Space and time scales of low frequency variability in the ocean
Citable URI
http://hdl.handle.net/1912/5567DOI
10.1575/1912/5567Keyword
Internal waves; Ocean tomographyAbstract
We have contrived a regional model Φ(K, ω, η, φ, λ) for the distribution of low
frequency variability energy in horizontal wavenumber, frequency, vertical mode and
geography. We assume horizontal isotropy, Φ(K, ω, η, φ, λ) = 2πKψ(k, l, ω, η, φ, λ),
with K designating the amplitude of total horizontal wavenumber.
The parameters of Φ(K, ω, η, φ, λ) can be derived from observations: (i) satellite
altimetry measurements yield the surface eddy kinetic energy wavenumber and frequency
spectra and the geographic distribution of surface eddy kinetic energy magnitude,
(ii) XBT measurements yield the temperature wavenumber spectra, (iii) current
meter and thermistor measurements yield the frequency spectra of kinetic energy and
temperature, (iv) tomographic measurements yield the frequency spectra of range—
and depth—averaged temperature, and (v) the combination of satellite altimetry and
current meter measurements yields the vertical partitioning of kinetic energy among
dynamical modes. We assume the form of the geography—independent part of our
model Φ(K, ω, η) ∝Kpωq. The observed kinetic energy and temperature wavenumber
spectra suggest p = 3/2 at K < K0 and p = —2 at K > K0 for the barotropic
mode, and p = —1/2 at K < K0 and p = —3 at K > K0 for the baroclinic mods,
where K0 is the transitional wavenumber of the wavenumber spectra. The observed
frequency spectra of temperature and kinetic energy suggest that q = —1/2 for ω < ω0
and q = —2 for ω > ω0, where ω0 is the transitional frequency of the frequency spectra.
The combination of satellite altimetry and current meter measurements suggests
the vertical structure of the low frequency variability is governed by the first few
modes. The geography—dependent part of our model is the energy magnitude.
Although we have shown analytically that the tomographic measurements behave
as a low—pass filter, it is impossible to identify this filtering effect in the real data
due to the strong geographic variability of the energy magnitude and the vertical
gradient of the mean temperature. The model wavenumber spectrum is appropriate
only where the statistical properties are relatively homogeneous in space.
Description
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 18, 1988
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