Causes of a freezing rain event in southern Heilongjiang province on November 8,2021
Using datasets of the hourly surface observation,upper-air observation,and ERA5 reanalysis,the study analyzes the precipitation phase characteristics and the causes of a freezing rain event in southern Heilongjiang province during the rain-snow weather process on November 8,2021.Results show that the atmospheric circulation background features an eastward-moving and intensifying upper-level low vortex.The southeastern jet stream trans-porting warm and moist air provides moisture and energy for the precipitation,forming a warm layer that causes the freezing rain.The stratification over the freezing rain area exhibits a"cold-warm-cold"structure.Ice crystal growth produces snow in the upper cold layer,which melts into rain upon entering the warm layer.As the rain descends through the cold layer near the surface,it remained in a supercooled liquid state,forming freezing rain i.e.a process consistent with the"ice-phase melting"mechanism.The warm advection-induced warming in the mid-to-lower atmosphere is indicative of freezing rain,while the northeasterly in the lower layer contributes to cold advec-tion.Sustained and strong northeasterly tends to enhance cold advection,causing a temperature drop in the cold layer and increasing the freezing rain intensity.Further comparison with a typical freezing rain event in Jilin province re-veals that a strong warm layer and pronounced inversion layer significantly contribute to the intensified freezing rain.
Temperature advectionWarm layer thicknessIce-phase melting
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