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The South Atlantic Anomaly

Posted on: July 22, 2020

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New insight into Earth's crust, mantle and outer core interactions

Earth's magnetic field is weakening – but it's not about to reverse

South Atlantic Anomaly





  1. The Mysterious Anomaly Weakening Earth’s Magnetic Field:  Satellite data from ESA show a mysterious anomaly weakening Earth’s magnetic field continues to evolve, with the most recent observations showing we could soon be dealing with more than one of these strange phenomena.
  2. The South Atlantic Anomaly is a vast expanse of reduced magnetic intensity in Earth’s magnetic field, extending all the way from South America to southwest Africa. Since our planet’s magnetic field acts as a kind of shield – protecting Earth from solar winds and cosmic radiation, any reduction in its strength is an important event we need to monitor closely.
  3. These changes could ultimately have significant implications for our planet. The ESA notes that the most significant effects right now are largely limited to technical malfunctions on board satellites and spacecraft, which can be exposed to a greater amount of charged particles in low-Earth orbit as they pass through the South Atlantic Anomaly in the skies above South America and the South Atlantic Ocean.
  4. In the last two centuries, Earth’s magnetic field has lost about 9 percent of its strength on average assisted by a drop in minimum field strength in the South Atlantic Anomaly from approximately 24,000 nanoteslas to 22,000 nanoteslas over the past 50 years. Exactly why this is happening remains a mystery. Earth’s magnetic field is generated by electrical currents produced by a swirling mass of liquid iron within the outer core of our planet, but while this phenomenon appears stable at any given moment, over vast timescales, it’s never really still.
  5. Research has shown that Earth’s magnetic field is constantly in a state of flux, and every few hundred thousand years, Earth’s magnetic field flips, with the north and south magnetic poles swapping places. That process could actually occur more frequently than people think, but while scientists continually debate when we might next witness such an event, even the regular, wandering movements of Earth’s magnetic poles keep geophysicists guessing.
  6. It is not fully clear how those reversals might be tied to what’s currently going on with the South Atlantic Anomaly – which some have suggested could be caused by a vast reservoir of dense rock underneath Africa called the African Large Low Shear Velocity Province. What is certain, though, is that the South Atlantic Anomaly is not sitting still. Since 1970, the anomaly has been growing in size, as well as moving westward at a pace of approximately 20 kilometres (12 miles) per year. But that’s not all.
  7. This suggests the whole thing could be in the process of splitting up into two separate cells – with the original centred above the middle of South America, and the new, emerging cell appearing to the east, hovering off the coast of southwest Africa. The new, eastern minimum of the South Atlantic Anomaly has appeared over the last decade and in recent years is developing vigorously. The challenge now is to understand the processes in Earth’s core driving these changes.
  8. Just how the anomaly will develop from here is unknown, but previous research has suggested disruptions in the magnetic field like this one might be recurrent events that take place every few hundred years. Whether that’s what we’re witnessing now isn’t fully clear – or how a split anomaly might end up playing out – but scientists are watching closely.




  1. CITATION: Elevated paleomagnetic dispersion at Saint Helena suggests long-lived anomalous behavior in the South Atlantic.  Yael A. Engbers, Andrew J. Biggin, and Richard K. Bono, PNAS, July 20, 2020  [LINK]
  2. ABSTRACT:  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.
  3. ALSO NOTED BY THE AUTHORS:  Earth’s magnetic field is generated in the outer core by convecting liquid iron and protects the atmosphere from solar wind erosion. The most substantial anomaly in the magnetic field is in the South Atlantic (SA). An important conjecture is that this region could be a site of recurring anomalies because of unusual core−mantle conditions, but this has not previously been tested on geological timescales. With paleodirectional data from rocks from Saint Helena, an island in the SA, we show that the directional behavior of the magnetic field in the SA did indeed vary anomalously between ∼8 million and 11 million years ago. This supports the hypothesis of core−mantle interaction being manifest in the long-term geomagnetic field behavior of this region.





  1. Hartmann, Gelvam A., and Igor G. Pacca. “Time evolution of the South Atlantic magnetic anomaly.” Anais da Academia Brasileira de Ciências 81.2 (2009): 243-255.  ABSTRACT: The South Atlantic Magnetic Anomaly (SAMA) is one of the most outstanding anomalies of the geomagnetic field. The SAMA secular variation was obtained and compared to the evolution of other anomalies using spherical harmonic field models for the 1590-2005 period. An analysis of data from four South American observatories shows how this large scale anomaly affected their measurements. Since SAMA is a low total field anomaly, the field was separated into its nondipolar, quadrupolar and octupolar parts. The time evolution of the non-dipole/total, quadrupolar/total and octupolar/total field ratios yielded increasingly high values for the South Atlantic since 1750. The SAMA evolution is compared to the evolution of other large scale surface geomagnetic features like the North and the South Pole and the Siberia High, and this comparison shows the intensity equilibrium between these anomalies in both hemispheres. The analysis of non-dipole fields in historical period suggests that SAMA is governed by (i) quadrupolar field for drift, and (ii) quadrupolar and octupolar fields for intensity and area of influence. Furthermore, our study reinforces the possibility that SAMA may be related to reverse fluxes in the outer core under the South Atlantic region.
  2. Abdu, M. A., et al. “South Atlantic magnetic anomaly ionization: A review and a new focus on electrodynamic effects in the equatorial ionosphere.” Journal of Atmospheric and Solar-Terrestrial Physics 67.17-18 (2005): 1643-1657ABSTRACTSatellite observations of enhanced energetic particle fluxes in the South Atlantic Magnetic Anomaly (SAMA) region have been supported by ground-based observations of enhanced ionization induced by particle precipitation in the ionosphere over this region. Past observations using a variety of instruments such as vertical sounding ionosondes, riometers and VLF receivers have provided evidences of the enhanced ionization due to energetic particle precipitation in the ionosphere over Brazil. The extra ionization at E-layer heights could produce enhanced ionospheric conductivity within and around the SAMA region. The energetic particle ionization source that is operative even under “quiet” conditions can undergo significant enhancements during magnetospheric storm disturbances, when the geographic region of enhanced ionospheric conductivity can extend to magnetic latitudes closer to the equator where the magnetic field line coupling of the E and F regions plays a key role in the electrodynamics of the equatorial ionosphere. Of particular interest are the sunset electrodynamic processes responsible for equatorial spread F/plasma bubble irregularity generation and related dynamics (zonal and vertical drifts, etc.). The SAMA represents a source of significant longitudinal variability in the global description of the equatorial spread F irregularity phenomenon. Recent results from digital ionosondes operated at Fortaleza and Cachoeira Paulista have provided evidence that enhanced ionization due to particle precipitation associated with magnetic disturbances, in the SAMA region, can indeed significantly influence the equatorial electrodynamic processes leading to plasma irregularity generation and dynamics. Disturbance magnetospheric electric fields that penetrate the equatorial latitudes during storm events seem to be intensified in the SAMA region based on ground-based and satellite-borne measurements. This paper will review our current understanding of the influence of SAMA on the equatorial electrodynamic processes from the perspective outlined above.
  3. Pinto Jr, O., et al. “The South Atlantic magnetic anomaly: three decades of research.” Journal of Atmospheric and Terrestrial Physics 54.9 (1992): 1129-1134.  ABSTRACT:  This brief review of advances in our understanding of some physical processes related to the South Atlantic Magnetic Anomaly (SAMA) is intended to highlight specific issues on which further research is needed. The discussion focuses on the origin of the SAMA, the geomagnetic storm-related effects and the impact of the SAMA on orbiting spacecraft.
  4. Freden, Stanley C., and George A. Paulikas. “Trapped protons at low altitudes in the South Atlantic magnetic anomaly.” Journal of Geophysical Research 69.7 (1964): 1259-1269.  ABSTRACT:  The fluxes of protons from 5 to 20 Mev and 60 to 120 Mev were measured in September and October 1962 at low altitudes over the South Atlantic magnetic anomaly. The ratio of the fluxes in these two energy intervals is essentially independent of B and is independent of L below L ≃ 1.4 but changes rapidly for L > 1.4. The flux in the 5‐ to 20‐Mev interval indicates that the spectrum turns back up below the local minimum (at L ≳ 1.5) near 20 Mev. This result is consistent with an increased absorption in the atmosphere for the albedo neutrons near 20 Mev. The integral flux above 31 Mev appears to have increased by a factor of about 3 at the lower L values and higher B values since the Explorer 4 measurements. This would be expected if the source had stayed essentially constant and the atmospheric density had decreased in these regions of space as we moved away from the period of solar maximum.
  5. Pinto Jr, O., and W. D. Gonzalez. “Energetic electron precipitation at the South Atlantic Magnetic Anomaly: a review.” Journal of Atmospheric and Terrestrial Physics 51.5 (1989): 351-365.  ABSTRACT;  This paper reviews the status of knowledge concerning energetic electron precipitation at the South Atlantic Magnetic Anomaly (SAMA). The main purpose is to place recent results in the context of the long-standing problems about energetic electron precipitation at the SAMA region. A synopsis of results achieved in the last two decades, in relation to the various physical mechanisms responsible for precipitating energetic electrons, are also presented. The major uncertainties in the understanding of the energetic electron precipitation at the SAMA include: (1) temporal and spatial precipitation changes from magnetically quiet to disturbed periods; (2) the role of wave-induced precipitation processes.
  6. Zmuda, A. J. “Ionization enhancement from Van Allen electrons in the South Atlantic magnetic anomaly.” Journal of Geophysical Research 71.7 (1966): 1911-1917.  ABSTRACTSatellite particle observations have shown that a longitudinal dependence exists for trapped electrons at B‐L points extending into the lower atmosphere over the South Atlantic anomaly. The longitudinal variation results from the precipitation and loss of trapped particles drifting through the anomaly and is a regular characteristic of the Van Allen radiation zones. The trapped electrons that collide with atmospheric constituents produce ionization and represent a significant source of local enhancements in the D and lower E regions of the ionosphere. Regions where electron‐ion augmentations may be expected are also discussed.




The Engbers et al paper of July 2020 presented above has explained the South Atlantic magnetic anomaly as a natural and well understood creation of known periodic anomalies in the outer core and mantle. In the bibliography presented above we find that the South Atlantic Anomaly, referred to as “SAMA” in the literature, has been a well understood magnetic phenomenon in the satellite era going back to the 1960s. In this context, it does not appear that the SAMA event of May 2020 was unusual. The only mysterious part of the May 2020 event is that it had been elevated to alarmism not unlike the climate change alarmism that appears to be the new normal for scientific research. We conclude from these findings that in the climate change era, alarmism has now been incorporated into the scientific method for all research questions having to do with the planet now claimed by climate science as being threatened to extinction by human activity in the form of burning fossil fuels. This implies that therefore the planet is now under the care of humans who must take care of the planet all the way down to the mantle and the core,  because it is no longer able to care for itself as it had done for billions of years before the humans came along.  RELATED POST [LINK]

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