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 (Delta H-sfe = 48.82 nT for cycle 23 and Delta H-sfe = 24.68 nT for cycle 24) registered in September and lowest in June for cycle 23 (Delta H-sfe = 8.69 nT) and July for cycle 24 (Delta H-sfe = 10.69 nT). Furthermore, the sfe was generally higher in cycle 23 than in cycle 24.