ON TOO FAST BAROCLINIC PLANETARY-WAVES IN THE GENERAL-CIRCULATION

Recent altimetric observations of the ocean surface reveal signatures of long planetary waves near the annual frequency band. Comparisons of the observed wave speeds and those predicted by standard linear theor y suggest that the latter is inadequate as it yields different westwar d speeds than those measured; in the extratropical latitudes the predi cted speeds are typically slower than the observations. Here the probl em of long, baroclinic wave propagation in a forced, stratified ocean is considered theoretically with a view toward explaining these observ ations of ''too fast'' planetary waves; From a quasigeostrophic analys is, it is argued that baroclinic waves in a sheared environment are ac celerated to the west via their interactions with both the mean advect ive field and the mean potential vorticity field. Conditions under whi ch the ratio of actual to linear phase speeds matches the observed rat io are computed and found to be typical of the open ocean. Extensions of these ideas to continuously stratified quasigeostrophic and layered planetary geostrophic systems are discussed.