On spatially growing baroclinic waves in the ocean

Abstract

It is shown that spatially growing waves with complex wavenumber and real frequency can exist in a baroclinic flow and that these waves are substantially different from the more commonly studied temporally growing ones. They are bounded by a low wavenumber cut-off which separates them from the temporally growing waves. Their amplitude and phase change most rapidly near their steering level and are almost depth independent away from it. Most of the energy conversion from mean flow to the waves occurs at this level. It is suggested that these motions may be forced by steady disturbances such as bottom relief.The theory is compared with recent observations of strong small-scale motions in a region of rough topography of MODE and in the vicinity of the Gulf Stream. The vertical structure can be well matched with the theory but the complex wavenumber appears to be a factor of 2–3 greater than that predicted.