Exploring the Sources of Acoustic and Gravity Waves in the Thermosphere (Invited)

One of the dominant features of the thermosphere is the presence of waves. These waves range from tides, which are extremely large scale to gravity waves, which can be small- to meso-scale and acoustic waves, which are quite localized. Using the Global Ionosphere Thermosphere Model (GITM), we can investigate waves that are generated within the thermosphere system. Because GITM does not enforce a hydrostatic solution, and because the time step is on the order of a few seconds, GITM can be used to explore the generation and evolution of both acoustic and gravity waves. This is done for a flare time period on July 14, 2000. When frequencies higher than the buoyancy frequency (approximately 16 minutes) are explored in the low latitude region, there are clear waves that are anti-correlated between the dayside and nightside. These acoustic wave appear to be driven by ion-neutral drag, with the ions being forced by rapid changes in the low latitude electric field. The ions drifts change rapidly, while the neutral variations appear to be tied to acoustic wave frequencies. The waves propagated primarily in the vertical direction, as expected. At lower frequencies, the largest wave is caused by the flare, which drives a large-scale gravity wave to propagate from the dayside to the nightside and back again. Later in the day, gravity waves and acoustic waves are generated in the high-latitude region when the storm is set off. We will explore the characteristics of these waves also.