Sensitivity of a Coupled Single-Column Model in the Tropics to Treatment of the Interfacial Parameterizations

Abstract

A coupled atmosphere?ocean single-column model has been developed for testing tropical ocean?atmosphere feedbacks. The model is evaluated against observational data (both in situ and satellite) during the Tropical Ocean Global Atmosphere Coupled Ocean?Atmosphere Response Experiment (TOGA COARE) intensive observation period. The coupled model is able to successfully reproduce variations in cloud parameters and surface fluxes; the model also overestimates the latent and sensible heat fluxes compared to observations. The overestimation is most likely due to errors in the atmospheric surface layer temperature and specific humidity. The sea surface temperatures produced by the model are reasonable. The mean bias in sea surface temperature as compared to buoy data is 0°C; the maximum deviation from the observed temperature is 0.4°C. This model is then used to investigate the sensitivity of the ocean and the ocean?atmosphere system to variations in the included interfacial parameterization in the tropical Pacific. The sensitivity of the model results to the turbulent flux model used in the coupled version is shown to produce daily averaged sea surface temperature variations of over 0.5°C. Of equal significance is the variation in model response to temperatures from different depths in the water column. Use of the typically cooler skin temperature as the interfacial temperature rather than the temperature at depth results in strong differences in the atmospheric profiles of heat, moisture, and cloud properties. These differences are not caused solely by the difference in temperature, but are also due to the much-reduced diurnal variation in sea surface temperature at depth. The extent to which a daily averaged sea surface temperature changes the resulting atmospheric profiles depends on whether the diurnal variability was strong; under low-wind conditions the differences are the most dramatic.