Abstract:
Garrett and Munk use linear dynamics to synthesize frequency-wavenumber energy
spectra for internal waves (GM72, GM75, GM79). The GM internal wave models are
horizontally isotropic, vertically symmetric, purely propagating, and universal in both
time and space. This set of properties effectively eliminates all the interesting physics,
since such models do not allow localized sources and sinks of energy. Thus an important
step in understanding internal wave dynamics is to make measurements of deviations
from the simple GM models.
This thesis continues the search for deviations from the GM models. It has three
advantages over earlier work: extensive data from an equatorial region, long time series (2
years), and relatively sophisticated linear internal wave models. Since the GM models are
based on mid-latitude data, having data from an equatorial region which has a strong mean
current system offers an opportunity to examine a region with a distinctly different basic
state. The longer time series mean there is a larger statistical ensemble of realizations,
making it possible to detect smaller internal wave signals. The internal wave models
include several important extensions to the GM models: horizontal anisotropy and vertical
asymmetry, resolution between standing modes and propagating waves, general vertical
structure, and kinematic effects of mean shear flow. Also investigated are the effects of
scattering on internal waves, effects that are especially strong on the equator because the
buoyancy frequency variability is a factor of ten higher than at mid-latitudes.
In the high frequency internal wave field considered (frequencies between .125 cph
and .458 cph), several features are found that are not included in the GM models. Both the
kinematic effects of a mean shear flow and the phase-locking that distinguishes standing
modes from propagating waves are observed. There is a seasonal dependence in energy
level of roughly 10% of the mean level. At times the wave field is zonally and vertically
asymmetric, with resulting energy fluxes that are a small (4% to 10%) fraction of the
maximum energy flux the internal wave field could support. The fluxes are, however, as
big as many of the postulated sources of energy for the internal wave field.
