Dual-polarization Radar-based Severe Convection Characteristic And Wind Field In Southeast Fujian

Hail is one of the most common severe convective weather in Coastal areas of Southeast China.Dual-polarization radar has obvious advantages in detecting the fine structure of strong convective weather,and plays an important role in monitoring such weather systems.In this paper,Xiamen S-band dual-polarization service radar is used.First,a preliminary analysis of the dual-polarization parameter data is made.Based on historical radar data,the localtion of the ground clutter are counted,and the ground clutter and areas affected by the ground clutter are filled.In order to study the application of dual-polarization radar in severe convective weather,multiple supercells,ordinary hail cells,and non-hail cells are presented during the development and maturity stages in this paper.The main contents and conclusions include:?1?Only when SNR reaches 22.0d B or above,the radar data is credible,and the SNR threshold value of the data can be decreased to 17.0d B after noise correction.The rotating joint of Xiamen radar antenna has limited influence on the amount of polarization,and the system error of Z_DR and?_DP fluctuates obviously with the azimuth.According to the location of the ground clutter by Xiamen polarization radar,the echo of the stratiform precipitation and the convective precipitation is removed,the position of the ground clutter is continuously located according to the vertical direction of the radar echo,and the ground clutter is filled in the direction of the earth object away from the radar,the ground clutter is blocked and attenuated in the direction,reducing the effect of the ground clutter on the radar data quality of the column,Makes the reflectivity factor more continuous.?2?For the applications of winter hailstones monitoring and warning,Xiamen dual polarization radar data are used to analyze the polarization echo characteristics of hailstones in Zhangzhou City,Fujian Province,21 December 2016.In polarimetric radar observations,hailstorm is observed to have largest horizontal reflectivity?Z,69d BZ?,the radial length of three-body scattering signature?TBSS,16km?and the tangential distance of side-lobe echo?20km?during the lifetime and obvious reflectivity hook and inflow region in low-level.The remarkable signatures of hailstones are low differential reflectivity(Z_DR)and low specific differential phase(K_DP),whereas low?_hv in rain mixed with hails.The analysis shows that this hail case is not a typical supercell thunderstorm,but there are partial polarization echo features of supercell thunderstorm.Besides,a shallow region of high Z_DR is found on the forward-flank downdraft?FFD?,called the Z_DR“arc”,extending to the midlevel.The Z_DR and K_DP columns in pairs and midlevel“rings”of depressed?_hv are observed in the inflow region and the rear-flank downdraft?RFD?.?3?Three cases of sever convection with different intensities,including super cell,common hail storm and non-hail storm,observed by Haicang S-band dual polarization weather radar are presented in this paper.The differences of dual polarization radar characteristics in these cases,containing Z_DR?differential reflectivity?,K_DP?specific differential phase?and?_hv?co-polar correlation coefficient?,during storm developing from growing stage to maturity stage are analyzed:The Z_DR and K_DPcolumns are common features existing in different intensities of storms.The super cell and common hail storm also have?_hv hole characteristics,characterizing the inflow area,near ground.In addition,Z_DR arc and K_DP foot also appear at low level and?_hv low value region with the great hail at high level in super cell maturity stage.The large Z_DR value zone that appears along the radial of the outer hail zone is related to the TBSS scattered by the big hail.It is the difference in reflected energy caused by the horizontally and vertically polarized electromagnetic waves scattered by the hail to the ground and reflected back to the hail caused by.The variation of Z_DR column can be used to identify updraft area and forecast the development trend of sever convective clouds.The?_hv hole can be used to identify the inflow area of convective cell.Then K_DP column,K_DP foot or its vacancy can be use to identify the areas of heavy rain or great hail.Therefore,the dual polarization radar characteristics have great potentials in short-term early warning of strong convection and hail suppression.?4?Based on the S-band dual-polarization operational radar at Xiamen,the hailstorm supercell is analyzed the microphysical characteristics and dynamic structure during the developmental and mature stages.In the development stage,?_hvvalleys can be observed at low elevation angles,and Z_DR columns and K_DP columns can be observed at middle elevation angles;Z_DR columns correspond to large droplets,which are consistent with the results of hydrometeor classification.At the maturity stage,Z_DR arcs and K_DP foot were observed in front of the direction of cloud movement,high Z values,low Z_DR values,and missing K_DP values can identify large hail areas in the cloud,and the corresponding hydrometeor classification results are rain and hail.The areas of low?_hv value,high Z value,and negative Z_DR value appearing in the upper layer can be characterized as hail area,which is consistent with the result of hydrometeor classification algorithm.At the stage of hailstorm development,cyclonic convergence occurred in the low-level horizontal flow field,and a strong frank updraft formed within the cloud body.At the mature hailfall stage,while the cyclone circulation is maintained at the lower level,the anticyclonic circulation appears at the upper level.The strongest updraft is 48m/s at the height of supercell overhang.Systemic downdraft appeared during weakening period of system,and strong echo reached the ground.The"red envelope black"polarization phenomenon is generated because the hail cell is affected by the warm and humid airflow of the southwest wind,and the vertical wind shear is large,which is conducive to the wet growth of the hail and then develops into a large hail.The hail that produces the polarization phenomenon of"ZDR large value"is mostly small and medium hail.