Global coupled general circulation models (CGCMs) have become indispensable tools in climate prediction and projection studies. However, even state-of-the-art CGCMs typically exhibit large systematic errors over the tropical oceans. These errors are often attributed to poor spatial resolution and distortions in air-sea coupling in specific areas, such as the coastal upwelling regions off the western coasts of Africa and South America. Our goal is try to increase the spatial resolution in climate models and assess its impact on the coupled simulation. It is computationally very expensive to increase the spatial resolution of climate models globally. Therefore, we consider the effect of increased resolution in a regional context, by developing a coupled regional climate model.

Our initial focus is on the tropical Atlantic sector, which is poorly simulated by CGCMs, with large biases in the simulations of sea surface temperature and precipitation fields. We have recently completed the coupling of a regional atmospheric model, the NCAR Weather Research & Forecast (WRF) model, to the Regional Ocean Modeling System (ROMS) regional ocean model, configured for the tropical Atlantic domain. The two models exchange fluxes of momentum, heat, and freshwater every 6 hours. Lateral boundary conditions derived from climatology are specified for both the atmospheric and oceanic models. We consider two configurations for this coupled regional climate model: a coarse resolution configuration with 30 km horizontal resolution in the atmosphere and ¼ degree resolution in the ocean, and a fine resolution configuration with 12 km atmospheric resolution and 1/10 degree ocean resolution. We report on the simulations of the climate mean and variability in extended simulations using these two configurations. Our analysis will focus on important features of this region in the context of climate change, such as the coastal upwelling, the intertropical convergence zone (ITCZ), and precipitation in the African Sahel and the Brazilian Nordeste regions. We will also consider proxies for Atlantic hurricane genesis and investigate how they are affected by model resolution.