Atmospheric loading and the oceanic “inverted barometer” effect

Authors

  • Carl Wunsch,

  • Detlef Stammer


Abstract

The response of the ocean to fluctuating atmospheric pressure loads is reviewed in theory and in observations. Major theoretical issues lie primarily with oceanic boundary reflectivity and with rates of dissipation, generally. Analytical solutions for a stratified ocean show that a static (“inverted barometer”) response is anticipated at all frequencies and wavenumbers not coincident with certain dispersion curves. Nonstatic behavior of two types is predicted: zero motion of the sea surface and a resonant response. Two types of resonance emerge. The first type corresponds to barotropic modes which are long gravity waves or Rossby waves at high and low frequencies, respectively. The second type excites internal modes, either gravity waves or Rossby waves depending on frequency, but modified from a conventional resonant response by the immediate juxtaposition in frequency/wavenumber space of the rigid-lid modes. The extent to which these actual resonances are generated is obscure owing to the same uncertainties about oceanic dissipation and scattering which affect all other forced oceanic motions, especially including the tides and other barotropic motions. Zero sea surface motion is predicted at frequencies and wavenumbers corresponding to “rigid-lid” modes. Observations support the wide applicability of the static response except in the tropics and in the western boundary current extension regions; there, the signal-to-noise ratios may be inadequate. The only other known clear nonstatic response occurs near 5 days in the Pacific and South Atlantic Oceans, indicative of a low-Q resonance in the former area and a forced nonresonant response in the latter, but there are remaining problems with these interpretations.

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