Pokharel, Ashok Kumar, Kaplan, Michael L. and Fiedler, Stephanie (2017) Subtropical Dust Storms and Downslope Wind Events. Journal of Geophysical Research: Atmospheres, 122 (19). 10,191-10,205. DOI 10.1002/2017jd026942.

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Abstract

We performed detailed mesoscale observational analyses and Weather Research and Forecasting (WRF) model simulations to study the terrain-induced downslope winds that generated dust-emitting winds at the beginning of three strong subtropical dust storms in three distinctly different regions of North Africa and the Arabian Peninsula. We revisit the Harmattan dust storm of 2 March 2004, the Saudi dust storm of 9 March 2009, and the Bodélé Depression dust storm of 8 December 2011 and use high-resolution WRF modeling to assess the dynamical processes during the onset of the storms in more depth. Our results highlight the generation of terrain-induced downslope winds in response to the transition of the atmospheric flow from a subcritical to supercritical state in all three cases. These events precede the unbalanced adjustment processes in the lee of the mountain ranges that produced larger-scale dust aerosol mobilization and transport. We see that only the higher-resolution data sets can resolve the mesoscale processes, which are mainly responsible for creating strong low-level terrain-induced downslope winds leading to the initial dust storms.

Key Points:
- Downslope winds resulted in strong low-level vertical wind shear, which interacted with the development of near-surface positively buoyant air during the morning and generated significant turbulence kinetic energy
- The strong and gusty winds caused moderate meso-γ- to β-scale dust storms as an early stage of precursor to later severe dust storms that affected large areas

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