1. Univ. Lille, CNRS, UMR 8518 - LOA - Laboratoire d'Optique Atmosphérique; Lille France
2. Department of Atmospheric Sciences; University of Utah; Salt Lake City UT USA
3. Now at Institute of Meteorology and Climate Research; Karlsruhe Institute of Technology; Karlsruhe Germany
4. School of Geoscience; University of Edinburgh; Edinburgh UK