Behavior of a Detached Eddy “Harukaze” around the Seamount of Daiiti- and Daini-Kinan Kaizan

Abstract

Very interesting phenomena were observed on board the R.V. Shumpu-Maru, Kobe Marine Observatry, on detached cold eddy from the Kuroshio in seas south of Japan early July 1977. There are ring-like low haline waters in the periphery of the eddy, anomalously high temperature in the central region of the eddy, where cold waters should occupy, and many visual slicks around the central part of the eddy. The ring-like low haline waters might be attributed to the heavy rain in the atmospheric stationary front, called “baiu-zensen”, late June in the area, according to Kamihira et al. (1978). Moreover, we propose a mechanism in which a forced upwelling by the seamount generates a convergence zone around the seamount, in which low-haline waters are accumulated. In regard to the anomalously high temperature region near the eddy center, Kamihira et al. attribute the event to the remnant of Kuroshio waters existing just before their observation was made. However, we may be obliged to consider the malfunction of the XBT systems responsible for it, because the current speed is too weak and temperature contrast is too intense to make a dynamical balance. Moreover a thermal fine structure, appearing at about 400 m depth, suggests a large instrumental error in the XBT record. Although we might ascribe the anomaly mainly to the instrumental error in the XBT record, it is possible to explain the generation of a warm core by modification of the mean current due to the topographic effect of the seamount, analogous to a Taylor column. The configuration of the eddy through its northwestward migration, first compressed to the seamount, then enlarged around it, then again elongated towards northwest and eventually absorbed into the Kuroshio, might apparently be due to the topographic effect of the seamount associated with the generation of the shed vorticity. These problems will be studied in future work. © 1978, Japan Meteorological Agency. All rights reserved.