Statistical Dependence of Albedo and Cloud Cover on Sea Surface Temperature for Two Tropical Marine Stratocumulus Regions

Abstract

The relationship between sea surface temperature (SST) and albedo or cloud cover is examined for two tropical regions with high values of cloud radiative forcing and persistent marine stratocumulus (mSc)?one off the west coast of Peru, the other off the west cost of Angola. The data span five years, from December 1984 to November 1989. Albedos are from the Earth Radiation Budget Experiment, cloud covers are from the International Satellite Cloud Climatology Project, and SSTs are from the Climate Analysis Center. Negative correlation coefficients between albedo and SST are found to be about ?0.8 when the seasonal variation of the entire dataset is analyzed. The interannual variation and the spatial variation of individual months also yields correlation coefficients that are negative. The correlation between cloud cover and SST is found to be similar to but weaker than the correlation between albedo and SST, suggesting a decrease in cloud amount and a decrease in cloud albedo with increasing SST for these regions. The corresponding albedo sensitivity averages ?0.018 K?1 with local values reaching ?0.04 K ?1. These findings are valid from 19°C to 25°*C for the Peru mSc and 22°C to 27°C for the Angola mSc. These temperatures approximately bound the domains over which mSc is the prevalent cloud type within each region. These results imply a potential positive feedback to global warming by marine stratocumulus that ranges from ?0.14 W m?2 K?1 to ?1 W m?2 K?1, depending on whether or not our results apply to all marine stratocumulus. While these values are uncertain to at least ±50%, the sensitivity of albedo to see surface temperature in the present climate may serve as a useful diagnostic tool in monitoring the performance of global climate models.