The magnetic field changing over the southern African continent: a unique behaviour

Mandéa, Mioara; Korte, Monika; Mozzoni, D. T.; Kotzé, P. B.

doi:10.2113/gssajg.110.2-3.193

Cited by 29 publications

(21 citation statements)

References 14 publications

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“…There, the field intensity reaches less than 60% of the field strength at comparable latitudes. The loca-tion of the minimum has moved from Southern Africa to South America over the last 300 yr (Mandea et al, 2007;Hartmann and Pacca, 2009). The total dipole strength has diminished by 9% from 1840 to 2015, although the field decrease occurs non-uniformly over the globe.…”

Section: Introduction: the Particle Flux In The South Atlantic Anomalymentioning

confidence: 99%

The South Atlantic Anomaly throughout the solar cycle

Domingos

Jault

Pais

et al. 2017

Earth and Planetary Science Letters

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The Sun-Earth's interaction is characterized by a highly dynamic electromagnetic environment, in which the magnetic field produced in the Earth's core plays an important role. One of the striking characteristics of the present geomagnetic field is denoted the South Atlantic Anomaly (SAA) where the total field intensity is unusually low and the flux of charged particles, trapped in the inner Van Allen radiation belts, is maximum. Here, we use, on one hand, a recent geomagnetic field model, CHAOS-6, and on the other hand, data provided by different platforms (satellites orbiting the Earth -POES NOAA for 1998 and CALIPSO for 2006. Evolution of the SAA particle flux can be seen as the result of two main effects, the secular variation of the Earth's core magnetic field and the modulation of the density of the inner radiation belts during the solar cycle, as a function of the L value that characterises the drift shell, where charged particles are trapped. To study the evolution of the particle flux anomaly, we rely on a Principal Component Analysis (PCA) of either POES particle flux or CALIOP dark noise. Analysed data are distributed on a geographical grid at satellite altitude, based on a L-shell reference frame constructed from the moving eccentric dipole. Changes in the main magnetic field are responsible for the observed westward drift. Three PCA modes account for the time evolution related to solar effects. Both the first and second modes have a good correlation with the thermospheric density, which varies in response to the solar cycle. The first mode represents the total intensity variation of the particle flux in the SAA, and the second the movement of the anomaly between different L-shells. The proposed analysis allows us to well recover the westward drift rate, as well as the latitudinal and longitudinal solar cycle oscillations, although the analysed data do not cover a complete (Hale) magnetic solar cycle (around 22 yr). Moreover, the developments made here would enable us to forecast the impact of the South Atlantic Anomaly on space weather. A model of the evolution of the eccentric dipole field (magnitude, offset and tilt) would suffice, together with a model for the solar cycle evolution.

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Section: Introduction: the Particle Flux In The South Atlantic Anomalymentioning

confidence: 99%

The South Atlantic Anomaly throughout the solar cycle

Domingos

Jault

Pais

et al. 2017

Earth and Planetary Science Letters

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“…As the changes in the geomagnetic field are not uniformly spread across the globe (Bullard 1948), regions exist where the field changes are more rapid than elsewhere, like Southern Africa (Kotzé 2003;Mandea et al 2007) and the South Atlantic ocean. Rapidly drifting core spots moving westwards towards South America have been ascribed by Bloxham and Gubbins (1985) to explain the observed high SV in Southern Africa.…”

Section: Introductionmentioning

confidence: 99%

The 2014 geomagnetic jerk as observed by southern African magnetic observatories

Kotzé

2017

Earth Planets Space

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Rapid secular variation pulses in the Earth's geomagnetic field have been identified during the last decade. In particular, the 2014 jerk is the latest in a series of localised rapid secular variation events observed at the Earth's surface which are thought to be the result of rapid oscillations at the core surface approximately at a depth of 3000 km. In Southern Africa, the 2014 jerk has been analysed using data from four observatories located at Hermanus, Hartebeesthoek, Keetmanshoop and Tsumeb and found that this event occurred with varying strengths in the different components at a particular observatory, while different observatories in the region showed strong individual characteristics. The changes in the secular variation patterns at individual magnetic observatories in this study took place in an area characterised by rapid changes in the geomagnetic field with time. Of particular interest is that global field models like CHAOS-6 and POMME 10 derived from various combinations of ground and satellite data do not always indicate similar short-period patterns in X, Y and Z as revealed by observatory measurements. This has been confirmed by comparing the secular variation pattern at the Kourou magnetic observatory located in French Guiana, a station close to the current centre of the South Atlantic Anomaly.

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“…Southern Africa lies on the brink of the South Atlantic Anomaly (SAA) where the field intensity is up to 30 % weaker than in comparable latitudes, and the secular variation is particularly strong in this region (e.g. Mandea et al 2007). These strong and inhomogeneous field changes call for frequent updates of regional field component maps for practical applications and for good secular variation descriptions.…”

Section: Introductionmentioning

confidence: 99%

Morphology of the southern African geomagnetic field derived from observatory and repeat station survey observations: 2005–2014

Kotzé

Korte

2016

Earth Planet Sp

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Geomagnetic field data from four observatories and annual field surveys between 2005 and 2015 provide a detailed description of Earth's magnetic field changes over South Africa, Namibia and Botswana on time scales of less than 1 year. The southern African area is characterized by rapid changes in the secular variation pattern and lies in close proximity to the South Atlantic Anomaly (SAA) where the geomagnetic field intensity is almost 30 % weaker than in other regions at similar latitudes around the globe. Several geomagnetic secular acceleration (SA) pulses (geomagnetic jerks) around 2007, 2010 and 2012 could be identified over the last decade in southern Africa. We present a new regional field model for declination and horizontal and vertical intensity over southern Africa (Southern African REGional (SAREG)) which is based on field survey and observatory data and covering the time interval from 2005 to 2014, i.e. including the period between 2010 and 2013 when no low Earth-orbiting vector field satellite data are available. A comparative evaluation between SAREG and global field models like CHAOS-5, the CHAMP, Orsted and SAC-C model of the Earth's magnetic field and International Geomagnetic Reference Field (IGRF-12) reveals that a simple regional field model based on a relatively dense ground network is able to provide a realistic representation of the geomagnetic field in this area. We particularly note that a global field model like CHAOS-5 does not always indicate similar short-period patterns in the field components as revealed by observatory data, while representing the general secular variation reasonably well during the time interval without near-Earth satellite vector field data. This investigation further shows the inhomogeneous occurrence and distribution of secular variation impulses in the different geomagnetic field components and at different locations in southern African.

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The magnetic field changing over the southern African continent: a unique behaviour

Cited by 29 publications

References 14 publications

The South Atlantic Anomaly throughout the solar cycle

The South Atlantic Anomaly throughout the solar cycle

The 2014 geomagnetic jerk as observed by southern African magnetic observatories

Morphology of the southern African geomagnetic field derived from observatory and repeat station survey observations: 2005–2014

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