northern and southern climates of China, and characterized by a complex geographical environment. Understanding flash droughts in the HRB is crucial for ensuring agricultural production. This study examines the spatiotemporal characteristics and data uncertainty of flash droughts in the HRB from 2000 to 2020 using four sets of soil moisture data: ERA5、ERA5-LAND、GLDAS 2.1 and GLEAM 3.8a. The annual flash drought statistics show that the average occurrence count of flash droughts is generally higher in the ERA5 dataset, with a relatively uniform spatial distribution, while the results of the other three datasets exhibit a spatial distribution with fewer occurrences in the north and more in the south. The average duration of flash droughts exhibits an approximately opposite distribution to their occurrence count distribution. The average occurrence count of flash droughts determines the occurrence of frequency of flash droughts spatial distribution. Additionally, there is significant interannual variability in the occurrence count of flash droughts with considerable data uncertainty. Flash droughts in the HRB occur frequently during the crop growing seasons (April to September). Focusing on the crop growing seasons, the spatial distribution of the average occurrence count of flash droughts is similar to that of the annual results; however, the average duration of flash droughts tends to be shorter compared to the annual results. The southern region of the HRB experiences more flash droughts during the crop growing seasons, and their interannual trends also exhibit significant data uncertainty.
The Huaihe River Basin (HRB), situated in the transitional zone between northern and southern climates of China, and characterized by a complex geographical environment. Understanding flash droughts in the HRB is crucial for ensuring agricultural production. This study examines the spatiotemporal characteristics and data uncertainty of flash droughts in the HRB from 2000 to 2020 using four sets of soil moisture data: ERA5、ERA5-LAND、GLDAS 2.1 and GLEAM 3.8a. The annual flash drought statistics show that the average occurrence count of flash droughts is generally higher in the ERA5 dataset, with a relatively uniform spatial distribution, while the results of the other three datasets exhibit a spatial distribution with fewer occurrences in the north and more in the south. The average duration of flash droughts exhibits an approximately opposite distribution to their occurrence count distribution. The average occurrence count of flash droughts determines the occurrence of frequency of flash droughts spatial distribution. Additionally, there is significant interannual variability in the occurrence count of flash droughts with considerable data uncertainty. Flash droughts in the HRB occur frequently during the crop growing seasons (April to September). Focusing on the crop growing seasons, the spatial distribution of the average occurrence count of flash droughts is similar to that of the annual results; however, the average duration of flash droughts tends to be shorter compared to the annual results. The southern region of the HRB experiences more flash droughts during the crop growing seasons, and their interannual trends also exhibit significant data uncertainty.
Available online: September 30, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.080502
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Under the influence of an upper trough, a squall line occurred in Sichuan Basin on April 11,2022 , which caused extreme thunderstorm wind(37.4).Due to the lack of understanding of the rapid development mechanism of the squall line, there were large deviations in the forecast of short-time heavy rainfall and strong winds.Based on multi-source observation data and ERA5 reanalysis data,the circulation background,evolution and extinction of the squall line were analyzed.The results are as follows.The squall line occurred in the mutual coupling area of upper trough at 500hPa and the southerly jet at 700hPa.Upper layer divergence and lower layer convergence were significantly enhanced before the squall line formed,and the enhanced uplift provided dynamic conditions for the development of the storm.In south-central basin,the convective available potential energy(CAPE) was greater than 1000 , the deep and shallow vertical wind shears were greater than 15 , the height of wet bulb temperature 0℃ was 3.8km and the height of -20℃ was 7km, the vertical temperature lapse rate was 6.88℃, and a "bell mouth" was exist in temperature humidity profile below Lifting Condensation Level. Especially the vertical wind shear, middle dry layer and DCAPE approached or exceeded the extreme value, which provided favorable environmental conditions for the development of the squall line and the occurrence of strong thunderstorms gales.Convections in the northern segment of squall line were triggered and developed by the combination influence of terrain Longquan Mountains, cold pool and surface convergence line.In the south section, convections were uplifted by the dynamic action of the lower level.Due to the 700 hPa jet stream,surface cold pool and convergence line,two sections of linear convection were intensified and merged into a north-south squall line system with super-cell storms and bow echoes when moving eastward to the high energy and humidity areas in central basin.Super-cells before the formation of squall line and the echoes of the mature squall line both have overhang echos, weak echo regions, rear inflow and middle radial convergence.Downdraft formed by the rear inflow and dry curl in the middle troposphere makes the supercell storm and cold pool move faster than other parts. Then, a bow echo was formed.Due to the gale and precipitation of downburst, propagation velocity of the cold pool was significantly stronger than 0—3 km vertical wind shear which an important reason for the rapid weakening of squall line.
Under the influence of an upper trough, a squall line occurred in Sichuan Basin on April 11,2022 , which caused extreme thunderstorm wind(37.4).Due to the lack of understanding of the rapid development mechanism of the squall line, there were large deviations in the forecast of short-time heavy rainfall and strong winds.Based on multi-source observation data and ERA5 reanalysis data,the circulation background,evolution and extinction of the squall line were analyzed.The results are as follows.The squall line occurred in the mutual coupling area of upper trough at 500hPa and the southerly jet at 700hPa.Upper layer divergence and lower layer convergence were significantly enhanced before the squall line formed,and the enhanced uplift provided dynamic conditions for the development of the storm.In south-central basin,the convective available potential energy(CAPE) was greater than 1000 , the deep and shallow vertical wind shears were greater than 15 , the height of wet bulb temperature 0℃ was 3.8km and the height of -20℃ was 7km, the vertical temperature lapse rate was 6.88℃, and a "bell mouth" was exist in temperature humidity profile below Lifting Condensation Level. Especially the vertical wind shear, middle dry layer and DCAPE approached or exceeded the extreme value, which provided favorable environmental conditions for the development of the squall line and the occurrence of strong thunderstorms gales.Convections in the northern segment of squall line were triggered and developed by the combination influence of terrain Longquan Mountains, cold pool and surface convergence line.In the south section, convections were uplifted by the dynamic action of the lower level.Due to the 700 hPa jet stream,surface cold pool and convergence line,two sections of linear convection were intensified and merged into a north-south squall line system with super-cell storms and bow echoes when moving eastward to the high energy and humidity areas in central basin.Super-cells before the formation of squall line and the echoes of the mature squall line both have overhang echos, weak echo regions, rear inflow and middle radial convergence.Downdraft formed by the rear inflow and dry curl in the middle troposphere makes the supercell storm and cold pool move faster than other parts. Then, a bow echo was formed.Due to the gale and precipitation of downburst, propagation velocity of the cold pool was significantly stronger than 0—3 km vertical wind shear which an important reason for the rapid weakening of squall line.
Available online: September 29, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.080401
Abstract:
Based on the observation data of island stations, buoy stations, and coastal stations in Shanghai during 2016-2020, sea fog events at six stations were identified and classified. On this basis, the spatio-temporal characteristics of sea fog events and the changes in space, season, duration, intensity, and generation and disappearance time of different types of sea fog were analyzed. The results showed that there were generally 20-30 sea fog events in different regions throughout the year, but there were significant differences in time and space. Radiation fog is the most common type of sea fog, followed by precipitation fog, and advection fog occurs more frequently at Yangshan station and Haijiao buoy. The seasonal variations of different types of fog varies greatly in different sea areas. In the Yangtze River Estuary sea area，radiation fog and precipitation fog occur every month, but radiation fog is the main type，advection fog mainly occurs in winter and spring, but its frequency is relatively small; The Jinshan and Yangshan sea areas are dominated by radiation fog every month, with precipitation fog and advection fog mainly occurring in spring, summer, and winter. The duration of advection fog is generally longer, while the duration of precipitation fog and radiation fog is shorter. The lowest atmospheric visibility value in precipitation fog events is generally higher than that in radiation fog and advection fog, and advection fog produces the most severe fog events. Precipitation fog can occur at all times of the day, while radiation fog and advection fog mainly occur at night. The dissipation time of radiation fog and advection fog is mainly 1-5 hours after sunrise, and the dissipation time of precipitation fog is more dispersed.
Based on the observation data of island stations, buoy stations, and coastal stations in Shanghai during 2016-2020, sea fog events at six stations were identified and classified. On this basis, the spatio-temporal characteristics of sea fog events and the changes in space, season, duration, intensity, and generation and disappearance time of different types of sea fog were analyzed. The results showed that there were generally 20-30 sea fog events in different regions throughout the year, but there were significant differences in time and space. Radiation fog is the most common type of sea fog, followed by precipitation fog, and advection fog occurs more frequently at Yangshan station and Haijiao buoy. The seasonal variations of different types of fog varies greatly in different sea areas. In the Yangtze River Estuary sea area，radiation fog and precipitation fog occur every month, but radiation fog is the main type，advection fog mainly occurs in winter and spring, but its frequency is relatively small; The Jinshan and Yangshan sea areas are dominated by radiation fog every month, with precipitation fog and advection fog mainly occurring in spring, summer, and winter. The duration of advection fog is generally longer, while the duration of precipitation fog and radiation fog is shorter. The lowest atmospheric visibility value in precipitation fog events is generally higher than that in radiation fog and advection fog, and advection fog produces the most severe fog events. Precipitation fog can occur at all times of the day, while radiation fog and advection fog mainly occur at night. The dissipation time of radiation fog and advection fog is mainly 1-5 hours after sunrise, and the dissipation time of precipitation fog is more dispersed.
Available online: September 29, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.092401
Abstract:
Thunderstorm gales refer to strong winds with a wind speed ≥17 m·s-1 caused by strong convective weather systems, which are one of meso-scale and micro-scale strong convective weather that causes huge disasters. Understanding their formation mechanisms and conducting accurate nowcasting and early warning are the keys to disaster prevention and mitigation. This paper summarizes the existing studies on the formation mechanisms and nowcasting of thunderstorm gales, including synoptic patterns, environmental characteristics, different formation mechanisms and windstorm morphologies, as well as nowcasting technology. Most thunderstorm gales are generated in supercells, squall lines, and bow echoes through strong downdraft, gust front, momentum transmission, horizontal pressure gradient between outflow and ambient wind, dynamic forcing and superimposed effect of mesoscale vortex, and pumping effect of updraft on low-level warm and moist inflow, etc. On the basis of above review, the difficulties and much-need issues of the formation mechanisms and nowcasting of thunderstorm gales are discussed.
Thunderstorm gales refer to strong winds with a wind speed ≥17 m·s-1 caused by strong convective weather systems, which are one of meso-scale and micro-scale strong convective weather that causes huge disasters. Understanding their formation mechanisms and conducting accurate nowcasting and early warning are the keys to disaster prevention and mitigation. This paper summarizes the existing studies on the formation mechanisms and nowcasting of thunderstorm gales, including synoptic patterns, environmental characteristics, different formation mechanisms and windstorm morphologies, as well as nowcasting technology. Most thunderstorm gales are generated in supercells, squall lines, and bow echoes through strong downdraft, gust front, momentum transmission, horizontal pressure gradient between outflow and ambient wind, dynamic forcing and superimposed effect of mesoscale vortex, and pumping effect of updraft on low-level warm and moist inflow, etc. On the basis of above review, the difficulties and much-need issues of the formation mechanisms and nowcasting of thunderstorm gales are discussed.
Available online: September 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.05601
Abstract:
Abstract: Using the 3-h national site observation data at Beijing area in spring (February to April) during 2019 to 2021, refined evaluation of temperature forecasts by current main-stream numerical models (ECMWF and CMA_GFS), national gridded guidance forecast product (SCMOC) and provincial and municipal revised feedback gridded forecast product (SMERGE) are conducted. The results show that, the temperature forecasts for spring in Beijing often show negative bias in the models of ECMWF and CMA_GFS. This bias has no significant difference between mountainous and plain areas, but is more prominent during nighttime periods. The gridded forecast products (SCMOC and SMERGE) have a good ability to correct the temperature forecasted by the models. The temperature forecast biases of the gridded products are concentrated between -1 to 1℃, and the forecast accuracy is higher and the mean absolute error is lower than that of model forecast. There are issues with the forecasts of 24-h temperature change and daily temperature range for the four products. The amplitude of strong 24-h temperature change forecasted by all products if relatively smaller than that of observation, and the gridded forecast products do not demonstrate significant correction ability. In addition, the daily temperature range forecasted by all products has a positive deviation of 1~3℃ compared to the observation. SCMOC has better correction ability for the daily temperature range forecasted by the models, while SMERGE overestimates more prominently than that in models. The positive deviation of daily temperature range forecast is closely related to the underestimation of low temperature (at 05:00 BT) in the model, while the overestimation of high temperature (at 14:00 BT) can not be ignored in the grid forecast. It is suggested that gridded forecast products should not only focus on improving (reducing) overall accuracy (biases), but also on the improvement of the forecasts of development and evolution of important synoptic processes.
Abstract: Using the 3-h national site observation data at Beijing area in spring (February to April) during 2019 to 2021, refined evaluation of temperature forecasts by current main-stream numerical models (ECMWF and CMA_GFS), national gridded guidance forecast product (SCMOC) and provincial and municipal revised feedback gridded forecast product (SMERGE) are conducted. The results show that, the temperature forecasts for spring in Beijing often show negative bias in the models of ECMWF and CMA_GFS. This bias has no significant difference between mountainous and plain areas, but is more prominent during nighttime periods. The gridded forecast products (SCMOC and SMERGE) have a good ability to correct the temperature forecasted by the models. The temperature forecast biases of the gridded products are concentrated between -1 to 1℃, and the forecast accuracy is higher and the mean absolute error is lower than that of model forecast. There are issues with the forecasts of 24-h temperature change and daily temperature range for the four products. The amplitude of strong 24-h temperature change forecasted by all products if relatively smaller than that of observation, and the gridded forecast products do not demonstrate significant correction ability. In addition, the daily temperature range forecasted by all products has a positive deviation of 1~3℃ compared to the observation. SCMOC has better correction ability for the daily temperature range forecasted by the models, while SMERGE overestimates more prominently than that in models. The positive deviation of daily temperature range forecast is closely related to the underestimation of low temperature (at 05:00 BT) in the model, while the overestimation of high temperature (at 14:00 BT) can not be ignored in the grid forecast. It is suggested that gridded forecast products should not only focus on improving (reducing) overall accuracy (biases), but also on the improvement of the forecasts of development and evolution of important synoptic processes.
Available online: September 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.092301
Abstract:
In June 2024, precipitation in eastern China exhibited a distinct spatial distribution, characterized by "droughts in northern China and floods in southern China". Notably, precipitation in the south of the Yangtze River exceeded the historic record since 1961. Both the results of the statistical analysis and the case study demonstrate that the anomalous southerly water transportation on the western side of the western Pacific subtropical high (WPSH) was a significant contributing factor. However, in June 2024, the general circulation in the west of 110°E exhibited distinctive characteristics compared to historical events. The eastern boundary of the North Africa high (NAH) exhibited a notable eastward and southward extension, establishing a connection with the western boundary of the WPSH over the southern tropical Indian Ocean. This resulted in the formation of an "inverted Ω" circulation pattern, a phenomenon that has never been observed previously. Besides the El Ni?o, the record-breaking warm sea surface temperature (SST) in the western tropical Indian Ocean was another significant influencing factor to the floods in the south of the Yangtze River in early summer. During the months of January and February 2024, the SSTa over (20°S-20°N, 40°-75°E), the west part of tropical Indian ocean, exceeded 1 °C for the first time. The thermal effect of the underlying surface resulted in an increase in air temperature below 600 hPa over the domain. The thermal expansion of the air column led to an increase in potential height over the eastern boundary of the NAH, which in turn led to an intensification of the north wind component. It can be concluded that the formation of the "inverted Ω" circulation pattern was a result of the eastward extension of the NAH and westward extension of the WPSH, respectively, which led to the development of a strong cyclonic anomaly circulation over the equatorial Indian Ocean. The anomalous southerly wind on its eastern side converged and enhanced the southwest moisture flow from the Bay of Bengal to the south of the Yangtze River, resulting in abnormal rainfall in the latter. Statistical analysis from historical observations also verified the conclusion.
In June 2024, precipitation in eastern China exhibited a distinct spatial distribution, characterized by "droughts in northern China and floods in southern China". Notably, precipitation in the south of the Yangtze River exceeded the historic record since 1961. Both the results of the statistical analysis and the case study demonstrate that the anomalous southerly water transportation on the western side of the western Pacific subtropical high (WPSH) was a significant contributing factor. However, in June 2024, the general circulation in the west of 110°E exhibited distinctive characteristics compared to historical events. The eastern boundary of the North Africa high (NAH) exhibited a notable eastward and southward extension, establishing a connection with the western boundary of the WPSH over the southern tropical Indian Ocean. This resulted in the formation of an "inverted Ω" circulation pattern, a phenomenon that has never been observed previously. Besides the El Ni?o, the record-breaking warm sea surface temperature (SST) in the western tropical Indian Ocean was another significant influencing factor to the floods in the south of the Yangtze River in early summer. During the months of January and February 2024, the SSTa over (20°S-20°N, 40°-75°E), the west part of tropical Indian ocean, exceeded 1 °C for the first time. The thermal effect of the underlying surface resulted in an increase in air temperature below 600 hPa over the domain. The thermal expansion of the air column led to an increase in potential height over the eastern boundary of the NAH, which in turn led to an intensification of the north wind component. It can be concluded that the formation of the "inverted Ω" circulation pattern was a result of the eastward extension of the NAH and westward extension of the WPSH, respectively, which led to the development of a strong cyclonic anomaly circulation over the equatorial Indian Ocean. The anomalous southerly wind on its eastern side converged and enhanced the southwest moisture flow from the Bay of Bengal to the south of the Yangtze River, resulting in abnormal rainfall in the latter. Statistical analysis from historical observations also verified the conclusion.
Available online: September 18, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.081901
Abstract:
This study utilized ERA5 reanalysis data and multiple observations to investigate the evolution of the remnants vortex of Typhoon Doksuri (2023) in the Northwest Pacific after it landfall, which caused significant damage in northern China. The main maintenance and recovery period were observed from the night of July 29th to the daytime of July 30th. The research revealed that during the maintenance of the remnant, it maintained a warm-core structure and was not influenced by dry and cold air. During the recovery process, a noticeable increase in water vapor convergence and moist potential vorticity was observed on the northeast side of the vortex center. Additionally, the northern movement of the remnant vortex was hindered by a zonal high-pressure belt, causing a reduction in its northward speed. Under the guidance of a mid-level high-pressure system, dry and cold air further intensified the temperature and moisture gradient between the mid-low-level remnant vortex and warm and moist air masses, resulting in a clear tilt of isentropic surfaces on the northern side of the vortex. This tilt in isentropic surfaces led to the vertical development of cyclonic vortex. Furthermore, during the sustaining and revival period, the remnant vortex continued to receive some heating from increased soil moisture. Additionally, significant latent heat release occurred due to radial moisture inflow and vertical upward motion on the northeast side of the remnant vortex. This release of latent heat provided the necessary conditions for the maintenance and strengthening of the remnant vortex.
This study utilized ERA5 reanalysis data and multiple observations to investigate the evolution of the remnants vortex of Typhoon Doksuri (2023) in the Northwest Pacific after it landfall, which caused significant damage in northern China. The main maintenance and recovery period were observed from the night of July 29th to the daytime of July 30th. The research revealed that during the maintenance of the remnant, it maintained a warm-core structure and was not influenced by dry and cold air. During the recovery process, a noticeable increase in water vapor convergence and moist potential vorticity was observed on the northeast side of the vortex center. Additionally, the northern movement of the remnant vortex was hindered by a zonal high-pressure belt, causing a reduction in its northward speed. Under the guidance of a mid-level high-pressure system, dry and cold air further intensified the temperature and moisture gradient between the mid-low-level remnant vortex and warm and moist air masses, resulting in a clear tilt of isentropic surfaces on the northern side of the vortex. This tilt in isentropic surfaces led to the vertical development of cyclonic vortex. Furthermore, during the sustaining and revival period, the remnant vortex continued to receive some heating from increased soil moisture. Additionally, significant latent heat release occurred due to radial moisture inflow and vertical upward motion on the northeast side of the remnant vortex. This release of latent heat provided the necessary conditions for the maintenance and strengthening of the remnant vortex.
Available online: September 18, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.082101
Abstract:
Typhoon Haikui(2311) moved west-northwestward, repeatedly wobbled and forming a serpentine path. It strengthened into super typhoon category before landing on Taiwan Island, then moved slowly after entering the Taiwan Strait. After landing again, the residual vortex sustained for about 5days, and the precipitation duration and accumulated rainfall were large. Different models and different members of ensemble forecast also have large errors and uncertainties in forecasting the landing point and landfall intensity of Haikui, which brings great challenges to forecast correction. In this paper, using ECMWF, NCEP and CMA determinate and ensemble forecast data, we analyze the main characteristics of Haikui and four important difficulties in the process of operational forecast: there are large errors and differences in the forecast of typhoon track in the offshore waters of China, and the operational correction problems in the intensity forecast are affected by the uncertainty of the track forecast. The quantitative estimation of slow moving time caused by weak circulation guidance and terrain influence after typhoon crossing Taiwan Island and entering Taiwan Strait; Quantitative estimation of typhoon residual circulation maintenance time, moving path and precipitation influence after landfall weakening.
Typhoon Haikui(2311) moved west-northwestward, repeatedly wobbled and forming a serpentine path. It strengthened into super typhoon category before landing on Taiwan Island, then moved slowly after entering the Taiwan Strait. After landing again, the residual vortex sustained for about 5days, and the precipitation duration and accumulated rainfall were large. Different models and different members of ensemble forecast also have large errors and uncertainties in forecasting the landing point and landfall intensity of Haikui, which brings great challenges to forecast correction. In this paper, using ECMWF, NCEP and CMA determinate and ensemble forecast data, we analyze the main characteristics of Haikui and four important difficulties in the process of operational forecast: there are large errors and differences in the forecast of typhoon track in the offshore waters of China, and the operational correction problems in the intensity forecast are affected by the uncertainty of the track forecast. The quantitative estimation of slow moving time caused by weak circulation guidance and terrain influence after typhoon crossing Taiwan Island and entering Taiwan Strait; Quantitative estimation of typhoon residual circulation maintenance time, moving path and precipitation influence after landfall weakening.
Available online: August 23, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.061701
Abstract:
In the context of global warming, it is important to accurately estimate the atmospheric CO2 content and its changes. CO2 over the ocean is the vital component of global atmospheric CO2, and it is necessary to monitor it with a high-frequency and full-coverage technology. The atmospheric CO2 content over the South China Sea is affected by continental, oceanic and atmospheric factors. In this paper, a random-forest-based model of atmospheric CO2 column concentration over the South China Sea was built with chlorophyll-a concentration, instantaneous photosynthetically active radiation, particulate inorganic carbon, particulate organic carbon, sea surface temperature, wind speed and wind direction, which were from multisource satellites remote sensing data. The accuracy of the model was verified for the year 2020, with Bias of 0.27ppm, R2 of 0.59 and the RMSE is 1.00 ppm, showing the accuracy is satisfactory. The results show that the atmospheric CO2 column concentration in the South China Sea presents obvious seasonal characteristics, which are spring>summer>winter>autumn. Moreover, the main influencing factors causing the seasonal differences of atmospheric CO2 column concentration in the South China Sea vary with time. In January and April, the main influencing factors are wind direction. In July, wind speed and wind direction are the two most influential factors. In October, sea surface temperature is the most influential factor. This method can realize the high-frequency and full-coverage monitoring of atmospheric CO2 column concentration in the South China Sea. The relevant results can provide help for the realization of carbon neutrality goal.
In the context of global warming, it is important to accurately estimate the atmospheric CO2 content and its changes. CO2 over the ocean is the vital component of global atmospheric CO2, and it is necessary to monitor it with a high-frequency and full-coverage technology. The atmospheric CO2 content over the South China Sea is affected by continental, oceanic and atmospheric factors. In this paper, a random-forest-based model of atmospheric CO2 column concentration over the South China Sea was built with chlorophyll-a concentration, instantaneous photosynthetically active radiation, particulate inorganic carbon, particulate organic carbon, sea surface temperature, wind speed and wind direction, which were from multisource satellites remote sensing data. The accuracy of the model was verified for the year 2020, with Bias of 0.27ppm, R2 of 0.59 and the RMSE is 1.00 ppm, showing the accuracy is satisfactory. The results show that the atmospheric CO2 column concentration in the South China Sea presents obvious seasonal characteristics, which are spring>summer>winter>autumn. Moreover, the main influencing factors causing the seasonal differences of atmospheric CO2 column concentration in the South China Sea vary with time. In January and April, the main influencing factors are wind direction. In July, wind speed and wind direction are the two most influential factors. In October, sea surface temperature is the most influential factor. This method can realize the high-frequency and full-coverage monitoring of atmospheric CO2 column concentration in the South China Sea. The relevant results can provide help for the realization of carbon neutrality goal.
Available online: August 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2027.070101
Abstract:
There was a mixed strong convective process occurred in Huang-Huai Area and Jiang-Huai Area from north to south on 19 September 2023, which accompanied by tornadoes. Funing strong tornado (corresponding to EF3) was the strongest tornado. Tongying village was 1.2 km away from the Funing strong tornado, which observed extremely strong wind of 41.8 m·s-1(level 14). Based on the data from ground automatic stations and sounding stations, data from S-band dual-polarization radar, the Funing strong tornado was analyzed. Results showed that: (1) Tornado occurred in strong warm and moist zone, which between the subtropical anticyclone and the eastern section of the low-level shear line. The slope of low level frontal was large. The convergence line moved southward on the ground rapidly, combined with extremely low LCL and CIN, high CAPE and vertical wind shear, favorable for tornados. (2) The cold pool and high-pressure center appeared behind the thunderstorm would contribute to the development of vertical vorticity near the ground before tornado occurred. But the heavy precipitation adjacent to the front side of the thunderstorm generated cold pool and strong downdrafts, would block the movement and development of the tornado. (3) The Funing strong tornado was a typical heavy rainfall supercell tornado, characterized by hook echo, BWER and deep strong meso-cyclone. The strong echo was slope and extended to 16 km. (4) TDS observed by dual-polarization radar was wide and deep, indicated the tornado process was strong and destructive. Strong ZDR arcs appeared at the head of the hook echo and separated from the strong KDP zone, formed tilt vertical circulation, would promote the development and maintenance of the supercell. Heavy precipitation echo with low centroid appeared in the front of TDS, precipitation and cooling appeared on the ground, and ZDR arcs and ZDR columns weakened and disappeared, and then tornado storm weakened rapidly.
There was a mixed strong convective process occurred in Huang-Huai Area and Jiang-Huai Area from north to south on 19 September 2023, which accompanied by tornadoes. Funing strong tornado (corresponding to EF3) was the strongest tornado. Tongying village was 1.2 km away from the Funing strong tornado, which observed extremely strong wind of 41.8 m·s-1(level 14). Based on the data from ground automatic stations and sounding stations, data from S-band dual-polarization radar, the Funing strong tornado was analyzed. Results showed that: (1) Tornado occurred in strong warm and moist zone, which between the subtropical anticyclone and the eastern section of the low-level shear line. The slope of low level frontal was large. The convergence line moved southward on the ground rapidly, combined with extremely low LCL and CIN, high CAPE and vertical wind shear, favorable for tornados. (2) The cold pool and high-pressure center appeared behind the thunderstorm would contribute to the development of vertical vorticity near the ground before tornado occurred. But the heavy precipitation adjacent to the front side of the thunderstorm generated cold pool and strong downdrafts, would block the movement and development of the tornado. (3) The Funing strong tornado was a typical heavy rainfall supercell tornado, characterized by hook echo, BWER and deep strong meso-cyclone. The strong echo was slope and extended to 16 km. (4) TDS observed by dual-polarization radar was wide and deep, indicated the tornado process was strong and destructive. Strong ZDR arcs appeared at the head of the hook echo and separated from the strong KDP zone, formed tilt vertical circulation, would promote the development and maintenance of the supercell. Heavy precipitation echo with low centroid appeared in the front of TDS, precipitation and cooling appeared on the ground, and ZDR arcs and ZDR columns weakened and disappeared, and then tornado storm weakened rapidly.
Available online: August 16, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.041101
Abstract:
The forecast of typhoon intensity, especially the rapid intensification (RI) forecast, is still a very challenging problem in current typhoon forecasting. This article is based on the XGBoost model, using NCEP GFS analysis and forecast data from 2015 to 2020, as well as IBTrACS data, to construct RI forecast models (FM) and forecast correction models (FCM) for typhoons in the northwest Pacific for the next 24 hours. Through predictor contribution analysis of the FM model, it was found that the five factors that have the greatest impact on model forecasting are typhoon abundance, average temperature at 200hPa, intensity changes over the past 6 hours, potential intensity, and average divergence at 200hPa. The model was independently tested using data from 2021 to 2022, and the results showed that the FM model had high accuracy when tested using analytical data, with FNR, FPR, and TS of 0.25, 0.24, and 0.32, respectively. However, due to the influence of forecast errors caused by forecast factors, the performance of FM models in real-time forecasting decreases. FCM models constructed using forecast data can effectively correct forecast errors by learning them, thereby reducing the impact of forecast errors. The FNR, FPR, and TS of the FCM model in real-time forecasting tests were 0.28, 0.25, and 0.30, respectively. Compared with the FM model (FNR, FPR, and TS were 0.32, 0.26, and 0.27, respectively), the FNR and FPR decreased by 0.04 and 0.01, and the TS increased by 0.03. The FCM model is convenient and easy to use, providing reference for real-time forecasting of typhoon intensity and typhoon RI.
The forecast of typhoon intensity, especially the rapid intensification (RI) forecast, is still a very challenging problem in current typhoon forecasting. This article is based on the XGBoost model, using NCEP GFS analysis and forecast data from 2015 to 2020, as well as IBTrACS data, to construct RI forecast models (FM) and forecast correction models (FCM) for typhoons in the northwest Pacific for the next 24 hours. Through predictor contribution analysis of the FM model, it was found that the five factors that have the greatest impact on model forecasting are typhoon abundance, average temperature at 200hPa, intensity changes over the past 6 hours, potential intensity, and average divergence at 200hPa. The model was independently tested using data from 2021 to 2022, and the results showed that the FM model had high accuracy when tested using analytical data, with FNR, FPR, and TS of 0.25, 0.24, and 0.32, respectively. However, due to the influence of forecast errors caused by forecast factors, the performance of FM models in real-time forecasting decreases. FCM models constructed using forecast data can effectively correct forecast errors by learning them, thereby reducing the impact of forecast errors. The FNR, FPR, and TS of the FCM model in real-time forecasting tests were 0.28, 0.25, and 0.30, respectively. Compared with the FM model (FNR, FPR, and TS were 0.32, 0.26, and 0.27, respectively), the FNR and FPR decreased by 0.04 and 0.01, and the TS increased by 0.03. The FCM model is convenient and easy to use, providing reference for real-time forecasting of typhoon intensity and typhoon RI.
Available online: August 02, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.080201
Abstract:
The temporal evolution of atmospheric convective boundary layer height (CBLH) has an important impact on weather and climate change, but there are few studies on the CBLH climatology over Beijing area. This study presents the CBLH climatology over Beijing by using high resolution ERA5 reanalysis data for the period 1992 - 2022. The ERA5 CBLH was first evaluated against radiosonde-derived CBLH. ERA5 can reproduced the CBLH variation characteristics by sounding reasonably well. Next, the interannual, seasonal and diurnal variations of the CBLHs, as well as the correlation between the CBLH and key meteorological parameters were analyzed. The results show that in the past 30 years, the CBLH in spring and autumn has decreased at the rate of 61.6 m per decade and 13.1 m per decade, respectively, while that in summer and winter has increased at the rate of 2.9 m per decade and 7.7 m per decade, respectively. The median value of CBLH at noon in spring, summer, autumn, and winter is about 1700 m, 1100 m, 950 m, and 800 m, respectively. The CBLH in spring is the highest among the four seasons, because of the large surface sensible heat flux and the weak atmospheric stability. By analyzing the relationship between CBLH and sensible heat flux, potential temperature lapse rate and Ts-Ta (surface temperature [Ts] and air temperature [Ta] difference), it is found that in spring, when the sensible heat flux increases by 100 W·m-2, the CBLH increases by 615 m. When the potential temperature lapse rate increases by 1 ℃·km-1, the CBLH increases by 1376 m. When the Ts-Ta increases by 1 ℃, the CBLH increases by 175 m.
The temporal evolution of atmospheric convective boundary layer height (CBLH) has an important impact on weather and climate change, but there are few studies on the CBLH climatology over Beijing area. This study presents the CBLH climatology over Beijing by using high resolution ERA5 reanalysis data for the period 1992 - 2022. The ERA5 CBLH was first evaluated against radiosonde-derived CBLH. ERA5 can reproduced the CBLH variation characteristics by sounding reasonably well. Next, the interannual, seasonal and diurnal variations of the CBLHs, as well as the correlation between the CBLH and key meteorological parameters were analyzed. The results show that in the past 30 years, the CBLH in spring and autumn has decreased at the rate of 61.6 m per decade and 13.1 m per decade, respectively, while that in summer and winter has increased at the rate of 2.9 m per decade and 7.7 m per decade, respectively. The median value of CBLH at noon in spring, summer, autumn, and winter is about 1700 m, 1100 m, 950 m, and 800 m, respectively. The CBLH in spring is the highest among the four seasons, because of the large surface sensible heat flux and the weak atmospheric stability. By analyzing the relationship between CBLH and sensible heat flux, potential temperature lapse rate and Ts-Ta (surface temperature [Ts] and air temperature [Ta] difference), it is found that in spring, when the sensible heat flux increases by 100 W·m-2, the CBLH increases by 615 m. When the potential temperature lapse rate increases by 1 ℃·km-1, the CBLH increases by 1376 m. When the Ts-Ta increases by 1 ℃, the CBLH increases by 175 m.
Available online: August 01, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.022102
Abstract:
A total of 184 hail weather cases in Chengde from April to September, 2000 to 2020 are analyzed by means of multi source data including the hail fact, CINRAD\CB weather radar, NCEP FNL reanalysis, and GFS forecast. Firstly, the distribution characteristics and prediction thresholds of relevant environmental parameters such as water vapor, thermal instability, dynamic lift and characteristic height are analyzed with the form of boxplot. And then, the initial optimal threshold values are set according to the results of the boxplot. The hail labels are determined according to the hail observational records or combined reflectivity (CR) greater than or equal to 60 dBZ from April to September 2014 to 2020. The hail labels are matched to the grids of reanalysis data on the basis of the principle of near location and proximity time to construct the training dataset for feature parameter selection, interval segmentation, probability calculation, and models training. Next, five models for 3h, 6h, 9h, 12h and 24h hail potential prediction are established by Bayesian method. The models are test from June to August during 2021 and 2022, and the results suggest that the Bayes-based hail potential prediction models have feasibility in daily weather forecast. The hit rates of all the models are above 90%, and the average CSI score is over 0.4. Differing from the traditional probability and ingredient methods, the based-methods can provide a stronger objective forecast of hail occurrence, which has a certain reference for predicting severe convective weather in mountainous areas. Nevertheless, there are some falsealarms as the spatiotemporal scale of the reanalysis data is much larger than that of severe convective weather, which need to be improved in the future.
A total of 184 hail weather cases in Chengde from April to September, 2000 to 2020 are analyzed by means of multi source data including the hail fact, CINRAD\CB weather radar, NCEP FNL reanalysis, and GFS forecast. Firstly, the distribution characteristics and prediction thresholds of relevant environmental parameters such as water vapor, thermal instability, dynamic lift and characteristic height are analyzed with the form of boxplot. And then, the initial optimal threshold values are set according to the results of the boxplot. The hail labels are determined according to the hail observational records or combined reflectivity (CR) greater than or equal to 60 dBZ from April to September 2014 to 2020. The hail labels are matched to the grids of reanalysis data on the basis of the principle of near location and proximity time to construct the training dataset for feature parameter selection, interval segmentation, probability calculation, and models training. Next, five models for 3h, 6h, 9h, 12h and 24h hail potential prediction are established by Bayesian method. The models are test from June to August during 2021 and 2022, and the results suggest that the Bayes-based hail potential prediction models have feasibility in daily weather forecast. The hit rates of all the models are above 90%, and the average CSI score is over 0.4. Differing from the traditional probability and ingredient methods, the based-methods can provide a stronger objective forecast of hail occurrence, which has a certain reference for predicting severe convective weather in mountainous areas. Nevertheless, there are some falsealarms as the spatiotemporal scale of the reanalysis data is much larger than that of severe convective weather, which need to be improved in the future.
Available online: July 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.061401
Abstract:
To study the mesoscale characteristics and causes of extreme short-time heavy rainfall at night in Tianjin，by using encrypted automatic station data, min precipitation data, Doppler weather Radar data, wind profile data and the 5th generation global Atmospheric Reanalysis product (ERA5) of the European Center for Medium-Range Weather Forecasts, an extreme short-time heavy precipitation occurred in Tianjin in the early morning of July 3, 2022 was diagnosed and analyzed. The results show that: There was no significant low-value weather system at 500 hPa and no synoptic low-level jet background at the lower level. It was a rainstorm process mainly caused by small and medium scale forcing under atypical circulation situation, with obvious local, sudden and extreme characteristics. The meso-β scale convective system that caused precipitation was presented in the form of a well-organized multi-cell storm, which was formed by the merger of scattered echo organizations, and its radar echo had a high centroid, showing the characteristics of continental strong convective echo. The enhancement of the 975hPa warm shear line in the boundary layer cooperated with the mesoscale convergence line on the ground, and synergizing with enhanced instability caused by mid-level dry cold air intrusion, which were the main reason for the triggering of the initial convection. The cold pool formed after precipitation formed a clear and irregular outflow boundary with the ambient wind, and the forcing action of the bottom cold pool led to the formation and development of γ-mesoscale vortex in front of the outflow boundary. The ageostrophic wind rotation caused by the inertial oscillation of the boundary layer at night and the gradually formed inversion stratification made the warm and moist air from the southeast from the sea continuously strengthen into the boundary layer jet, and then caused the vertical wind shear of 0-2.5km to increase correspondingly. The interaction between the low-level wind shear and the gradually enhanced cold pool reached a temporary equilibrium. Resultly, the vortex in front of the outflow boundary continue to strengthened and developed from the bottom to up, and the strong dynamic convergence accompanying the vortex directly leaded to the rapid growth of minute-level rain intensity and lasted for several minutes, which finally leaded to the emergence of extreme short-term heavy precipitation. The results provide a reference basis for predicting local short-time heavy precipitation at night and exploring its occurrence and development mechanism in North China.
To study the mesoscale characteristics and causes of extreme short-time heavy rainfall at night in Tianjin，by using encrypted automatic station data, min precipitation data, Doppler weather Radar data, wind profile data and the 5th generation global Atmospheric Reanalysis product (ERA5) of the European Center for Medium-Range Weather Forecasts, an extreme short-time heavy precipitation occurred in Tianjin in the early morning of July 3, 2022 was diagnosed and analyzed. The results show that: There was no significant low-value weather system at 500 hPa and no synoptic low-level jet background at the lower level. It was a rainstorm process mainly caused by small and medium scale forcing under atypical circulation situation, with obvious local, sudden and extreme characteristics. The meso-β scale convective system that caused precipitation was presented in the form of a well-organized multi-cell storm, which was formed by the merger of scattered echo organizations, and its radar echo had a high centroid, showing the characteristics of continental strong convective echo. The enhancement of the 975hPa warm shear line in the boundary layer cooperated with the mesoscale convergence line on the ground, and synergizing with enhanced instability caused by mid-level dry cold air intrusion, which were the main reason for the triggering of the initial convection. The cold pool formed after precipitation formed a clear and irregular outflow boundary with the ambient wind, and the forcing action of the bottom cold pool led to the formation and development of γ-mesoscale vortex in front of the outflow boundary. The ageostrophic wind rotation caused by the inertial oscillation of the boundary layer at night and the gradually formed inversion stratification made the warm and moist air from the southeast from the sea continuously strengthen into the boundary layer jet, and then caused the vertical wind shear of 0-2.5km to increase correspondingly. The interaction between the low-level wind shear and the gradually enhanced cold pool reached a temporary equilibrium. Resultly, the vortex in front of the outflow boundary continue to strengthened and developed from the bottom to up, and the strong dynamic convergence accompanying the vortex directly leaded to the rapid growth of minute-level rain intensity and lasted for several minutes, which finally leaded to the emergence of extreme short-term heavy precipitation. The results provide a reference basis for predicting local short-time heavy precipitation at night and exploring its occurrence and development mechanism in North China.
Available online: July 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.063002
Abstract:
The Round-trip Drifting Sounding System (RDSS) can realize vertical detection of the atmospheric temperature profile from ground to the lower stratosphere and the continuous 4h horizontal temperature distribution in the lower stratosphere. Round-trip Drifting Sounding observation tests have been carried out in the middle and lower reaches of the Yangtze River, Guangdong, Inner Mongolia and other places, and the results is were very successful. Based on the data of Round-trip Drifting Sounding experiment in the middle and lower reaches of the Yangtze River from March to September 2021, this paper completed the verification of atmospheric humidity profile data of satellite. The results show that: 1)The validation results of the Descending Phase data of the Round-trip Drifting Sounding indicate that the average absolute error of the satellite humidity profile is approximately 15%, and the root mean square error is approximately 20%. 2) At noon and night, the quality of humidity profile data of satellite is better than that in the morning and evening. 3) The humidity error of the satellite decreases with increasing altitude and increases with increasing humidity. 4) Below 50% humidity, the satellite retrieved humidity is relatively large, and above 50% humidity, the satellite retrieved humidity is relatively small.
The Round-trip Drifting Sounding System (RDSS) can realize vertical detection of the atmospheric temperature profile from ground to the lower stratosphere and the continuous 4h horizontal temperature distribution in the lower stratosphere. Round-trip Drifting Sounding observation tests have been carried out in the middle and lower reaches of the Yangtze River, Guangdong, Inner Mongolia and other places, and the results is were very successful. Based on the data of Round-trip Drifting Sounding experiment in the middle and lower reaches of the Yangtze River from March to September 2021, this paper completed the verification of atmospheric humidity profile data of satellite. The results show that: 1)The validation results of the Descending Phase data of the Round-trip Drifting Sounding indicate that the average absolute error of the satellite humidity profile is approximately 15%, and the root mean square error is approximately 20%. 2) At noon and night, the quality of humidity profile data of satellite is better than that in the morning and evening. 3) The humidity error of the satellite decreases with increasing altitude and increases with increasing humidity. 4) Below 50% humidity, the satellite retrieved humidity is relatively large, and above 50% humidity, the satellite retrieved humidity is relatively small.
Available online: July 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.071501
Abstract:
Aerosols and cloud microphysics observational researches have been carried out by aircraft which equipped with cloud physics detection instruments for many years in Hebei Province, China. A series of research results have been obtained and published in the fields of aerosols, cloud condensation nuclei (CCN), clouds and precipitation macro and micro structure characteristics, especially some weather modification catalytic experiments by aircraft. In this paper, the research progress of aerosols and cloud precipitation physical observations over Hebei Province in the recent 20 years were systematically summarized, and the microphysical characteristics of aerosols, CCN and clouds, such as vertical structure, spatial distribution and seasonal variation, were summarized. Four observation field campaigns for aircraft precipitation enhancement operation and the effect test are introduced in detail, and the physical evidence of macro and micro physical characteristics changes in the supercooled water area before and after cloud catalysis is objectively demonstrated. This paper puts forward the future development direction on the basis of summarizing a large number of research results, and provides some suggestions for aerosol-cloud physical aircraft observation and weather modification activities through aircraft catalysis in North China.
Aerosols and cloud microphysics observational researches have been carried out by aircraft which equipped with cloud physics detection instruments for many years in Hebei Province, China. A series of research results have been obtained and published in the fields of aerosols, cloud condensation nuclei (CCN), clouds and precipitation macro and micro structure characteristics, especially some weather modification catalytic experiments by aircraft. In this paper, the research progress of aerosols and cloud precipitation physical observations over Hebei Province in the recent 20 years were systematically summarized, and the microphysical characteristics of aerosols, CCN and clouds, such as vertical structure, spatial distribution and seasonal variation, were summarized. Four observation field campaigns for aircraft precipitation enhancement operation and the effect test are introduced in detail, and the physical evidence of macro and micro physical characteristics changes in the supercooled water area before and after cloud catalysis is objectively demonstrated. This paper puts forward the future development direction on the basis of summarizing a large number of research results, and provides some suggestions for aerosol-cloud physical aircraft observation and weather modification activities through aircraft catalysis in North China.
Available online: July 08, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.070301
Abstract:
The wind field observation play an important role in the weather research and forecasting. The IVAP technique which is based on the azimuth uniform assumption retrieval relationship, offers good compatibility and practical simplicity for 2-D wind field retrieval. This paper selected the large-scale precipitation event from July to August 2020, established the wind fields based on the operational Doppler radar network using the IVAP technique, and used the secondly radiosonde data as a reference to conduct a quality assessment and analysis of the retrieved wind fields. The results indicate that: retrieved wind fields of Doppler radar network have high correlation with radiosonde data, and the quality of wind direction is better than the wind speed on higher altitude. The quality of the retrieved winds are better in the areas with precipitation than non-precipitation areas. The quality is worst in clear sky areas, especially when the altitude is higher than 4 km. The retrieved winds of a scattered precipitation event on 6 July 2019 demonstrate that the vortex structure, shear line and other dynamic field characteristics were captured. This study shows that based on the single Doppler radar wind retrieval, the IVAP technique has the ability to retrieve wind fields of Doppler radar network. This method has good application prospect in practical operations, and can provide a better basis for weather forecasting services as well as wind field data assimilation.
The wind field observation play an important role in the weather research and forecasting. The IVAP technique which is based on the azimuth uniform assumption retrieval relationship, offers good compatibility and practical simplicity for 2-D wind field retrieval. This paper selected the large-scale precipitation event from July to August 2020, established the wind fields based on the operational Doppler radar network using the IVAP technique, and used the secondly radiosonde data as a reference to conduct a quality assessment and analysis of the retrieved wind fields. The results indicate that: retrieved wind fields of Doppler radar network have high correlation with radiosonde data, and the quality of wind direction is better than the wind speed on higher altitude. The quality of the retrieved winds are better in the areas with precipitation than non-precipitation areas. The quality is worst in clear sky areas, especially when the altitude is higher than 4 km. The retrieved winds of a scattered precipitation event on 6 July 2019 demonstrate that the vortex structure, shear line and other dynamic field characteristics were captured. This study shows that based on the single Doppler radar wind retrieval, the IVAP technique has the ability to retrieve wind fields of Doppler radar network. This method has good application prospect in practical operations, and can provide a better basis for weather forecasting services as well as wind field data assimilation.
Available online: July 05, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.061801
Abstract:
To study the causes for rapid weakening and dissipation of Typhoon Bavi(2008) after its landfall in the north , a numerical simulation was carried out using the non-hydrostatic mesoscal model WRF(Weather Research Forecast) , and the simulated results were verified by the observation data. Furthermore, based on the high-resolution simulation results, the weather circulation background and the characteristics of environmental field change were analyzed before and after the landfall of Bavi. The results indicate that the simulated track, intensity change and precipitation distribution of Bavi all matched with the observations well before and its landfall. Bavi was guided by the southwestly airflow in front of the mid-latitude westerly trough, and was located on the right side of the upper-level jet entrance area before its landfall, the divergence field at upper levels was conducive to maintaining the typhoon circulation. After Bavi made landfall, on the one hand, the reduction of the upper-level jet on the north side of typhoon and the weakening of the upper-level divergence inhibited the development of typhoon convection; on the other hand, the sinking strong cold air invaded into the center of typhoon from the northeast side of the low level, which destroyed the vertical warm-core structure of Bavi, then the height was reduced and inclined to the east. In addition, the strong vertical wind shear, especially from middle to up levels, was unfavorable for typhoon sustention, and the lack of water vapor supply is another reason for the rapid weakening and disappearance of the typhoon after its landfall.
To study the causes for rapid weakening and dissipation of Typhoon Bavi(2008) after its landfall in the north , a numerical simulation was carried out using the non-hydrostatic mesoscal model WRF(Weather Research Forecast) , and the simulated results were verified by the observation data. Furthermore, based on the high-resolution simulation results, the weather circulation background and the characteristics of environmental field change were analyzed before and after the landfall of Bavi. The results indicate that the simulated track, intensity change and precipitation distribution of Bavi all matched with the observations well before and its landfall. Bavi was guided by the southwestly airflow in front of the mid-latitude westerly trough, and was located on the right side of the upper-level jet entrance area before its landfall, the divergence field at upper levels was conducive to maintaining the typhoon circulation. After Bavi made landfall, on the one hand, the reduction of the upper-level jet on the north side of typhoon and the weakening of the upper-level divergence inhibited the development of typhoon convection; on the other hand, the sinking strong cold air invaded into the center of typhoon from the northeast side of the low level, which destroyed the vertical warm-core structure of Bavi, then the height was reduced and inclined to the east. In addition, the strong vertical wind shear, especially from middle to up levels, was unfavorable for typhoon sustention, and the lack of water vapor supply is another reason for the rapid weakening and disappearance of the typhoon after its landfall.
Available online: June 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.022003
Abstract:
Based on forecast products of the European Center for Medium-Range Weather Forecasts - Integrated Forecasting System(ECMWF-IFS) and hourly temperature observation data from the China Meteorological Administration Land Data Assimilation System(CLDAS), an enhanced model named ED-LSTM-FCNN is constructed, incorporating an embedding layer module to handle high-dimensional spatial and temporal features. A fully connected neural network was utilized to integrate various features types and achieve regression prediction of temperature, generating gridded hourly temperature forecast products with a resolution of 0.05°×0.05°. Verification for the 2022 forecast in Hunan Province revealed that the model exhibits a notable capacity to mitigate forecast errors inherent in the numerical model, thereby enhancing the overall forecast stability. The root mean square errors (RMSE) for forecast lead times ranging from 1 to 24 hours exhibit a reduction of 25.4% to 37.7% when compared to ECMWF-IFS and a decrease of 15.8% to 40.0% in comparison to the SCMOC. The model significantly enhances the forecast performance of ECMWF-IFS in spatial prediction, particularly in regions characterized by intricate terrain features. The RMSEs across most areas vary within the range of 1.2 ℃ to 1.6 ℃. The forecast accuracy of the model, with an error margin of ±2 ℃, surpasses 85.0% across various seasons, demonstrating a significant improvement compared to both ECMWF-IFS and SCMOC. The forecasting performance is notably superior, particularly in stable extreme high-temperature weather conditions, when compared to alternative products. In conclusion, this method proved to be effective for high-resolution temperature grid forecasting operations.
Based on forecast products of the European Center for Medium-Range Weather Forecasts - Integrated Forecasting System(ECMWF-IFS) and hourly temperature observation data from the China Meteorological Administration Land Data Assimilation System(CLDAS), an enhanced model named ED-LSTM-FCNN is constructed, incorporating an embedding layer module to handle high-dimensional spatial and temporal features. A fully connected neural network was utilized to integrate various features types and achieve regression prediction of temperature, generating gridded hourly temperature forecast products with a resolution of 0.05°×0.05°. Verification for the 2022 forecast in Hunan Province revealed that the model exhibits a notable capacity to mitigate forecast errors inherent in the numerical model, thereby enhancing the overall forecast stability. The root mean square errors (RMSE) for forecast lead times ranging from 1 to 24 hours exhibit a reduction of 25.4% to 37.7% when compared to ECMWF-IFS and a decrease of 15.8% to 40.0% in comparison to the SCMOC. The model significantly enhances the forecast performance of ECMWF-IFS in spatial prediction, particularly in regions characterized by intricate terrain features. The RMSEs across most areas vary within the range of 1.2 ℃ to 1.6 ℃. The forecast accuracy of the model, with an error margin of ±2 ℃, surpasses 85.0% across various seasons, demonstrating a significant improvement compared to both ECMWF-IFS and SCMOC. The forecasting performance is notably superior, particularly in stable extreme high-temperature weather conditions, when compared to alternative products. In conclusion, this method proved to be effective for high-resolution temperature grid forecasting operations.
Available online: June 05, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031405
Abstract:
Abstract: Based on the ground observation data of daily precipitation, snow depth, daily mean temperature, daily minimum temperature and weather phenomena in Henan Province from November to March, 1991-2020, the low temperature threshold, the process and duration of cryogenic freezing rain and snow were determined by mathematical statistics. The factors that characterize the intensity of rain and snow and the degree of low temperature were selected to construct the meteorological index of cryogenic freezing rain and snow. The calculation and standardization of the cryogenic freezing rain and snow meteorological index were carried out at each observation station over the past years, and the standard deviation classification method was adopted, combined with the percentage distribution of each interval of the standardized meteorological index and the practical performance. Based on the above operations, the cryogenic freezing rain and snow events were divided into four levels: light, medium, heavy and extra heavy, respectively. The meteorological index and its standardized calculation of cryogenic freezing rain and snow at each observation station were carried out. According to the classification standard, the frequency of cryogenic freezing rain and snow of the multi-year average of each station and the representative stations in the past years were classified and counted. The results showed that: The mountainous area of western Henan is a high incidence area of cryogenic freezing rain and snow, while the basin of southwestern Henan and northwestern Henan are the low incidence areas. The multi-year average frequency of occurrence at all sites showed a decreasing trend from light to extra heavy. There is not a positive correlation between latitude and the frequency of cryogenic freezing rain and snow, and extra-heavy events occur even more frequently at low-latitude sites than at high-latitude and mountain sites.
Abstract: Based on the ground observation data of daily precipitation, snow depth, daily mean temperature, daily minimum temperature and weather phenomena in Henan Province from November to March, 1991-2020, the low temperature threshold, the process and duration of cryogenic freezing rain and snow were determined by mathematical statistics. The factors that characterize the intensity of rain and snow and the degree of low temperature were selected to construct the meteorological index of cryogenic freezing rain and snow. The calculation and standardization of the cryogenic freezing rain and snow meteorological index were carried out at each observation station over the past years, and the standard deviation classification method was adopted, combined with the percentage distribution of each interval of the standardized meteorological index and the practical performance. Based on the above operations, the cryogenic freezing rain and snow events were divided into four levels: light, medium, heavy and extra heavy, respectively. The meteorological index and its standardized calculation of cryogenic freezing rain and snow at each observation station were carried out. According to the classification standard, the frequency of cryogenic freezing rain and snow of the multi-year average of each station and the representative stations in the past years were classified and counted. The results showed that: The mountainous area of western Henan is a high incidence area of cryogenic freezing rain and snow, while the basin of southwestern Henan and northwestern Henan are the low incidence areas. The multi-year average frequency of occurrence at all sites showed a decreasing trend from light to extra heavy. There is not a positive correlation between latitude and the frequency of cryogenic freezing rain and snow, and extra-heavy events occur even more frequently at low-latitude sites than at high-latitude and mountain sites.
Available online: June 05, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.052801
Abstract:
In order to enhance the prediction accuracy of 0-2 h now-casting of short-time heavy precipitation and thunderstorm gale, this paper proposes a severe convection probability now-casting method based on the vertical profile characteristics of the dual-polarization radar (referred to as the CSCPVP method). By using the improved Bayesian probability method, the vertical profile characteristics of polarization radar of two types of severe convection disasters are introduced into the extrapolation model to realize the advanced identification of severe convection attributes, and the broad constraints of regional model prediction are integrated to ensure that the proximity extrapolation prediction results of severe convection are more consistent with the actual dynamic and microphysical characteristics. The evaluation results of the entire flood season (June-September 2023) in Zhejiang show that the CSCPVP method has significantly improved 0-2 h now-casting ability of two types of severe convection than the existing operational methods. The new method significantly improves 0-2 h now-casting ability of systematic, local and distributed classified severe convection (the critical success index of short-time heavy precipitation increases from 8%-16% to 22%-26%; The critical success index of thunderstorm gale was increased from 7% to 10%-11%), which effectively improved the problem of false alarms and missing prediction.
In order to enhance the prediction accuracy of 0-2 h now-casting of short-time heavy precipitation and thunderstorm gale, this paper proposes a severe convection probability now-casting method based on the vertical profile characteristics of the dual-polarization radar (referred to as the CSCPVP method). By using the improved Bayesian probability method, the vertical profile characteristics of polarization radar of two types of severe convection disasters are introduced into the extrapolation model to realize the advanced identification of severe convection attributes, and the broad constraints of regional model prediction are integrated to ensure that the proximity extrapolation prediction results of severe convection are more consistent with the actual dynamic and microphysical characteristics. The evaluation results of the entire flood season (June-September 2023) in Zhejiang show that the CSCPVP method has significantly improved 0-2 h now-casting ability of two types of severe convection than the existing operational methods. The new method significantly improves 0-2 h now-casting ability of systematic, local and distributed classified severe convection (the critical success index of short-time heavy precipitation increases from 8%-16% to 22%-26%; The critical success index of thunderstorm gale was increased from 7% to 10%-11%), which effectively improved the problem of false alarms and missing prediction.
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2012,38(12):1482-1491, DOI: 10.7519/j.issn.1000-0526.2012.12.005
Abstract:
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
2017,43(7):769-780, DOI: 10.7519/j.issn.1000-0526.2017.07.001
Abstract:
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
2006,32(10):64-69, DOI: 10.7519/j.issn.1000-0526.2006.10.010
Abstract:
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
2010,36(3):9-18, DOI: 10.7519/j.issn.1000-0526.2010.3.002
Abstract:
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
Zhou Yuquan, Chen Yingying, Li Juan, Huang Yimei, He Xiaodong, Zhou Feifei, Wu Menxin, Hu Bo, Mao Jietai
2008,34(12):27-35, DOI: 10.7519/j.issn.1000-0526.2008.12.004
Abstract:
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
FU Jiaolan, MA Xuekuan, CHEN Tao, ZHANG Fang, ZHANG Xidi, SUN Jun, QUAN Wanqing, YANG Shunan, SHEN Xiaolin
2017,43(5):528-539, DOI: 10.7519/j.issn.1000-0526.2017.05.002
Abstract:
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
2013,39(10):1284-1292, DOI: 10.7519/j.issn.1000-0526.2013.10.006
Abstract:
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
2009,35(1):55-64, DOI: 10.7519/j.issn.1000-0526.2009.1.007
Abstract:
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
2014,40(2):133-145, DOI: 10.7519/j.issn.1000-0526.2014.02.001
Abstract:
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
2012,38(10):1255-1266, DOI: 10.7519/j.issn.1000-0526.2012.10.012
Abstract:
Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.01.001
Abstract:
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
2011,37(10):1262-1269, DOI: 10.7519/j.issn.1000-0526.2011.10.009
Abstract:
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
2014,40(7):816-826, DOI: 10.7519/j.issn.1000-0526.2014.07.005
Abstract:
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
2011,37(5):599-606, DOI: 10.7519/j.issn.1000-0526.2011.5.012
Abstract:
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
ZHANG Xiaoling, ZHANG Tao, LIU Xinhua, ZHOU Qingliang, CHEN Yun, ZHOU Xiaoxia, ZHENG Yongguang, ZHAO Surong
2010,36(7):143-150, DOI: 10.7519/j.issn.1000-0526.2010.7.021
Abstract:
Mesoscale severe weather forecasting ability is limited, in some sense for a lack of valid analysis on mesoscale convective systems and its favorable environments. This paper introduces the mesoscale weather chart analysis techniq ue which was tested in the National Meteorological Center (NMC). Mesoscale weath er chart analyzes the favorable environmental conditions of mesoscale convective systems based on observational data and numerical weather forecast outputs. It includes upper air composite chart and surface chart. In the upper air composite ch art, by analyzing wind, temperature, moisture, temperature change and height change, the diagnostic systems and features in all the lower, middle and upper t roposphere isobaric layers are combined into one plot, which can clearly displa y the available environments and synoptic pattern of severe convective weather. In the surface chart, the analysis contents are pressure, wind, temperature, moi sture, convective weather phenomena and all kinds of boundaries (fronts). The te st in NMC shows that mesoscale weather chart analysis is a dependable means for severe convective weather outlook forecasting.
Mesoscale severe weather forecasting ability is limited, in some sense for a lack of valid analysis on mesoscale convective systems and its favorable environments. This paper introduces the mesoscale weather chart analysis techniq ue which was tested in the National Meteorological Center (NMC). Mesoscale weath er chart analyzes the favorable environmental conditions of mesoscale convective systems based on observational data and numerical weather forecast outputs. It includes upper air composite chart and surface chart. In the upper air composite ch art, by analyzing wind, temperature, moisture, temperature change and height change, the diagnostic systems and features in all the lower, middle and upper t roposphere isobaric layers are combined into one plot, which can clearly displa y the available environments and synoptic pattern of severe convective weather. In the surface chart, the analysis contents are pressure, wind, temperature, moi sture, convective weather phenomena and all kinds of boundaries (fronts). The te st in NMC shows that mesoscale weather chart analysis is a dependable means for severe convective weather outlook forecasting.
2013,39(9):1163-1170, DOI: 10.7519/j.issn.1000-0526.2013.09.011
Abstract:
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
2011,37(1):122-128, DOI: 10.7519/j.issn.1000-0526.2011.1.017
Abstract:
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
2014,40(4):400-411, DOI: 10.7519/j.issn.1000-0526.2014.04.002
Abstract:
Based on the synoptic environment analysis of about 100 severe convection cases in China since 2000 and the reference of related literatures, from the perspectives of the three essential conditions for the development of severe convection, namely the thermal instability, lift and moisture, five basic synoptic situation configurations of severe convection in China are proposed and expounded. They are cold advection forcing category, warm advection forcing category, baroclinic frontogenesis category, quasi barotropic category and elevated thunderstorm category. The typical characteristics of the upper cold advection forcing category is that the mid upper strong cold advection above 500 hPa strengthens and reaches the boundary warm convergence zone. The warm advection forcing category is characterized by trough with special structure moving over low level strong warm and moist advection. The deep convection produced by the mid lower layer convergence of cold and warm air features the baroclinic frontogenesis category. The quasi barotropic category mostly occurs at the northern and the southern edges or the interior of summer subtropical high and the area with weak baroclinicity, where the dynamic forcing and the surface inhomogeneous local heating play major roles. The features of elevated thunderstorms are the southwest jet in 700-500 hPa lifted by boundary cold wedge and the instable energy is from above 700 hPa. The classification based on the difference of the formation mechanisms can grasp accurately the synoptic characteristics, the situation configurations, the dynamic and thermal properties and the key points in analyzing short term potential forecast, providing more technical support to further enhance the level of weather prediction.
Based on the synoptic environment analysis of about 100 severe convection cases in China since 2000 and the reference of related literatures, from the perspectives of the three essential conditions for the development of severe convection, namely the thermal instability, lift and moisture, five basic synoptic situation configurations of severe convection in China are proposed and expounded. They are cold advection forcing category, warm advection forcing category, baroclinic frontogenesis category, quasi barotropic category and elevated thunderstorm category. The typical characteristics of the upper cold advection forcing category is that the mid upper strong cold advection above 500 hPa strengthens and reaches the boundary warm convergence zone. The warm advection forcing category is characterized by trough with special structure moving over low level strong warm and moist advection. The deep convection produced by the mid lower layer convergence of cold and warm air features the baroclinic frontogenesis category. The quasi barotropic category mostly occurs at the northern and the southern edges or the interior of summer subtropical high and the area with weak baroclinicity, where the dynamic forcing and the surface inhomogeneous local heating play major roles. The features of elevated thunderstorms are the southwest jet in 700-500 hPa lifted by boundary cold wedge and the instable energy is from above 700 hPa. The classification based on the difference of the formation mechanisms can grasp accurately the synoptic characteristics, the situation configurations, the dynamic and thermal properties and the key points in analyzing short term potential forecast, providing more technical support to further enhance the level of weather prediction.
2007,33(12):116-120, DOI: 10.7519/j.issn.1000-0526.2007.12.018
Abstract:
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
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ISSN:1000-0526 CN:11-2282/P