Studies of inertio-gravity waves induced by geostrophic adjustment of the atmospheric jet stream

Abstract

Motivated by observations revealing very low frequency gravity waves throughout the lower and middle atmosphere, this thesis investigates inertio-gravity waves (IGWs) radiating from an ageostrophic jet stream assuming geostrophic adjustment to be the source mechanism. Fourier integral and Green's function techniques are employed to solve this problem. The ageostrophic components of the motion field are described by an initially unbalanced Gaussian velocity field which has been chosen to have infinite and localized zonal extents corresponding to two-dimensional (2-D) and three-dimensional (3-D) cases. The adjustment process permits the radiation of IGWs and the attainment of an induced geostrophically balanced mean circulation. The results of this thesis reveal IGW radiation from the initially unbalanced momentum source with frequencies near f (inertial frequency) and most of the disturbance energy associated with the IGW field. This research thus confirms geostrophic adjustment may be a major source of the low frequency gravity waves in the atmosphere. IGW structure includes primarily meridional wave propagation, with vertical and horizontal scales that depend on the initial unbalance configuration. The 3-D solutions at large distances from the jet core along the jet axis exhibit a change in IGW character from primarily meridional propagation at early times to largely zonal propagation at later times due to delayed arrival of IGW activity from more distant source regions. The induced mean flows in the 2-D and 3-D cases represent small fractions of the initial energy, insure conservation of potential vorticity, and reflect to a large degree the character of the momentum source.