[P-EM10] Space Weather and Space Climate

[PEM10-P17] Statistical analysis of geomagnetically induced current data measured around Tokyo

*Shinichi Watari, Yusuke Ebihara¹, Aoi Nakamizo² (1.Research Institute for Sustainable Humanosphere, Kyoto University, 2.National Institute of Information and Communications Technology)

Keywords:geomagnetically induced current (GIC), geomagentic storm, sudden commencement (SC)

We started geomagnetically induced current (GIC) measurement at two substations around Tokyo in 2017 and we are measuring GIC at four substations now. We analyzed GIC data for approximately 7 years at SFS because the amplitude of GIC observed at SFS was larger than other substations and artificial noise in the data was small. We defined magnitude of one-minute GIC of 3 A or more continuously as a GIC event in our analysis. During the analysis period, solar activity became a minimum in December 2019 and then began to increase toward a maximum. As solar activity increased, the number of geomagnetic disturbances increased and the number of GIC events also increased. Many of GIC events were caused by large geomagnetic variations during magnetic storms according to the list of geomagnetic disturbances from the Kakioka magnetic observatory. With respect to phases of a magnetic storm, our analysis showed that the GIC events occur more frequently in main and recovery phases. It is known that a large-amplitude GIC occurs in response to a sudden commencement (SC), which is produced by arrival of an interplanetary shock, in initial phase of a magnetic storm, but duration of the initial phase is shorter than that of main and recovery phases and there are magnetic storms without SCs. As a result, the number of GIC events in the initial phase becomes smaller than that in other phases. In our analysis, a GIC event of maximum amplitude measured associated with a SC of the magnetic storm on October 10, 2024, and a GIC event of maximum duration measured in the main phase of the magnetic storm on May 10, 2024.