Abstract : A.5
Downslope windstorm in Iceland - WRF/MM5 model comparison

Ólafur Rögnvaldsson, Jian-Wen Bao, Hálfdán Ágústsson, Haraldur Ólafsson
Institute for Meteorlogical Research

A severe windstorm downstream of the mountain Öræfajökull in SE-Iceland is simulated on a 1 km horizontal resolution with the PSU/NCAR model MM5 and the Advanced Research WRF model. Initial and boundary data are from the European Centre for Medium range Weather Forecasts (ECMWF). The MM5 model is run on 9, 3 and 1 km resolution, using one-way nesting. Data from the 3 km MM5 simulation are used to initialise and drive the 1 km WRF simulation.

Model simulations show that the WRF model has somewhat less wave activity over the mountain than the MM5 model. The MM5 model shows signs of breaking waves but does not capture the full strength of the downslope windstorm. Simulated surface winds only reach about 20 m/s whilst observed mean winds reached over 30 m/s. The WRF model, in spite of having less wave activity (there is no apparent sign of breaking waves over the mountain), simulates surface winds that exceed 30 m/s and are much closer to observed values.

Since observations are not available to verify the MM5 simulated wave breaking and the accuracy of the simulated surface winds is the only measurable performance of both MM5 and WRF simulations in this case, our preliminary results suggest that the WRF model is better than the MM5 model for high-resolution simulations of near surface winds in Iceland.