Analysis Of Dual Polarization Radar Echo And Wind Field Characteristics In Extreme Rainstorm In Zhengzho

This paper utilizes dual-polarization radar data,ERA5 reanalysis data,ground automatic station data,sounding data,and Atmospheric Motion Vector(AMV)product data from FY-4A satellite to retrieval the wind field during the extreme rainfall period of the Zhengzhou 7.20 heavy rainfall process.After preprocessing the radar data,other data are combined as background field constraints,and the variational method is used to retrieval the wind field.The method with constraints is tested to have smaller inversion errors than the velocity-azimuth display(VAD)method by comparing the root mean square errors between the variational method,ERA5,and VAD with ERA5.Finally,combined with dual-polarization parameters,the echo characteristics,radial velocity features,and wind field structures during the convective development and mature period are analyzed,and the particle phase characteristics,convective system dynamic characteristics,and convective structure are analyzed in both planar and vertical polarization parameters.The results show that :(1)After multiple preprocessing steps,the radar raw data can yield relatively good results.For radial velocity data,in particular,velocity dealiasing is necessary before wind field inversion can be carried out.To improve wind field inversion for single radar,a variational algorithm is adopted,which incorporates background field constraints using multi-source observation data.Compared with the velocity-azimuth display(VAD)method,this algorithm can effectively reduce inversion errors and obtain more accurate results.(2)The characteristic of the reflectivity factor echo showed that the convective heavy precipitation area was shaped from a north-south oriented band to a cluster by convergence;the characteristic of radial velocity showed that low-level convergence and wind direction existed with a height of oblique rotation accompanied by the transport of warm and humid air.It was conducive to water vapor uplift and the continuous development of precipitation.The wind field structure is a large vertical wind shear.(3)The differential reflectivity ring and cross correlation ratio ring on the plane were used to determine the height of melting layer.The increase of differential reflectivity and specific differential phase under melting layer reflected the melting process of ice phase particles and the touching and growth process of liquid particles.The large value of differential reflectivity also developed into a narrow and high-intensity arc and influenced by the particle sorting mechanism.It indicated the existence of strong upward motion in this region,which provided favorable dynamic conditions for the continuous development of rainstorms.(4)The differential reflectivity column area on the profile was distributed to south area of specific differential phase column.Under the action of strong upward flow,it also showed the separation phenomenon in spatial distribution and the higher levels may be due to the exotherm of water vapor deposition making the higher areas warm up,forming smaller density,irregularly dendritic disc-shaped ice crystal particles or melting ice crystals,etc.