Influences of dust on landfalling atmospheric rivers in an idealized framework

Landfalling atmospheric rivers can provide as much as 50% of the total annual rainfall to the U.S. west coast via orographic precipitation. Dust, acting as ice nuclei, is expected to enhance orographic precipitation via the "seeder-feeder" mechanism, in which ice particles from a high cloud fall through a lower orographic cloud, seeding precipitation in the low cloud. Using the WRF-ARW model, we systematically evaluate dust impacts on precipitation by varying the strength of the dust forcing in simulations of two-dimensional flow over a mountain. This simple idealized framework allows us to test the sensitivity of the precipitation-dust response to variables such as the size and shape of the topography, and the model microphysical parameterizations. Furthermore, by classifying landfalling atmospheric rivers by their vertical moisture profile, we are able to compare the strength of the dust effects on precipitation during atmospheric rivers with a deep moist layer vs. atmospheric rivers where moisture is confined to the lower troposphere. This study allows us to build a more comprehensive understanding for the conditions under which dust aerosol can have a significant impact on precipitation during atmospheric rivers, with implications for future developments in forecasting.