ON THE PROPAGATION AND DISSIPATION OF GRAVITY-WAVE SPECTRA THROUGH A REALISTIC MIDDLE ATMOSPHERE

The one-dimensional propagation of a spectrum of gravity waves through a realistic middle atmosphere is investigated, separating as far as p ossible the propagation-invariant aspects from the more empirical wave -breaking and other nonlinear aspects. The latter are parameterized by a simple broadband spectral saturation criterion, but the conceptual framework allows for other wave-breaking parameterizations. An upward propagating initial or ''launch'' spectrum is prescribed in the lower stratosphere. The propagation aspects are handled with careful attenti on to the mappings and their Jacobians between spectral spaces. Result s for several test cases produce realistic behavior, including cases w here some of the waves are back-reflected, as in the summer stratosphe re, with much of the spectrum propagating conservatively through subst antial altitude ranges. Any launch spectrum can be used in the computa tional scheme; for definiteness attention is concentrated on the model spectrum of Fritts and VanZandt, but sensitivity tests are also carri ed out in which the shape and total energy are varied. Other sensitivi ty tests include varying the steepness of the saturation criterion. Th e shapes and magnitudes of the computed profiles of wave-induced force , as a function of altitude, are sensitive to some of these changes, e specially to the asymptotic shape of the launch spectrum at the smalle st values of vertical wavenumber m, about which there is little direct observational evidence. However, the maxima and minima of the profile s are located at similar altitudes in each case. Besides pointing to w ays of improving gravity wave parameterization schemes for general cir culation models, the results may help to tighten observational constra ints on spectra for small m.