The effect of north-south gyre width on the inertial recirculation

The effect of the gyre north-south width on the inertial recirculation has been studied using a non-eddy resolving QG model. It is found that for the traditional sinusoidal Ekman pumping profile with a fixed maximum interior transport and fixed viscosity, a smaller north-south width will produce a s tronger inertial recirculation, unless the north - south width of the gyre becomes comparable with that of the inertial recirculation. This is because the intensity of the inertial recirculation is mainly determined by the lo cal advection of the potential vorticity anomaly in the vicinity of midlati tude. In a case of small north-south gyre width, the local speed of the nor thern parr of the western boundary current will be increased by the northwa rd shift of the latitude with the maximum interior Sverdrup transport. This tends to enhance the advection of potential vorticity anomaly, namely, non linearity within the northwestern corner and in turn a strong Q-anomaly in the midlatitude jet. As a positive feedback, the resulting recirculation ca n dramatically increase the speed of the western boundary current, and in t urn a stronger potential vorticity advection which further intensify the re circulation. As a result, in a double-gyre circulation that has a subpolar gyre of a smaller north-south width, and that has the same Sverdrup flows i n both gyres, the recirculation can be significantly stronger in the subpol ar gyre than in the subtropical gyre.