Analysis of Climatic Characteristics and Influencing Factors of Sand-Dust Events in Northwest China

In the present study, on the basis of the statistics and diagnosis methods, the sand-dust events of Northwest China are studied by the use of 135 stations monthly data from National Meteorological Information Center during 1960-2005. The 500 hPa height field and the sea surface temperature (SST) data are from NCEP/NCAR and NOAA, respectively. Results show that the climatic characteristics of sand-dust events in Northwest China are: the annual mean numbers of sand-dust occurrence days in the most part of Northwest China is more than 5 days. The areas with high frequency sand-dust occurrence days more than 50 days are mainly in the deserts and their surroundings. This shows that the characteristics of underlying surface and the distribution of sand source play an important role in forming sand-dust events. The events are frequent in spring and scarce in autumn. The occurrence days of sand-dust in the last 4 decades appears a generally decrease trend which is more significant in the high frequency areas. There is a transform from a relative frequent period to a relative scarce period in the middle 1970s, and this decreasing tendency is very remarkable in recent 30 years. There is negative correlation between the numbers of sand-dust days and the precipitation in the most part of Northwest China; the higher correlation coefficient areas are mainly located in south Xinjiang, Dunhuang to Qaidam Basin, and west of Inner Mongolia. The correlation coefficient is negative between the sand dust occurrence days and the temperature, except for the south of Qinghai province. The negative anomaly of sand dust days in Northwest China companied with the negative anomaly of geopotential height in the north Pacific, the abnormal strong 500hPa ridge of high pressure, and the abnormal high geopotential height field in the extratropical latitude of Asia, and vice versa. The typical EL Nino (La Nina) style consist with the negative (positive) anomaly of sand dust days in spring at the corresponding period.