Joint two-dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents: Current systems associated with local auroral break-ups

Baumjohann, W.; Pellinen, R.; Opgenoorth, H. J.; Nielsen, E.

doi:10.1016/0032-0633(81)90087-8

Cited by 230 publications

(130 citation statements)

References 58 publications

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“…They proposed that the ground magnetic signature observed is related to an auroral breakup. Our resulting current system in fact shows some similarities to the geometry of the breakup current system as shown in Baumjohann et al (1981), in that a locally enhanced westward electrojet is diverged by concentrated upward¯owing FACs. On the other hand, there are also important di erences between their current system and ours.…”

Section: Discussionsupporting

confidence: 64%

“…On the other hand, there are also important di erences between their current system and ours. Whereas in the breakup model of Baumjohann et al (1981), the enhanced westward jet is fed by distant and more distributed downward-¯owing FACs, in our case this feeding occurs locally at the northeastern edge of the auroral form (compare Fig. 8b).…”

Section: Discussionmentioning

confidence: 51%

“…Many of these works addressed the spatial conductance, electric ®eld, currents, and FAC distribution associated with auroral forms, such as the westward traveling surge (WTS; e.g., Inhester et al, 1981;Opgenoorth et al, 1983a), the auroral breakup (e.g., Opgenoorth et al, 1980;Baumjohann et al, 1981), or omega bands (e.g., AndreÂ and Baumjohann, 1982;Opgenoorth et al, 1983b). The method of analysis used in these studies was the`trial and error' method, i.e., the searched ionospheric parameters were modeled until a su cient ®t between the measured quantities and their values as calculated by the models was obtained.…”

Section: Introductionmentioning

confidence: 99%

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Spatial distribution of conductances and currents associated with a north-south auroral form during a multiple-substorm period

1999

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Abstract. Using the method of characteristics to invert ground-based data of the ground magnetic ®eld disturbance and of the ionospheric electric ®eld, we obtain spatial distributions of ionospheric conductances, currents, and ®eld-aligned currents (FACs) associated with a north-south auroral form that drifts westwards over northern Scandinavia around 2200 UT on December 2, 1977. This auroral form is one in a sequence of such north-south structures observed by all-sky cameras, and appears 14 min after the last of several breakups during that extremely disturbed night. Our analysis shows that the ionospheric Hall conductance reaches values above 200 S in the center of the form, and upward¯owing FACs of up to 25 lA/m 2 are concentrated near its westward and equatorward edge. The strong upward owing FACs are fed by an area of more distributed, but still very strong downward-¯owing FACs northeastward of the auroral form. In contrast to the conductances, the electric ®eld is only slightly a ected by the passage of the form. We point out similarities and di erences of our observations and results to previously reported observations and models of`auroral ®ngers', north-south aurora', and`auroral streamers' which are suggested to be ionospheric manifestations of bursty bulk¯ows in the plasma sheet.

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Section: Discussionsupporting

confidence: 64%

Section: Discussionmentioning

confidence: 51%

Section: Introductionmentioning

confidence: 99%

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Spatial distribution of conductances and currents associated with a north-south auroral form during a multiple-substorm period

1999

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“…As previously mentioned, we believe the wedge current system discussed in this paper is an oversimplification of the real current systems [Baumjohann et al, 1981]. There are several situations that could account for discrepancies between observations and model.…”

Section: Ti-ioe D^t^ Soetmentioning

confidence: 72%

Polarization patterns of Pi 2 magnetic pulsations and the substorm current wedge

Lester¹,

Hughes²,

Singer³

1983

J. Geophys. Res.

150

178

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The results of an analysis of 16 Pi 2 pulsations observed with an extended east-west chain of midlatitude, ground-based magnetometers are reported. The events were chosen such that the center of the substorm current system, defined by using the midlatitude bays associated with these pulsations, was within the longitudinal extent of the station chain. A current wedge model is also used to interpret the observed polarization pattern of the Pi 2 pulsations. This pattern is used to locate the center of the Pi 2 current system. The centers of the Pi 2 and substorm current systems occur at the same meridian for only -65% of the events. This result suggests that the Pi 2 current system and the substorm current wedge are not always the same. The longitudinal extent of the Pi 2 current system estimated from the Pi 2 polarization pattern averages --•90 ø or -6 hours local time for the events in the study. The sense of ellipticity of the waves, anticlockwise looking down the field line in the northern hemisphere, agrees with previous results from these latitudes. Estimates of the wave-phase difference between stations show that, in general, the eastern station of a station pair leads the western one at all local times for both H and D components. When plotted in a substorm coordinate system based on the mid-latitude bay, the phase difference per degree of longitude shows a tendency to decrease in the eastern portion of the current wedge. This longitudinal pattern of phase difference is consistent with the eastern, downward, field-aligned currents being less localized than the western, upward, field-aligned currents. , 1980], the predominant observation is that eastern stations lead in phase. This result has been interpreted as western phase propagation on the entire nightside. Since no physical interpretation consistent with substorm models has been developed, we concluded that a further study of phase variations was warranted. Our results confirm that eastern stations lead in phase, but that the phase variation is not uniform across the substorm current wedge.The following section describes the magnetometer array and data set used. We then describe the model of the substorm current wedge and the associated, predicted Pi 2 polarization pattern. Examples of Pi 2 pulsations, their polarization pattern, and the related bay structure are then given. The polarization pattern is described for 16 events where it is possible to locate the center of the substorm 7958

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“…These ionospheric electric ®eld and conductivity changes combine to produce the characteristic ground magnetic perturbations during the substorm expansion phase. VHF coherent scatter radars were ®rst used to study the spatial structure of the substorm electric ®elds (Baumjohann et al, 1981;Inhester et al, 1981;Opgenoorth et al, 1983) and suggested a region of low-electric ®eld within the dynamic structure of the substorm electrojets. Incoherent scatter radars also o er an excellent technique for the study of both the ionospheric¯ow velocities and ionospheric particle precipitation during the substorm expansion phase.…”

Section: Introductionmentioning

confidence: 99%

Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm

et al. 2000

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Abstract. On August 21st 1998, a sharp southward turning of the IMF, following on from a 20 h period of northward directed magnetic ®eld, resulted in an isolated substorm over northern Scandinavia and Svalbard. A combination of high time resolution and large spatial scale measurements from an array of coherent scatter and incoherent scatter ionospheric radars, ground magnetometers and the Polar UVI imager has allowed the electrodynamics of the impulsive substorm electrojet region during its ®rst few minutes of evolution at the expansion phase onset to be studied in great detail. At the expansion phase onset the substorm onset region is characterised by a strong enhancement of the electron temperature and UV aurora. This poleward expanding auroral structure moves initially at 0.9 km s )1 poleward, ®nally reaching a latitude of 72.5°. The optical signature expands rapidly westwards at 6 km s )1 , whilst the eastward edge also expands eastward at 0.6 km s )1 . Typical¯ows of 600 m s )1 and conductances of 2 S were measured before the auroral activation, which rapidly changed to 100 m s )1 and 10±20 S respectively at activation. The initial¯ow response to the substorm expansion phase onset is a¯ow suppression, observed up to some 300 km poleward of the initial region of auroral luminosity, imposed over a time scale of less than 10 s. The high conductivity region of the electrojet acts as an obstacle to the¯ow, resulting in a region of low-electric ®eld, but also low conductivity poleward of the high-conductivity region. Rapid¯ows are observed at the edge of the high-conductivity region, and subsequently the high¯ow region develops,¯owing around the expanding auroral feature in a direction determined by the¯ow pattern prevailing before the substorm intensi®cation. The enhanced electron temperatures associated with the substorm-disturbed region extended some 2°further poleward than the UV auroral signature associated with it.

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Joint two-dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents: Current systems associated with local auroral break-ups

Cited by 230 publications

References 58 publications

Spatial distribution of conductances and currents associated with a north-south auroral form during a multiple-substorm period

Spatial distribution of conductances and currents associated with a north-south auroral form during a multiple-substorm period

Polarization patterns of Pi 2 magnetic pulsations and the substorm current wedge

Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm

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