甘肃省春季一次连续浮尘天气过程分析

Analysis of a Continuous Floating Dust Weather in Gansu Province in Spring

2013年3月8~9日甘肃省出现了一次区域性的大风沙尘暴天气过程,此后到14日甘肃中东部一直维持浮尘天气,这样范围广、持续时间长的沙尘天气为近年来罕见。本文分析了此次沙尘天气过程的天气气候特征以及特殊气象条件对连续浮尘天气的影响,并以兰州市为例基于HYSPLIT-4轨迹模式探讨了浮尘天气过程的沙尘颗粒传输特征。结果表明：（1）前期暖干的气候背景有利于此次大范围沙尘天气的发生;（2）8~9日冷锋后的偏北大风引发甘肃省出现区域性大风沙尘暴天气,11日河西再次出现扬沙、沙尘暴天气,沙尘粒子沿西北气流向下游地区输送,致使12日河东出现浮尘天气的站数明显增多;（3）9日大风沙尘暴天气过后,甘肃省中东部边界层处在弱的偏东风环境中,大气层结长时间较稳定,沙尘污染物不易扩散;（4）在连续浮尘天气期间,甘肃省各地上空频繁出现逆温层,且逆温层高度在9日沙尘暴天气过后有明显抬升,阻挡了低层空气的上升运动,以致沙尘粒子聚集在700 h Pa以下。同时还发现,边界层上部逆温层的逆温温差越大,厚度越厚,造成浮尘天气的强度越强;（5）兰州市9~10日出现的浮尘天气起源于8日河西走廊及蒙古地区的沙尘暴,11日河西走廊再次爆发的沙尘暴天气对河东的浮尘天气影响较大。此外,10~13日陕西南部也出现了浮尘天气,＂东高西低＂的地面形势使此地上空漂浮的沙尘粒子处在偏东风的环境中,对甘肃中东部地区的浮尘天气有一定的回流输送作用。

A regional gale and dust- storm weather occurred in Gansu Province from 8 to 9 March 2013,and untill 14 March the floating dust continued in central and eastern Gansu. The floating dust with such wide range and long duration had been rarely seen in recent years. This paper mainly analyzed the climate characteristics and the influence of the special meteorological conditions on the floating dust weather,and the main features of dust transportation were discussed over Lanzhou of Gansu. The results are as follows：（1）The early warm and dry climate background was favorable to the occurrence of dust weather.（ 2） The regional gale and dust- storm weather happened in Gansu from 8 to 9 March was caused by the northerly gale behind the cold front,and the dust and duststorm weather appeared again on 11 March in Hexi Corridor. Due to the downstream transportation of dust particulates along the northwest airflow,the stations appearing the floating dust in Hedong of Gansu increased obviously on 12 March.（3） After the gale and dust- storm the boundary layer in central and eastern Gansu was in a weak easterly wind,and the atmospheric stratification was stable for a long time so that the dust pollutants weren＇t conductive to spread.（4） During the floating dust weather,the inversion layer frequently appeared over Gansu,and the height of inversion layer was obviously uplifted after 9 March,which blocked the atmospheric rising movement in lower layer,consequently,the dust particulates gathered below 700 h Pa. In addition,the intensity of the floating dust weather was positively correlated with the temperature difference and thickness of inversion layer.（5） The floating dust weather in Lanzhou from 9 to 10 March derived from the sandstorm in Hexi Corridor and Mongolia on 8 March,while the sandstorm once again in Hexi Corridor on 11 March had greatly influenced on the floating dust in Hedong area. Furthermore,the floating dust weather appeared in southern Shaanxi from 10 to 13 March due to the dust transport from the north. The dust particulates kept in easterly wind because of the surface situation with higher in the eastern part and lower in the western part of Shaanxi,which played a certain role in returning transpertation of dust particulates to the floating dust weather in central and eastern Gansu.