Convection, Sinking and the Poleward Heat Transport
There is widespread belief that convective regions are
water is made dense and sinks, thus identifying convective locations
with the sinking limb of the overturning circulation. Instead, both
theory, high-resolution non-hydrostatic models and observations show
that very little sinking occurs in the open-ocean deep convection
regions, where the bulk of the dense water formation occurs, due to
rotational constraints inhibiting large-scale vertical motion. The
sinking can, on the other hand, occur in the boundary current. The
boundary current sinking, however, is not equivalent to the amount of
dense water formed. Instead only a fraction of the dense water sinks.
From this, it also follows that the poleward heat transport related to
convection regions is not all achieved by an overturning cell. In turn,
this implies that one expects the variability in the overturning and in
the poleward heat transport, due to dense water formation, to differ.
||Schematic of a two layer model that represents dense water
formation in a marginal sea. The interior is a region of
net heat loss and of dense water formation - thus maintaing
a reservoir of dense fluid. The boundary current that flows around it
exchanges heat with the interior (via instability processes) and becomes
progressively colder. A net sinking and associated barotropization of
the flow are associated with the boundary current transformation.
To learn more about this:
short: Straneo, F., 2005,
Dense Water Formation and Overturning: What is the Connection?
presented at European Geophysical Union 2005
longer: Straneo, F., 2005, On the connection between convection and sinking and its implication for
presented at the Potsdam Institute for Climate Impact Research, May 2005
long: Straneo, F., 2006, On the connection between dense water formation, overturning and
its implication for overturning variability. J.
Phys. Ocean. 36(9), 1822-1840.