Abstract
Abstract. The regime of intense desert dust (DD) episodes over the broader Mediterranean Basin is studied for the period 2000–2007 at a complete spatial coverage. An objective and dynamic algorithm has been set up which uses daily measurements of various aerosol optical properties taken by different satellite databases, enabling the identification of DD episodes and their classification into strong and extreme ones. The algorithm's performance was tested against surface-based (in situ) particulate matter (PM) and (columnar) sun-photometric AERONET (AErosol RObotic NETwork) measurements from stations distributed across the Mediterranean. The comparisons have shown the reasonable ability of the algorithm to detect the DD episodes taking place within the study region. The largest disagreements with PM data were found in the western Mediterranean in summer, when African dust transport has a great vertical extent that cannot be satisfactorily captured by surface measurements. According to our results, DD episodes in the Mediterranean Basin are quite frequent (up to 11.4 episodes yr−1), while there is a significant spatial and temporal variability in their frequency of occurrence and their intensity. Strong episodes occur more frequently in the western Mediterranean Basin, whilst extreme ones appear more frequently over central Mediterranean Sea areas. Apart from this longitudinal variation, there is a predominant latitudinal variability in both frequency and intensity, with decreasing values from south to north. A significant seasonal variation was also found for the frequency of DD episodes, with both strong and extreme episodes being more frequent during summer in the western Mediterranean Basin, but during spring in its central and eastern parts. In most cases (> 85%) the Mediterranean dust episodes last a bit longer than a day on average, although their duration can reach six days for strong episodes and four days for extreme episodes. A noticeable year-to-year variability was also found, especially for the frequency of the episodes.
Highlights
Desert dust aerosols are coarse particles with size distribution showing a dominant coarse mode at 1–5μm and a secondary fine mode around 0.5μm (Tanré et al, 2001) being mainly produced by natural processes and only to a small extent (< 10 %) by agricultural activities (Tegen et al, 2004)
The present study aims to describe, for the first time, to our knowledge, the regime of intense desert dust episodes that takes place over the entire Mediterranean Basin
An objective and dynamic algorithm has been set up which identified the desert dust (DD) episodes that occurred over the period 2000–2007
Summary
Desert dust aerosols are coarse particles with size distribution showing a dominant coarse mode at 1–5μm and a secondary fine mode around 0.5μm (Tanré et al, 2001) being mainly produced by natural processes and only to a small extent (< 10 %) by agricultural activities (Tegen et al, 2004) They affect climate since they perturb the radiation budget of the Earth–atmosphere system interacting (through scattering and absorption) mainly with solar (shortwave – SW) and with terrestrial (longwave – LW) radiation, respectively producing. Hatzianastassiou et al, 2004; Papadimas et al, 2012), and depending on the surface albedo (Osborne et al, 2011; Yang et al, 2009) Because of their high loadings and large radiative impacts, dust should be considered in climate and weather studies. All these impacts of dust along with those on radiation become maximum under conditions of extreme loadings in the atmosphere, namely in the case of dust episodes (or events, Gkikas et al, 2010, 2011; Benas et al, 2011)
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