Computer simulation of a magnetohydrodynamic dynamo. II

Abstract

A computer simulation of a magnetohydrodynamic dynamo in a rapidly rotating spherical shell is performed. Extensive parameter runs are carried out changing electrical resistivity. When resistivity is sufficiently small, total magnetic energy can grow more than ten times larger than total kinetic energy of convection motion which is driven by an unlimited external energy source. When resistivity is relatively large and magnetic energy is comparable or smaller than kinetic energy, the convection motion maintains its well-organized structure. However, when resistivity is small and magnetic energy becomes larger than kinetic energy, the well-organized convection motion is highly irregular. The magnetic field is organized in two ways. One is the concentration of component parallel to the rotation axis and the other is the concentration of perpendicular component. The parallel component tends to be confined inside anticyclonic columnar convection cells, while the perpendicular component is confined outside convection cells.

Experimental study of global-scale turbulence in a librating ellipsoid

“…σ Data is extracted from a fit of the spatially averaged magnitude of velocity ⟨|U |⟩ filtered through a moving window average over 10 libration cycles with an overlap of 90%. (a) The comparison with the WKB stability analysis from (15). (b) The comparison with the asymptotic multipolar stability analysis from (16).…”

“…6 The fluid layer response to the librational forcing through viscous, 7-9 topographic, 10,11 and electromagnetic coupling [12][13][14] is important for understanding the thermal, magnetic, and orbital evolution of the body. Importantly, while it is often assumed that thermo-compositional convection drives the fluid motions responsible for dynamo generation, [15][16][17] recent studies [18][19][20][21] have characterized how mechanical forcing can also drive dynamos by injecting a portion of the vast quantity of rotational energy from primary-satellite orbital systems into driving fluid motions. a) Electronic mail: agrannan@ucla.edu…”

Laboratory-numerical models of rapidly rotating convection in planetary cores

“…These models strive to simulate the global scale processes occurring in planetary interiors by solving the governing equations of magnetohydrodynamic flow in a rotating spherical shell of electrically conductive fluid (e.g. Kageyama & Sato 1995;Glatzmaier & Roberts 1996;Christensen & Aubert 2006). The strength of these models is that they are capable of reproducing some major features of the geomagnetic field, including the dipolar morphology, flux patches at high latitudes and polarity reversals (e.g.…”

A 15.2 TFlops Simulation of Geodynamo on the Earth Simulator

“…From the beginning of this new and exciting simulation area, we have been making important contributions by combining large scale simulation and advanced visualization technology: demonstration of the strong magnetic field generation by MHD dynamo [4], physical mechanism of the dipole field generation [6], and spontaneous and repeated reversals of the dipole moment (north-south polarity) [5,11,13].…”