ELUCIDATION OF THE PHYSICS OF THE GRAVITY WAVE-TID RELATIONSHIP WITH THE AID OF THEORETICAL SIMULATIONS

The physics of the relationship between atmospheric gravity waves (AGW s) and traveling ionospheric disturbances (TIDs) is thoroughly investi gated with emphasis on large-scale AGW/TIDs at F region heights at mid dle and high latitudes (provided field-perpendicular drifts are small) . In support, simulations using a realistic AGW model (''Clark-based A GW model'') in combination with a realistic ionospheric model (''Graz Ionospheric Flux Tube Simulation (GIFTS) model'') were performed. All fundamental AGW/TID quantities are treated consistently, i.e., perturb ations in neutral densities, wind, and temperature as well as disturba nces in electron density, ion drift, and ion and electron temperature. The AGW-induced ionospheric response is inspected for all TID quantit ies, based on their governing conservation equations. The results are discussed by means of detailed and approximative formulae as well as i nstructive figures which provide a firm quantitative understanding sig nificantly beyond the current state of knowledge. Especially the physi cs of the electron temperature disturbance (T-e-TID), up to now not ye t quantitatively inspected, is thoroughly explored. A major finding is that the disturbance in specific terms of the electron energy equatio n is an order of magnitude more pronounced than the net disturbance de termining the strength of the T-e-TID. Furthermore, simulation results illustrating the natural variability of the AGW/TID quantities (1) du e to varying AGW properties and (2) due to changing thermosphere/ionos phere background conditions are discussed. Features observed include t he following: AGW period and magnetic field line-induced south-north a symmetries are major causes of variability. Change from high/moderate to low solar activity enhances amplitudes of most AGW/TID quantities, electron density and temperature being likely exceptions; nighttime co nditions tend to lower amplitudes versus daytime. The insight gained i s valuable from a basic research point of view and also for suitable A GW/TID descriptions for thermosphere/ionosphere weather modeling.