Numerical simulation of Pacific water intrusion into Otsuchi Bay, northeast of Japan, using a nested-grid OGCM

Numerical simulation of Otsuchi Bay located on the northeast coast of the Honshu, the largest island of Japan, is conducted, using an OGCM with a nested-grid system in order to illustrate seasonal variability of the circulation in the bay. Otsuchi Bay is a narrow inlet running east-west, 8 km long and 2 km wide, and opens to the North Pacific on the east. Previous observational studies have suggested that water circulation in the bay is controlled by river discharges from the western boundary of the bay and two Pacific waters; one is a warm-saline water called Tsugaru Warm Water that is a branch of the Tsushima Warm Current in the Sea of Japan flowing through Tsugaru Strait, and the other is a cold-fresh water called Oyashio Water. It has been considered that there are two mechanisms of the Pacific waters' intrusion into the bay; horizontal advections and internal tides. The OGCM used the present study has a horizontal resolution of about 15 m, and is driven by climatological atmospheric forcings (10-day interval) and hourly averaged outputs of a numerical simulation of the North Pacific with CORE2 normal-year atmospheric forcings with tides. In the present study, it will be discussed how the water circulation in the bay changes through a year, especially how seasonal variation of the vertical stratification affects Oyashio Water intrusion into the bay through internal tides.