关键词: 甘肃, 沙尘暴, 环流特征, 时间尺度, 诊断分析

Abstract: According to the departure sequences of spring sand-dust storm days happened in Gansu during 43 years, the years in which sand-dust storm took place at high frequency and at low frequency have been selected. The 500 hPa departure height fields during spring (Mar.-May) and pre-winter (Dec.-Feb.) synthetically showed that the pre-winter East Asian Trough and the homochronous Mongolia cyclone are the main systems influenced the spring sand-dust storms in Gansu. The calculating results of the Westerly Index and the East Asian Boreas Index indicated that there existed remarkable differentiation of indexes between in the years of sand-dust storm frequently occurred and in the years of less sand-dust storms; the East Asian circulation in pre-winter is the main background causing the spring sand-dust storms in Gansu. The Mexican Hat Wavelet transform analysis clearly reflected the different temporal scales of the spring sand-dust storms in Gansu; it also showed that there were 2 more and less phases about the spring sand-dust storms. The positive and negative extremum of different temporal coefficients wavelet transform respectively corresponded well to the phases of more spring sand-dust storm years and less spring sand-dust storms years in Gansu. The changing trend of different wavelet coefficients suggests that the spring sand-dust storms in Gansu will increase at the beginning of the 21st century.

Key words: Gansu, sand-dust storm, circulation character, temporal scales, diagnosis analysis