Research On Downburst And Short-term Small-scale Convective Weather Based On Array Weather Radar

In the paper,the evolution of typical small-scale convective weather systems are analyzed,by using the high spatial and temporal resolution data from two Array Weather Radars(AWRs),which are located at Huanghua International Airport,Changsha,Hunan province and Shanghai,China.The high spatial and temporal resolution data of the AWRs in 2018-2019 are mainly screened and analyzed in this paper,five convection processes in Changsha and Shanghai are includes.By using Equivalent Potential Energy per Unit Area(EPEUA),the algorithm for monitoring and early warning downburst according to the characteristics and scanning modes of phased array antenna for single detection subarray is improved in this paper.The reasonability of the algorithm was verified by the observation data of the automatic weather stations at the airport.Besides,not only analyzed the change of the EPEUA,the divergence and vorticity in wind fields,but also the evolution processes in detail are analyzed.Moreover,the echoes are further analyzed by using the conventional sounding data,wind profile data and observation data of the automatic weather stations.The conclusions are follows:(1)The coalescence growth of the storm cells results in forming a new storm cell and accelerates the development of the new storm.The convection process on May 20,2018 in Changsha generated a local downdraft with,the instantaneous maximum wind speed of 11.6 m/s on the ground.The storm began to develop around the height of 5km.The echo top was up to 14.8 km,and the height of the strong echo center was up to 7.5 km in the entire life of the storm.The occurrence of the middle radial convergence and surface divergence are consistent with changing of the wind speed and direction according to the data of the automatic weather stations.The mid-level radial convergence had an early warning effect on the ground wind.The increase of dew point temperature and air pressure of the automatic weather stations has indicative function referential on the downdraft phenomena of the storm.According to the analysis of the release ratio of EPEUA,the threshold of the release ratio was set to20%.When the release ratio exceeds 20%,the early warning information can be issued.For the "5·20" convection process,the AWR can give the warning information20 min before the ground wind speed achieved its peak value,which is 8 min earlier than original algorithm.(2)The increase of water vapor near the ground is caused by the change of underlying surface changing,the warm and wet inflow of the echo convergence cyclone enhanced,and the area,the height,and the intensity of the echoes increased on August 13,2019 in Shanghai at the middle period of the development.In the maturity period,the rotation center of the internal wind corresponds to the center of the strong echo,and the upper divergence has indicative function on the height of the strong echo center(intensity >45 d BZ).The rotating of the ground wind fields shows the growth of the echo.The AWR provides higher spatial and temporal resolution data,and continuously captures the evolution of the strong echo center(intensity >60 d BZ)for 4 minutes after one 6-min SA radar volume scanning was completed.Therefore,the high spatial and temporal resolution data have advantages of detecting severe convective weather which usually changes rapidly.(3)There was a local hail in Songjiang district of Shanghai on August 18,2019.The accumulated precipitation in four hours reached the maximum of 61.4mm and the maximum ground wind speed was 25.7 m/s.Similarly,the coalescence growth accelerates the development of the new echo.The echo top grew up to 13 km within10 minutes,and the echo maximum area is 25 km*20 km.The wind fields in strong echo center rotated obviously,and there was an obvious pair of cyclonic and anticyclonic in the echo.The AWR captured the pair of positive and negative velocities,with a rotation velocity of 11.5 m/s.The ground wind speed increased sharply at 14:13(BJT)and 9 minutes later,reached the maximum of 24.3 m/s.According to the analysis of EPEUA,the echo's release ratio reached 21.83% at14:10(BJT),and the early warning can be given 12 minutes before the ground wind speed reached its peak value.The ground thunderstorm caused a sudden increase in wind speed of the ground automatic weather stations at around,the strong echo dropped down,the upper-air rotation was weaken,and the upper-air wind speed increased to the maximum of 30 m/s.A large number of precipitation particles were carried by the wind near the ground,and new hail cell was rapidly generated in the northwest direction of the parent storm of thunderstorm wind under the influence of the wind at high altitude.The hail process can be divided into three periods:development,maturity,and extinction.In the period of development,the mid-level divergence at the rear of the echo and the mid-level anticyclone at the front indicate that the mature period started.And the vertical landing in the rear divergence marked the beginning of precipitation.At the same time,a three-body scatter spike echo appeared on the echoes captured by the WSR-88 D.Strong cyclonic is one of the important features of this strong convection process,and the strong cyclonic was maintained for 18 minutes(14:54-15:12,BJT)in the period of mature,which is greatly significant to analyze the mechanism of strong convection in the further.