ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-11383-2012 Impact of mineral dust on cloud formation in a Saharan outflow region Smoydzin L. 1 Teller A. 2 5 Tost H. 3 Fnais M. 4 Lelieveld J. 1 2 4 Max-Planck-Institute for Chemistry, Department of Atmospheric Chemistry, P.O. Box 3060, 55020 Mainz, Germany The Cyprus Institute, Centre for Energy, Environment and Water Research, Nicosia, Cyprus Institute for Atmospheric Physics, Johannes-Gutenberg University, Mainz, Germany King Saud University, Riyadh, Saudi Arabia Weizmann Institute of Science, Rehovot, Israel 03 12 2012 12 23 11383 11393 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/11383/2012/acp-12-11383-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/11383/2012/acp-12-11383-2012.pdf

We present a numerical modelling study investigating the impact of mineral dust on cloud formation over the Eastern Mediterranean for two case studies: (i) 25 September 2008 and (ii) 28/29 January 2003. In both cases dust plumes crossed the Mediterranean and interacted with clouds forming along frontal systems. For our investigation we used the fully online coupled model WRF-chem. <br><br> The results show that increased aerosol concentrations due to the presence of mineral dust can enhance the formation of ice crystals. This leads to slight shifts of the spatial and temporal precipitation patterns compared to scenarios where dust was not considered to act as ice nuclei. However, the total amount of precipitation did not change significantly. The only exception occurred when dust entered into an area of orographic ascent, causing glaciation of the clouds, leading to a local enhancement of rainfall. The impact of dust particles acting as giant cloud condensation nuclei on precipitation formation was found to be small. Based on our simulations the contribution of dust to the CCN population is potentially significant only for warm phase clouds. Nevertheless, the dust-induced differences in the microphysical structure of the clouds can contribute to a significant radiative forcing, which is important from a climate perspective.

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