[M-IS10] Interdisciplinary studies on pre-earthquake processes

[MIS10-P04] Seasonal variation characteristics of geomagnetic Sq external and internal equivalent current systems in East-Asia and Oceania regions

*Xiaocan Liu¹, Peng Han², Katsumi Hattori^3,4, Huaran Chen¹, Chie Yoshino³, Xudong Zhao¹, Liguo Jiao¹, Xinxin Ma¹, Jiyao Tu¹, Yu Lei^1,5, Junhao Zhao¹ (1.Institute of geophysics China Earthquake Administrition, 2.Department of Earth and Space Sciences Southern University of Science and Technology, ShenZhen, China, 3.Graduate School of Science Chiba University ,Chiba, Japan, 4.Center for Environmental Remote Sensing, Chiba University, Chiba, Japan, 5.School of Earth and Space Sciences, Peking University, Beijing, China)

Keywords:Seasonal variation, Sq equivalent currents, internal current and external current

Abstract Geomagnetic quiet daily variation (Sq) is a significant regular variation of the geomagnetic field, which originates from the ionospheric (external) Sq current system located at an altitude of 110 km, and the induced (internal) current system produced by the external current in the underground conductive layer[Chapman and Bartels, 1940; Chapman, 1951; Campbell, 1989; Kane, 1976; Xu, 2003; Yamazaki, 2009, 2017]. The Sq field recorded at the ground geomagnetic observatory is the sum of the geomagnetic effects of the two current parts. The study of the variation characteristics of the two-part Sq current is a basic research subject of geomagnetism. The previous studies [Matsushita and Maeda, 1965; Yamazaki, 2009; 2011a; 2011b] on the variation characteristics of the Sq current system in the East Asia-Oceania sector are incomplete, especially the research on the variation of the internal current system is rare. In this work, the deduction of internal and external Sq current is carried out by using the observations of multiple stations from the Geospatial Information Authority of Japan (GSI), the Japan Meteorological Agency (JMA) and the INTERMAGNET. And the similarities and differences of the seasonal variation characteristics of the two parts of the current system are systematically analyzed, as well as the two related relationship.
Using the observations from 20 geomagnetic stations in the East Asia-Oceania sector from 2008 to 2012, the season (D winter, E equinox, J summer) models are constructed by spherical harmonic analysis (SHA) [Chapman and Bartels, 1940; Xu, 1994, 2003; Takeda, 2002; Yamazaki, 2011a; Liu et al., 2019]. The seasonal variation characteristics of the model current vortex center parameters (local time T, latitude Φ, and current intensity J) were analyzed. The main results are obtained as follows: (1) The local time T of the northern vortex moves from local noon to pre-noon from D to E to J season for both external and internal currents; meanwhile, in southern hemisphere, the T moves from local noon to afternoon. (2) The vortex intensity J increases from local winter to equinox then to local summer. The inter-seasonal change rate of internal current is larger than that of external current. (3) The latitude Φ of the external current vortex exhibits seasonal variation in the southern hemisphere, while in the northern hemisphere the latitude Φ of the internal current vortex shows obvious seasonal changes. (4) The correlations between the internal and external currents are further analyzed. In the E season the correlation of T is the highest, and in the local summer and winter, the correlation of J is the strongest.