THE FLOW SYSTEM IN THE JAPAN SEA CAUSED BY A SEA-LEVEL DIFFERENCE THROUGH SHALLOW STRAITS

We investigate how the current system through the Japan Sea is driven and what determines the volume transport. We suppose that a part of th e difference in geopotential anomaly between the subtropical and subpo lar gyre is converted into a barotropic sea level difference across th e three shallow straits which connect the Japan Sea with the Pacific a nd that this difference is the primary driving force of the current sy stem. Then, we examine the flow under the condition that there is a co nstant sea level difference between two oceans connected through a sha llow strait. We found that the strait acts as a source of arrested she lf waves or steady coastal flows for the timescale beyond the inertial period; in the northern hemisphere, steady flows axe established alon g the shelves with the coast to the right (left) in the ocean of low ( high) sea level. We apply this notion to the current system through th e Japan Sea. The Tsushima nearshore branch, the Tsugaru coastal mode, and the Soya Current can all be interpreted as a coastally trapped flo w whose source is the upstream strait. Further, a series of northeastw ard flows along the South and East China Seas shelves should be interp reted as coastally trapped flows whose source is the downstream Tsushi ma Strait. Numerical model experiments incorporating the realistic top ography also simulate the observed flow fields. The volume flux throug h each strait being limited geostrophically, relations between the sea level difference and volume transport can be represented by simple fo rmulas.