Gaoyuan qixiang (Jun 2023)
Analysis on the Genesis Mechanism of Freezing Rain and Extreme Heavy Snowstorm under the Background of Cold Cushion
Abstract
Based on meteorological observations， Doppler radar observation data of Tongliao station and Chifeng station， climate extreme snowfall and FNL （1°×1°） reanalysis data of NECP every 6h， this paper analyzes the disastrous extreme backflow heavy snowstorm in early winter in the central and eastern Inner Mongolia from November 17 to 19， 2020.The results show that 500 hPa eastward moving upper-level trough， 700 hPa southwest jet and warm shear line provide abundant moisture and dynamic convergence lifting mechanism for heavy snowfall.The northeast cold air cushion is located from the surface to 850 hPa， and the warm and humid air in the middle and high-altitude southwest climbs along the low-level cold cushion to generate frontogenesis， which is the main reason for this heavy snowstorm.During the heavy snowfall stage， the whole layer moves upward from the lower layer to the upper layer， and the moisture in the middle and lower layers is almost saturated.The deep wet layer is conducive to the production of high-efficiency heavy snowfall.The T-lnP in Tongliao has a variety of special stratifications such as ice facies， temperature inversion， melting， and neutral layers.It also has a "trunk" stratification curve that clearly characterizes freezing rain.The low-level northeast wind jet and the middle and high-level southwest jet are formed strong vertical wind shear and temperature difference.The dynamic frontogenesis is maintained during the snowfall and the strongest stage of the dynamic frontogenesis corresponds to the moment when the snowfall is the strongest； The radar reflectivity has a bright zone of 0 °C and a 50~55 dBz band echo； the low layer of basic radial velocity maintains the cold pad formed by the northeast jet stream for a long time， and there is a pair of wind velocity cores at the center of positive and negative velocity， forming a "bull's eye".The radar's basic radial velocity map shows the low-level northeasterly wind and the middle-level and high-level southwest jet， which can reflect the synoptic structure of the southwest warm and humid jet climbing on the cold cushion.It plays a very effective indication for the short-term forecast and warning of snowstorm.
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