Broad-scale magnetic anomalies over central and eastern Canada: a discussion

1981 ◽  
Vol 18 (3) ◽  
pp. 657-661 ◽  
Author(s):  
R. L. Coles ◽  
G. V. Haines ◽  
W. Hannaford
Keyword(s):  
Magnetic Field ◽  
Sea Level ◽  
Vertical Component ◽  
Magnetic Anomalies ◽  
Superior Province ◽  
The South ◽  
Earth’S Magnetic Field ◽  
Eastern Canada ◽  
Earth's Magnetic Field ◽  
Broad Scale

Profiles of anomalies in the vertical component of the Earth's magnetic field over central and eastern Canada, observed at an average altitude of 4 km above sea level, show broad regions with distinctive anomaly character. These subdivisions indicate major differences in the evolutions of regions within individual structural provinces. Particularly notable is a region of intense anomalies in the northern part of the Superior Province in Quebec, contrasting with much weaker anomaly relief to the south and east.

LIMITING VALUES OF GRAVITATIONAL AND MAGNETIC ANOMALIES DUE TO A SUBTERRANEAN STRUCTURE BOUNDED BY A SINGLE DIFFERENTIAL SURFACE

Geophysics ◽  
1941 ◽  
Vol 6 (1) ◽  
pp. 1-12 ◽  
Author(s):  
J. W. Fisher
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Magnetic Anomalies ◽  
Effective Thickness ◽  
Earth’S Magnetic Field ◽  
Magnetic Effects ◽  
Earth's Magnetic Field ◽  
Survey Results ◽  
Limiting Values

Calculations are made of gravitational and magnetic anomalies supposed due to local variations in the form of a single differential surface separating an overlying rock from an underlying one, the effective thickness of the latter being infinite. Both layers are homogeneous in density or magnetic susceptibility and only those magnetic effects are considered which are due to induction in the earth’s magnetic field. The maximum possible values of these anomalies and of their first and second horizontal derivatives are calculated under these simplified conditions, and it is pointed out that the numerical readings of these quantities, provided by survey results, may lead to useful estimates of the extreme depth and proportions of the structure responsible.

scholarly journals A magnetometer for the measurement of the Earth's vertical magnetic intensity in C. G. S. measure

1928 ◽  
Vol 117 (777) ◽  
pp. 434-458 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Vertical Component ◽  
Field Measurements ◽  
Horizontal Component ◽  
Magnetic Intensity ◽  
Earth’S Magnetic Field ◽  
Simple Operation ◽  
Horizontal Field ◽  
Earth's Magnetic Field

The measurement of the vertical component of the earth’s magnetic field is a less simple operation than that of the horizontal component. The horizontal field measurements are on a satisfactory basis, whether made by the swinging magnet method, or by the more recently developed electric magnetometers, in which known magnetic fields may be provided by means of known currents flowing through coils of known dimensions.

scholarly journals Latitudinal variation rate of geomagnetic cutoff rigidity in the active Chilean convergent margin

2018 ◽  
Vol 36 (1) ◽  
pp. 275-285 ◽  
Author(s):  
Enrique G. Cordaro ◽  
Patricio Venegas ◽  
David Laroze
Keyword(s):  
Magnetic Field ◽  
Vertical Component ◽  
Cutoff Rigidity ◽  
Earth’S Magnetic Field ◽  
Convergent Margin ◽  
Flat Slab ◽  
Geomagnetic Cutoff Rigidity ◽  
Geomagnetic Cutoff ◽  
Variation Rate ◽  
Earth's Magnetic Field

Abstract. We present a different view of secular variation of the Earth's magnetic field, through the variations in the threshold rigidity known as the variation rate of geomagnetic cutoff rigidity (VRc). As the geomagnetic cutoff rigidity (Rc) lets us differentiate between charged particle trajectories arriving at the Earth and the Earth's magnetic field, we used the VRc to look for internal variations in the latter, close to the 70° south meridian. Due to the fact that the empirical data of total magnetic field BF and vertical magnetic field Bz obtained at Putre (OP) and Los Cerrillos (OLC) stations are consistent with the displacement of the South Atlantic magnetic anomaly (SAMA), we detected that the VRc does not fully correlate to SAMA in central Chile. Besides, the lower section of VRc seems to correlate perfectly with important geological features, like the flat slab in the active Chilean convergent margin. Based on this, we next focused our attention on the empirical variations of the vertical component of the magnetic field Bz, recorded in OP prior to the Maule earthquake in 2010, which occurred in the middle of the Chilean flat slab. We found a jump in Bz values and main frequencies from 3.510 to 5.860 µHz, in the second derivative of Bz, which corresponds to similar magnetic behavior found by other research groups, but at lower frequency ranges. Then, we extended this analysis to other relevant subduction seismic events, like Sumatra in 2004 and Tohoku in 2011, using data from the Guam station. Similar records and the main frequencies before each event were found. Thus, these results seem to show that magnetic anomalies recorded on different timescales, as VRc (decades) and Bz (days), may correlate with some geological events, as the lithosphere–atmosphere–ionosphere coupling (LAIC).

scholarly journals Characterization of the South Atlantic Anomaly

2019 ◽  
Vol 26 (1) ◽  
pp. 25-35
Author(s):  
Khairul Afifi Nasuddin ◽  
Mardina Abdullah ◽  
Nurul Shazana Abdul Hamid
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Storm ◽  
South Atlantic ◽  
Active Period ◽  
The South ◽  
Earth’S Magnetic Field ◽  
South Atlantic Anomaly ◽  
Normal Period ◽  
Earth's Magnetic Field ◽  
Latitude Region

Abstract. This research intends to characterize the South Atlantic Anomaly (SAA) by applying the power spectrum analysis approach. The motivation to study the SAA region is due to its nature. A comparison was made between the stations in the SAA region and outside the SAA region during the geomagnetic storm occurrence (active period) and the normal period where no geomagnetic storm occurred. The horizontal component of the data of the Earth's magnetic field for the occurrence of the active period was taken on 11 March 2011 while for the normal period it was taken on 3 February 2011. The data sample rate used is 1 min. The outcome of the research revealed that the SAA region had a tendency to be persistent during both periods. It can be said that the region experiences these characteristics because of the Earth's magnetic field strength. Through the research, it is found that as the Earth's magnetic field increases, it is likely to show an antipersistent value. This is found in the high-latitude region. The lower the Earth's magnetic field, the more it shows the persistent value as in the middle latitude region. In the region where the Earth's magnetic field is very low like the SAA region it shows a tendency to be persistent.

scholarly journals Atmospheric tides in the ionosphere - I. Solar tides in the F 2 region

1947 ◽  
Vol 189 (1017) ◽  
pp. 241-260 ◽  
Keyword(s):  
Magnetic Field ◽  
Vertical Component ◽  
Vertical Motion ◽  
Atmospheric Tides ◽  
Recombination Coefficient ◽  
Earth’S Magnetic Field ◽  
Dynamo Theory ◽  
Night Time ◽  
Geographical Variations ◽  
Earth's Magnetic Field

A theory, based on solar tides, is advanced to explain the anomalous seasonal, diurnal and geographical variations of F 2 region ionization. It is shown that the horizontal winds due to these tides must cause electrons to move along the lines of the earth’s magnetic field. The resultant motion has a vertical component. Account is taken of polarization of the medium by the ‘dynamo’ electric forces. Owing to viscosity the vertical motion decreases upwards in the F 2 region. Application of the equation of continuity shows that the F 2 region becomes greatly distorted. A ‘longitude effect’ is found to arise by reason of the asymmetry of the earth’s magnetic field. The theory is used to explain the high F 2 ionization densities found in low latitudes, and the high values of h' F 2 at noon near the equator. It is also used to explain the afternoon and night-time increases in ionization found at certain locations. It is suggested that the effective recombination coefficient in F 2 is much lower than the generally accepted values. It is shown that Appleton & Weekes’s evidence of lunar tidal effects in the E region does not conflict with the ‘dynamo’ theory of magnetic variations or with Pekeris’s calculations. Observational evidence of the existence of solar tides in the F 2 region is presented.

Pigeons at Magnetic Anomalies: The Effects of Loft Location

1992 ◽  
Vol 170 (1) ◽  
pp. 127-141 ◽  
Author(s):  
CHARLES WALCOTT
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Earth’S Magnetic Field ◽  
Homing Pigeons ◽  
Magnetic Gradient ◽  
Earth's Magnetic Field

Homing pigeons from our old lofts at Fox Ridge Farm in Lincoln, MA, were disoriented when released at places where the earth's magnetic field was irregular-so-called ‘magnetic anomalies’. The orientation of pigeons raised in our lofts at Cornell in Ithaca, NY, was unaffected by anomalies. Further experiments in Lincoln showed that sibling pigeons raised and trained to lofts only 2.5 km apart behaved differently when released at a strong magnetic anomaly. Pigeons from the loft situated in a magnetic gradient of 450 nT km−1 were disoriented at anomalies, whereas birds raised in a loft in a magnetic gradient of 88nT km−1 were well oriented. This suggests that the location of the home loft may play an important role in determining which cues pigeons use for their navigation, and that these cues are learned sometime after weaning from their parents at 4–6 weeks after hatching.

7. The Earth’s magnetic field

2018 ◽  
pp. 106-126
Author(s):  
William Lowrie
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Plate Tectonics ◽  
Magnetic Anomalies ◽  
Earth’S Magnetic Field ◽  
The Earth ◽  
Earth's Magnetic Field ◽  
Reversed Polarity ◽  
Harmful Radiation ◽  
The Magnetic Field

The Earth is surrounded by a magnetic field, which originates inside its molten core, and which for centuries has helped travellers to navigate safely across uncharted regions. The magnetic field protects life on the Earth by acting as a shield against harmful radiation from space, especially from the Sun. ‘The Earth’s magnetic field’ explains that the magnetic field at the Earth’s surface is dominantly that of an inclined dipole. The Sun’s deforming effect on the magnetic field outside the Earth is described, as are the magnetic fields of other planets. The magnetism of rocks forms the basis of palaeomagnetism, which explains how plate tectonics displaced the continents and produced oceanic magnetic anomalies whenever the geomagnetic field reversed polarity.

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