Multi-Scale Atmospheric Dynamics of Extreme Saharan Dust Storms Resulting in Dust Transport Out of Africa to Iberia and the Atlantic

Abstract

Understanding the meteorological processes that organize Saharan dust plumes and their subsequent long-range transport is a major global concern. However, the state-of-the-science of the meteorological forcing mechanisms for dust emission over the complex terrain of North Africa is incomplete due to very few upper-air and ground-based operational meteorological networks. We investigated multi-scale meteorological processes responsible for organizing four extreme large-scale African dust storms that had a strong impact over the Iberian Peninsula (IP) and the Cape Verde Islands using observations and a high-resolution Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) simulation. The current new findings include: (1) a double Rossby wave breaking (RWB) process in the polar jet stream linked through nonlinear wave reflection as an upper-level synoptic precursor prior to forming strong dust plumes and (2) the downscale dust plume organization/restructuring by different meso-β/γ scale terrain-induced features including: (a) density current-like cold fronts, (b) undular bores, (c) barrier jets, (d) hydraulic jumps, and (e) mesoscale internal gravity waves. Moreover, we also highlight that the interaction between moisture from the Eastern Atlantic and a residual convective cold pool could trigger unseasonably strong moist convection and a haboob on the Atlas' southern foothills. The lifted dust can mix and extend over a depth of 2-3 km in the growing daytime Saharan atmospheric boundary layer and ultimately is advected poleward by the southerly/southwesterly mid-tropospheric flow set up by the previous double RWB. The coupling of an upper-level isentropic potential vorticity vortex over the Atlas due to the precursor double RWB and thermally driven daytime mountain-plains solenoidal circulation in response to differential heating between the Atlas Mountains' southern slope and the nearby atmosphere also collaboratively rotates and transports dust poleward.