The CHAOS-4 geomagnetic field model

Olsen, Nils; Lühr, H.; Finlay, Christopher C.; Sabaka, Terence J.; Michaelis, Ingo; Rauberg, Jan; Tøffner-Clausen, Lars

doi:10.1093/gji/ggu033

Cited by 180 publications

(256 citation statements)

References 45 publications

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“…The distinctive pattern of SV is caused by a westward motion of the flux lobes [12,7], situated in the regions between A (80 • E) and B (120 • E), between C (170 • E) and D (220 • E), and a weaker patch between E (280 • E) and F (310 • E): see also the supplementary movies S1 and S2 of the time-evolution of the main field and its SV. As the patches of negative radial flux move, they create negative signatures in the SV at their leading edges (A, C, E) and positive signatures at their trailing edges (B, D, F).…”

Section: Observations Of Intense High-latitude Secular Variationmentioning

confidence: 99%

“…The most recent high resolution data from the Ørsted, CHAMP and Swarm satellite missions, along with ground-based observatory data, show that, over the past decade, the northern flux lobes over Canada and Siberia have not only been moving but accelerating [7,1]. In this article, we provide an explanation of this new observation based on an accelerating tangent cylinder jet that sheds light on the hidden internal dynamics of the core, and which adds to the body of evidence suggesting a marked difference in magnetic change between low and high latitudes [8,9,6,10,11].…”

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confidence: 99%

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An accelerating high-latitude jet in Earth’s core

2016

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Observations of the change in Earth's magnetic field, the secular variation, provide information on the motion of liquid metal within the core that is responsible for its generation. The very latest high-resolution observations from ESA's Swarm satellite mission show intense field change at high-latitude localised in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we explain this feature with a localised, non-axisymmetric, westwards jet of 420 km width on the tangent cylinder, the cylinder of fluid within the core that is aligned with the rotation axis and tangent to the solid inner core.We find that the jet has increased in magnitude by a factor of three over the period 2000-2016 to about 40 km/yr, and is now much stronger than typical large-scale flows inferred for the core. The current accelerating phase may be a part of a longer term fluctuation of the jet causing both eastwards and westwards movement of magnetic features over historical

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Section: Observations Of Intense High-latitude Secular Variationmentioning

confidence: 99%

mentioning

confidence: 99%

An accelerating high-latitude jet in Earth’s core

2016

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“…Therefore a new index called RC (Appendix B) was proposed as part of the CHAOS-4 geomagnetic field model (Olsen et al 2014). It was originally derived from observatory hourly means (OHMs) at 21 globally distributed locations at low and mid geomagnetic latitudes (−41 • ≤ θ M ≤ 54 • ), excluding regions close to the geomagnetic equator that are affected by the equatorial electrojet.…”

Section: Introductionmentioning

confidence: 99%

An annual proxy for the geomagnetic signal of magnetospheric currents on Earth based on observatory data from 1900–2010

Pick

Korte

2017

Geophysical Journal International

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S U M M A R YWe introduce the Annual Magnetospheric Currents index as long-term proxy for the geomagnetic signal of magnetospheric currents on Earth valid within the time span 1900-2010. Similar to the widely used disturbance storm time and 'Ring Current' indices, it is based on geomagnetic observatory data, but provides a realistic absolute level and uncertainty estimates. Crucial aspects to this end are the revision of observatory crustal biases as well as the implementation of a Bayesian inversion accounting for uncertainties in the main field estimate, both required for the index derivation. The observatory choice is based on a minimization of index variance during a reference period spanning 1960-2010. The new index is capable of correcting observatory time series from large-scale external signals in a user-friendly manner. At present the index is only available as annual mean values. An extension to hourly values for the same time span is in progress.

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“…The Dst index (or its refined version, the RC index) and its time derivative are used to search magnetically quiet periods and to characterize time variations in the external field with its induction effect (Maus and Lühr 2005;Olsen et al 2005b). Magnetically quiet times are associated with the conditions of |Dst| < 30 nT and |dDst/dt| or |dRC/dt| being less than 2 or 5 nT /h (Olsen et al 2014;Maus et al 2010;Sabaka et al 2015). CHAOS, CM-5 and SIFM characterize weak global activity with the condition Kp ≤ 2 o (Olsen et al 2006;Sabaka et al 2015;Olsen et al 2015).…”

Section: Introductionmentioning

confidence: 99%

“…−2nT < B z < 6 nT and |B y | < 8 nT Maus et al (2010)). For MEF (or for its revised version by Newell et al (2007)) a typical condition for weak electrojet activity is M EF < 0.8 mV /m (Olsen et al 2014;Maus et al 2010;Sabaka et al 2015).…”

Section: Introductionmentioning

confidence: 99%

On the Usage of Geomagnetic Indices for Data Selection in Internal Field Modelling

et al. 2016

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We present a review on geomagnetic indices describing global geomagnetic storm activity (Kp, am, Dst and dDst/dt) and on indices designed to characterize high latitude currents and substorms (PC and AE-indices and their variants). The focus in our discussion is in main field modelling, where indices are primarily used in data selection criteria for weak magnetic activity. The publicly available extensive data bases of index values are used to derive joint conditional Probability Distribution Functions (PDFs) for different pairs of indices in order to investigate their mutual consistency in describing quiet conditions. This exercise reveals that Dst and its time derivative yield a similar picture as Kp on quiet conditions as determined with the conditions typically used in internal field modelling. Magnetic quiescense at high latitudes is typically searched with the help of Merging Electric Field (MEF) as derived from solar wind observations. We use in our PDF analysis the PC-index as a proxy for MEF and estimate the magnetic activity level at auroral latitudes with the AL-index. With these boundary conditions we conclude that the quiet time conditions that are typically used in main field modelling (P C < 0.8, Kp < 2 and |Dst| < 30 nT ) correspond to weak auroral electrojet activity quite well: Standard size substorms are unlikely to happen, but other type of activations

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The CHAOS-4 geomagnetic field model

Cited by 180 publications

References 45 publications

An accelerating high-latitude jet in Earth’s core

An accelerating high-latitude jet in Earth’s core

An annual proxy for the geomagnetic signal of magnetospheric currents on Earth based on observatory data from 1900–2010

On the Usage of Geomagnetic Indices for Data Selection in Internal Field Modelling

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