Density currents as a desert dust mobilization mechanism

This discussion paper is/has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP if available. Abstract The formation and propagation of density currents are well studied processes in fluid dynamics with many applications to other science fields. In the atmosphere, density currents are usually meso-β/γ mechanisms and are often associated with storm down-drafts. These storms are responsible for the formation of severe dust episodes (ha-5 boobs) over desert areas. In the present study, the formation of a convective cool pool and the associated dust mobilization is examined for a representative event over the western part of Sahara desert. The physical processes involved in the mobilization of dust are described in the framework of the integrated atmospheric-air quality RAMS/ICLAMS model. Dust is effectively produced due to the development of near 10 surface vortices and increased turbulence mixing along the frontal line. Increased dust emissions and recirculation of the elevated particles inside the density current head result in the formation of a moving " dust wall ". Transport of the uplifted dust in higher layers – outside of the density current – occurs mainly in three ways: (1) uplifting of pre-existing dust over the frontal line with the aid of the strong updraft (2) entrainment at the 15 upper part of the density current head due to turbulent mixing (3) vertical mixing after the dilution of the system. The role of the produced dust in the associated convective cloud system was found to be limited. Proper representation of convective processes and dust fluxes requires the use of high resolution (cloud resolving) model configuration and online parameterization of dust production. Haboob-type of dust storms are 20 effective dust sources and should be treated accordingly in dust modeling applications.