9:00 AM - 9:15 AM
[PEM08-13] Statistical analysis of variations of geoelectric field during magnetic storms/substorms in Japan
Keywords:geoelectric field , magnetic storms, coronal mass ejections, corotating interaction regions
Since the GIC (geomagnetically induced current) of power grids is a global problem, to effectively prevent geomagnetic storm disaster is an important problem. Predicting the GIC is considered as a possible solution to this problem. Since GIC is directly generated by GIE (geomagnetically induced electric field), we used GIE measured at Kakioka Magnetic Observatory (geomagnetic latitude of 28 deg) as a proxy of GIC flowing in the Japanese power grid to acquire a statistical view of the response of GIC to magnetic storms and substorms, and to understand how the magnetospheric and ionospheric current systems affect GIC. The magnetic storms were sorted in accordance with the minimum value of the SYM-H index. The magnetic storms driven by coronal mass ejections (CMEs) and the corotating interaction regions (CIRs) were in particular focused on. A total of 38 intense storms associated with (during 1996-2004), 31 CME- and 69 CIR-associated moderate storms (during 1996-2008), as well as 17,273 substorms (during 1996-2004) are used to perform superposed epoch analyses. The east-west component of the electric field |Ey| dominates the north-south component |Ex| for all the three kinds of magnetic storms. For the CME-associated storms, Ey tends to show a negative excursion during the initial phase, a positive one during the main phase and a negative one during the recovery phase, which can be understood the contribution from the magnetopause current and the ring current. Ey responds largely to substorms with its polarity depending on magnetic local time. We discuss the possible current systems that can cause the large-amplitude GIE at geomagnetically low latitude by shown histograms of the maximum |Ey| during the magnetic storms and substorms.