Observations of mesoscale auroral plasma cavity crossings with the Freja satellite
We have used data from the Freja satellite, with an apogee of 1700 km over the auroral oval, to make a statistical analysis of mesoscale auroral plasma density cavities. Such cavities are defined to be regions in the auroral zone with size scales between discrete arcs and inverted‐V events in which...
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Veröffentlicht in: | Journal of Geophysical Research 1998-05, Vol.103 (A5), p.9391-9404 |
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creator | Mäkelä, Jakke S. Mälkki, Anssi Koskinen, Hannu Boehm, Manfred Holback, Bengt Eliasson, Lars |
description | We have used data from the Freja satellite, with an apogee of 1700 km over the auroral oval, to make a statistical analysis of mesoscale auroral plasma density cavities. Such cavities are defined to be regions in the auroral zone with size scales between discrete arcs and inverted‐V events in which the plasma density abruptly drops to less than 50% of the ambient plasma density. We present occurrence distributions by magnetic activity, local time, and magnetic latitude. It is found that cavity occurrence does not depend on magnetic activity. In contrast to earlier studies, we find cavities at all local times; however, a dawn‐dusk asymmetry is found in the distribution. There is likewise a weak dawn‐dusk asymmetry in the latitudinal distribution. Since our data cover a full year, seasonal dependence of cavity occurrence can also be investigated. We find a small seasonal trend, with cavities found more commonly during the dark season, but the trend is not quite statistically significant. We also study several plasma depletion processes that could be responsible for cavities at this altitude. The results suggest that more than one process is compatible with the distributions we find. |
doi_str_mv | 10.1029/98JA00212 |
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Such cavities are defined to be regions in the auroral zone with size scales between discrete arcs and inverted‐V events in which the plasma density abruptly drops to less than 50% of the ambient plasma density. We present occurrence distributions by magnetic activity, local time, and magnetic latitude. It is found that cavity occurrence does not depend on magnetic activity. In contrast to earlier studies, we find cavities at all local times; however, a dawn‐dusk asymmetry is found in the distribution. There is likewise a weak dawn‐dusk asymmetry in the latitudinal distribution. Since our data cover a full year, seasonal dependence of cavity occurrence can also be investigated. We find a small seasonal trend, with cavities found more commonly during the dark season, but the trend is not quite statistically significant. We also study several plasma depletion processes that could be responsible for cavities at this altitude. The results suggest that more than one process is compatible with the distributions we find.</description><identifier>ISSN: 0148-0227</identifier><identifier>EISSN: 2156-2202</identifier><identifier>DOI: 10.1029/98JA00212</identifier><language>eng</language><publisher>Washington, DC: Blackwell Publishing Ltd</publisher><subject>Earth, ocean, space ; Exact sciences and technology ; External geophysics ; Physics of the magnetosphere ; Plasma motion, convection, circulation. Plasma instabilities</subject><ispartof>Journal of Geophysical Research, 1998-05, Vol.103 (A5), p.9391-9404</ispartof><rights>Copyright 1998 by the American Geophysical Union.</rights><rights>1998 INIST-CNRS</rights><lds50>peer_reviewed</lds50><oa>free_for_read</oa><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c3641-4c35f22ae69c51189a4f9ef3bd75a5815b6647d833ecd57026afc3c1e26b93183</citedby><cites>FETCH-LOGICAL-c3641-4c35f22ae69c51189a4f9ef3bd75a5815b6647d833ecd57026afc3c1e26b93183</cites></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><linktopdf>$$Uhttps://onlinelibrary.wiley.com/doi/pdf/10.1029%2F98JA00212$$EPDF$$P50$$Gwiley$$H</linktopdf><linktohtml>$$Uhttps://onlinelibrary.wiley.com/doi/full/10.1029%2F98JA00212$$EHTML$$P50$$Gwiley$$H</linktohtml><link.rule.ids>314,780,784,1417,1433,11514,27924,27925,45574,45575,46409,46468,46833,46892</link.rule.ids><backlink>$$Uhttp://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=2297030$$DView record in Pascal Francis$$Hfree_for_read</backlink></links><search><creatorcontrib>Mäkelä, Jakke S.</creatorcontrib><creatorcontrib>Mälkki, Anssi</creatorcontrib><creatorcontrib>Koskinen, Hannu</creatorcontrib><creatorcontrib>Boehm, Manfred</creatorcontrib><creatorcontrib>Holback, Bengt</creatorcontrib><creatorcontrib>Eliasson, Lars</creatorcontrib><title>Observations of mesoscale auroral plasma cavity crossings with the Freja satellite</title><title>Journal of Geophysical Research</title><addtitle>J. Geophys. Res</addtitle><description>We have used data from the Freja satellite, with an apogee of 1700 km over the auroral oval, to make a statistical analysis of mesoscale auroral plasma density cavities. Such cavities are defined to be regions in the auroral zone with size scales between discrete arcs and inverted‐V events in which the plasma density abruptly drops to less than 50% of the ambient plasma density. We present occurrence distributions by magnetic activity, local time, and magnetic latitude. It is found that cavity occurrence does not depend on magnetic activity. In contrast to earlier studies, we find cavities at all local times; however, a dawn‐dusk asymmetry is found in the distribution. There is likewise a weak dawn‐dusk asymmetry in the latitudinal distribution. Since our data cover a full year, seasonal dependence of cavity occurrence can also be investigated. We find a small seasonal trend, with cavities found more commonly during the dark season, but the trend is not quite statistically significant. We also study several plasma depletion processes that could be responsible for cavities at this altitude. The results suggest that more than one process is compatible with the distributions we find.</description><subject>Earth, ocean, space</subject><subject>Exact sciences and technology</subject><subject>External geophysics</subject><subject>Physics of the magnetosphere</subject><subject>Plasma motion, convection, circulation. 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Plasma instabilities</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Mäkelä, Jakke S.</creatorcontrib><creatorcontrib>Mälkki, Anssi</creatorcontrib><creatorcontrib>Koskinen, Hannu</creatorcontrib><creatorcontrib>Boehm, Manfred</creatorcontrib><creatorcontrib>Holback, Bengt</creatorcontrib><creatorcontrib>Eliasson, Lars</creatorcontrib><collection>Istex</collection><collection>Pascal-Francis</collection><collection>CrossRef</collection><collection>Meteorological & Geoastrophysical Abstracts</collection><collection>Meteorological & Geoastrophysical Abstracts - Academic</collection><collection>Technology Research Database</collection><collection>Aerospace Database</collection><collection>Advanced Technologies Database with Aerospace</collection><jtitle>Journal of Geophysical Research</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Mäkelä, Jakke S.</au><au>Mälkki, Anssi</au><au>Koskinen, Hannu</au><au>Boehm, Manfred</au><au>Holback, Bengt</au><au>Eliasson, Lars</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Observations of mesoscale auroral plasma cavity crossings with the Freja satellite</atitle><jtitle>Journal of Geophysical Research</jtitle><addtitle>J. Geophys. Res</addtitle><date>1998-05-01</date><risdate>1998</risdate><volume>103</volume><issue>A5</issue><spage>9391</spage><epage>9404</epage><pages>9391-9404</pages><issn>0148-0227</issn><eissn>2156-2202</eissn><abstract>We have used data from the Freja satellite, with an apogee of 1700 km over the auroral oval, to make a statistical analysis of mesoscale auroral plasma density cavities. Such cavities are defined to be regions in the auroral zone with size scales between discrete arcs and inverted‐V events in which the plasma density abruptly drops to less than 50% of the ambient plasma density. We present occurrence distributions by magnetic activity, local time, and magnetic latitude. It is found that cavity occurrence does not depend on magnetic activity. In contrast to earlier studies, we find cavities at all local times; however, a dawn‐dusk asymmetry is found in the distribution. There is likewise a weak dawn‐dusk asymmetry in the latitudinal distribution. Since our data cover a full year, seasonal dependence of cavity occurrence can also be investigated. We find a small seasonal trend, with cavities found more commonly during the dark season, but the trend is not quite statistically significant. We also study several plasma depletion processes that could be responsible for cavities at this altitude. The results suggest that more than one process is compatible with the distributions we find.</abstract><cop>Washington, DC</cop><pub>Blackwell Publishing Ltd</pub><doi>10.1029/98JA00212</doi><tpages>14</tpages><oa>free_for_read</oa></addata></record> |
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subjects | Earth, ocean, space Exact sciences and technology External geophysics Physics of the magnetosphere Plasma motion, convection, circulation. Plasma instabilities |
title | Observations of mesoscale auroral plasma cavity crossings with the Freja satellite |
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