Numerical simulations of short-timescale geomagnetic field variations
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| Published in: | Геофизический журнал |
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| Date: | 2010 |
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| Language: | English |
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Інститут геофізики ім. С.I. Субботіна НАН України
2010
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| Online Access: | https://nasplib.isofts.kiev.ua/handle/123456789/103535 |
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| Cite this: | Numerical simulations of short-timescale geomagnetic field variations / A. Sakuraba // Геофизический журнал. — 2010. — Т. 32, № 4. — С. 217. — англ. |
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Sakuraba, A. 2016-06-19T11:56:02Z 2016-06-19T11:56:02Z 2010 Numerical simulations of short-timescale geomagnetic field variations / A. Sakuraba // Геофизический журнал. — 2010. — Т. 32, № 4. — С. 217. — англ. 0203-3100 https://nasplib.isofts.kiev.ua/handle/123456789/103535 en Інститут геофізики ім. С.I. Субботіна НАН України Геофизический журнал Numerical simulations of short-timescale geomagnetic field variations Article published earlier |
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Numerical simulations of short-timescale geomagnetic field variations |
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Numerical simulations of short-timescale geomagnetic field variations Sakuraba, A. |
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Numerical simulations of short-timescale geomagnetic field variations |
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Numerical simulations of short-timescale geomagnetic field variations |
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Numerical simulations of short-timescale geomagnetic field variations |
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Numerical simulations of short-timescale geomagnetic field variations |
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numerical simulations of short-timescale geomagnetic field variations |
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Sakuraba, A. |
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Sakuraba, A. |
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2010 |
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English |
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Геофизический журнал |
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Інститут геофізики ім. С.I. Субботіна НАН України |
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0203-3100 |
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https://nasplib.isofts.kiev.ua/handle/123456789/103535 |
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Numerical simulations of short-timescale geomagnetic
field variations
A. Sakuraba, 2010
Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan
sakuraba @eps.s.u-tokyo.ac.jp
Numerical modeling of the convection in the Earth's liquid outer core has succeeded in simulat-
ing generation of a dipole-dominated magnetic field and its intermittent polarity reversals. However, pre-
vious models have used unrealistically high viscosity for the core fluid because of computational diffi-culty
to resolve small-scale turbulence that would otherwise happen. It is still an open question whether lower-
viscosity Earth-type dynamo models can simulate the geomagnetic field and its time variations. Recent
models have succeeded in reducing viscosity by about one order of magnitude, com-pared to previous
models. However, such models seem to fail to produce an Earth-like strong mag-netic field even though
the viscosity is more realis-tic. I explained that this paradoxical result was caused by geophysically
unrealistic boundary con-dition for the core surface temperature (Sakuraba, Roberts, Nature Geosci.
2009. — 2. 802 p.). If the core surface temperature is laterally uniform like recent low-viscosity models,
the magnetic field is dipolar but its strength is relatively weak. If the sur-face heat flux is laterally uniform,
which allows a pole-equator temperature difference, westward (ret-rograde) thermal wind naturally blows
beneath the core equator and generates a strong toroidal mag-netic field by its omega effect. The
resultant dipole moment is relatively strong too. I concluded that the former boundary condition was not
only theo-retically unrealistic at the Earth's core-mantle bound-ary, but failed to produce Earth-like
magnetic fields. Small viscosity generally enables the dynamo model to simulate field variations of short
timescales. Here I report on attempts to find Earth-like signatures of short-timescale field variations in the
low-viscosity geodynamo model. I focus on three char-acteristic geomagnetic secular variations:
westward drift, torsional oscillations, and jerks. The simulated westward drift is confined in the equatorial
belt like the geomagnetic field variations for the last 400 years. The drift is primarily caused by advection,
but larger-scale (lower-wavenumber) fields tend to be stationary or rather move eastward, which sug-
gests that some planetary-scale MHD waves modu-late the field behaviors. The drift velocity is slower
than the Earth's probably because the simulated magnetic Reynolds number is too small. The axial
angular velocity of a cylinder in the liquid outer core can be defined as a function of the cylinder's radius
and the time, and this shows wavelike propagation both toward the rotation axis and toward the core
equator. The phase velocity is slightly slower than that predicted by the Braginsky's theory of torsional
oscillations. All three magnetic field components in my model sometimes show zigzag variations in time
like the geomagnetic jerk. The simulated jerk seems to be a local phenomenon, but the cause is still under
investigation.
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| citation_txt |
Numerical simulations of short-timescale geomagnetic field variations / A. Sakuraba // Геофизический журнал. — 2010. — Т. 32, № 4. — С. 217. — англ. |
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2025-11-25T15:32:13Z |
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2025-11-25T15:32:13Z |
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