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Geomagnetic Field Effects on Living Systems
Published in Shoogo Ueno, Tsukasa Shigemitsu, Bioelectromagnetism, 2022
The typical periods of GMF reversals are as follows: the Gilbert–Gauss reversal, 3.58 Ma (Hill et al., 2006); the Gauss–Matuyama reversal, 2.581 Ma (Clague et al., 2006); the Matuyama–Brunhes (M–B) reversal, 774 ka (Valet et al., 2019; Simon et al., 2019). As described above, the rate of reversals in the GMF has varied widely over time. It is not yet known when and how the GMF reversal will occur, but the mechanism by which the Earth becomes a magnet has been elucidated by the “dynamo theory (geodynamo theory)” (Elsasser, 1950; Bullard and Gellman, 1954). This dynamo theory was first proposed by a German-born American physicist, Walter M. Elsasser in 1946 (Elsasser, 1950), and is the first mathematical model to show that the GMF is generated by the current (~3 × 109 A) induced by the convection in the Earth’s outer core (Elsasser, 1950). The dynamo theory was proposed not only by Elsasser but also by a British geophysicist, Edward Bullard during the mid-1900s (Bullard and Gellman, 1954). Bullard showed that the movement of fluid in the outer core can generate the GMF (Bullard and Gellman, 1954; Massey, 1980).
A geometric look at MHD and the Braginsky dynamo
Published in Geophysical & Astrophysical Fluid Dynamics, 2021
Andrew D. Gilbert, Jacques Vanneste
In geometric parlance, this is the push forward of the field under the map ψ and is a standard way of looking at the transport of magnetic field in ideal or near-ideal MHD or dynamo theory. What is less intuitive perhaps, is that some quantities are not transported in this way, as a (contravariant) vector field, but as a 1-form field (or covariant vector field), an example of this being momentum. In a key paper, Soward (1972) showed that the natural way of transporting momentum from place to place is using the inverse transpose of the same Jacobian, In the language of differential geometry, this is a push forward of the momentum considered as a 1-form, under the map ψ.
Chiral fermion asymmetry in high-energy plasma simulations
Published in Geophysical & Astrophysical Fluid Dynamics, 2020
J. Schober, A. Brandenburg, I. Rogachevskii
Laminar dynamo theory predicts a scale-dependent growth rate of the magnetic field according to Equation (12). If the initial magnetic field is distributed over all wavenumbers within the box, like, for example, in case of Gaussian noise, the instability is strongest on the scale and the rms magnetic field strength grows at the maximum rate . If the initial magnetic field is, however, concentrated at a single wavenumber , which is the case for a force-free Beltrami field, e.g., for a vector potential , increases at the rate .
Topology of Rayleigh–Bénard convection and magnetoconvection in plane layer
Published in Geophysical & Astrophysical Fluid Dynamics, 2019
Hari Ponnamma Rani, Yadagiri Rameshwar, Jozef Brestenský
One important simplification of dynamo theory, related to the mechanism of the self-consistent hydromagnetic dynamo, is in the study of rotating convection with an a priori given initial magnetic field. Our rotating magnetoconvection (henceforth RMC) simplification is only in the a priori given magnetic field which can evolve in time to be modified possibly for different values in comparison with initially given value (very small in the self-consistent dynamo or large in the so called magnetoconvection dynamo). However, all non-linearities arising in the momentum, heat and magnetic field equations are considered contrary to linear studies of RMC at the onset. Our RMC can mimic the magnetoconvection dynamo conveniently applied to some moons of Jupiter. Thus, henceforth in the present paper dynamo means the magnetoconvection dynamo as well as the self-consistent dynamo.