Analysis of polarimetric signatures in the supercell thunderstorm occurred in Zhucheng on 16 August 2019
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Abstract
Using Qingdao dual-polarization CINRAD/SA data, conventional observation data and regional automatic station meteorological data, the polarimetric radar signatures of a supercell storm occurred in Zhucheng, Shandong Province on 16 August 2019 are analyzed. The results show that the supercell storm occurred under the background of interaction between the northeast cold vortex and a surface mesoscale convergence line. The CAPE was small, but the vertical wind shear between 0 and 6 km altitude was very strong. This configuration was conducive to the formation and maintenance of supercell storms. The average values of DBZM, C-VIL, HT and TOP of Zhucheng supercell storm, which lasted about 3 hours and accompanied by a deep and persistent mesocyclone, were 74.1 dBz, 67.9 kg/m2, 6.3 km and 11.3 km respectively in its mature stage. The echo area with reflectivity above 60 dBz in lower levels of the storm had small Zdr and CC but large Kdp, indicating that a certain number of wet (or dry) hails and liquid raindrops existed at the same time. In addition, obvious Zdr arcs near the inflow gap in lower levels of the storm were found. The bounded weak echo region (BWER) was detected in the strong updraft area located in middle levels of the storm, and the top of BWER reached about 7 km. Zdr and CC rings around the BWER were observed in middle levels, and the top of Zdr ring reached the −10℃ layer height. The deep Zdr and Kdp columns above the 0℃ layer were observed in the vicinity of the main rotating updraft with their tops reaching the height of −20℃ layer. The Zdr column was located to the east of the BWER and the Kdp column was located to the west of the BWER. The Zdr column between −10℃ and −20℃ layer corresponded to strong Zh (35—60 dBz) and small Kdp, indicating that there were a few large liquid and/or wet ice particles. The Kdp column corresponded to strong Zh (55—72 dBz) and small Zdr, indicating that there were a number of small liquid and/or small wet ice particles and large ice particles. Significant negative Zdr values in the radial direction behind the strong reflectivity core at lower levels of the storm can be used as signals for identification of extremely large hails (diameter ≥50 mm). The strong reflectivity core at lower levels of the storm corresponded to an abnormally large Kdp value, indicating that it contained hail particles covered by water film and high concentration of liquid raindrops.
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