The “separation formula” and its application to the Pacific Ocean

The “separation formula”, a new method for computing the adiabatic inter-hemispheric meridional transport, is applied to the Pacific Ocean. The method involves an integration of the wind stress along a “horseshoe” path. It begins at the separation point of the East Australian Current, continues eastward across the ocean, progresses northward along the continental boundary, and then turns back westward across the ocean to the separation point of the Kuroshio. Since the Pacific is closed on the northern side, such an integration gives the wind-driven Indonesian throughflow.The analytical formulas show that, in order for the adiabatic wind-driven throughflow to exist, it is necessary that there be an asymmetry in the winds associated with the two zonal cross-sections connecting the (northern and southern) separation points in the west to the continents in the east. It turns out that these asymmetries in the Pacific are relatively small and, consequently, do not allow for a significant (i.e. more than one Sverdrup) Indonesian transport. Specifically, in the Pacific, this wind-driven transport is directed to the south, implying a very small net Indian-to-Pacific transport rather than a Pacific-to-Indian transport. The adiabatic model fails, therefore, to explain the observed Pacific-to-Indian throughflow of 5-6 Sv.When an upwelling is added to the model (to simulate diabatic processes), then one obtains the result that all the water upwelled in the Pacific must exit the Pacific via the Indonesian seas, i.e. the wind field is effectively blocking the oceanic region between Australia and South America, forcing the upwelled water into the Indian Ocean. This model suggests, therefore, that the observed Pacific-to-Indian throughflow is a measure of the upwelling in the Pacific.