Formation process of a warm-core ring in the Kuroshio-Oyashio frontal zone-December 1981-October 1982

Using AVHRR images (36 scenes) from the NOAA-6 and -7 satellites combined with some hydrographic data, a scenario is presented for the behavior of the Kuroshio Extension from December 1981 to October 1982, resulting in the formation of a warm-core ring in the Tohoku Area. The behavior can be characterized by two drastic events. The first was the abrupt movement of the Kuroshio Front in December 1981, forming a bulge of the Kuroshio Water with a diameter of about 200 km. The bulge was cooled uniformly by an active air-sea interaction in winter, and became mixed with other waters. The analysis of the mixing process shows isopycnal mixing modifying almost the whole bulge water, and also a diapycnal mixing caused by an advection of the Kuroshio Water across the Kuroshio Front. The latter is closely connected with the second event, which started around 18 April and resulted in a warm-core ring detachment early in June. The formation process of the ring is described in detail by combining hydrographic data with the satellite data, and a hypothesis of the ring formation is given.