Impact Of Eurasian Atmospheric Circulation On Dust Events Over Northern China

China’s northwest and northern regions, as parts of the Central Asia sandstorm high incidence area, is not only a high incidence region of dust weather and the hardest hit in China, but also the main source region of the Dust Disaster which were Observed in Yangtze River Valley. Due to the fact of global warming and northern ecological environment which is difficult to change in a short period of time, it is very important to carry out the research on the circulation changes and its effects on dust weather. By using the meteorological date from701stations in China during the years1960-2010and the reanalyzed circulation data from NCEP/NCAR, the time characteristics of dust weather and the effect from circulation changes were investigated. In addition, the influence of Southern Xinjiang dust aerosol in summer to the precipitation of the middle and lower reaches of Changjiang River were discussed. The result shows that:First, dust storms in China are mainly distributed in five northwestern provinces and the Inner Mongolia region, the high incidence regions are southern Xinjiang and the western Inner Mongolia; The blowing dust distribution range extends somewhat to the northeast, but a high incidence still appear in southern Xinjiang and western Inner Mongolia; The floating dust distribution extends to the south of the Yangtze River region. The spring dust weather distributions are relatively similar to the annul-averaged distribution, but there are some differences between the summer and annul-averaged dust weather distribution. For example, the spatial distribution of dust weather in summer is significantly smaller than that all year round; summer dust storms are mainly distributed over the southern Xinjiang and western Inner Mongolia; the Blowing dusts are mainly distributed in Xinjiang, Inner Mongolia, Hetao area and the North China Plain region; summer floating dust is mainly distributed in the southern Xinjiang-western Inner Mongolia-Hetao area.Second, in southern Xinjiang spring dust storm, blowing dust and floating dust respectively account for53.2%,45%and39%of the annual total, in summer the ratios are35.2%,36.8%and31.3%.While in Inner Mongolia the ratios are49.4%,45.3%,52.5%in spring and32.2%,28.0,18.7%in summer respectively. Both in southern Xinjiang and Inner Mongolia the total of spring and summer dust weather accounts for2/3of the whole year.Third, both the TDI and GDI in spring and summer have been decreasing in the past51years with their high values during the mid-1970s to the mid-80s. The values significantly reduced from the late1980s and early1990s, and kept low in1990s and2000s. The results show that the spring TDI and GDI anomalies both changed into the negative zone in the mid-1980s, while the summer TDI and GDI anomalies changed into the negative zone respectively in late1980s and early1990s. From the results of T-test, the steep reduction of the spring TDI occurred in1987over Nanjiang area; the steep reduction of the spring GDI occurred twice in1988and1991over Inner Mongolia; while the steep reduction of both summer TDI and GDI occurred twice inNanjiang, and the same thing occurred in1990and1999over Inner Mongolia.Fourth, the low frequency of dust events in Xinjiang was likely caused by the waken Mongolia cyclone and the thermal low pressure in the Taklimakan region, but the intensity of Siberia cold high pressure and the Mongolia high pressure became waken was the main mechanism in the Gobi desert region, which caused the less dust events in the inner Mongolia region; By analyzing the summer circulation field during the typical strong and weak summer dust index years of 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, 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 became waken was the main mechanism in the Gobi desert region, which caused the less dust events in the inner Mongolia and Xinjiang region.Fifth, by analyzing the monthly correlation coefficient distributions of the TDI with the national precipitation, we found that:The precipitation in July in middle and lower reaches of the Yangtze River has significant positive correlation with the TDI, and the detrend correlation coefficient is0.352high. By using the anomalies of TDI and precipitation in middle and lower reaches of the Yangtze River, we divided the period of1960to2010into four types and found that:In type Ⅰ,it revealed from the500hPa geopotential height field that the dust aerosol originated in Nanjiang could be transferred to the middle and lower reaches of the Yangtze River from the northern part of the plateau with the strengthening of the westerly jet. In the meantime the westerly vapor transportation on500hPa, the vapor transportation from the bay of Bengal and transportation from western Pacific on850hPa were stronger than the normal years. Because of the influence of the circulation field and the vapor transportation also the dust aerosol, precipitation in July in middle and lower reaches of the Yangtze River was23.6%which is greater than those in normal years. In type Ⅲ, as the vapor transportation from South China Sea was stronger, and the middle and lower reaches of the Yangtze River was in the front of the trough and the northwest of the West Pacific subtropical high, so the precipitation in this type is the highest in the four types. The reason why the precipitation in type Ⅱ and type Ⅳ were lower was the lack of suitable circulation field or water vapor transportation.