Free and Laterally Nudged Antarctic Climate of an Atmospheric General Circulation Model

Genthon, Christophe; Krinner, Gerhard; Cosme, Emmanuel
June 2002
Monthly Weather Review;Jun2002, Vol. 130 Issue 6, p1601
Academic Journal
Because many of the synoptic cyclones south of the 60°S parallel originate from 60°S and lower latitudes, nudging an atmospheric general circulation model (AGCM) with meteorological analyses at the periphery of the Antarctic region may be expected to exert a strong control on the atmospheric circulation inside the region. Here, the ECMWF reanalyses are used to nudge the atmospheric circulation of the Laboratoire de Météorologie Dynamique Zoom (LMDZ) stretched-grid AGCM in a 15-yr simulation spanning the 1979–93 period. The horizontal resolution (grid spacing) in the model reaches ∼100 km south of 60°S. Nudging is exerted along the 60°S parallel, and this is called lateral nudging for the Antarctic region. Nudging is also performed farther north, near 50° and 40°S, but this is not essential for the results discussed here. Surface pressure and winds in the atmospheric column are nudged without relaxation to maximize control by the meteorological analyses, at the expense of some “noise” confined to the latitudes where nudging is exerted. The performances of lateral nudging are evaluated with respect to station observations, the free (unnudged) model, the ECMWF reanalyses, and in limited instances with respect to nudging the surface pressure only. It is shown that the free model has limited but persistent surface pressure and geopotential defects in the Antarctic region, which are efficiently corrected by lateral nudging. Also, the laterally nudged simulations confirm, and to some extent correct, a geopotential deficiency of the ECMWF reanalyses over the east Antarctic continent previously identified by others. The monthly mean variability of surface climate at several stations along a coast-to-pole transect is analyzed. A significant fraction of the observed variability of surface pressure and temperature is reproduced. The fraction is often less than in the reanalyses. However, the differences...


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