A numerical study on seasonal variation of the branches of the Tsushima Warm Current

Abstract

We present our results in a numerical experiment for the East/Japan Sea using POM. Our main focus of the numerical experiment is to investigate the seasonal variability of branches of the Tsushima Warm Current. The horizontal grid resolution of our model is 1/12o by 1/12o and varies from 8km in the north to 9km in the south. The mean temperature and salinity in January from the Japan Oceanographic Data Center is used for initializing the present model. The temperature and salinity at open boundaries and at sea surface are forced with the Generalized Digital Environmental Model data (version 2.5). The wind field is forced with the Na & Seo data (1998 version). Surface thermal and momentum flux are monthly mean fields, and inflow transport is imposed by observation data (Perkins et al, 2001).After passing through the Korea Strait, the Tsushima Warm Current is divided into flow along the Japanese coast and flow along Korean coast, that is, the Japanese Coastal Branch (JCB) and the East Korean Warm Current (EKWC). The JCB exists all the year round and becomes strong from April. In summer and fall, the JCB meanders widely, generates eddies near the Oki Spur, and reaches the Nato Peninsular. Eddy of the Yamato Basin becomes large in spring and summer, but it becomes relatively small after summer. This is because eddy generation between the JCB and the Yamato Basin increases from summer. The EKWC along the Korean coast is wide and weak in winter, and it separates 38oN. On the other hand, it is narrow and strong in summer and separates 39oN. When the EKWC becomes strong, there is an eddy over the northwestern part of the Ulleung Basin, which moves northward following the EKWC. Another minor eddy is generated over the southeastern part of the Ulleung Basin from September to November. After that time, minor eddies are integrated into one large eddy that occupies over the whole Ulleung Basin from December to next May.