Regional modelling of the Southern African geomagnetic field using harmonic splines

Geese, Anne; Mandea, Mioara; Lesur, Vincent; Hayn, M.

doi:10.1111/j.1365-246x.2010.04575.x

Cited by 12 publications

(11 citation statements)

References 23 publications

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“…As, currently, there are no available regional magnetic field models based on satellite data only, we compute our own regional model of the magnetic anomaly field using the localized basis functions described by Lesur (2006). This approach is a predecessor of the harmonic splines used by Geese et al (2010). The harmonics splines have also been used by Shure et al (1982) in modelling the geomagnetic field at global scale.…”

Section: Resultsmentioning

confidence: 99%

Error distribution in regional inversion of potential field data

Schachtschneider¹,

Holschneider²,

Mandea³

2010

Geophysical Journal International

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S U M M A R YAn increasing number of regional inversions of gravity and magnetic field data have recently been computed, some based on satellite and ground data, some on satellite data only. In each case it is important to quantify the errors resulting from the confined data region or the satellite parameters. In this study we investigate the error distribution of regional inversions for scalar gravity and vector geomagnetic data from satellite data only. We include the effects of satellite altitude, size of the data region, signal-to-noise ratio and spherical harmonic degree of an a priori global field model. We evaluate our results on the basis of a regional inversion of the Earth's magnetic field.

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Section: Resultsmentioning

confidence: 99%

Error distribution in regional inversion of potential field data

Schachtschneider¹,

Holschneider²,

Mandea³

2010

Geophysical Journal International

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“…Different methods to model the geomagnetic field on a regional scale were reviewed by Haines (1990). The southern African ground survey data have been used to derive various regional main field and/or secular variations models, using the methods of polynomials for the time intervals 2004-2005) and 2005(Kotzé 2011Geese et al 2011), spherical cap harmonic functions for 1975-2000 (Kotzé 2003) and harmonic splines for 1961-2001(Geese et al 2010) and 2005(Geese et al 2011. Polynomials have also been applied to model the CHAllenging Minisatellite Payload (CHAMP) satellite data of southern Africa (Nahayo and Kotzé 2012).…”

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 southern African region has also been known for many years to have high spatial and temporal field variations with strong abrupt changes in the linear geomagnetic secular variation (Mandea et al, 2007;Kotzé and Korte, 2016;Kotzé, 2020). Some scholars have recently conducted studies of rapid geomagnetic time variations in southern Africa using regional models (Geese et al, 2009(Geese et al, , 2011Nahayo and Kotzé, 2012;Nahayo et al, 2015Nahayo et al, , 2018.…”

Section: Introductionmentioning

confidence: 99%

A regional geomagnetic field model over Southern Africa derived with harmonic splines from Swarm satellite and ground-based data recorded between 2014 and 2019

Nahayo

Korte

2022

Earth Planets Space

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A regional harmonic spline geomagnetic main field model, Southern Africa Core Field Model (SACFM-3), is derived from Swarm satellite and ground-based data for the southern African region, in the eastern part of the South Atlantic Anomaly (SAA) where the field intensity continues to decrease. Using SACFM-3 and the global CHAOS-6-×9 model, a detailed study was conducted to shed light on the high spatial and temporal geomagnetic field variations over Southern Africa between 2014 and 2019. The results show a steady decrease of the radial component Z in almost the entire region. In 2019, its rate of decrease in the western part of the region has reached high values, 76 nT/year and 78 nT/year at Tsumeb and Keetmanshoop magnetic observatories, respectively. For some areas in the western part of the region the radial component Z and field intensity F have decreased in strength, from 1.0 to 1.3% and from 0.9 to 1.2%, respectively, between the epochs 2014.5 and 2019.5. There is a noticeable decrease of the field intensity from the south-western coast of South Africa expanding towards the north and eastern regions. The results show that the SAA area is continuing to grow in the region. Abrupt changes in the linear secular variation in 2016 and 2017 are confirmed in the region using ground-based data, and the X component shows an abrupt change in the secular variation in 2018 at four magnetic observatories (Hermanus, Hartebeesthoek, Tsumeb and Keetmanshoop) that needs further investigation. The regional model SACFM-3 reflects to some extent these fast core field variations in the Z component at Hermanus, Hartebeesthoek and Keetmanshoop observatories. Graphical Abstract

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Regional modelling of the Southern African geomagnetic field using harmonic splines

Cited by 12 publications

References 23 publications

Error distribution in regional inversion of potential field data

Error distribution in regional inversion of potential field data

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

A regional geomagnetic field model over Southern Africa derived with harmonic splines from Swarm satellite and ground-based data recorded between 2014 and 2019

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