ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-6-9995-2006 Defintion of “banner clouds" based on time lapse movies Schween J. H. 1 Kuettner J. 2 Reinert D. 3 Reuder J. 4 Wirth V. 3 Meteorological Institute, Ludwig-Maximilian-University, Munich, Germany National Center for Atmospheric Research, Boulder, CO, USA Institute for Atmospheric Physics, Johannes-Gutenberg-University, Mainz, Germany Geophysical Institute, University of Bergen, Norway 10 10 2006 6 5 9995 10019 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/6/9995/2006/acpd-6-9995-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/6/9995/2006/acpd-6-9995-2006.pdf

Banner clouds appear on the leeward side of a mountain and resemble a banner or a flag. This article provides a comprehensive definition of "banner clouds". It is based primarily on an extensive collection of time lapse movies, but previous attempts at an explanation of this phenomenon are also taken into account. The following ingredients are considered essential: the cloud must be attached to the mountain but not appear on the windward side; the cloud must originate from condensation of water vapour contained in the air (rather than consist of blowing snow); the cloud must be persistent; and the cloud must not be of convective nature. The definition is illustrated and discussed with the help of still images and time lapse movies taken at Mount Zugspitze in the Bavarian Alps.