欧亚大气环流对中国北方夏季沙尘天气的影响

根据1960—2010年全国701个地面站沙尘天气观测资料分析了中国夏季沙尘天气的空间分布和年际变化,发现南疆和内蒙古两个沙尘源区的夏季沙尘指数51年来均呈现出减小的趋势。通过分析夏季沙尘指数典型高、低值年环流场发现:500hPa高度场上强烈发展的高原贝加尔湖平均脊和减弱的东亚大槽,减少了高空低值系统对南疆和内蒙古中西部地区的影响,地面场上"北负南正"的变压场分布使得两个地区西风和西北风减小,最终导致夏季南疆和内蒙古地区沙尘天气减少。沙尘指数高值年时影响两个地区天气系统的差异在于:影响南疆地区的天气系统主要是高空的西路冷空气和地面场上发展的南疆热低压,而影响内蒙古地区的则是北路和偏北路冷空气以及地面场上强烈发展的蒙古内蒙古热低压。

Impact of Eurasian Atmospheric Circulation on Dust Events in Summer over Northern China

Based on the frequency of dust events in summer from 701 meteorological stations, two dust indices, which are Taklimakan Desert Index (TDI) and the Gobi Desert Index (GDI) were established to characterize the statistical feature of the summer dust occurrence. The two indices both exhibit a sudden decrease in the late 1980s and early 1990s. By analyzing the summer circulation field during the typical strong and weak summer dust index years of Southern Xinjiang and Inner Mongolia regions, we found that the Geopotential height of Mongolia-Inner Mongolia strongly elevated and developed into a ridge of high pressure, Southern Xinjiang and western Inner Mongolia were controlled by the ridge, altitude low value system reducing the influence of the two regions, the intensity of Siberia cold high pressure and the thermal low pressure in East Asian waken was the main mechanism in the Gobi desert region, which caused the less dust events in the Inner Mongolia and Southern Xinjiang.