Ionospheric model effects on thermospheric calculations

The sensitivity of thermospheric calculations to assumptions concerning the ionospheric structure is investigated by the use of different representations of the global behavior of the height of the F2-layer, hmF2. It is found that the amplitude of the diurnal variation of hmF2 at all latitudes and its phase at high latitudes (> 45°) has negligible effect on the results of model calculations. On the other hand noticeable changes in horizontal wind speeds and times of wind reversal were produced when the diurnal mean value of hmF2 was increased by 60 km, roughly a scale height at F-region altitudes. The response to changes in the ionospheric structure is complex, depending on altitude, latitude and local time, and differs between the zonal and meridional wind components. The complex nature is due to the competing effects of ion drag, viscosity, and the Coriolis force in balancing the pressure gradient forces arising from global heat sources. The largest changes in wind speed (~75 m/s) were obtained in ‘fixed-temperature’ calculations; changes were significantly smaller (