M.S. Thesis

Critical Level Directional Filtering of Atmospheric Gravity Waves: A Comparison of OH Airglow Observations and a Wind Profile Model

Abstract

Optical observations of nighttime OH airglow over a three month period (May, June and July of 1988) in Colorado show gravity waves propagating predominantly in the northward to eastward directions. The continuous asymmetry of these observations suggest heavy directional filtering of the gravity waves. As gravity waves propagate upwards in the atmosphere, they can be blocked by critical levels where the horizontal phase velocity of the gravity wave equals the horizontal wind velocity. To test for the possibility of directional filtering of the gravity waves due to critical level blocking, a wind profile model using climatological background winds and numerical models of tidal modes is constructed. Blocking diagrams, which show the blocked phase velocities and directions of propagation of gravity waves, are made using the wind profile model and critical level theory.

The blocking diagrams, when compared with the observed wave parameters (phase velocity and direction of propagation) show that the OH observations are in agreement with the directional filtering predicted by the wind profile model and critical level blocking. Although the most accurate method of analysis would be making simultaneous wind measurements with the airglow observations, this thesis shows that reasonable results over an extended period of time can be obtained using climatological and model data for wind profiles.