Using WRF-Chem to Examine the Role of Antecedent Snow and Soil Moisture Conditions on Dust Emissions during a Powerful Dust Storm That Affected Northern China in the Spring of 2021.

On March 14^th 2021, a powerful cold front swept south across the Northern Gobi Desert in Mongolia creating a historic and far-reaching dust storm that affected visibility and air quality over northern China for several days. One of the more unique aspects of this storm is that it occurred during the early spring over a region that is often influenced by snow and frozen soil. In fact, numerous studies on this event have suggested anomalously low snow across the northern Gobi Desert was a significant factor in the event magnitude. If antecedent soil and snow conditions have significant influence on springtime dust emission in the Gobi Desert, climate change may lead to more severe dust storms over northern China. Here we explore the role of antecedent snow and soil moisture conditions in the dust source region on this event using the Weather Research and Forecasting (WRF)-Chem model and the Land Information System (LIS). We use the LIS to perform multi-year Noah-MP simulations, and then perform simulations of the March 14, 2021 dust event with varying initial snow and soil moisture conditions pulled from the LIS climatology. We show that the antecedent soil moisture across the dust source region had a substantial impact on the simulated dust event. The high sensitivity of dust to soil moisture in this region is a combination of the strong sensitivity of the threshold friction speed (u*_t) to soil moisture at low soil moisture values, combined with the fact that the dust emission flux is proportional to the difference between the imposed friction velocity (u*) and u*_t cubed. The influence of uncertainties related to the simulated dust sources and simulated soil moisture and snow is discussed.