ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 50,Issue 10,2024 Table of Contents
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.
5 Dual-Polarization Parameter Structure and Evolution Characteristics of a Long-Life Supercell Storm
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.
Mobile website
® 2024 All Rights Reserved
Supported by:Beijing E-Tiller Technology Development Co., Ltd.
ISSN:1000-0526 CN:11-2282/P