Formation and circulation processes of intermediate water in the Japan Sea

The formation and circulation processes of intermediate water in the Japan Sea have been investigated by study of the subduction of mixed layer water. To simulate realistic seasonal variations in the velocity and hydrographic structures, a numerical model with a nudging method for potential temperat ure and salinity, which reproduced the general features in the Japan Sea, i s used. Close investigation of the subduction process reveals two major for mation areas (A and B) of intermediate water. Area A (41 degrees similar to 43 degrees N, west of 135 degrees E) corresponds to the region reported by recent observations, whereas Area B (40 degrees similar to 43 degrees N, e ast of 136 degrees E) has not been reported so far. The mixed layer water s ubducted in Area A is advected southwestward and eventually its upper porti on (above 200 m) reaches the eastern part of the Japan Basin, whereas the l ower branch (below 200 m) reaches the Tsushima Basin. This indicates that t he East Sea Intermediate Water originates from the mixed layer in Area A, a nd suggests that the East Sea Intermediate Water and the upper portion of t he Japan Sea Proper Water represent the same type of intermediate water. In contrast, the water subducted in Area B is advected northward and some of it flows out through the Soya Strait, while another portion is reentrained into the mixed layer off the Primorye coast. Tracking of the subducted wate r particles clearly shows that the southward transport of the intermediate water takes a seasonally varying path: for example, a path along the contin ental coast in winter and one along the Japanese coast in summer. The total formation rate of the intermediate water is estimated to range between 0.4 8 and 0.69 (x10(6) m(3) s(-1)) according to the strength of nudging terms, and the corresponding range in ventilation time is 20.3 similar to 25.6 yea rs.