SM051-0002
Effects of an intrinsic magnetic field on ion escape under different solar XUV and solar wind conditions

Wednesday, 16 December 2020
Poster
Ryoya Sakata, University of Tokyo, Bunkyo-ku, Japan, Kanako Seki, The University of Tokyo, Tokyo, Japan, Shotaro Sakai, Tohoku University, Department of Geophysics, Graduate School of Science, Sendai, Japan, Naoki Terada, Tohoku University, Sendai, Japan, Hiroyuki Shinagawa, NICT, Tokyo, Japan and Takashi Tanaka, Kyushu University, International Center for Space Weather Science and Education, Fukuoka, Japan
Abstract:
Effects of a planetary intrinsic magnetic field on ion escape is essential for understanding atmospheric escape and climate change on Mars because it had an intrinsic magnetic field during its early period (Lillis et al., 2013). In our previous study, we showed that the effects of an intrinsic magnetic field depend on the pressure balance between the solar wind dynamic pressure and the magnetic pressure of the intrinsic magnetic field (Sakata et al., 2020). This study investigated how the effects of an intrinsic magnetic field change under different solar XUV and solar wind conditions based on global multispecies magnetohydrodynamic simulations. Multiple simulation cases with different dipole field strength were conducted under solar XUV and solar wind conditions relevant to 3.5-4.0 Ga, when the drastic climate change is considered to take place at Mars. The intrinsic magnetic field facilitates the cusp outflow through open field lines and enhanced particularly molecular ion escape in the overpressure cases where the solar wind dynamic pressure exceeds the magnetic pressure of the intrinsic magnetic field. The cusp outflow was strongly reduced in the non-overpressure cases where the intrinsic magnetic field is strong enough to sustain the solar wind. These effects were the same as those in the previous study. The O+ escape rate showed different dependences in the overpressure cases. The intrinsic magnetic field pushed up the magnetopause and suppressed the pick-up escape of O+ in the oxygen corona, while it enhanced O+ escape via the cusp outflow as with molecular ions. The relative contribution of these two escape processes depends on the property of the oxygen corona determined by the solar XUV flux. The suppression of the O+ pick-up loss was dominant when the weak XUV flux resulted in the thinner oxygen corona. The thinner oxygen corona also caused the O2+-rich polar outflow into the lobe region in the non-overpressure cases. The results suggest that the effects of an intrinsic magnetic field on ion escape also depend on the solar XUV flux.

References

Lillis, R., et al., J. Geophys. Res., 118, 1488-1511, doi:10.1002/jgre.20105, 2013.

Sakata, R., et al., J. Geophys. Res., 125, e2019JA026945. doi:10.1029/2019JA026945, 2020.

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