Largescale propagating disturbances: approximation by vertical normal modes
Killworth, P.D.; Blundell, J.R.. 2001 Largescale propagating disturbances: approximation by vertical normal modes. Journal of Physical Oceanography, 31 (10). 28522870. 10.1175/15200485(2001)031<2852:LSPDAB>2.0.CO;2
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Abstract/Summary
Propagating features and waves occur everywhere in the ocean. This paper derives a concise description of how such smallamplitude, largescale oceanic internal disturbances propagate dynamically against a slowly varying background mean flow and stratification, computed using oceanic data. For a flatbottomed ocean, assumed here, the linear internal modes, computed using the local stratification, form a useful basis for expanding the oceanic shear modes of propagation. Remarkably, the shear modal structure is largely independent of orientation of the flow. The resulting advective velocities, which are termed pseudovelocities, comprise background flow decomposed onto normal modes, and westward planetary wave propagation velocities. The diagonal entries of the matrix of pseudovelocities prove to be reasonably accurate descriptors of the speed and direction of propagation of the shear modes, which thus respond as if simply advected by this diagonalentry velocity field. The complicated threedimensional propagation problem has thus been systematically reduced to this simple rule. The first shear mode is dominated by westward propagation, and possesses a midlatitude speedup over the undisturbed linear firstmode planetary wave. The pseudovelocity for the second shear mode, in contrast, while still dominated by westward propagation at lower latitudes, shows a gyrelike structure at latitudes above 30°. This resembles in both shape and direction the geostrophic baroclinic flow between about 500 and 1000m depth, but are much slower than the flow at these depths. Features may thus be able to propagate some distance around a subtropical or subpolar gyre, but not, in general, at the speed of the circulation.
Item Type:  Publication  Article 

Digital Object Identifier (DOI):  10.1175/15200485(2001)031<2852:LSPDAB>2.0.CO;2 
ISSN:  00223670 
Additional Keywords:  WOCE, INTERNAL DISTURBANCES, ADVECTION, VELOCITY, WAVE NUMBER 
Date made live:  04 Aug 2004 +0 (UTC) 
URI:  http://nora.nerc.ac.uk/id/eprint/107935 
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