Albert J. Plueddemann
James F. Lynch
Woods Hole Oceanogr. Inst., 360 Woods Hole Rd., Woods Hole, MA 02543-1541
The well-known Garrett and Munk description of the internal wave spectrum synthesizes many observations into a spectral model that reproduces the general features of the mid-latitude, deep-ocean internal wave field. The general applicability of this ``kinematic'' spectral model is related to the dynamic balance of the internal wave field, but the model itself includes no dynamics and is meant to represent only the average or steady-state spectrum, away from the direct influence of sources, sinks, or boundaries. In shallow water, the kinematic model is typically not appropriate, since some or all of the simplifying assumptions about the wave field may be invalidated. Variable topography, strong tidal currents, fronts, and ice cover (at high latitudes) are the principal reasons for these complications, and result in an internal wave field which varies both spatially and temporally from the steady-state kinematic description. The most straightforward way to address the inadequacy of steady-state models for shallow water acoustics experiments is direct observation of the internal wave field at the site. Profiles sufficient to define the ``mean'' or background density gradient along with time series of temperature and horizontal velocity are the most common observations.