On the Propagation and Dissipation of Gravity Wave Spectra through a Realistic Middle Atmosphere

Abstract

The one-dimensional propagation of a spectrum of gravity waves through a realistic middle atmosphere is investigated, separating as far as possible 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 attention to the mappings and their Jacobians between spectral spaces. Results for several test cases produce realistic behavior, including cases where some of the waves are back-reflected, as in the summer stratosphere, with much of the spectrum propagating conservatively through substantial altitude ranges. Any launch spectrum can be used in the computational scheme; for definiteness attention is concentrated on the model spectrum of Fritts and VanZandt, but sensitivity tests are also carried out in which the shape and total energy are varied. Other sensitivity tests include varying the steepness of the saturation criterion. The shapes and magnitudes of the computed profiles of wave-induced force, as a function of altitude, are sensitive to some of these changes, especially to the asymptotic shape of the launch spectrum at the smallest values of vertical wavenumber m, about which there is little direct observational evidence. However, the maxima and minima of the profiles are located at similar altitudes in each case. Besides pointing, to ways of improving gravity wave parameterization schemes for general circulation models, the results may help to tighten observational constraints on spectra for small m.