Core flow instabilities and geomagnetic storms during reversals: The Steens Mountain impulsive field variations revisited

Ultré-Guérard, Pascale; Achache, J.

doi:10.1016/0012-821x(95)00149-7

Cited by 11 publications

(7 citation statements)

References 38 publications

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“…These geomagnetic time constants could be constrained by estimates of the cooling times of individual flows. However, such rapid changes do not seem to be compatible with accepted values of mantle conductivity [see Ultré‐Guérard and Achache , 1995]. Additional detailed investigations have therefore been conducted in order to see whether this situation could not have arisen because of remagnetization of the flows.…”

Section: Evaluation Of Observational Constraintsmentioning

confidence: 99%

Numerical models of the geodynamo and observational constraints

Dormy

Valet

Courtillot

2000

Geochem Geophys Geosyst

164

114

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[1]0 Abstract: The past few years have seen the emergence of a large number of numerical simulations of the geodynamo. In parallel, both new and old geomagnetic, archeomagnetic, and paleomagnetic observations have been interpreted as actual geomagnetic features and used as constraints for dynamo models. Naturally, model predictions should be tested against actual characteristics of the geomagnetic field. Despite huge differences (sometimes in excess of a billion) between the values of parameters used in the simulations and those estimated for the Earth, it is intriguing that many available simulations succeed in producing largely axial dipolar magnetic fields with weaker nondipolar structures, in agreement with the first-order characteristics of the geomagnetic field. Yet, when considering finer characteristics, there are significant differences, and failures to actually produce a number of fundamental characteristic features. In this presentation, we first review numerical results obtained to date, then we attempt to summarize which field characteristics derived from observational data sets can be considered robust. On the basis of simple criteria used to evaluate the degree of confidence that can be placed in each datum, we sort presumably characteristic geomagnetic features into three categories (robust, controversial, and unlikely). We conclude that numerical models should be illustrated with a number of key``predictions,'' averaged over at least 10 dipole diffusion times. These predictions should be tested against the subset of robust observations only. Controversial observations should await additional confirmation.

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Section: Evaluation Of Observational Constraintsmentioning

confidence: 99%

Numerical models of the geodynamo and observational constraints

Dormy

Valet

Courtillot

2000

Geochem Geophys Geosyst

164

114

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“…Changes of 300 nT and several degrees per day in a paleomagnetic recording as the Steens Mountain reversal record is hard to be explained as a result of changes in the Earth's outer core and its dynamo, but most probably require external magnetic field variations as an explanation (Ultré-Guérard and Achache, 1995;Jackson, 1995).…”

Section: Introductionmentioning

confidence: 99%

“…This energy input scales with R 2 T , the tail cross section. Using R T ∝R MP gives one Siscoe and Chen's (1975) scaling relation (see also Ultré-Guérard and Achache, 1995).…”

Section: Introductionmentioning

confidence: 99%

Concerning long-term geomagnetic variations and space climatology

et al. 2004

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Abstract. During geomagnetic polarity transitions the surface magnetic field of the Earth decays to about 25% and less of its present value. This implies a shrinking of the terrestrial magnetosphere and posses the question of whether magnetospheric magnetic field variations scale in the same manner. Furthermore, the geomagnetic main field also controls the magnetospheric magnetic field and space weather conditions. Long-term geomagnetic variations are thus intimately related to space climate. We critically assess existing scaling relations and derive new ones for various magnetospheric parameters. For example, we find that ring current perturbations do not increase with decreasing dipole moment. And we derive a scaling relation for the polar electrojet contribution, indicating a weak increase with increasing internal field. From this we infer that the ratio between external and internal field contributions may be weakly enhanced during polarity transitions. Our scaling relations also provide more insight on the importance of the internal geomagnetic field contribution for space climate.

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“…Several studies have suggested that the maximum surface field strength will decrease by approximately one order of magnitude (Glassmeier et al., 2004; Siscoe & Sibek, 1980; Ultre‐Geurard & Achache, 1995; Vogt et al., 2004). However, given the lack of observational constraint on changes to overall magnetic field strength during a pole reversal, we explored the sensitivity of the dipole and quadrupole plasmaspheres to changes in magnetic field strength to understand how the plasmasphere erodes with smaller magnetic field strengths.…”

Section: Methodsmentioning

confidence: 99%

“…Several studies have suggested that the maximum surface field strength will decrease by approximately one order of magnitude (Glassmeier et al, 2004;Siscoe & Sibek, 1980;Ultre-Geurard & Achache, 1995;Vogt et al, 2004).…”

Section: Variable Field Strengthmentioning

confidence: 99%

Analysis of E × B Drifts in Earth's Magnetosphere During Geomagnetic Reversals: Potential Consequences for Plasmasphere Behavior and Stability

Caggiano

Paty

2022

JGR Space Physics

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Geomagnetic pole reversals occur frequently throughout geologic history, although one has not yet occurred in recorded time. Magnetohydrodynamic models of Earth's core have revealed that during a reversal, the magnetic dipole moment disappears, leaving higher‐order moments. Previous research examined quadrupole magnetic field topologies and quantitatively specified the magnetic equators of those topologies but did not fully examine charged particle drift motion and stability in the inner magnetosphere. Earth's closed magnetosphere is primarily dominated by two electric fields, the corotational and convection generated electric fields. trueE⃗×trueB⃗ $\vec{E}\times \vec{B}$ drifts from these fields ultimately drives the behavior of the cold plasma of the plasmasphere. In a quadrupole‐dominated magnetic field, the plasma motion generated by the trueE⃗×trueB⃗ $\vec{E}\times \vec{B}$ drifts would be dramatically different from the classical dipole field plasma convection. Three quadrupole topologies were evaluated, and the trueE⃗×trueB⃗ $\vec{E}\times \vec{B}$ drift was analyzed along the magnetic equators of these topologies to characterize and quantify the resultant plasma motion and evaluate the behavior, structure and stability of the plasmasphere. We also tested for plasmaspause and magnetopause boundary sensitivity to magnetic field strength. The direction of the convection flow is hemispherically dependent for the η = 0 and 0.5 quadrupole topologies, that is, the plasma in the Northern Hemisphere convects tailward, and the Southern Hemisphere convects sunward. The η = 1 topology demonstrates evidence of strong plasmasphere erosion due to the intersection of the magnetic equators, and the magnetopause and plasmapause of the η = 1 topology are particularly sensitive to reductions in magnetic field strength.

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Core flow instabilities and geomagnetic storms during reversals: The Steens Mountain impulsive field variations revisited

Cited by 11 publications

References 38 publications

Numerical models of the geodynamo and observational constraints

Numerical models of the geodynamo and observational constraints

Concerning long-term geomagnetic variations and space climatology

Analysis of E × B Drifts in Earth's Magnetosphere During Geomagnetic Reversals: Potential Consequences for Plasmasphere Behavior and Stability

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