COMBINED GLOBAL CLIMATE MODEL AND MESOSCALE MODEL SIMULATIONS OF ANTARCTIC CLIMATE

Simulations of high southern latitudes with the high-resolution, limit ed-area Penn State/NCAR mesoscale model, version 4 (MM4), examine the impact of a moist physics parameterization and the success of a one-wa y nesting inside the global NCAR community climate model, version 2 (C CM2). Discretization is by 100 km resolution in the horizontal and 15 or 16 levels in the vertical. Initial and boundary conditions for the simulations are provided by analyses of the European Centre for Medium -Range Weather Forecasts or CCM2 simulations. Comparisons of dry and m oist simulations of an austral winter month, June 1988, are used to ex amine the role of clouds in the regional meteorology A cloud-free MM4 simulation with boundary conditions provided by CCM2 run 422 indicates that the one-way nesting of the mesoscale model can produce significa nt differences in the model output, including an improvement in the lo cation of one longwave trough, reduced cold bias, and a more detailed surface wind field. The improved location of the longwave trough over the Atlantic Ocean is hypothesized to result from blocking induced by the reduced cold bias. The nested simulation is sensitive to the forci ng at the horizontal boundaries. Consequently, proper location of trou ghs and ridges at the boundaries is required for the model to well rep resent ail the major troughs and ridges inside the domain. The additio n of moist physics to the mesoscale simulations tends to improve the q uality of the simulated fields over the Southern Ocean. In particular, the intensity of the circumpolar trough is increased. Over Antarctica , serious deficiencies are found in the simulations with moist physics . Excessive moisture is apparently stored in the simulated clouds:lead ing to excessive atmospheric back radiation and, consequently, excessi ve temperatures at the surface and higher up in the troposphere.