Mesoscale modeling of katabatic winds over Greenland with the Polar MM5

Verification of two months, April and May 1997, of 48-h mesoscale model sim ulations of the atmospheric state around Greenland are presented. The simul ations are performed with a modified version of The Pennsylvania State Univ ersity-National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5), referred to as the Polar MM5. Global atmospheric analyses as w ell as automatic weather station and instrumented aircraft observations fro m Greenland are used to verify the forecast atmospheric state. The model is found to reproduce the observed atmospheric state with a high degree of re alism. Monthly mean values of the near-surface temperature and wind speed p redicted 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 va riables. Comparisons of modeled profiles of wind speed, direction, and pote ntial temperature in the katabatic layer with aircraft observations are als o 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 p hysical processes, such as turbulence in the very stable surface layer and cloud-radiation interaction.