Posted by RandyW on November 06, 2000 at 21:09:31:
In Reply to: Gulf Stream abyssal "storms" posted by Bo Qiu on September 20, 2000 at 13:57:10:
: One of the scientifically exciting results from the SYNOP program
: is the finding of the equivalent barotropic nature associated with
: the troughs of the meandering Gulf Stream. For those of us who
: studied the western boundary current variability largely using
: near-surface observational data, it is both fascinating and
: eye-opening to read the poster by Watts et al. and to see the rapid
: evolution (and the slow evolution, if one prefers that mode on
: their well-designed website) of the abyssal "storms" captured by
: the unprecedented SYNOP observations. Watts et al.'s poster
: convincingly shows that rather than being forced passively by the
: baroclinic instability of the surface-intensified Gulf Stream, these
: equivalent barotropic eddies not only affect cross-frontal exchanges,
: but may also determine the time scales of the evolution of the
: meandering Gulf Stream.
Bo, thanks for the comments. Note I disagree with the terminology
you used in these first lines. An "equivalent barotropic" current
is aligned top to bottom in the same direction. This
is NOT what we observed in SYNOP. The currents turned
strongly with depth -- deep currents were sometimes
turned 90 degrees from surface currents. (They
"veered" or "backed", using meteorological terminology.)
In fact, it's the "cross-frontal" or normal component
that mediates the cross-frontal exchange.
: There are two related issues I found rather intriguing after
: viewing the poster:
: (1) Abyssal cyclones/anticyclones: The chosen site for the SYNOP
: Central Array appears to be dominated by troughs of the meandering
: Gulf Stream. In other words, there are more abyssal cyclones than
: anticyclones. Do we know why this happens to be the case? The
: topography map indicates that the array is partially overriding an
: abyssal canyon. Does this local bottom topography contribute to
: the preference of the local persistent Gulf Stream troughs?
I have a favorite hypothesis for why, in the SYNOP
Central Array region, troughs dominated over
crests: The bottom slope is relatively steep to
the north and relatively weak to the south of the
mean path of the Gulf Stream here. Steep slopes correspondingly
inhibit meander crests to the north and favor meander
troughs to the south. Georgi Sutyrin has been
nicely demonstrating analogous behavior in his
intermediate model of the Gulf Stream.
(Incidentally, the influence of Hudson Canyon is
mainly northwest of this study region.)
: (2) Warm core rings: The formation process for a WCR described
: in the poster is very interesting. This may be related to the above
: point in that the meandering troughs at this site are so much more
: energetic than the meandering crests, so that the resultant barotropic
: cyclones are able to swirl the weaker anticyclones northward and
: cause their pinching-off eventually. Is the SYNOP Central Array
: site a preferred location for the WCR formation?
Yes, the WCR's in this case are more the product
or TROUGH formation than of crests per se.
I'll have to check the lit and get back to you on
this localization question. -RW