The Oceanic forecasting system near the Shimokita Peninsula, Japan

In, Teiji*; Nakayama, Tomoharu*; Matsuura, Yasutaka*; Shima, Shigeki*; Ishikawa, Yoichi*; Awaji, Toshiyuki*; Kobayashi, Takuya ; Kawamura, Hideyuki  ; Togawa, Orihiko ; Toyoda, Takahiro*

The Shimokita Peninsula (hereafter SP)is located at the northeast tip of Honshu (the main island of Japan) and borders on the northwestern part of the North Pacific Ocean (hereafter NWNP) in the east and the Tsugaru Strait (hereafter TS) in the north. It is known that the NWNP off the SP assumes a complex water mass structure. Seawater of Japan Sea origin, called the Tsugaru Warm Water (TWW) component, takes on a characteristic seasonal variation. Conlon (1982) pointed out that during winter and spring, the TWW in the NWNP propagates southward along the coast of the peninsula (the coastal mode), and swirls off the peninsula from summer to autumn (the gyre mode). It is necessary to accurately reproduce the striking circulation patterns and the complicated water mass structures in this area with an ocean general circulation model (OGCM). We need to use a fine-scale grid, probably such as 1-2 km in size to reproduce the water mass structure around the TS and the off the SP in detail. To initialize the forecast system, we use a 4-dimensional variational method of data assimilation. A forecast experiment on the basis of oceanographic observations made in 2003 (a hindcast experiment) illustrates the good performance of our system. We shall focus, in particular, on the shift from the coastal mode to the gyre mode and vice versa.