DREP (Defense Research Establishment Pacific) Internal Wave Normal Mode Model-Theoretical Background

摘要

This report contains the theoretical background material for a linearized internal gravity wave normal mode computational scheme. Currents predicted by this model have been used extensively in the production of simulated synthetic aperture radar images of internal wave signatures produced by moving vessels. A full derivation is given for the steady state internal wave fields produced by a distribution of fluid volume sources undergoing common uniform horizontal motion in a finite depth ocean. A modification of the standard eigenfunction expansion leads to accelerated convergence of the modal sums. Computation of all relevant fluid dynamical fields (3-component velocity, density, pressure and vertical particle displacement) is considered. Both sub- and super-critical source speeds can be handled. An extensive discussion of the effects of interior regions of high evanescence for certain wavenumber regimes shows how the eigenfunction expansion can be readily modified to handle such regions in a straightforward manner. The method properly accounts for trapping of energy generated within multiple thermoclines and may be of interest in certain underwater acoustics problems, where the mathematics are similar. Efficient computation of extensive sets of field data is discussed. Examples are presented for a submerged source in the N.E. Pacific Ocean. Also included is a brief comparison with measured surface-ship-generated internal wave current data. Canada. (jhd)