Seasonal variation of the North Equatorial Current bifurcation in regional model: Role of open boundary conditions

Abstract

The role of open boundary conditions in modelling the seasonal variation of the North Equatorial Current Bifurcation latitude (NBL) is studied based on a linear Rossby wave model, 1.5-layer reduced-gravity model and Hybrid Coordinate Ocean Model (HYCOM). For a regional ocean model that covers the western Pacific, it is found that the seasonal variation of the NBL can be well reproduced as long as the data at the open boundary is provided by the corresponding basin experiment, no matter where the location is. However, the south–north migration of NBL as well as its peak seasons is not properly simulated if we apply other types of data at the open boundary as its location is close to the west. Sensitivity experiments indicate that the bad performance is attributed to the over-specification error and incomplete adjustment of interaction between wind forcing and westward propagating signals from incompatible open boundary data. The performance gets better as we set the open boundary at proper location and choose suitable open boundary condition. These conclusions can be extended to the simulations of low-latitude western boundary currents.