Haboobs on Slopes

Abstract The impacts of topographic slope on daytime haboob propagation speeds and dust lofting are examined along with how these impacts are modulated by surface roughness length. A suite of 20 idealized, large‐eddy simulations are run with varied linear topographic slopes and surface roughness lengths. It is found that on flat ground, greater surface roughness increases drag on haboobs and causes haboobs to dissipate faster, thereby decreasing both haboob propagation speeds and dust lofting. In simulations with sloped topography, upslope anabatic winds form due to solar heating. As topographic slope and surface roughness are increased, the anabatic winds become faster. Greater surface roughness causes more drag on the anabatic wind, but this is counteracted by greater sensible heat fluxes driving a stronger pressure gradient. These anabatic winds act to advect haboobs upslope. Hence, as the topographic slope is increased, downslope haboob propagation speeds are decreased, and upslope haboob propagation speeds remain mostly unchanged. Anabatic winds act to loft dust as well leading to increased dust lofting jointly by the haboob and anabatic winds as topographic slopes are increased.