Non-Seasonal SSTs of the Western Tropical North Pacific

Abstract

Seasonal changes in SSTs are very small in the western tropical North Pacific, in spite of the fact that significantly more solar radiation per unit time and per unit area is absorbed by the surface layer in summer than in winter and mainly at lower latitudes. Therefore, an efficient heat transport mechanism must be operating to keep up with the solar input. Sea surface temperatures from a world atlas are analyzed where it is found that the areas between the 80 and 82.5 F contours and the equator have marked seasonal variations: increasing in spring and summer as the contours move north, then decreasing in fall and winter as the contours return south. Between winter and summer, the area under the 80 F contour doubles in size. The increase of surface areas is likely due to the increase of absorption of solar radiation. When the areas decrease with time, the inferred heat in the surface layer must go somewhere. Arguments consistent with the available data suggest that the accumulated heat in spring and summer is advected north out of the tropics. The surface temperature gradient, related to the driving force for the flow, computed between the contours and the Aleutian Islands, increases slowly from January to June but then increases much faster till September, after which it rapidly decreases again. It is conjectured that cold surface water from the subarctic surges south beginning in June causing a warm tropical water pulse simultaneously to go north. The large volume of high temperature water of the surface layer in the western tropical North Pacific is thought to be the source of the permanent northward wide warm current off California as well as the additional northward warm surge in summer, both of which have been established previously on the basis of very many observations.