ISSN 1000-0526
CN 11-2282/P

Volume 47,Issue 11,2021 Table of Contents

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  • 1  Research Advances in the Convective Initiation Mechanisms
    CUI Xinyan CHEN Mingxuan QIN Rui HAN Lei
    2021, 47(11):1297-1318. DOI: 10.7519/j.issn.1000-0526.2021.11.001
    [Abstract](107) [HTML](193) [PDF 885.18 K](655)
    Convective initiation (CI) means the beginning of severe convective weather activities. The study of CI mechanisms is a critical and difficult problem of mesoscale meteorology, and is critical to improve the scientific knowledge of the evolution of local sudden severe convection and the nowcasting of severe convective weather. In this paper, the research results of surfacebased CI mechanisms and elevated CI mechanisms at home and abroad are summarized. Surfacebased CIs are usually triggered by boundary layer convergence lines. In addition, temperature and humidity disturbance, instability, misocyclone, vertical shear, topography and other factors also have a certain impact on the time and position of surfacebased CIs. Atmospheric instability is sensitive to the change of local temperature, especially humidity, and has a great influence on CI. The interaction of ambient vertical wind shear and thermonamic field of boundary, the feedback between vertical velocity and vorticity of misocyclone, and the thermodynamic effects caused by topography all can influence the surfacebased CIs. Most elevated CIs are related to the bores, gravity waves and lowlevel jets. The lowlevel jets transport water vapor upward and northward, reducing the stability of the environment, and the shear associated with the lowlevel jets can also produce updraft, which is important for nocturnal elevated CI. Convectively generated gravity waves and bores are conducive to the elevated CI, which can lift the lower atmosphere and reduce the stability. Elevated convergence and weak but persistent mesoscale lifting also help to increase the possibility of elevated CI. This article can be used for reference in the CIreleated research and the prediction and early warning of localized sudden severe convection.
    2  Advances in Tornado Research in China
    ZHENG Yongguang LIU Feifan ZHANG Hengjin
    2021, 47(11):1319-1335. DOI: 10.7519/j.issn.1000-0526.2021.11.002
    [Abstract](92) [HTML](1083) [PDF 3.62 M](560)
    Several intense tornadoes (≥EF3) in China in recent years resulted in heavy casualties and serious economic losses. Tornado has a very small scale, and its occurrence frequency in China is extremely low. At present, China still does not have the operational capability of forecasting tornadoes. However, with the development of observation networks of new-generation weather radar and surface automatic weather stations, damage survey and numerical weather prediction model, remarkable progress in tornado research in China has been made. The spatio-temporal and climatological characteristics, favorable synoptic backgrounds and environmental conditions for tornado in China have been understood more comprehensively, and it has also been found that the favorable environmental conditions for tornado in different synoptic backgrounds are somewhat different. The damage survey process and analysis technology of tornado disaster have been developed. The damage surveys and analyses of several intense tornadoes, such as the 2016 Funing, Jiangsu Province EF4 tornado, have been made in detail, which provide indispensable data for disaster prevention and mitigation. More understandings of meso- and micro-scale characteristics of tor-nadic convective storms have been got, including the findings of the storm cold pool with appropriate intensity, the bottom of the mesocyclone generally lower than the height of 1 km, the positive intensity correlation between tornado and its parent mesocyclone, slantwise mesocyclone, tornadic debris signature, descending reflectivity core, and multi-vortex structure of some tornadoes. Two tornadoes have successfully been ideally simulated using a fine-resolution cloud model, and the tornado-scale vortices in the convective eye wall of 2005 Typhoon Matsa and the multiple vortices of the 2016 Funing Tornado have been successfully simulated by the WRF (Weather Research and Forecasting) model. In future, we still need to further develop tornado detection technology, and to study fine surface meteorological element distribution and structure features, tornado vortex and lightning activity of tornadic convective storms. What’s more, researches on the development mechanisms of tornado are more needed through finer-resolution observation data and higher-resolution numerical weather simulation so as to provide more scientific foundations for promoting the tornado forecasting and warning capability in China.
    3  Uncertainty Analysis of Heavy Rain Belt Forecast During the 2020 Meiyu Period
    SU Xiang KANG Zhiming ZHUANG Xiaoran CHEN Shengjie
    2021, 47(11):1336-1346. DOI: 10.7519/j.issn.1000-0526.2021.11.003
    [Abstract](83) [HTML](85) [PDF 4.42 M](465)
    For the uncertainty of heavy rain belt forecast of the ECMWF model in the Yangtze-Huaihe River Basin in China during the extremely long Meiyu period in 2020, 10 typical long and narrow heavy rain belts are selected to analyze the location forecast bias, forecast stability and continuity of forecast bias using the method for object-based diagnostic evaluation (MODE). Ensemble sensitivity analysis (ESA) is also used to analyze the key synoptic systems which caused the typical forecast bias of the heavy rain belts. The results show that forecast uncertainty of the eastern part of rain belts is generally higher than that of the western part, especially during the medium range in which forecast uncertainty further strengthens. During the short range, both the western and eastern parts of rain belts have obvious northward systematic forecast bias. The forecast of the western part of rain belts has relatively lower missing rate, better stabil-ity and continuity than the eastern part. During the medium range, the forecast error of the eastern part of rain belts grows obviously and the average latitude variation of the eastern part is also higher than that of the western part. The results of ESA indicate that the northward forecast bias of the eastern part of rain belts is caused by the joint effect of the 500 hPa high-level trough, the subtropical high, the 850 hPa low-level jet, the shear line and the unrealistic positive feedback between them and precipitation latent heat releasing, of which the development and strengthen of high-level trough and low-level jet is one of the background characteristics of the northward forecast bias of the eastern part of rain belts.
    4  Analysis of Abnormal Characteristics and Causes of Meiyu over the Yangtze-Huaihe River Basin in 2019
    NIU Ruoyun ZHOU Bing
    2021, 47(11):1347-1358. DOI: 10.7519/j.issn.1000-0526.2021.11.004
    [Abstract](73) [HTML](47) [PDF 4.57 M](463)
    Based on the Meiyu monitoring data, precipitation observation, NCEP reanalysis data and sea surface temperature data, the abnormal characteristics of Meiyu over the Yangtze-Huaihe River Basin (YHRB) in 2019 and its causes of large-scale circulation are analyzed. The results are as follows. The abnormal characteristics of the 2019 Meiyu obviously showed that the Meiyu onset date was later than normal with a shorter duration. The Meiyu rain was generally less than normal, presenting a distribution pattern of the more in the south and the less in the north of the Yangtze River over YHRB. Since 1951, the 2019 Meiyu belt stagnated the longest time in the south of the Yangtze River. Among the three subareas, the Meiyu period in the middle and lower reaches of Yangtze River was almost simultaneous with that in the south of Yangtze River, and the Yangtze-Huaihe River Subarea did not receive Meiyu obviously. Due to the periodical enhancement of the cold air from 8 to 15 June, the seasonal northward of East Asian summer monsoon was impeded and delayed, leading to the late conversion of the circulation pattern in East Asian from winter to early summer and also the late onset of Meiyu over YHRB. It can be regarded as the precursory signals of Meiyu onset date later over YHRB in 2019 that the sea surface temperature in Indian Ocean was warmer than normal in May-June and the reverse date of meridional temperature gradient of the middle-upper troposphere, was later over 60°-80°E of South Asia. Compared with climate mean state, the eastern ridge of South Asian high and East Asia westerly jet were southward in upper air, the circulation meridionality in the middle-high latitude in Eurasia was stronger and the western ridge of Northwest Pacific subtropical high was southward and the geopotential height east of Australia was higher at middle level, the strength of the low-level East Asia summer monsoon was weaker and the northernmost of the monsoon was southward. As a result of the combined influence of the above-mentioned abnormal characteristics, the south of the Yangtze River over YHRB was under the control of the strong divergence at high level and the strong meridional gradient convergence of vapor flux at low level, which is greatly conducive to the development of vertical upward movement and the occurrence of heavy rainfall, contributing to the distribution of the Meiyu precipitation in 2019 with the more in the south and the less in the north of the Yangtze River over YHRB.
    5  Numerical Simulation of a Meiyu Frontal Precipitation Process with the Global High-Resolution Non-Hydrostatic Model GRAPES_YY
    JIAO Han ZHAO Yifan CHANG Fei PENG Xindong
    2021, 47(11):1359-1368. DOI: 10.7519/j.issn.1000-0526.2021.11.005
    [Abstract](82) [HTML](51) [PDF 7.74 M](370)
    For global high-resolution numerical weather prediction, based on the GRAPES developed by China Meteorological Administration, an updated version, the GRAPES_YY, has been developed on the Yin-Yang grid, which is now available at 0.1°×0.1° resolution. The “violent Meiyu” process that took place in the middle and lower reaches of Yangtze River during 6-8 July 2020 is selected as the object of simulation. A case of Meiyu severe rainfall in south of Anhui Province is analyzed by using the 0.1°×0.1° model outputs , FNL 0.25°×0.25° reanalysis data and hourly rainfall observation and weather radar reflectivity. Results show that the severe rainfall was a direct result of eastward moving mesoscale convective systems under the joint action of upper trough, low vortex shear lines and low-level jets. The simulated position and intensity of the large-scale systems is comparable with the FNL 0.25°×0.25° reanalysis results. The orientation and position of the 24 h precipitation are well described in the simulation although distinction on severe-rainfall intensity and weak-rainfall region is found. Persistent severe rainfall depends on the low-level vapor convergence and smooth vapor transport. The severe rainfall is in accordance with the large θse region at 500 hPa, showing up as convectively neutral zone. Except the instable below 850 hPa in frontal zone, convectively instable layer appears at both south and north of the front.
    6  Study on the Maintenance Mechanism of a Quasi-Stationary Mesoscale Convective System
    WANG Xiaohua ZHENG Yuanyuan ZHANG Shengxi MU Ruiqi LYU Runqing
    2021, 47(11):1369-1379. DOI: 10.7519/j.issn.1000-0526.2021.11.006
    [Abstract](81) [HTML](60) [PDF 8.55 M](460)
    In the early morning of 7 July 2016, due to the influence of mesoscale convective system (MCS), a sudden local rainstorm occurred in Nanjing. Development of the MCS including convection triggering, quasi-stationary backward propagation, heavy rainfall supercell and cold pool driving lasted for nearly 8 hours, resulting in serious waterlogging. The synoptic background and MCS evolution characteristics of this heavy rainfall process are analyzed in detail by using multi-source datasets from Doppler radar, automatic stations, wind profile, China regional reanalysis (CNRR), Jiangsu merged assimilation analysis and so forth. The results show that a mesoscale forward-tilting trough induced low pressure at the surface, strengthening convergence, forming an uplifting movement and triggering linear convective storms. The warm and humid southwesterly flow between 3 km and 6 km was significantly enhanced. The favorable configuration of the uplifted left side of meso-β scale secondary circulation, the meso-γ scale low-level low pressure and the southwesterly flow made the MCS over Nanjing exhibit a quasi-stationary feature of backward propagation, eventually leading to a heavy precipitation supercell in eight consecutive radar volume scans. The drag effect of heavy precipitation formed a downdraft, which led to the outflow near the surface and stimulated a new convection on the south side, causing the MCS to move slowly to the south. As the downdraft strengthened in the MCS, a cold pool appeared on the ground. The strong divergence accelerated the movement of the MCS, and then the heavy precipitation process ended.
    7  Comparative Analysis of Two Severe Convective Weather Events Under the Influence of Upper-Tropospheric Cold Vortex in Easterlies
    SHEN Hangfeng LIN Hongwei LOU Xiaofen CUI Jie ZHANG Honglei
    2021, 47(11):1380-1390. DOI: 10.7519/j.issn.1000-0526.2021.11.007
    [Abstract](89) [HTML](92) [PDF 9.15 M](505)
    The comparative analysis of the severe convective weather processes on 29 July 2015 and 14 July 2018 is carried out based on conventional observation data, automatic weather station data, NCEP/NCAR GFS analysis data, Doppler radar data and satellite data. The results demonstrate that there was a cold vortex in easterlies at 200 hPa, an easterly wave at 500 hPa but subtropical high at 850 hPa in both cases, which means the weather events were under the influence of upper-tropospheric cold vortex in easterlies. The vortex in easterlies with shallow depth, high relative humility and low temperature was significantly different from typhoon or easterly wave. Furthermore, the cold vortex could not bring gale and rainstorm by itself. However, it inccurred severe convection with thunderstorm, heavy rain and hail triggered by surface mesoscale convergence line which was caused by east and west winds on 29 July 2015. On the contrary, there was no occurrence of convection due to the lack of trigger mechanism on 14 July 2018. The divergent rotation characteristics in front of the cold vortex moving could enhance the ascending motion so that it made the convection severely, which was significant different from the weather systems under westerlies. Therefore, it should be paid special attention to in the early-warning operation.
    8  Observation Characteristics of FY-4A Lightning Mapping Imager During a Severe Rainfall
    ZHANG Pingping LIU Wenting ZHANG Cuihong MING Shaohui DONG Liangpeng
    2021, 47(11):1391-1401. DOI: 10.7519/j.issn.1000-0526.2021.11.008
    [Abstract](80) [HTML](142) [PDF 13.44 M](783)
    The FY-4 lightning mapping imager (LMI) can continuously observe the lightning activity, having great application potential in severe convective weather monitoring and warning. Taking the heavy rainfall process on 25 May 2019 as an example, this paper studies the observation characteristics of the convective system in different properties and evolution stages with the data of FY-4 lightning imager, ADTD (advanced time of arrival and direction) system, FY-4 infrared cloud image, radar and other conventional observation data. The study shows that in the early stage of the rapid development of convection, LMI lightning observation is ahead of ADTD lightning observation, and this advance feature lasts longer in the frontal precipitation stage. When the LMI lightning observation is located in front of the current convective cloud cluster movement at the same time, there will be obvious cloud top temperature variability in the LMI lightning distribution area in the next hour, and cumulus has a development trend. When the strongest echo on the vertical section of radar reflectivity appears to move forward, the LMI lightning observation often appears in front of the moving direction of the convective system observed by radar. At this time, the LMI lightning observation has a good early indication for the development and evolution of the convective system. When the strongest echo on the vertical section of radar reflectivity shows up quasi vertical structure, the LMI lightning observation often coincides with the radar observation of the convective system. At this time, the LMI lightning observation has a weak indication for the development and evolution of the convective system.
    9  Radar Echo Characteristics of Short-Time Severe Precipitation in Xinjiang
    ZHUANG Xiaocui ZHANG Yunhui ZHOU Xueying YANG Lianmei ZHU Xiaomei HUANG Yan LUO Ji
    2021, 47(11):1402-1415. DOI: 10.7519/j.issn.1000-0526.2021.11.009
    [Abstract](94) [HTML](507) [PDF 1.53 M](541)
    Using the data of 8 Doppler weather radars in Xinjiang, this paper statistically analyzes the main radar echo parameters of 229 short-time severe precipitations without hail in the warm season from 2010 to 2018 in the effective detection range, and compares the results with those in central and eastern parts of China. The results show that the convective storms affecting Xinjiang’s short-time severe precipitation mainly include three types: merged-enhanced, train-effect, and locally developing. The merged-enhanced type is the most (45%), and the train-effect type is the least (20%). Because of the topography of the Tianshan Mountains, it mainly occurs on the northern slope of the Tianshan Mountains. Besides, the main echo parameter thresholds of various types of radars in various regions are summarized. In general, the short-time severe precipitation threshold in southern Xinjiang is smaller than that in northern Xinjiang, the largest in the Ili Valley, and the smallest in the Aksu area. The short-time severe precipitation in the Ili Valley is dominated by low-centroid echo. The maximum echo intensity of the short-time rainstorm is more than 50 dBz in northern Xinjiang and northern Bazhou, more than 45 dBz and 40 dBz in the western part of southern Xinjiang and Aksu Region, respectively. In most 〖JP2〗cases, strong convergence can be found on the radial velocity chart, but the western part of southern Xinjiang and the northern slope of Tianshan Mountain have more strong convergence due to the influence of special topography. Short-time severe precipitation caused by supercells occurs relatively frequently in Aksu Region, not often seen in other regions. In Xinjiang, the probability of short-time severe precipitation accompanied by hail is small. The maximum echo intensity threshold of short-time severe precipitation and rainstorm in Xinjiang is generally higher than that in central and eastern China.
    10  Analysis of Variation Characteristics of Floods in South Asia and Southeast Asia During 1985-2019 Using Different Disaster Databases
    WANG Yi LIU Shuang ZHOU Qingliang BAO Hongjun YIN Yizhou YANG Kun
    2021, 47(11):1416-1425. DOI: 10.7519/j.issn.1000-0526.2021.11.010
    [Abstract](81) [HTML](327) [PDF 1.14 M](366)
    Based on Emergency Events Database (EM-DAT) and Dartmouth Flood Observatory disaster datasets, this study compares the variation characteristics of frequency, magnitude and fatalities of floods in South Asia and Southeast Asia during 1985-2019. The trends of tropical cyclone (TC)-associated floods are also discussed. The results show that frequency of floods in Southeast Asia is about 15% more than that in South Asia for recent 35 years. Among all floods, the frequency of TC-associated floods in Southeast Asia is around 4 times more than that in South Asia. The TC-associated floods account for test of averaged floods by two databases indicates that both floods in South Asia and Southeast Asia have significantly increased in occurrence frequency over recent 35 years but the flood-induced fatalities per flood event have decreased significantly. On average, the magnitude of floods in Southeast Asia is smaller than that in South Asia, but there is a significant increasing trend in the magnitude of floods in Southeast Asia during recent 35 years. In addition, both economic losses of floods in South Asia and Southeast Asia based on EM-DAT data exhibit obvious increasing trend over the past 35 years. approximately 20% of all floods in Southeast Asia. Monthly distribution shows that floods in South Asia concentrate in June-August, exhibiting a unimodal pattern while TC-associated floods in South Asia present a bimodal distribution. Floods in Southeast Asia are evenly distributed throughout the year. The trend
    11  Analysis of the August 2021 Atmospheric Circulation and Weather
    ZHOU Guanbo GAO Shuanzhu
    2021, 47(11):1426-1432. DOI: 10.7519/j.issn.1000-0526.2021.11.011
    [Abstract](84) [HTML](233) [PDF 5.81 M](527)
    The main characteristics of the general atmospheric circulation in August 2021 are as follows. The polar vortex of Northern Hemisphere presented a single pattern. In the midhigh latitudes of Asia, the circulation presented a twotrough and oneridge pattern. The subtropical high lay westward obviously. Meanwhile, the monthly mean precipitation was 118.3 mm, which is more than its normal value (105.2 mm) by 12.0%. The monthly mean temperature was 21.1℃, 0.3℃ higher than its climatological mean (20.8℃). Ten regional torrential rainfall events happened in August, and one of them was caused by tropical cyclone. In August, four tropical cyclones were active over the northwestern Pacific Ocean and the South China Sea, and Typhoon Lupit (2109) made landfall in Fujian Province and Guangdong Province of China. During this month, southern China suffered from heavy rains and floods, and drought continued over eastern areas of Northwest China. In addition, persistent hightemperature occurred in northwest of South China, southwest of Jiangnan and southeast of Sichuan Province. Many provinces experienced severe convections, and some areas suffered from serious disasters.

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