Solving the Coarse Dust Conundrum: What Processes Cause Large-scale Models to Underestimate Coarse Dust Transport?

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At any given time, our atmosphere contains tens of millions of metric tons of desert dust. This dust seeds clouds and scatters and absorbs sunlight and, when it settles from our atmosphere, fertilizes ecosystems and darkens snow and ice. Basic physics predicts that coarse dust particles - still no larger than the thickness of a human hair - quickly settle out of the atmosphere. However, measurements indicate that this is not the case; instead, coarse dust can remain in the atmosphere for days and travel thousands of kilometers from its source. This dust therefore has more time to impact the Earth and its weather and climate. This makes it critical to determine the processes that cause dust to stay in the atmosphere longer than expected, and account for these missing processes in climate and weather models.This project uses Large Eddy Simulations (LES) and other techniques to test three hypotheses of the nature of the process(es) that help keep coarse dust aloft. Specifically, this project tests whether dust asphericity, electrification, and / or turbulence in dusty layers keep dust aloft against the action of gravitational settling. The project will result in a parameterization of dust gravitational settling that includes these missing processes and that can be used in weather and climate models. This will allow these models to more accurately represent desert dust in the atmosphere and its impact on the Earth system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.