日本地球惑星科学連合2014年大会

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セッション記号 P (宇宙惑星科学) » P-CG 宇宙惑星科学複合領域・一般

[P-CG38_1PO1] 惑星大気圏・電磁圏

2014年5月1日(木) 18:15 〜 19:30 3階ポスター会場 (3F)

コンビーナ:*今村 剛(宇宙航空研究開発機構 宇宙科学研究本部)、関 華奈子(名古屋大学太陽地球環境研究所)、高橋 幸弘(北海道大学・大学院理学院・宇宙理学専攻)、高橋 芳幸(惑星科学研究センター)、深沢 圭一郎(九州大学情報基盤研究開発センター)、中川 広務(東北大学 大学院理学研究科 地球物理学専攻太陽惑星空間物理学講座 惑星大気物理学分野)

18:15 〜 19:30

[PCG38-P15] 木星オーロラ電波の長期変動特性 - II

*三澤 浩昭1米田 瑞生2森岡 昭1土屋 史紀1水口 岳宏1 (1.東北大学惑星プラズマ・大気研究センター、2.東北大学惑星プラズマ・大気研究センター / ハワイ大学天文学研究所)

キーワード:木星, オーロラ電波, 長期変動, イオ火山活動, イオ起源ガス

It is known that Jupiter's auroral radio emission (hereafter JAR) shows long term variations with the time scale of about a decade. The variations were first considered to be initiated by the solar activities in 1960's, however, longer term analyses in 1970's showed the variations relate with the Jovicentric declination of the earth (De). So far, their plausible causalities are considered to be brought by 1) De relating to amount of reachable rays to the earth, and 2) the geocentric declination of Jupiter relating to incidence angle of the radio wave to the terrestrial ionosphere. However, considering solar cycle dependence on the terrestrial auroral radio activity (e.g. Kumamoto et al., 2003), the solar activity control may not be negligible for the long term variations. Furthermore, we have not known well long term relationship between JAR and Jupiter's substorm-like process which may be controlled by Io's volcanic activity.
In order to assess the previously proposed causalities and the other effects, we have investigated occurrence features of JAR using the radio wave data observed outside the terrestrial ionosphere; i.e., by the WIND satellite after 1995. We have derived year-scale occurrence probabilities for 0.7 - 14 MHz around Jupiter's occultation periods, where the frequency range includes both Jupiter's decameter and hectometer radio emissions (so-called DAM and HOM, respectively). As the result, the yearly-scale occurrence probabilities show almost monotonous decrease from 1995 to 2005, then gradual increase after 2005, but change to somewhat complex nature with increase and decrease after 2009. The tendency is roughly similar for DAM and HOM, and also quite roughly similar for Io-related and non-Io-related DAMs. On the other hand, the JAR variation features do not seem to correspond to individual variation of De, solar activity and solar wind, but seem to somewhat correlate with those of Iogenic gas luminosity. These results imply that multiple causalities and/or Jupiter's internal process(es) control the long term variations.

Acknowledgements: We would greatly appreciate M. Kaiser and the WIND/WAVES team for providing the radio wave data.