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Found 2 entries in the Bibliography.


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2016

Ion nose spectral structures observed by the Van Allen Probes

We present a statistical study of nose-like structures observed in energetic hydrogen, helium, and oxygen ions near the inner edge of the plasma sheet. Nose structures are spectral features named after the characteristic shapes of energy bands or gaps in the energy-time spectrograms of in situ measured ion fluxes. Using 22 months of observations from the Helium Oxygen Proton Electron (HOPE) instrument onboard Van Allen Probe A, we determine the number of noses observed, and the minimum L-shell reached and energy of each nose on each pass through the inner magnetosphere. We find that multiple noses occur more frequently in heavy ions than in H+, and are most often observed during quiet times. The heavy-ion noses penetrate to lower L shells than H+ noses and there is an energy-magnetic local time (MLT) dependence in the nose locations and energies that is similar for all species. The observations are interpreted using a steady-state model of ion drift in the inner magnetosphere. The model is able to explain the energy and MLT dependence of the different types of nose structures. Different ion charge exchange lifetimes are the main cause for the deeper penetration of heavy-ion noses. The species dependence and preferred geomagnetic conditions of multiple-nose events indicate that they must be on long drift paths, leading to strong charge-exchange effects. The results provide important insight into the spatial distribution, species dependence, and geomagnetic conditions under which nose structures occur.

Ferradas, C.; Zhang, J.-C.; Spence, H.; Kistler, L.; Larsen, B.; Reeves, G.; Skoug, R.; Funsten, H.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2016

YEAR: 2016     DOI: 10.1002/2016JA022942

inner magnetosphere; ion injection; Ion structure; plasma sheet; ring current; Van Allen Probes

2015

\textquotedblleftTrunk-like\textquotedblright heavy ion structures observed by the Van Allen Probes

Dynamic ion spectral features in the inner magnetosphere are the observational signatures of ion acceleration, transport, and loss in the global magnetosphere. We report \textquotedbllefttrunk-like\textquotedblright ion structures observed by the Van Allen Probes on 2 November 2012. This new type of ion structure looks like an elephant\textquoterights 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\textendash2.6, MLT = 9.1\textendash10.5, and MLAT = -2.4\textendash0.09\textdegree, vary monotonically from 3.5 to 0.04 keV. The values at the two end points of the O+ trunk are: energy = 4.5\textendash0.7 keV, L = 3.6\textendash2.5, MLT = 9.1\textendash10.7, and MLAT = -2.4\textendash0.4\textdegree. 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.

Zhang, J.-C.; Kistler, L.; Spence, H.; Wolf, R.; Reeves, G.; Skoug, R.; Funsten, H.; Larsen, B.; Niehof, J.; MacDonald, E.; Friedel, R.; Ferradas, C.; Luo, H.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2015

YEAR: 2015     DOI: 10.1002/2015JA021822

inner magnetosphere; ion injection; Ion structure; magnetic cloud; magnetic storm; Van Allen Probes



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