暴雨灾害 (Oct 2023)
Synoptic conditions and radar characteristics for elevated thunderstorm during a snowstorm event in Henan Province
Abstract
A snowstorm event followed by the elevated thunderstorm occurred in Henan Province from February 24 to 25 in 2021. The operational forecast of all meteorological stations failed to capture the thunderstorm of this event, with the snowfall being underestimated. Using the conventional meteorological observations, the dual polarization weather radar products, and the NCEP/NCAR reanalysis with special resolution of 1° and temporal resolution of 6 h, we conducted the analysis of the synoptic conditions and the characteristics of the dual polarization radar parameters for the elevated thunderstorm during this event. Results are as follows. (1) Due to the interaction of synoptic scale systems such as the mid-latitude upper trough moving eastward and deepening, the southwest jet developing northward at 700 hPa, and the cold air diffusing southward from the surface, the convection is triggered, which resulted in the elevated thunderstorms during the snowstorm event. (2) The strongest water vapor transport is located at 700 hPa, the great value belt of water vapor flux is located in the region along the Yellow River in Henan, and there is the abundant water vapor over Henan in this event, which provide favorable thermodynamic condition for the establishment of unstable stratification in the middle level and the triggering of convection. (3) The superposition of upward branches of two secondary circulations in front of the trough provides strong upward motion for the occurrence of thunderstorms and the maintenance of snowfall. The strong vertical wind shear at 0-6 km is beneficial to the development of symmetric instability. The instability energy in the mid-and upper-level is released due to the convergence of southwest wind jet at 700 hPa and the large-scale forcing by the upper trough, thus triggering convection. (4) When the elevated thunderstorm occurs, the intensity of radar echo is greater than or equal to 45 dBz and its top height is over -20 ℃. The "bull's eye" structure and maintain of the convergence rising area are favorable for generating the thunderstorm. The main characteristics of dual polarization radar parameters during the elevated thunderstorm are that the correlation coefficient (CC) is low of 0.7-0.9, the specific differential phase (KDP) is high of 0.5°- 0.7°·km-1, and the differential reflectivity factor (ZDR) is more than 2 dB. Echo intensity over 55 dBz with large KDP of 0.5°-0.7°·km-1 corresponds to the period of frequent lightning and heavy snowfall.
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