Analysis of multipoint magnetometer data

Dunlop, M. W.; Southwood, D. J.; Glaßmeier, Karl‐Heinz; Neubauer, F. M.

doi:10.1016/0273-1177(88)90141-x

Cited by 209 publications

(249 citation statements)

References 2 publications

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“…In-flight calibrations on FGM data routinely determine the maximum error in the data to within 0.1 nT. The "Curlometer" technique has been developed to derive currents from four-point magnetic field measurements (Dunlop et al, 1988(Dunlop et al, , 2002Robert et al, 1998) based on MaxwellAmpere's law…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, it was stable and mainly <0.5 (under red line) within the interval of the ring current. Dunlop et al (1988) suggested that the ratio Div(B)/|Curl(B)| can provide a quality estimate for J calculated in place of the unknown error (J calculated − J real ) when the shape and orientation of the spacecraft configuration is regular tetrahedron, and the magnetic field structure is nearly isotropic within the tetrahedron. The use of Div(B) does not give a direct indication of the actual error in the current estimate and is less relevant for distorted tetrahedral configurations.…”

Section: Introductionmentioning

confidence: 99%

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The distribution of the ring current: Cluster observations

et al. 2011

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Abstract.Extending previous studies, a full-circle investigation of the ring current has been made using Cluster 4-spacecraft observations near perigee, at times when the Cluster array had relatively small separations and nearly regular tetrahedral configurations, and when the Dst index was greater than −30 nT (non-storm conditions). These observations result in direct estimations of the near equatorial current density at all magnetic local times (MLT) for the first time and with sufficient accuracy, for the following observations. The results confirm that the ring current flows westward and show that the in situ average measured current density (sampled in the radial range accessed by Cluster ∼4-4.5 R E ) is asymmetric in MLT, ranging from 9 to 27 nA m −2 . The direction of current is shown to be very well ordered for the whole range of MLT. Both of these results are in line with previous studies on partial ring extent. The magnitude of the current density, however, reveals a distinct asymmetry: growing from 10 to 27 nA m −2 as azimuth reduces from about 12:00 MLT to 03:00 and falling from 20 to 10 nA m −2 less steadily as azimuth reduces from 24:00 to 12:00 MLT. This result has not been reported before and we suggest it could reflect a number of effects. Firstly, we argue it is consistent with the operation of region-2 field aligned-currents (FACs), which are expected to flow upward into the ring current around 09:00 MLT and downward out of the ring current around 14:00 MLT. Secondly, we note that it is also consistent with a possible asymmetry in the radial distribution profile of current density (resulting in higher peak at ∼4-4.5 R E ). We note that part of the enhanced current could reflect an increase in the mean AE activity (during the periods in which Cluster samples those MLT).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The distribution of the ring current: Cluster observations

et al. 2011

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“…The method to obtain two-dimensional pressure gradient is similar as calculating the magnetic gradient using the curlometer technique [Dunlop et al, 1988] but has been simplified to two dimensions.…”

Section: 1002/2014ja020186mentioning

confidence: 99%

Current reduction in a pseudo‐breakup event: THEMIS observations

Yao

Owen³

et al. 2014

JGR Space Physics

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Pseudo-breakup events are thought to be generated by the same physical processes as substorms. This paper reports on the cross-tail current reduction in an isolated pseudo-breakup observed by three of the THEMIS probes (THEMIS A (THA), THEMIS D (THD), and THEMIS E (THE)) on 22 March 2010. During this pseudo-breakup, several localized auroral intensifications were seen by ground-based observatories. Using the unique spatial configuration of the three THEMIS probes, we have estimated the inertial and diamagnetic currents in the near-Earth plasma sheet associated with flow braking and diversion. We found the diamagnetic current to be the major contributor to the current reduction in this pseudo-breakup event. During flow braking, the plasma pressure was reinforced, and a weak electrojet and an auroral intensification appeared. After flow braking/diversion, the electrojet was enhanced, and a new auroral intensification was seen. The peak current intensity of the electrojet estimated from ground-based magnetometers,~0.7 × 10 5 A, was about 1 order of magnitude lower than that in a typical substorm. We suggest that this pseudo-breakup event involved two dynamical processes: a current-reduction associated with plasma compression ahead of the earthward flow and a current-disruption related to the flow braking/diversion. Both processes are closely connected to the fundamental interaction between fast flows, the near-Earth ambient plasma, and the magnetic field.

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“…But a fundamental problem always exists: how should the comparative information between spacecraft be built into any analysis? The determination of di erent properties demands di erent methods of coordination (Dunlop et al, 1988); often having a large overlap between them, with parameters in common. In terms of boundary analysis, although there is an apparent distinction between macroscopic parameters (such as motion, orientation and form) and the boundary structure itself (as sampled individually by each spacecraft), it is not always a priori obvious how spacecraft di erences are to be combined with time series information, except where the boundary is planar or`thin' (Dunlop and Woodward, 1998).…”

Section: Introductionmentioning

confidence: 99%

Analysis of thick, non-planar boundaries using the discontinuity analyser

Dunlop

Woodward

1999

Ann. Geophys.

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Abstract. The advent of missions comprised of phased arrays of spacecraft, with separation distances ranging down to at least mesoscales, provides the scienti®c community with an opportunity to accurately analyse the spatial and temporal dependencies of structures in space plasmas. Exploitation of the multi-point data sets, giving vastly more information than in previous missions, thereby allows unique study of their small-scale physics. It remains an outstanding problem, however, to understand in what way comparative information across spacecraft is best built into any analysis of the combined data. Di erent investigations appear to demand di erent methods of data co-ordination. Of the various multispacecraft data analysis techniques developed to a ect this exploitation, the discontinuity analyser has been designed to investigate the macroscopic properties (topology and motion) of boundaries, revealed by multi-spacecraft magnetometer data, where the possibility of at least mesoscale structure is considered. It has been found that the analysis of planar structures is more straightforward than the analysis of non-planar boundaries, where the e ects of topology and motion become interwoven in the data, and we argue here that it becomes necessary to customise the analysis for non-planar events to the type of structure at hand. One issue central to the discontinuity analyser, for instance, is the calculation of normal vectors to the structure. In the case of planar and`thin' non-planar structures, the method of normal determination is wellde®ned, although subject to uncertainties arising from unwanted signatures. In the case of`thick', non-planar structures, however, the method of determination becomes particularly sensitive to the type of physical sampling that is present. It is the purpose of this article to ®rstly review the discontinuity analyser technique and secondly, to discuss the analysis of the normals to thick non-planar structures detected in magnetometer data.

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Analysis of multipoint magnetometer data

Cited by 209 publications

References 2 publications

The distribution of the ring current: Cluster observations

The distribution of the ring current: Cluster observations

Current reduction in a pseudo‐breakup event: THEMIS observations

Analysis of thick, non-planar boundaries using the discontinuity analyser

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