The Double ITCZ Problem in IPCC AR4 Coupled GCMs: Ocean Atmosphere Feedback Analysis
Abstract This study examines the double intertropical convergence zone (ITCZ) problem in the coupled general circulation models (CGCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) The twentieth century climate simulations of 22 IPCC AR4 CGCMs are analyzed, together with the available Atmospheric Model Intercomparison Project (AMIP) runs from 12 of them. To understand the physical mechanisms for the double ITCZ problem, the main ocean atmosphere feedbacks, including the zonal sea surface temperature (SST) gradient trade wind feedback (or Bjerknes feedback) the SST surface latent heat flux (LHF) feedback, and the SST surface shortwave flux (SWF) feedback, are studied in detail. The results show that most of the current state of the art CGCMs have some degree of the double ITCZ problem, which is characterized by excessive precipitation over much of the Tropics (e.g. Northern Hemisphere ITCZ, South Pacific convergence zone, Maritime Continent, and eq.