Land Surface Impacts on Cold Pools, Haboobs, and Dust Lofting in Dryland Regions

Haboobs are dust storms formed in arid environments by strong surface winds in convective storm outflow boundaries, also known as density currents and cold pools, which can loft large quantities of mineral dust as they propagate. Both cold pools and the dust they loft are impacted by land surface properties, resulting in complex surface interactions unique to dryland areas. As a result of these additional complexities brought about by surface interactions, it is unclear which surface parameters and physical processes are important for predicting cold pool intensity and dust concentrations in these arid to semi-arid regions.

Here we apply the Morris-one-at-a-time (MOAT) global sensitivity statistical method to an ensemble of 120 idealized simulations of daytime and nighttime dust-lofting density currents to investigate the land surface properties that affect both dust mobilization and cold pool dynamics. MOAT identifies and ranks the importance of different input factors, which for the prediction of haboob strength and dust concentrations are: (1) initial cold pool temperature, (2) surface type (vegetation), (3) soil type (clay content), and (4) soil moisture.

The underlying physical mechanisms driving these feedbacks are then analyzed using a traditional one-at-a-time factor analysis. Time of day is significant for determining boundary layer height and dissipation via surface fluxes, leading to shallower, more intense cold pools / haboobs at night. Most of the land parameters modify the cold pool through impacts on surface fluxes, while surface type is dominated by roughness length effects. Finally, by ranking the importance of these factors, we identify and discuss which variables are most sensitive and must be constrained via observations and data assimilation in numerical weather and dust prediction models.