ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 49,Issue 12,2023 Table of Contents
2023, 49(12):1421-1434.
DOI: 10.7519/j.issn.1000-0526.2023.103003
Abstract:
Based on surface and radiosonde observations in China and ERA5 reanalysis data, the characteristics of water vapor transport, budget and extremity of the severe torrential rain in North China from 29 July to 1 August 2023 (referred to as the “23·7” event) and the important role of the terrain of the Taihang Mountains in persistent moisture convergence and vertical transportation are studied. The results show that this extreme torrential rain event occurred in the north of the residual vortex of Typhoon Doksuri, obstructed by a high pressure barrier, and with the favorable background of water vapor transport by two typhoons Doksuri and Khanun. The event had significant extreme features in its long duration, intense daily precipitation and enormous accumulated rainfall amount. The low-level strong southeast jet stream continuously transported water vapor to North China. The southern and eastern boundaries of the torrential rain central area were both net inflow of water vapor, especially the southern boundary. The easterly wind was forced to lift in the high gradient area of the terrain height at the eastern foot of the Taihang Mountains, forming a strong water vapor convergence and vertical transport center, and maintaining the state stably, which was an important cause for this severe torrential rain event. The maximum of precipitable water exceeded 75 mm and the normalized value exceeded 3.0. The comparison results also indicate that the low-level water vapor source in the “23·7” event was quite different from another severe torrential rain that occurred on 19-20 July 2016 in North China. The former had the water vapor source mainly from the Northwest Pacific Ocean and the South China Sea, while the water vapor of the latter was mainly from the South China Sea and the Bay of Bengal. Besides, the average water vapor convergence in the former was significantly weaker than that in the latter, and the number of short-time severe precipitation stations was also less than the latter, but the duration of the former was longer. This indicates that compared to the intensity of precipitation, the prolonged duration was a more critical factor in producing this severe torrential rain.
Based on surface and radiosonde observations in China and ERA5 reanalysis data, the characteristics of water vapor transport, budget and extremity of the severe torrential rain in North China from 29 July to 1 August 2023 (referred to as the “23·7” event) and the important role of the terrain of the Taihang Mountains in persistent moisture convergence and vertical transportation are studied. The results show that this extreme torrential rain event occurred in the north of the residual vortex of Typhoon Doksuri, obstructed by a high pressure barrier, and with the favorable background of water vapor transport by two typhoons Doksuri and Khanun. The event had significant extreme features in its long duration, intense daily precipitation and enormous accumulated rainfall amount. The low-level strong southeast jet stream continuously transported water vapor to North China. The southern and eastern boundaries of the torrential rain central area were both net inflow of water vapor, especially the southern boundary. The easterly wind was forced to lift in the high gradient area of the terrain height at the eastern foot of the Taihang Mountains, forming a strong water vapor convergence and vertical transport center, and maintaining the state stably, which was an important cause for this severe torrential rain event. The maximum of precipitable water exceeded 75 mm and the normalized value exceeded 3.0. The comparison results also indicate that the low-level water vapor source in the “23·7” event was quite different from another severe torrential rain that occurred on 19-20 July 2016 in North China. The former had the water vapor source mainly from the Northwest Pacific Ocean and the South China Sea, while the water vapor of the latter was mainly from the South China Sea and the Bay of Bengal. Besides, the average water vapor convergence in the former was significantly weaker than that in the latter, and the number of short-time severe precipitation stations was also less than the latter, but the duration of the former was longer. This indicates that compared to the intensity of precipitation, the prolonged duration was a more critical factor in producing this severe torrential rain.
FU Jiaolan
,
QUAN Wanqing
,
MAI Zi
,
LUO Qi
,
CHEN Tao
,
LI Xiaolan
,
XU Xianhuang
,
ZHU Wenjian
,
HUA Shan
,
HAN Xuqing
2023, 49(12):1435-1450.
DOI: 10.7519/j.issn.1000-0526.2023.112701
Abstract:
Based on the ERA5 reanalysis data and the multi-source observations such as ground national and regional automatic weather stations, dual polarization radar, ground raindrop spectrometer, lightning locator, wind-profiling radar, we analyze the refined characteristics of rainfall intensity, the mesoscale convective system (MCS) responsible for the extreme precipitation, the microphysical features as well as dynamic and thermodynamic conditions of the July 2023 extremely severe precipitation process in North China. The results indicate that the hourly rainfall intensity in this event was characterized by weak in most areas but strong at some stations, and the local hourly and minute-level rainfall intensities both reached the extremity level. The stage feature of the rainfall intensity was obvious, with the rainfall intensity being strongest in the second stage from 08:00 BT 30 to 20:00 BT 31 July. This was caused by several β-MCSs and accompanied by mesoscale processes such as backward propagation and train effect. The severe precipitation was mainly composed of high concentration raindrops with medium diameters, and had a certain amount of low-concentration large particle raindrop samples. Thus, this extreme rainfall event belonged to a mixed type with precipitation of oceanic and continental nature, in which warm clouds collided, coexisting with ice crystal aggregation and melting. In the first stage (from 08:00 BT 29 to 08:00 BT 30 July) and the third stage (from 20:00 BT 31 July to 08:00 BT 2 August) the rainfall intensity was relatively small. The former had a low vertical extension height and weak intensity of MCS, dominated by warm-cloud precipitation, and the raindrops had high concentrations and medium diameters. The MCS responding to the latter developed vigorously, but it moved fast. So, it also had the characteristics of mixed-type oceanic and continental precipitation. The maximum values of integrated precipitable water in the three stages all exceeded 70 mm. In the first stage, the synoptic scale forcing was strong, and the convective available potential energy (CAPE) was around 500 J·kg-1. The vertical height of MCS was relatively low. In the second half period of the second stage, the synoptic scale forcing was weakened, but the unstable convective energy in the central and southern parts of North China was rebuilt again. The CAPE in the upstream region became increased compared to the value in the first stage (600-1000 J·kg-1), causing the extreme-rainfall-related MCS to have developed into a deep wet convective system and the rainfall intensity increased significantly. In the third stage, the synoptic scale forcing was greatly weakened. The convergence of southerly wind pulsations at low level and the large CAPE provided favorable conditions for the vigorous development of MCS.
Based on the ERA5 reanalysis data and the multi-source observations such as ground national and regional automatic weather stations, dual polarization radar, ground raindrop spectrometer, lightning locator, wind-profiling radar, we analyze the refined characteristics of rainfall intensity, the mesoscale convective system (MCS) responsible for the extreme precipitation, the microphysical features as well as dynamic and thermodynamic conditions of the July 2023 extremely severe precipitation process in North China. The results indicate that the hourly rainfall intensity in this event was characterized by weak in most areas but strong at some stations, and the local hourly and minute-level rainfall intensities both reached the extremity level. The stage feature of the rainfall intensity was obvious, with the rainfall intensity being strongest in the second stage from 08:00 BT 30 to 20:00 BT 31 July. This was caused by several β-MCSs and accompanied by mesoscale processes such as backward propagation and train effect. The severe precipitation was mainly composed of high concentration raindrops with medium diameters, and had a certain amount of low-concentration large particle raindrop samples. Thus, this extreme rainfall event belonged to a mixed type with precipitation of oceanic and continental nature, in which warm clouds collided, coexisting with ice crystal aggregation and melting. In the first stage (from 08:00 BT 29 to 08:00 BT 30 July) and the third stage (from 20:00 BT 31 July to 08:00 BT 2 August) the rainfall intensity was relatively small. The former had a low vertical extension height and weak intensity of MCS, dominated by warm-cloud precipitation, and the raindrops had high concentrations and medium diameters. The MCS responding to the latter developed vigorously, but it moved fast. So, it also had the characteristics of mixed-type oceanic and continental precipitation. The maximum values of integrated precipitable water in the three stages all exceeded 70 mm. In the first stage, the synoptic scale forcing was strong, and the convective available potential energy (CAPE) was around 500 J·kg-1. The vertical height of MCS was relatively low. In the second half period of the second stage, the synoptic scale forcing was weakened, but the unstable convective energy in the central and southern parts of North China was rebuilt again. The CAPE in the upstream region became increased compared to the value in the first stage (600-1000 J·kg-1), causing the extreme-rainfall-related MCS to have developed into a deep wet convective system and the rainfall intensity increased significantly. In the third stage, the synoptic scale forcing was greatly weakened. The convergence of southerly wind pulsations at low level and the large CAPE provided favorable conditions for the vigorous development of MCS.
YANG Xiaoliang
,
JIN Xiaoqing
,
SUN Yun
,
CHEN Biying
,
LIANG Tian
,
YANG Min
,
YAN Xuejin
,
LI Jiangbo
2023, 49(12):1451-1467.
DOI: 10.7519/j.issn.1000-0526.2023.102301
Abstract:
Influenced by the weakening low pressure of Typhoon Doksuri, the Beijing-Tianjin-Hebei Region suffered the unprecedented extremely severe torrential rain from 29 July to 1 August 2023, with catastrophic floods in the Haihe River Basin causing serious casualties and economic losses. A preliminary analysis of this rarely seen severe precipitation event is conducted in this article based on conventional observations, S-band Doppler weather radar data, wind profile radar data, and ERA5 reanalysis data. The results show that this extremely severe torrential rain process was characterized by enormous accumulated rainfall, and long duration, affected significantly by terrain. Typhoons Doksuri and Khanun provided extremely favorable water vapor conditions, but the high pressure barrier formed in northern part of North China blocked the northward typhoons. The North China Region experienced three stages: intermittent rainfall, typhoon inverted-trough precipitation and convective precipitation during the weakening stage of the inverted-trough, and the superposition of precipitation areas in three stages was the main cause for the formation of the extremely severe torrential rain. During the stage of weakening inverted-trough, the shear line at 850 hPa moved slowly due to the obstruction of the Taihang Mountains, causing the long duration of precipitation. The atmosphere was in a near neutral state with stable rainfall intensity in the early stages. From the afternoon of 30 July, convective precipitation began to strengthen. The convergence line formed by the northerly wind which was generated by the outflow of the cold pool in the central rainfall area of Hebei Province and the surface southeast wind triggered the release of unstable energy and also strengthened the development of triggered convective cells into mesoscale convective system (MCS) in the high-energy area of southeastern Hebei. This MCS moved into Baoding, resulting in the “train effect”. The convergence line between the surface north wind generated by the cold pool of Taihang Mountains and the southeast wind triggered the release of unstable energy, which was the reason for the maintenance of severe precipitation in southwestern Hebei over the night of 30 July. On the morning of 31 July, a southeast low-level jet over 20 m·s-1 was established again, leading to the extremely severe torrential rain exceeding 110 mm·h-1 in the southern part of Beijing.
Influenced by the weakening low pressure of Typhoon Doksuri, the Beijing-Tianjin-Hebei Region suffered the unprecedented extremely severe torrential rain from 29 July to 1 August 2023, with catastrophic floods in the Haihe River Basin causing serious casualties and economic losses. A preliminary analysis of this rarely seen severe precipitation event is conducted in this article based on conventional observations, S-band Doppler weather radar data, wind profile radar data, and ERA5 reanalysis data. The results show that this extremely severe torrential rain process was characterized by enormous accumulated rainfall, and long duration, affected significantly by terrain. Typhoons Doksuri and Khanun provided extremely favorable water vapor conditions, but the high pressure barrier formed in northern part of North China blocked the northward typhoons. The North China Region experienced three stages: intermittent rainfall, typhoon inverted-trough precipitation and convective precipitation during the weakening stage of the inverted-trough, and the superposition of precipitation areas in three stages was the main cause for the formation of the extremely severe torrential rain. During the stage of weakening inverted-trough, the shear line at 850 hPa moved slowly due to the obstruction of the Taihang Mountains, causing the long duration of precipitation. The atmosphere was in a near neutral state with stable rainfall intensity in the early stages. From the afternoon of 30 July, convective precipitation began to strengthen. The convergence line formed by the northerly wind which was generated by the outflow of the cold pool in the central rainfall area of Hebei Province and the surface southeast wind triggered the release of unstable energy and also strengthened the development of triggered convective cells into mesoscale convective system (MCS) in the high-energy area of southeastern Hebei. This MCS moved into Baoding, resulting in the “train effect”. The convergence line between the surface north wind generated by the cold pool of Taihang Mountains and the southeast wind triggered the release of unstable energy, which was the reason for the maintenance of severe precipitation in southwestern Hebei over the night of 30 July. On the morning of 31 July, a southeast low-level jet over 20 m·s-1 was established again, leading to the extremely severe torrential rain exceeding 110 mm·h-1 in the southern part of Beijing.
2023, 49(12):1468-1480.
DOI: 10.7519/j.issn.1000-0526.2023.101201
Abstract:
The South China Sea summer monsoon usually breaks out earlier in the La Nina year, but a late onset (6th pentad of May) appeared in 2021, though 2020/2021 was the year of La Nina. Using NCEP/NCAR reanalysis data, the reasons for the late onset of the South China Sea summer monsoon in 2021 are analyzed from the perspective of tropical sea surface temperature anomaly (SSTA) and intraseasonal oscillation (ISO) northward propagation. The results show that La Nina did weaken the Western Pacific subtropical high in spring, especially before April. However, the tropical Indian Ocean sea surface temperature in the winter and spring continued to be warmer, offsetting the impact of La Nina, especially in May. The influence of La Nina was less than that of the tropical Indian Ocean, resulting in the stronger Western Pacific subtropical high in May and the late onset of the South China Sea summer monsoon. In addition, due to the influence of La Nina, the Western Pacific subtropical high in April was weak and the background barotropic southerly in the South China Sea was weak, which unfavored the equatorial ISO in the South China Sea propagating northward. As the influence of tropical Indian Ocean SSTA became more and more significant, the Western Pacific subtropical high has gradually strengthened, and the background barotropic southerly did not extend to the area south of 10°N until late May, casusing a late northward propagation of the equatorial ISO in the South China Sea in 2021, which is the opposite of the climatic state. This is also an important reason for the late onset of the South China Sea summer monsoon in 2021. The tropical Indian Ocean and Pacific SSTAs together have an impact on the onset of the South China Sea summer monsoon through competition, so it is very important to pay attention to the development of the two in winter and spring.
The South China Sea summer monsoon usually breaks out earlier in the La Nina year, but a late onset (6th pentad of May) appeared in 2021, though 2020/2021 was the year of La Nina. Using NCEP/NCAR reanalysis data, the reasons for the late onset of the South China Sea summer monsoon in 2021 are analyzed from the perspective of tropical sea surface temperature anomaly (SSTA) and intraseasonal oscillation (ISO) northward propagation. The results show that La Nina did weaken the Western Pacific subtropical high in spring, especially before April. However, the tropical Indian Ocean sea surface temperature in the winter and spring continued to be warmer, offsetting the impact of La Nina, especially in May. The influence of La Nina was less than that of the tropical Indian Ocean, resulting in the stronger Western Pacific subtropical high in May and the late onset of the South China Sea summer monsoon. In addition, due to the influence of La Nina, the Western Pacific subtropical high in April was weak and the background barotropic southerly in the South China Sea was weak, which unfavored the equatorial ISO in the South China Sea propagating northward. As the influence of tropical Indian Ocean SSTA became more and more significant, the Western Pacific subtropical high has gradually strengthened, and the background barotropic southerly did not extend to the area south of 10°N until late May, casusing a late northward propagation of the equatorial ISO in the South China Sea in 2021, which is the opposite of the climatic state. This is also an important reason for the late onset of the South China Sea summer monsoon in 2021. The tropical Indian Ocean and Pacific SSTAs together have an impact on the onset of the South China Sea summer monsoon through competition, so it is very important to pay attention to the development of the two in winter and spring.
2023, 49(12):1481-1494.
DOI: 10.7519/j.issn.1000-0526.2023.083101
Abstract:
The forecast results of radar echo extrapolation algorithm based on recurrent neural network are gradually blurred and distorted with time, and it is difficult to forecast the severe echo area. To solve the above problems, this paper proposes a spatio-temporal long short-term memory network model based on context fusion and attention mechanism. The method fully extracts the short-term context information of different scales of radar image through the context fusion module. The attention module broadens the time perception domain of the prediction unit, so that the model perceives more time dynamics. Taking the weather radar data of Jiangsu Province from April to September in 2019-2021 as a sample, the spatio-temporal long short-term memory network based on context fusion and attention mechanism achieves better prediction performance through experimental comparison and analysis. Under the conditions of 60 min extrapolation and the thresholds of 10, 20 and 40 dBz, the critical success index (CSI) and heidke skill score (HSS) reach 0.7611, 0.5326, 0.2369 and 0.7335, 0.5735, 0.3075, respectively, which effectively improved the prediction accuracy.
The forecast results of radar echo extrapolation algorithm based on recurrent neural network are gradually blurred and distorted with time, and it is difficult to forecast the severe echo area. To solve the above problems, this paper proposes a spatio-temporal long short-term memory network model based on context fusion and attention mechanism. The method fully extracts the short-term context information of different scales of radar image through the context fusion module. The attention module broadens the time perception domain of the prediction unit, so that the model perceives more time dynamics. Taking the weather radar data of Jiangsu Province from April to September in 2019-2021 as a sample, the spatio-temporal long short-term memory network based on context fusion and attention mechanism achieves better prediction performance through experimental comparison and analysis. Under the conditions of 60 min extrapolation and the thresholds of 10, 20 and 40 dBz, the critical success index (CSI) and heidke skill score (HSS) reach 0.7611, 0.5326, 0.2369 and 0.7335, 0.5735, 0.3075, respectively, which effectively improved the prediction accuracy.
2023, 49(12):1495-1508.
DOI: 10.7519/j.issn.1000-0526.2023.052801
Abstract:
Wind farms have obvious impact on the local climate. However, whether there exist obvious differences in environmental effects of local wind between the inland and offshore wind farms still need to be explored. Based on the inland wind farm data from Shangyi, Hebei Province and offshore wind farms in Rudong, Jiangsu Province and the data of meteorological observation and wind gradient tower around wind farm the influence difference of the inland and offshore wind farms on local wind environment, turbulence intensity (TI) and wind shear exponent (WSE) are preliminarily analyzed. The results show that the inland and offshore wind farms have significant effects on TI and WSE. The constructed inland and offshore wind farms have an enhancement effect on TI, and the average annual TI increased by 31% and 37%, respectively. The largest increment occurred in spring (47%) and winter (49%) in inland and offshore wind farms respectively. Moreover, the TI increasing range of high-level was greater than that in low-level, and greater at night than in day in inland wind, while the TI increasing range was relatively stable at different heights and diurnal variation in offshore wind farms. In terms of WSE, the constructed inland and offshore wind farms have significant differences in their influences on WSE. The WSE increased during the day and decreased at night, and the diurnal variation was significantly reduced with the average annual WSE decreased by 8%, and the largest decline in WSE in autumn (12%) in the inland wind farms. By contrast, the WSE increased obviously during both day and night with average annual WSE increased by 24%, and the largest rise seen in spring (37%) in offshore wind farms.
Wind farms have obvious impact on the local climate. However, whether there exist obvious differences in environmental effects of local wind between the inland and offshore wind farms still need to be explored. Based on the inland wind farm data from Shangyi, Hebei Province and offshore wind farms in Rudong, Jiangsu Province and the data of meteorological observation and wind gradient tower around wind farm the influence difference of the inland and offshore wind farms on local wind environment, turbulence intensity (TI) and wind shear exponent (WSE) are preliminarily analyzed. The results show that the inland and offshore wind farms have significant effects on TI and WSE. The constructed inland and offshore wind farms have an enhancement effect on TI, and the average annual TI increased by 31% and 37%, respectively. The largest increment occurred in spring (47%) and winter (49%) in inland and offshore wind farms respectively. Moreover, the TI increasing range of high-level was greater than that in low-level, and greater at night than in day in inland wind, while the TI increasing range was relatively stable at different heights and diurnal variation in offshore wind farms. In terms of WSE, the constructed inland and offshore wind farms have significant differences in their influences on WSE. The WSE increased during the day and decreased at night, and the diurnal variation was significantly reduced with the average annual WSE decreased by 8%, and the largest decline in WSE in autumn (12%) in the inland wind farms. By contrast, the WSE increased obviously during both day and night with average annual WSE increased by 24%, and the largest rise seen in spring (37%) in offshore wind farms.
2023, 49(12):1509-1520.
DOI: 10.7519/j.issn.1000-0526.2023.060601
Abstract:
Based on daily observation data of wire icing of 191 meteorological stations in Guizhou, Hunan and Jiangxi provinces from 1961 to 2019, the number of wire icing days, the extreme values of standard ice thickness, the maximum consecutive icing days, and the beginning and ending dates of wire icing in the study area are calculated. The wire icing risk indicator is constructed to evaluate the risk of wire icing. The results show that the number of wire icing days shows a slight downward trend on the whole in the past 60 years, and it reached the maximum value in the 1980s. Wire icing occurs most in January. The extreme values of standard ice thickness are concentrated in 20-50 mm, and most of the extreme values are found in Hunan. The interdecadal distribution is extremely uneven, the most of the extreme values are seen in 2011-2019. The maximum consecutive icing days are concentrated in 5-15 days. On the whole, the maximum consecutive icing days in Guizhou are more than in Hunan and Jiangxi. The beginning date of wire icing tends to be advanced in fluctuation, but the ending date tends to be postponed in fluctuation. The annual change of the wire icing risk indicator shows a decreasing trend. The high-risk areas for wire icing are mainly located in central and western Guizhou, central Hunan and northern Jiangxi, with a wire icing risk indicator greater than 0.6.
Based on daily observation data of wire icing of 191 meteorological stations in Guizhou, Hunan and Jiangxi provinces from 1961 to 2019, the number of wire icing days, the extreme values of standard ice thickness, the maximum consecutive icing days, and the beginning and ending dates of wire icing in the study area are calculated. The wire icing risk indicator is constructed to evaluate the risk of wire icing. The results show that the number of wire icing days shows a slight downward trend on the whole in the past 60 years, and it reached the maximum value in the 1980s. Wire icing occurs most in January. The extreme values of standard ice thickness are concentrated in 20-50 mm, and most of the extreme values are found in Hunan. The interdecadal distribution is extremely uneven, the most of the extreme values are seen in 2011-2019. The maximum consecutive icing days are concentrated in 5-15 days. On the whole, the maximum consecutive icing days in Guizhou are more than in Hunan and Jiangxi. The beginning date of wire icing tends to be advanced in fluctuation, but the ending date tends to be postponed in fluctuation. The annual change of the wire icing risk indicator shows a decreasing trend. The high-risk areas for wire icing are mainly located in central and western Guizhou, central Hunan and northern Jiangxi, with a wire icing risk indicator greater than 0.6.
2023, 49(12):1521-1531.
DOI: 10.7519/j.issn.1000-0526.2023.040101
Abstract:
In order to better carry out the monitoring and early warning of hail weather in Jiangxi Province, using MICAPS data, automatic weather station data, radar mosaic data, radar PUP product data, dual-Doppler radar retrieved wind field data, hail disaster photos and videos, and WeChat hail information feedback, as well as principles and methods such as meteorology and radar meteorology, this paper analyzes the characteristics of the hail echoes in Jiangxi and surrounding regions on 14 March 2022. The results show that hails occurred in many places in Jiangxi and surrounding regions, with strong winds of ≥17.2 m·s-1 occurring at 20 regional stations, precipitation ≥50.0 mm occurring at 24 regional stations, and the mixture of thunderstorm gales and cold air. The main impact systems of the hail weather were the 200 hPa outflow zone, the 500 hPa south branch trough and wind speed shear, the 850 hPa low vortex and shear line, the surface convergence line, and the southwest inverted trough. After the correction the larger CAPE value, the stronger inversion layer, the mid-level dry region, and the lower-level wet zone provided ambient conditions for the occurrence of hail weather in Nanchang. Hailstones are mainly composed of supercell echoes, which were sometimes isolated, and sometimes in echo groups and bands. Echo intensity was ≥60 dBz. The minimum strong echo area was ≥18 km2, and the maximum ≥180 km2. The strong echo gradient at a distance of 30-60 dBz was ≤6 km, with obvious cloud anvil forward echo. The life spans of hail echoes were mostly more than 2 hours. In hail echo identification, the vertically integrated liquid (VIL) was a very important feature. The VIL of a single radar of Jiangxi hail was between 35-60 kg·m-2, and the VIL on the radar mosaic was 35-50 kg·m-2. On the CAPPI map of 2.5 km of hail echo, the hail echo intensity was ≥60 dBz, with a maximum of 65 dBz. Most echo centers of dual Doppler radar retrieved wind field had the characteristics of medium vortex structure, lateral convergence wind field, and convergence of north south wind field. Some individual wind fields were relatively messy. The above analysis results could provide an analytical basis for monitoring and early warning of hail weather in Jiangxi.
In order to better carry out the monitoring and early warning of hail weather in Jiangxi Province, using MICAPS data, automatic weather station data, radar mosaic data, radar PUP product data, dual-Doppler radar retrieved wind field data, hail disaster photos and videos, and WeChat hail information feedback, as well as principles and methods such as meteorology and radar meteorology, this paper analyzes the characteristics of the hail echoes in Jiangxi and surrounding regions on 14 March 2022. The results show that hails occurred in many places in Jiangxi and surrounding regions, with strong winds of ≥17.2 m·s-1 occurring at 20 regional stations, precipitation ≥50.0 mm occurring at 24 regional stations, and the mixture of thunderstorm gales and cold air. The main impact systems of the hail weather were the 200 hPa outflow zone, the 500 hPa south branch trough and wind speed shear, the 850 hPa low vortex and shear line, the surface convergence line, and the southwest inverted trough. After the correction the larger CAPE value, the stronger inversion layer, the mid-level dry region, and the lower-level wet zone provided ambient conditions for the occurrence of hail weather in Nanchang. Hailstones are mainly composed of supercell echoes, which were sometimes isolated, and sometimes in echo groups and bands. Echo intensity was ≥60 dBz. The minimum strong echo area was ≥18 km2, and the maximum ≥180 km2. The strong echo gradient at a distance of 30-60 dBz was ≤6 km, with obvious cloud anvil forward echo. The life spans of hail echoes were mostly more than 2 hours. In hail echo identification, the vertically integrated liquid (VIL) was a very important feature. The VIL of a single radar of Jiangxi hail was between 35-60 kg·m-2, and the VIL on the radar mosaic was 35-50 kg·m-2. On the CAPPI map of 2.5 km of hail echo, the hail echo intensity was ≥60 dBz, with a maximum of 65 dBz. Most echo centers of dual Doppler radar retrieved wind field had the characteristics of medium vortex structure, lateral convergence wind field, and convergence of north south wind field. Some individual wind fields were relatively messy. The above analysis results could provide an analytical basis for monitoring and early warning of hail weather in Jiangxi.
9 Application Research on Abnormal Temperature Forecast Products in China Based on Ensemble Forecast
2023, 49(12):1532-1541.
DOI: 10.7519/j.issn.1000-0526.2023.101101
Abstract:
Based on the fifth generation global reanalysis data (ERA5) of the European Centre for Medium-Range Weather Forecasts (ECMWF), the model climate is constructed. The ensemble mean abnormal temperature forecast and abnormal temperature probability forecast products for China are constructed according to the maximum and minimum temperatures by using ECMWF ensemble forecast and standardized anomaly forecast method. The forecast performance was tested and compared with the extreme forecast index (EFI). Furthermore, based on “abnormal temperature impact matrix”, forecast index of impact degree of abnormal temperature event was constructed. The forecast application of related products was discussed through the cases of abnormal temperature events. The results show that the ensemble mean abnormal temperature forecast product based on ERA5 and ECWMF ensemble forecast has a good forecasting effect for both summer and winter abnormal temperature events in China, and the forecast performance is better than or close to EFI through comparative verification. The product can be used as a supporting product for forecasting abnormal temperature events. Abnormal temperature probability forecast products can reflect the information of abnormal temperature events predicted in the ensemble members of the set, have advantages in finding early abnormal temperature event signals in medium-range forecast, and can reflect the uncertainty information of abnormal weather forecast. The forecast index of impact degree of abnormal temperature event combines the prediction information of the probability of abnormal weather and the prediction information of the anomaly of abnormal weather. It can give the objective and quantitative prediction results of the abnormal temperature time in one product. The prediction of the abnormal low temperature event caused by a cold surge weather process proves that this index has a relatively good prediction effect. It has certain indicative significance and application prospect for the prediction and early warning of abnormal temperature events.
Based on the fifth generation global reanalysis data (ERA5) of the European Centre for Medium-Range Weather Forecasts (ECMWF), the model climate is constructed. The ensemble mean abnormal temperature forecast and abnormal temperature probability forecast products for China are constructed according to the maximum and minimum temperatures by using ECMWF ensemble forecast and standardized anomaly forecast method. The forecast performance was tested and compared with the extreme forecast index (EFI). Furthermore, based on “abnormal temperature impact matrix”, forecast index of impact degree of abnormal temperature event was constructed. The forecast application of related products was discussed through the cases of abnormal temperature events. The results show that the ensemble mean abnormal temperature forecast product based on ERA5 and ECWMF ensemble forecast has a good forecasting effect for both summer and winter abnormal temperature events in China, and the forecast performance is better than or close to EFI through comparative verification. The product can be used as a supporting product for forecasting abnormal temperature events. Abnormal temperature probability forecast products can reflect the information of abnormal temperature events predicted in the ensemble members of the set, have advantages in finding early abnormal temperature event signals in medium-range forecast, and can reflect the uncertainty information of abnormal weather forecast. The forecast index of impact degree of abnormal temperature event combines the prediction information of the probability of abnormal weather and the prediction information of the anomaly of abnormal weather. It can give the objective and quantitative prediction results of the abnormal temperature time in one product. The prediction of the abnormal low temperature event caused by a cold surge weather process proves that this index has a relatively good prediction effect. It has certain indicative significance and application prospect for the prediction and early warning of abnormal temperature events.
2023, 49(12):1542-1552.
DOI: 10.7519/j.issn.1000-0526.2023.051501
Abstract:
Based on the wind speed observation data of Marine Booster Station in Rudong Wind Farm, this paper proposes a method of identifying gale event. Three identification schemes of gale event forecast are developed and compared through the determination of the crucial parameters. Then, based on the decision tree method and a single linear regression method, the correction methods for gale events are studied. The results show that the gale event forecast of equal cumulative frequency scheme is superior to other schemes, having the hit rate of 76.1% and the hit rate of matching duration of 87.6%. The duration of gale event forecast of eliminating deviation and equal cumulative frequency schemes are more in agreement with the observation data. Besides, the equal cumulative frequency scheme can cover the duration of every observation gale event, so it is good for proposing the beginning and end time of gale warning. The above-mentioned two correction methods can improve the forecast performance to a certain extent. However, the improvement done by the decision tree method is more obvious, for it can significantly reduce the MAE, RE, RMSE.
Based on the wind speed observation data of Marine Booster Station in Rudong Wind Farm, this paper proposes a method of identifying gale event. Three identification schemes of gale event forecast are developed and compared through the determination of the crucial parameters. Then, based on the decision tree method and a single linear regression method, the correction methods for gale events are studied. The results show that the gale event forecast of equal cumulative frequency scheme is superior to other schemes, having the hit rate of 76.1% and the hit rate of matching duration of 87.6%. The duration of gale event forecast of eliminating deviation and equal cumulative frequency schemes are more in agreement with the observation data. Besides, the equal cumulative frequency scheme can cover the duration of every observation gale event, so it is good for proposing the beginning and end time of gale warning. The above-mentioned two correction methods can improve the forecast performance to a certain extent. However, the improvement done by the decision tree method is more obvious, for it can significantly reduce the MAE, RE, RMSE.
2023, 49(12):1553-1560.
DOI: 10.7519/j.issn.1000-0526.2023.110701
Abstract:
The main characteristics of the atmospheric circulation in the Northern Hemisphere in September 2023 are shown as follows. The polar vortex was unipolar with the same intensity as normal, leaning towards the Eastern Hemisphere. The Eurasian circulation in the middle and high latitudes, to the west of Lake Baikal, was more meridional, and the Western Pacific subtropical high was significantly more westward and stronger than usual. Most of the northern part of China was affected by the horizontal westerly circulation, while most of the southern part was controlled by the subtropical high. In September, the national average temperature was 18.2℃, 1.3℃ higher than that of the same period of normal years (16.9℃), with high temperature mainly appeared in the south to Yangtze River and the South China. The national average precipitation was 69.1 mm, 5.8% higher than the normal value (65.3 mm). Two typhoons were generated in the Northwest Pacific and the South China Sea, which were fewer than those in the same period of the year. In addition, typhoons Saola and Haikui landed in China, successively affecting South China and leading to extremely severe precipitation. The number of landfall typhoons was close to normal. There were six extensive areal severe precipitation processes and two severe convective weather processes in this month. Besides, strong tornadoes hit Suqian and Yancheng of Jiangsu Province.
The main characteristics of the atmospheric circulation in the Northern Hemisphere in September 2023 are shown as follows. The polar vortex was unipolar with the same intensity as normal, leaning towards the Eastern Hemisphere. The Eurasian circulation in the middle and high latitudes, to the west of Lake Baikal, was more meridional, and the Western Pacific subtropical high was significantly more westward and stronger than usual. Most of the northern part of China was affected by the horizontal westerly circulation, while most of the southern part was controlled by the subtropical high. In September, the national average temperature was 18.2℃, 1.3℃ higher than that of the same period of normal years (16.9℃), with high temperature mainly appeared in the south to Yangtze River and the South China. The national average precipitation was 69.1 mm, 5.8% higher than the normal value (65.3 mm). Two typhoons were generated in the Northwest Pacific and the South China Sea, which were fewer than those in the same period of the year. In addition, typhoons Saola and Haikui landed in China, successively affecting South China and leading to extremely severe precipitation. The number of landfall typhoons was close to normal. There were six extensive areal severe precipitation processes and two severe convective weather processes in this month. Besides, strong tornadoes hit Suqian and Yancheng of Jiangsu Province.
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ISSN:1000-0526 CN:11-2282/P