Diagnostic Study of a Severe Dust Storm over North Africa and the Arabian Peninsula

This work aimed to study the synoptic evolution and dynamics of the dust activity associated with the desert cyclone occurring over North Africa and the Arabian Peninsula on 4-8 April 2007 based on ECMWF analysis (ERA5) data. This desert cyclone formed over North Africa (Algeria) in the lee of the Atlas Mountains in response to a powerful upper-level trough transporting cold air into northern Africa coming from high latitudes. The development of the cyclone was initiated when the contrast in temperature between the Mediterranean Sea and northern Africa (the desert) was strong, which increased the meridional temperature gradient. The isobaric vorticity analysis illustrated that the strong advection of positive vorticity and warm air ahead of the cyclone triggered cyclogenesis and low-level jet (LLJ) formation. The strong LLJ maintained the development of the cyclone inside the area of baroclinicity at a low-level. The horizontal divergence of 700 hPa level covered the region downstream of the cyclone trough and is coupled with the lower-level convergence. The study of frontogentical function concluded that the first stage of cyclogenesis is associated with frontogenesis working at the initial front of the cyclone. The vertical motions are then dominated by the direct transverse circulation with the ascent of the warmer and descent of the colder air. The mass transport within the circulation causes pressure falls along the surface front connected with convergence leading to the production of vorticity. The dust emissions linked to the cyclone during its duration and along its path were also investigated.