Simulation of the atmospheric state over the Arctic River Basins with Polar MM5 and the NCAR Land Surface Model

As part of the Arctic RIMS project, we examine the success of a modified version of the Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) fifth-generation mesoscale model (MM5, version 3.4) and the NCAR Land Surface Model (LSM version 1.0) in simulating meteorological features over the North American Arctic at a resolution of 60 km. MM5 was adapted by the Polar Meteorology Group at the Byrd Polar Research Center for use in the polar regions, and is termed Polar MM5 (http://www-bprc.mps.ohio-state.edu/PolarMet/pmm5.html). The NCAR Land Surface Model is implemented into the Polar MM5 to describe the land surface characteristics in detail. Three experiments are conducted to evaluate the forecast skill of standard MM5, Polar MM5 and the coupled model (Polar MM5 +LSM) over the North American Arctic. The initial and boundary conditions are obtained from the daily run of the Aviation Model (AVN) issued by the National Centers for Environmental Prediction (NCEP). The models are initialized at 00 UTC for a 48-h short duration simulation with the first 24-h simulation discarded for spin-up purposes. Global surface and upper air observations obtained from http:// weather.uwyo.edu are used to verify the mesoscale model simulations.

Parallel simulations of the Polar MM5 and the original MM5 for 19-29 April 1997 reveal that Polar MM5 performs better than the original MM5 over the North American Arctic. The Polar MM5 time series of the near-surface meteorological variables are in good agreement with the observations, apart from a slight cold bias. On the other hand, the standard MM5 generally predicted too warm near-surface temperatures and much more moisture than observed. For the 12-16 June 2002, parallel simulations were carried out using Polar MM5 and the coupled model. The two models captured the detailed variation of the surface variables at sites considered. However, the coupled model improved the forecast skill of near-surface temperature and dew-point temperature. Extended evaluation of Polar MM5+LSM simulations (15 October to 15 December 2002) in term of surface and upper air variables indicate that the coupled model accurately forecasts the atmospheric behavior over the North American Arctic.