日本地球惑星科学連合2021年大会

講演情報

[J] ポスター発表

セッション記号 S (固体地球科学) » S-EM 固体地球電磁気学

[S-EM13] 地磁気・古地磁気・岩石磁気

2021年6月6日(日) 17:15 〜 18:30 Ch.11

コンビーナ:加藤 千恵(九州大学比較社会文化研究院)、佐藤 哲郎(東京大学地震研究所)

17:15 〜 18:30

[SEM13-P07] 磁気ロスビー波ソリトン

*堀 久美子1,2、Tobias Steve2、Jones Chris2 (1.神戸大学システム情報学研究科、2.リーズ大学応用数学科)

キーワード:磁気流体力学、回転流体波、地球コア

Finite-amplitude hydromagnetic Rossby waves in the magnetostrophic regime are studied. We consider the slow mode, which travels in the opposite direction to the hydrodynamic or fast mode, in the presence of a toroidal magnetic field and zonal flow by means of quasi-geostrophic models for thick spherical shells. The weakly nonlinear long waves are derived asymptotically using a reductive perturbation method. The problem at the first order is found to obey a second-order ordinary differential equation, leading to a hypergeometric equation for a Malkus field and a confluent Heun equation for an electrical wire field, and is non-singular when the wave speed approaches the mean flow. Investigating its neutral non-singular eigensolutions for different basic states, we find the evolution is described by the Korteweg–de Vries equation. This implies that the nonlinear slow wave forms solitons and solitary waves. These may take the form of a coherent eddy, such as a single anticyclone. We speculate on the relation of the anticyclone to the asymmetric gyre seen in the Earth’s fluid core, and in state-of-the-art dynamo direct numerical simulations.