A Study of Solar Flare Effects on the Geomagnetic Field Components during Solar Cycles 23 and 24

In this paper, we investigated the impact of solar flares on the horizontal (H), eastward (Y) and vertical (Z) components of the geomagnetic field during solar cycles 23 and 24 (SC23/24) using data of magnetometer measurements on the sunlit side of the Earth. We examined the relation between sunspot number and solar flare occurrence of various classes during both cycles. During SC23/24, we obtained correlation coefficient of 0.93/0.97, 0.96/0.96 and 0.60/0.56 for C-class, M-class and X-class flare, respectively. The three components of the geomagnetic field reached a peak a few minutes after the solar flare occurrence. Generally, the magnetic crochet of the H component was negative between the mid-latitudes and Low-latitudes in both hemispheres and positive at low latitudes. By contrast, the analysis of the latitudinal variation of the Y and Z components showed that unlike the H component, their patterns of variations were not coherent in latitude. The peak amplitude of solar flare effect (sfe) on the various geomagnetic components depended on many factors including the local time at the observing station, the solar zenith angle, the position of the station with respect to the magnetic equator, the position of solar flare on the sun and the intensity of the flare. Thus, these peaks were stronger for the stations around the magnetic equator and very low when the geomagnetic field components were close to their nighttime values. Both cycles presented similar monthly variations with the highest sfe value (ΔHsfe = 48.82 nT for cycle 23 and ΔHsfe = 24.68 nT for cycle 24) registered in September and lowest in June for cycle 23 (ΔHsfe = 8.69 nT) and July for cycle 24 (ΔHsfe = 10.69 nT). Furthermore, the sfe was generally higher in cycle 23 than in cycle 24.

Geomagnetic solar flare effects: a review

Solar flare effects (Sfe) are rapid variations in the Earth’s magnetic field and are related to the enhancement of the amount of radiation produced during Solar flare events. They mainly appear in the Earth’s sunlit hemisphere at the same time as the flare observation and have a crochet-like shape. Much progress has been made since Carrington’s first observations in 1859 which are considered to represent the first direct evidence of the connection between the Sun and the Earth’s environment but there is still much to discover. In this paper, we review state-of-the-art developments and the advances made in the knowledge concerning Sfe phenomena while also looking at the challenges that lie ahead. First, we offer a historical approach with a comprehensive description that allows for a better understanding of the main characteristics of Sfe. This frames specific topics like the puzzling reversed-Sfe or the nighttime Sfe. The role played by the Service of Rapid Magnetic variations (SRMV) is also assessed, followed by a discussion of the main current limiting factors in the process of detection and proposed ways to overcome challenges such as by creating an automatic detection method. The paper clarifies some aspects related to the geo-effectiveness of the solar flares producing magnetic disturbances. The importance of the global modelling studies covering critical aspects needed to understand this Sun–Earth system is assessed. Also, we provide an overview of the temporal evolution of the electric currents producing Sfe. The importance of key subjects such as the dynamic aspects of Sfe is developed in another section. Finally, estimations of the size of large flares using ionospheric and magnetic data are reviewed as well as the prospects of these large flare events putting technological systems in danger.

An investigation of solar flare effects on equatorial ionosphere and thermosphere using co-ordinated measurements

The response of equatorial ionosphere–thermosphere system to the X3.8 solar flare of January 17, 2005 has been studied using the coordinated measurements of GPS-derived Total Electron Content (TEC), OI 630.0 nm dayglow and magnetic field measurements over a dip equatorial station Trivandrum (8.5° N, 77° E, dip 0.5° N), in India. It has been observed that Equatorial Electrojet (EEJ) as inferred using the ground-based magnetometers and GPS-derived TEC measurements show prompt enhancements during the peak flare, as expected. Interestingly, the temporal evolution of TEC at different latitudes revealed that the X3.8 class flare produced significant weakening of the plasma fountain and hence in the Equatorial Ionization Anomaly (EIA). Furthermore, the response of OI 630.0 nm dayglow during the flare is found to be strongly affected by the prevailing electrodynamics. The plausible physical mechanism for these effects is discussed in context of the current understanding of the neutral and electrodynamical coupling processes.

Effects of solar flares on the ionosphere as shown by the dynamics of ionograms recorded in Europe and South Africa

We have investigated the solar flare effects on ionospheric absorption with the systematic analysis of ionograms measured at midlatitude and low-latitude ionosonde stations under different solar zenith angles. The lowest recorded ionosonde echo, the minimum frequency (fmin, a qualitative proxy for the “nondeviative” radio wave absorption occurring in the D-layer), and the dfmin parameter (difference between the value of the fmin and the mean fmin for reference days) have been considered. Data were provided by meridionally distributed ionosonde stations in Europe and South Africa during eight X- and M-class solar flares in solar cycle 23. Total and partial radio fade-out was experienced at every ionospheric station during intense solar flares (> M6). The duration of the total radio fade-out varied between 15 and 150 min and it was highly dependent on the solar zenith angle of the ionospheric stations. Furthermore, a solar-zenith-angle-dependent enhancement of the fmin (2–9 MHz) and dfmin (1–8 MHz) parameters was observed at almost every station. The fmin and dfmin parameters show an increasing trend with the enhancement of the X-ray flux. Based on our results, the dfmin parameter is a good qualitative measure for the relative variation of the “nondeviative” absorption, especially in the case of the less intense solar flares, which do not cause total radio fade-out in the ionosphere (class < M6).