The effects of solar radiation and geomagnetic disturbance during consecutive 27-day recurrent geomagnetic storms on variations of equatorial ionospheric parameters and spread F

Abstract

This study investigates contributions of solar radiation and geomagnetic activity of consecutive 27-day recurrent geomagnetic storms (RGSs) to the variabilities in the equatorial ionospheric F-region in American Peruvian sector during 2007. Results show the ionospheric responses to the RGSs are quasi-periodic and multifaceted with highly evolved in the summer months. In High-Intensity Long-Duration Continuous \(AE\) Activity (HILDCAA) events, the ionospheric responses are more variable than in non-HILDCAA. The critical frequency and peak height of the F-layer tend to increase during storm-time in summer months. The maximum density enhancements are more than 70% in the three RGSs and they are long-lasting in the summer months. A new classification of daily variations in the virtual height of the F-layer (\(h'F\)) is proposed: Mode A shows mixing of great height before noon and low height near midnight, Mode B shows moderate height near midnight, and Mode C shows mixing of high height before noon and great height near midnight. These \(h'F\) Modes efficiently characterize the ionospheric variabilities and processes. The great uplifts of \(h'F\) during night-time in the summer months coincide with the presence of strong disturbance dynamo electric fields and disturbed neutral winds generated by intensified Joule heating. The solar EUV plays a role in the uplifts of \(h'F\) during the daytime. Zonal electric field disturbances and perturbations in the neutral meridional winds critically contribute to the equatorial ionospheric responses and ESF variabilities. Most cases of inhibited/suppressed ESF were observed in Mode A and occurred under overshielding conditions. The inhibited ESF associated with \(h'F\) not raised in the recovery phase is mainly contributed by a cooling state after great uplifts by daytime thermospheric winds.