A Very Little Dynamo Theory
Simple example:
The disk dynamo
(Roberts, 2007)
A Very Little Dynamo Theory
The Omega effect
● Conversion of poloidal field to toroidal field.
● Caused by differential rotation (shear) of toroidal flows.
The Alpha effect
● Regeneration of poloidal field from toroidal field.
● Caused by upwelling poloidal flows possessing vorticity.
(Fig. 4.6.1-notes)
A Very Little Dynamo Theory
The Alpha-effect
The Omega-effect
(Roberts, 2007)
A Very Little Dynamo Theory
Omega-effect: Poloidal field -> Toroidal field
Alpha-effect: Toroidal field -> Poloidal field
(Love, 1999)
References
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Baumjohann, W.A. and Treumann, R.A. (1997) Basic Space Plasma Physics,
Imperial College Press.
Roberts, P.H. (2007) Theory of the geodynamo. In Treatise on Geophysics, Vol 5
Love, J. J. (1999) Reversals and excursions of the geodynamo. Astronomy and
Geophysics, Vol 40, 6, 14-19.
Numerical simulation of the geodynamo
A snapshot of the 3D magnetic field structure simulated with the Glatzmaier-Roberts
geodynamo model.
500 years before the middle
of a magnetic dipole reversal
at the middle of the reversal
500 years after the middle
of the reversal
(Glatzmaier & Olson, 2005)
References
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Olsen N. and Mandea, M. (2007) Investigation of a secular variation impulse with
satellite data: The 2003 Jerk. Earth. Planet. Sci. Lett. 255, 94-105.
Jackson, A. and Finlay C.C. (2007) Geomagnetic secular variation and its
applications to the core. In Treatise on Geophysics, Vol 5 Geomagnetism, Ed. M.
Kono, Chapter 5.05, pp.147-193
Finlay, C.C. and Jackson, A. (2003) Equatorially dominated magnetic field change
at the surface of Earth's core. Science, 300, 2084
Gubbins, D., Jones, A.L. and Finlay, C.C. (2006) Fall in Earth's magnetic field is
erratic. Science, 312, 900
Gallet, Y., Genevey, A. and Courtillot, V. (2003) On the possible occurrence of
‘archaeomagnetic jerks’ in the geomagnetic field over the past three millennia.
Earth. Planet. Sci. Lett. 214, 237-242.
Ziegler, L.B., Constable, C.G., Johnson, C.L., and Tauxe, L. (2011) PADM2M: a
penalized maximum likelihood model of the 0-2 Ma palaeomagnetic axial dipole
moment. Geophys. J. Int., 184, 1069–1089.