The midlatitude F2 layer during solar eclipses: Observations and modeling

Abstract

We conducted a statistical analysis on the changes in foF2 during seven eclipse events on the basis of the data derived from 23 ionosonde stations. To model eclipse effects on the ionosphere, we constructed a solar spectrum model for solar eclipses. The background hmF2, local time, solar cycle, and dip angle effects on the ionospheric response to solar eclipses are investigated in the four controlled case studies. Both the measurements and simulations show that the eclipse effect is larger in the midday than in the morning and afternoon and that larger dip angle results in smaller eclipse effect. Furthermore, the simulated results show that the local time effect is actually due to the neutral concentration effect. Compared to at low solar activity, the eclipse effect in the F2 region is larger at high solar activity. This solar cycle effect is caused by the differences not only in the solar radiation but also in the background neutral gas concentration. In addition, an eclipse will produce a smaller change in NmF2 if the hmF2 is higher. In conclusion, the central finding of this paper is that most of the observed differences in the behavior of NmF2 during eclipses can be attributed to the differences in O+loss rate brought about by the background differences in the neutral molecular densities. The solar zenith angle, local time, and dip angle effects should be explained from this starting point.