Can Long Meridional Length Scales Yield Faster Rossby Waves?

Abstract

There is much interest in better understanding the westward-propagating subinertial signal in the ocean basins because it influences many aspects of the ocean?s circulation. One explanation for the origin of this signal is that it is predominantly composed of Rossby waves. Chelton and Schlax assumed the observations were Rossby waves and compared their phase speeds with those predicted from nondispersive linear quasigeostrophic wave speeds. They concluded that the theory underestimated the observed wave speeds. Recently, in the context of the shallow-water model, Paldor, Rubin, and Mariano found that by including the full meridional variation of the Coriolis parameter, the Rossby waves have faster phase speeds. Here, their analysis is extended to derive a general dispersion relation for stratified Rossby waves that is suitable for both mesoscale and synoptic length scales. Then, realistic profiles of the buoyancy frequency are used to compare the phase speeds from the Ocean Topography Experiment (TOPEX)/Poseidon data with the new theory. It is found that the new theory does not yield any significant increase in Rossby wave speeds.