THE NEAR-SURFACE LAYER OF THE OCEAN
short cutting the horizontal exchange (...) Therefore, there is a form of gate
that opens or closes to allow horizontal flux of properties in the mixed layer,
and it depends on the joint signs of displacement and local horizontal density
gradient. For convenience this phenomenon may be called the overturning
gate.”
Stommel’s overturning gate is open when the surface wind drift current
is directed toward higher density and closed when directed toward lower
density, as it is schematically illustrated in Figure 5-34a, b. In case b, the
wind drift current stabilizes the sharp frontal interface, which then resembles
an arrested wedge.
The spatial anisotropy of noncompensated interfaces (Figure 5-31a, c)
can therefore be explained by the fact that most sharp frontal interfaces are
observed when the wind stress is directed towards higher density (the
overturning gate is opened). When the wind stress is towards lower density
336
Figure 5-34. Interaction of sharp frontal interface with wind stress: (a) Stommel’s overturning
gate is closed; (b) Stommel’s overturning gate is opened. Reproduced from Soloviev et al.
(2002) by permission from Elsevier.