Evaluation of the Predicted Particle Properties (P3) Microphysics Scheme in Simulations of Stratiform Clouds with Embedded Convection

Abstract

To evaluate the ability of the Predicted Particle Properties (P3) scheme in the Weather Research and Forecasting (WRF) model, we simulated a stratiform rainfall event over northern China on 22 May 2017. WRF simulations with two P3 versions, P3-nc and P3-2ice, were evaluated against rain gauge, radar, and aircraft observations. A series of sensitivity experiments were conducted with different collection efficiencies between ice and cloud droplets. The comparison of the precipitation evolution between P3-nc and P3-2ice suggested that both P3 versions overpredicted surface precipitation along the Taihang Mountains but underpredicted precipitation in the localized region on the leeward side. P3-2ice had slightly lower peak precipitation rates and smaller total precipitation amounts than P3-nc, which were closer to the observations. P3-2ice also more realistically reproduced the overall reflectivity structures than P3-nc. A comparison of ice concentrations with observations indicated that P3-nc underestimated aggregation, whereas P3-2ice produced more active aggregation from the self-collection of ice and ice-ice collisions between categories. Efficient aggregation in P3-2ice resulted in lower ice concentrations at heights between 4 and 6 km, which was closer to the observations. In this case, the total precipitation and precipitation pattern were not sensitive to riming. Riming was important in reproducing the location and strength of the embedded convective region through its impact on ice mass flux above the melting level.

摘 要

本文采用WRF模式可预报冰雪晶特性的P3微物理方案,对2017年5月22日我国北方地区一次积层混合云降水过程进行了数值模拟,并结合地面降水、雷达和飞机探测数据,评估了P3方案两个版本P3-nc(单一类别冰雪晶)和P3-2ice(冰雪晶分为两类)的数值模拟能力。为探讨凇附过程的影响,本文采用不同的冰雪晶-云滴碰并系数开展了数值敏感性试验。对降水演变的分析表明,两个P3版本都高估了太行山沿线的地面降水,而低估了背风面局部地区的降水。当把冰雪晶分为两类时,模拟的小时降雨强度比采用单一类别冰雪晶时稍低,结果更接近观测值,并且雷达回波结构更合理。与飞机观测的冰雪晶数浓度相比,P3-nc低估了聚合过程,而P3-2ice从冰雪晶自身的碰并过程和不同类别冰雪晶之间的碰并过程中产生了更活跃的聚合过程,从而改进了对4–6 km高度冰雪晶浓度的模拟效果。对本次降水过程,地面总降水量和降水分布对凇附过程不敏感,尽管改进凇附过程不能解决WRF模式模拟降水量偏大的问题,完善凇附过程参数化方案仍然对改进对流雨核区位置和强度的模拟效果有重要影响。