高原和盆地间山谷风对四川霾日变化的影响分析

Analysis of the Influence of Mountain-basin Wind between Plateau and Basin on the Diurnal Variations of Haze in Sichuan Province

为研究高原与盆地间山谷风对四川霾日变化的影响,利用NCEP提供的1日4次的FNL再分析资料,使用天气分析和数值模拟等方法,研究了山谷风对2015年1月21日严重霾天气的日变化影响,得到如下结论:2015年1月21日四川盆地空气质量指数AQI和污染物PM10、PM2.5的浓度具有明显的日变化特征,污染物峰值由21日凌晨2时一直持续到上午11时,到15时污染物浓度最低;高原和盆地间的山谷风对该日霾的日变化有明显影响。1月21日8时至11时,携带冷空气的山风从盆地两侧吹向盆地,冷空气下沉凝结,在相对湿度高于80%的条件下,有利于霾的生成和维持;同时山风在四川盆地形成的辐合线,有利于污染物聚积,造成此时的污染物浓度达到峰值。14时后,地面风由山风变为谷风,相对湿度也降低到80%以下;谷风导致了污染物浓度迅速扩散,使污染物浓度处于谷值。中尺度数值模式WRF对高原与盆地间山谷风有较好的模拟能力。

In order to study the impacts of the mountain-basin wind between plateau and basin on the diurnal variation of haze in Sichuan, based on FNL reanalysis data four times a day which are provided by NCEP, the impacts of the mountain-basin wind on the diurnal variation of severe haze weather on January 21, 2015 was studied by using weather analysis and mesoscale numerical model WRF, etc. The following conclusions were obtained. On January 21, 2015, Air quality index(AQI) and the concentration of pollutant PM10 and PM2.5 in Sichuan Basin showed obvious diurnal variation. The peak value of pollutants lasted from 2:00 a.m. to 11:00 a.m. on the 21 st, and the concentration of pollutants was the lowest at 15:00. The mountain-basin wind between plateau and basin has a significant impact on the diurnal variation of haze on that day. From 8 a.m. to 11 a.m. on January 21, mountain wind carrying cold air blows from both sides of the basin to the basin, and the cold air sinks and condenses. When the relative humidity is above 80%, it is conducive to the generation and maintenance of haze. At the same time, the convergence line formed by mountain wind in Sichuan basin is conducive to pollutant accumulation, causing the concentration of pollutants to reach the peak at this time. After 14:00, the ground wind changed from mountain wind to valley wind, and the relative humidity also dropped below 80%. Valley wind leads to the rapid diffusion of pollutant concentration, which makes the pollutant concentration in the valley value. The mesoscale numerical model WRF has a good ability to simulate the mountain-basin wind between plateau and basin.