日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 M (領域外・複数領域) » M-IS ジョイント

[M-IS18] 地球流体力学:地球惑星現象への分野横断的アプローチ

2019年5月27日(月) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:伊賀 啓太(東京大学大気海洋研究所)、吉田 茂生(九州大学大学院理学研究院地球惑星科学部門)、柳澤 孝寿(海洋研究開発機構 地球深部ダイナミクス研究分野)、相木 秀則(名古屋大学)

[MIS18-P05] 強磁場の下での熱対流に見られる二次元的なロール構造とその振動

*柳澤 孝寿1田坂 裕司2宮腰 剛広1櫻庭 中3 (1.海洋研究開発機構 地球深部ダイナミクス研究分野、2.北海道大学大学院 工学研究院、3.東京大学大学院 理学系研究科)

キーワード:磁気対流、ロール構造、振動の開始

Effects of the magnetic field, together with effects of the rotation, are important to understand coherent flow structures that should be generated in the Earth’s outer core. To investigate the nature of liquid metal flow where a strong magnetic field exists, we studied magnetoconvection on the Rayleigh-Benard setting in which flows are driven by the temperature difference between the top and bottom boundaries, by laboratory experiments and numerical simulations. The control parameters for this setting are the Rayleigh number (Ra) and the Chandrasekhar number (Q). Ra represents the relative intensity of the buoyancy to the viscous force, while Q represents that of the Lorentz force. In applying a homogeneous magnetic field in the horizontal direction, the flow pattern tends to be a roll-like one whose axes are aligned to the direction of the magnetic field. Under a sufficiently strong magnetic field, that means high Q/Ra, an almost steady two-dimensional flow is observed even at high Ra far from the critical Ra for the onset of convective motion. The Ra corresponds to a state of developed turbulence when Q is zero or small, but significant reduction of fluctuations is observed under high Q. With reducing Q from this steady roll flow regime, an oscillatory motion of rolls is observed. The style of the oscillation shows two-dimensional signatures, that is, little difference of motion is observed in the direction of the magnetic field. On the other hand, the circulation style of rolls shows various interesting features those never observed for the well-known roll type convection near the critical Ra. It is due to the large circulation velocities of the roll-like flow. We can get to this new regime of convection by applying a strong magnetic field in the experiment, and make details of the regime clear by our numerical simulation with high resolutions.