Causes analysis of snowfall during different stages of a rare heavy snowstorm event in Liaoning province under the background of Northeast Cold Vortex
Utilizing conventional observations,intensified snowfall observations,wind profiler radars,microwave radiometers,and other multi-source monitoring data,as well as CMA-RA reanalysis data,a rare snowfall event in Liaoning province in November of 2021 was analyzed for its water vapor and thermodynamic characteristics and causes stage by stage.The results indicated that the strong development of the Northeast Cold Vortex(NCV)and ground cyclone,coupled with the interaction between northern and southern frontal zones,led to the southward transport of strong cold advection from western Jilin,forming a cold air cushion.The strong warm advection in front of the offshore cyclone ascended along this cold cushion,providing the large-scale circulation background for this snowfall event.The Yellow Sea and the East China Sea are the main moisture sources.During the heavy snowfall phase of this process,mid-level warm and moist air overlapped vertically with low-level returning cold and moist air,form a deep moist layer.Convectively unstable stratification existed in the lower troposphere below 850 hPa and near 700 hPa in central Liaoning province.Frontogenesis intensified along the inclined direction of the cold cushion between 925～700 hPa,at the same time horizontal wind field convergence below 925 hPa gener-ated frontogenesis in the horizontal direction.The combination of frontogenetic dynamic lifting and ascending mo-tion in front of the NCV resulted in strong upward motion from near-surface to approximately 5 km altitude.Dur-ing the sustained weak snowfall phase,the intrusion of dry cold air and the weakening of moisture conditions,the weakened warm and moist air in the middle levels and dry and cold air in the lower levels overlapped vertically.Symmetric instability stratification persisted,and the influence of multiple short-wave troughs at the bottom of the NCV led to the continuous weakening of snowfall.
Convective instabilityFrontogenesisWarm and moist airMulti-source monitoring
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