Observed and simulated seasonal co-variations of outgoing longwave radiation spectrum and surface temperature

We analyze the seasonal variations of Outgoing Longwave Radiation (OLR) accompanying the variations in sea surface temperature (SST) from satellite observations and model simulations, focusing on the tropical oceans where the two quantities are strikingly anti-correlated. A spectral perspective of this "super-greenhouse effect" is provided, which demonstrates the roles of water vapor line and continuum absorptions at different altitudes and the influences due to clouds. A model-satellite comparison indicates that the GFDL General Circulation Model can fairly well represent the total-sky radiative response to SST in the water vapor infrared absorption band despite the significant bias in the mean state, but this comprises compensating water vapor- and cloud-related errors. The analysis also reveals that the GCM significantly underestimates the cloud induced radiative responses in the window region which arises from the model bias in the mean cloud forcing in convectively active regions. Thus, spectral decomposition proves essential to understand and assess the OLR-SST relationship and the impacts of water vapor and cloud upon this linkage.