Downslope windstorm in Iceland – WRF/MM5 model comparison Ó. Rögnvaldsson1,2, J.-W. Bao3, H. Ágústsson1,4, and H. Ólafsson4,5,* 1Institute for Meteorological Research, Reykjavík, Iceland 2University of Bergen – UiB, Bergen, Norway 3NOAA/ESRL, Boulder, USA 4University of Iceland, Reykjavík, Iceland 5Icelandic Meteorological Office, Reykjavík, Iceland *now at: Bergen school of meteorology, Geophysical Institute UiB, Norway
Abstract. 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.
Citation: Rögnvaldsson, Ó., Bao, J.-W., Ágústsson, H., and Ólafsson, H.: Downslope windstorm in Iceland – WRF/MM5 model comparison, Atmos. Chem. Phys., 11, 103-120, doi:10.5194/acp-11-103-2011, 2011.