Where does the dust deposited over the Sierra Nevada snow come from?

Abstract

Mineral dust contributes up to one-half of surface aerosol loading in spring over the southwestern U.S., posing an environmental challenge that threatens human health and the ecosystem. Using the self-organizing map (SOM) analysis, we identify four typical dust transport patterns across the Sierra Nevada, associated with the mesoscale winds, Sierra-Block-Jets (SBJ), North-Pacific-High (NPH), and long-range cross-Pacific westerlies, respectively. We find dust emitted from the Central Valley is persistently transported eastward, while dust from the Mojave Desert and Great Basin influences the Sierra Nevada during mesoscale transport occurring mostly in the winter and early spring. Asian dust reaching the mountain range comes either from the west through straight isobars (cross-Pacific transport) or from the north in the presence of NPH. Extensive dust depositions are found on the west slope of the mountain, contributed by Central Valley emissions and cross-Pacific remote transport. Especially, the SBJ-related transport produces deposition through landfalling atmospheric rivers, whose frequency might increase in a warming climate.