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

Emmanuel Nahayo,Monika Korte

doi:10.1186/s40623-021-01563-5

Abstract

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

Highlights

Introduction TheEarth’s magnetic field variation in southern Africa has been marked by unusual changes where the field intensity has been decreasing rapidly in some of its regions
The SACFM-3 model is compared to the global models CHAOS-6- × 9, IGRF-13 (Alken et al, 2021) and groundbased data recorded at southern Africa INTERMAGNET observatories (Hermanus (HER), Hartebeesthoek (HBK), Tsumeb (TSU) and Keetmanshoop (KMH)) in “Results and discussions” section, and it is used to study the evolution of the South Atlantic Anomaly (SAA) at the Earth’s surface in the region, and investigate recent observed geomagnetic jerks and other possible abrupt changes in the linear secular variation
The parameter fl defines the shape of the Results and discussion The developed regional core field model, SACFM-3, is based on harmonic spline fitting of vector Swarm satellite data and ground-based data recorded between January 2014 and December 2019

Summary

Introduction

Introduction TheEarth’s magnetic field variation in southern Africa has been marked by unusual changes where the field intensity has been decreasing rapidly in some of its regions. A Southern Africa Core Field Model (SACFM-3) was developed combining Swarm satellite and ground-based data recorded between 2014 and 2019.

Results

Conclusion