A THEORETICAL INVESTIGATION OF SOURCES OF LARGE AND MEDIUM-SCALE ATMOSPHERIC GRAVITY-WAVES IN THE AURORAL OVAL

Many papers have been published to devise models to describe the sources of large and medium scale atmospheric gravity waves (AGWs) in the auroral oval ionosphere. One of the models proposed by CHIMONAS and HINES [(1970) Planet. Space Sci. 18, 565] calculated the relative importance of Lorentz force and Joule heating as sources of AGWs in the auroral regions based on certain assumptions. In this paper, we develop a general theory to describe the behavior of the AGW source terms. It has been found that the source terms which generate AGWs are closely related to the velocities and frequencies of AGWs, and that the Lorentz force is dominant in generating the vertical velocity perturbation of large scale AGWs. The formulas which determine the source term contributions are derived. This relationship gives us the possibility to predict what kind of AGW will be generated by observing the source terms, or conversely perhaps to deduce some of the source characteristics by measuring properties of the traveling ionospheric disturbances (TIDs).