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Filters: Author is Foster, John C.  [Clear All Filters]
Authors: Yue Chao, Bortnik Jacob, Zou Shasha, Nishimura Yukitoshi, Foster John C., et al.
Title: Episodic Occurrence of Field‐Aligned Energetic Ions on the Dayside
Abstract: 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 th. . .
Date: 01/2020 Publisher: Geophysical Research Letters DOI: 10.1029/2019GL086384 Available at:
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Authors: Omura Yoshiharu, Hsieh Yi‐Kai, Foster John C., Erickson Philip J., Kletzing Craig A., et al.
Title: Cyclotron Acceleration of Relativistic Electrons Through Landau Resonance With Obliquely Propagating Whistler‐Mode Chorus Emissions
Abstract: Efficient acceleration of relativistic electrons at Landau resonance with obliquely propagating whistler‐mode chorus emissions is confirmed by theory, simulation, and observation. The acceleration is due to the perpendicular component of the wave electric field. We first review theoretical analysis of nonlinear motion of resonant electrons interacting with obliquely propagating whistler‐mode chorus. We have derived formulae of inhomogeneity factors for Landau and cyclotron resonances to analyze nonlinear wave trapping of energetic electrons by an obliquely propagating chorus element. We performed test particle simulations to confirm that nonlinear wave trapping by both Landau and cyclotron resonances can take place for a wide range of energies. For an element of large amplitude chorus . . .
Date: 04/2019 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA026374 Available at:
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Authors: Thomas Evan G., Yan Jingye, Zhang Jiaojiao, Baker Joseph B. H., Ruohoniemi Michael, et al.
Title: An examination of the source of decameter-scale irregularities in the geomagnetically disturbed mid-latitude ionosphere
Abstract: We present first results from a study of the plasma instability mechanism responsible for the small-scale (∼10 m) ionospheric density irregularities commonly observed by the Super Dual Auroral Radar Network (SuperDARN) HF radars in the vicinity of Sub Auroral Polarization Streams (SAPS) during periods of geomagnetic disturbance. A focus is placed on the mid-latitude region of the ionosphere over North America where recent expansion of the SuperDARN network allows for extensive direct comparisons with total electron content (TEC) measurements from a dense network of ground-based GPS receivers. The TEC observations indicate that high-speed SAPS channels and the associated small-scale irregularities are typically located within the mid-latitude ionospheric trough. The Millstone Hill Incoher. . .
Date: 08/2014 Publisher: IEEE DOI: 10.1109/URSIGASS.2014.6929853 Available at:
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