日本地球惑星科学連合2018年大会

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[EE] Eveningポスター発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT22] 核-マントルの相互作用と共進化

2018年5月22日(火) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:飯塚 毅(東京大学)、渋谷 秀敏(熊本大学大学院先端科学研究部基礎科学部門地球環境科学分野)、土屋 卓久(愛媛大学地球深部ダイナミクス研究センター、共同)、太田 健二(東京工業大学大学院理工学研究科地球惑星科学専攻)

[SIT22-P12] Kinematic dynamos associated with top-down and bottom-up convection in rotating spherical shells

*谷口 陽菜実1高橋 太1 (1.九州大学)

キーワード:運動学的ダイナモ

Terrestrial planets which maintain their intrinsic fields have convection driven by either thermal or compositional, or both kind of buoyancy in the cores. In case of the Earth, it is believed that compositional convection, which is fed by light element ejection from the ICB upon inner core growth, is currently dominant and powers the geodynamo: it is so-called “bottom-up” type convection. On the other hand, the geodynamo would be driven by thermal convection alone in the past mostly fueled by removal of core heat through the CMB by mantle convection: namely “top-down” type convection. Although it is well known that the velocity field powered by these driving forces and the resultantly generated magnetic fields are different from each other, the reason why they are distinct is not evident. In this study, the basic features of the two types of dynamo action are investigated by numerically solving a kinematic dynamo problem.

We consider an electrically conducting fluid contained in a rotating spherical shell, in which a stationary flow given by linear stability analysis for bottom-up and top-down convection exists. Ekman number Ek is adopted in the range of 2×10-4 to 10-3. The induction equation is solved by time-marching with an initial axial dipole field given as a seed. In results, it is found that the top-down dynamo is easier to be maintained the than the bottom-up one. We will report detail about these issues.