On 19 May 2020,a mixed strong convective weather process(hail,strong wind,and heavy precipitation)occurred under the influence of northwest airflow in Guizhou,and various numerical models omitted this process.Using ground and high-altitude observa-tion data,Doppler radar data,NCEP 1°×1° reanalysis data and ERA5 0.25°×0.25° reanalysis data,the weather characteristics,mesoscale environmental conditions,evolution and structure of medium-scale convective systems,trigger and maintenance mechanism of this con-vection were analyzed.The results show that:(1)This convection occurred in warm sector of the low-level southerly wind under the influ-ence of 500 hPa northwest airflow and was triggered by the intersection of two warm-humid air streams from the Bay of Bengal through Yunnan and from the Beibu Gulf through Guangxi in the northwest of Guizhou.The wind and hail characteristics were significant and the locality was strong in this process.(2)The characteristics of the environmental field were as follows:the upper layer of the atmosphere was dry and the lower layer was wet,the instability was large,the Convective Available Potential Energy(CAPE)was high,the Convect-ive Inhibition(CIN)energy was low,and the vertical wind shear was strong.(3)On the radar echo,a supercell moved from northwest to southeast with typical features such as hook shaped echo,low-level weak echo area,mid to high-level echo overhang,mesocyclone,high vertical cumulative liquid water content.(4)Dynamic forced uplift was beneficial for convective triggering under the influence of meso-scale-βcyclonic vortex and complex terrain.Using the gas block theory,the lifting height of the gas block caused by dynamic forcing was closely related to the strength of horizontal convergence,vertical convergence height,and convergence duration.In this process,the rising height(H)of the gas block calculated by quantitative values was much greater than the height of the free convection height(LFC),and the dynamic forcing was transformed into thermal forcing,leading to the development of rising movement,triggering a convective storm.(5)The main reason for numerical model omissions was a large deviation between the atmospheric CAPE forecast and the situation of the weather.
Northwest airflowGuizhouConvection in warm sectorTrigger mechanism
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