This paper introduces a simple method for deriving climatological values of the longwave flux emitted from the clear sky atmosphere to the ice-free ocean surface. Simulations of the clear sky longwave fluxes to space and to the surface are employed in this study to assist in the development of this flux retrieval which requires monthly averaged column-integrated water vapor w and the clear sky top-of-atmosphere (TOA) outgoing longwave flux (both available from satellite measurements). It is shown using both theory and data from simulations how the ratio of the surface to TOA flux is a simple function of w and a validation of the simple relationship is presented based on a limited set of surface flux measurements. The rms difference between the retrieved surface fluxes and the simulated surface fluxes is approximately 6 W m-2. The clear sky column cooling rate of the atmosphere is derived from the Earth Radiation Budget Experiment (ERBE) values of the clear sky TOA flux and the surface flux retrieved using Special Scanning Microwave Imager (SSM/I) measurements of w together with ERBE clear sky fluxes. The relationship between this column cooling rate, w, and the sea surface temperature (SST) is explored and it is shown how the cooling rate systematically increases as both w and SST increase.

The uncertainty implied in these estimates of cooling are approximately ¿0.2 K d-1. The effects of clouds on this longwave cooling are also explored in a limited way be placing bounds on the possible impact of clouds on the column cooling rate based on certain assumptions about the effect of clouds on the longwave flux to the surface. While a more global assessment of the cloud effect must await use of new satellite data that will allow us to estimate the contributions by clouds to these surface fluxes, it is shown in this paper how the longwave effects of clouds in a moist atmosphere where the column water vapor exceeds approximately 30 kg m-2 may be estimated from presently available satellite data with an uncertainty estimated to be approximately 0.2 K d-1. Based on an approach described in this paper, we show clouds in these relatively moist regions decrease the column cooling by almost 50% of the clear sky values and the existence of significant longitudinal gradients in column radiative heating across the equatorial and subtropical Pacific Ocean. ¿ American Geophysical Union 1994