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

Mineral dust contributes up to one-half of surface aerosol loading in spring over the southwestern United States, posing an environmental challenge that threatens human health and the ecosystem. Using self-organizing map (SOM) analysis with dust deposition and flux data from WRF-Chem and Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), we identify four typical dust transport patterns across the Sierra Nevada, associated with the mesoscale winds, Sierra barrier jet (SBJ), North Pacific High (NPH), and long-range cross-Pacific westerlies, respectively. We find that 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 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 the NPH. Extensive dust depositions are found on the west slope of the mountain, contributed by Central Valley emissions and cross-Pacific remote transport. In particular, the SBJ-related transport produces deposition through landfalling atmospheric rivers, whose frequency might increase in a warming climate.

Automated summary

Mineral dust, which makes up around half of the surface aerosol loading in spring over the southwestern United States, poses a threat to human health and the ecosystem. Through analysis of dust deposition and flux data, researchers have identified four typical dust transport patterns across the Sierra Nevada mountain range. These patterns are associated with mesoscale winds, the Sierra barrier jet, the North Pacific High, and long-range cross-Pacific westerlies. The study finds that dust emitted from the Central Valley consistently moves eastward, while dust from the Mojave Desert and Great Basin primarily affects the Sierra Nevada during mesoscale transport in winter and early spring. Asian dust reaching the mountain range either comes from the west through straight isobars or from the north in the presence of the North Pacific High. Extensive dust depositions, contributed by Central Valley emissions and cross-Pacific remote transport, are found on the west slope of the mountain. Particularly, dust transport related to the Sierra barrier jet produces deposition through landfalling atmospheric rivers, and this frequency may increase as the climate warms.