Evaluation of Precipitation and High-Level Cloud Areas Associated with Large-Scale Circulation over the Tropical Pacific in the CMIP3 Models

Abstract

Precipitation and high-level cloud (HLC) areas in association with the large-scale circulation over the tropical Pacific are analyzed for simulations of nineteen Coupled Model Intercomparison Project Phase 3 (CMIP3) models with observations for 16 years of 1984–1999. The distribution of rainfall and HLC areas are composited around the geographical center of tropospheric upper-level (200 hPa) divergence (DIV) along Intertropical Convergence Zone (ITCZ) using monthly anomaly data. Datasets with a finer temporal sampling than monthly means were not available for the present purposes. The most notable feature is that the horizontal spread of enhanced circulation and the related rainfall and HLC areas are all underestimated around the DIV center in the models compared to the observation. Particularly, the underestimation is pronounced in HLC, presumably owing to di‰culties in the physical processes relevant to the spatial distribution of HLC area. In general, a model with a higher correlation between the large-scale circulation field and rainfall tends to have a wider spread of HLC area around the DIV center.