Ocean radiant heating. Part II: Parameterizing solar radiation transmission through the upper ocean

Accurate determination of sea surface temperature (SST) is critical to the success of coupled ocean-atmosphere models and the understanding of global climate. To accurately predict SST. both the quantity of solar radiation in cident at the sea surface and its divergence, or transmission, within the w ater column must be known. Net irradiance profiles modeled with a radiative transfer model are used to develop an empirical solar transmission paramet erization that depends on upper ocean chlorophyll concentration, cloud amou nt, and solar zenith angle. These factors explain nearly all of the variati ons in solar transmission. The parameterization is developed by expressing each of the modeled irradiance profiles as a sum of four exponential terms. The tit parameters are then written as linear combinations of chlorophyll concentration and cloud amount under cloudy skies, and chlorophyll concentr ation and solar zenith angle during clear-sky periods. Model validation giv es a climatological rms error profile that is less than 4 W m(-2) throughou t the water column (when normalized to a surface irradiance of 200 W m(-2)) . Compared with existing solar transmission parameterizations this is a sig nificant improvement in model skill. The two-equation solar transmission pa rameterization is incorporated into the TOGA COARE hulk flux model to quant ify its effects on SST and subsequent rates of air-sea heat exchange during a low wind, high insolation period. The improved solar transmission parame terization gives a mean 12 W m(-2) reduction in the quantity of solar radia tion attenuated within the top few meters of the ocean compared with the tr ansmission parameterization originally used. This results in instantaneous differences in SST and the net air-sea hear flux that often reach 0.2 degre es C and 5 W m(-2), respectively.