Atmospheric Dynamics of a Saharan Dust Outbreak over Mindelo, Cape Verde
Islands: Multi-scale Observational Analyses and Simulations
Abstract
We investigate the synoptic precursors to the Harmattan wind and dust
frontogenesis during the high impact Saharan dust outbreak over the Cape
Verde Islands on 13 November 2017. We employ multi-scale observations
including ship data and Weather Research and Forecasting model Coupled
with Chemistry simulations. The analyses indicate that the dust storm
was initiated on the leeside of the Saharan Atlas Mountains (SAM) in
Algeria on the 10. This dust storm was associated with a double Rossby
Wave Break (RWB) linked through non-linear wave reflection. Two
successive RWB contributed to the wave amplification over the Eastern
North Atlantic Ocean which transported large magnitude potential
vorticity air into the North African continent. The resulting coupled
pressure surge was associated with cold air advected equatorward over
the SAM which organized the strong near-surface wind that ablated the
dust. The simulation results indicate that the dust front was initially
related to a density current which formed due to the cold airflow over
the SAM. The density current then triggered undular bores on the
leeside. Each bore perturbed the dust loading and then the subsequent
diurnal heating generated differential planetary boundary layer (PBL)
turbulence kinetic energy strengthening the dust frontogenesis. Dust
became confined behind the cold surge and interacted with the daytime
Saharan PBL leading to increased dust loading while the dust front
propagated equatorward. Two distinct dust plumes arrived successively at
low-levels at Mindelo, Cape Verde Islands; (1) from the coasts of
Mauritania and Senegal and (2) from the SAM southern flank.