VIBRATIONAL NITROGEN CONCENTRATION IN THE IONOSPHERE AND ITS DEPENDENCE ON SEASON AND SOLAR-CYCLE

A fully time-dependent mathematical model, SUPIM, of the Earth's plasm asphere is used in this investigation. The model solves coupled time-d ependent equations of continuity, momentum and energy balance for the O+, H+, He+, N-2(+), O-2(+), NO+ ions and electrons; in the present st udy, the geomagnetic field is represented by an axial-centred dipole. Calculation of vibrationally excited nitrogen molecules, which has bee n incorporated into the model, is presented here. The enhanced model i s then used to investigate the behaviour of vibrationally excited nitr ogen molecules with F 10.7 and solar EUV flux, during summer, winter a nd equinox conditions. The presence of vibrational nitrogen causes a r eduction in the electron content. The diurnal peak in electron content increases linearly up to a certain value of F 10.7, and above this va lue increases at a lesser rate, in agreement with previous observation s and modelling work. The value of F 10.7 at which this change in grad ient occurs is reduced by the presence of vibrational nitrogen. Vibrat ional nitrogen is most effective at F-region altitudes during summer d aytime conditions when a reduction in the electron density is seen. A lesser effect is seen at equinox, and in winter the effect is negligib le. The summer reduction in electron density due to vibrational nitrog en therefore reinforces the seasonal anomaly.