How important are cyclones for emitting mineral dust aerosol in North Africa?

Abstract

This study presents the first quantitative estimate of the mineral dust emission associated to atmospheric depressions and migrating, long-lived cyclones in North Africa. Results from a tracking algorithm are combined with dust emission flux calculations based on ERA-Interim data from the European Centre for Medium-Range Weather Forecasts for 1989-2008. The results highlight that depressions are abundant and associated with 55% of the dust emission amount annually and spatially averaged over North African dust sources. Even larger contributions to dust emission from depressions are found south of the Atlas Mountains during spring with regionally up to 90 %. It is spring when the largest monthly totals of 250-380 gm-2 of dust emission occur in North Africa. The remaining months have a total dust emission smaller than 80 gm-2. In summer, depressions, particularly Saharan heat lows, coincide with up to 90% of the seasonal total dust emission over wide areas of North Africa. In contrast to depressions, migrating cyclones that live for more than two days are rare and are associated to 4% of the annual and spatial dust emission average. Migrating cyclones over North Africa occur primarily in spring north of 20_ N with eastwards trajectories and typical life times of three to seven days. Regionally larger seasonal totals of dust emission are associated to cyclones with up to 25% over Libya. In summer, near-surface signatures of African Easterly Waves (AEWs) emit regionally up to 15% of the total emission. The diurnal cycle of dust emission underlines that emission associated to cyclones at mid-day is substantially larger than at night by a factor of three to five. Soil moisture weakens dust emission during cyclone passage by 10 %. Despite the overall small contribution of migrating cyclones to dust emission, cyclones coincide with particularly intense dust emission events exceeding the climatological mean flux by a factor of four to eight. This implies, that both depressions and migrating, long-lived cyclones are important for dust emission in North Africa. [ABSTRACT FROM AUTHOR] Copyright of Atmospheric Chemistry & Physics Discussions is the property of Copernicus Gesellschaft mbH and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)