[S-EM17] 地磁気・古地磁気・岩石磁気

[SEM17-01] 地球コアにおける遅い磁気ロスビー波

★招待講演

*堀 久美子^1,2、Jones Chris²、Teed Rob³ (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、3.グラスゴー大学 数学・統計学部)

キーワード：波動、回転磁気流体、永年変動、トロイダル磁場

Magnetohydrodynamic waves excited in fluid cores of rapidly-rotating terrestrial planets can produce time variations of the magnetic fields. Magnetic Rossby waves riding on a mean zonal flow may account for some of the geomagnetic westward drifts observed at mid-latitudes and have the potential to allow the 'hidden' toroidal field strength within the planetary core to be estimated. The nonaxisymmetric, quasi-geostrophic waves are investigated in spherical dynamo simulations. We find that a predicted dispersion relation matches well with the longitudinal drifts seen in our strong-field dynamos, in which the Coriolis and Lorentz forces predominantly balance in the vorticity equation. The validity of our linear theory is also discussed to yield that the nonlinear Lorentz terms influence the observed waveforms. Finally we report the corresponding radial magnetic field variations observed at the surface of the shell in our simulations where the fields are not too strong, suggesting that the internal core field should be the Elsasser number of O(1) to host detectable magnetic Rossby wave motions.