Meridional Location and Profile of a Prematurely Separated WBC Extension Jet in a Two-layer System


Western boundary currents (WBCs) under no-slip boundary conditions tend to separate from the coast prematurely (without reaching the intergyre boundary) and form eastward jets. This study theoretically considers the meridional structure and location of a prematurely separated WBC extension jet using a two-layer quasigeostrophic model. Assuming homogenized potential vorticity (PV) regions on both sides of and below the jet, we constructed a simple model for the meridional profiles of the zonal flows in the western subtropical gyre. This work clarifies that the meridional structure can be determined if two variables, such as the strength of the PV front (difference in PV across the jet) and the value of the stream function at the jet’s center, are given in addition to the meridional profile of the Sverdrup zonal flow and the vertical stratification. The zonal velocity profiles in both layers agreed well with those obtained by numerical experiments. When the jet is close to the intergyre boundary, the meridional location of the jet depends only on the front’s strength. When the northern recirculation gyre is detached from the intergyre boundary and the local wind effect on the jet is negligible, comparisons with the numerical experiments suggest that the jet’s central streamline connects to the central streamline of the eastward Sverdrup flow. We also found that a downward Ekman pumping velocity shifts the jet southward.