WRF模式对一次中低纬降雪天气的数值模拟分析

Simulation and Study of a Snowfall Weather Process in Mid-to-Low Latitude with WRF Model

基于NCEP再分析资料,选取中低纬度滇西南普洱作为研究区域,利用WRF模式模拟2013年12月一次小雪及雪后霜冻天气过程,通过模式输出资料对降雪天气进行诊断分析。结果表明:此次降雪过程的主要影响系统为南支槽,降雪天气发生在强冷空气形成的低空切变线北部;该过程大气为稳定性层结并具有湿斜压性,垂直剖面上MPV1正值中心向下延伸至500 h Pa,此高度以下MPV1以弱的正值为主;干冷空气的输送造成湿斜压性增强,MPV2负值中心达到-0.2PVU,同时配合南支槽提供的水汽条件形成了此次降雪天气。南支槽东移出境后,大气湿斜压性减弱(MPV2负值中心-0.05PVU);前期大气湿斜压性造成局地平流降温,与其后的对流稳定性及高层冷空气的向下输送引起辐射降温,共同造成了较强的混合型霜冻。WRF模式对中低纬滇西南降雪天气过程的范围、时间及雪后强降温天气有较好的模拟效果。

Based on intensive observations,NCEP reanalysis data and FNL data,Choosing southwestern of Yunnan as the study area; A snowfall and frost process during 15—17 December 2013 in southwestern of Yunnan was simulated by WRF model（ Weather Research Forecasting）,The analysis of the output data indicates that the WRF model can make good simulation about the snowfall distribution and time and temperature field. Main conclusions are as follows： The process of main influencing system for the south westerly trough and severe cold air,the area of snowfall in the north of the location of low level wind shear. The atmospheric possess the characteristic of steady and moist baroclinity in the process. The positive region of MPV1 down into 500 h Pa,but MPV1 is weak positive under the 500 h Pa,So it is concluded that the atmospheric is steady. That increased moist baroclinity because of dry cold air. At the same time,MPV2 is negative and approached-0. 2 PVU. Based on this condition with plentiful vapor by the south westerly trough,the snowfall process appeared in southwestern of Yunnan. MPV2 is reduced to about-0. 05 PVU when the south westerly trough have already moved to east of Yunnan. The temperature advection led to drop in temperature in the baroclinic atmosphere and the combination of the stable stratification and the downward transport of cold air due to upper troposphere have formed severe frost in puer.