[P-EM11] Space Weather and Space Climate

[PEM11-16] Diurnal and Seasonal Variability of Geomagnetically Induced Currents (GICs) in Power Transmission Systems: A Case Study in Japan

*出井 駿¹、中村 紗都子¹、三好 由純¹、海老原 祐輔²、亘 慎一³ (1.名古屋大学宇宙地球環境研究所、2.京都大学生存圏研究所、3.情報通信研究機構)

キーワード：地磁気誘導電流

This study investigates the characteristics of long-period variations in geomagnetically induced currents (GICs) in Japan, particularly in the Kanto region. In response to growing awareness of GIC risks in Japan, targeted fixed-point observations have started since several years ago, which is used for an analysis of this study. The purpose of this study is to quantitatively elucidate the characteristics and effects of long-period variations in GICs in Japan. We focus on GIC measurements at a single station and investigate diurnal and seasonal variation in detail. We reveal both daily and seasonal periodic variations during geomagnetically quiet periods. We investigated the average diurnal variations of both GIC and geomagnetic variations using superposed epoch analysis. Our findings indicate a strong correlation between the diurnal variation of GIC and the diurnal Sq variation of geomagnetic data. Moreover, we employed the method developed by Ebihara et al. (2021) to estimate GIC from the geomagnetic data. The estimated diurnal variation of GIC accurately reproduces the observed pattern. Seasonal variations show that GIC patterns are influenced by the Earth's axial tilt, affecting the Sq current's pattern across seasons. We show that the geomagnetic variation by the ionospheric Sq current is a dominant factor of the diurnal and seasonal variation in the background level of GIC at the latitude of Japan.