Abstract: Kessler and McCreary, 1993
The annual wind-driven Rossby wave in the subthermocline
equatorial Pacific
Journal of Physical Oceanography 23(6), 1192-1207
(1993)
The annual cycle of temperature in the subthermocline equatorial
Pacific is studied using a
new
compilation of historical hydrographic profiles. The
observations have several characteristics
suggestive of a vertically propagating, first meridional mode
(l = 1) long-wavelength
Rossby wave: phase lines that slope downward from east to west
indicative of upward and
westward phase propagation, amplitude maxima parallel to phase
lines, and nearly symmetric
off-equatorial maxima of annual amplitude. Estimates of zonal
wavenumber, vertical
wavenumber,
and the location of maxima of isotherm displacements are
consistent with those of the
l
= 1 Rossby wave. A solution to a linear continuously stratified
model, driven by a version of
the observed annual wind field, confirms this interpretation.
The solution is dominated by a
vertically propagating, l = 1 Rossby wave. The wave is
generated primarily by the
westward-propagating component of the equatorial zonal wind
field; it carries energy along
WKB
ray paths into the deep ocean. Both amplitude and phase of the
model density field agree
well
with the observations. There are, however, two prominent
differences between the
observations
and the solution: first, in the solution a boundary-reflected
l = 3 Rossby wave is
present
in the deep eastern Pacific but is apparently absent in the data;
second, the model solution is
nearly symmetric about the equator, while the observations are
symmetric in phase but have
larger amplitude in the Northern Hemisphere. Thus, efficient
vertical propagation of Rossby
wave energy through the thermocline into the deep ocean appears
to be an important oceanic
process. The lack of this process in single active-layer models
may explain the unrealistically
high amplitudes of off-equatorial variability that are produced
in them, since such models
necessarily trap all energy in the surface layer.
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