The Cryosphere www.the-cryosphere.net 1994-0416 1994-0424 2 1 2008 10.5194/tc-2-1-2008 http://www.the-cryosphere.net/2/1/2008/ http://www.the-cryosphere.net/2/1/2008/tc-2-1-2008.html http://www.the-cryosphere.net/2/1/2008/tc-2-1-2008.pdf 1 12 2008-01-08 Spatial structures in the heat budget of the Antarctic atmospheric boundary layer W. J. van de Berg M. R. van den Broeke E. van Meijgaard IMAU, University of Utrecht, Utrecht, The Netherlands KNMI, De Bilt, The Netherlands Output from the regional climate model RACMO2/ANT is used to calculate the heat budget of the Antarctic atmospheric boundary layer (ABL). The main feature of the wintertime Antarctic ABL is a persistent temperature deficit compared to the free atmosphere. The magnitude of this deficit is controlled by the heat budget. During winter, transport of heat towards the surface by turbulence and net longwave emission are the primary ABL cooling terms. These processes show horizontal spatial variability only on continental scales. Vertical and horizontal, i.e. along-slope, advection of heat are the main warming terms. Over regions with convex ice sheet topography, i.e. domes and ridges, warming by downward vertical advection is enhanced due to divergence of the ABL wind field. Horizontal advection balances excess warming caused by vertical advection, hence the temperature deficit in the ABL weakens over domes and ridges along the prevailing katabatic wind. Conversely, vertical advection is reduced in regions with concave topography, i.e. valleys, where the ABL temperature deficit enlarges along the katabatic wind. Along the coast, horizontal and vertical advection is governed by the inability of the large-scale circulation to adapt to small scale topographic features. Meso-scale topographic structures have thus a strong impact on the ABL winter temperature, besides latitude and surface elevation. During summer, this mechanism is much weaker, and the horizontal variability of ABL temperatures is smaller. Bromwich, D H. and Fogt, R L.: Strong Trends in the Skill of the ERA-40 and NCEP-NCAR Reanalyses in the High and Midlatitudes of the Southern Hemisphere, 1958–2001, J. Climate, 17, 4603–4619, 2004. King, J C., Connolley, W M., and Derbyshire, S H.: Sensitivity of Modelled Antarctic Climate to Surface and Boundary-Layer Flux Parameterizations, Q. J. Roy. Meteor. Soc., 127, 779–794, 2001. Parish, T R. and Cassano, J J.: The Role of Katabatic Winds on the Antarctic Surface Wind Regime, Mon. Weather Rev., 131, 317–333, 2003. Reijmer, C H., Van Meijgaard, E., and Van~den Broeke, M R.: Evaluation of temperature and wind over Antarctica in a Regional Atmospheric Climate Model using 1 year of automatic weather station data and upper air observations, J. Geophys. Res., 110, D04103, doi:10.1029/2004JD005234, 2005. Sterl, A.: On the (In)homogeneity of Reanalysis Products, J. Climate, 17, 3866–3873, 2004. Stull, R B.: An Introduction to Boundary Layer Meteorology, Kluwer Academic Publishers, 1988. Undén, P., Rontu, L., Järvinen, H., et al.: The High Resolution Limited Area Model, Hirlam-5 scientific documentation, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden, 2002. Van~As, D. and Van~den Broeke, M R.: Structure and dynamics of the summertime atmospheric boundary layer over the Antarctic Plateau: 2. Heat, moisture and momentum budgets, J. Geophys. Res., 111, D07103 doi:10.1029/2005JD006956, 2006. Van~de Berg, W J., Van~den Broeke, M R., Reijmer, C H., and Van Meijgaard, E.: Reassessment of the Antarctic surface mass balance using calibrated output of a regional atmospheric climate model, J. Geophys. Res., 111, doi:10.1029/2005JD006495, 2006. Van~de Berg, W J., Van~den Broeke, M R., and Van Meijgaard, E.: Heat budget of the East Antarctic lower atmosphere derived from a regional atmospheric climate model, J. Geophys. Res., 112, D23101, doi:10.1029/2007JD008613, 2007. Van~den Broeke, M R. and Van Lipzig, N. P M.: Factors Controlling the Near-Surface Wind Field in Antarctica, Mon. Weather Rev., 131, 733–743, 2003. Van~den Broeke, M R., Van Lipzig, N. P M., and Van Meijgaard, E.: Momentum Budget of the East Antarctic Atmospheric Boundary Layer: Results of a Regional Climate Model Budget of the East Antarctic Atmospheric Boundary Layer: Results of a Regional Climate Model, J. Atmos. Sci., 59, 3117–3129, 2002. White, P W.: Part IV, Physical processes (CY23R4), Tech. Rep., European Centre For Medium-Range Weather Forecasts (ECMWF), 2001. Zhang, Y., Rossow, W B., Lacis, A A., Oinas, V., and Mishchenko, M I.: Calculation of radiative fluxes from the surface to top of atmosphere based on ISCCP and other global data sets: Refinements of the radiative transfer model and the input data, J. Geophys. Res., 109, D19105, doi:10.1029/2003JD004457, 2004.