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Kelly, B G / Meyers, S D / Obrien, J J : On A Generating Mechanism For Yanai Waves And The 25-Day Oscillation : Journal Of Geophysical Research-Oceans V. 100 No. C6 95 Jun 15 P. 10589-10612
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Abstract: A spectral. Chebyshev-collocation method applied to the linear, 1.5 layer reduced-gravity ocean model equations is
used to study the dynamics of Yanai (or mixed Rossby- gravity) wave packets. These are of interest because of the
observations of equatorial instability waves (which have the characteristics of Yanai waves) and their role in the
momentum and heat budgets in the tropics. A series of experiments is performed to investigate the generation of
the waves by simple cross-equatorial wind stress forcings in various configurations and the influence of a western
boundary on the waves. They may be generated in the interior ocean as well as from a western boundary. The
observations from all the oceans indicate that the waves have a preferential period and wavelength of around 25 days
and 1000 km respectively. These properties are also seen in the model results and a plausible explanation is provided
as being due to the dispersive properties of Yanai waves. Notes: 28 References
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Meyers, S.D. / Kelly, B.G. / O'Brien, J.J. : An Introduction to Wavelet Analysis in Oceanography and Meteorology: With Application to the Dispersion of Yanai Waves : Monthly weather review OCT 01 1993 v 121 n 10 Page: 2858
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Abstract: Wavelet analysis is a relatively new technique that is an important addition to standard signal analysis methods.
Unlike Fourier analysis that yields an average amplitude and phase for each harmonic in a dataset, the wavelet transform
phase for each harmonic in a dataset, the wavelet transform produces an 'instantaneous' estimate or local value for the
amplitude and phase of each harmonic. This allows detailed study of nonstationary spatial or time-dependent signal
characteristics. The wavelet transform is discussed, examples are given, and some methods for preprocessing data
for wavelet analysis are compared. By studying the dispersion of Yanai waves in a reduced gravity equatorial
model, the usefulness of the transform is demonstrated. The group velocity is measured directly over a finite range of
group velocity is measured directly over a finite range of wavenumbers by examining the time evolution of the
transform. The results agree well with linear theory at higher wavenumber but the measured group velocity is reduced
at lower wavenumbers, possibly due to interaction with the basin boundaries (27 Refs.)
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| Tsai, P.T.H.; O'Brien, J.J.; Luther, M.E. : The 26-day oscillation observed in the satellite sea surface temperature measurements in the equatorial western Indian Ocean : Journal of Geophysical Research, vol.97, no.C6, p. 9605-18
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Abstract: A 26-day oscillation in sea surface temperature data is observed in the western Indian Ocean, from 52 to 60 degrees
E and in the vicinity of the equator. The SST data used in this study are obtained from the NOAA 9 satellite and are
for the years 1987 and 1988. This fluctuation of SST at a for the years 1987 and 1988. This fluctuation of SST at a
period near 26 days is found to be antisymmetric about the equator and is trapped within the equatorial waveguide. The
variance associated with this oscillation has a maximum located at about 3 degrees latitude; furthermore, the
variance decreases at a faster rate toward the equator than poleward. These characteristics are consistent with the
latitudinal structure for the mixed Rossby-gravity (or Yanai) waves as predicted from linear wave theory (28 Refs.)
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| Woodberry, K.E.; Luther, M.E.; O'Brien, J.J. : The wind-driven seasonal circulation in the southern tropical Indian Ocean : Journal of Geophysical Research, vol.94, no.C12, p. 17,985-18002
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Abstract: A numerical model of the Indian Ocean, driven by
climatological monthly mean winds, realistically simulates
the major features of the large scale upper ocean
circulation observed in the southern hemisphere and
equatorial regions. The principal feature in the tropical
Indian Ocean is a basin-wide clockwise southern hemisphere
Indian Ocean is a basin-wide clockwise southern hemisphere
(cyclonic) gyre comprised of the South Equatorial Current to
the south, the South Equatorial Countercurrent to the north,
and the East African Coastal Current in the west. Rossby
waves propagate westward in the shear zone between the South
Equatorial Current and the South Equatorial Countercurrent,
and are obstructed and partially reflected by the banks
along the Seychelles-Mauritius Ridge (60 degrees E). A
region of high eddy activity northwest of Madagascar is an
extension of the tropical gyre. Oscillations in meridional
extension of the tropical gyre. Oscillations in meridional
transport at the equator have westward phase speed and
eastward group velocity and are the result of mixed Rossby-
gravity (Yanai) waves forced by oscillations in the highly
nonlinear western boundary current region (63 Refs.)
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