Anticyclonic eddy revealing low sea surface temperature in the sea south of Japan: Case Study of the eddy observed in 1999-2000

Various kinds of datasets, such as satellite-derived sea surface temperature (SST), sea surface height, surface velocity produced by combining surface drifter and satellite altimeter data, and hydrographic data, led to the discovery of an anticyclonic eddy with lower SST than those of surrounding waters in the Kuroshio recirculation region south of Shikoku, as if the eddy were cyclonic. This anticyclonic eddy was formed east of Kyushu in late August to early September 1999 from the merger of two anticyclonic eddies which had migrated in the recirculation region to the sea south of Japan from the east. After the merger, the anticyclonic eddy strengthened abruptly and began to exhibit the low SST. In October, this eddy coalesced with the Kuroshio and moved swiftly eastward, accompanied by an amplitude growth of the Kuroshio meander. In mid November, off the Kii Peninsula, the eddy detached from the meandering Kuroshio. It then moved southwestward and again slowly propagated westward along the 30°N line. During this period, at least from late October 1999 to January 2000, SSTs over the anticyclonic eddy were found to be continuously lower than those of surrounding waters. This case tells us that we have to pay careful attention to the interpretation of mesoscale SST distributions.