Reproducibility of the Geomagnetically Induced Currents at Middle Latitudes During Space Weather Disturbances

• Published in: Frontiers in astronomy and space sciences Vol. 8
• Main Authors: Kikuchi, Takashi, Ebihara, Yusuke, Hashimoto, Kumiko. K., Kitamura, Kentaro, Watari, Shin-Ichi
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 11.10.2021
• Subjects: geomagnetic by dependence of GIC; geomagnetically induced current (GIC); induced electric field in the two-layer conductivity model; middle latitude; polar-equatorial ionospheric currents; TM0 mode in the earth-ionosphere waveguide
• ISSN: 2296-987X; 2296-987X
• DOI: 10.3389/fspas.2021.759431

Watari et al. ( Space Weather, 2009 , 7) found that the geomagnetically induced current (GIC) in Hokkaido, Japan (35.7° geomagnetic latitude (GML)), is well correlated with the y-component magnetic field ( B y ) (correlation coefficients >0.8) and poorly correlated with B x , z and d B x , y , z / d t . The linear correlation with B y would help predict the GIC, if we have capabilities of reproducing the magnetosphere–ionosphere currents during space weather disturbances. To validate the linear correlation with B y for any periods ( T ) of disturbances, we made correlation analyses for the geomagnetic sudden commencements and pulsations ( T = 1–10 min), quasi-periodic DP2 fluctuations (30 min), substorm positive bays (60 min), geomagnetic storms (1–20 h), and quiet-time diurnal variations (8 h). The linear correlation is found to be valid for short periods (cc > 0.8 for T < 1 h) but not for long periods (cc < 0.3 for T > 6 h). To reproduce the GIC with any periods, we constructed one-layer model with uniform conductor and calculated the electric field (IEF) induced by B y using the convolution of d B y / d t and the step response of the conductor. The IEF is found to be correlated with the GIC for long periods (cc > 0.9), while the GIC- B y correlation remains better for short periods. To improve the model, we constructed a two-layer model with highly conductive upper and less conductive lower layers. The IEF is shown to reproduce the GIC with cc > 0.9 for periods ranging from 1 min to 24 h. The model is applied to the GIC measured at lower latitudes in Japan (25.3° GML) with strong B y dependence. The mechanism of the strong B y dependence of the GIC remains an issue, but a possible mechanism for the daytime GIC is due to the zeroth-order transverse magnetic (TM 0 ) mode in the Earth-ionosphere waveguide, by which the ionospheric currents are transmitted from the polar to equatorial ionosphere.