On the Observability of the Time-Variable Lithospheric Signal in Satellite Magnetic Data
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The lithospheric magnetic field, which is one of the main objectives of ESA’s mission Swarm, is slowly varying in time due to an induced component. This variation is small (usually it is omitted in the lithospheric modelling) but recent advances in processing strategies and still-growing amount of satellite data open questions whether such an effect should be considered in the development of the lithospheric models—when using data from missions like CHAMP and Swarm. This effect can now be estimated over a period of 17 years (since the launch of CHAMP), and it is shown how the satellite measurements (over the observable part of the spectrum) can be referenced to one common epoch. For this purpose, we first inverted the magnetic field vector from CHAOS-6 over degrees 21–120, after subtraction of a remanent model, to a vertically integrated susceptibility map. Using this susceptibility distribution and taking into account the evolving core fields from the CHAOS-6 model, the time-varying lithospheric signal is computed. The results depend on the time span and the altitude considered, e.g., an altitude of 400 km and a span of 17 years can produce more than 0.5 nT variations resulting in a peak-to-peak value of nearly 1 nT. The vertically integrated quantities appear to be a useful choice for parameterising lithospheric time variations, also for providing data corrections at the satellite altitude. The effect of the choice of the core field, which enters the inversion, on the lithospheric time variation is also studied—this effect is found less important even for core fields 20 years apart.
KeywordsGeomagnetic field Lithosphere Swarm Time variation
Josef Sebera acknowledges the European Space Agency for providing an inspiring environment in which a large part of this study was carried out during the research fellowship. Eldar Baykiev was supported by the Research Council of Norway as part of the project “Swarm Explorer: Combined use of satellite and airborne magnetic field data to explore lithospheric magnetization”, No. 222678. Special thanks go to Leonardo Uieda for his gravity calculation code that was used to create magnetic tesseroids and to Martin Pitoňák for the discussion on the VCE method. Aleš Bezděk was supported by the project LG15003. The editor-in-chief and the anonymous reviewers are acknowledged for the help with the manuscript. We also thank the authors of CHAOS-6 for making the model public at http://www.spacecenter.dk.
- Hildebrand FB (1987) Introduction to numerical analysis. Courier Dover Publications, MineolaGoogle Scholar
- Hulot G, Sabaka T, Olsen N, Fournier A (2015) 5.02—the present and future geomagnetic field. In: Schubert G (ed) Treatise on geophysics, 2nd edn. Elsevier, Oxford, pp 33–78. https://doi.org/10.1016/B978-0-444-53802-4.00096-8 Google Scholar
- Jackson A (1994) Statistical treatment of crustal magnetization. Geophys J Int 119(3):991–998Google Scholar
- Kusche J (2003b) Noise variance estimation and optimal weight determination for GOCE gravity recovery. Adv Geosci 1:81–85Google Scholar
- Laske G, Masters G, Ma Z, Pasyanos M (2013) Update on CRUST1.0—A 1-degree Global Model of Earth’s CrustGoogle Scholar
- Olsen N, Stolle C (2012) Satellite geomagnetism. Ann Rev Earth Planet Sci 40(1):441–465. https://doi.org/10.1146/annurev-earth-042711-105540 Google Scholar
- Olsen N, Holme R, Hulot G, Sabaka T, Neubert T, Tøffner-Clausen L, Primdahl F, Jørgensen J, Léger JM, Barraclough D, Bloxham J, Cain J, Constable C, Golovkov V, Jackson A, Kotzé P, Langlais B, Macmillan S, Mandea M, Merayo J, Newitt L, Purucker M, Risbo T, Stampe M, Thomson A, Voorhies C (2000) Ørsted initial field model. Geophys Res Lett 27(22):3607–3610. https://doi.org/10.1029/2000GL011930 Google Scholar
- Purucker M, Whaler K (2015) 5.06—crustal magnetism. In: Schubert G (ed) Treatise on geophysics, 2nd edn. Elsevier, Oxford, pp 185–218. https://doi.org/10.1016/B978-0-444-53802-4.00100-7 Google Scholar
- Stolle C et al (2013) Product specification for L2 products and auxiliary products. Doc no SW-DS-DTU-GS-0001Google Scholar