Abstract
We aim to obtain a modal decomposition of the internal geomagnetic field. In order to do so, we perform a principal component analysis of two virtual observatory datasets, with 4-month sampling time, from the CHAMP (2001–2009) and Swarm (2014–2017) satellite records. The spatial patterns of well-resolved modes calculated from the three field components all have internal origin as expected for these datasets, except for one Swarm mode. For both datasets, we find that the modes with the shortest timescales have also the smallest length scales as expected from a physical standpoint. Also, the energy ordering of the modes is from the least to the most variable, in agreement with independent results on the main field data spectrum. This is not achieved in regularised inversions of geomagnetic field data into time-varying spherical harmonic decomposition, where the highest degree terms have also the poorest time resolution. The improved accuracy of Swarm data is reflected in the lower level of the noise variance.
Highlights
Over more than a century, the temporal variations of the Earth’s magnetic field have been mainly monitored by continuous recordings in geomagnetic observatories
We showed that Principal component analysis (PCA) is an interesting alternative to the widely used spherical harmonic (SH) by decomposing the signal into decorrelated modes
PCA seems to more retrieve a behaviour where the most rapid oscillations come from the smallest scale features, which is expected on a physical ground
Summary
Over more than a century, the temporal variations of the Earth’s magnetic field have been mainly monitored by continuous recordings in geomagnetic observatories. The number of observatories has steadily increased, their geographic coverage remains highly uneven. To overcome this difficulty, satellite data are available, albeit for only the past two decades. Recent magnetic field models have been constructed from measurements obtained from low Earth orbiting satellites carrying magnetometers, mainly Ørsted, CHAMP, SAC-C and Swarm. These satellite missions are short in comparison with the correlation times of the Earth’s core magnetic field (Hulot and Le Mouël 1994). Lack of satellite vectorial data between September 2010 (de-orbiting of CHAMP) and November 2013 (launch of Swarm mission) has contributed to the decrease in spatial resolution
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
