河西走廊东部强沙尘暴分布特征及飑线天气引发强沙尘暴特例分析

利用2004年1月～2008年10月河西走廊东部6站的地面观测资料,采用统计学方法分析了强沙尘暴的分布特征.发现强沙尘暴主要出现在2～6月,1～3月出现的强沙尘暴主要为高压脊前强西北气流动量下传风所致;4～7月出现的强沙尘暴主要为冷空气东移南下伴随地面冷锋过境锋面大风所致.河西走廊东部的飑线活动造成的强沙尘暴出现在4～6月,均为冷锋型,其中5月居多,出现的7次强沙尘暴中有4次伴有飑线,说明5月份强冷锋东移经河西走廊特殊峡管地形时易诱发飑线,飑线活动造成的强沙尘暴爆发性强,往往造成严重灾情.利用常规探测、地面加密观测、T213数值预报产品和fy-2c/2 d红外卫星云图资料对2008年5月2日河西走廊东部飑线引发的强沙尘暴过程进行了天气动力诊断和中尺度分析.结果表明:中尺度飑线所伴随的强风暴是产生强沙尘暴的主要原因;500 hPa阶梯短波槽是中尺度飑线产生的大尺度触发系统,河西走廊中西部700 hp变形场、中尺度低压为强沙尘暴形成和维持提供了必要的动力条件;地面冷锋前上升运动与高空急流入口区次级环流的上升气流的叠加,为深对流发展提供了深厚的垂直环流发展条件,是促使飑线发生和沙尘卷起的基本动力;地面热低压的加强和午后气温的日变化加大了冷锋前后的温度和气压梯度,为大风、强沙尘暴爆发提供了必要的热力不稳定条件;强沙尘暴出现在垂直螺旋度为-200 m~2/s~2中心的下游,垂直螺旋度对飑线的发展和沙尘暴的落区具有较好的指示意义;中尺度飑线发生在不稳定层结内,较强的不稳定层结为强沙尘暴形成、发展提供了位能转化为动能的基本条件.

Distribution characteristic of strong sandstorm and special case analysis of strong sandstorm initiated by squall line in the eastern of Hexi Corridor

Using surface observation material of the six stations in Jan. 2004 to Oct. 2008 in east of Hexi Corridor, distribution characteristic of strong sandstorm was analyzed with statistics method. The result shows that the strong sandstorm mainly appeared in Feb. to Jun. , the strong sandstorm was caused mainly by momentum downloading gale of strong northwest air current before the high-pressure ridge in Jan. to Mar. , the strong sandstorm was caused mainly by frontal area wind of cold air moving to southeast with ground cold front transiting. The strong sandstorm was caused by squall line activity of eastern Hexi Corridor in Apr. to Jun. that was cold front, majority is in May, four times strong sandstorm is accompanied by the squall line in seven times. It was explained that the squall line was suggested easily when the strong cold front moved east to Hexi Corridor where special canyon tube terrain was in, the strong sandstorm which was created by squall line activity have very strong paroxysm that often created seri-ous disaster. Using conventional survey and ground encryption observations and T213 amount prediction product and fy-2c/2d infrared satellite cloud chart data, weather power diagnosis and mesoscale analysis of gale and strong sandstorm process initiated by squall line are carried on May 2, 2008 in east of Hexi corridor. The result showed that the strong storm followed by mesoscale squall line was primary cause of strong sandstorm producing, steps and ladders short wave trough of 500 hPa was great criterion triggering system for the mesoscale squall line producing, the essential dynamic condition was provided by distortion field and the mesoscale low pressure of 700 hPa for the strong sandstorm forming and maintaining in mid-west of Hexi Corridor, the deep vertical circulation development condition was basic power that urged squall line to occur and sand dust to curl up, which was provided for the deep convection development by superimposition of lifting movement before ground cold front and ascendant current of secondary circulation in upper air jet entrance region, temperature and the barometric gradient around the cold front was enlarged by enhancement of ground thermal low and temperature diurnalvariation of afternoon, by which essen-tial thermal energy unstable condition was provided for the gale and strong sandstorm eruption, the strong sandstorm nificance for development of squall line and landing region of sandstorm, the mesoscale squall line occurred in un-stable stratification, basic condition of potential energy transforming as kinetic energy was provided by strong unsta-ble stratification for the strong sandstorm forming and developing.