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The Earth's Magnetic Field (the + earth_magnetic_field)

Distribution by Scientific Domains
Physics and Astronomy57%

Selected Abstracts

Profile of the climate change in the Kingdom of Bahrain

ENVIRONMETRICS, Issue 8 2003
W. E. Alnaser
Abstract Long-term meteorological data from the Kingdom of Bahrain (1902 to 2001), along with other data from the Sultanate of Oman and the Kingdom of Saudi Arabia, were used to study the profile and the characteristics of the climate changes in the Kingdom of Bahrain. This article illustrates the possible effects of several factors, such as greenhouse gases (GHG), sunspot number, cosmic ray flux, planet conjunctions, the Earth's magnetic field, as well as volcanic eruption, on the profile of the climate change. In general, we found that the temperature variations, to a certain extent, are associated with the cyclic variations in sunspot number (the 11-year cycle), which in turn affect the pattern of the cosmic ray flux due to the distortion of the interplanetary magnetic field. The latter is believed to influence cloud formation. In addition, the discrepancy in the climate change pattern in Bahrain was also attributed to the combined effect of the high local level of CO2 emissions as well as that of other cooling gases in the region. Copyright © 2003 John Wiley & Sons, Ltd. [source]

The SGR 1806-20 magnetar signature on the Earth's magnetic field

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2006
M. Mandea
SUMMARY SGRs denote ,soft ,-ray repeaters', a small class of slowly spinning neutron stars with strong magnetic fields. On 2004 December 27, a giant flare was detected from magnetar SGR 1806-20. The initial spike was followed by a hard-X-ray tail persisting for 380 s with a modulation period of 7.56 s. This event has received considerable attention, particularly in the astrophysics area. Its relevance to the geophysics community lies in the importance of investigating the effects of such an event on the near-Earth electromagnetic environment. However, the signature of a magnetar flare on the geomagnetic field has not previously been investigated. Here, by applying wavelet analysis to the high-resolution magnetic data provided by the CHAMP satellite, a modulated signal with a period of 7.5 s over the duration of the giant flare appears in the observed data. Moreover, this event was detected by the energetic ion counters onboard the DEMETER satellite. [source]

Non-random distribution of ring recoveries from trans-Saharan migrants indicates species-specific stopover areas

JOURNAL OF AVIAN BIOLOGY, Issue 1 2005
Thord Fransson
Many long-distance migrant birds regularly have to pass ecological barriers, like the Saharan desert, where fuelling is very difficult, and large fuel loads have to be stored in advance. In this paper, we have investigated how seven species of birds are distributed in autumn close to the Saharan desert in the eastern Mediterranean area by using ring recoveries from northern Europe. The result clearly shows that the species included are not randomly distributed at this point, about 3,000 km from the breeding area. Birds from rather large breeding areas were shown to converge in confined areas, which in several cases completely differ between species. This means that birds of the same species have to follow different migratory directions depending on the location of their starting point. The observed pattern support earlier findings indicating that birds, in combination with a clock-and-compass orientation procedure, must use some external cues in order to find confined species-specific areas. The possibility for birds to use information from the Earth's magnetic field as an external cue in this area is discussed. [source]

In situ identification, pairing, and classification of meteorites from Antarctica through magnetic susceptibility measurements

METEORITICS & PLANETARY SCIENCE, Issue 3 2006
Luigi Folco
Magnetic susceptibility measurements carried out with a pocket meter (SM30) during the 2003/04 PNRA meteorite collection expedition to northern Victoria Land (Antarctica) proved to be a rapid, sensitive, non-destructive means for the in situ identification, pairing, and classification of meteorites. In blue ice fields characterized by the presence of moraines and glacial drifts (e.g., Miller Butte, Roberts Butte, and Frontier Mountain), magnetic susceptibility measurements allowed discrimination of meteorites from abundant terrestrial stones that look like meteorites thanks to the relatively high magnetic susceptibility of the former with respect to terrestrial rocks. Comparative measurements helped identify 16 paired fragments found at Johannessen Nunataks, thereby reducing unnecessary duplication of laboratory analyses and statistical bias. Following classifications schemes developed by us in this and previous works, magnetic susceptibility measurements also helped classify stony meteorites directly in the field, thereby providing a means for selecting samples with higher research priority. A magnetic gradiometer capable of detecting perturbations in the Earth's magnetic field induced by the presence of meteorites was an efficient tool for locating meteorites buried in snow along the downwind margin of the Frontier Mountain blue ice field. Based on these results, we believe that magnetic sensors should constitute an additional payload for robotic search for meteorites on the Antarctic ice sheet and, by extension, on the surface of Mars where meteorite accumulations are predicted by theoretical works. Lastly, magnetic susceptibility data was successfully used to crosscheck the later petrographic classification of the 123 recovered meteorites, allowing the detection of misclassified or peculiar specimens. [source]

Dependence of the permeability-frequency spectra of Fe88Zr7B4Cu alloys on dc magnetic fields

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2004
W. Qin
Abstract Effects of applied dc transverse and longitudinal magnetic fields on the dynamic magnetization of Nanoperm alloys are studied by using permeability spectroscopy. It is observed that the permeability-frequency spectra of Nanoperm alloys are very sensitive to the dc transverse magnetic fields. The applied dc transverse magnetic fields may strengthen the domain wall pinning, making the permeability decrease and the relaxation frequency move toward higher frequency. The dc longitudinal magnetic fields have no significant influence on the permeability-frequency spectra. The contribution to initial permeability only results from the bulging of the domain walls parallel to the applied ac magnetic field. The effect of the Earth's magnetic field on the dynamic magnetic properties of Nanoperm alloys must be considered in actual application. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The cause of superchrons

ASTRONOMY & GEOPHYSICS, Issue 6 2001
J A Jacobs
Superchrons , long periods in the geomagnetic record when the Earth's magnetic field did not reverse its polarity , are a challenge to observers and theorists. Jack Jacobs outlines the problems and some possible solutions. Reversals of polarity are a feature of the geomagnetic record for all the time it has been documented. Although not regular, reversals are sufficiently frequent for their absence to be noticeable. When the Earth's magnetic field retains the same polarity for over 20 million years, a superchron is established. Superchrons demand the attention of geophysicists concerned with the generation of the Earth's field: either they must result from an intrinsic feature of the geodynamo, or they reflect the influence of some external force. Here I discuss internal and external mechanisms for the formation of superchrons, including the role of the inner core, true polar wander, Earth's orbital variations and tides. [source]

SPICeD: imaging the deep Earth

ASTRONOMY & GEOPHYSICS, Issue 3 2001
Michael Kendall FRAS
Michael Kendall and George Helffrich respond to Alan Douglas's paper in the previous issue of Astronomy & Geophysics with a prototype three-component broadband seismic network for the UK. There are two boundaries in the Earth's deep interior that are as significant in terms of contrast in material properties and dynamics as the lithosphere,atmosphere boundary, where we live. The natures of the core-mantle boundary and the inner-core/outer-core boundary have significant implications for the stability of the Earth's magnetic field, style of convection, moment of inertia and length of day. An array of broadband three-component seismometers (SPICeD) spanning Scotland, England and France has been deployed with the aim of studying these dramatic interfaces within the Earth. A secondary aim of the deployment was to install a working prototype for a permanent three-component broadband seismic network in the UK, as advocated by Alan Douglas in the previous issue of this journal (Douglas 2001). [source]