The diurnal variability of sea surface temperature (SST) is the cycle of temperature within the course of a day.
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This variability is driven by the daily cycle of sunlight, which heats the ocean predominantly in the upper few metres. Typically the amplitude of the diurnal variability of SST is only a few tenths of °C, because wind action mixes down heated water from the surface, sharing the solar heating over a significant depth. However, in light wind and strong sunlight conditions, the upper metres of water can form a shallow (0.3 m to 3 m) stable warm layer, and the diurnal excursion of the surface temperature can exceed 5°C in extreme cases.
Satellite observations of the ocean temperature are sensitive to the skin SST (infrared observations) or sub-skin SST (microwave observations). The upper-ocean heat content is better described by the foundation SST (the temperature at dawn at a depth below diurnal variability). The skin SST differs from the foundation SST in general because of the combination of cool-skin and warm-layer effects.
(Last Updated: 03-08-2007)