Linear Spectral Numerical Model for Internal Gravity Wave Propagation

Abstract

A three-dimensional linear spectral numerical model is proposed to simulate the propagation of internal gravity wave fluctuations in a stably stratified atmosphere. The model is developed to get first-order estimations of gravity wave fluctuations produced by identified sources. It is based on the solutions of the linearized fundamental fluid equations and uses the fully compressible dispersion relation for inertia?gravity waves. The spectral implementation excludes situations involving spatial variations of buoyancy frequency or background wind. However, density stratification variations are taken into account in the calculation of fluctuation amplitudes. In addition to gravity wave packet free propagation, the model handles both impulsive and continuous sources. It can account for spatial and temporal variations of the sources, encompassing a broad range of physical situations. The method is validated with a monochromatic pressure monopole, which is known to generate St. Andrew?s cross?shaped waves. It is then applied to the case of the ozone layer cooling during a total solar eclipse. The asymptotic response to a Gaussian thermal forcing traveling at constant velocity and the transient response to the 4 December 2002 eclipse show good agreement with previous numerical simulations. Further applications for the model are discussed.