Open AccessGlobal Patterns of Low-Mode Internal-Wave Propagation. Part II: Group Velocity
Author(s) -
Matthew H. Alford,
Zhongxiang Zhao
Publication year - 2007
Publication title -
journal of physical oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.706
H-Index - 143
eISSN - 1520-0485
pISSN - 0022-3670
DOI - 10.1175/jpo3086.1
Subject(s) - internal wave , latitude , group velocity , inertial wave , energy flux , geology , geodesy , physics , inertial frame of reference , flux (metallurgy) , wavenumber , geophysics , middle latitudes , wave propagation , mechanics , atmospheric sciences , mechanical wave , longitudinal wave , classical mechanics , optics , materials science , astronomy , metallurgy
Using a set of 80 globally distributed time series of near-inertial and semidiurnal energy E and energy flux F computed from historical moorings, the group velocity ĉg ≡ FE−1 is estimated. For a single free wave, observed group speed |ĉg| should equal that expected from linear wave theory. For comparison, the latitude dependence of perceived group speed for perfectly standing waves is also derived. The latitudinal dependence of observed semidiurnal |ĉg| closely follows that expected for free waves at all latitudes, implying that 1) low-mode internal tides obey linear theory and 2) standing internal-tidal waves are rare in the deep ocean for latitudes equatorward of about 35°. At higher latitudes, standing waves cannot be easily distinguished from free waves using this method because their expected group speeds are similar. Near-inertial waves exhibit scattered |ĉg| values consistent with the passage of events generated at various latitudes, with implied frequencies ω ≈ 1.05–1.25 × f, as typically observed in frequency spectra.