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SUMMARY:Contributed talk: Detection of hydro-magnetic waves in Earth's cor
 e - Nicolas Gillet (Université Grenoble Alpes)
DTSTART:20221129T111500Z
DTEND:20221129T114500Z
UID:TALK192086@talks.cam.ac.uk
DESCRIPTION:Reanalysis of geomagnetic field changes over the satellite era
  have unveiled Magneto-Coriolis (MC) waves in Earth&rsquo\;s core\, with a
  period close to 7 years [1]. These are responsible for a large part of th
 e rapid field changes recorded over the past two decades. Such motions are
  Quasi-Geostrophic (QG)\, i.e. invariant along the rotation axis due a dom
 inating Coriolis force. QG MC modes were previously thought to be detectab
 le only on centennial and longer periods [2]. However\, an eigenmode study
  has recently revealed the existence of QG MC solutions on interannual tim
 e- scales\, presenting a low azimuthal complexity [3]. The dispersion rela
 tion for these very dispersive waves indeed indicates that a short period 
 is associated with a shear much stronger along the cylindrical radial dire
 ction\, and a low azimuthal wavenumber. Their reconstruction is easier in 
 the vicinity of the core equator because there small radial length-scales 
 project onto large horizontal patterns. Our analysis of geophysical observ
 ations suggests that (i) their detection is facilitated by the advent of t
 he continuous satellite era since 2000 and (ii) similar waves also exist a
 t decadal periods. This scenario is supported by the reanalysis of synthet
 ic magnetic data computed from geodynamo simulations run at extreme parame
 ters [4]\, where modulated QG MC waves are triggered over a large range of
  periods.\n&nbsp\;\n[1] Gillet\, Gerick\, Jault\, Schwaiger\, Aubert\, & I
 stas\, Satellite magnetic data reveal interannual waves in Earth&rsquo\;s 
 core\, Proc. Nat. Acad. Sci. 119(13)\, e2115258119 (2022)\n[2] Hide\, Free
  hydromagnetic oscillations of the Earth&rsquo\;s core and the theory of t
 he geomagnetic secular variation\, Philos. Trans. R. Soc. Lond. A 259\, 61
 5&ndash\;647 (1966)\n[3] Gerick\, Jault & Noir\, Fast quasi-geostrophic Ma
 gneto-Coriolis modes in the Earth&rsquo\;s core\, Geophys. Res. Lett. 48\,
  e2020GL090803 (2021).\n[4] Aubert & Gillet\, The interplay of fast waves 
 and slow convection in geodynamo simulations nearing Earth&rsquo\;s core c
 onditions\, Geophys. J. Int. 225\, 1854&ndash\;1873 (2021).
LOCATION:Seminar Room 1\, Newton Institute
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