ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-103-2011 Downslope windstorm in Iceland – WRF/MM5 model comparison Rögnvaldsson Ó. 1 2 Bao J.-W. 3 Ágústsson H. 1 4 Ólafsson H. 4 5 6 Institute for Meteorological Research, Reykjavík, Iceland University of Bergen – UiB, Bergen, Norway NOAA/ESRL, Boulder, USA University of Iceland, Reykjavík, Iceland Icelandic Meteorological Office, Reykjavík, Iceland now at: Bergen school of meteorology, Geophysical Institute UiB, Norway 05 01 2011 11 1 103 120 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/11/103/2011/acp-11-103-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/103/2011/acp-11-103-2011.pdf

A severe windstorm downstream of Mt. Öræfajökull in Southeast Iceland is simulated on a grid of 1 km horizontal resolution by using the PSU/NCAR MM5 model and the Advanced Research WRF model. Both models are run with a new, two equation planetary boundary layer (PBL) scheme as well as the ETA/MYJ PBL schemes. The storm is also simulated using six different micro-physics schemes in combination with the MYJ PBL scheme in WRF, as well as one "dry" run. Output from a 3 km MM5 domain simulation is used to initialise and drive both the 1 km MM5 and WRF simulations. Both models capture gravity-wave breaking over Mt. Öræfajökull, while the vertical structure of the lee wave differs between the two models and the PBL schemes. The WRF simulated downslope winds, using both the MYJ and 2EQ PBL schemes, are in good agreement with the strength of the observed downslope windstorm. The MM5 simulated surface winds, with the new two equation model, are in better agreement to observations than when using the ETA scheme. Micro-physics processes are shown to play an important role in the formation of downslope windstorms and a correctly simulated moisture distribution is decisive for a successful windstorm prediction. Of the micro-physics schemes tested, only the Thompson scheme captures the downslope windstorm.

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