A Study Of Temporal And Spatial Characteristics Of Dust Weather In Northern China

It is necessary to examine whether the satellite monitoring results are consistent with ground-based observations if using satellite data in studying dust weather frequency or dust aerosol optical thickness. In this paper, the dust weather event frequency (DF) data from the ground-based observations record and aerosol optical thickness Index (AI) from TOMS for time period1979-2002is compared, and the temporal and spatial characteristics of dust aerosol optical depth in northern Chinais analyzed based on the long-term AI data series. A preliminary discussion on the implications of the findings for the formation and evaluation of the loess on the Loess Plateau is made. Finally, the paper illustrates a newly developed East Asian monsoon index and the analysis of the possible effect of winter monsoon intensityon springtime dust weather frequency in northern China. The main conclusions are as follows:(1) Overall, the comparison well reflect the spatial and temporal characteristics of dust aerosol obtained based on the dust weather observation data in northern China, with higher consistency being seen in northwestern arid and semi-arid regions. It is concluded that TOMS AI data can well represent the spatial distribution and seasonal evolution of the atmospheric mineral aerosol deposition flux in northern China, and the further analysis of the data will help in understanding the formation and evolution of China loess in Quaternary.(6) It is interesting to note that the pentad mean AI values in Northwest, North and Northeast China witness an obvious seasonal transformation in16-20April and1-5November each year, with the AI values of Northeast China being larger than those of Northwest and North China in cold half year, and AI values of Northwest China being larger than those of Northeast and North China in warm half year.(7) A new East Asian winter monsoon index is developed based on land-sea thermal difference between Asia and the Pacific and Indian Oceans. The new index shows that of the East Asian winter monsoon intensity has similar inter-annual and interdecadal variability as indicated by the index used in the monitoring operation of the National Climate Center of China, with both showing that the winter monsoon was strong in1950s to1970s, and weak in the late 1980s and early1990s. A obvious difference between the two indices, however, occurs for the time period after mid-1990s, with the new index showing a continuous decline of the winter monsoon intensity.(8) The newly developed East Asian monsoon index bears a good positive correlation with the dust weather frequency in springtime in northern China. The relationship is more significant in the Loess Plateau, Northwest China and the Qinghai-Tibetian Plateau. Therefore, a possible effect of the winter monsoon intensity on springtime duststorms is expected, with the strong (weak) winter monsoon followed by the more (less) frequent dust weathers in springtime in northern China.