Solar Radiation and Geomagnetic Contribution of Consecutive 27-Day Recurrent Geomagnetic Storms to Variations of Equatorial Ionospheric Parameters and Spread F

Abstract

This study investigates solar radiation and geomagnetic effects of consecutive 27-day recurrent geomagnetic storms (RGSs) during 2007 on the variabilities in the equatorial ionospheric F-region in American Peruvian sector. Results show correspondence of quasi-periodic variations between geomagnetic activities and ionospheric responses in the F-region. 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 heights of the F-layer tend to increase during storm-time in summer months, but decrease in response to enhanced equatorial electrojets. A new classification of daily variations in the virtual height of the F-layer (h′F) is proposed: (mode A) mixing of great height before noon and low height before midnight, (mode B) moderate height before midnight, and (mode C) mixing of low height before noon and great height before midnight. These (h′F) modes efficiently characterize ionospheric variabilities and processes. The great uplifts of (h′F) during night-time coincide with the presence of strong disturbance dynamo electric fields and disturbed neutral winds generated by intensified Joule heating in the summer months. The solar EUV plays a role in the uplifts during daytime. Zonal electric field disturbances and perturbations in neutral meridional winds critically contribute to the equatorial ionospheric responses and ESF variability. Most of inhibited/suppressed ESF occurred in mode A and in overshielding conditions. The inhibited ESF in the recovery phase is mainly contributed by a cooling state after great uplifts by daytime thermospheric winds.