Nocturnal decay of peak ionospheric density at a midlatitude location during sunspot minimum equinox conditions: Closed form solutions

The ionosphere is that part of the upper atmosphere where ions and electrons are present in sufficient quantities to affect the propagation of radio waves. It is a vast region having multi-faceted properties and variations which comprises a subject matter by itself. All scientific studies of the ionosphere invariably require global, regional or local numerical modeling. In this paper, we study a limited aspect of the ionosphere using analytical exact solutions in closed forms. Specifically, we analyze the nocturnal decay of the ionospheric peak electron or ion density above Arecibo, Puerto Rico during sunspot minimum and equinox conditions. Two kinds of loss processes are recognized: (1) a quadratic ion-electron recombination reaction; and (2) a linear ion-neutral charge transfer process. The nocturnal decay of the peak electron density is studied under each loss process separately, and compared with that obtained from a numerical model. It is found that the ion-neutral charge-transfer is the dominant loss process, nine times more effective that the ion-electron recombination process.