Magnetic dipolarizations inside geosynchronous orbit with tailward ion flows
<p>Electromagnetic field and plasma data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) near-Earth probes are used to investigate magnetic dipolarizations inside geosynchronous orbit on 27 August 2014 during an intense substorm with <span class="i...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-05-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/37/289/2019/angeo-37-289-2019.pdf |
| Summary: | <p>Electromagnetic field and plasma data from the Time History of Events and
Macroscale Interactions during Substorms (THEMIS) near-Earth probes are used
to investigate magnetic dipolarizations inside geosynchronous orbit on
27 August 2014 during an intense substorm with <span class="inline-formula">AE<sub>max</sub>∼1000</span> nT. THEMIS-D (TH-D) was located inside geosynchronous orbit around
midnight in the interval from 09:25 to 09:55 UT. During this period, two
distinct magnetic dipolarizations with tailward ion flows are observed by
TH-D. The first one is indicated by the magnetic elevation angle increase from
15 to 25<span class="inline-formula"><sup>∘</sup></span> around 09:30:40 UT. The tailward perpendicular velocity is
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>V</mi><mrow><mo>⊥</mo><mi mathvariant="normal">x</mi></mrow></msub><mo>∼</mo><mo>-</mo><mn mathvariant="normal">50</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="826bf632c156da00cbb31ba70094db72"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="angeo-37-289-2019-ie00001.svg" width="50pt" height="12pt" src="angeo-37-289-2019-ie00001.png"/></svg:svg></span></span> km s<span class="inline-formula"><sup>−1</sup></span>. The second one is presented by
the elevation angle increase from 25 to 45<span class="inline-formula"><sup>∘</sup></span> around 09:36 UT, and the
tailward perpendicular velocity is <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>V</mi><mrow><mo>⊥</mo><mi mathvariant="normal">x</mi></mrow></msub><mo>∼</mo><mo>-</mo><mn mathvariant="normal">70</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="b91ecb5e1d593155c8230c6eb959cf71"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="angeo-37-289-2019-ie00002.svg" width="50pt" height="12pt" src="angeo-37-289-2019-ie00002.png"/></svg:svg></span></span> km s<span class="inline-formula"><sup>−1</sup></span>. These two significant dipolarizations are accompanied
with the sharp increase in the energy flux of energetic electron inside
geosynchronous orbit. After a 5 min expansion
of the near-Earth plasma sheet (NEPS), THEMIS-E (TH-E) located outside geosynchronous orbit also detected this tailward expanding plasma sheet with ion flows of <span class="inline-formula">−</span>150 km s<span class="inline-formula"><sup>−1</sup></span>. The dipolarization propagates tailward
with a speed of <span class="inline-formula">−</span>47 km s<span class="inline-formula"><sup>−1</sup></span> along a 2.2 <span class="inline-formula"><i>R</i><sub>E</sub></span> distance in the
<span class="inline-formula"><i>X</i></span> direction between TH-D and TH-E within 5 min. These dipolarizations with tailward ion flows observed inside geosynchronous orbit indicate a new
energy transfer path in the inner magnetosphere during substorms.</p> |
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| ISSN: | 0992-7689 1432-0576 |