Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit

T Motoba; S Ohtani; M Gkioulidou; A. Y Ukhorskiy; D. G Mitchell; K Takahashi; L. J Lanzerotti; C. A Kletzing; H. E Spence; J. R Wygant

doi:10.1029/2018JA025557

Back

Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit

Journal article

Peer reviewed

Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit

T Motoba, S Ohtani, M Gkioulidou, A. Y Ukhorskiy, D. G Mitchell, K Takahashi, L. J Lanzerotti, C. A Kletzing, H. E Spence and J. R Wygant

Journal of geophysical research. Space physics, Vol.123(7), pp.5420-5434

07/2018

DOI: 10.1029/2018JA025557

View Online

Abstract

This paper examines how hydrogen, helium, and oxygen (H, He, and O) ion fluxes at 1–1,000 keV typically respond to local magnetic dipolarization inside geosynchronous orbit. We extracted 144 dipolarizations that occurred at magnetic inclination >30° from the 2012–2016 tail seasons' observations of the Van Allen Probes spacecraft and then defined typical flux changes of these ion species by performing a superposed epoch analysis. On average, the dipolarization inside geosynchronous orbit is accompanied by a precursory transient decrease in the northward magnetic field component, transient impulsive enhancement in the westward electric field component, and decrease (increase) in the proton density (temperature). The coincident ion species experience an energy‐dependent flux change, consisting of enhancement (depression) at energies above (below) ~50 keV. These properties morphologically resemble those around dipolarization fronts (or fast flows) in the near‐Earth tail. A distinction among the ion species is the average energy of the flux ratio peak, being at 200–400 keV (100–200 keV) for He (H and O) ions. The flux ratio peaks at different energies likely reflect the different charge states of injected ionospheric and/or solar wind origin ion species. The ion spectra become harder for sharp dipolarizations, suggesting the importance of accompanying electric field in transporting and/or energizing the ions efficiently. Interestingly, the average flux ratio peak does not differ significantly among the ion species for ~2 min after onset, which implies that mass‐dependent acceleration process is less important in the initial stage of dipolarization. Key Points Dipolarizations inside GEO have similar field/plasma variations to those around dipolarization fronts in the near‐Earth tail Dipolarization‐induced H, He, and O ion flux changes indicate energy‐ and charge state‐dependent signatures Mass‐dependent ion flux enhancements are less pronounced at least in the initial stage of dipolarization

deep inside geosynchronous orbit

dipolarizations

ion injections

ion species

Details

Title: Subtitle: Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit
Creators: T Motoba - Johns Hopkins University Applied Physics Laboratory
S Ohtani - Johns Hopkins University Applied Physics Laboratory
M Gkioulidou - Johns Hopkins University Applied Physics Laboratory
A. Y Ukhorskiy - Johns Hopkins University Applied Physics Laboratory
D. G Mitchell - Johns Hopkins University Applied Physics Laboratory
K Takahashi - Johns Hopkins University Applied Physics Laboratory
L. J Lanzerotti - New Jersey Institute of Technology
C. A Kletzing - University of Iowa
H. E Spence - University of New Hampshire
J. R Wygant - University of Minnesota
Resource Type: Journal article
Publication Details: Journal of geophysical research. Space physics, Vol.123(7), pp.5420-5434
DOI: 10.1029/2018JA025557
ISSN: 2169-9380
eISSN: 2169-9402
Number of pages: 15
Grant note: National Aeronautics and Space Administration (NASA) (NNX16AF74G; NNX15AI95G; NAS5–01072)
Language: English
Date published: 07/2018
Academic Unit: Physics and Astronomy
Record Identifier: 9984199740902771

Metrics

6 Record Views

15 Times Cited - Web of Science