Evaluation of the Vertical Structure of Zonally Averaged Cloudiness and Its Variability in the Atmospheric Model Intercomparison Project

Estimates of zonally averaged cloudiness at each pressure level in 24 models participating in the Atmospheric Model Intercomparison Project are compared with the ISCCP C2 as well as the Nimbus 7 (N7) and Warren et al. (hereafter WH) observations. The global means of model high cloudiness are about two to five times greater than the C2 satellite observations. The large differences are probably related to excessive high, thin cloud in most models. Nearly all of the models have the observed maximum in high cloud at the equator, but also maxima near 60°N and 60°S, which are not observed. The globally averaged annual mean low cloud in most models is generally 15%–20% less than the WH observations and 10%–15% less than the C2 observations. The meridional structure of model annual mean low cloud both as observed from below and as observed from above show excesses north of about 50°N and deficits south of about 40°S when compared with WH and C2 observations, respectively. The amplitude of the model seasonal cycle of high cloud in most cases is comparable to that of the C2 observations. However, nearly all models have tropical peaks in seasonal variability that are poleward of those in the observations. In most models the variation of the seasonal cycle of low cloud as observed from above differs considerably in both temporal phase and spatial pattern from that of the C2 observations.