On induction effects at EISCAT and IMAGE magnetometer stations

Viljanen, A.; Kauristie, Kirsti; Pajunpää, K.

doi:10.1111/j.1365-246x.1995.tb06446.x

Cited by 31 publications

(43 citation statements)

References 29 publications

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“…Based on the studies of the Earth's conductivity structure in Scandinavia (e.g. Viljanen, 1995;Tanskanen et al, 2001), we set a perfectly conducting layer at a depth of 100 km for the variations with T ∼ 1 min.…”

Section: Quantitative Characterization Of the Equivalent Current Systmentioning

confidence: 99%

Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations

et al. 2004

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Abstract.To learn about the geometry and sources of the ionospheric current systems which generate strong geomagnetically induced currents, we categorize differential equivalent current systems (DEC) for events with strong dB/dt by decomposing them into the contributions of electrojet-type and vortex-type elementary systems. By solving the inverse problem we obtain amplitudes and locations of these elementary current systems. One-minute differences of the geomagnetic field values at the IMAGE magnetometer network in 1996-2000 are analysed to study the spatial distributions of large dB/dt events. The relative contributions of the two components are evaluated. In particular, we found that the majority of the strongest dB/dt events (100-1000 nT/min) appear to be produced by the vortex-type current structures and most of them occur in the morning LT hours, probably caused by the Ps6 pulsation events associated with auroral omega structures. For strong dB/dt events the solar wind parameters are shifted toward strong (tens nT) southward IMF, enhanced velocity and dynamic pressure, in order for the main phase of the magnetic storms to occur. Although these events appear mostly during magnetic storms when the auroral oval greatly expands, the area of large dB/dt stays in the middle part of the auroral zone; therefore, it is connected to the processes taking part in the middle of the magnetosphere rather than in its innermost region populated by the ring current.

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Section: Quantitative Characterization Of the Equivalent Current Systmentioning

confidence: 99%

Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations

et al. 2004

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“…During the time span of 2010 campaign, only one such disturbance connected with geomagnetic pulsations occurred, with duration of 128 min that begun in 20:32 UTC July 27 (Gjerloev, 2012). However, after finding the so-called plane wave events (Viljanen et al, 1995) out of records given in Fig. 3, when correlation coefficients of X and Y components between PALA and GCK were above 0.9 in this case, it was possible to use such events for calculations (eight events with duration of 128 min).…”

Section: Resultsmentioning

confidence: 99%

“…In geomagnetic deep sounding, at mid-latitudes under certain assumptions follows the relation in the frequency domain (Gough et al, 1973;Viljanen et al, 1995):…”

Section: Where F(t -2) F(t -1) F(t) F(t + 1) and F(t + 2) Are Fivementioning

confidence: 99%

“…Thus defined real induction arrow lies in the preferred plane, and rotated by 180° is directed towards the area of anomalous concentration of induced currents. Imaginary induction arrow is defined analogously, and is directed from the conductor in which the current leads the phase in respect to the normal external field (Gough et al, 1973;Viljanen et al, 1995).…”

Section: Where F(t -2) F(t -1) F(t) F(t + 1) and F(t + 2) Are Fivementioning

confidence: 99%

“…The next analysis uses geomagnetic transfer function for detection of the anomalous inductive effects, such as geomagnetic coastal effect (Viljanen et al, 1995), and was performed on O-dIdD and corresponding observatory data. In geomagnetic deep sounding, at mid-latitudes under certain assumptions follows the relation in the frequency domain (Gough et al, 1973;Viljanen et al, 1995):…”

Section: Where F(t -2) F(t -1) F(t) F(t + 1) and F(t + 2) Are Fivementioning

confidence: 99%

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Recent geomagnetic investigations of Palagruža island

2017

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Intention of this work was to examine all available recent geomagnetic survey data, in order to assess Palagruža as a potential location for a permanent variometer station. The most recent data consist of absolute, total intensity vertical gradients and Overhauser effect dIdD vector measurements, carried out in period 2008-2010. Evidences were found in low crustal field estimates, relatively low total field vertical gradient distribution over the island, quite high time series correlation with the near observatories, as well as in low noise level of geomagnetic components. These preliminary results indicate Palagruža as appropriate location for the repeat station as well as for the variometer station. However, additional investigations of the geomagnetic sea and coastal effects by using much longer time series are needed.

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Comparison of auroral ionospheric and field‐aligned currents derived from Swarm and ground magnetic field measurements

et al. 2016

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Derivation of the auroral ionospheric currents from magnetic field measurements can produce drastically different results depending on the data and method used. We have cross tested several methods for obtaining instantaneous field‐aligned and horizontal currents from Swarm satellite and International Monitor for Auroral Geomagnetic Effects (IMAGE) ground magnetic field measurements. We found that Swarm can yield latitude profiles of the east‐west component of the divergence‐free current density at most at ∼200 km resolution, typically resolving the electrojets. The north‐south divergence‐free component, on the other hand, is not always well reproduced due to the small longitudinal distance between the side‐by‐side flying satellite pair. Swarm can yield the field‐aligned and curl‐free current density at a wider range of latitude resolutions (∼7.5–200 km) than the divergence‐free current density. While 7.5 km is suitable for comparison with auroras, 200 km typically resolves the Regions 1 and 2 field‐aligned currents. IMAGE can yield maps of the divergence‐free current density at ∼50 km resolution. Induced telluric currents should be accounted for in the derivation. Not accounting for them in the Swarm analysis, however, does not appear to introduce significant errors. Ionospheric conductances can be estimated by combining the total horizontal current density, consisting of the curl‐free and divergence‐free components, with the electric field measurements. Our results indicate that Swarm can only yield these at ∼200 km scale size when there is no significant dependence on longitude. However, combining the divergence‐free current from IMAGE with the curl‐free current and electric field from Swarm could yield conductance maps at ∼50 km resolution.

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On induction effects at EISCAT and IMAGE magnetometer stations

Cited by 31 publications

References 29 publications

Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations

Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations

Recent geomagnetic investigations of Palagruža island

Comparison of auroral ionospheric and field‐aligned currents derived from Swarm and ground magnetic field measurements

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