A Comprehensive Classification and Analysis of Geomagnetic Storms Over Solar Cycle 24

A geomagnetic storm is a global disturbance of Earth?s magnetosphere,occurring as a result of the interaction with magnetic plasma ejected from the Sun.Despite considerable research,a comprehensive classification of storms for a complete solar cycle has not yet been fully developed,as most previous studies have been limited to specific storm types.This study,therefore,attempted to present complete statistics for solar cycle 24,detailing the occurrence of geomagnetic storm events and classifying them by type of intensity(moderate,intense,and severe),type of complete interval(normal or complex),duration of the recovery phase(rapid or long),and the number of steps in the storm?s development.The analysis was applied to data from ground-based magnetometers,which measured the Dst index as provided by the World Data Center for Geomagnetism,Kyoto,Japan.This study identified 211 storm events,comprising moderate(177 events),intense(33 events),and severe(1 event)types.About 36%of ICMEs and 23%of CIRs are found to be geoeffective,which caused geomagnetic storms.Up to four-step development of geomagnetic storms was exhibited during the main phase for this solar cycle.Analysis showed the geomagnetic storms developed one or more steps in the main phase,which were probably related to the driver that triggered the geomagnetic storms.A case study was additionally conducted to observe the variations of the ionospheric disturbance dynamo(Ddyn)phenomenon that resulted from the geomagnetic storm event of 2015July 13.The attenuation of the Ddyn in the equatorial region was analyzed using the H component of geomagnetic field data from stations in the Asian sector(Malaysia and India).The variations in the Ddyn signatures were observed at both stations,with the TIR station(India)showing higher intensity than the LKW station(Malaysia).