Diurnal Cycle

The diurnal cycle is the variation of a geophysical quantity over a 24-hour day driven by the rotation of Earth relative to the Sun. In the upper ocean it appears as daytime warming of a thin near-surface layer, the diurnal warm layer, when solar heating exceeds wind-driven and convective mixing under light winds. Diurnal sea surface temperature amplitudes commonly reach 1 to 3 K and can exceed 5 K in calm, sunny conditions, then erode by nighttime convection. The cycle also modulates the marine boundary layer, sea breeze, and air-sea fluxes, and it must be resolved to reconcile satellite SST observed at different overpass times.