Roles of surface wind, NDVI and snow cover in the recent changes in Asian dust storm occurrence frequency

This paper describes the recent variations in dust outbreak during the period from 1996 to 2007 over the Asian dust source regions. The Asian dust source regions were divided into four sub-regions; S1, Taklamakan; S2, Gobi; S3, Inner Mongolia-Manchuria; and S4, Loess, and the WMO SYNOP observation and satellite data were employed to analyze the features of recently changed dust outbreak frequencies (DOFs). There was no particular variation in region S1, but the recent spatiotemporal variations in DOFs over S2–S4 were well characterized by a severe and widespread increase in 2001–2002, and significant decreasing in 2003–2004 over the most source regions, with a steadily increasing trend again during 2005–2007. Seasonal features showed that the highest DOFs occurred in March–April before 2002, but was delayed by a month toward April–May during the next five years because of the shift in the month of highest strong wind-speed frequencies (SWFs). A secondary peak of DOF was also found, occurring in October–November since the year 2000. Over all the source regions, the primary controlling factor for explaining the spatiotemporal DOF patterns was the SWF, with a pattern correlation coefficient (PCC) of 0.66–0.76. Other secondary controlling factors varied from region to region. For example, the DOFs observed in region S2–S3 showed relatively greater sensitivity to the snow-cover fraction, and region S4 showed a better correlation with the normalized difference vegetation index (NDVI) than the other regions. Other recent significant changes in DOFs over the Asian dust source regions and their causes are also discussed in this study.