ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-7-13203-2007 Alignment of atmospheric mineral dust due to electric field Ulanowski Z. 1 Bailey J. 2 Lucas P. W. 1 Hough J. H. 1 Hirst E. 1 Science and Technology Research Institute, Univ. of Hertfordshire, Hatfield AL10 9AB, UK Australian Centre for Astrobiology, Macquarie University, Sydney NSW 2109, Australia 10 09 2007 7 5 13203 13241 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-discuss.net/7/13203/2007/acpd-7-13203-2007.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/7/13203/2007/acpd-7-13203-2007.pdf

Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode show dichroic extinction consistent with the presence of vertically aligned particles in the atmosphere. Modelling of the extinction together with particle orientation indicates that the alignment could have been due to an electric field of the order of 2 kV/m. Two alternative mechanisms for the origin of the field are examined: the effect of reduced atmospheric conductivity and charging of the dust layer, the latter effect being a more likely candidate. It is concluded that partial alignment may be a common feature of Saharan dust layers. The modelling also indicates that the alignment can significantly alter dust optical depth. This "Venetian blind effect" may have decreased optical thickness in the vertical direction by as much as 10% for the case reported here.

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