Characterizing the distributions and sources of dust during atmospheric river landfall in the western U.S.

Abstract:

Atmospheric rivers (ARs) are prominent features of the global water cycle. On long-term average, 20%–50% of annual precipitation over California is attributed to several AR events in the cool season that produce heavy precipitation. Local and trans-Pacific dust has been found to interact with ARs and affect clouds and precipitation along the US West Coast. The impacts of dust on clouds and precipitation are dependent on dust distributions and its sizes and mineral compositions. Therefore, local and long-range transported dust from different sources may modulate clouds and precipitation differently. In this study, a state-of-the-art model WRF-Chem is used to characterize the dust distributions and sources during AR events that made landfall in the western U.S. in 2010-2014. Quasi-global WRF-Chem simulations are evaluated with reanalysis and observations. The model simulations successfully capture the AR events and aerosol distributions in 2010-2014. During AR landfall in the cool season (September-March), a higher fraction of dust mass is associated with trans-Pacific dust than local dust compared to the average conditions, suggesting that the circulation patterns associated with ARs may enhance transport of dust across the Pacific Ocean. Over the West Coast, local source dominates the total dust amount below 2 km and to the south of 40^oN during the AR landfall. East Asian, African, and Central Asian dust have comparable contributions above 2 km. The contribution of East Asian dust mass is higher during the AR landfall than the average conditions.