Evaluation of cloud amount trends and connections to large scale dynamics

Recent studies by Wielicki et al. (2002) and Chen et al. (2002) provide evidence of a decadal-scale trend in the cloud amount (cloud fraction) in the tropics. Wielicki et al. use data from the Earth Radiation Budget Experiment (ERBE, Barkstrom 1984) to demonstrate a decadal-scale upward trend in the tropical mean long wave (LW) flux time series since 1985. They argue that this trend must be reflected in changes in the cloud amount in the tropics. Chen et al. use International Satellite Cloud Climatology Project (ISCCP, Schiffer and Rossow 1983) data to show that there was an overall change in the cloud amount in the tropical and subtropical regions over the same time period. Figure 1 shows one representation of how the global cloud amount has changed in the last 20 years.