Tropical response to increased CO2 in a GCM with a simple mixed layer ocean: similarities to an observed pacific warm event

Abstract A version of the NCAR Community Climate Model (CCM), a global spectral atmospheric general circulation model, is coupled to a simple ocean mixed layer model with fixed depth. This mixed layer model is a simple slab of water that crudely accounts for seasonal heat storage but has no dynamics (e.g., advection, diffusion or upwelling). As a result, tropical sea surface temperatures (SSTs) produced by the simple mixed layer are warmer than observed in the equatorial tropics, in particular, in the tropical eastern Pacific. When CO2 is doubled in the model, SSTs increase at all longitudes in the equatorial tropics on the order of 1°–2°C. However, this uniform longitudinal warming is not associated with uniform longitudinal increases of tropical precipitation. Greatest area-averaged increases of precipitation occur in the tropical Pacific, while decreases of area-averaged precipitation are noted in the Asian monsoon regions. This is attributed to a disruption of the east–west circulation between the Pac...