A Scheme of Sea Surface Upward Longwave Radiation With Sea Spray Layer Effect

Abstract

Estimation of sea surface upward longwave radiation (SULR) are generally dependent on sea surface temperature (SST), in accordance with the Stefan-Boltzmann law. The consensus is that the inaccuracy in estimating SST contributes to bias in the estimation. This study proposes the incorporation of the spray layer in estimating upward longwave radiation, as when the sea surface is covered by the spray layer, it becomes the primary source of longwave radiation emitted to the atmosphere. Analysis of ERA5 data suggests that the bias in sea SULR is associated with the temperature of the sea spray layer and the whitecap coverage. Incorporating the spray layer in the estimation of sea SULR results in a decrease of the overestimation in ERA5 by over 15%. The revised scheme, implemented in CESM2.1.3, led to an average percentage bias improvement around 16%. The percentage bias improvement in localized areas of the southeastern Pacific and the southeastern Indian Oceans reaches up to 40%. The regions where bias has been effectively reduced are mainly found within latitudes of 30°, and the negative bias in the Southern Ocean is increased. This study offers a novel insight into the errors in estimating sea SULR.