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Thermodynamics and Microphysical Characteristics of an Extreme Rainfall Event Under the Influence of a low-level jet over the South China Coast

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Journal of Tropical Meteorology 2023年第2期29卷 216-235页

作者：徐碧裕黎慧琦叶朗明刘显通饶晓娜肖辉徐加民林青蒲义良黄青兰 Jiangmen Meteorological Bureau JiangmenGuangdong 529030 China Guangzhou Institute of Tropical and Marine Meteorology China Meteorological AdministrationGuangzhou 510641 China China Meteorological Administration Tornado Key Laboratory Guangzhou 510641 China Xinhui Meteorological Bureau JiangmenGuangdong 529100 China Guangdong Meteorological Bureau Guangzhou 510080 China

In this paper,the data of Automatic Weather Stations(AWSs),ERA5 reanalysis,sounding,wind profile radar,and dual-polarization radar are used to study an extreme rainfall event in the south China Coast on 11 to 12 May 2022 from the aspects of thermodynamics and microphysical characteristics under the influence of low-level jets(LLJs).Results show that:(1)The extreme rainfall event can be divided into two stages:the first stage(S1)from 0000 to 0600 LST on May 12 and the second stage(S2)from 0700 to 1700 LST on the same day.During S1,the rainfall is mainly caused by the upper-level shortwave trough and the boundary layer jet(BLJ),characterized by strong upward motion on the windward side of mountains.In S2,the combined influence of the BLJ and synoptic-system-related low-level jet(SLLJ)increases the vertical wind shear and vertical vorticity,strengthening the rainstorm.In combination with the effect of topography,a warm and humid southwest flow continuously transports water vapor to farther north,resulting in a significant increase in rainfall over the study area(on the terrain’s windward slope).From S1 to S2,the altitude of a divergence center in the upper air decreases obviously.(2)The rainfalls in the two stages are both associated with the mesoscale convergence line(MCL)on the surface,and the wind field from the mesoscale outflow boundary(MOB)in S1 is in the same direction as the environmental winds.Due to a small area of convergence that is left behind the MOB,convection moves eastward quickly and causes a short duration of heavy rainfall.In S2,the convergence along the MOB is enhanced,which strengthens the rainfall and leads to strong outflows,further enhancing the surface convergence near the MOB and forming a positive feedback mechanism.It results in a slow motion of convection and a long duration of heavy rainfall.(3)In terms of microphysics,the center of a strong echo in S1 is higher than in S2.The warm-rain process of the oceanic type characterizes both stages,but the convective intensity in S2 is signific

关键词： low-level jet thermodynamics microphysics heavy rain south China coast

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Maintenance and Sudden Change of a Strong Elevated Ducting Event Associated with High Pressure and Marine low-level jet

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Journal of Meteorological Research 2020年第6期34卷 1287-1298页

作者： Zhichao LIANG Juli DING Jianfang FEI Xiaoping CHENG Xiaogang HUANG College of Meteorology and Oceanography National University of Defense TechnologyNanjing 211101 296746 Troops of PLA Korla 841000

Capture of a strong elevated ducting event,especially its maintenance and sudden change,is of great value to airborne radar to achieve its beyond-the-line-of-sight detection.However,the knowledge is not easily accessible over the open ocean and hence very rare.During the Air–Sea Interaction Survey(ASIS)over the western North Pacific(WNP)in May 2016,a strong elevated ducting event with a long-life period and sudden change in its evolution was observed.Measurements from the ASIS,images from the Himawari-8 satellite,reanalysis data from the ECMWF,and Weather Research and Forecasting(WRF)model,were used to analyze the maintenance and sudden change of this strong ducting event,together with the model performance on simulating it.The results showed that the maintenance of strong elevated ducts,with their tops ranging from 750 to 1050 m and average strength of approximately 38 M units,was caused by a strong dry air mass capping over the wet marine atmospheric boundary layer(MABL),together with the subsidence inversion associated with high pressure.The WRF model performs well in simulating them.However,a sudden increase in duct height with a slight decrease of strength was recorded by the subsequent GPS radiosonde,which was finally contributed to the mechanical turbulent inversion and hydrolapse associated with the marine low-level jet(MLLJ).The height of the maximum horizontal wind speed(Umh)of the MLLJ corresponds well with the bottom of the trapping layer.However,these jet-relevant ducts are generally weak and it is difficult to accurately simulate them by using the mesoscale numerical model,since the wind-shear produced eddies are too small to be properly parameterized.

关键词： atmospheric ducts elevated ducts marine atmospheric boundary layer(MABL) low-level jet numerical simulation

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Advances in low-level jet Research and Future Prospects

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Journal of Meteorological Research 2014年第1期28卷 57-75页

作者：刘鸿波何明洋王斌张庆红 LASG Institute of Atmospheric PhysicsChinese Academy of Sciences University of Chinese Academy of Sciences Laboratory for Climate and Ocean-Atmosphere Studies Department of Atmospheric and Oceanic SciencesSchool of PhysicsPeking University

The low-level jet （LLJ） is closely related to severe rainfall events, air pollution, wind energy utilization, aviation safety, sandstorms, forest fire, and other weather and climate phenomena. Therefore, it has attracted considerable attention since its discovery. Scientists have carried out many studies on LLJs and made significant achievements during the past five or six decades. This article summarizes and assesses the current knowledge on this subject, and focuses in particular on three aspects： 1） LLJ classification, definition, distribution, and structure; 2） LLJ formation and evolutionary mechanisms; and 3） relationships between LLJ and rainfall, as well as other interdisciplinary fields. After comparing the status of LLJ research at home （China） and abroad, we then discuss the shortcomings of LLJ research in China. We suggest that this includes： coarse definitions of the LLJ, lack of observations and inadequate quality control, few thorough explorations of LLJ characteristics and formation mechanisms, and limited studies in interdisciplinary fields. The future prospects for several LLJ research avenues are also speculated.

关键词： low-level jet structural and evolutionary mechanisms rainfall interdisciplinary research

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A Study of the Relationship between low-level jet and inversion Layer over an Agroforest Ecosystem in East China Plain

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Advances in Atmospheric Sciences 2000年第2期17卷 299-310页

作者：钟中王汉杰 Eco-Environmental Research Center in Atmospheric Boundary Layer P.O.Box 003 Naming 211101

The relationship between the super–low–level jet (LLJ) and inversion layer over an agroforest ecosystem on the Huang–Huai–Hai plain in the eastern China is studied by means of a time–independent K–closure model. It is found that the intensified inversion near the surface of a luxuriantly growing agroforest ecosystem leads to the formation and development of the LLJ, the more intense the inversion, the stronger is the LLJ. The critical value of inversion intensity index for the LLJ formation is 0.75°C/ 100 m, which relates to the necessary geostraphic wind velocity of 6.0 to 10 m / s at the top level of the model. The numerical calculations show that the roughness length of the underlying surface has considerable effects on the LLJ structure. Key words low?level jet - Temperature inversion - Agroforest ecosystem The project was supported by the National Natural Science Foundation of China (NSFC) (49975016).

关键词： low-level jet Temperature inversion Agroforest ecosystem

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low-level jet（LLJ） and western Iran heavy rain:case study Dec 1991

Low-level Jet（LLJ） and western Iran heavy rain:case study ...

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International Conference on Environmental Science and Technology（ICEST 2011）

作者： Elham Mobarak Hassan Amir Hossein Meshkatee Faculty of Agriculture & natural resources Islamic Azad universityAhvaz branch Faculty of Basic Science Science and ResearchIslamic Azad university

The western Iran is affected by Mediterranean cyclones in the cold season.In this study the role of low-level jet（LLJ） in forming and developing heavy rain,exceeding more than 30 mm,and relationship between them are investigated in Dec 1991 by using Mediterranean cyclone location,humidity flux convergence,equivalent potential temperature and maximum wind situation.The Initial data was obtained by NCAR reanalysis.Six hours prior to rain event,the cyclone center is located over Turkey associated with extending pressure trough to Iraq and western Iran thus pressure gradient is increased in these regions,showing by smysn ?o1 p,itnic 8 5a0n ahlyPsai,s.i s lTohcaet emd asxoiumthu mto wsoiuntdh wspeeset do f mcyocrleo n the aanlo n20g North Africa coast.Prior to occurrence of rain,southerly wind 12-16 ms-1 has formed over Saudi Arabia resulted by meridional wind component（v） enhanced to 14 ms-1 in exit of low-level jet.The warm advection demonstrates transports low-latitude（Saudi Arabia,Sudan） warm air toward Iraq and Iran which is associated with forming and increasing southerly wind speed it can provide favorable conditions for the convective rain.Moreover,southerly wind can transport humid air from Red sea and Eden Gulf to high latitude,consequently low-level humid is increased in southwestern Iran.Forming in exit of LLJ,the southerly wind is coincided with equivalent potential temperature advection and humidity flux convergence.As a result,southerly wind over Saudi Arabia provide some favorable condition for produce convective heavy rain by humidity and instability enhancement in western Iran.The maximum humidity flux convergence increased to-8 ×10-8grkg-1s-1 in 700 hPa level and also mixing ratio to 8 grkg-1 in 850 hPa in west of Iran six hours before rain events.

关键词： low-level jet souterly wind equivalent potential temperature humidity flux convergence

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Assessment of Wet Season Precipitation in the Central United States by the Regional Climate Simulation of the WRFG Member in NARCCAP and Its Relationship with Large-Scale Circulation Biases

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Advances in Atmospheric Sciences 2024年第4期41卷 619-638页

作者： Yating ZHAO Ming XUE Jing JIANG Xiao-Ming HU Anning HUANG School of Atmospheric Sciences Nanjing UniversityNanjing 210023China Center for Analysis and Prediction of Storms and School of Meteorology The University of OklahomaNorman 73072U.S.A

Assessment of past-climate simulations of regional climate models(RCMs)is important for understanding the reliability of RCMs when used to project future regional climate.Here,we assess the performance and discuss possible causes of biases in a WRF-based RCM with a grid spacing of 50 km,named WRFG,from the North American Regional Climate Change Assessment Program(NARCCAP)in simulating wet season precipitation over the Central United States for a period when observational data are available.The RCM reproduces key features of the precipitation distribution characteristics during late spring to early summer,although it tends to underestimate the magnitude of precipitation.This dry bias is partially due to the model’s lack of skill in simulating nocturnal precipitation related to the lack of eastward propagating convective systems in the simulation.Inaccuracy in reproducing large-scale circulation and environmental conditions is another contributing factor.The too weak simulated pressure gradient between the Rocky Mountains and the Gulf of Mexico results in weaker southerly winds in between,leading to a reduction of warm moist air transport from the Gulf to the Central Great Plains.The simulated low-level horizontal convergence fields are less favorable for upward motion than in the NARR and hence,for the development of moist convection as well.Therefore,a careful examination of an RCM’s deficiencies and the identification of the source of errors are important when using the RCM to project precipitation changes in future climate scenarios.

关键词： NARCCAP Central United States precipitation low-level jet large-scale environment diurnal variation

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The Roles of low-level jets in “21·7” Henan Extremely Persistent Heavy Rainfall Event

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Advances in Atmospheric Sciences 2023年第3期40卷 350-373页

作者： Yuhan LUO Yu DU School of Atmospheric Sciences Sun Yat-sen Universityand Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)Zhuhai 519082China Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies Sun Yat-sen UniversityZhuhai 519082China Key Laboratory of Tropical Atmosphere-Ocean System(Sun Yat-sen University) Ministry of EducationZhuhai 519082China

An extremely heavy rainfall event lasting from 17 to 22 July 2021 occurred in Henan Province of China, with accumulated precipitation of more than 1000 mm over a 6-day period that exceeded its mean annual precipitation. The present study examines the roles of persistent low-level jets(LLJs) in maintaining the precipitation using surface station observations and reanalysis datasets. The LLJs triggered strong ascending motions and carried moisture mainly from the outflow of Typhoon In-fa(2021). The varying directions of the LLJs well corresponded to the meridional shifts of the rainfall. The precipitation rate reached a maximum during 20-21 July as the LLJs strengthened and expanded vertically into double LLJs, including synoptic-weather-system-related LLJs(SLLJs) at 850–700 hPa and boundary-layer jets(BLJs)at ~950 hPa. The coupling of the SLLJ and BLJ provided strong mid-and low-level convergence on 20 July, whereas the SLLJ produced mid-level divergence at its entrance that coupled with low-level convergence at the terminus of the BLJ on21 July. The formation mechanisms of the two types of LLJs are further examined. The SLLJs and the low-pressure vortex(or inverted trough) varied synchronously as a whole and were affected by the southwestward movement of the WPSH in the rainiest period. The persistent large total pressure gradient force at low levels also maintained the strength of low-level geostrophic winds, thus sustaining the BLJs on the synoptic scale. The results based on a Du-Rotunno 1D model show that the Blackadar and Holton mechanisms jointly governed the BLJ dynamics on the diurnal scale.

关键词： extremely persistent heavy rainfall low-level jet dynamic and thermodynamic effect diurnal cycle

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An Extreme Monsoonal Heavy Rainfall Event over Inland South China in June 2022: A Synoptic Causes Analysis

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Journal of Tropical Meteorology 2023年第1期29卷 16-25页

作者：邓文剑任鹏飞张东孙宇吴乃庚 Guangdong Meteorological Observatory Guangzhou 510641 China Guangzhou Institute of Tropical and Marine Meteorology China Meteorological AdministrationGuangzhou 510641 China

An extreme monsoonal heavy rainfall event lasted for nine days and recurred in the interior of northern south China from June 13 to 21, 2022. Using regional meteorological stations and ERA5 reanalysis data, the causes of this extreme monsoonal rainfall event in south China were analyzed and diagnosed. The results are shown as follows. A dominant South Asian high tended to be stable near the Qinghai-Tibet Plateau, providing favorable upper-level dispersion conditions for the occurrence of heavy rainfall in south China. A western Pacific subtropical high dominated the eastern part of the South China Sea, favoring stronger and more northward transport of water vapor to the northern part of south China at lower latitudes than normal. The continuous heavy precipitation event can be divided into two stages. The first stage(June 13-15) was the frontal heavy rainfall caused by cold air(brought by an East Asian trough)from the mid-latitudes that converged with a monsoonal airflow. The heavy rains occurred mostly in the area near a shear in front of the center of a synoptic-system-related low-level jet(SLLJ), and the jet stream and precipitation were strongest in the daytime. The second stage(June 16-21) was the warm-sector heavy rainfall caused by a South China Sea monsoonal low-level jet penetrating inland. The heavy rainfall occurred on the windward slope of the Nanling Mountains and in the northern part of a boundary layer jet(BLJ). The BLJ experienced five nighttime enhancements, corresponding well with the enhancement of the rainfall center, showing significant nighttime heavy rainfall characteristics. Finally, a conceptual diagram of inland-type warm-sector heavy rainfall in south China is summarized.

关键词： monsoonal heavy rainfall south China low-level jet synoptic causes

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Influence of Coastal Marine Boundary Layer jets on Rainfall in South China

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Advances in Atmospheric Sciences 2022年第5期39卷 782-801页

作者： Yu DU Yian SHEN Guixing CHEN School of Atmospheric Sciences Sun Yat-sen Universityand Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)Zhuhai 519082China Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies Sun Yat-sen UniversityZhuhai 519082China Key Laboratory of Tropical Atmosphere-Ocean System(Sun Yat-sen University) Ministry of EducationZhuhai 519082China Huzhou Meteorological Bureau Huzhou 313000China

Coastal marine boundary layer jets(CMBLJs)play an important role in coastal and inland rainfall in South China.Using 21 years of ERA5 and CMORPH rainfall data,two main CMBLJs are found,one on each side of Hainan Island(named BLJ-WEST and BLJ-EAST),which are always strengthened jointly.Both CMBLJs often occur in the pre-summer rainy season and exhibit an evident diurnal cycle with a maximum at night.With the emergence of the CMBLJs,rainfall is significantly enhanced in South China,particularly downstream of each CMBLJ.The response of rainfall to the CMBLJs is mainly attributed to convergence at the terminus of each CMBLJ,terrain-induced lifting,and relevant atmospheric stratification.Coastal rainfall downstream of the BLJ-WEST is much weaker than that downstream of the BLJ-EAST because of higher CIN over the Beibu Gulf,which is caused by lower temperature lapse rates and adiabatic heating in the lee of the Annamite Range.The inland rainfall increases along with CMBLJ intensity,whereas coastal rainfall reaches a maximum in the presence of moderate CMBLJs rather than stronger CMBLJs.Stronger CMBLJs induce stronger dynamic lifting but higher CIN near the coastal area.Additionally,CAPE near the coast does not become highest with strongest CMBLJs,because the CAPE generation contributed by coastal dynamic lifting can be offset by the negative contribution caused by the horizontal advection of cold and dry air from the Indochina Peninsula.Therefore,anomalous dynamic lifting,moisture flux convergence,and CAPE/CIN associated with CMBLJ intensity jointly result in anomalous rainfall.

关键词： low-level jet rainfall CAPE CIN coastal region

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Atmospheric Rivers and Mei-yu Rainfall in China:A Case Study of Summer 2020

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Advances in Atmospheric Sciences 2021年第12期38卷 2137-2152页

作者： Ting WANG Ke WEI Jiao MA Center for Monsoon System Research Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing 100049China

Atmospheric rivers(ARs)are long,narrow,and transient filaments of strong horizontal water vapor transport that can lead to extreme precipitation.To investigate the relationship between ARs and mei-yu rainfall in China,the mei-yu season of 2020 in the Yangtze-Huaihe River basin is taken as an example.An adjusted AR-detection algorithm is applied on integrated water vapor transport(IVT)of the ERA5 reanalysis.The JRA-55 reanalysis and the data from Integrated Multi-satellite Retrievals for GPM(IMERG)are also utilized to study the impacts of ARs on mei-yu rainfall in 2020.The results reveal that ARs in East Asia have an average length of 5400 km,a width of 600 km,a length/width ratio of 9.3,and a northeastward orientation of 30°.ARs are modulated by the western North Pacific subtropical high.The IVT core is located at the south side of low pressure systems,moving eastward with a speed of 10°d−1.For the cross sections of ARs in the Yangtze-Huaihe River basin,75%of the total flux is concentrated below 4 km with low-level jets near AR cores.Moreover,ARs occur mainly in the mei-yu period with a frequency of 20%–60%.The intensity of AR-related precipitation is 6–12 times that of AR-unrelated precipitation,and AR-related precipitation contributes about 50%–80%to total mei-yu precipitation.As shown in this case study of summer 2020,ARs are an essential part of the mei-yu system and have great impacts on mei-yu rainfall.Thus,ARs should receive more attention in research and weather forecast practices.

关键词： atmospheric rivers East Asian summer monsoon mei-yu front low-level jet western North Pacific subtropical high

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