Copyright © The Oceanographic Society of Japan. Branching of the Tsushima Current by an Abrupt Increase of Bottom Depth

An analytical model of the branching of an inertial current partly afloat incident upon a step fall in bottom topography is considered to account for the branching of the Tsushima Current induced by an abrupt increase of the bottom depth near the northern end of the Korea-Tsushima Strait. The grounded portion of the incident current is constraint by bottom topography and eventually runs along the depth dis-continuity over the shallow region. Due to the inertia of the incident current, how-ever, the ungrounded portion crosses the depth discontinuity and forms a free iner-tial jet, giving rise to the branching. The deflection angle of this free inertial jet is determined through an integrated momentum balance. The branching is more re-stricted as the grounded portion of the incident current becomes relatively more im-portant, in terms of the momentum transport, than the ungrounded portion. For typi-cal values of the bottom depth, the transport of the Tsushima Current through the Korea-Tsushima Strait, and for acceptable values of other physical parameters, it appears that branching is possible. Hence, the abrupt increase of the bottom depth near the northern end of the Korea-Tsushima Strait, combined with the inertia of current, may indeed be an important factor in the branching of the Tsushima Cur-rent. The Tsushima Current in the KT Strait generally ex-tends down to the bottom (e.g., Miita and Ogawa, 1984; Teague et al., 2002). In summer, however, there is usu-ally a thin cold layer called the Korea Strait Bottom Cold Water (KSBCW) below the Tsushima Current (e.g., Fig. 2), extending up to the coastal areas following the bot-tom (Lim and Chang, 1969). Consequently, the western coastal areas of the KT Strait are very susceptible to coastal upwelling in the summer season (Lee et al., 2003). The KSBCW is either sluggish or weakly in southward motion and is known to originate from the north carried by the NKCC (Kim and Kim, 1983). The contrast betwee