Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles
According to observations, the discrete auroral arcs can sometimes be found, either deep inside the auroral oval or at the poleward border of the wide (so-called double) auroral oval, which map to very different regions of the magnetotail. To find common physical conditions for the auroral-arc g...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
1997-08-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/15/943/1997/angeo-15-943-1997.pdf |
| _version_ | 1828157046234546176 |
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| author | A. G. Yahnin V. A. Sergeev B. B. Gvozdevsky S. Vennerstrøm |
| author_facet | A. G. Yahnin V. A. Sergeev B. B. Gvozdevsky S. Vennerstrøm |
| author_sort | A. G. Yahnin |
| collection | DOAJ |
| description | According to observations, the discrete
auroral arcs can sometimes be found, either deep inside the auroral oval or at
the poleward border of the wide (so-called double) auroral oval, which map to
very different regions of the magnetotail. To find common physical conditions
for the auroral-arc generation in these magnetotail regions, we study the
spatial relationship between the diffuse and discrete auroras and the isotropic
boundaries (IBs) of the precipitating energetic particles which can be used to
characterise locally the equatorial magnetic field in the tail. From comparison
of ground observation of auroral forms with meridional profiles of particle flux
measured simultaneously by the low-altitude NOAA satellites above the ground
observation region, we found that (1) discrete auroral arcs are always situated
polewards from (or very close to) the IB of >30-keV electrons, whereas (2)
the IB of the >30-keV protons is often seen inside the diffuse aurora. These
relationships hold true for both quiet and active (substorm) conditions in the
premidnight-nightside (18-01-h) MLT sector considered. In some events the
auroral arcs occupy a wide latitudinal range. The most equatorial of these arcs
was found at the poleward edge of the diffuse auroras (but anyway in the
vicinity of the electron IB), the most poleward arcs were simultaneously
observed on the closed field lines near the polar-cap boundary. These
observations disagree with the notion that the discrete aurora originate
exclusively in the near-Earth portion of plasma sheet or exclusively on the PSBL
field lines. Result (1) may imply a fundamental feature of auroral-arc
formation: they originate in the current-sheet regions having very curved and
tailward-stretched magnetic field lines. |
| first_indexed | 2024-04-11T23:22:52Z |
| format | Article |
| id | doaj.art-12ab7feb17e846778fdc1124ed17bd11 |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-04-11T23:22:52Z |
| publishDate | 1997-08-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-12ab7feb17e846778fdc1124ed17bd112022-12-22T03:57:25ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05761997-08-011594395810.1007/s00585-997-0943-zMagnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particlesA. G. Yahnin0V. A. Sergeev1B. B. Gvozdevsky2S. Vennerstrøm3Polar Geophysical Institute, Apatity, Murmansk region, 184200, Russia<br>Tel: +7 815 55 37 475; Fax: +7 815 55 30925; e-mail: yahnin@pgi-ksc.murmansk.suInstitute of Physics, University of St. Petersburg, St. Petersburg, RussiaPolar Geophysical Institute, Apatity, Murmansk region, 184200, Russia<br>Tel: +7 815 55 37 475; Fax: +7 815 55 30925; e-mail: yahnin@pgi-ksc.murmansk.suDanish Meteorological Institute, Solar-Terrestrial Physics Division, Copenhagen, DenmarkAccording to observations, the discrete auroral arcs can sometimes be found, either deep inside the auroral oval or at the poleward border of the wide (so-called double) auroral oval, which map to very different regions of the magnetotail. To find common physical conditions for the auroral-arc generation in these magnetotail regions, we study the spatial relationship between the diffuse and discrete auroras and the isotropic boundaries (IBs) of the precipitating energetic particles which can be used to characterise locally the equatorial magnetic field in the tail. From comparison of ground observation of auroral forms with meridional profiles of particle flux measured simultaneously by the low-altitude NOAA satellites above the ground observation region, we found that (1) discrete auroral arcs are always situated polewards from (or very close to) the IB of >30-keV electrons, whereas (2) the IB of the >30-keV protons is often seen inside the diffuse aurora. These relationships hold true for both quiet and active (substorm) conditions in the premidnight-nightside (18-01-h) MLT sector considered. In some events the auroral arcs occupy a wide latitudinal range. The most equatorial of these arcs was found at the poleward edge of the diffuse auroras (but anyway in the vicinity of the electron IB), the most poleward arcs were simultaneously observed on the closed field lines near the polar-cap boundary. These observations disagree with the notion that the discrete aurora originate exclusively in the near-Earth portion of plasma sheet or exclusively on the PSBL field lines. Result (1) may imply a fundamental feature of auroral-arc formation: they originate in the current-sheet regions having very curved and tailward-stretched magnetic field lines.https://www.ann-geophys.net/15/943/1997/angeo-15-943-1997.pdf |
| spellingShingle | A. G. Yahnin V. A. Sergeev B. B. Gvozdevsky S. Vennerstrøm Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles Annales Geophysicae |
| title | Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles |
| title_full | Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles |
| title_fullStr | Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles |
| title_full_unstemmed | Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles |
| title_short | Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles |
| title_sort | magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles |
| url | https://www.ann-geophys.net/15/943/1997/angeo-15-943-1997.pdf |
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