Ionospheric currents and field-aligned currents generated by dynamo action in an asymmetric Earth magnetic field

2002 ◽  
Vol 107 (A2) ◽  
pp. SIA 4-1-SIA 4-14 ◽  
Author(s):  
P. Le Sager ◽  
T. S. Huang
Keyword(s):  
Magnetic Field ◽  
Ionospheric Currents ◽  
Dynamo Action ◽  
Earth Magnetic Field

Regular Motions in the Ionosphere: Electric and Magnetic Relationships

1961 ◽  
Vol 42 (2) ◽  
pp. 85-100 ◽  
Author(s):  
Sydney Chapman
Keyword(s):  
Magnetic Field ◽  
Electric Current ◽  
Electron Density ◽  
Geomagnetic Field ◽  
Sunspot Cycle ◽  
Ionospheric Currents ◽  
Electric Currents ◽  
Dynamo Action ◽  
Ionospheric Electron Density ◽  
The Earth

Regular worldwide motions in the ionosphere produce daily varying currents there by dynamo action in association with the geomagnetic field. The changing field of these currents induces electric currents within the earth. At the earth's surface, the combined magnetic field of these currents is measured. The parts of primary and secondary origin can be determined separately. The form and intensity of the ionospheric currents can be found. Their height is inferred from the study of the ionospheric electron density and conductivity; it can also be measured by rockets. The daily varying airflow in the layer bearing the electric current, at heights from about 90 to 125 km, can to some extent be inferred. The motion is due partly to the sun's thermal and tidal action and partly to the moon's tidal action. Many aspects of the magnetic variations and the inferred ionospheric motions are considered in some detail, especially their seasonal and sunspot-cycle changes and their variations from day to day.

A THEORY OF IONOSPHERIC CURRENTS ASSOCIATED WITH AURORAE. I

1960 ◽  
Vol 38 (8) ◽  
pp. 1089-1103 ◽  
Author(s):  
J. T. Weaver ◽  
R. Skinner
Keyword(s):  
Magnetic Field ◽  
Perpendicular Magnetic Field ◽  
Ionospheric Currents ◽  
Dynamo Action ◽  
Ionized Gas ◽  
Line Current ◽  
Uniform Velocity ◽  
Ionization Density ◽  
Current Distributions ◽  
Partially Ionized

The current distributions induced by dynamo action in a sheet of partially ionized gas moving with uniform velocity across a perpendicular magnetic field are derived for the case when the gas contains an elliptical region of greater ionization density. Special attention is paid to processes occurring away from the ends of a long narrow ellipse in which the ionization density is much greater than the surrounding region.The results are discussed in relationship to conditions pertaining in the ionosphere when a long homogeneous auroral arc is present. It is concluded that a line current, whose magnitude is linearly dependent on the height-integrated Cowling conductivity within the arc, flows along the arc.

scholarly journals Stability and bifurcation of planetary dynamo models

2011 ◽  
Vol 688 ◽  
pp. 1-4 ◽  
Author(s):  
E. Dormy
Keyword(s):  
Magnetic Field ◽  
Analytical Methods ◽  
Numerical Models ◽  
Dynamo Action ◽  
The Earth ◽  
Stability And Bifurcation ◽  
Earth Magnetic Field ◽  
Numerical And Analytical Methods

AbstractRapidly rotating dynamos, relevant to the origin of the Earth magnetic field, are difficult to model owing to the extreme parameter regimes that occur in their dynamics. Numerical models alone fail to approach the correct regime. However, progress can be achieved by combining numerical and analytical methods. This can offer a better understanding of the variety of behaviour observed near the onset of dynamo action, as seen in the recent study of Sreenivasan & Jones (J. Fluid Mech., this issue, vol. 688, 2011, pp. 5–30).

Solar Internal Rotation and Dynamo Waves: A Two-Dimensional Asymptotic Solution in the Convection Zone

2000 ◽  
Vol 179 ◽  
pp. 379-380
Author(s):  
Gaetano Belvedere ◽  
Kirill Kuzanyan ◽  
Dmitry Sokoloff
Keyword(s):  
Magnetic Field ◽  
Asymptotic Solution ◽  
Internal Rotation ◽  
Convection Zone ◽  
General Idea ◽  
Dynamo Model ◽  
Axially Symmetric ◽  
Dynamo Action ◽  
Regeneration Rate ◽  
Dynamo Waves

Extended abstractHere we outline how asymptotic models may contribute to the investigation of mean field dynamos applied to the solar convective zone. We calculate here a spatial 2-D structure of the mean magnetic field, adopting real profiles of the solar internal rotation (the Ω-effect) and an extended prescription of the turbulent α-effect. In our model assumptions we do not prescribe any meridional flow that might seriously affect the resulting generated magnetic fields. We do not assume apriori any region or layer as a preferred site for the dynamo action (such as the overshoot zone), but the location of the α- and Ω-effects results in the propagation of dynamo waves deep in the convection zone. We consider an axially symmetric magnetic field dynamo model in a differentially rotating spherical shell. The main assumption, when using asymptotic WKB methods, is that the absolute value of the dynamo number (regeneration rate) |D| is large, i.e., the spatial scale of the solution is small. Following the general idea of an asymptotic solution for dynamo waves (e.g., Kuzanyan & Sokoloff 1995), we search for a solution in the form of a power series with respect to the small parameter |D|–1/3(short wavelength scale). This solution is of the order of magnitude of exp(i|D|1/3S), where S is a scalar function of position.

Turbulent dynamo action at low magnetic Reynolds number

1970 ◽  
Vol 41 (2) ◽  
pp. 435-452 ◽  
Author(s):  
H. K. Moffatt
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Large Scale ◽  
Isotropic Turbulence ◽  
Magnetic Energy ◽  
Magnetic Reynolds Number ◽  
Dynamo Action ◽  
Ohmic Dissipation ◽  
Magnetic Energy Density ◽  
Magnetic Diffusivity

The effect of turbulence on a magnetic field whose length-scale L is initially large compared with the scale l of the turbulence is considered. There are no external sources for the field, and in the absence of turbulence it decays by ohmic dissipation. It is assumed that the magnetic Reynolds number Rm = u0l/λ (where u0 is the root-mean-square velocity and λ the magnetic diffusivity) is small. It is shown that to lowest order in the small quantities l/L and Rm, isotropic turbulence has no effect on the large-scale field; but that turbulence that lacks reflexional symmetry is capable of amplifying Fourier components of the field on length scales of order Rm−2l and greater. In the case of turbulence whose statistical properties are invariant under rotation of the axes of reference, but not under reflexions in a point, it is shown that the magnetic energy density of a magnetic field which is initially a homogeneous random function of position with a particularly simple spectrum ultimately increases as t−½exp (α2t/2λ3) where α(= O(u02l)) is a certain linear functional of the spectrum tensor of the turbulence. An analogous result is obtained for an initially localized field.

scholarly journals Torsional waves driven by convection and jets in Earth’s liquid core

2018 ◽  
Vol 216 (1) ◽  
pp. 123-129 ◽  
Author(s):  
R J Teed ◽  
C A Jones ◽  
S M Tobias
Keyword(s):  
Magnetic Field ◽  
Density Gradient ◽  
Inner Core ◽  
Liquid Core ◽  
Outer Core ◽  
Dynamo Action ◽  
Radial Magnetic Field ◽  
Torsional Waves ◽  
Plausible Mechanism ◽  
Rich Liquid

SUMMARY Turbulence and waves in Earth’s iron-rich liquid outer core are believed to be responsible for the generation of the geomagnetic field via dynamo action. When waves break upon the mantle they cause a shift in the rotation rate of Earth’s solid exterior and contribute to variations in the length-of-day on a ∼6-yr timescale. Though the outer core cannot be probed by direct observation, such torsional waves are believed to propagate along Earth’s radial magnetic field, but as yet no self-consistent mechanism for their generation has been determined. Here we provide evidence of a realistic physical excitation mechanism for torsional waves observed in numerical simulations. We find that inefficient convection above and below the solid inner core traps buoyant fluid forming a density gradient between pole and equator, similar to that observed in Earth’s atmosphere. Consequently, a shearing jet stream—a ‘thermal wind’—is formed near the inner core; evidence of such a jet has recently been found. Owing to the sharp density gradient and influence of magnetic field, convection at this location is able to operate with the turnover frequency required to generate waves. Amplified by the jet it then triggers a train of oscillations. Our results demonstrate a plausible mechanism for generating torsional waves under Earth-like conditions and thus further cement their importance for Earth’s core dynamics.

scholarly journals Interpolation of externally-caused magnetic fields over large sparse arrays using Spherical Elementary Current Systems

2010 ◽  
Vol 28 (9) ◽  
pp. 1795-1805 ◽  
Author(s):  
S. A. McLay ◽  
C. D. Beggan
Keyword(s):  
Magnetic Field ◽  
External Field ◽  
Current System ◽  
Electrical Current ◽  
Ionospheric Currents ◽  
Large Area ◽  
Physically Based ◽  
Subsurface Current ◽  
Current Systems ◽  
The Magnetic Field

Abstract. A physically-based technique for interpolating external magnetic field disturbances across large spatial areas can be achieved with the Spherical Elementary Current System (SECS) method using data from ground-based magnetic observatories. The SECS method represents complex electrical current systems as a simple set of equivalent currents placed at a specific height in the ionosphere. The magnetic field recorded at observatories can be used to invert for the electrical currents, which can subsequently be employed to interpolate or extrapolate the magnetic field across a large area. We show that, in addition to the ionospheric currents, inverting for induced subsurface current systems can result in strong improvements to the estimate of the interpolated magnetic field. We investigate the application of the SECS method at mid- to high geomagnetic latitudes using a series of observatory networks to test the performance of the external field interpolation over large distances. We demonstrate that relatively few observatories are required to produce an estimate that is better than either assuming no external field change or interpolation using latitudinal weighting of data from two other observatories.

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