The observed dispersion relationship for North Pacific Rossby wave motions

The phase speeds of ocean surface height variability obtained by analyzing the time-longitude sections of altimetric anomalies have been widely report ed as being generally faster than those of free, first baroclinic linear mo de flat-bottom Rossby (planetary) waves. In contrast to previous analyses, extraction of the different signals in the time-longitude domain is perform ed here by array processing methods better able to separate different frequ ency and wavenumber bands. Although an incomplete description of oceanic va riability in the North Pacific, real oceanic motions with energy levels var ying from about 10% to 40% of the total in each frequency band are indistin guishable from the simplest theoretical description. Ar higher latitudes, a s the linear waves slow, they disappear altogether. Nonequatorial latitudes display some energy with frequencies too high for consistency with linear theory; this energy produces a positive bias if a lumped average westward p hase speed is computed for all the motions present.