The observed variation in cloud-induced longwave radiation in response to sea surface temperature over the Pacific warm pool from MTSAT-1R imagery

This study investigated variations in outgoing longwave radiation (OLR) in response to changes in sea surface temperature (SST) over the Pacific warm pool area (20°N-20°S, 130°E-170°W). OLR values were obtained from recent (January 2008-June 2010) geostationary window channel imagery at hourly resolution, which resolves processes associated with tropical convective clouds. We used linear regression analysis with the domain-averaged OLR and SST anomalies (i.e., δOLR, δSST; deviations from their 90-day moving averages). Results show that the regression slope appears to be significant only with SST least-affected by cloud radiative forcing, for which SST needs to be obtained as daily average over cloud-free regions (δSSTclear). The estimated value of δOLR/δSSTclear is 15.72 W m^-2 K ^-1, indicating the presence of strong outgoing longwave radiation in response to surface warming. This atmospheric cooling effect is found to be primarily associated with reduced areal coverage of clouds (-14.4% K ^-1).