ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 49,Issue 11,2023 Table of Contents
2023, 49(11):1285-1298.
DOI: 10.7519/j.issn.1000-0526.2023.032601
Abstract:
A climatology, which includes interannual variability, annual and diurnal cycles, intensities according to the “Enhanced Fujita Scale”, geographic distribution, and environmental conditions derived from reanalysis data, is developed in this study for the tornadoes in Liaoning Province during 1971-2020 in order to understand the climatic characteristics of tornado. The tornado reports are obtained from the Chinese Meteorological Disaster Dictionary, Chinese Meteorological Disaster Yearbook and other associated data. The differences in environmental background between Liaoning Province in China and the tornado-prone areas in United States are compared, and the typical circulation conditions and atmospheric characteristics of Liaoning tornadoes are analyzed. The major findings are as follows. Over the 50 years (1971-2020), there were 105 tornadoes recorded (including 17 EF2 or stronger tornadoes) in 97 tornadic days in Liaoning Province, which suggests that Liaoning has 2.1 tornadoes per year with the annual generation density to be 1.4×10-5 km-2, approximately equal to 1/10 tornadoes in the United States. A total of 17 EF2 or stronger tornadoes are recorded, with an average annual occurrence of 0.3. The tornadoes occur mostly (95%) from May through September, and 67% of tornado genesis are between 14:00 BT and 19:00 BT. Significant tornadoes (EF2/EF3/EF4) mainly occur in the central and western part of Liao-ning, while weak tornadoes (EF0/EF1) happen more in the coastal region of the southeastern Liaoning. The tornadic season in the northwest of Liaoning is much earlier than in the southeast. CAPE and mid-level wind shear often change in opposite phases with seasons, and the appropriate configuration of the two is the prerequisite for the occurrence of tornadoes and other convective weather. Additionally, the lower low-level the storm relative helicity (SRH) is the major cause for the apparently lower tornado density in Liaoning relative to the United States. About 87% of tornadoes are related to the cold vortices, which can be mainly divided into the short-wave trough category at the cold vortex bottom and cold vortex front category dominated by low-level frontogenesis (65%), the mid-level dry cold air forcing category dominated by mid-to-high level dry cold airflow (12%), and the cold vortex central area category dominated by mesoscale near-storm environment under severe thermal instability (6%). The environmental conditions in the high-incidence area of Liaoning tornadoes have the following characteristics: the mid-level impact system is cold vortex, the ground corresponds to frontal cyclones, tornadoes often appear in the northwest quadrant of the center of SRH and in the large-value zone of CAPE gradient, corresponding to the east side of cold front and the dry line at surface as well as the top of the temperature ridge.
A climatology, which includes interannual variability, annual and diurnal cycles, intensities according to the “Enhanced Fujita Scale”, geographic distribution, and environmental conditions derived from reanalysis data, is developed in this study for the tornadoes in Liaoning Province during 1971-2020 in order to understand the climatic characteristics of tornado. The tornado reports are obtained from the Chinese Meteorological Disaster Dictionary, Chinese Meteorological Disaster Yearbook and other associated data. The differences in environmental background between Liaoning Province in China and the tornado-prone areas in United States are compared, and the typical circulation conditions and atmospheric characteristics of Liaoning tornadoes are analyzed. The major findings are as follows. Over the 50 years (1971-2020), there were 105 tornadoes recorded (including 17 EF2 or stronger tornadoes) in 97 tornadic days in Liaoning Province, which suggests that Liaoning has 2.1 tornadoes per year with the annual generation density to be 1.4×10-5 km-2, approximately equal to 1/10 tornadoes in the United States. A total of 17 EF2 or stronger tornadoes are recorded, with an average annual occurrence of 0.3. The tornadoes occur mostly (95%) from May through September, and 67% of tornado genesis are between 14:00 BT and 19:00 BT. Significant tornadoes (EF2/EF3/EF4) mainly occur in the central and western part of Liao-ning, while weak tornadoes (EF0/EF1) happen more in the coastal region of the southeastern Liaoning. The tornadic season in the northwest of Liaoning is much earlier than in the southeast. CAPE and mid-level wind shear often change in opposite phases with seasons, and the appropriate configuration of the two is the prerequisite for the occurrence of tornadoes and other convective weather. Additionally, the lower low-level the storm relative helicity (SRH) is the major cause for the apparently lower tornado density in Liaoning relative to the United States. About 87% of tornadoes are related to the cold vortices, which can be mainly divided into the short-wave trough category at the cold vortex bottom and cold vortex front category dominated by low-level frontogenesis (65%), the mid-level dry cold air forcing category dominated by mid-to-high level dry cold airflow (12%), and the cold vortex central area category dominated by mesoscale near-storm environment under severe thermal instability (6%). The environmental conditions in the high-incidence area of Liaoning tornadoes have the following characteristics: the mid-level impact system is cold vortex, the ground corresponds to frontal cyclones, tornadoes often appear in the northwest quadrant of the center of SRH and in the large-value zone of CAPE gradient, corresponding to the east side of cold front and the dry line at surface as well as the top of the temperature ridge.
2023, 49(11):1299-1314.
DOI: 10.7519/j.issn.1000-0526.2023.081601
Abstract:
By using the object-oriented method of contiguous rain area (CRA), this paper investigates sources of the rainfall forecast error in deterministic forecasts by the ECMWF, and their changes with different rainfall levels and forecast periods when typhoons influenced China in 2019. Then, the correlations between typhoon track errors and displacement errors of rainfall events are analyzed and the performance improvements of rainfall forecasts calculated with track correction or CRA shifting are compared. Finally, forecast errors of rainfall probability distribution, radial and asymmetric rainfall distribution are verified and analyzed. The results are as follows. In general, the main forecast errors come from displacement error and shape error. Except for enormous amount of rainfall, track error is significantly correlated to the displacement error of CRA rainfall events. The improvement of rainfall forecasts made by track error correction is less than that made by CRA shifting correction. The shape of probability density distribution for rainfall forecasts resembles the observed one， but the forecasted rainfall intensity in typhoon core area is stronger than the observed one. Before and after typhoons’ making landfall or approaching the coast, the forecasted rainfall is much closer to typhoon center than the observed one, and it lags behind the observation. The asymmetric structure of forecasted rainfall is significantly weaker than the observed one.
By using the object-oriented method of contiguous rain area (CRA), this paper investigates sources of the rainfall forecast error in deterministic forecasts by the ECMWF, and their changes with different rainfall levels and forecast periods when typhoons influenced China in 2019. Then, the correlations between typhoon track errors and displacement errors of rainfall events are analyzed and the performance improvements of rainfall forecasts calculated with track correction or CRA shifting are compared. Finally, forecast errors of rainfall probability distribution, radial and asymmetric rainfall distribution are verified and analyzed. The results are as follows. In general, the main forecast errors come from displacement error and shape error. Except for enormous amount of rainfall, track error is significantly correlated to the displacement error of CRA rainfall events. The improvement of rainfall forecasts made by track error correction is less than that made by CRA shifting correction. The shape of probability density distribution for rainfall forecasts resembles the observed one， but the forecasted rainfall intensity in typhoon core area is stronger than the observed one. Before and after typhoons’ making landfall or approaching the coast, the forecasted rainfall is much closer to typhoon center than the observed one, and it lags behind the observation. The asymmetric structure of forecasted rainfall is significantly weaker than the observed one.
ZHANG Guilian
,
LI Yiping
,
JIANG Jing
,
CHANG Xin
,
HUO Zhili
,
ZHONG Xia
,
GUO Bingyao
,
JIA Kehan
2023, 49(11):1315-1327.
DOI: 10.7519/j.issn.1000-0526.2023.083001
Abstract:
In Taipusi Banner of Xilin Gol League, Inner Mongolia, a rarely-seen EF3 strong tornado occurred on 25 June 2021, resulting in 6 deaths and a large number of buildings’ damage and other losses. Based on meteorological observation data, automatic weather station data, CB-Doppler radar observation data of Zhangbei, Hebei Province, FY-4 satellite data and NCEF FNL (1°× 1°) 6 h reanalysis data, this paper comprehensively analyzes the process of the strong tornado. The results show that this tornado occurred in the background of unstable stratification environment of the forward-tilted trough. The strong conditional instability in the middle and low troposphere (the vertical temperature lapse rate at 850 hPa and 500 hPa was about 7.7 ℃·km-1), abundant water vapor in the lower layers, medium-strength convective available potential energy, and strong 0-6 km vertical wind shear provided favorable environmental conditions for supercell storms and tornadoes. In addition, the 0-1 km vertical wind shear was 8 m·s-1, and the lifting condensation height was 1.0 km, which provided relatively favorable environmental conditions for the occurrence of supercell storms and tornadoes. The convergence line accompanying the ground dry line triggered the parent storm that produced the tornado, and then evolved into the supercell. The radar reflectivity factor showed the characteristics of a typical hook echo, the inflow gap of warm and wet air at low level, the weak echo region at low level, the overhang echo at middle and high level, and the moderate-strength mesocyclone, etc. In the process of the formation and extinction of the tornado, three supercell storms formed successively, and all of them appeared in the isolated convective storm form. The tornado occurred at the top of one of the supercells, which was the junction of the front updraft and the rear downdraft. The possible start time and path of tornado based on the evolution of mesocyclone intensity analyzed by radar are in good agreement with the time of field investigation. Except for the strong tornado, this series of supercells also produced large hail and linear convection gale (thunderstorm gale), the strong echo center was significantly tilted from low to high, and the maximum reflectivity factor was as high as 65 dBz. In addition to the moderate-strength mesoclones, there was also obvious mid-level radial convergence in the diagram of radial velocity. At the time of supercell storm formation, the vertical integrated liquid water content (VIL) was as high as 73 kg·m-2, the VIL density was 4-5 g·m-3. These radar echo characteristics indicate the existence of large-sized hail, while the mid-level radial convergence was the radar echo characteristic of thunderstorm gale.
In Taipusi Banner of Xilin Gol League, Inner Mongolia, a rarely-seen EF3 strong tornado occurred on 25 June 2021, resulting in 6 deaths and a large number of buildings’ damage and other losses. Based on meteorological observation data, automatic weather station data, CB-Doppler radar observation data of Zhangbei, Hebei Province, FY-4 satellite data and NCEF FNL (1°× 1°) 6 h reanalysis data, this paper comprehensively analyzes the process of the strong tornado. The results show that this tornado occurred in the background of unstable stratification environment of the forward-tilted trough. The strong conditional instability in the middle and low troposphere (the vertical temperature lapse rate at 850 hPa and 500 hPa was about 7.7 ℃·km-1), abundant water vapor in the lower layers, medium-strength convective available potential energy, and strong 0-6 km vertical wind shear provided favorable environmental conditions for supercell storms and tornadoes. In addition, the 0-1 km vertical wind shear was 8 m·s-1, and the lifting condensation height was 1.0 km, which provided relatively favorable environmental conditions for the occurrence of supercell storms and tornadoes. The convergence line accompanying the ground dry line triggered the parent storm that produced the tornado, and then evolved into the supercell. The radar reflectivity factor showed the characteristics of a typical hook echo, the inflow gap of warm and wet air at low level, the weak echo region at low level, the overhang echo at middle and high level, and the moderate-strength mesocyclone, etc. In the process of the formation and extinction of the tornado, three supercell storms formed successively, and all of them appeared in the isolated convective storm form. The tornado occurred at the top of one of the supercells, which was the junction of the front updraft and the rear downdraft. The possible start time and path of tornado based on the evolution of mesocyclone intensity analyzed by radar are in good agreement with the time of field investigation. Except for the strong tornado, this series of supercells also produced large hail and linear convection gale (thunderstorm gale), the strong echo center was significantly tilted from low to high, and the maximum reflectivity factor was as high as 65 dBz. In addition to the moderate-strength mesoclones, there was also obvious mid-level radial convergence in the diagram of radial velocity. At the time of supercell storm formation, the vertical integrated liquid water content (VIL) was as high as 73 kg·m-2, the VIL density was 4-5 g·m-3. These radar echo characteristics indicate the existence of large-sized hail, while the mid-level radial convergence was the radar echo characteristic of thunderstorm gale.
HOU Shumei
,
ZHU Xiaoqing
,
SHI Qian
,
TANG Qiaoling
,
MENG Xiangui
,
LIU Chang
,
GAO Rongzhen
,
DIAO Xiuguang
2023, 49(11):1328-1342.
DOI: 10.7519/j.issn.1000-0526.2023.053101
Abstract:
A large-scale extremely severe convective weather named “5·17” severe convection occurred in Shandong Province on 17 May 2020, and the hail coverage was the largest in the resent 10 years. The convective storms were highly organized. The regional supercell clusters and a strong squall line over 500 km in length caused this extremely severe convection. Based on ERA5 reanalysis data, automatic weather station data and Doppler weather radar data, the ambient conditions of this extremely severe convective weather are analyzed. The results show as follows. The cold vortex was located in the key area which was most conducive to the Shandong severe convection. The large-scale weather system forcing was strong, and the unusually strong cold air in the middle troposphere moved southward impacting the previously abnormally warm Shandong Province and resulting in the “5·17” extremely severe convection weather. The anomaly of weather system is more representative of the intensity of dynamic and thermal forcing, and when anomaly level is above 2σ, the extremely severe convection would be caused. When the intensity of the cold vortex weakened during its southward moving, accompanied by increasing anomaly, it may still cause extremely severe convective weather in its southeast quadrant. The strong deep vertical wind shear was conducive to storms organization and development. The long axis of the squall line orientated the same direction as the 0-6 km vertical wind shear vector. The area where new cells were generated, developed and merged was located in the front of the large value center of the wind vector difference. The low-level warm and moist advection continuously transported warm and humid air to Shandong, which was the mechanism of CAPE reconstruction and the main energy source for the long-term maintenance of supercell group and long squall line.
A large-scale extremely severe convective weather named “5·17” severe convection occurred in Shandong Province on 17 May 2020, and the hail coverage was the largest in the resent 10 years. The convective storms were highly organized. The regional supercell clusters and a strong squall line over 500 km in length caused this extremely severe convection. Based on ERA5 reanalysis data, automatic weather station data and Doppler weather radar data, the ambient conditions of this extremely severe convective weather are analyzed. The results show as follows. The cold vortex was located in the key area which was most conducive to the Shandong severe convection. The large-scale weather system forcing was strong, and the unusually strong cold air in the middle troposphere moved southward impacting the previously abnormally warm Shandong Province and resulting in the “5·17” extremely severe convection weather. The anomaly of weather system is more representative of the intensity of dynamic and thermal forcing, and when anomaly level is above 2σ, the extremely severe convection would be caused. When the intensity of the cold vortex weakened during its southward moving, accompanied by increasing anomaly, it may still cause extremely severe convective weather in its southeast quadrant. The strong deep vertical wind shear was conducive to storms organization and development. The long axis of the squall line orientated the same direction as the 0-6 km vertical wind shear vector. The area where new cells were generated, developed and merged was located in the front of the large value center of the wind vector difference. The low-level warm and moist advection continuously transported warm and humid air to Shandong, which was the mechanism of CAPE reconstruction and the main energy source for the long-term maintenance of supercell group and long squall line.
2023, 49(11):1343-1358.
DOI: 10.7519/j.issn.1000-0526.2022.122601
Abstract:
To promote the application level of hydrometeor classification for Chinese Doppler polarimetric radar, based on the hydrometeor classification algorithm (HCA) developed by the National Severe Storm Laboratory (NSSL) of the United States, we design an optimum algorithm, named HCA-Opt, by adding the amendatory identification for the hydrometeor in hail and three-body scatter area, using the temperature of the numerical weather model analysis field to detect the location of the melting layer, and integrating restricted condition of vertical distribution for all hydrometeors. HCA-Opt is utilized to analyze the distribution characteristics of hydrometeor during a hailstorm cloud weather in Zhangqiu of Jinan City on 9 July 2021, and the location of the hail and the hydrometeor classification result are verified. The conclusions are as follows. The type of hydrometeor wrongly recognized as ground clutter by the HCA in the hail and the three-body scatter region can be correctly identified by the HCA-Opt. HCA-Opt can use the temperature from model analysis field to accurately identify the height of melting layer, solving the defect that the melting layer could not be detected by the algorithm in severe convective weather in HCA. Compared to HCA, the vertical distribution of hydrometeor identified by HCA-Opt is more reasonable. Besides, the classification result retrieved from the HCA-Opt can better describe the spatial distribution of hydrometeor at newborn and hailfalling stages of hailstorm, and initially reflect the characteristics of phase transformation at different heights. Through the verification, the reliability of the moderate (light) rain and graupel identified by the HCA-Opt is the highest, while that of the crystal and wet snow is lower, and easy to be mixed with the dry snow. Overall, the HCA-Opt can improve the skill of hydrometeor identification to certain extent, provide indicative information for warning and detecting the hailfalling area and have a good operational application prospect.
To promote the application level of hydrometeor classification for Chinese Doppler polarimetric radar, based on the hydrometeor classification algorithm (HCA) developed by the National Severe Storm Laboratory (NSSL) of the United States, we design an optimum algorithm, named HCA-Opt, by adding the amendatory identification for the hydrometeor in hail and three-body scatter area, using the temperature of the numerical weather model analysis field to detect the location of the melting layer, and integrating restricted condition of vertical distribution for all hydrometeors. HCA-Opt is utilized to analyze the distribution characteristics of hydrometeor during a hailstorm cloud weather in Zhangqiu of Jinan City on 9 July 2021, and the location of the hail and the hydrometeor classification result are verified. The conclusions are as follows. The type of hydrometeor wrongly recognized as ground clutter by the HCA in the hail and the three-body scatter region can be correctly identified by the HCA-Opt. HCA-Opt can use the temperature from model analysis field to accurately identify the height of melting layer, solving the defect that the melting layer could not be detected by the algorithm in severe convective weather in HCA. Compared to HCA, the vertical distribution of hydrometeor identified by HCA-Opt is more reasonable. Besides, the classification result retrieved from the HCA-Opt can better describe the spatial distribution of hydrometeor at newborn and hailfalling stages of hailstorm, and initially reflect the characteristics of phase transformation at different heights. Through the verification, the reliability of the moderate (light) rain and graupel identified by the HCA-Opt is the highest, while that of the crystal and wet snow is lower, and easy to be mixed with the dry snow. Overall, the HCA-Opt can improve the skill of hydrometeor identification to certain extent, provide indicative information for warning and detecting the hailfalling area and have a good operational application prospect.
2023, 49(11):1359-1370.
DOI: 10.7519/j.issn.1000-0526.2023.052401
Abstract:
PM2.5 and O3 which interact with each other have become the most important pollutants in the cities of Fenwei Plain. The pollution often occurs simultaneously in warm seasons and is closely related to meteorological conditions. Based on the daily PM2.5 and O3 concentration data, surface meteorological observation data and ERA5 high-altitude reanalysis data of 12 cities in the Fenwei Plain from 2015 to 2021, the spatio-temporal characteristics of PM2.5 and O3 in the Fenwei Plain, as well as the relationship between PM2.5 and O3 when compound pollution occurs are analyzed. Besides, the impact of local meteorological conditions and synoptic situation on compound pollution is also studied. The results show that the average annual PM2.5 and MDA8 O3 (maximum daily 8 h average ozone) concentrations in the Fenwei Plain began to decline continuously in 2017 and 2018, respectively, and the number of compound pollution days also began to decrease continuously after 2019. Compound pollution mainly occurs in March to September, frequently seen in the cities of eastern Fenwei Plain, mostly in condition of high temperature and low humidity. Finally, the synoptic circulation situation of compound pollution is divided into four types by principal component analysis with the T-PCA algorithm, featured with the northwest or westerly air flow in high-altitude and the southerly wind or breeze in the low-level warm zone. These findings could provide some basis for controlling pollution in the Fenwei Plain and are of great significance for cooperative governance of PM2.5 and O3 pollution.
PM2.5 and O3 which interact with each other have become the most important pollutants in the cities of Fenwei Plain. The pollution often occurs simultaneously in warm seasons and is closely related to meteorological conditions. Based on the daily PM2.5 and O3 concentration data, surface meteorological observation data and ERA5 high-altitude reanalysis data of 12 cities in the Fenwei Plain from 2015 to 2021, the spatio-temporal characteristics of PM2.5 and O3 in the Fenwei Plain, as well as the relationship between PM2.5 and O3 when compound pollution occurs are analyzed. Besides, the impact of local meteorological conditions and synoptic situation on compound pollution is also studied. The results show that the average annual PM2.5 and MDA8 O3 (maximum daily 8 h average ozone) concentrations in the Fenwei Plain began to decline continuously in 2017 and 2018, respectively, and the number of compound pollution days also began to decrease continuously after 2019. Compound pollution mainly occurs in March to September, frequently seen in the cities of eastern Fenwei Plain, mostly in condition of high temperature and low humidity. Finally, the synoptic circulation situation of compound pollution is divided into four types by principal component analysis with the T-PCA algorithm, featured with the northwest or westerly air flow in high-altitude and the southerly wind or breeze in the low-level warm zone. These findings could provide some basis for controlling pollution in the Fenwei Plain and are of great significance for cooperative governance of PM2.5 and O3 pollution.
2023, 49(11):1371-1383.
DOI: 10.7519/j.issn.1000-0526.2023.051603
Abstract:
In order to improve the practical prediction ability of refined grid precipitation, the performance of ECMWF （EC）, CMA-MESO, SXWRF and SCMOC precipitation forecast products in Shaanxi Province during the rainy season of 2021 are compared and evaluated, and the correction effect of Kalman dynamic frequency matching method on different models is discussed. Then, for the shortcomings of this method, based on the optimal TS scoring threshold method and SCMOC’s judgment of weather process, the small-magnitude precipitation is revised for the second time. Finally, the heavy precipitation is revised by using the precipitation sub process modeling and the improved Kalman dynamic frequency matching method which is based on image similarity recognition technology. The results show that SCMOC has the highest accuracy of sunny and rainy forecast and the highest TS score of heavy precipitation, which are 81.60% and 0.30 respectively. The Kalman dynamic frequency matching method can significantly improve the accuracy of sunny and rainy forecast of EC, CMA-MESO and SXWRF precipitation forecast products, but the improvement effect of heavy rainfall forecast is unstable. The improvement ranges of the EC model sunny and rainy forecast accuracy and the TS score of rainstorm forecast are the largest, 6.35% and 6.99% respectively. This correction method is more suitable for EC model. Compared with the EC model modified by Kalman dynamic frequency matching method, the accuracy of sunny rain and light rain prediction of EC model after the second correction of sunny rain spaced elimination is improved by 0.51% and 0.64%, respectively. The correction of the precipitation sub process modeling can further improve the TS score of EC model heavy precipitation, which is 1.05% higher than the TS score of heavy precipitation without sub process correction. Other scoring indicators of heavy precipitation are also better. The improved Kalman dynamic frequency matching method can significantly further improve the TS score of EC precipitation of all magnitudes, especially the TS score of heavy precipitation, improved by 2.79%.
In order to improve the practical prediction ability of refined grid precipitation, the performance of ECMWF （EC）, CMA-MESO, SXWRF and SCMOC precipitation forecast products in Shaanxi Province during the rainy season of 2021 are compared and evaluated, and the correction effect of Kalman dynamic frequency matching method on different models is discussed. Then, for the shortcomings of this method, based on the optimal TS scoring threshold method and SCMOC’s judgment of weather process, the small-magnitude precipitation is revised for the second time. Finally, the heavy precipitation is revised by using the precipitation sub process modeling and the improved Kalman dynamic frequency matching method which is based on image similarity recognition technology. The results show that SCMOC has the highest accuracy of sunny and rainy forecast and the highest TS score of heavy precipitation, which are 81.60% and 0.30 respectively. The Kalman dynamic frequency matching method can significantly improve the accuracy of sunny and rainy forecast of EC, CMA-MESO and SXWRF precipitation forecast products, but the improvement effect of heavy rainfall forecast is unstable. The improvement ranges of the EC model sunny and rainy forecast accuracy and the TS score of rainstorm forecast are the largest, 6.35% and 6.99% respectively. This correction method is more suitable for EC model. Compared with the EC model modified by Kalman dynamic frequency matching method, the accuracy of sunny rain and light rain prediction of EC model after the second correction of sunny rain spaced elimination is improved by 0.51% and 0.64%, respectively. The correction of the precipitation sub process modeling can further improve the TS score of EC model heavy precipitation, which is 1.05% higher than the TS score of heavy precipitation without sub process correction. Other scoring indicators of heavy precipitation are also better. The improved Kalman dynamic frequency matching method can significantly further improve the TS score of EC precipitation of all magnitudes, especially the TS score of heavy precipitation, improved by 2.79%.
2023, 49(11):1384-1395.
DOI: 10.7519/j.issn.1000-0526.2023.051602
Abstract:
Based on the EAR5 reanalysis data in June from 1979 to 2016, the moist thermodynamic advection parameter, thermal helicity, divergence flux, moisture divergence flux and the thermodynamic wave-activity density are selected as five comprehensive factors. The probability prediction model of regional persistent rainstorm in Hunan is constructed by the means of nuclear density estimation and based on the optimal factor and weight combination which is established with the best TS score as the test standard. The results show that the average TS of independent samples from 2017 to 2019 reaches 29.9%, which is a positive skill relative to the European Centre for Medium-Range Weather Forecasts (ECMWF) fine grid forecast (with an average TS score of 22.4%). During the two regional persistent rainstorm operational experiments in the 2021 and 2022 flood seasons, the rainstorm forecast with a 24 h leadtime by the Hunan regional perisistent rainstorm probability prediction model is superior to the forecasts of ECMWF and CMA-GFS large-scale model as well as CMA-SH and CMA-GD regional mesoscale model. Therefore, the Hunan regional persistent rainstorm prbability prediction model has a strong ability to forecast the regional persistent rainstorm in Hunan.
Based on the EAR5 reanalysis data in June from 1979 to 2016, the moist thermodynamic advection parameter, thermal helicity, divergence flux, moisture divergence flux and the thermodynamic wave-activity density are selected as five comprehensive factors. The probability prediction model of regional persistent rainstorm in Hunan is constructed by the means of nuclear density estimation and based on the optimal factor and weight combination which is established with the best TS score as the test standard. The results show that the average TS of independent samples from 2017 to 2019 reaches 29.9%, which is a positive skill relative to the European Centre for Medium-Range Weather Forecasts (ECMWF) fine grid forecast (with an average TS score of 22.4%). During the two regional persistent rainstorm operational experiments in the 2021 and 2022 flood seasons, the rainstorm forecast with a 24 h leadtime by the Hunan regional perisistent rainstorm probability prediction model is superior to the forecasts of ECMWF and CMA-GFS large-scale model as well as CMA-SH and CMA-GD regional mesoscale model. Therefore, the Hunan regional persistent rainstorm prbability prediction model has a strong ability to forecast the regional persistent rainstorm in Hunan.
2023, 49(11):1396-1404.
DOI: 10.7519/j.issn.1000-0526.2023.030703
Abstract:
Sub-seasonal to seasonal (S2S) climate and runoff prediction is of great importance for active disaster reduction. The prediction models of runoff anomaly and extreme drought for the future 40 days are developed based on CMA-CPS v3 climate model by National Climate Center, China Meteorological Administration, and a hydrological model HBV. The performance of the models are evaluated with the indices of MSSS, ACC, AUC and BSS for hindcast, and verified for the runoff anomaly prediction over the Yellow River Basin in 2021. The results suggest that runoff mean prediction for the future 40 days is skillful, and the skill is higher in dry season than wet season. Moreover, the extreme drought prediction is skillful in later autumn (November) and the winter months (December, January and February). The direction of monthly runoff anomaly from May to October in 2021 are predicted correctly except in June and September, but the anomaly degrees are different from observation. Finally, the analysis of skill variation with lead time and seasons, and the skill difference between runoff and precipitation reveals that the skill of precipitation prediction by S2S climate model influences runoff skill, especially during wet season. However, there are also other factors than precipitation affecting the skill of runoff prediction.
Sub-seasonal to seasonal (S2S) climate and runoff prediction is of great importance for active disaster reduction. The prediction models of runoff anomaly and extreme drought for the future 40 days are developed based on CMA-CPS v3 climate model by National Climate Center, China Meteorological Administration, and a hydrological model HBV. The performance of the models are evaluated with the indices of MSSS, ACC, AUC and BSS for hindcast, and verified for the runoff anomaly prediction over the Yellow River Basin in 2021. The results suggest that runoff mean prediction for the future 40 days is skillful, and the skill is higher in dry season than wet season. Moreover, the extreme drought prediction is skillful in later autumn (November) and the winter months (December, January and February). The direction of monthly runoff anomaly from May to October in 2021 are predicted correctly except in June and September, but the anomaly degrees are different from observation. Finally, the analysis of skill variation with lead time and seasons, and the skill difference between runoff and precipitation reveals that the skill of precipitation prediction by S2S climate model influences runoff skill, especially during wet season. However, there are also other factors than precipitation affecting the skill of runoff prediction.
10 Diurnal Variation of Wet Season Precipitation at Different Altitudes of Cangshan Mountain in Dali
2023, 49(11):1405-1413.
DOI: 10.7519/j.issn.1000-0526.2023.060402
Abstract:
Based on the hourly precipitation data in the wet season during 2011-2020 from the gradient observation system between Cangshan Mountain and Erhai Lake of Dali National Climate Observatory, the diurnal variation characteristics of precipitation at the mountain top, hillside and dam area are analyzed. The results show that the diurnal variation of rainfall amount at the dam station presented one peak, while that at mountain side and hilltop stations presented two peaks. The diurnal variation of rainfall frequency at dam and hilltop stations displayed a single peak, while that at the hillside station was relatively stable. All hourly rainfall amount and rainfall frequency for a whole day basically increased with the rise of altitudes. The diurnal variation of rainfall intensity at hilltop station exhibited double peaks, while that the hillside and dam stations showed remarkable fluctuation with small values in the afternoon and large values over night. There were no significant differences in rainfall intensity from 14:00 BT to 17:00 BT among the three stations, but the rainfall intensities at the hillside and dam stations were obviously greater than that at the hilltop station during other periods. The rainfall amount with a duration of 2-16 h over night was a large value area, which maintained a longer duration with the rise of altitude. The rainfall amount with a duration of less than 6 h during the daytime was a large value area, and the occurrence of the large value was delayed with the increase of altitude. The rainfall frequencies at all the three stations had a large value area during the day (night) when the rainfall duration was less than 6 h, while that at the hilltop station only had a large value area at night when the duration was 7-18 h. The rainfall frequencies over night were greater than that during the day at the dam and hilltop stations, while there was little difference in the rainfall frequency during the day and night at the hillside station. The accumulated rainfall amount and frequency of long (medium and short) duration increased (decreased) with the increase of altitudes. The contribution of long duration rainfall amount (long duration rainfall frequency) to accumulated rainfall amount (accumulated rainfall frequency) at each station was the largest, but the contribution of short duration rainfall amount (medium duration rainfall frequency) was the least.
Based on the hourly precipitation data in the wet season during 2011-2020 from the gradient observation system between Cangshan Mountain and Erhai Lake of Dali National Climate Observatory, the diurnal variation characteristics of precipitation at the mountain top, hillside and dam area are analyzed. The results show that the diurnal variation of rainfall amount at the dam station presented one peak, while that at mountain side and hilltop stations presented two peaks. The diurnal variation of rainfall frequency at dam and hilltop stations displayed a single peak, while that at the hillside station was relatively stable. All hourly rainfall amount and rainfall frequency for a whole day basically increased with the rise of altitudes. The diurnal variation of rainfall intensity at hilltop station exhibited double peaks, while that the hillside and dam stations showed remarkable fluctuation with small values in the afternoon and large values over night. There were no significant differences in rainfall intensity from 14:00 BT to 17:00 BT among the three stations, but the rainfall intensities at the hillside and dam stations were obviously greater than that at the hilltop station during other periods. The rainfall amount with a duration of 2-16 h over night was a large value area, which maintained a longer duration with the rise of altitude. The rainfall amount with a duration of less than 6 h during the daytime was a large value area, and the occurrence of the large value was delayed with the increase of altitude. The rainfall frequencies at all the three stations had a large value area during the day (night) when the rainfall duration was less than 6 h, while that at the hilltop station only had a large value area at night when the duration was 7-18 h. The rainfall frequencies over night were greater than that during the day at the dam and hilltop stations, while there was little difference in the rainfall frequency during the day and night at the hillside station. The accumulated rainfall amount and frequency of long (medium and short) duration increased (decreased) with the increase of altitudes. The contribution of long duration rainfall amount (long duration rainfall frequency) to accumulated rainfall amount (accumulated rainfall frequency) at each station was the largest, but the contribution of short duration rainfall amount (medium duration rainfall frequency) was the least.
2023, 49(11):1414-1420.
DOI: 10.7519/j.issn.1000-0526.2023.092701
Abstract:
The main characteristics of the general atmospheric circulation in August 2023 are as follows. The intensity of the polar vortex was slightly stronger in the Northern Hemisphere. The circulation over the mid-to-high latitudes of Asia at 500 hPa showed “two troughs” and “one ridge”. The high-altitude trough affecting the northeastern and northern of China is stronger. The mean location of the ridge line in the western part of the Western Pacific subtropical high was more southward compared to that in normal years. In August, the monthly average temperature was 21.9℃, 0.8℃ higher than in the same period of normal years (21.1℃). The monthly average precipitation was 110.9 mm, which is 3.5% higher than normal (107.1 mm). During this month, the high temperature days were more than normal, with regional high temperature processes appearing successively in China. Meteorological drought continued to in the northwest and northeast of China. Six torrential rain events were reported in China. In August, six typhoons were active in the South China Sea and the Western North Pacific. The generation number of tropical cyclones was higher than that in the previous years, but the number of landfall typhoons was lower than usual. Severe convective weather was frequent and local disasters were severe. In addition, one tornado hit the Dafeng District, Yancheng of Jiangsu Province.
The main characteristics of the general atmospheric circulation in August 2023 are as follows. The intensity of the polar vortex was slightly stronger in the Northern Hemisphere. The circulation over the mid-to-high latitudes of Asia at 500 hPa showed “two troughs” and “one ridge”. The high-altitude trough affecting the northeastern and northern of China is stronger. The mean location of the ridge line in the western part of the Western Pacific subtropical high was more southward compared to that in normal years. In August, the monthly average temperature was 21.9℃, 0.8℃ higher than in the same period of normal years (21.1℃). The monthly average precipitation was 110.9 mm, which is 3.5% higher than normal (107.1 mm). During this month, the high temperature days were more than normal, with regional high temperature processes appearing successively in China. Meteorological drought continued to in the northwest and northeast of China. Six torrential rain events were reported in China. In August, six typhoons were active in the South China Sea and the Western North Pacific. The generation number of tropical cyclones was higher than that in the previous years, but the number of landfall typhoons was lower than usual. Severe convective weather was frequent and local disasters were severe. In addition, one tornado hit the Dafeng District, Yancheng of Jiangsu Province.
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ISSN:1000-0526 CN:11-2282/P