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Earth's magnetic field

About: Earth's magnetic field is a research topic. Over the lifetime, 20360 publications have been published within this topic receiving 446747 citations. The topic is also known as: magnetic field of Earth & geomagnetic field.


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Journal ArticleDOI
TL;DR: In this article, a line of 7 magnetic stations was set up in western Canada between the geomagnetic latitudes of 59° and 77°N and within ∼2° of 302°E corrected geOMagnetic longitude.
Abstract: In summer 1969 a line of 7 magnetic stations was set up in western Canada between the geomagnetic latitudes of 59° and 77°N and within ∼2° of 302°E corrected geomagnetic longitude. This paper concerns the analysis of the horizontal components of quasi-monochromatic, geomagnetic micropulsations recorded at these stations over 3 days. Both the amplitude spectra and the sense of polarization of the micropulsations exhibit marked latitude dependence, thus implying that much of the micropulsation energy is distributed in the toroidal mode of eigenoscillations of the geomagnetic lines of force. A switch in the sense of polarization around 1200–1400 LT strongly suggests that Pc micropulsations are generated through the development of Kelvin-Helmholtz instabilities at the magnetopause.

314 citations

Journal ArticleDOI
01 May 1988-Nature
TL;DR: In this article, it was shown that the change in the zonal toroidal flow inside the core consists of motions in which axial cylindrical annuli rotate rigidly about the Earth's axis of rotation.
Abstract: The westward drift is one of the most well known features of the geomagnetic field. In this paper we come back to the apparent drift of the main field as seen at the Earth's surface, and show that there is no evidence for a body drift but rather clear evidence for a latitude-dependent drift. Computing the fluid flow at the core mantle boundary (CMB), in the frozen flux and geostrophic hypothesis, we also obtain, among other components, a clear differential zonal rotation of the fluid, symmetrical with respect to the Equator. This differential rotation changes with time, with a time constant of the order of 10 years. Dynamic considerations lead us to think that, during such a time interval, the change in the zonal toroidal flow inside the core consists of motions in which axial cylindrical annuli rotate rigidly about the Earth's axis of rotation. Then, for the 1969–85 time-span, the change in the core angular momentum is shown to balance the change in the mantle angular momentum.

313 citations

Journal ArticleDOI
TL;DR: In this article, a probability model based on the theory of Bernouli trials was proposed to analyze variations in the lengths of geomagnetic polarity, intervals are analyzed by means of the probability that a polarity inversion will occur during one cycle of change in the geOMagnetic dipole moment.
Abstract: Variations in the lengths of geomagnetic polarity, intervals are analyzed by means of a probability model based on the theory of Bernouli trials. Polarity reversals are assumed to occur as the result of the interaction between steady oscillations of the geomagnetic dipole and secular variations of the nondipole field. The particular cycle on which a polarity inversion occurs is determined by the magnitude of the nondipole field, which is assumed to vary randomly and independently of dipole variations. The reversal properties of the geomagnetic dynamo are characterized by the single parameter p, the probability that a polarity inversion will occur during one cycle of change in the geomagnetic dipole moment. From an analysis of polarity changes during the past 10 m.y., the value of p is estimated to be 0.05. During the Permian period, it was at least two orders of magnitude smaller. The analysis suggests that within the past 10 m.y. there have occurred hitherto undiscovered short geomagnetic polarity events with durations shorter than 0.05 m.y.

312 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reconstructed the total solar irradiance from the end of the Maunder minimum to the present based on variations of the surface distribution of the solar magnetic field.
Abstract: Context. Total solar irradiance changes by about 0.1% between solar activity maximum and minimum. Accurate measurements of this quantity are only available since 1978 and do not provide information on longer-term secular trends.Aims. In order to reliably evaluate the Sun's role in recent global climate change, longer time series are, however, needed. They can only be assessed with the help of suitable models.Methods. The total solar irradiance is reconstructed from the end of the Maunder minimum to the present based on variations of the surface distribution of the solar magnetic field. The latter is calculated from the historical record of the sunspot number using a simple but consistent physical model.Results. Our model successfully reproduces three independent data sets: total solar irradiance measurements available since 1978, total photospheric magnetic flux since 1974 and the open magnetic flux since 1868 empirically reconstructed using the geomagnetic aa -index. The model predicts an increase in the solar total irradiance since the Maunder minimum of Wm-2 .

311 citations

Journal ArticleDOI
TL;DR: In this paper, numerical calculations of fluid dynamos powered by thermal convection in a rotating, electrically conducting spherical shell are analyzed and two regimes of nonreversing, strong field dynamos at Ekman number 10 -4 and Rayleigh numbers up to 11 times critical are found.
Abstract: Numerical calculations of fluid dynamos powered by thermal convection in a rotating, electrically conducting spherical shell are analyzed. We find two regimes of nonreversing, strong field dynamos at Ekman number 10 -4 and Rayleigh numbers up to 11 times critical. In the strongly columnar regime, convection occurs only in the fluid exterior to the inner core tangent cylinder, in the form of narrow columnar vortices elongated parallel to the spin axis. Columnar convection contains large amounts of negative helicity in the northern hemisphere and positive helicity in the southern hemisphere and results in dynamo action above a certain Rayleigh number, through a macroscopic α 2 mechanism. These dynamos equilibrate by generating concentrated magnetic flux bundles that limit the kinetic energy of the convection columns. The dipole-dominated external field is formed by superposition of several flux bundles at middle and high latitudes. At low latitudes a pattern of reversed flux patches propagates in the retrograde direction, resulting in an apparent westward drift of the field in the equatorial region. At higher Rayleigh number we find a fully developed regime with convection inside the tangent cylinder consisting of polar upwelling and azimuthal thermal wind flows. These motions modify the dynamo by expelling poloidal flux from the poles and generating intense toroidal fields in the polar regions near the inner core. Convective dynamos in the fully developed regime exhibit characteristics that can be compared with the geomagnetic field, including concentrated flux bundles on the core-mantle boundary, polar minima in field intensity, and episodes of westward drift.

305 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023657
20221,202
2021477
2020553
2019604
2018581