Premium
Episodic Occurrence of Field‐Aligned Energetic Ions on the Dayside
Author(s) -
Yue Chao,
Bortnik Jacob,
Zou Shasha,
Nishimura Yukitoshi,
Foster John C.,
Coppeans Thomas,
Ma Qianli,
Zong Qiugang,
Hull A. J.,
Henderson Mike,
Reeves Geoffrey D.,
Spence Harlan E.
Publication year - 2020
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 - 10.1029/2019gl086384
Subject(s) - ring current , ionosphere , ion , magnetosphere , pitch angle , local time , population , geosynchronous orbit , physics , earth's magnetic field , magnetic field , computational physics , geophysics , field (mathematics) , atomic physics , astrophysics , astronomy , satellite , statistics , demography , mathematics , quantum mechanics , sociology , pure mathematics
The tens of kiloelectron volt ions observed in the ring current region at L ~ 3–7 generally have pancake pitch angle distributions, that is, peaked at 90°. However, in this study, by using the Van Allen Probe observations on the dayside, unexpectedly, we have found that about 5% time, protons with energies of ~30 to 50 keV show two distinct populations, having an additional field‐aligned population overlapping with the original pancake population. The newly appearing field‐aligned populations have higher occurrence rates at ~12–16 magnetic local time during geomagnetically active times. In particular, we have studied eight such events in detail and found that the source regions are located around 12 to 18 magnetic local time which coincides with our statistical result. Based on the ionospheric and geosynchronous observations, it is suggested that these energetic ions with field‐aligned pitch angle distributions probably are accelerated near postnoon in association with ionospheric disturbances that are triggered by tail injections.