Radiometric measurements of ocean surface thermal variability

Abstract

Measurements of diurnal temperature variability at the ocean surface have been available primarily from satellite Sea Surface Temperature (SST) retrievals and a small number of ship‐based radiometers. Since most areas are sampled from polar orbiting satellites at most twice a day, surface diurnal variability studies relied on theoretical modeling or extrapolation of results from in situ measurements at depth. The ocean surface responds very rapidly to changes in fluxes of heat and momentum, therefore diurnal variability at the ocean surface may be quite different than heating at depth. Measurements from the Marine Atmospheric Emitted Radiance Interferometer (M‐AERI) provide one of the few skin SST data sets augmented by ancillary measurements necessary for investigations into surface diurnal heating and cooling. This unique data set spans all major ocean basins and contains many days with diurnal warming. The timing of the peak in diurnal warming is directly related to the minimum wind speed and varies from 8:00 to 18:00 local‐mean‐time. Fluctuations in wind speed can result in multiple peaks in diurnal heating during a single afternoon. As wind speed increases, diurnal warming decreases (negatively correlated) and as insolation increases, diurnal warming increases (positively correlated). Changes in wind speed affect diurnal warming amplitudes very rapidly, while changes in insolation have a more gradual effect. The maximum correlation of wind speed (insolation) with changes in diurnal warming is at a time lag of 0 (50) min.