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Evidence of strong energetic ion acceleration in the near‐Earth magnetotail
Author(s) -
Luo H.,
Kronberg E. A.,
Grigorenko E. E.,
Fränz M.,
Daly P. W.,
Chen G. X.,
Du A. M.,
Kistler L. M.,
Wei Y.
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl060252
Subject(s) - ion , physics , atomic physics , plasma sheet , anisotropy , flux (metallurgy) , cluster (spacecraft) , substorm , plasma , materials science , magnetosphere , nuclear physics , quantum mechanics , computer science , metallurgy , programming language
Until now it is still questionable whether ions are accelerated to energies above 100 keV in the near‐Earth current sheet (CS), in the vicinity of a possible near‐Earth neutral line. By using 11 years of 3‐D energetic ion flux data for protons, helium, and oxygen (~150 keV–1 MeV) from the RAPID instrument on board Cluster 4, we statistically study the energetic ion acceleration by investigating ion anisotropies in the near‐Earth magnetotail (−20 R E < X <−16 R E ). It is found that the earthward (tailward) anisotropy of the energetic (>150 keV) ions (protons, He + , and O + ) tend to become higher as the earthward (tailward) plasma bulk flows (measured by Cluster Ion Spectrometry experiment) become stronger. During such periods the presence of a strong acceleration source tailward (earthward) of Cluster spacecraft (S/C) is confirmed by the hardening energy spectra of the earthward (tailward) energetic ion flows. A good statistical correlation between tailward bulk flow, negative Bz , and the tailward anisotropy of energetic ions indicates that the strong ion acceleration might be related to a near‐Earth reconnection, which occurred earthward of the Cluster S/C. The energetic ion anisotropies do not show a clear dependence on the AE index, which may indicate that the acceleration source(s) for the energetic ions could be spatially localized.