Geomagnetic polarity reversals, transition field structure, and convection in the outer core

1990 ◽  
Vol 95 (B4) ◽  
pp. 4609 ◽  
Author(s):  
Peter Olson ◽  
V. Lee Hagee
Keyword(s):  
Outer Core ◽  
Field Structure ◽  
Polarity Reversals ◽  
Transition Field ◽  
Geomagnetic Polarity

Cretaceous-Tertiary profile, rhythmic deposition, and geomagnetic polarity reversals of marine sediments near Bjala, Bulgaria

2002 ◽  
Author(s):  
Anton Preisinger ◽  
Selma Aslanian ◽  
Franz Brandstaetter ◽  
Friedrich Grass ◽  
Herbert Stradner ◽  
...  
Keyword(s):  
Marine Sediments ◽  
Polarity Reversals ◽  
Geomagnetic Polarity

scholarly journals Nonlinear quenching of current fluctuations in a self-exciting homopolar dynamo

1997 ◽  
Vol 4 (4) ◽  
pp. 201-205 ◽  
Author(s):  
R. Hide
Keyword(s):  
Boundary Conditions ◽  
Outer Core ◽  
Angular Speed ◽  
Current Fluctuations ◽  
Geological Time ◽  
Dynamo Action ◽  
Lorentz Forces ◽  
In Series ◽  
Geomagnetic Polarity ◽  
New Evidence

Abstract. In the interpretation of geomagnetic polarity reversals with their highly variable frequency over geological time it is necessary, as with other irregularly fluctuating geophysical phenomena, to consider the relative importance of forced contributions associated with changing boundary conditions and of free contributions characteristic of the behaviour of nonlinear systems operating under fixed boundary conditions.  New evidence -albeit indirect- in favour of the likely predominance of forced contributions is provided by the discovery reported here of the possibility of complete quenching by nonlineax effects of current fluctuations in a self-exciting homopolar dynamo with its single Faraday disk driven into rotation with angular speed y(τ) (where τ denotes time) by a steady applied couple.  The armature of an electric motor connected in series with the coil of the dynamo is driven into rotation' with angular speed z(τ) by a torque xf (x) due to Lorentz forces associated with the electric current x(τ) in the system (just as certain parts of the spectrum of eddies within the liquid outer core are generated largely by Lorentz forces associated with currents generated by the self-exciting magnetohydrodynamic (MHD) geodynamo).   The discovery is based on bifurcation analysis supported by computational studies of the following (mathematically novel) autonomous set of nonlinear ordinary differential equations: dx/dt = x(y - 1) - βzf(x), dy/dt = α(1 - x²) - κy, dz/dt = xf (x) -λz,          where f (x) = 1 - ε + εσx, in cases when the dimensionless parameters (α, β, κ, λ, σ) are all positive and 0 ≤ ε ≤ 1. Within those regions of (α, β, κ, λ, σ) parameter space where the applied couple, as measured by α, is strong enough for persistent dynamo action (i.e. x ≠ 0) to occur at all, there are in general extensive regions where x(τ) exhibits large amplitude regular or irregular (chaotic) fluctuations.  But these fluctuating régimes shrink in size as increases from zero, and they disappear altogether when ε = 1, leaving only steady régimes of dynamo action.

scholarly journals Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals

2000 ◽  
Vol 18 (1) ◽  
pp. 11-27 ◽  
Author(s):  
D. M. Willis ◽  
A. C. Holder ◽  
C. J. Davis
Keyword(s):  
Magnetic Field ◽  
Spherical Cavity ◽  
Exact Equation ◽  
Outer Magnetosphere ◽  
Special Cases ◽  
Magnetospheric Configuration And Dynamics ◽  
Polarity Reversals ◽  
Field Lines ◽  
Geomagnetic Polarity ◽  
The Magnetic Field

Abstract. Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals are investigated by considering the idealized problem of a magnetic multipole of order m and degree n located at the centre of a spherical cavity surrounded by a boundless perfect diamagnetic medium. In this illustrative idealization, the fixed spherical (magnetopause) boundary layer behaves as a perfectly conducting surface that shields the external diamagnetic medium from the compressed multipole magnetic field, which is therefore confined within the spherical cavity. For a general magnetic multipole of degree n, the non-radial components of magnetic induction just inside the magnetopause are increased by the factor {1 + [(n + 1)/n]} relative to their corresponding values in the absence of the perfectly conducting spherical magnetopause. An exact equation is derived for the magnetic field lines of an individual zonal (m = 0), or axisymmetric, magnetic multipole of arbitrary degree n located at the centre of the magnetospheric cavity. For such a zonal magnetic multipole, there are always two neutral points and n-1 neutral rings on the spherical magnetopause surface. The two neutral points are located at the poles of the spherical magnetopause. If n is even, one of the neutral rings is coincident with the equator; otherwise, the neutral rings are located symmetrically with respect to the equator. The actual existence of idealized higher-degree (n>1) axisymmetric magnetospheres would necessarily imply multiple (n + 1) magnetospheric cusps and multiple (n) ring currents. Exact equations are also derived for the magnetic field lines of an individual non-axisymmetric magnetic multipole, confined by a perfectly conducting spherical magnetopause, in two special cases; namely, a symmetric sectorial multipole (m = n) and an antisymmetric sectorial multipole (m = n-1). For both these non-axisymmetric magnetic multipoles, there exists on the spherical magnetopause surface a set of neutral points linked by a network of magnetic field lines. Novel magnetospheric processes are likely to arise from the existence of magnetic neutral lines that extend from the magnetopause to the surface of the Earth. Finally, magnetic field lines that are confined to, or perpendicular to, either special meridional planes or the equatorial plane, when the multipole is in free space, continue to be confined to, or perpendicular to, these same planes when the perfectly conducting magnetopause is present.Key words. Geomagnetism and paleomagnetism (reversals-process, time scale, magnetostratigraphy) · Magnetospheric physics (magnetopause, cusp, and boundary layers; magnetospheric configuration and dynamics)

scholarly journals Polar caps during geomagnetic polarity reversals

2018 ◽  
Vol 216 (2) ◽  
pp. 1334-1343 ◽  
Author(s):  
Bruno Zossi ◽  
Mariano Fagre ◽  
Hagay Amit ◽  
Ana G Elias
Keyword(s):  
Polar Caps ◽  
Polarity Reversals ◽  
Geomagnetic Polarity

scholarly journals A simplified correlation between vertebrate evolution and Paleozoic geomagnetism

2019 ◽  
Author(s):  
John P Staub
Keyword(s):  
Atmospheric Oxygen ◽  
Low Frequency ◽  
Strong Relationship ◽  
Evolutionary Patterns ◽  
Geologic Time Scale ◽  
Polarity Reversals ◽  
Low Levels ◽  
Geomagnetic Polarity ◽  
Taxonomic Groups ◽  
Biologic Factors

Background. Despite a fifty-year failure of paleontologists to find a viable connection between geomagnetic polarity reversals and evolutionary patterns, recent paleobiology databases show that the early appearance, radiation, and diversification of Paleozoic vertebrates tends to occur during periods having frequent collapses of the Earth’s geomagnetic field. The transition time during the collapse of the Earth’s protective magnetic shield can last thousands of years, and the effects on biota are unknown. Solar and cosmic radiation, volcanism, climate alteration, low-frequency electromagnetic fields, depletion of ozone, the stripping of atmospheric oxygen, and increasing production of Carbon14 in the stratosphere have been proposed as possible causes, but previous studies have found no effects. Methods. Using published databases, we compiled a spreadsheet showing the first appearance of 2104 genera with each genus assigned to one of 8 major taxonomic groups. From Gradstein’s Geologic Time Scale 2012, we delineated 17 Paleozoic zones with either high or low levels of polarity reversals. Results. From our compilation, 727 Paleozoic vertebrates represent the initial radiation and diversification of individual Paleozoic vertebrate clades. After compensating for sample-size and external geologic and sampling biases, the resulting Pearson’s correlation coefficient between the 727 genera and geomagnetic polarity zones equals 0.8, a result that suggests a strong relationship exists between Paleozoic vertebrates and geomagnetism. Discussion. The question: is this apparent connection between geomagnetism and the evolution of Paleozoic vertebrate due to environmental or biologic factors. If biologic, why are vertebrates the only biota effected? And after an indeterminate period of time, how do vertebrates become immune to the ongoing effects of polarity reversals?

scholarly journals Polarity Reversals in the Earth's Magnetic Field

Eos ◽  
2016 ◽  
Vol 97 ◽  
Author(s):  
Fabio Florindo
Keyword(s):  
Magnetic Field ◽  
Solid Earth ◽  
Earth’S Magnetic Field ◽  
Earth's Magnetic Field ◽  
Polarity Reversals ◽  
Geomagnetic Polarity

Studies of geomagnetic polarity reversals have generated some of the biggest and most interesting debates in the paleomagnetic and wider solid Earth geophysics communities over the last 25 years.

scholarly journals A simplified correlation between vertebrate evolution and Paleozoic geomagnetism

2019 ◽  
Author(s):  
John P Staub
Keyword(s):  
Atmospheric Oxygen ◽  
Low Frequency ◽  
Strong Relationship ◽  
Evolutionary Patterns ◽  
Geologic Time Scale ◽  
Polarity Reversals ◽  
Low Levels ◽  
Geomagnetic Polarity ◽  
Taxonomic Groups ◽  
Biologic Factors

Background. Despite a fifty-year failure of paleontologists to find a viable connection between geomagnetic polarity reversals and evolutionary patterns, recent paleobiology databases show that the early appearance, radiation, and diversification of Paleozoic vertebrates tends to occur during periods having frequent collapses of the Earth’s geomagnetic field. The transition time during the collapse of the Earth’s protective magnetic shield can last thousands of years, and the effects on biota are unknown. Solar and cosmic radiation, volcanism, climate alteration, low-frequency electromagnetic fields, depletion of ozone, the stripping of atmospheric oxygen, and increasing production of Carbon14 in the stratosphere have been proposed as possible causes, but previous studies have found no effects. Methods. Using published databases, we compiled a spreadsheet showing the first appearance of 2210 age-dated genera with each genus assigned to one of eleven major taxonomic groups. From Gradstein’s Geologic Time Scale 2012, we delineated 17 Paleozoic zones with either high or low levels of polarity reversals. Results. From our compilation, 737 Paleozoic vertebrates represent the initial radiation and diversification of individual Paleozoic vertebrate clades. After compensating for sample-size and external geologic and sampling biases, the resulting Pearson’s correlation coefficient between the 737 genera and geomagnetic polarity zones equals 0.89. These results suggest a strong relationship exists between Paleozoic vertebrates and geomagnetism. Discussion. The question: is this apparent connection between geomagnetism and the evolution of Paleozoic vertebrate due to environmental or biologic factors. If biologic, why are vertebrates the only biota effected? And after an indeterminate period of time, how do vertebrates become immune to the ongoing effects of polarity reversals?

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