Thermosphere-Ionosphere Coupling: An Experiment in Interactive Modeling

摘要

The NCAR thermosphere general circulation model (TGCM) is used to perform aseries of controlled experiments aimed at better understanding the interactive coupling between ionospheric plasma densities and thermospheric neutral winds. The experiments are simple and controlled to facilitate identification of governing mechanisms. The interaction is accomplished by parameterizing the F layer peak height (hmF2) in an empirical ionospheric model in terms of the meridional wind (Vsouth) and forcing hmF2 and Vsouth to remain mutually coupled in a dynamic calculation. Interactive computations are performed where the TGCM is driven by 30-kV and 90-kV cross polar cap potentials and are compared with corresponding reference simulations where hmF2 is constrained to a balance height near 280 km with a small (about 20 km) diurnal variation. Mutual coupling between hmF2 and Vsouth is found to be weak during the daytime when the F layer exhibits a broad vertical structure. At night, when the F2 layer is more localized, the neutral dynamic structure is dependent on whether hmF2 is significantly above or below the altitude (approximately 275-300 km) at which ion drag effectively competes with viscosity in the neutral momentum balance. At Arecibo during both levels of high-latitude forcing the premidnight elevation (+75 km) of hmF2 relative to a nighttime height of approximately 290 km is accompanied by an increase (about 50 m/s) in the zonal wind above 250 km relative to the noninteractive simulation. A much smaller effect, characterized by an 8-hour periodicity spanning 24 hours, is seen in the meridional windcomponent. Ionospheric models; Thermosphere coupling interaction. Reprints. (edc)