Characterizing the Impact of Atmospheric Rivers on Aerosols in the Western U.S.

Abstract

Two 5-year (2010–2014) quasi-global simulations using the Weather Research and Forecasting model coupled with Chemistry have been analyzed to quantify the impacts of atmospheric rivers (ARs) on aerosols in the western United States (U.S.). We find that AR days have reduced trans-Pacific as well as U.S. aerosol mass because of enhanced rainfall and hence, wet removal of aerosols, compared to non-AR days. ARs reduce trans-Pacific aerosol mass through the cyclonic circulation that shifts the aerosol transport pathway southward and brings cleaner air from the north. However, ARs have larger impact on aerosols that originate over the U.S., which are concentrated closer to the surface compared to trans-Pacific aerosols that are distributed more uniformly with altitude. While dust and sulfates dominate the mass for both trans-Pacific and U.S. aerosols, ARs reduce dust composition fractions of trans-Pacific aerosols but the AR impacts on composition fractions of U.S. aerosols are more variable.