[M-IS04] Interdisciplinary studies on pre-earthquake processes

[MIS04-P10] Longitudinal Effects of the Seasonal Variations for Sq Current Systems

*Xiaocan Liu¹、Peng Han²、Katsumi Hattori^3,4、Huaran Chen¹、Junjie Chen⁵ (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.Department of Earth Sciences, The University of Hong Kong, Pokfulam, China)

キーワード：Sq currents, low and middle latitudes, seasonal variations, longitudinal effects

Years of geomagnetic observatory data during the geomagnetic quiet days (Kp <= 3) at the low and middle dip latitudes from INTERMAGNET and SuperMAG were utilized. Seasonal models of Sq currents for the Asian-Oceania (A-O) chain and the North-South America (N-SA) chain were constructed by spherical harmonic analysis respectively. The results show that the seasonal variations vary between the two longitudinal chains of the Sq ionospheric currents. The patterns for the Sq focus local time (T) are different for the two chains, especially in the SH, T of the A-O chain from D season to J season increases more than that of N-SA chain. It is shown that T of N-SA chain is always ahead of that of the A-O chain, and the advanced time in the NH is not changed with season, always about 0.5 hr. However, in the SH the advanced time increases from about 0.5 hr to about 1.5 hr with the season shifts from December to June solstices, and more in the solar low year. In addition, with the enhancement of solar activity, the current focus of NH and SH both move to noon and become close, significantly in the A-O chain. In the NH, T of the N-SA chain also shifts to noon as solar activity changes from low to high. Next, the differential activity of the Sq focus latitude (Φ) is also obvious. Seasonal variations of Φ for the A-O chain are not obvious, and it is uniform both in the solar high and low years. However, Φ of the N-SA chain has significant seasonal variations, that is, as the season varies from hemispheric winter to summer Φ increases. In particular, in the NH, at E season it increases more than in summer during the solar high year. From the value of Φ, it is indicated that the current vortices of the A-O chain are located in the south of those of the N-SA chain. Moreover, J of the N-SA chain is higher than that of the A-O chain most of the time, particularly during the equinoxes both at low and high solar activity years. Except in the high year, J of the A-O chain is higher than that of the N-SA chain in the SH during local summer. Meanwhile, T of the current focus for the Sq internal currents in the N-SA chain is also ahead of that of the A-O chain most of the time. In the NH, the advanced time is almost the same in each season, with about 0.5 and 1 hr for the low and the high solar activity year respectively. In the SH, T of the two chains is a little complex, T of the A-O chain in winter is slightly earlier than that of the N-SA chain. The difference between the two chains of Φ shows that the current vortices of the A-O chain are still southern than those of the N-SA chain (blue line) for the internal currents, except Φ of the A-O chain in the NH is significantly higher in winter (i.e., D season) than in other seasons, even beyond Φ of the N-SA chain in the low solar activity year. J of the N-SA chain is still higher than that of the A-O chain in most cases, significantly during the equinoxes, except in the summer (D season) of the SH.