On the propagation of baroclinic waves in the general circulation

The propagation of long, first mode, baroclinic planetary waves in eddy-res olving quasigeostrophic general circulation models is studied. Recent TOPEX /Poseidon observations argue oceanic first-mode planetary waves move with s peeds other than those predicted by simple theory. These data have prompted theoretical analyses of wave propagation in a mean flow, with the results suggesting mean shear can have a controlling effect on the planetary wave g uide. Some of the predicted effects appear to be relevant to the observatio ns, while others are less obvious. This, coupled with other explanations fo r the observations, motivates the calculations. Based on these experiments, the authors suggest that the predicted effects of mean shear on wave propagation are consistent with those computed in a f ully geostrophically turbulent ocean. These are that a two-layer model miss es the dominant component of long-wave interaction with a mean flow, a thre e-layer model captures this interaction qualitatively, and the correction t o wave propagation is in the direction opposite to the mean flow. Quantitat ive comparisons between the theory and the numerical experiments are good i n the northern latitudes and questionable in the southern latitudes. Reason s for the southern discrepancy are offered.