Stationary magnetospheric convection on November 24, 1981. 1. A case study of &quot;pressure gradient/minimum-<i>B</i>&quot; auroral arc generation

We present two case studies in the night and evening sides of the auroral oval, based on plasma and field measurements made at low altitudes by the AUREOL-3 satellite, during a long period of stationary magnetospheric convection (SMC) on November 24, 1981. The basic feature of both oval crossing...

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Main Authors: Y. I. Galperin, J. M. Bosqued
Format: Article
Language:English
Published: Copernicus Publications 1999-03-01
Series:Annales Geophysicae
Online Access:https://www.ann-geophys.net/17/358/1999/angeo-17-358-1999.pdf
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spelling doaj-705c33442cc9460b831b211e722b16d72020-11-24T22:00:33ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05761999-03-011735837410.1007/s00585-999-0358-0Stationary magnetospheric convection on November 24, 1981. 1. A case study of &quot;pressure gradient/minimum-<i>B</i>&quot; auroral arc generationY. I. Galperin0J. M. Bosqued1Space Research Institute of Russian Academy of Sciences, 117810, Moscow, RussiaCentre d'Etude Spatiale des Rayonnements, CNRS/UPS, 9, Avenue du Colonel Roche-31028 Toulouse Cedex, FranceWe present two case studies in the night and evening sides of the auroral oval, based on plasma and field measurements made at low altitudes by the AUREOL-3 satellite, during a long period of stationary magnetospheric convection (SMC) on November 24, 1981. The basic feature of both oval crossings was an evident double oval pattern, including (1) a weak arc-type structure at the equatorial edge of the oval/polar edge of the diffuse auroral band, collocated with an upward field-aligned current (FAC) sheet of \sim1.0 µA m<sup>-2</sup>, (2) an intermediate region of weaker precipitation within the oval, (3) a more intense auroral band at the polar oval boundary, and (4) polar diffuse auroral zone near the polar cap boundary. These measurements are compared with the published magnetospheric data during this SMC period, accumulated by Yahnin <i>et al</i>. and Sergeev <i>et al</i>., including a semi-empirical radial magnetic field profile <i>B<sub>Z</sub></i> in the near-Earth neutral sheet, with a minimum at about 10-14 <i>R<sub>E</sub></i>. Such a radial <i>B<sub>Z</sub></i> profile appears to be very similar to that assumed in the &quot;minimum- <i>B</i>/cross-tail line current&quot; model by Galperin <i>et al</i>. (GVZ92) as the &quot;root of the arc&quot;, or the arc generic region. This model considers a FAC generator mechanism by Grad-Vasyliunas-Boström-Tverskoy operating in the region of a narrow magnetic field minimum in the near-Earth neutral sheet, together with the concept of ion non-adiabatic scattering in the &quot;wall region&quot;. The generated upward FAC branch of the double sheet current structure feeds the steady auroral arc/inverted-V at the equatorial border of the oval. When the semi-empirical <i>B<sub>Z</sub></i> profile is introduced in the GVZ92 model, a good agreement is found between the modelled current and the measured characteristics of the FACs associated with the equatorial arc. Thus the main predictions of the GVZ92 model concerning the &quot;minimum-B&quot; region are consistent with these data, while some small-scale features are not reproduced. Implications of the GVZ92 model are discussed, particularly concerning the necessary conditions for a substorm onset that were not fulfilled during the SMC period.<br><br><b>Key words. </b>Magnetospheric physics (auroral phenomena; magnetospheric configuration and dynamics; plasma sheet).https://www.ann-geophys.net/17/358/1999/angeo-17-358-1999.pdf
collection DOAJ
language English
format Article
sources DOAJ
author Y. I. Galperin
J. M. Bosqued
spellingShingle Y. I. Galperin
J. M. Bosqued
Stationary magnetospheric convection on November 24, 1981. 1. A case study of &quot;pressure gradient/minimum-<i>B</i>&quot; auroral arc generation
Annales Geophysicae
author_facet Y. I. Galperin
J. M. Bosqued
author_sort Y. I. Galperin
title Stationary magnetospheric convection on November 24, 1981. 1. A case study of &quot;pressure gradient/minimum-<i>B</i>&quot; auroral arc generation
title_short Stationary magnetospheric convection on November 24, 1981. 1. A case study of &quot;pressure gradient/minimum-<i>B</i>&quot; auroral arc generation
title_full Stationary magnetospheric convection on November 24, 1981. 1. A case study of &quot;pressure gradient/minimum-<i>B</i>&quot; auroral arc generation
title_fullStr Stationary magnetospheric convection on November 24, 1981. 1. A case study of &quot;pressure gradient/minimum-<i>B</i>&quot; auroral arc generation
title_full_unstemmed Stationary magnetospheric convection on November 24, 1981. 1. A case study of &quot;pressure gradient/minimum-<i>B</i>&quot; auroral arc generation
title_sort stationary magnetospheric convection on november 24, 1981. 1. a case study of &quot;pressure gradient/minimum-<i>b</i>&quot; auroral arc generation
publisher Copernicus Publications
series Annales Geophysicae
issn 0992-7689
1432-0576
publishDate 1999-03-01
description We present two case studies in the night and evening sides of the auroral oval, based on plasma and field measurements made at low altitudes by the AUREOL-3 satellite, during a long period of stationary magnetospheric convection (SMC) on November 24, 1981. The basic feature of both oval crossings was an evident double oval pattern, including (1) a weak arc-type structure at the equatorial edge of the oval/polar edge of the diffuse auroral band, collocated with an upward field-aligned current (FAC) sheet of \sim1.0 µA m<sup>-2</sup>, (2) an intermediate region of weaker precipitation within the oval, (3) a more intense auroral band at the polar oval boundary, and (4) polar diffuse auroral zone near the polar cap boundary. These measurements are compared with the published magnetospheric data during this SMC period, accumulated by Yahnin <i>et al</i>. and Sergeev <i>et al</i>., including a semi-empirical radial magnetic field profile <i>B<sub>Z</sub></i> in the near-Earth neutral sheet, with a minimum at about 10-14 <i>R<sub>E</sub></i>. Such a radial <i>B<sub>Z</sub></i> profile appears to be very similar to that assumed in the &quot;minimum- <i>B</i>/cross-tail line current&quot; model by Galperin <i>et al</i>. (GVZ92) as the &quot;root of the arc&quot;, or the arc generic region. This model considers a FAC generator mechanism by Grad-Vasyliunas-Boström-Tverskoy operating in the region of a narrow magnetic field minimum in the near-Earth neutral sheet, together with the concept of ion non-adiabatic scattering in the &quot;wall region&quot;. The generated upward FAC branch of the double sheet current structure feeds the steady auroral arc/inverted-V at the equatorial border of the oval. When the semi-empirical <i>B<sub>Z</sub></i> profile is introduced in the GVZ92 model, a good agreement is found between the modelled current and the measured characteristics of the FACs associated with the equatorial arc. Thus the main predictions of the GVZ92 model concerning the &quot;minimum-B&quot; region are consistent with these data, while some small-scale features are not reproduced. Implications of the GVZ92 model are discussed, particularly concerning the necessary conditions for a substorm onset that were not fulfilled during the SMC period.<br><br><b>Key words. </b>Magnetospheric physics (auroral phenomena; magnetospheric configuration and dynamics; plasma sheet).
url https://www.ann-geophys.net/17/358/1999/angeo-17-358-1999.pdf
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