The most up-to-date scenario for these interbasin circulation processes starts with 14 Sv of upper and intermediate level water being converted to NADW in the North Atlantic and flowing southward across the equator to join the ACC. This loss from the Atlantic is compensated by 10 Sv of upper level entering via the Drake Passage and 4 Sv entering from the Indonesian Throughflow through the Australasian Mediterranean and around Africa. The Indian Ocean receives 24 Sv of lower level cold water from the ACC, returning 14 Sv as cold water and transforming 10 Sv to upper level water. This latter 10 Sv flows south of Australia, across the South Pacific, and through the Drake Passage into the Benguela Current regime. This joins the afore mentioned Indonesian Throughflow, crosses the equator, and flow with the Gulf Stream into the North Atlantic to replace the lost NADW. The Pacific takes 20 Sv of cold water from the ACC and returns it as less cold water, with about half of it traversing the North Pacific.
This is a simplified two-layer version of a more complicated four-layer circulation scheme developed by Schmitz (1995) which includes intermediate and upper layer compensations flows as well as abyssal and deep interbasin thermohaline circulation layers. The greatest uncertainties remain in the Indian and Pacific Oceans, especially with the flows associated with vertical exchange, which in itself is perhaps the least well established feature of ocean circulation.
where I is the radiance, the zenith angle, and the infinitesimal solid angle. The rate at which radiation is incident upon a unit area.
The isopycnal method was originally applied such that all densities were calculated relative to the ocean surface, i.e. as either sigma-t or sigma- . This was later modified when it was found that, due to the nonlinearity of the equation of state for seawater, maximum values could exist well above the ocean bottom - ostensibly signifying a hydrostatic instability. The problem was rectified by the use of potential densities calculated relative to different pressures as was required by the situation, i.e. sigma-1 for densities relative to 1000 decibars (db), sigma-2 for 2000 db, etc., a procedure that is still followed today.