Estimation of Threshold Friction Velocity Using a Physical Parameterization Over the Asian Dust Source Region

Threshold friction velocity distribution over the Asian dust source region is estimated for a dust storm event period in April 2006 and compared with the values reported previously based on statistical analysis. It is shown that the Asian dust source region can be identified using the combined information of land-use and soil moisture content. Soil moisture effect is shown to be more important than the effect of soil texture in determining the threshold friction velocity in this region. The threshold friction velocity estimated is the largest in loess area due to high soil moisture content and the smallest in Gobi desert due to low soil moisture content. This result is opposite to the trend reported in previous studies in which the threshold value was the highest in Gobi desert and the lowest in loess area. This discrepancy is attributed to the questionable definition of the threshold value used in the previous studies. It is argued that the threshold friction velocity should be defined based on the dust occurrence probability (DOP), not on the normalized cumulative DOP. An important strength of the method presented in this paper is that it can account for the surface wetness effect without requiring additional restraints.