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.

Geomagnetic Polarity Time Scale

Abstract: The patterns of marine magnetic anomalies for the Late Cretaceous through Neogene (C-sequence) and Middle Jurassic through Early Cretaceous (M-sequence with deep-tow extension) have been calibrated through magnetostratigraphic studies to biostratigraphy, cyclostratigraphy and selected radio-isotope-dated levels. The majority of the geomagnetic polarity time scale for the past 160 myr is constructed by fitting spreading-rate models to these constraints. The status of the geomagnetic polarity time scale for each geological period is summarized in the appropriate period chapters.

Whistler studies of the plasmapause in the magnetosphere: 1. Temporal variations in the position of the knee and some evidence on plasma motions near the knee

Abstract: The position of the knee in the density of magnetospheric ionization was measured on a high time-resolution basis using whistlers recorded during July and part of August 1963. (The knee is an abrupt decrease in magnetospheric ionization density, frequently observed at field lines with an equatorial radius of about 4 RE.) The data were obtained at Eights (64°S dipole latitude) and Byrd (70°S dipole latitude) in the Antarctic. The whistler results and results from other experiments confirm that the knee is a regular feature of the magnetosphere. For conditions of steady, moderate geomagnetic agitation (Kp = 2–4), the diurnal variation in geocentric equatorial range to the knee is remarkably repeatable. It is characterized by (1) a slow inward movement of the knee on the nightside, covering about 1.5 RE in 10 hours; (2) a slight outward movement on the dayside covering about 0.5 RE and (3) a rapid outward shift in the late afternoon covering about 1 RE in 1 hour. During periods of changing magnetic activity, the knee position changes with at most a few hours' delay, moving inward with increasing magnetic activity. The results from Eights and Byrd may be generalized to describe a three-dimensional model of thermal ionization in the magnetosphere involving a dense (∼100 el/cm3) inner region and a tenuous (∼1 el/cm3) outer region separated by a sharp field-aligned boundary, the plasmapause. During the postmidnight hours, the inward motion of the knee involves a corresponding inward motion of the ionization just inside the plasmapause. The rapid outward shift of the knee near 1800 LT does not involve an outward plasma motion, but instead involves the presence of a region of ‘new’ high-density (∼100 el/cm3) plasma in the equatorial range of about 4–5 RE. Preliminary evidence shows that, at least in the period 0000–1700 LT, the ionization inside the plasmapause rotates at approximately the angular velocity of the earth.

Modeling the global magnetic field of the large‐scale Birkeland current systems

Abstract: Quantitative models are developed for representing the global distribution of the average magnetic field produced by the region 1 and 2 Birkeland current systems. The problem is solved in four following steps: (1) constructing a realistic tilt-dependent model of the Birkeland current sheets, based on the formalism of Euler potentials, (2) numerically computing their field at a large number of points within the modeling region, (3) finding a best-fit analytical approximation for that field, and (4) adding a current-free shielding field which confines the Birkeland field within the model magnetopause. At low altitudes, the model field-aligned currents reach the ionosphere along eccentric ovals, which fit the observed region 1 and 2 zones of Iijima and Potemra, and they continue there as horizontal currents. At larger distances, the nightside region 1 currents map to the plasma sheet boundary layer and are then diverted toward the tail flanks, while currents in the dawn-dusk and dayside sectors connect directly to the higher-latitude magnetopause. The region 2 current closes azimuthally near the equator, forming a spread-out partial ring current system. The described approach allows a great flexibility in the geometry of the Birkeland currents, making it feasible to infer their properties from spacecraft data.

A doubling of the Sun's coronal magnetic field during the past 100 years

Abstract: The solar wind is an extended ionized gas of very high electrical conductivity, and therefore drags some magnetic flux out of the Sun to fill the heliosphere with a weak interplanetary magnetic field1,2. Magnetic reconnection—the merging of oppositely directed magnetic fields—between the interplanetary field and the Earth's magnetic field allows energy from the solar wind to enter the near-Earth environment. The Sun's properties, such as its luminosity, are related to its magnetic field, although the connections are still not well understood3,4. Moreover, changes in the heliospheric magnetic field have been linked with changes in total cloud cover over the Earth, which may influence global climate5. Here we show that measurements of the near-Earth interplanetary magnetic field reveal that the total magnetic flux leaving the Sun has risen by a factor of 1.4 since 1964: surrogate measurements of the interplanetary magnetic field indicate that the increase since 1901 has been by a factor of 2.3. This increase may be related to chaotic changes in the dynamo that generates the solar magnetic field. We do not yet know quantitatively how such changes will influence the global environment.