Ionospheric signatures during G2, G3 and G4 storms in mid-latitude

This paper presents a wavelet-based analysis of ionospheric irregularities induced by three different geomagnetic storms of varying strength and interplanetary origin over three mid-latitudes stations, viz. Moscow, Fairford, and Rome. We observed the highest decrease in ionospheric variables (foF2, total electron content (TEC), and NmF2) during the negative phase of the G4 storm. Interestingly, hmF2 exhibits the opposite trend in terms of variation. The maximum ionization height (hmF2) for the G4 event is 500 km (during the main phase) and 150 km (during the recovery phase). Within 2-3 hr of the G4 event, the value of hmF2 is found to decline by 70%. The largest reduction (80%) in critical frequency (foF2) is observed during the negative phase of this event, which is also confirmed by the continuous wavelet transform results. During the negative phase, we observed noticeable power shifts in the signal of the ionospheric parameters toward the lower Fourier period band. During the G4 storm—Particularly during the negative phase—The lowest power linked with the ionospheric parameter's signal was discovered. Additionally, we used detrended cross-correlation analysis to investigate the correlation and time lag between geomagnetic indices (Symmetric H-component (SYM-H) & auroral electrojet) and ionospheric parameters (foF2, NmF2, hmF2 & TEC). The significant association between SYM-H and ionospheric parameters suggests that the magnetosphere-ionosphere interaction produces intense electric field disturbances and winds in the mid-latitudes, resulting in the perturbation of hmF2, foF2, TEC, and NmF2.