影响三大洲的北非强沙尘暴动力机制WRF-chem模拟与分析

基于WRF-chem模式对北非2018年3月下旬的典型强沙尘暴过程进行模拟,分析了此次强沙尘发生季节、持续时间、局地特征以及传输路径的关键动力系统与动力机制。鉴于起沙是沙尘暴发生的关键点之一,并且起沙主要取决于风力和下垫面沙源性质,本文测试了三种起沙参数化方案的影响,并将模拟结果与卫星MODIS监测及其再分析资料MERRA-2进行了对比,又经系列统计方法检验。结果显示,宏观思路的起沙方案GOCART比AFWA和UoC两种起沙方案更适合此次大尺度强沙尘暴数值模拟(锋面跨度接近60个经度)。综合沙尘暴关键系统的动力机制分析和数值模拟结果显示,强沙尘暴关键系统为深厚的西风槽、沙尘冷锋锋面和锋后的地面高压反气旋。北非中部深厚的西风槽为后倾槽,该系统稳定,造成沙尘暴持续时间长。沙尘暴锋后反气旋中的下沉气流抑制了扬沙向高层扩散,造成低层能见度恶劣。沙尘锋区结合了动力、热动力以及湿热动力不稳定,因此锋区风力大,地面沙尘驱动力强。而西风槽和强大反气旋依托环流形势,提供了沙尘传输到三大洲的长途输送力。

WRF-chem simulation and analysis on the dynamic mechanism of the strong dust storm in North Africa affecting three continents

Based on the WRF-Chem model, a typical North Africa severe dust storm process in late March 2018 is simulated, and the key synoptic systems and dynamic mechanisms of the occurrence seasons, last period, local features and transmission paths are analyzed. Due to the dust emission is one of key points of dust storm happening,and the dust emission mainly depends on the wind force and the nature of the underlying surface of dust source, the research of the paper focuses on the effect comparison of three parameterization schemes of the dust emission, then the numerical simulation results are compared with the satellite MODIS monitoring and its reanalysis data Merra-2,also a series of statistical tests are done, the results shows that it may be related to the circulation systems and the dust storm source all being with large scales (the front span is close to 60 longitudes), the dust emission scheme Gocart is more suitable for the strong synoptic dust storm numerical simulation than both AFWA and UoC schemes. The dynamic mechanism analysis and numerical simulation results of the strong dust storm show that the key systems of the strong dust storm are a deep westerly trough, a dust cold front and a surface high-pressure anticyclone behind the front. The deep westerly trough in central North Africa is a backward inclined trough and the system is stable in circulations, it causes the dust storms lasts a long duration .The descending flow in the anticyclone behind the dust storm front inhibits the diffusion of dust to the upper layer, it causes poor visibility in the near surface layer. The strong dust front area is with dynamic, thermal and moisture dynamic instabilities, so the wind in the front area is stronger and its drive force to the ground dust is more powerfully. The westerly trough and strong anticyclone provide the long-distance transport force of dust to the three continents based on the circulations.