High resolution regional climate simulations over Iceland using Polar MM5

Based on the experience of previous research into mesoscale modeling by the Polar Meteorology Group of the Byrd Polar Research Center at The Ohio State University, the MM5 has been modified for use in polar regions (referred to as the Polar MM5). The key modifications are: revised cloud / radiation interaction; modified explicit ice phase microphysics; modified turbulence (boundary layer) parameterization; implementation of a sea ice surface type; and improved treatment of heat transfer through snow / ice surfaces. Model validations and case studies of Polar MM5 simulations over Greenland and Antarctica have been performed, and the model is currently being used for synoptic and climate scale studies in the data sparse high latitudes.

The Polar MM5 with 8 km high-resolution has been applied to simulate the regional climate over Iceland. Three nested model domains are used. The horizontal resolution and grid points are 73x85, 72km for domain 1; 121x103, 24km for domain 2; and 73x85, 8km for domain 3. The 2.5o horizontal resolution ECMWF TOGA surface and upper air operational analyses are used to provide the initial and boundary conditions for the model. The Polar MM5 is used to produce short duration (30 h) simulations from 1991 to 2000. The integration strategy is a sequence of 30 h simulations, with the first 6h being discarded for spin-up reasons. Two test simulations are performed using standard MM5 and Polar MM5 for January 1998 to investigate the performance of Polar MM5. The comparison between the two simulations shows that Polar MM5 more accurately reproduces the mesoscale meteorological fields over Iceland than standard MM5.

The simulated results are compared with the surface observations for January 1998 and July 1998. The surface wind direction, surface wind speed, surface temperature, surface dew point and sea level pressure simulated by Polar MM5 are in good agreement with the observations for both months.

The simulated long-term mean annual precipitation simulated by Polar MM5 for 1991-2000 is compared to the observed long-term mean annual precipitation. The time-averaged mesoscale precipitation distribution over Iceland is reasonably well simulated by Polar MM5. The modeled interannual precipitation variations during winter for 1992-2000 well match those observed from accumulation measurements on Vatnajökull ice cap in southeast Iceland.