How a mesoscale cyclonic vortex over Sahara leads to a dust outbreak in South-western Iberia

Abstract

The study focused on an exceptional desert dust outbreak episode, in particular on the role of atmospheric circulation transporting high amounts of dust toward Portugal in February 2017. In order to assess the atmospheric conditions behind the mineral dust layer observed in Évora from lidar observations, two simulations were performed with the Meso-NH model including dust emission but with different initialization times. The simulations were performed over a single domain that covers 3000×3600 km and with a 10 km resolution. The episode was governed by a variety of complex interactions between surface and atmospheric dynamics during nine days. The study highlights the role played by the regional orography of the North Africa producing mesoscale circulations, namely the airflow convergence and the development of a cyclonic vortex in the lower troposphere. The intense winds near the surface was the main factor controlling the mobilization of mineral dust particles. In addition, a low pressure system approaching from mid-latitudes was fundamental for the longlasting event, as well as for the transport of desert dust toward Portugal.