Oxygen Ion Flow Reversals in Earth's Magnetotail: A Cluster Statistical Study

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Authors
De Spiegeleer, A.
Hamrin, M.
Volwerk, M.
Karlsson, T.
Gunell, H.
Chong, G.S.
Pitkänen, T.
Nilsson, H.
Discipline
Physical sciences
Subject
Earth's magnetotail
oxygen ions
velocity reversal
pitch angle distribution
Cluster
field aligned
Audience
Scientific
Date
2019Metadata
Show full item recordDescription
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° to 180° or from 180° to 0°. These structures are called “Pitch Angle Slope Structures” (PASSes). PASSes for which the pitch angle changes from 0° to 180° are observed in the Northern Hemisphere while those for which the pitch angle changes from 180° to 0° 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 ∼0 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 <25RE 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.
Citation
De Spiegeleer, A.; Hamrin, M.; Volwerk, M.; Karlsson, T.; Gunell, H.; Chong, G.S.; Pitkänen, T.; Nilsson, H. (2019). Oxygen Ion Flow Reversals in Earth's Magnetotail: A Cluster Statistical Study. , Journal of Geophysical Research: Space Physics, Vol. 124, Issue 11, 8928-8942, DOI: 10.1029/2019JA027054.Identifiers
Type
Article
Peer-Review
Yes
Language
eng