A diagnostic model of the diurnal cycle of sea surface temperature for use in coupled ocean-atmosphere models

On the basis of a method of estimating the diurnal amplitude of sea surface temperature (SST) as a function of the diurnal integrals of surface heat and momentum fluxes, a parameterization scheme of the diurnal cycle of SST is implemented in a one-dimensional ocean mixed-layer model. Many coupled ocean-atmosphere models using bulk mixed-layer schemes underestimate the diurnal cycle in sea surface temperature by up to 2 degrees C. This discrepancy is caused by coarse vertical resolution in the upper grid boxes of the ocean components. A simple solution is suggested by adding one extra transient level: a variable-depth diurnal sublayer within the top model level which accommodates the diurnal buoyancy cycle. A one-dimensional mixed-layer model with 10-m resolution and with sublayer simulates diurnal SSTs close to those observed from the Tropical Ocean Global Atmosphere/Coupled Ocean Atmosphere Response Experiment (TOGA/COARE) with typical errors of about 0.1 degrees C. The impact of improved SSTs on surface heat fluxes is also shown by coupling the one-dimensional mixed-layer model with sublayer to an atmospheric boundary layer model.