Study On The Microphysical And Dynamic Characteristics Extraction Algorithm Of Hailstorm Evolution Utilized With Dual-polarization Radar And Its Application

This paper uses observation data from China’s networked dual-polarization operational radars in recent years.Firstly,we propose an improved mesocyclone detection algorithm for the defects of the mesocyclone detection algorithm used in the current observation operation.Then,in order to fully utilize the main advantages of the hydrometeor classification of this dualpolarization radar,a method that can recognize and track hailstorms and extract their hail/graupel characteristics by using hydrometeor classification data as input is proposed.Considering the contribution of mesocyclones to hail development in hailstorms,we solve the problem of difficult automatic matching between mesocyclones and hailstorms,enabling the addition of dynamical characteristics to hailstorms.Finally,the advantages of the application of hailstorm characteristic parameters in the analysis of strong convective processes are investigated.Using the observations of S-band dual-polarization radar in Guangdong and Hebei,the structural characteristics(maximum reflectivity,hailstorm-based VIL and maximum echo top height,etc.),microphysical characteristics(hail/graupel area and their distribution height),dynamical characteristics(rotational velocity and development height of the mesocyclone)and tracking characteristics(movement speed)of the convective system during the period from its post-primary to its pre-dissipation are initially analyzed.The study also examines the relationships between these characteristics and their effects on the generation,duration,and intensity of severe weather such as hail and gales.The main research contents and conclusions include:(1)The improved mesocyclone algorithm in this paper mainly solves the problems of low detection capability of operational mesocyclone detection algorithm for weak storm-scale vortices,identification of false vortices,and the impact of small-scale perturbations inside vortices.As a result,it has achieved good performance in terms of probability of detection(POD),false alarm rate(FAR),quality of convective characteristic parameters,and tracking effect.Using the 882 vortices from four convective processes observed in Guangdong Province as samples,the comparative results under the same definition criteria show that the modified mesocyclone algorithm has significantly improved the recognition of weak storm-scale vortices,reflected in an increase of the POD from 7.3% to 97.7%,a decrease of the FAR from 65.7% to3.4%,and a tracking accuracy of the newly added tracking function of basically over 95%.We compared 65 vortex samples identified by both methods,the main vortex characteristics parameters(base,top,total depth,maximum rotational velocity,maximum shear,number of vortex detection,etc.)were significantly improved.Especially,the weak vortex information at the higher levels of storm can be obtained,the inbound and outbound velocities inside the vortex can be larger,and the detection time continuity of the same vortex is also higher.(2)The hailstorm identification and tracking algorithm established in this paper through the steps of reflectivity threshold selection,establishment of new vertical association,and incorporation of hail/graupel characteristics statistics can identify the complete mesoscale convective systems with reflectivity above 30 dBZ for all storm types,and can also extract the complete hail/graupel distribution within them.It can track the evolution of a convective system from its post-primary to its pre-dissipation without any drastic changes in its morphology,and the tracking is not affected by the transition of the storm type,and it can reliably obtain the changes of hail/graupel characteristics during the evolution of the convective system.(3)Through analyzing the impact of the changes in mesocyclone characteristics during the Guangzhou 411 event and Shijiazhuang 625 event on the hail/graupel characteristics and storm structural characteristics,this study found that the initiation and development of mesocyclones contribute to the intensification of hailstorms and the growth of hail within the hailstorms.The temporal variations in structural characteristics are generally synchronous with mesocyclone characteristics but not completely synchronized with hail/graupel characteristics.In particular,during the weakening phase of the mesocyclone,the area of graupel may still increase or remain unchanged while the structural characteristics weaken synchronously.In general,the mid-level mesocyclones in the convective system can promote the growth of graupel to a certain extent,while the mesocyclones in the low-level convective system(especially near the ground)significantly facilitate the growth of hail and graupel.Compared to the structural characteristics,the hail/graupel characteristics can more sensitively reflect the variations in mesocyclone strength,especially when the hailstorm is mature and the mid-low-level mesocyclone is sustained.The changes in structural characteristics may not be apparent,but the variations in mesocyclones can be directly observed in the degree of increase or decrease in hail/graupel areas.(4)This study conducts a comparative analysis of the variations in convective characteristic parameters during the Guangzhou 411 event and Shijiazhuang 625 event and their connection to the occurrence of severe weather.It is found that the maximum area of graupel occurs at altitudes above-20°C environment temperature and serves as a certain warning indicator for the occurrence of large-scale hail and severe weather.When the storm intensifies,its movement speed also increases,and higher movement speeds are closely related to gale weather.As the mesocyclone rapidly develops and then weakens and dissipates,it corresponds to the significant increase and decrease of hail and graupel area within the storm.These stages respectively correspond to the initial occurrence and large-scale occurrence of gale and hail weather.The individual storms that occurred in Hebei during this period were stronger,had faster movement speeds,and had deep mesocyclones near the surface that lasted for a long time,resulting in continuous and frequent occurrences of hail and gale weather.In contrast,although the storms in Guangdong evolved into supercells,their internal cyclones were not as strong,and it is possible that the rapid melting of hail(resulting in a smaller area of hail in the hail melting layer)contributed to the fact that the actual hail disasters were not severe and primarily involved gale hazards.