Observed dependence of outgoing longwave radiation on sea surface temperature and moisture

In the midlatitudes, the surface temperature explains over 80% of the variability in the clear-sky OLR (F_cs) and almost half of the variability in the total OLR (F_tot). It fails badly in the tropics and subtropics, however, where T_s explains only about 20% of the variability in F_cs, and is largely decoupled from F_tot. The two-dimensional contour plot of the OLR binned with respect to T_s and R̄H̄ is marked by distinct changes in the gradient that are consistent with inferences from earlier investigations. For low values of T_s (<10°C), the OLR depends mainly on T_s. For values of T_s above 10°C, the OLR depends increasingly on R̄H̄. Specifically, in the tropics (T_s ~ 25°C), the total and clear-sky OLR depend significantly on both T_s and R̄H̄. The well-known drop in OLR in the tropics with increasing T_s correlates directly to an increase in R̄H̄, and not to changes in T_s. -from Authors