Physics – Fluid Dynamics
Scientific paper
Oct 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981natur.293..728h&link_type=abstract
Nature, vol. 293, Oct. 29, 1981, p. 728, 729.
Physics
Fluid Dynamics
17
Dynamo Theory, Geomagnetism, Magnetic Field Configurations, Planetary Magnetic Fields, Polarity, Stellar Magnetic Fields, Conducting Fluids, Conductive Heat Transfer, Fluid Dynamics, Ohmic Dissipation, Self Excitation
Scientific paper
A demonstration of the generalization of Cowlings' (1934) theorem concerning the impossibility of generating a steady magnetic field with an axis of symmetry by fluid motions, to the case of nonsteady fields, compressible fluids and position- and time-dependent scalar electrical conductivity and magnetic permeability coefficients is presented and its implications for planetary and stellar magnetic fields are considered. On the basis of an equation for the magnetic field derived from the law of Gauss, Faraday, Ampere and Ohm for a moving medium in which Nernst-Ettinghausen emfs, generated by the conductive flow of heat down a temperature gradient in the presence of a magnetic field, are present, it is shown that effects due to motional induction and the Nernst-Ettinghausen emfs cannot prevent the ohmic decay of an axisymmetric magnetic field. The failure to observe pronounced asymmetries in the surface or above surface magnetic fields of planetary and stellar magnetic fields is explained in terms of the dominance of the dipole component of any magnetic field configuration at great distances from the field source, or the observation of the field during an ohmic decay phase when the emfs due to motional induction are temporarily inoperative.
No associations
LandOfFree
Self-exciting dynamos and geomagnetic polarity changes does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Self-exciting dynamos and geomagnetic polarity changes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Self-exciting dynamos and geomagnetic polarity changes will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1470347