甘肃夏季特强沙尘暴分析

Analysis of Summer Severe Sand-Dust Storms in Gansu Province

夏季沙尘暴的气候特征表明，夏季是甘肃省沙尘暴的次多发季节，主要集中在民勤、鼎新、金塔。通过对一次罕见的甘肃省夏季强沙尘暴天气分析发现：高空小槽、切变线、热低压是引发夏季沙尘暴的主要天气系统，而春季沙尘暴一般是大尺度天气系统造成的；夏季沙尘暴发生前期高空急流反映并不明显，急流风速的突然加大和沙尘暴几乎同时发生，这是夏季沙尘暴预报的难点之一；沙尘暴发生前8～12h的螺旋度场对沙尘暴预报有较好的指示意义，正值越大，沙尘暴越强，但当沙尘暴与强降水同时发生时，沙尘暴区螺旋度值明显小于强降水中心螺旋度值。

Sand-dust storms in Gansu Province occurred most frequently in summer. The summer sand-dust storms concentrated around Minqin, INngxin and Jinta. The weather patterns for severe sand-dust storms in summer in Gansu Province are analyzed. The results show that upper troughs and shear lines and hot lows are main synoptic systems that result in summer sand-dust storms. Spring sand-dust storms are mostly induced by large-scale synoptic systems. Before the occurrence of summer sand-dust storms, the upper-level jet currents are not apparent. The sudden wind speed increase of the jet stream happens almost at the same time with a sand- dust storm, and that is one of difficulties in summer sand-dust storm prediction. The helicity field 8 to 12 hours before sand-dust storm occurring is a good indicator in forecasting sand-dust storms. The larger the helicity is, the severer the sand-dust storm is. But when a sand-dust storm and severe precipitation occur concurrently, the value of helicity in the sand-dust storm region is obviously less than that in the severe precipitation region.