日本地球惑星科学連合2015年大会

講演情報

インターナショナルセッション(ポスター発表)

セッション記号 P (宇宙惑星科学) » P-EM 太陽地球系科学・宇宙電磁気学・宇宙環境

[P-EM09] Dynamics in magnetosphere and ionosphere

2015年5月27日(水) 18:15 〜 19:30 コンベンションホール (2F)

コンビーナ:*中野 慎也(情報・システム研究機構 統計数理研究所)、三好 由純(名古屋大学太陽地球環境研究所)、長谷川 洋(宇宙航空研究開発機構宇宙科学研究所)、田中 良昌(国立極地研究所)、堀 智昭(名古屋大学太陽地球環境研究所 ジオスペース研究センター)

18:15 〜 19:30

[PEM09-P05] グローバルMHDモデルで再現される「2 null - 2 separator」磁気圏におけるリコネクション電場

*渡辺 正和1藤田 茂2田中 高史1 (1.九州大学、2.気象大学校)

It is known that the magnetic reconnection rate is proportional to the field-aligned electric field along the so-called X line. It represents the rate of the magnetic field vanishing in the diffusion region. In global magnetohydrodynamic (MHD) modeling of the magnetosphere, the field-aligned electric field can be used to identify the reconnection mode occurring in the simulated magnetosphere. This is particularly useful when antiparallel field line geometry are not formed. One example is the magnetosphere for northward interplanetary magnetic field (IMF). Global MHD simulations generally reproduces the magnetospheric structure characterized by two magnetic nulls and two separators (which we call here the "2 null - 2 separator" structure, or "null-separator" structure for short). In this configuration, antiparallel magnetic fields do not exist. In addition, the field line geometry for northward IMF is often too complicated to grasp intuitively. In this study, in order to identify the reconnection mode clearly, we explicitly calculate the reconnection electric fields in the simulated magnetosphere during northward IMF periods. We apply this approach to the modeling of the interchange cycle proposed by Watanabe and Sofko [2009, doi:10.1029/2008JA013426]. Although Watanabe et al. [2010, doi:10.1029/2009JA015041] reported observations showing ionospheric signatures of the interchange cycle, there seem to be some debates on the interpretation of the observational data. We aim to support Watanabe et al. [2010] from the modeling point of view. We also discuss the partial collapse of the null-separator structure when the IMF clock angle (measured from due north) is around 45 degrees. In this case, unconnected IMF lines tangle in the closed field lines on the nightside, showing a collapse of the null-separator structure. We argue how such a topology is created by analyzing the field-aligned electric field on separatrices.