Observed periodicities and the spectrum of field variations in Holocene magnetic records

Panovska, Sanja; Finlay, Christopher C.; Hirt, Ann M.

doi:10.1016/j.epsl.2013.08.010

Cited by 18 publications

(11 citation statements)

References 48 publications

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“…This was observed from both paleomagnetic records (Constable and Johnson 2005 ; Panovska et al. 2013 ) and dynamo calculations (Olson et al. 2012 ; Buffett and Matsui 2015 ; Bouligand et al.…”

Section: Methodsmentioning

confidence: 70%

“…Investigations on the frequency spectrum of this latter coefficient instead show a f −2 dependence for intermediate frequencies from about 10 −5 to 10 −2 years −1 . This was observed from both paleomagnetic records (Constable and Johnson 2005;Panovska et al 2013) and dynamo calculations (Olson et al 2012;Buffett and Matsui 2015;Bouligand et al 2016). To account for this effect, we modify the AR-2 prior for the axial dipole g 0 1 in COV-OBS.x2, in comparison with previous COV-OBS models.…”

Section: Stochastic Prior For the Axial Dipolementioning

confidence: 96%

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COV-OBS.x2: 180 years of geomagnetic field evolution from ground-based and satellite observations

Huder

Gillet

Finlay

et al. 2020

Earth Planets Space

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We present the geomagnetic field model COV-OBS.x2 that covers the period 1840–2020. It is primarily constrained by observatory series, satellite data, plus older surveys. Over the past two decades, we consider annual differences of 4-monthly means at ground-based stations (since 1996), and virtual observatory series derived from magnetic data of the satellite missions CHAMP (over 2001–2010) and Swarm (since 2013). A priori information is needed to complement the constraints carried by geomagnetic records and solve the ill-posed geomagnetic inverse problem. We use for this purpose temporal cross-covariances associated with auto-regressive stochastic processes of order 2, whose parameters are chosen so as to mimic the temporal power spectral density observed in paleomagnetic and observatory series. We aim this way to obtain as far as possible realistic posterior model uncertainties. These can be used to infer for instance the core dynamics through data assimilation algorithms, or an envelope for short-term magnetic field forecasts. We show that because of the projection onto splines, one needs to inflate the formal model error variances at the most recent epochs, in order to account for unmodeled high frequency core field changes. As a by-product of the core field model, we co-estimate the external magnetospheric dipole evolution on periods longer than 2 years. It is efficiently summarized as the sum of a damped oscillator (of period 10.5 years and decay rate 55 years), plus a short-memory (6 years) damped random walk.

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Section: Methodsmentioning

confidence: 70%

Section: Stochastic Prior For the Axial Dipolementioning

confidence: 96%

COV-OBS.x2: 180 years of geomagnetic field evolution from ground-based and satellite observations

Huder

Gillet

Finlay

et al. 2020

Earth Planets Space

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“…The geomagnetic signal emanating from Earth's convecting fluid outer core contains energy over a wide range of time scales, from the longest paleomagnetic features on hundreds of million years down to the shortest variations observed over years and less at observatories and in satellite surveys. Throughout this range, time series of the palaeomagnetic dipole (Constable & Johnson, 2005;Panovska et al, 2013) as well as series of the field components at ground observatories (De Santis et al, 2003;Lesur et al, 2018) support the existence of several power-law ranges in the geomagnetic frequency power spectrum. At centennial periods and longer, synthetic time series produced by numerical simulations of the geodynamo have been used to relate the properties of this spectrum to key features of Earth's core geodynamics and magnetohydrodynamics (Olson et al, 2012) and to calibrate stochastic evolution models describing these processes (Buffett & Matsui, 2015;Meduri & Wicht, 2016).…”

Section: Introductionmentioning

confidence: 69%

The interplay of fast waves and slow convection in geodynamo simulations nearing Earth’s core conditions

Aubert

Gillet

2021

Geophysical Journal International

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Summary Ground observatory and satellite-based determinations of temporal variations in the geomagnetic field probe a decadal to annual time scale range where Earth’s core slow, inertialess convective motions and rapidly propagating, inertia-bearing hydromagnetic waves are in interplay. Here we numerically model and jointly investigate these two important features with the help of a geodynamo simulation that (to date) is the closest to the dynamical regime of Earth’s core. This model also considerably enlarges the scope of a previous asymptotic scaling analysis, which in turn strengthens the relevance of the approach to describe Earth’s core dynamics. Three classes of hydrodynamic and hydromagnetic waves are identified in the model output, all with propagation velocity largely exceeding that of convective advection: axisymmetric, geostrophic Alfvén torsional waves, and non-axisymmetric, quasi-geostrophic Alfvén and Rossby waves. The contribution of these waves to the geomagnetic acceleration amounts to an enrichment and flattening of its energy density spectral profile at decadal time scales, thereby providing a constraint on the extent of the f−4 range observed in the geomagnetic frequency power spectrum. As the model approaches Earth’s core conditions, this spectral broadening arises because the decreasing inertia allows for waves at increasing frequencies. Through non-linear energy transfers with convection underlain by Lorentz stresses, these waves also extract an increasing amount of energy from the underlying convection as their key time scale decreases towards a realistic value. The flow and magnetic acceleration energies carried by waves both linearly increase with the ratio of the magnetic diffusion time scale to the Alfvén time scale, highlighting the dominance of Alfvén waves in the signal and the stabilising control of magnetic dissipation at non-axisymmetric scales. Extrapolation of the results to Earth’s core conditions supports the detectability of Alfvén waves in geomagnetic observations, either as axisymmetric torsional oscillations or through the geomagnetic jerks caused by non-axisymmetric waves. In contrast, Rossby waves appear to be too fast and carry too little magnetic energy to be detectable in geomagnetic acceleration signals of limited spatio-temporal resolution.

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“…Nilsson et al (2011) identified a 1350 yr cycle in the dipole tilt for the last 9 kyr from United States, Finland, Japan, Australia and Argentina sediment records. On the contrary, Panovska et al (2013) found no evidence for globally periodic signals from nearly 50 sediment records. The two aforementioned studies focused on searching for periodicities in paleodirections but not in the paleointensity of the geomagnetic field.…”

Section: Introductionmentioning

confidence: 82%

“…Yokoyama and Yamazaki 2000;Yamazaki and Oda 2002;Roberts et al 2003;Thouveny et al 2008). More recently, Nilsson et al (2011) and Panovska et al (2013) analyzed the secular variation over the Holocene making use of sediment magnetic records distributed around the world. Nilsson et al (2011) identified a 1350 yr cycle in the dipole tilt for the last 9 kyr from United States, Finland, Japan, Australia and Argentina sediment records.…”

Section: Introductionmentioning

confidence: 99%

Characteristic periods of the paleosecular variation of the Earth's magnetic field during the Holocene from global paleoreconstructions

González-López

Campuzano

Molina‐Cardín

et al. 2021

Physics of the Earth and Planetary Interiors

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Observed periodicities and the spectrum of field variations in Holocene magnetic records

Cited by 18 publications

References 48 publications

COV-OBS.x2: 180 years of geomagnetic field evolution from ground-based and satellite observations

COV-OBS.x2: 180 years of geomagnetic field evolution from ground-based and satellite observations

The interplay of fast waves and slow convection in geodynamo simulations nearing Earth’s core conditions

Characteristic periods of the paleosecular variation of the Earth's magnetic field during the Holocene from global paleoreconstructions

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