Examining the impact of wind and surface vegetation on the Asian dust occurrence over three classified source regions

In this paper, we examine the possible influences of wind and surface vegetation on the dust occurrence over the Asian dust source regions using meteorological and dust information from synoptic observation reports and the satellite-based normalized difference vegetation index for the period 1998-2006. It is found that the wind is the most important parameter controlling dust occurrence and is largely modulated by Mongolian cyclonic activity and the progress of the annual monsoon. By combining the spatial and temporal variations in the wind with the land cover types, the dust source regions are classified into three subregions: (1) region I, the nonvegetated Taklimakan region, with dust occurrence in spring and summer despite the persistent weak wind throughout the year; (2) region II, the nonvegetated regions of northern China and southern Mongolia, with significant temporal variations in both dust occurrence and wind speed; and ( 3) region III, the vegetated areas with dust occurrence mostly in spring. It is found that region I is most susceptible to wind because of the fine particles and smooth ground surface present. In the vegetated region (region III), the probability of dust occurrence seems to increase exponentially with wind speed but decreases with increasing vegetation. Accordingly, dust occurrence seems to be substantially suppressed after April because of the weaker Mongolian cyclonic activity and seasonal monsoon progress after April, concomitant with increasing vegetation.