A regional climate model for South America

A numerical nesting system is developed to simulate climate of the eastern South Pacific-South America-western South Atlantic region. The nesting system consists of a large-scale global atmospheric model (a version of the LMD general circulation model, LMD-Z) and a regional model (CIMA version of LAHM GFDL model). Such nested model is called CIMA regional climate model (RCM). Large-scale model information has been transferred from the global model to the specific region through a one-way nesting technique. The singularity of this nesting system is that the global model itself has a variable horizontal resolution stretched grid irregularly spaced in the meridional direction. This stretched grid is introduced in order to improve resolution in a latitudinal band over the region of interest.

This pilot study introduces an initial diagnosis of the capabilities of the RCM for simulating climate in the South American region. The global model, despite its relatively low resolution, could simulate reasonably well the more significant large-scale circulation patterns. The use of the regional model often results in improvements, but not universally. Many of the systematic errors of the global model are also present in the regional model, although the biases tend to be rectified. Our preliminary results suggest that nesting technique is a computationally low-cost alternative suitable to simulate regional climate features. However, additional simulations, parameterizations tuning and further diagnosis are clearly needed to represent local patterns more precisely.