“Trunk-like” heavy ion structures observed by the Van Allen Probes

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Dynamic ion spectral features in the inner magnetosphere are the observational signatures of ion acceleration, transport, and loss in the global magnetosphere. We report “trunk-like” ion structures observed by the Van Allen Probes on 2 November 2012. This new type of ion structure looks like an elephant's trunk on an energy-time spectrogram, with the energy of the peak flux decreasing Earthward. The trunks are present in He+ and O+ ions but not in H+. During the event, ion energies in the He+ trunk, located at L = 3.6–2.6, magnetic local time (MLT) = 9.1–10.5, and magnetic latitude (MLAT) = −2.4–0.09°, vary monotonically from 3.5 to 0.04 keV. The values at the two end points of the O+ trunk are energy = 4.5–0.7 keV, L = 3.6–2.5, MLT = 9.1–10.7, and MLAT = −2.4–0.4°. Results from backward ion drift path tracings indicate that the trunks are likely due to (1) a gap in the nightside ion source or (2) greatly enhanced impulsive electric fields associated with elevated geomagnetic activity. Different ion loss lifetimes cause the trunks to differ among ion species.

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Zhang, J.-C., Kistler, L.M., Spence, H.E., et al.. "“Trunk-like” heavy ion structures observed by the Van Allen Probes." Journal of Geophysical Research: Space Physics, 120, no. 10 (2015) Wiley: 8738-8748. http://dx.doi.org/10.1002/2015JA021822.

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