Interrelationships between Cloud Properties and Sea Surface Temperatures on Seasonal and Interannual Time Scales

Monthly means of selected variables of the 2.5° International Satellite Cloud Climatology Project (ISCCP) C2 total cloud cover (CC), cloud-top pressure (CTP), and cloud water (CW) are statistically related to sea surface temperature (SST). The statistical tools utilized include intra- and interannual correlation, regression, and composite empirical orthogonal function (EOF) analyses. The dominant intra- and interannual composite EOFs all show that CC, CTP, and CW departures have spatially coherent links with those of SST. The second most important intra-annual functions also show coherent relations, which are about three months out of phase with those of the dominant functions. The regression analysis suggests that this phase relation may be explained by significant correlations of the cloud variables with not only SST, but also with the time derivative of SST (dSST/dt). For instance, in the tropical Pacific increased CC is accompanied by increases in SST but decreases in dSST/dt, and increased CTP is associated with decreases in SST. However, at middle and high latitudes other relationships exist, such that larger CCs may be associated with decreased SSTs, or higher CTPs may be related to higher SSTs. These diagnosed relationships have important implications for understanding cloud and cloud radiative feedbacks in weather and climate.