Water vapor and cloud microphysical characteristics of a sea-effect snowstorm in Shandong Peninsula, China

Sea-effect snowfall is a special form of snow in the coastal areas of the Bohai Sea in China. However, a quantitative understanding of its water vapor and cloud microphysical mechanisms is still lacking. In this study, the Weather Research and Forecasting model version 4.0 with three microphysics schemes was employed to investigate a sea-effect snowstorm that occurred in the north of Shandong Peninsula on 9–10 January 2018. The simulated snowfall amount, temperature and humidity profiles, and radar reflectivity were in general agreement with the observations. The moisture budget revealed that the water vapor came completely from evaporation of the surface of Bohai Sea. The largest water vapor sink term was the moisture advection, followed by the deposition and condensation (accounting for only 15% of the sea surface evaporation). This phenomenon is analogous to heating water in a kettle and then the water vapor drifting away with the wind. In the main snowfall area, the total water vapor transport was positive (i.e., inflow) below the height of 1.5 km, and was almost zero above 3.0 km. The period of maximum moisture inflow in the low layer was about 30 min ahead of the maximum surface snowfall. In addition, the hydrometeor distributions in this sea-effect snowstorm were relatively simple compared to those in non-sea-effect snowstorm; the snow content was the most (0.09 g kg⁻¹), followed by the supercooled cloud water (0.01 g kg⁻¹), owing to the weak convection in it. Snow growth was dominated by the vapor deposition, and the process of rimming accounted for only 1/4 of the vapor deposition. The evidently weaker vapor condensation than vapor deposition is quite different from that in summertime heavy rainfall.