Synoptic observations of the oceanic frontal system east of Japan

Abstract

A series of seven flights was conducted during 2 weeks in October 1976 to obtain synoptic thermal measurements of the Kuroshio and Oyashio fronts and to determine the distribution and physical properties of eddies formed by these fronts. Sea surface temperature was measured continuously with an airborne radiation thermometer, and airborne expendable bathythermographs (XBT's) provided subsurface temperature profiles. These data were supplemented with shipboard XBT and salinity temperature depth (STD) measurements of selected features. The Kuroshio was tracked from the coast of Japan eastward to 158°E. It had a width at the surface of approximately 75 km and exhibited two large anticyclonic meanders. Maximum horizontal temperature difference across the front was 12°C at 300 m; maximum horizontal gradient at this depth was 0.3°C/km. STD stations showed that the Kuroshio extended to a depth of 2500 m. The Oyashio Front was tracked eastward to 154°E, and at depths less than 100 m it displayed horizontal temperature gradients equal to those of the Kuroshio. The Oyashio was observed to be a much shallower feature, however, weakening rapidly with depth. A total of nine eddies generated by both fronts was found: three Kuroshio cold eddies, three Kuroshio warm eddies, two Oyashio warm eddies, and one Oyashio cold eddy. They were of varying ages and ranged in size from 100 to 240 km. This is believed to be the largest number of eddies ever observed east of Japan and indicates that these features occupy a significant portion of this complex frontal system.