[P-CG21] Planetary atmosphere, ionosphere and magnetosphere

[PCG21-P12] Study of the solar wind influence on the Jovian inner magnetosphere using an ionospheric potential solver

*Koichiro Terada¹, Naoki Terada¹, Yasumasa Kasaba¹, Hajime Kita², Chihiro Tao³, Aoi Nakamizo³, Akimasa Yoshikawa⁴, Shinichi Ohtani⁵, Fuminori Tsuchiya², Masato Kagitani², Takeshi Sakanoi², Go Murakami⁶, Kazuo Yoshioka⁷, Tomoki Kimura⁸, Atsushi Yamazaki⁶, Ichiro Yoshikawa⁹ (1.Dep. Geophysics Graduate School of Science Tohoku University, 2.Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University, 3.Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology, 4.Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, / International Center for Space Weather Science and Education, Kyushu University, 5.The Johns Hopkins University Applied Physics Laboratory, 6.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 7.Department of Earth & Planetary Science, Graduate School of Science, The University of Tokyo, 8.Nishina-Center for Accelerator Based Science, RIKEN, 9.The University of Tokyo)

Keywords:Jupiter, Io plasma torus, dawn-to-dusk electric field

The solar wind hardly influences the convection in the Jovian inner magnetosphere, because the corotation of magnetospheric plasma dominates the convection there. However, the extreme ultraviolet spectroscope (EXCEED) aboard the Hisaki satellite observed change in a dawn-to-dusk asymmetry in the brightness distribution of the Io plasma torus. This asymmetry can be explained by assuming the existence of a dawn-to-dusk electric field of ~3-7 [mV/m] around Io’s orbit. The influence of the solar wind is suggested as its cause: First, the solar wind compresses the Jovian magnetosphere. Then, the magnetosphere-ionosphere current system is modified, and the field-aligned current into the high-latitude ionosphere increases. As a result, the ionospheric electric field increases and penetrates to low-latitude regions. It is mapped to the equatorial plane of the magnetosphere along the magnetic field line, and the dawn-to-dusk electric field is created at Io’s orbit in the inner magnetosphere.
An ionospheric potential solver is one of the best tools to test this scenario quantitatively. The ionospheric potential solver is a simulation code by which we can investigate how the global ionospheric potential gets distributed responding to the input of the field-aligned current. We constructed an ionospheric potential solver and investigated whether the dawn-to-dusk electric field generated by the solar wind interaction could penetrate into the Jovian inner magnetosphere. We validated this potential solver by applying it to the Earth’s ionosphere and comparing with an established code [Nakamizo et al., 2012]. Our code succeeded to reproduce a similar potential distribution, however there remain minor differences caused by minor differences in the assumption of the ionospheric conductivities, i.e., their spatial distributions including relative positions to the field-aligned current. Then, we applied this code to the Jovian magnetosphere-ionosphere current system. As a peak intensity of the field-aligned current, we used a value based on the observation of FUV aurora by HST [Gustin et al., 2004] and adopted the Earth’s empirical model for its distribution [Hori et al., 2009]. We assumed the Jovian ionospheric conductivities as 10 percent of the Earth’s values [Tao et al., 2009]. The electric field mapped to Io’s orbit appears to be on the same order as or smaller than the value suggested by the Hisaki satellite observation. In this paper, we will present a result using more realistic spatial distributions of the ionospheric conductivities and the field-aligned current obtained from the Galileo spacecraft observation and a Jovian upper atmospheric model.