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Variations of diurnal and inertial spectral peaks near the bi‐diurnal critical latitude
Author(s) -
Xie XiaoHui,
Shang XiaoDong,
Chen GuiYing,
Sun Lu
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2008gl036383
Subject(s) - inertial wave , latitude , internal wave , atmospheric sciences , wind shear , physics , kinetic energy , inertial frame of reference , shear (geology) , amplitude , eddy , geology , spectral line , geophysics , turbulence , geodesy , wind speed , mechanics , meteorology , optics , wave propagation , classical mechanics , longitudinal wave , mechanical wave , petrology , astronomy
Three sets of ADCP data obtained from the upper ocean are used to examine possible influence of parametric subharmonic instability (PSI) at ϕ c ≈ 13–15°N. Both kinetic‐energy and shear spectra at ϕ c reveal that significant peaks appear at subharmonic frequencies of diurnal internal tides. Especially, the 0.5 K 1 (subharmonic of K 1 tides) can be trapped poleward of its critical latitude (14.52°N), significantly distinguished from wind generated near‐inertial internal waves. Moreover, the enhanced 0.5 K 1 motions are more or less subject to a fortnightly spring‐neap circle. Relative to a higher latitude (say 18°N), diurnal motions at ϕ c are greatly weakened. In contrast, small vertical‐scale motions in the inertial band and the shear induced by these motions are significantly enhanced. Likely, PSI mechanism plays an important role in these observations, whilst trapped sub‐inertial waves (0.5 K 1 ) may be associated with the presence of negative sub‐inertial eddies.