Variation Of Extratropical Cyclone Activity In Northern East Asia And Impact Of Mongolian Cyclone On Dust Storms In Spring Over Northern China

Based on the ERA-40 SLP data during 1958～2001, the cyclone detection andtracking algorithm is further improved in this study. Refering to objective definitionof extratropical cyclones of East Asia, the data files about the position, intensity andtrack are obtained. Variation of extratropical cyclones in northern East Asia is studiedand the climate characteristic of the Mongolia cyclone and the relationship betweenthe Mongolia cyclone and the Chinese northern sandstorm in spring is analyzed. Therelationship among the variation of extratropical cyclones of East Asia and theintensity of baroclinic front zone in lower of troposphere and climate change of EastAsia temperature is further discussed. The possible reasons of variation ofextratropical cyclones under the background of global warming are revealed. Theresults indicate1) The decadal variability is important characteristic of extratropical cyclones innorthern East Asia. The number of cyclones increased from the mid-1970s toend-1980s. Then, the number of cyclones decreased up to early 1990s. Since themid-1990s, cyclone frequencies have increased again. The highest cyclone numberoccurs in spring (MAM). The annual and decadal variability contribute main inspring. Extratropical cyclones move mainly follows 40°-50°N, Mongolia is a regionwith high frequency of extratropical cyclones. From 1980s to 1990s, variation ofextratropical cyclones in northern East Asia in spatial distribution shows thatfrequency decreasing is mainly at about 45°N, 100°～110°E. The high frequentactivity centres have northward shift about two latitudinal bands from 1980s to1990s.The intensity of extratropical cyclone has decreased under annual and seasonalbases.2) During 1958～2001, the frequency and intensity of Mongolia cyclonesdecreased. There is significant tropospheric temperature anomalous differencebetween its active years and its suppressed years, respectively corresponding tostronger negative and positive departure.3) Dust storms are consistent with strong wind regions, which generally locatenearby the center or the periphery of cyclone. The further analysis shows that thesecular trends of dust storms are consistent with the variation of Mongolian cycloneactivities and there are obvious correlation coefficients between both. The regionswith high correlation coefficient are consistent with the distribution of the deserts.4) When calculating the correlation for the period f 1958～2001, wit is found that the annual number of cyclones and the mean intensities of the baroclinic front zoneare significantly positively correlated, stronger (weaker) frontal zone arecorresponding to more (less) cyclone frequency. It indictes that variation in thenumber of extratropical cyclones is influenced by that of the intensity of thebaroclinic front zone, which is mainly related to the temperature change in the lowertroposphere at the higher latitudes in NE Asia region.