Day-to-Day Variability of H Component of the Geomagnetic Field in the South Atlantic Islands at Low Latitudes

2017 ◽  
Author(s):  
L. Freire ◽  
S. R. Laranja ◽  
L. Benyosef
Keyword(s):  
Geomagnetic Field ◽  
South Atlantic ◽  
The South ◽  
Low Latitudes

scholarly journals Elevated paleomagnetic dispersion at Saint Helena suggests long-lived anomalous behavior in the South Atlantic

2020 ◽  
Vol 117 (31) ◽  
pp. 18258-18263 ◽  
Author(s):  
Yael A. Engbers ◽  
Andrew J. Biggin ◽  
Richard K. Bono
Keyword(s):  
Geomagnetic Field ◽  
Anomalous Behavior ◽  
Magnetic Polarity ◽  
South Atlantic ◽  
Polarity Reversal ◽  
The South ◽  
Geomagnetic Secular Variation ◽  
Core Dynamics ◽  
Geocentric Axial Dipole ◽  
Magnetic Polarity Reversal

Earth’s magnetic field is presently characterized by a large and growing anomaly in the South Atlantic Ocean. The question of whether this region of Earth’s surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics, core−mantle interaction, and the possibility of an imminent magnetic polarity reversal. Here we present paleomagnetic data from Saint Helena, a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the South Atlantic on timescales of millions of years. Our results, supported by positive baked contact and reversal tests, produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago, but with very large associated directional dispersion. These findings indicate that, on geological timescales, geomagnetic secular variation is persistently enhanced in the vicinity of Saint Helena. This, in turn, supports the South Atlantic as a locus of unusual geomagnetic behavior arising from core−mantle interaction, while also appearing to reduce the likelihood that the present-day regional anomaly is a precursor to a global polarity reversal.

scholarly journals The CHAOS-7 geomagnetic field model and observed changes in the South Atlantic Anomaly

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Christopher C. Finlay ◽  
Clemens Kloss ◽  
Nils Olsen ◽  
Magnus D. Hammer ◽  
Lars Tøffner-Clausen ◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
Field Model ◽  
Internal Field ◽  
South Atlantic ◽  
Time Dependent ◽  
The South ◽  
Spherical Harmonic Degree ◽  
Core Mantle Boundary ◽  
The Pacific ◽  
Harmonic Degree

Abstract We present the CHAOS-7 model of the time-dependent near-Earth geomagnetic field between 1999 and 2020 based on magnetic field observations collected by the low-Earth orbit satellites Swarm, CryoSat-2, CHAMP, SAC-C and Ørsted, and on annual differences of monthly means of ground observatory measurements. The CHAOS-7 model consists of a time-dependent internal field up to spherical harmonic degree 20, a static internal field which merges to the LCS-1 lithospheric field model above degree 25, a model of the magnetospheric field and its induced counterpart, estimates of Euler angles describing the alignment of satellite vector magnetometers, and magnetometer calibration parameters for CryoSat-2. Only data from dark regions satisfying strict geomagnetic quiet-time criteria (including conditions on IMF $$B_z$$ B z and $$B_y$$ B y at all latitudes) were used in the field estimation. Model parameters were estimated using an iteratively reweighted regularized least-squares procedure; regularization of the time-dependent internal field was relaxed at high spherical harmonic degree compared with previous versions of the CHAOS model. We use CHAOS-7 to investigate recent changes in the geomagnetic field, studying the evolution of the South Atlantic weak field anomaly and rapid field changes in the Pacific region since 2014. At Earth’s surface a secondary minimum of the South Atlantic Anomaly is now evident to the south west of Africa. Green’s functions relating the core–mantle boundary radial field to the surface intensity show this feature is connected with the movement and evolution of a reversed flux feature under South Africa. The continuing growth in size and weakening of the main anomaly is linked to the westward motion and gathering of reversed flux under South America. In the Pacific region at Earth’s surface between 2015 and 2018 a sign change has occurred in the second time derivative (acceleration) of the radial component of the field. This acceleration change took the form of a localized, east–west oriented, dipole. It was clearly recorded on ground, for example at the magnetic observatory at Honolulu, and was seen in Swarm observations over an extended region in the central and western Pacific. Downward continuing to the core–mantle boundary, we find this event originated in field acceleration changes at low latitudes beneath the central and western Pacific in 2017.

A palaeomagnetic survey of South American rock formations - Palaeomagnetic studies on rock formations from Northwest Argentina

1970 ◽  
Vol 267 (1183) ◽  
pp. 481-501 ◽  
Keyword(s):  
Atlantic Ocean ◽  
Geomagnetic Field ◽  
South Atlantic ◽  
South American ◽  
South Pole ◽  
The South ◽  
Remanent Magnetism ◽  
Rock Formations ◽  
Lower Palaeozoic ◽  
La Rioja

Cambrian, Cambro-Ordovician and Ordovician formations of red sandstones and siltstones from the sub-Andean regionso f the Provinces of Salta and Jujuy have been studied. The grouping of n.r.m . directions suggests partial remagnetization after folding in the Tertiary or Quaternary geomagnetic field. Thermal cleaning at 300 °C and higher temperatures destroys this secondary magnetization leaving a magnetization which is accepted as representing the lower Palaeozoic geomagnetic field. Palaeomagnetic south pole positions have been computed and lie in the Atlantic Ocean to the NNE of Brazil. The period between the Carboniferous and Triassic is covered by the Paganzo formation which is exposed in La Rioja Province. The older part (Paganzo II) is reversely magnetized with a south p.m . pole in the South Atlantic, while the upper part (Paganzo III) is normally magnetized with a south palaeomagnetic pole in the vicinity of poles obtained for Triassic rock formations from elsewhere in S. America. Formations of red beds from Salta province regarded as Upper Palaeozoic or Mesozoic yield a south palaeomagnetic pole in the South Atlantic corresponding to a Triassic age. Ore microscope and thermal decay curves suggest that the remanent magnetism is due to haematite.

scholarly journals New geomagnetic field observations in the South Atlantic Anomaly region

2010 ◽  
Vol 52 (1) ◽  
Author(s):  
Monika Korte ◽  
Mioara Mandea ◽  
Hans-Joachim Linthe ◽  
Anne Hemshorn ◽  
Pieter Kotzé ◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
South Atlantic ◽  
Field Observations ◽  
The South ◽  
South Atlantic Anomaly ◽  
Anomaly Region

scholarly journals Effects of solar activity and geomagnetic field on noise in CALIOP profiles above the South Atlantic Anomaly

2013 ◽  
Vol 6 (5) ◽  
pp. 8589-8602
Author(s):  
V. Noel ◽  
H. Chepfer ◽  
C. Hoareau ◽  
M. Reverdy ◽  
G. Cesana
Keyword(s):  
Solar Activity ◽  
Geomagnetic Activity ◽  
Geomagnetic Field ◽  
High Energy ◽  
South Atlantic ◽  
Noise Levels ◽  
The South ◽  
High Energy Radiation ◽  
South Atlantic Anomaly ◽  
One Year

Abstract. By documenting noise levels in 6.5 yr of nighttime measurements by the spaceborne lidar CALIOP above the South Atlantic Anomaly (SAA), we show they contain information about the evolution of upwelling high-energy radiation levels in the area. We find the amount of noisy profiles is influenced by the 11 yr cycle of solar activity, fluctuates by ±5% between 2006 and 2013, and is anticorrelated with solar activity with a 1 yr lag. The size of the SAA grows as solar activity decreases, and an overall westward shift of the SAA region is detectable. We predict SAA noise levels will increase anew after 2014, and will affect future spaceborne lidar missions most near 2020. In other areas, supposedly unaffected by incoming sunlight, nighttime noise levels are much weaker but follow the same 11 yr cycle, superimposed with a one-year cycle that affects both hemispheres similarly and could be attributed to geomagnetic activity.

POLITICAL AND STRATEGIC COORDINATION AND COOPERATION FOR DEVELOPMENT: THE CASES OF ZPCSA AND GGC

2016 ◽  
Vol 31 (2) ◽  
pp. 19-36
Author(s):  
Paulo Fagundes Visentini ◽  
Analúcia Danilevicz Pereira
Keyword(s):  
South Atlantic ◽  
Strategic Orientation ◽  
International Affairs ◽  
The South ◽  
Strategic Issues ◽  
Strategic Coordination ◽  
Regional Order ◽  
Energy Products ◽  
A Site ◽  
Political Economic

The creation of the Zone of Peace and Cooperation of the South Atlantic (ZPCSA) in 1986 and the Gulf of Guinea Commission (GGC) in 2001 was about changes in the distribution of world power. This article argues that though they emerged at different times, their strategic orientation converges in a number of areas related to the significant interests in the South Atlantic as an area of stability in the region to be marked by strong political, economic and military ties. They also converge on the ideal for development, security and greater projection of power and influence in international affairs. The South Atlantic being a route of passage and trade, as a means of access and flow of energy products, the region became a site for new calculations of regional strategic powers about world affairs. The article also argues that ZPCSA and GGC are therefore crucial for the regional order and the development of higher capacities for cooperation on strategic issues. The actual point of convergence extends to ensuring the sovereignty through dialogue between the states in the region that are involved.

Observed seasonal regimes of North-South Atlantic Ocean interbasin exchange

2019 ◽  
Author(s):  
Hamed D. Ibrahim
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
South Atlantic ◽  
Meridional Overturning Circulation ◽  
Volume Flux ◽  
The South ◽  
The North ◽  
Basin Scale ◽  
Interbasin Exchange ◽  
North And South

North and South Atlantic lateral volume exchange is a key component of the Atlantic Meridional Overturning Circulation (AMOC) embedded in Earth’s climate. Northward AMOC heat transport within this exchange mitigates the large heat loss to the atmosphere in the northern North Atlantic. Because of inadequate climate data, observational basin-scale studies of net interbasin exchange between the North and South Atlantic have been limited. Here ten independent climate datasets, five satellite-derived and five analyses, are synthesized to show that North and South Atlantic climatological net lateral volume exchange is partitioned into two seasonal regimes. From late-May to late-November, net lateral volume flux is from the North to the South Atlantic; whereas from late-November to late-May, net lateral volume flux is from the South to the North Atlantic. This climatological characterization offers a framework for assessing seasonal variations in these basins and provides a constraint for climate models that simulate AMOC dynamics.

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