Topic
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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TL;DR: In this paper, a model current system, in which magnetospheric and ionospheric sections are connected by currents flowing along the geomagnetic field lines, is proposed to represent the current system responsible for polar magnetic substorms.
Abstract: A model current system, in which magnetospheric and ionospheric sections are connected by currents flowing along the geomagnetic field lines, is proposed to represent the current system responsible for polar magnetic substorms. The magnetic perturbations from model current systems of this type are studied in terms of elementary loops, whose magnetic effects are evaluated numerically. The influence of currents induced in the ground is studied for a time-independent case, but it is found that such effects do not change the gross character of the perturbation pattern. Using a north-south chain of stations and an appropriate coordinate system, the model predictions are compared with the magnetic variations observed during some substorms. It is found that the model is capable of explaining the gross features of the magnetic perturbation pattern observed. However, at times there are minor deviations from the predictions, which suggest the presence of additional ionospheric and magnetospheric current systems.
128 citations
01 Oct 1978
TL;DR: In this paper, the Imp 6 and Hawkeye satellites were used in a study of very intense electrostatic waves near the upper hybrid resonance frequency in the region just outside the plasmapause, where the polarization of these waves is such that the wave electric field vector is oriented perpendicular to the geomagnetic field.
Abstract: Plasma wave measurements using instruments on the Imp 6 and Hawkeye satellites are utilized in a study of very intense electrostatic waves near the upper hybrid resonance frequency in the region just outside the plasmapause. Studies of these electrostatic disturbances show that the events occur at local times and at magnetic latitudes varying from the equator to 50 deg, and the polarization of these waves is such that the wave electric field vector is oriented perpendicular to the geomagnetic field. In most cases the center frequency of the intense waves corresponds to an (n + 1/2) fg(-) harmonic near the upper hybrid resonance frequency. The hot distribution on function is described for a few events showing temperature anisotropy and a loss cone distribution. A possible mechanism for producing intense waves near the upper hybrid resonance frequency is suggested, and evidence which indicates that the intense electrostatic waves may be a source of nonthermal continuum radiation is given.
128 citations
TL;DR: In this paper, it was shown that coronal mass ejections propagating through the streamer belt can contribute to the peak intensities of recurrent geomagnetic activity, and that both peak recurrent activity and the following sustained activity that correlates with the high-speed flows are controlled by the Russell McPherron effect.
Abstract: The discovery of coronal holes in the early 1970s was heralded as the discovery of the mysterious M-regions responsible for recurrent geomagnetic activity. High-speed flow from the holes, sweeping past Earth on successive solar rotations, was directly correlated with sustained increases in activity indices. We argue that this view of M-regions as coronal holes is incomplete because it ignores work dating from the 1960s demonstrating that peak recurrent activity coincides with passage of corotating interaction regions between high- and low-speed flows. Thus, in an important way, M-regions include the boundary between coronal holes and coronal streamers, since streamers supply the slowest flows. In addition, we suggest that coronal mass ejections propagating through the streamer belt can contribute to the peak intensities of recurrent storms. Finally, we demonstrate that both peak recurrent activity and the following sustained activity that correlates with the high-speed flows are controlled by the Russell-McPherron effect: They are prominent only when the azimuthal component of the Parker spiral field projects a southward component in Earth's tilted dipole frame.
128 citations
TL;DR: In this article, the authors show that most of the jerk has an internal origin, and that such a short-lived phenomenon originated in the Earth's core, and were still detectable after passing through the mantle to the surface, implying a much lower conductivity for the lower mantle than had been believed previously.
Abstract: Annual mean data from worldwide magnetic observatories show that there was a jerk1 (step-change in the second time derivative) in the geomagnetic field, which took place over an interval of <2 yr around 1970. If such a short-lived phenomenon originated in the Earth's core, and were still detectable after passing through the mantle to the surface, this would imply a much lower conductivity for the lower mantle than had been believed previously. Here we show by an objective test that most of the jerk has an internal origin.
128 citations
TL;DR: In this article, the authors used all-sky camera records obtained during the IGY 1957-1958 from a close-spaced network of stations in Alaska and from an array of stations extending from Choteau, Montana, northward across Canada to Thule, Greenland.
Abstract: This study is based on the all-sky camera records obtained during the IGY 1957–1958 from a close-spaced network of stations in Alaska and from an array of stations extending from Choteau, Montana, northward across Canada to Thule, Greenland. The aspects of auroral morphology discussed here include the time and latitude dependency of the incidence, azimuthal alignment, and direction of horizontal motion of auroral forms, and the relation of these aspects to magnetic disturbance.
The diurnal variation of auroral incidence at geomagnetic latitudes 60° to 68° has a single maximum. Near latitude 70° three maxima appear, while farther north, at and above 75°, two maxima occur; these maxima merge into a single peak at the geomagnetic pole. The azimuthal alignment of auroral forms is nearly geomagnetic east-west at geomagnetic latitudes 55° to 68°, and is approximately in the direction of the sun at latitudes above 80°; at latitudes 68° to 80° the azimuthal alignment is transitional between that at lower latitudes and that near the geomagnetic pole. At the auroral zone, horizontal auroral motions are in the longitudinal direction—westward in the evening, and eastward in the morning—whereas meridional motions are primarily southward throughout the night. The reversal from westward to eastward auroral motion occurs rather abruptly on any night, but its time of occurrence varies from night to night. Detailed analyses of individual auroral displays and the concurrent magnetic disturbance indicate detailed association of the alignment and direction of motion of auroral forms with the magnitude and direction of ionospheric currents. The ionospheric current is generally parallel to the alignment of auroral forms and is opposite in direction to the observed motion within the forms.
Patterns representing the average incidence, alignment, and direction of motion of the aurora throughout the polar region are deduced from the results of the analysis. These patterns are centered about the boreal geomagnetic pole and are fixed with respect to the direction toward the sun.
128 citations