Mesoscale modeling of katabatic winds over Greenland with the Polar MM5

Verification of two months, April and May 1997, of 48-h mesoscale model simulations of the atmospheric state around Greenland are presented. The simulations are performed with a modified version of The Pennsylvania State University-National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5), referred to as the Polar MM5. Global atmospheric analyses as well as automatic weather station and instrumented aircraft observations from Greenland are used to verify the forecast atmospheric state. The model is found to reproduce the observed atmospheric state with a high degree of realism. Monthly mean values of the near-surface temperature and wind speed predicted by the Polar MM5 differ from the observations by less than 1 K and 1 m s^-1, respectively, at most sites considered. In addition, the model is able to simulate a realistic diurnal cycle for the surface variables, as well as capturing the large-scale, synoptically forced changes in these variables. Comparisons of modeled profiles of wind speed, direction, and potential temperature in the katabatic layer with aircraft observations are also favorable, with small mean errors. The simulations of the katabatic winds are found to be sensitive to errors in the large-scale forcing (e.g., the large-scale pressure gradient) and to errors in the representation of key physical processes, such as turbulence in the very stable surface layer and cloud-radiation interaction.