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Teiji In¹
Tomoharu Nakayama¹, Yasutaka Matsuura, Shigeki Shima¹, Yoichi Ishikawa², Toshiyuki Awaji², Takuya Kobayashi³, Hideyuki Kawamura ³ and Orihiko Togawa ³

(1) Mutsu Marine Laboratory, Marine Science Foundation, Japan
(2) Kyoto University, Kyoto, Japan
(3) Japan Atomic Energy Agency, Ibaraki, Japan

Main authors appear in bold

We have been developing an oceanic forecasting/nowcasting system for the coastal area near Rokkasho village, which locates in the northern part of Honshu Island of Japan. Associated with the geographic features, the oceanographic condition in this area is very complicated. For example, the circulation there is controlled primarily by the seasonally-varying Tsugaru current flowing from the Japan Sea and the Oyashio cold current which is the western boundary current in the subarctic North Pacific. Previous observations show that the seasonal variation in this region is characterized by the two different modes: the coastal mode in a cold season in which flow takes a straight path along the Japan coast, and the gyre mode in a warm season in which swirl-like circulation appears (e.g., Conlon, 1982). When attempting the accurate nowacast/forecast of this complicated regional circulation, a downscaling method is an effective approach since it enables us to use such a high resolution 4-dimensional variational data assimilation system that horizontal grids sizes of the numerical model used are about 1.5 km in both directions. In fact, our forecast result using the high resolution data assimilation system demonstrates the good performance of reproducing both modes in a hindcast sense.

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