Measurements of the Effects of Gravity Waves in the Middle Atmosphere Using Parametric Models of Density Fluctuations. Part II: Energy Dissipation and Eddy Diffusion

Abstract

Part I of this series demonstrated the advantages of parametric models in estimating the gravity wave spectrum from density fluctuation measurements using a large power-aperture-product Rayleigh-scatter lidar. The spectra calculated using the parametric models are now used to estimate energy dissipation due to gravity waves. Energy dissipation for an individual wave in the spectrum is also estimated using Prony’s method, which allows the frequency, amplitude, damping, and phase of individual waves to be estimated. These two independent estimates of energy dissipation highlight the variability of the energy dissipation on short timescales due to gravity waves and turbulence. A combination of the information obtained from the parametric models of the spatial and temporal spectra with the theoretical work of M. E. McIntyre is used to estimate profiles of the eddy diffusion coefficient. This estimate attempts to include the degree of saturation of the vertical wavenumber spectrum, which determines the constant used in the calculation of the eddy diffusion coefficient. The height profile of the eddy diffusion coefficient thus obtained in the upper stratosphere and mesosphere is in good agreement with previous estimates. The degree of saturation of the vertical wavenumber spectrum is shown to increase proportionally to the Hines parameter, a measure of the transition wavenumber from a linear to a nonlinear tail spectrum. It is speculated that this fact can be interpreted as a change in the atmosphere from an “amplifier” state where the tail spectrum is highly nonlinear, but weak when the spectral “gain” is high, to a state of saturation where the high wavenumber tail spectrum is more linear, but has lower gain and more energy available to dissipate at smaller spatial scales.