Vibrational nitrogen concentration in the ionosphere and its dependence on season and solar cycle

Abstract

A fully time-dependent mathematical model, SUPIM, of the Earth's plasmasphere is used in this investigation. The model solves coupled time-dependent equations of continuity, momentum and energy balance for the O⁺, H⁺, He⁺, N⁺₂, O⁺₂, NO⁺ ions and electrons; in the present study, the geomagnetic field is represented by an axial-centred dipole. Calculation of vibrationally excited nitrogen molecules, which has been incorporated into the model, is presented here. The enhanced model is then used to investigate the behaviour of vibrationally excited nitrogen molecules with <i>F</i>10.7 and solar EUV flux, during summer, winter and equinox conditions. The presence of vibrational nitrogen causes a reduction in the electron content. The diurnal peak in electron content increases linearly up to a certain value of <i>F</i>10.7, and above this value increases at a lesser rate, in agreement with previous observations and modelling work. The value of <i>F</i>10.7 at which this change in gradient occurs is reduced by the presence of vibrational nitrogen. Vibrational nitrogen is most effective at F-region altitudes during summer daytime conditions when a reduction in the electron density is seen. A lesser effect is seen at equinox, and in winter the effect is negligible. The summer reduction in electron density due to vibrational nitrogen therefore reinforces the seasonal anomaly.