The Performance of Four Spectral GCMs in the Southern Hemisphere: The January and July Climatology and the Semiannual Wave

Abstract

Monthly mean sea level pressure (SLP) data from four low-resolution spectral GCMs?ECMWF T21, CCC, NCAR CCM and GFDL R15?are compared with observations for the Southern Hemisphere. Characteristics of the observed Southern Hemisphere January and July mean mass distribution are: (i) high pressure areas in the subtropics; (ii) a steep meridional gradient at midlatitudes; (iii) a circumpolar trough in the Antarctic; (iv) a zonal asymmetry dominated by zonal wave 1, which has an almost complete phase reversal near 40°S; (v) a double westerly wind maximum during the colder part of the year. The CCC model reproduces some of these features. The ECMWF model, the NCAR CCM, and the GFDL models fail with respect to (ii) and (iii). All GCMs underestimate the intensity of the stationary eddies. None of the models considered reproduces the double westerly wind maximum. Another marked feature of the Southern Hemisphere circulation is the semiannual wave that dominates the annual curve of SLP at mid- and polar latitudes. Regardless of the various models? degree of success in reproducing the mean circulation, all fail in simulating the general features of the semiannual wave.