An Audit of Geomagnetic Field in Polar and South Atlantic Anomaly Regions Over Two Centuries

Geomagnetic jerks are sudden changes in the geomagnetic field secular variation related to changes in outer core flow patterns. Finding geophysical phenomena related to geomagnetic jerks provides a vital contribution to better understand the geomagnetic field behavior. Here, we link the geomagnetic jerks occurrence with one of the most relevant features of the geomagnetic field nowadays, the South Atlantic Anomaly (SAA), which is due to the presence of reversed flux patches (RFPs) at the Core-Mantle Boundary (CMB). Our results show that minima of acceleration of the areal extent of SAA calculated using the CHAOS-7 model (CHAOS-7.2 release) coincide with the occurrence of geomagnetic jerks for the last 2 decades. In addition, a new pulse in the secular acceleration of the radial component of the geomagnetic field has been observed at the CMB, with a maximum in 2016.2 and a minimum in 2017.5. This fact, along with the minimum observed in 2017.8 in the acceleration of the areal extent of SAA, could point to a new geomagnetic jerk. We have also analyzed the acceleration of the areal extent of South American and African RFPs at the CMB related to the presence of the SAA at surface and have registered minima in the same periods when they are observed in the SAA at surface. This reinforces the link found and would indicate that physical processes that produce the RFPs, and in turn the SAA evolution, contribute to the core dynamics at the origin of jerks.

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Eccentric dipole of the geomagnetic field during the last reversal, last excursions, and the most significant Holocene anomalies

10.5194/egusphere-egu21-4237 ◽

2021 ◽

Author(s):

Alicia González-López ◽

Saioa A. Campuzano ◽

Pablo Rivera ◽

Alberto Molina-Cardín ◽

F. Javier Pavón-Carrasco ◽

...

Keyword(s):

Iron Age ◽

Spherical Harmonic ◽

Geomagnetic Field ◽

South Atlantic ◽

Mono Lake ◽

The Holocene ◽

South Atlantic Anomaly ◽

Harmonic Representation ◽

Eccentric Dipole ◽

Tilted Dipole

<p>The geomagnetic field is commonly approximated to a geocentric tilted dipole. However, a next step in the approach of the geomagnetic field is the eccentric dipole which takes the first and second terms of the spherical harmonic representation of the geomagnetic field. In this work, we analyze the behavior of the eccentric dipole during the last reversal (Matuyama &#8211; Brunhes, 780 ka), the last excursions (Laschamp, 41 ka, and Mono Lake, 34 ka), and during two interesting features of the geomagnetic field observed during the Holocene (the South Atlantic Anomaly, from 1840 AD or older, and the Levantine Iron Age Anomaly, around 1000 BC). The last reversal and excursions are studied by using the IMMAB4 and LSMOD2 paleoreconstructions, respectively. We found that for these events the center of the eccentric dipole follows a common longitude path. The Holocene anomalies have been analyzed by using two of the most up-to-date paleoreconstructions for the last 3 millennia: the SHAWQ2k and the SHAWQ Iron Age paleoreconstructions. A common longitude path has not been observed between these anomalies.</p>

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Earth’s magnetic field is probably not reversing

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1722110115 ◽

2018 ◽

Vol 115 (20) ◽

pp. 5111-5116 ◽

Cited By ~ 23

Author(s):

Maxwell Brown ◽

Monika Korte ◽

Richard Holme ◽

Ingo Wardinski ◽

Sydney Gunnarson

Keyword(s):

Magnetic Field ◽

Geomagnetic Field ◽

Extreme Event ◽

South Atlantic ◽

Field Structure ◽

Mono Lake ◽

Dipole Field ◽

South Atlantic Anomaly ◽

Cosmogenic Nuclide ◽

The Relationship

The geomagnetic field has been decaying at a rate of ∼5% per century from at least 1840, with indirect observations suggesting a decay since 1600 or even earlier. This has led to the assertion that the geomagnetic field may be undergoing a reversal or an excursion. We have derived a model of the geomagnetic field spanning 30–50 ka, constructed to study the behavior of the two most recent excursions: the Laschamp and Mono Lake, centered at 41 and 34 ka, respectively. Here, we show that neither excursion demonstrates field evolution similar to current changes in the geomagnetic field. At earlier times, centered at 49 and 46 ka, the field is comparable to today’s field, with an intensity structure similar to today’s South Atlantic Anomaly (SAA); however, neither of these SAA-like fields develop into an excursion or reversal. This suggests that the current weakened field will also recover without an extreme event such as an excursion or reversal. The SAA-like field structure at 46 ka appears to be coeval with published increases in geomagnetically modulated beryllium and chlorine nuclide production, despite the global dipole field not weakening significantly in our model during this time. This agreement suggests a greater complexity in the relationship between cosmogenic nuclide production and the geomagnetic field than is commonly assumed.

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New geomagnetic field observations in the South Atlantic Anomaly region

Annals of Geophysics ◽

10.4401/ag-4631 ◽

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

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

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-6-8589-2013 ◽

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.

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