河西走廊一次强沙尘暴动力机制分析

Dynamic mechanism of a severe sandstorm occurred in the Hexi Corridor

2011年甘肃省沙尘暴次数较常年明显偏少,但在4月28日河西走廊出现了范围大、强度强的沙尘暴过程,值得关注的是,甘肃省沙尘暴第一高发地民勤却仅出现扬沙。文中利用常规观测、加密自动站及T639数值预报初始场资料,对这次强沙尘暴天气过程进行分析。结果表明:前期气温偏高、降水稀少是大风、沙尘天气出现的气候背景;500hPa斜压槽强烈发展,带动地面冷高压前部锋面气旋强烈发展是引发沙尘暴的动力条件;200hPa高空急流位置及其调整与沙尘暴天气有直接关系;三小时变压中心的移动方向指示了沙尘暴的移动发展方向。通过对Q矢量散度和螺旋度的诊断,发现:冷锋后Q矢量散度>0,冷空气强烈下沉,将高空动量下传到地面,锋前Q矢量散度<0,对应上升运动,使地面锋面后部出现强烈西北大风,造成沙尘暴。沙尘暴一般出现在螺旋度零线附近等值线密集处,螺旋度负中心强度与沙尘暴强度正相关。另外,通过中尺度资料的分析,能更精准的确定沙尘暴落区,提高短时临近预警的准确率。

In 2011, the number of sandstorms was obviously less than other years in Gansu province,but on April 28th, a strong sandstorm occurred in the Hexi Corridor. It was noteworthy, the Minqin, where is the highest sandstorm incidence area in Gansu Province, was only with sand that day. By using the observation, regional automatic stations and T639 initial field data, the dynamic mechanism during the severe sandstorm occurred in the Hexi corrdior on April 28, 2011 was diagnosed. The results showed that before the occurrence of sandstorm, continual temperature rising and precipitation deficit were the weather background. The baroclinic trough on 500hPa develop strong was the major dynamic factor that caused the sand storm, and 200hPa jet location and dust storms were directly related. The pressure transformation in 3 hours was the early warning for sandstorm shortterm forecast. Analysis showed that after the cold front, the Q -vector divergence 〉 0, cold air sank, and in front of the front the Q - vector divergence 〈 0, corresponding upward motion. Sandstorm generally appeared in the helicity density near the zero line contours; the intensity of the negative helicity positively correlated with the intensity of storms. Analysis of the mesoscale data, can more accurately determine the sandstorm area, and improve the accuracy of short - term near the warning.