Color and Temperature Signatures of Ocean Fronts Observed with the Nimbus-7 CZCS

Abstract

The Nimbus-7 Coastal Zone Color Scanner has a unique capability for imaging simultaneously the optical (ocean color) and surface temperature (thermal infrared) signatures of ocean fronts. Examples of such color and temperature visualizations of some ocean fronts delineate virtually identical morphology. In other cases, however, the two signatures are displaced horizontally by tens of km, and display markedly different morphology and fine structure. For example, an image of the Gulf Stream’s north wall over the Grand Banks shows the sharpest color front to occur ~50 km away from the sharpest temperature front. Moreover, the fine-structure of the color front is qualitatively suggestive of disorganized turbulent diffusion, whereas that of the thermal front shows distinctive shear instabilities. These differences can occur because the infrared temperature image represents the top 0.05 millimeter of the sea surface, whereas the ocean color image represents the upper meters to decameters of the sea. Near simultaneous aircraft data show a vertical temperature structure which demonstrates that the region between the thermal infrared and ocean color fronts overlies the sloping isotherms of the Grand Banks front. Further research will be required to identify the mechanisms which result in the observed ocean color structure.