Hindawi Publishing Corporation Advances in Meteorology Volume 2012, Article ID 828301, 17 pages doi:10.1155/2012/828301 Research Article Meteorological Patterns Associated with Intense Saharan Dust Outbreaks over Greece in Winter P. T. Nastos Laboratory of Climatology and Atmospheric Environment, University of Athens, Faculty of Geology and Geoenvironment, Panepistimiopolis, 15784 Athens, Greece Correspondence should be addressed to P. T. Nastos, nastos@geol.uoa.gr Received 14 February 2012; Accepted 21 March 2012 Academic Editor: Dimitris G. Kaskaoutis Copyright © 2012 P. T. Nastos. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Mediterranean Basin and southern Europe are often affected by Saharan dust outbreaks, which influence the aerosol load and properties, air quality standards, visibility and human health. The present work examines, mainly of the meteorological point of view, three intense dust outbreaks occurred over Greece with duration of one or two days, on 4 and 6 February and 5-6 March 2009. The synoptic analysis on the dusty days showed the presence of low-pressure systems in the west coasts of Europe and the north Tyrrhenian Sea, respectively, associated with a trough reaching the north African coast. The result of these conditions was the strong surface and mid troposphere winds that carried significant amounts of dust over Greece. During the dusty days extensive cloud cover associated with the dust plume occurred over Greece. The air-mass trajectories showed a clear Saharan origin in all atmospheric levels, while the satellite (MODIS Terra/Aqua) observations as well as the model (DREAM) predictions verified the intense dust outbreaks over eastern Mediterranean and Greece. The ground based particulate matter concentrations in Athens were excessively increased on the dusty days (PM 10 : 150–560 μg/m 3 ), while significant dry and wet deposition occurred as forecasted by DREAM model. 1. Introduction According to the Earth Observatory website (http://earthob- servatory.nasa.gov/), intense dust outbreaks are considered natural hazards, which affect the global and regional radia- tive balance, cloud microphysical properties, atmospheric heating and stability, tropical cyclone activity, ecosystems, marine environments and phytoplankton, photolysis rates, ozone chemistry, and human health [1, 2]. Mineral and desert dust play an important role in radiative forcing, with an estimated top of atmosphere (TOA) radiative forcing in the range −0.6 to 0.4 Wm −2 [2]. However, the radiative forcing caused by dust particles is very uncertain in both magnitude and sign, mainly triggered by the chemical composition of mineral particles [3], by the wavelength dependence of their optical properties (like single scattering albedo, asymmetry factor), as well as by the albedo of the underlying surface and also the relative height between the dust layer and the clouds [4, 5]. Desert dust can be transported over long distances from the source regions [6], with the larger particles to be deposited near the source, while the smaller ones to be suspended in the air for a few days or weeks, thus travelling over large distances. The Saharan desert is the most important dust source region in the world [7]. Exports of dust plumes to the North Atlantic and Mediterranean Sea occur throughout the year [8]. The occurrence of Saharan dust (SD) events above eastern Mediterranean has a marked seasonal cycle, with a spring maximum and a winter minimum [9–11]. In the summer, dust identification over the region is also frequent due to the longer duration of the dust particles favored by the stable weather conditions, the absence of depressions and precipitation that favor their wet deposition. Many studies [8, 12–14] have shown that the Saharan dust events over Mediterranean are mainly driven by the intense cyclones called Sharav, south of Atlas Mountains (Morocco). These cyclones are generated by the thermal contrast between cold Atlantic air and warm continental air that cross North Africa during spring and summer. Moreover, the thermal lows developed over the desert regions in the warm period of the