Sack Lunch Seminar (SLS)

Abstract:
An idealized eddy-resolving numerical model and an analytical model are used to study the buoyancy-forced circulation in an idealized Red Sea on a β-plane. The surface buoyancy losses increase northward. The mean circulation consists of an anticyclonic gyre in the south and a cyclonic gyre in the north. In mid-basin, the northward surface flow crosses from the western boundary to the eastern boundary. Numerical experiments with different parameters indicate that the crossover latitude of the boundary currents changes with f0, β and the meridional gradient of the buoyancy forcing, which can be explained by a balance between potential vorticity (PV) advection and a frictional torque. PV is the sum of stretching PV associated with stratification and planetary PV. In these experiments, stretching PV decreases with latitude and planetary PV increases with latitude. The contribution of the advection of stretching (planetary) PV to the total PV budget must be balanced with a negative (positive) PV production due to friction, which requires a cyclonic (anticyclonic) circulation. It is the competition between the advection of planetary PV and advection of stretching PV that determines the crossover latitude. Accordingly, an analytical model is developed to predict the crossover latitude of the boundary currents.