Low-latitude geomagnetic signatures during major solar energetic particle events of solar cycle-23

摘要

The frequency of occurrence of disruptive transient processes inthe Sun is enhanced during the high solar activity periods. Solarcycle-23 evidenced major geomagnetic storm events and intensesolar energetic particle (SEP) events. The SEP events are theenergetic outbursts as a result of acceleration of heliosphericparticles by solar flares and coronal mass ejections (CMEs). Thepresent work focuses on the geomagnetic variations at equatorialand low-latitude stations during the four major SEP events of 14July 2000, 8 November 2000, 24 September 2001 and 4 November 2001.These events have been reported to be of discernible magnitudefollowing intense X-ray flares and halo coronal mass ejections.Low-latitude geomagnetic records evidenced an intense main phasedevelopment subsequent to the shock impact on the Earth'smagnetosphere. Satellite observations show proton-fluxenhancements associated with solar flares for all events.Correlation analysis is also carried out to bring out thecorrespondence between the polar cap magnetic field perturbations,AE index and the variations of low-latitude magnetic field. The results presented inthe current study elucidate the varying storm developmentprocesses, and the geomagnetic field response to the plasma andinterplanetary magnetic field conditions for the energetic events.An important inference drawn from the current study is the closecorrespondence between the persistence of a high level of protonflux after the shock in some events and the ensuing intensemagnetic storm. Another interesting result is the role ofthe pre-shock southward IMF B_z duration ingenerating a strong main phase.