南疆盆地翻山型沙尘暴环流动力结构分析

Circulation Dynamical Structure of Sand-Dust Storm Caused by Cold Air Crossing Mountains in Southern Xinjiang

2003年4月8日至9日发生了一次超极地冷空气入侵新疆并翻越天山造成南疆盆地大范围强沙尘暴过程,分析沙尘暴强盛期的高度场、高空急流异变、螺旋度场、散度场和不稳定发展,揭示了该类沙尘暴强盛期的环流动力结构。结果表明:①伊朗高压的爆发性发展与乌拉尔山脊叠加形成长波脊,导致泰米尔半岛的极地强冷空气南下,并直插新疆越过天山到达塔里木盆地,造成大范围沙尘暴天气;②强沙尘暴天气产生的根本原因是西西伯利亚地面冷高压爆发性南下并强烈发展;③高空西风急流发生异变在南疆盆地上空形成急流区,并通过动量下传导致地面大风,是大范围沙尘暴发生的动力条件;④沙尘暴区上空螺旋度垂直分布低层为正值、高层为负值,揭示强的旋转上升运动是大范围沙尘暴发生的动力条件。⑤低层辐合高层辐散的垂直结构,易于发生近地面大风和上升气流;⑥该次沙尘暴是一次大范围强对流天气,大气层结处于对流中性或对流不稳定状态,但都有强的斜压不稳定发展,并冷暖空气交换剧烈。沙尘暴影响前塔里木盆地有一个能量明显聚集期,但聚集时间很短。

The fields of geopotential height, anomalous change of high-level jet-stream, helicity, divergence and stratification conditions as the circulation dynamical structure in course of the sand-dust storm occurrence in southern Xinjiang in spring of 2003 are analyzed based on observed data and T213 data. The results show that （1）the polar cold air entering into Tarim basin caused sanddust storms in large extent because of eruptive development of Iran high and Ural ridge pile up; （2）The eruptive and violence development of west cold Siberian high pressure principally caused strong sand-dust storms; （3）The jetstream over South Xin- jiang caused by anomalous change of high jetstream resulted in ground gale by descending momentum, which are one of the dynamical conditions of sand-dust storm; （4）The distribution feature of helicity over the sanddust storm area is negative at the high level and positive at the lower, which implied that the strong rotating ascend is another one of the dynamical conditions of sand-dust storm; （5）There is a vertical Structure with convergence at lower level and divergence at upper level over the sand-dust storm area, this is favorable for occurring strong wind near ground and rising stream; （6）The case of sandstorm is a strong convection process, when the air stratification is convection neutral or instability, but all with strong development of baroclinic instability. Cold air and warm air meet strongly; there is energy collecting period before sand-dust storm, and the period is very short.