166
Fig. 3.11.3b
Vertical Structure: Baroclinic Quasi-Geostrophic Models
0
'
1------1
CM /SEC
layer represents a layer with little or no motion even though the q contours
avoid the eastern boundary. Keffer (1985) associates this layer with the
subtropical recirculation of Subpolar Mode Water and suggests that it actually
forms south of the zero Ekman pumping line so that it is a layer which is
ventilated and in motion. Indeed, Keffer has suggested that in the North
Atlantic the region of uniform q seen on the ae = 26.75 surface may be not
connected at all with potential vorticity homogenization. He argues that this
surface is in fact far enough south of the inter-gyre boundary that it is subject
to forcing of its potential vorticity by the mixed layer, and that the uniformity
may be due to a fortuitous uniformity of the potential vorticity in the source
region for the layer. There is general agreement, however, that the equivalent
layer in the North Pacific, ao = 26.5 (see also Talley 1988) is absent of sources
of potential vorticity and contains a large zone of uniform potential vorticity,