A study of the dynamic factors of the summer-time upwelling in the Tsushima Warm Current region

The dynamic factors governing the summer-time upwelling along the Japanese shelf area and its structures are examined using an eddy-resolving ocean general circulation model. A sensitivity experiment suggests that the dominant factor is the topographic irregularities that enhance the upwelling along the shelf slope but the influences of the seasonal variation of the Tsushima Warm Current (TWC) inflow and wind stress are insignificant. The dynamic analysis shows that the upwelling is a part of the secondary, overturning circulation that appears along the shelf from April to October. The dynamic structure shows the dominant term balance in essence, i.e. a triad of the term of pressure gradient, Coriolis force, and horizontal advection. The local pattern of the upwelling is closely correlated to the horizontal variations of the shelf slope and the horizontal advection term. The horizontal variation in the shelf topography is a key factor to determine the local pattern of the summer-time upwelling.