Studies of polar current systems using the IMS Scandinavian magnetometer array

Untiedt, J.; Baumjohann, W.

doi:10.1007/bf00750770

Cited by 150 publications

(168 citation statements)

References 166 publications

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“…This conclusion is not in agreement with our spatial observations. Finally, we note that nearly the same ground magnetic situation (1 min earlier) as analyzed in our study was discussed by Untiedt and Baumjohann (1993) in their review on SMA observations, and classi®ed as one of the most inhomogeneous situations observed by this array. However, the authors did not carry out a combined analysis with radar and ASC data.…”

Section: Discussionsupporting

confidence: 78%

“…They can be ordered into two groups: one of them makes use of simultaneous observations from loworbiting satellites to detect the magnetic ®eld e ect of FACs, and of either ground-based all-sky cameras or high orbiting satellites that provide global auroral images (e.g., Bythrow and Potemra, 1987;Lopez et al, 1991;. The other focuses on combining the auroral images with ground-based data from magnetometers, radars, and other instruments if available (e.g., Robinson et al, 1985, Kamide et al, 1989Untiedt and Baumjohann, 1993, and references therein), while other satellite data may be used as supplementary evidence.…”

Section: Introductionmentioning

confidence: 99%

“…During and after the International Magnetospheric Study (IMS, 1976±1979), several studies were carried out that combined ground magnetic ®eld data from the arrays set up during this period with ionospheric electric ®eld data measured by coherent scatter radars (e.g., Akasofu et al, 1980;Kamide et al, 1982; see the review of Untiedt and Baumjohann, 1993, for the studies carried out with observations from Scandinavia). 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).…”

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: 78%

Section: Introductionmentioning

confidence: 99%

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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“…Such features are usually associated with auroral loop and surge features (see relevant parts of Sect. 4, Untiedt and Baumjohann, 1993 and references therein), and in this case an eastward motion may be calculated from the azimuthally separated stations KIL, MAS and KEV, to be 0.6 km s )1 . It is the electrodynamics of these two surge features which are the focus of the present study.…”

Section: Ground Magnetometer Datamentioning

confidence: 98%

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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“…A large variety of ionospheric current systems exist which differ by their time and spatial scales and motions. Examples of the most intense systems are the eastward and westward auroral electrojets (AEJ), westward travelling surges (WTS), and auroral omega bands (Untiedt and Baumjohann, 1993). The two latter systems have very complicated structures, including a pronounced vortex part.…”

Section: Introductionmentioning

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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Studies of polar current systems using the IMS Scandinavian magnetometer array

Cited by 150 publications

References 166 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

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

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

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