Daytime F2-layer positive storm effect at middle and lower latitudes

Abstract

Daytime F2-layer positive storm effects at middle and lower latitudes in the winter thermosphere are analyzed using AE-C, ESRO-4 neutral gas composition data, ground-based ionosonde observations and model calculations. Different longitudinal sectors marked by the storm onset as 'night-time' and 'daytime' demonstrate different F2-layer positive storm mechanisms. Neutral composition changes in the 'night-time' sector with increased [O] and [N<sub>2</sub>] absolute concentrations, while (N<sub>2</sub>/O)<i><sub>storm</sub></i>/(N<sub>2</sub>/O)<i><sub>quiet</sub></i>approx1 at F2-layer heights, are shown to contribute largely to the background N<i><sub>m</sub></i>F2 increase at lower latitudes lasting during daytime hours. Storm-induced surges of the equatorward wind give rise to an additional N<i><sub>m</sub></i>F2 increase above this background level. The mid-latitude F2-layer positive storm effect in the 'daytime' sector is due to the vertical plasma drift increase, resulting from the interaction of background (poleward) and storm-induced (equatorward) thermospheric winds, but not to changes of [O] and [N<sub>2</sub>] concentrations