Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Trans-pacific Dust during Atmospheric River Landfall in the Western U.S.

Monday, December 12, 2016 - 13:40
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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 U.S. West Coast. Such interactions depend on the dust vertical and size distributions and its 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 evolution of dust distributions and source contributions during AR events that made landfall in the western U.S. in 2010-2015. Quasi-global WRF-Chem simulations are evaluated with reanalysis and observations. The model simulations successfully capture the AR events and aerosol distributions in 2010-2015. 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. In the U.S. west coast, dust of local origin dominates the total dust amount below 2 km and to the south of 40oN during the AR landfall, while trans-pacific dust dominates above 2 km with comparable contributions from East Asian, African, and Central Asian sources, respectively. The contribution of East Asian dust mass is higher during AR landfall than the average conditions. These results suggest that trans-Pacific dust could be incorporated in orographic clouds at high altitude, with implications to precipitation produced by landfalling ARs in the U.S. west coast.

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