Toward mitigating the double ITCZ problem in NCAR CCSM3

Abstract

The appearance of a spurious Inter-Tropical Convergence Zone south of the equator in the eastern and central equatorial Pacific, in addition to the observed one north of the equator, is a common problem in coupled global climate models. The present study investigates this "double ITCZ" problem in the NCAR CCSM3. It shows that use of a modified Zhang-McFarlane convection scheme significantly mitigates the double ITCZ problem in boreal summer. This has a profound impact on the simulated sea surface temperature through cloud radiative forcing feedback. Both the warm bias in the southern ITCZ region and the cold bias in the cold tongue over the equator are reduced. Examination of the time series of precipitation, SST and surface energy fluxes shows that, depending on the convection parameterization used, double or single ITCZ emerges quickly within the first few months after the model start. Copyright 2006 by the American Geophysical Union.