Evidence for geomagnetic jerks in comprehensive models

Chambodut, Aude; Mandéa, Mioara

doi:10.1186/bf03352558

Cited by 36 publications

(37 citation statements)

References 17 publications

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“…We observe the signature of geomagnetic jerks in the secular acceleration computed from the CM4 model at 39 observatory locations, which provide continuous monthlymean series during the period 1960-2002 (the same set of observatories as in Chambodut and Mandea (2005) is used here). As an example, Fig.…”

Section: At Observatoriesmentioning

confidence: 99%

“…The secular variation of the magnetic field from observatory data was already compared with that from the comprehensive model CM4 by Chambodut and Mandea (2005), where a good agreement between the real and synthetic data was shown. The secular acceleration calculated from the CM4 model should also be a possible tool to detect the signature of geomagnetic jerks as sudden changes of sign of the secular acceleration (Courtillot et al, 1978).…”

Section: Distribution Of Geomagnetic Jerks Inferred From Cm4 Secular mentioning

confidence: 99%

“…Some previous studies have already attempted to characterise the temporal occurrences and extents of geomagnetic jerks at the Earth's surface using the magnetic field itself (Alexandrescu et al,1996;Nagao et al, 2002) or its secular variation (Macmillan, 1996;Le Huy et al, 1998;De Michelis et al, 1998;Chambodut and Mandea, 2005). Alexandrescu et al (1996) note the non-synchronous occurrence of geomagnetic jerks at global scale: a time shift appears for the events around 1968 and 1978 with an earlier arrival in the Northern hemisphere.…”

Section: Introductionmentioning

confidence: 99%

“…The events around 1968 and 1990 appear similar in their shape and sign while the one of 1978 shows a change of sign. More recently, Chambodut and Mandea (2005) used the CM4 model (Sabaka et al, 2002(Sabaka et al, , 2004 to study geomagnetic jerks, and suggested that these events might not be worldwide in occurrence.…”

Section: Introductionmentioning

confidence: 99%

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Geomagnetic jerks from the Earth’s surface to the top of the core

2007

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Rapid changes in the magnetic field characterised by an abrupt change in the secular variation have been named “secular variation impulses” or “geomagnetic jerks”. Three of these events, around 1968, 1978 and 1990, occurred during the time-span covered by the comprehensive model CM4 (Sabaka et al., 2002, 2004). This model, providing the best temporal resolution between 1960 and 2002 as well as a fine separation of the different magnetic sources, can be used to study rapid phenomena of internal origin. In order to analyse these events all over the globe, synthetic time series were obtained from the CM4 model between 1960–2002. Geomagnetic jerks are detected here as a rapid movement of the zero isoline of the second field derivative. Analysis of the area swept out by this isoline as a function of time allows us to map the spatial extent of jerks though time, and to identify an event around 1985 that is localized in the Pacific area. At the core surface, we compute the fluid flows under the frozen-flux and tangentially geostrophic assumptions. The flows do not exhibit any special pattern at jerk times, but instead show a smooth temporal evolution over the whole time period. However, the mean amplitude of the dynamical pressure associated with these flows present maxima at each jerk occurrence and helps to confirm the identification of a jerk in 1985.

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Section: At Observatoriesmentioning

confidence: 99%

Section: Distribution Of Geomagnetic Jerks Inferred From Cm4 Secular mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geomagnetic jerks from the Earth’s surface to the top of the core

2007

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“…This model is estimated using magnetic data primarily from ground-based observatories, supplemented by satellite measurements. Its accuracy may not compare with that of GRIMM due to the limited quantity and quality of data, but it features the well-known geomagnetic jerks which occurred succesively around the years 1969, 1978, 1991(Sabaka et al, 2004Chambodut and Mandea, 2005). In our analysis we pay particular attention to the jerks, because we think of these abrupt events as special among all other SVs with respect that they are the core's magnetic signals observed at the shortest timescale.…”

Section: Core Field Modelsmentioning

confidence: 99%

Geomagnetic secular variation violating the frozen-flux condition at the core surface

2010

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We consider a method to extract the part of a given geomagnetic secular variation (SV) model that is not consistent with a frozen-flux condition. This condition is usually derived from the diffusionless radial induction equation at the core-mantle boundary (CMB), and is defined explicitly in the spatial domain: radial flux changes within closed null-flux curves at the core surface are not allowed at any instant. We study here this condition in the spherical harmonic (SH) domain, relying on the SH expansion of the diffusionless equation. SV models at a certain epoch are separated into advective and non-advective parts. The advective (resp. non-advective) part satisfies (resp. does not satisfy) the frozen-flux condition redefined in the SH domain. We show that this separation is not unique. In this work, we achieve a unique separation by assuming the orthogonality of the two parts in terms of the radial SV energy at the CMB. From the recent geomagnetic models, GRIMM and CM4, we find that the non-advective part shows up mainly in the small reverse patches of the radial magnetic field at the CMB. However, non-advective behaviors are also observed outside these patches. As far as no restriction is imposed on core flow configuration, time variations of the non-advective part are not correlated to those of the SV models. However, if the flow is restricted to be tangentially geostrophic, time variations of the SV models have to be partly non-advective. Furthermore, for this flow configuration, the secular decrease of the axial dipole has to be largely non-advective.

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