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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 paper, the residual magnetic dipole moment was estimated from twenty-one orbits of the Moon during an extended passage through a lobe of the geomagnetic tail in April 1998.
Abstract: Twenty-one orbits of Lunar Prospector magnetometer data obtained during an extended passage of the Moon through a lobe of the geomagnetic tail in April 1998 are applied to estimate the residual lunar induced magnetic dipole moment. Editing and averaging of individual orbit segments yields a negative induced moment with amplitude −2.4 ±1.6 × 1022 Gauss-cm³ per Gauss of applied field. Assuming that the induced field is caused entirely by electrical currents near the surface of a highly electrically conducting metallic core, the preferred core radius is 340±90 km. For an iron-rich composition, such a core would represent 1 to 3% of the lunar mass.

131 citations

Journal ArticleDOI
TL;DR: In this article, the location of the separatrix between unconnected IMF magnetosheath field lines and reconnected field lines which penetrate the magnetopause and connect to the polar ionosphere is investigated.
Abstract: Magnetic reconnection between the interplanetary magnetic field (IMF) and the geomagnetic field is thought to play a major role in the transfer of solar wind momentum and energy to the magnetosphere. As the angle between the IMF and the geomagnetic field is changed at the bow of the magnetosphere, the topological record of the location of the reconnection region should be recorded in the magnetosheath and on the magnetopause along the flanks of the tail, because the super fast flow freezes strong magnetic gradients formed in the bow reconnection regions into the plasma downstream. In this report, we present results from a three-dimensional, magnetohydrodynamic (MHD), global numerical simulation code for the location of the separatrix between unconnected IMF magnetosheath field lines and reconnected field lines which penetrate the magnetopause and connect to the polar ionosphere. The angle between the IMF direction and the line where the separatrix crosses the magnetopause is shown to be a sensitive function of the IMF clock angle. We also explain how this behavior can be used to derive an approximate relation for the dependence of the cross-polar voltage on the IMF clock angle. We conclude with a note of caution concerning the importance of physical boundary conditions in magnetoplasma simulations.

131 citations

Journal ArticleDOI
TL;DR: The results of a detailed palaeointensity study performed on 54 samples from 9 volcanic units of late Archaean age (2724-2772 Ma) from the Pilbara Craton, Western Australia were presented in this article.
Abstract: We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9 volcanic units of late Archaean age (2724-2772 Ma) from the Pilbara Craton, Western Australia. These results were severely affected by magnetomineralogical alteration occurring during the laboratory heating process necessitating the application of a correction procedure. The correction allowed results from three lavas to pass strict selection criteria but we deem that only one of these exhibits sufficient internal consistency to be considered moderately reliable. It yields a virtual dipole moment of 47±6 ZAm2which is 60% of the present-day value. We combine this determination with a filtered dataset from the updated IAGA (International Association of Geomagnetism and Aeronomy) palaeointensity database, PINT08. Directional secular variation has recently been shown to have changed fundamentally since the Archaean, probably as a consequence of inner core growth since that time. However, here we argue that it is still unclear whether this evolution was accompanied by a single long timescale change in average poloidal field intensity. While the distribution of Precambrian palaeointensity determinations as a whole is significantly lower than that for the last 300 Myr, we show that this finding largely reflects data from the Proterozoic aeon. The distribution of more ancient measurements from the late Archaean-earliest Proterozoic is indistinguishable from that of the last 300 Myr which might suggest that a ‘Proterozoic dipole low’ period existed between two periods of higher field intensity. Were this pattern of long-term geomagnetic intensity variation to be supported by the addition of new data in the future, then it could indicate a related three-stage evolution in core dynamics, namely: vigorous thermal convection caused by high core-mantle heat flux early in the Earth’s history, weaker thermal convection later as the heat flux fell, and finally, strong compositional convection since the inner core nucleated.

131 citations

Journal Article
TL;DR: In this paper, a spherical harmonic model is derived with degree and order 13 in its constant and first time derivative terms, six in its second derivative terms and four in its third derivative terms.
Abstract: The utilization of satellite and surface data together permitted the incorporation of a solution for the anomaly field at each observatory. The residuals of the observatory measurements to such models is commensurate with the actual measurment accuracy. Incorporation of the anomaly estimation enabled the inclusion of stable time derivatives of the spherical harmonic coefficients up to the third derivative. A spherical harmonic model is derived with degree and order 13 in its constant and first time derivative terms, six in its second derivative terms and four in its third derivative terms.

131 citations

Journal ArticleDOI
TL;DR: In this article, an electrodynamic heating mechanism is proposed to account for the precipitation of kilovolt energy electrons during an auroral disturbance, given the existence of an electric field transverse to the geomagnetic field caused by space charges in the magnetosphere, currents will flow along the magnetic field connecting the space charges to the conducting ionosphere.
Abstract: An electrodynamic heating mechanism is proposed to account for the precipitation of kilovolt energy electrons during an auroral disturbance. It is shown that given the existence of an electric field transverse to the geomagnetic field caused by space charges in the magnetosphere, currents will flow along the magnetic field connecting the space charges to the conducting ionosphere. It is shown that the longitudinal current deduced from magnetic observations can be of sufficient intensity to become unstable, resulting in growing ion acoustic waves. In the nonlinear limit these waves tend to inhibit current flows in a collisionless plasma and transform the ordered flow energy into turbulent energy, thus resulting in extreme electrodynamic heating of the electrons. The flow of these ‘hot’ electrons down the geomagnetic field lines is believed to be responsible for the bright aurora and accompanying ionospheric absorption.

131 citations


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