GFD オンラインセミナー 第 17 回 (NINS ネットワーク化加速事業セミナー, RIMS 流体力学セミナーとの共同開催)

• 日時, 場所:

  2024 年 10 月 31 日 (木) 10:30 - 12:00

  Zoom あるいは京大数理研 110 号室

• 話題提供者とタイトル

  Dr. Robert Teed (School of Mathematics and Statistics, University of Glasgow, UK)

  「The force hierarchy and geodynamo regimes of Earth's core」

• 要旨:

  Planetary magnetic fields are produced by dynamo action through turbulent motions of an electrically conducting fluid within the interior of the planet. Numerical experiments of dynamo action relevant to Earth's magnetic field have produced different regime branches identified within bifurcation diagrams [1]. Notable are separate branches in which the resultant magnetic field is either weak or strong (when compared with the fluid flow), as long predicted [2]. Weak field solutions can be identified by the prominent role of viscosity on the motion whereas the magnetic field has a leading order effect on the flow in strong field solutions.

  One measure of the success of numerical models of the geodynamo is the ability to replicate the expected balance between forces operating within Earth's core; Coriolis and Lorentz forces are predicted to be most important. The importance of considering lengthscale dependent force balances [3] and ‘gradient-free’ solenoidal forces has been highlighted recently [4].

  We review the branches/bifurcations of dynamo action previously explored and introduce new results of branching across wider parameter space. We also review the (lengthscale-dependent) forces and solenoidal forces and examine their use in identifying regimes and branches of dynamo action.

• 参考文献:

  [1] E. Dormy et al, Fluid Dynamics Res. 50,011415 (2018)

  [2] P. Roberts, In: Cupal, I. (ed.), Proc. First Int. Workshop on Dynamo Theory and the Generation of the Earth’s Magnetic Fieldpp. 7–12. Czech. Geophys. Inst. Rep (1979)

  [3] T. Schwaiger et al, Geophys. J. Inter. 219, S101–S114 (2019)

  [4] R. J. Teed & E. Dormy, J. Fluid Mech. 964, A26 (2023)