Sunrise effects in the equatorial F-layer

Abstract

Abstract In the sunrise period, under certain conditions, a cavity of a low electron density arises in the equatorial ionosphere at altitudes between the peaks of the night F-layer and the morning F-layer. The dependence of the cavity parameters on the initial conditions, solar activity, season, photochemistry, geomagnetic disturbance, diffusion, and vertical drift of the ionospheric plasma is studied theoretically. It is shown that temporal variations of the electron density, as well as of the cavity parameters, depend mainly on the initial profile parameters, ionizing solar radiation flux, ion formation rate, diffusion, and geomagnetic activity. It is concluded that reduced diffusion can be one of the major physical mechanisms which can assist the preservation, at large heights in the pre-sunrise F-layer, of the electron density at the day-time level.