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A Multi-Scale Dynamical Analysis of the Saharan Dust Outbreak Towards the Cape Verde in Early November 2017
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  • Saroj Dhital,
  • Michael L. Kaplan,
  • Jose Antonio Garcia Orza,
  • Stephanie Fiedler
Saroj Dhital
Division of atmospheric science, Desert Research Institute, Reno, NV, USA

Corresponding Author:[email protected]

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Michael L. Kaplan
Applied Meteorology Program, Embry-Riddle Aeronautical University, 3700 Willow Creek Road, Prescott, AZ 86301, USA
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Jose Antonio Garcia Orza
SCOLAb, Department of Applied Physics, Universidad Miguel Hernández de Elche, Av. de la Universidad s/n, 03202 Elche, Spain.
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Stephanie Fiedler
Max Planck Institute for Meteorology, Hamburg, Germany
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On 13 November 2017, a strong continental-scale Saharan dust outbreak was observed in satellite imagery over Mindelo, Cape Verde, located about 650 km off the coast of Senegal in West Africa. Horizontal visibility was reduced to 1100 m leading to major disruptions of the local air traffic. Dust mobilization was already observed over the foothills of the Saharan Atlas Mountains at 0600 UTC on 10 November 2019 but did not appear clearly in SEVIRI pink dust images in the subsequent days. In this study, we examined the multi-scale dynamical processes associated with this particular dust storm using ECMWF ERA-Interim reanalysis data, newly performed very-high resolution WRF-CHEM simulations with horizontal grids of 18 km and less, NAAPS aerosol forecast output, ship-based observation dataset from the North Atlantic Expedition MSM 68/2, as well as surface observations, and upper-air soundings from weather stations in North Africa. Our analyses of this storm highlights the following meteorological processes: (1) the event was associated with a typical Harmattan surge, i.e., the post-frontal strengthening of the northerly winds behind an eastward moving cyclone, (2) a series of earlier Rossby Wave Breaking events (RWBs) made the environment favorable for the Harmattan surge, (3) the dust storm was composed of two distinct dust surges, (4) the dust aerosol from the first surge was later mixed with the dust from the second surge while simultaneously propagating south-westward and later westward, (5) the PBL became adiabatic along the leading edge of the leftover cold front between the southern/southeastern flank of the Atlas Mountains and western/northwestern flank of the Hoggar Mountains, and (6) vertical dust mixing then occurred due to very strong surface heating associated with the development of a deep daytime PBL in the region behind the cold front. The results of this research demonstrate that very-high spatial resolution WRF-CHEM model can resolve the dynamical processes and realistically simulate large-scale North African dust storm.