Global 60 km simulations with CCAM: evaluation over the tropics

A six-member ensemble of 60 km resolution global atmospheric simulations has been performed for studying future climate scenarios of Pacific island nations. The simulations were performed using the CSIRO Conformal Cubic Atmospheric Model (CCAM), driven by bias-corrected sea surface temperatures (SSTs) provided by six Coupled Model Intercomparison Project phase 3 global climate models (GCMs) from the Intergovernmental Panel on Climate Change Fourth Assessment Report for the period 1971-2100. This paper focuses on results for the representation of the current climate in the tropical region, a region where the "cold tongue" problem is apparent in all host GCMs. The SST bias-correction and the fine horizontal resolution employed in the CCAM simulations produce a significant improvement over the host GCMs in the rainfall patterns for the transient seasons March-April-May and September-October-November, and a moderate improvement for December-January-February and June-July-August. CCAM also simulates improved rainfall patterns over the South Pacific Convergence Zone. The performance of other tropical features, such as El Nio Southern Oscillation and the Walker circulation, is also evaluated.