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Oxygen Ion Flow Reversals in Earth's Magnetotail: A Cluster Statistical Study
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.ORCID-id: 0000-0003-1167-8055
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.ORCID-id: 0000-0002-2043-4442
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2019 (Engelska)Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402Artikel i tidskrift (Refereegranskat) Epub ahead of print
Abstract [en]

We present a statistical study of magnetotail flows that change direction from earthward to tailward using Cluster spacecraft. More precisely, we study 318 events of particle flux enhancements in the O+ data for which the pitch angle continuously changes with time, either from 0 degrees to 180 degrees or from 180 degrees to 0 degrees. These structures are called "Pitch Angle Slope Structures" (PASSes). PASSes for which the pitch angle changes from 0 degrees to 180 degrees are observed in the Northern Hemisphere while those for which the pitch angle changes from 180 degrees to 0 degrees are observed in the Southern Hemisphere. These flux enhancements result in a reversal of the flow direction from earthward to tailward regardless of the hemisphere where they are observed. Sometimes, several PASSes can be observed consecutively which can therefore result in oscillatory velocity signatures in the earth-tail direction. The PASS occurrence rate increases from 1.8% to 3.7% as the AE index increases from similar to 0 to similar to 600 nT. Also, simultaneously to PASSes, there is typically a decrease in the magnetic field magnitude due to a decrease (increase) of the sunward component of the magnetic field in the Northern (Southern) Hemisphere. Finally, based on the 115 (out of 318) PASSes that show energy-dispersed structures, the distance to the source from the spacecraft is estimated to be typically R-E along the magnetic field line. This study is important as it sheds light on one of the causes of tailward velocities in Earth's magnetotail.

Ort, förlag, år, upplaga, sidor
2019.
Nyckelord [en]
Earth's magnetotail, oxygen ions, velocity reversal, pitch angle distribution, Cluster, field aligned
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
URN: urn:nbn:se:umu:diva-166575DOI: 10.1029/2019JA027054ISI: 000497604100001OAI: oai:DiVA.org:umu-166575DiVA, id: diva2:1380617
Tillgänglig från: 2019-12-19 Skapad: 2019-12-19 Senast uppdaterad: 2019-12-19

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De Spiegeleer, AlexandreHamrin, MariaGunell, HerbertChong, Ghai SiungPitkänen, Timo

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De Spiegeleer, AlexandreHamrin, MariaGunell, HerbertChong, Ghai SiungPitkänen, Timo
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Journal of Geophysical Research - Space Physics
Fusion, plasma och rymdfysik

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