Sensitivity studies of the treatment of interfacial parameterizations in the tropics using a coupled single -column model

A coupled atmosphere-ocean single-column model with an improved cloud scheme has been developed for testing tropical ocean-atmosphere feedbacks and compared with observations during the TOGA COARE IOP. The coupled model is able to successfully reproduce variations in cloud parameters and surface fluxes. The new improved cloud scheme is able to produce more realistic cloud liquid water path and cloud amounts than the original atmospheric model. The sea surface temperatures produced by the model are reasonable. During light wind periods, the mean bias in sea surface temperature as compared to buoy data are 0°C and the maximum deviation from the observed temperature is 0.4°C. During strong wind periods, the mean bias in sea surface temperature as compared to buoy data are about 0.5°C and the maximum deviation from the observed temperature is 1°C. The sensitivity of the coupled model to the turbulent flux parameterizations is then tested. Short-term variations in both the daily mean surface shortwave and surface turbulent fluxes can reach over 100 W M−2 . These translate into significant biases in sea surface temperature, with hourly average differences reaching 1.5°C and daily-averaged sea surface temperature differences reaching maximum values of 0.5°C. These sea surface temperature differences appear to be mostly related to variations in shortwave radiation and its stabilizing influence on the mixed layer depth. The depth of the ocean temperature used as the sea surface temperature, and the temporal resolution of that sea surface temperature, had as great an impact on the biases between model simulations as did the differing turbulent flux parameterizations. Use of the skin temperature as opposed to a temperature from deeper within the water column produced strong variability in the coupled model during low-wind conditions; the simulations are much more similar during higher wind speeds. These differences are shown to be due to a combination of the use of a consistently warmer sea surface temperature and the lack of diurnal variability, although it appears that these two processes do not equally influence the coupled model at all times