Abstract
Recent models of Earth’s core magnetic field based on geomagnetic satellite data suggest an existence of interannual core dynamics. The related magnetic signal of the interannual core dynamics is found to be small, which makes an observational detection of interannual variations of the core flow and the associated oscillations of the core angular momentum (CAM) difficult. However, it has been shown that the phase of the interannual oscillation is robustly determined, according to numerous CAM computations from diverse core flow models that are all estimated as a result of inverting a single geomagnetic model C3FM2. Here, we show that the phase identification depends on the secular acceleration (SA) of a geomagnetic model. Estimates of the phase still vary with geomagnetic models, C3FM2, gufm1, and COV-OBS, for the pre-satellite era, whose differences are readily recognisable in their SA representations. None of them may be an optimal model for describing the SA. Compared with the SA of a satellite model GRIMM3, C3FM2 is overdamped in time, but it may be improved for resolving the interannual CAM oscillations by properly modifying its temporal smoothness in reference to the SA of satellite models.
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Notes
- 1.
The second-order time derivative of core field time series is commonly referred to as secular acceleration (SA) such as in Wardinski et al (2008), while the first-order time derivative as secular variation (SV).
- 2.
This time-dependent geomagnetic field model consists of two variants, each constructed with and without the frozen-flux constraint (Lesur et al 2010), In this chapter, ‘C3FM2’ always refers to the latter only.
References
Asari, S., Lesur, V.: Radial vorticity constraint in core flow modeling. J. Geophys. Res. 116 (2011). doi:10.1029/2011JB008267
Asari, S., Wardinski, I.: On magnetic estimation of Earth’s core angular momentum variation. J. Geophys. Res. 120 (2015). doi:10.1002/2014JB011458
Bloxham, J.: Dynamics of angular momentum in the Earth’s core. Ann. Rev. Earth Planet. Sci. 26, 501–517 (1998)
Chulliat, A., Maus, S.: Geomagnetic secular acceleration, jerks, and a localized standing wave at the core surface from 2000 to 2010. J. Geophys. Res. 119 (2014). doi:10.1002/2013JB010604
Chulliat, A., Hulot, G., Newitt, L.R.: Magnetic flux expulsion from the core as a possible cause of the unusually large acceleration of the north magnetic pole during the 1990s. J. Geophys. Res. 115 (2010). doi:10.1029/2009JB007143
Finlay, C.C., Olsen, N., Kotsiaros, S., Gillet, N., Tøffner-Clausen, L.: Recent geomagnetic secular variation from Swarm and ground observatories as estimated in the CHAOS-6 geomagnetic field model. Earth Planets Space 68(1), 112 (2016). doi:10.1186/s40623-016-0486-1. http://dx.doi.org/10.1186/s40623-016-0486-1
Friis-Christensen, E., Lühr, H., Hulot, G.: Swarm: a constellation to study the earth’s magnetic field. Earth Planets Space 58, 351–358 (2006). doi:10.1186/BF03351933
Gillet, N., Jault, D., Canet, E., Fournier, A.: Fast torsional waves and strong magnetic field within the Earth’s core. Nature 465, 74–77 (2010)
Gillet, N., Jault, D., Finlay, C., Olsen, N.: Stochastic modelling of the Earth’s magnetic field: inversion for covariances over the observatory era. Geochem. Geophys. Geosyst. 14, 766–786 (2013). doi:10.1002/ggge.20041
Gillet, N., Jault, D., Finlay, C.C.: Planetary gyre, time-dependent eddies, torsional waves, and equatorial jets at the Earth’s core surface. J. Geophys. Res. 120 (2015). doi:10.1002/2014JB011786
Holme, R.: Large scale flow in the core. In: Schubert, G. (ed.) Treatise in Geophysics, Core Dynamics, Elsevier, vol. 8, pp. 91–113 (2015)
Holme, R., de Viron, O.: Characterization and implications of intradecadal variations in length of day. Nature 499, 202–204 (2013)
Hulot, G., Le Mouël, J.L., Wahr, J.: Taking into account truncation problems and geomagnetic model accuracy in assessing computed flows at the core-mantle boundary. Geophys. J. Int. 108, 224–246 (1992)
Jackson, A.: Time-dependency of tangentially geostrophic core surface motions. Phys. Earth Planet. Inter. 103, 293–311 (1997)
Jackson, A., Jonker, A.R.T., Walker, M.R.: Four centuries of geomagnetic secular variation from historical records. Philos. Trans. R. Soc. Lond. A 358, 957–990 (2000)
Jault, D., Gire, C., Le Mouël, J.L.: Westward drift, core motion and exchanges of angular momentum between core and mantle. Nature 333, 353–356 (1988)
Le Mouël, J.L.: Outer-core geostrophic flow and secular variation of Earth’s geomagnetic field. Nature 311, 734–735 (1984)
Lesur, V., Wardinski, I., Asari, S., Minchev, B., Mandea, M.: Modelling the Earth’s core magnetic field under flow constraint. Earth Planets Space 62, 503–516 (2010)
Neubert, T., Mandea, M., Hulot, G., von Frese, R., Primdahl, F., Jørgensen, J.L., Friis-Christensen, E., Stauning, P., Olsen, N., Risbo, T.: Ørsted satellite captures high-precision geomagnetic field data. Eos, Transactions American Geophysical Union, vol. 82(7), pp. 81–88 (2001). doi:10.1029/01EO00043. http://dx.doi.org/10.1029/01EO00043
Pais, M.A., Jault, D.: Quasi-geostrophic flows responsible for the secular variation of the Earth’s magnetic field. Geophys. J. Int. 173, 421–443 (2008)
Reigber, C., Lühr, H., Schwintzer, P.: CHAMP mission status. Adv. Space Res. 30, 129–134 (2002). doi:10.1016/S0273-1177(02)00276-4
Silva, L., Jackson, L., Mound, J.: Assessing the importance and expression of the 6 year geomagnetic oscillation. J. Geophys. Res. 117 (2012). doi:10.1029/2012JB009405
Torta, J.M., Pavón-Carrasco, F.J., Marsal, S., Finlay, C.C.: Evidence for a new geomagnetic jerk in 2014. Geophys. Res. Lett. 42(19), 7933–7940 (2015). doi:10.1002/2015GL065501, 2015GL065501
Wardinski, I., Lesur, V.: An extended version of the C3FM geomagnetic field model: application of a continuous frozen-flux constraint. Geophys. J. Int. 189, 1409–1429 (2012)
Wardinski, I., Holme, R., Asari, S., Mandea, M.: The 2003 geomagnetic jerk and its relation to the core surface flows. Earth Planet. Sci. Lett. 267, 468–481 (2008)
Zatman, S., Bloxham, J.: Torsional oscillations and the magnetic field within the Earth’s core. Nature 388, 760–763 (1997)
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Asari, S., Wardinski, I. (2018). Interannual Fluctuations of the Core Angular Momentum Inferred from Geomagnetic Field Models. In: Lühr, H., Wicht, J., Gilder, S.A., Holschneider, M. (eds) Magnetic Fields in the Solar System. Astrophysics and Space Science Library, vol 448. Springer, Cham. https://doi.org/10.1007/978-3-319-64292-5_4
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DOI: https://doi.org/10.1007/978-3-319-64292-5_4
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