Vertical Structure and Dynamical Properties during Snow Events in Middle Latitudes of China from Observations by the C-band Vertically Pointing Radar

Abstract

 Data from the continuous observations of 4 shallow snow events (echo top < 8 km) and 2 deep events (> 10 km) were obtained by the C-band vertically pointing radar with frequency modulation continuous wave technology (VPR-CFMCW) with extremely high resolution during the winter of 2015-2016 in middle latitudes of China. Generating cells (GCs) were found near the cloud top in each event. Reflectivity (Z), radial velocity (V_r), the vertical gradient of Z (dZ/dh, h is the vertical distance) and V_r (dV_r/dh) showed different vertical distribution characteristics between the upper GC and lower stratiform (St) regions. The fall streaks (FSs) associated with GCs were embedded in the St regions. In the deep events, the proportions of GC regions were slightly larger, but the average contributions to the growth of Z (33 %) were lower than those in the shallow events (42 %). The average dZ/dh were usually 2-3 times larger inside GCs and FSs compared to outside. Bimodal Doppler spectra were used to establish the relationships between the Z and the reflectivity-weighted particle fall speed (V_z) for the 2 regions. The vertical air velocity (W_a) and V_z were then retrieved. The results show that both updraft and downdraft were alternately observed in GC regions. GC locations usually accompanied strong upward air motions, with average speeds mostly distributed around 1.2 m s⁻¹, while downward air motions often appeared between GCs. In the St regions, the speeds of W_a were mainly within 0.5 m s⁻¹. The upper areas of the St regions consisted primarily of weak upward motions, while weak downward motions dominated the lower areas. There was no apparent difference in W_a inside and outside the FSs. The average V_z was slightly larger inside GCs and FSs compared to outside, with the differences of 0.1-0.3 m s⁻¹ and 0.2-0.4 m s⁻¹ respectively.