宁夏不同强度沙尘天气动力机制

利用常规气象观测资料和ECMWF逐6 h 0.25°×0.25°再分析资料,对宁夏2013年5月18日雷暴大风、2月28日大风沙尘和3月9日大风强沙尘天气过程的环流形势和高、低空急流的耦合作用进行了对比分析。结果表明:在“西高东低”环流形势下,受蒙新高压脊、西风槽、地面气旋和冷锋、高低空急流的共同影响,在中低层90°-110°E形成次级环流,对流层中上部高空急流和高位涡通过次级环流动量下传使中低层形成低空急流,同时在边界层发生强烈湍流混合,产生地面强风及沙尘,但由于冷空气强度及南下方式、高压脊线位置及强度、高低空急流活动的区域、低空急流南下位置、高空强风速下传的高度、次级环流的强弱不同,高层高位涡和低层850 hPa低空急流在宁夏上空活动与否,是导致宁夏出现不同强度风沙天气的重要动力因素。

Dynamic Mechanism of Dust Weather with Different Intensities in Ningxia,China

By using conventional observation data and the ECWMF 6-hourly reanalysis data with resolution 0.25°×0.25°,the circulation systems, high and low jets effected on strong wind and dust weather on May 18, February 28, March 9 in 2013 are analyzed. The results show that under the circulation background that high pressure at west Ningixa and low pressure at east Ningxia and affected by the combined effects of Mongolia-Xinjiang high pressure ridge, temperature, westerly trough, ground cyclone, cold front, high and low jets, secondary circulation formed in the middle and lower atmosphere in 90°-110°E. Due to downward momentum of the upper jet stream and high potential vorticity through the secondary circulation, low level jet begin to form. Meanwhile strong turbulent mixing occurs in the boundary layer, strong winds and dust weather produces. The important motivation factors that cause different intensities of dust weather in Ningxia are the intensity and the southward way of the cold air, the position and strength of high pressure ridge, the area of high and low jets, the southward location of low level jet, the height reached by the upper strong wind, the strength of the secondary circulation, and the activities of high potential vorticity at upper level and low level jet at 850 hPa over Ningxia.