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Krupp N.,Max Planck Institute for Solar System Research | Roussos E.,Max Planck Institute for Solar System Research | Kollmann P.,Max Planck Institute for Solar System Research | Paranicas C.,Johns Hopkins University | And 7 more authors.
Icarus | Year: 2012

The moon Enceladus, embedded in Saturn's radiation belts, is the main internal source of neutral and charged particles in the Kronian magnetosphere. A plume of water ice molecules and dust released through geysers on the south polar region provides enough material to feed the E-ring and also the neutral torus of Saturn and the entire magnetosphere. In the time period 2005-2010 the Cassini spacecraft flew close by the moon 14 times, sometimes as low as 25. km above the surface and directly through the plume. For the very first time measurements of plasma and energetic particles inside the plume and its immediate vicinity could be obtained. In this work we summarize the results of energetic electron measurements in the energy range 27. keV to 21. MeV taken by the Low Energy Magnetospheric Measurement System (LEMMS), part of the Magnetospheric Imaging Instrument (MIMI) onboard Cassini in the vicinity of the moon in combination with measurements of the magnetometer instrument MAG and the Electron Spectrometer ELS of the plasma instrument CAPS onboard the spacecraft. Features in the data can be interpreted as that the spacecraft was connected to the plume material along field lines well before entering the high density region of the plume. Sharp absorption signatures as the result of losses of energetic electrons bouncing along those field lines, through the emitted gas and dust clouds, clearly depend on flyby geometry as well as on measured pitch angle/look direction of the instrument. We found that the depletion signatures during some of the flybys show " ramp-like" features where only a partial depletion has been observed further away from the moon followed by nearly full absorption of electrons closer in. We interpret this as partially/fully connected to the flux tube connecting the moon with Cassini. During at least two of the flybys (with some evidence of one additional encounter) MIMI/LEMMS data are consistent with the presence of dust in energetic electron data when Cassini flew directly through the south polar plume. In addition we found gradients in the magnetic field components which are frequently found to be associated with changes in the MIMI/LEMMS particles intensities. This indicates that complex electron drifts in the vicinity of Enceladus could form forbidden regions for electrons which may appear as intensity drop-outs. © 2012 Elsevier Inc..

Gerrard A.,New Jersey Institute of Technology | Lanzerotti L.,New Jersey Institute of Technology | Gkioulidou M.,Laurel University | Mitchell D.,Laurel University | And 3 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2014

H-ion (∼45 keV to ∼600 keV), He-ion (∼65 keV to ∼520 keV), and O-ion (∼140 keV to ∼1130 keV) integral flux measurements, from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft B, are reported. These abundance data form a cohesive picture of ring current ions during the first 9 months of measurements. Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio. Of unique interest to ring current dynamics are the spatial-temporal decay characteristics of the two injected populations. We observe that He-ions decay more quickly at lower L shells, on the order of ∼0.8 day at L shells of 3-4, and decay more slowly with higher L shell, on the order of ∼1.7 days at L shells of 5-6. Conversely, O-ions decay very rapidly (∼1.5 h) across all L shells. The He-ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange. The O-ion decay time is much faster than predicted and is attributed to the inclusion of higher-energy (> 500 keV) O-ions in our decay rate estimation. We note that these measurements demonstrate a compelling need for calculation of high-energy O-ion loss rates, which have not been adequately studied in the literature to date. © 2014. The Authors.

Paranicas C.,Johns Hopkins University | Mitchell D.G.,Johns Hopkins University | Krimigis S.M.,Johns Hopkins University | Carbary J.F.,Johns Hopkins University | And 9 more authors.
Journal of Geophysical Research: Space Physics | Year: 2010

We present both energetic proton and electron data from the main radiation belts of Saturn. When organized by L shell and equatorial pitch angle, data from Cassini's Magnetospheric Imaging Instrument reveal proton radiation belts that are highly symmetric in local time. The energetic electron radiation belts are asymmetric in two principal ways. Using data from two close passes of the planet, we find for energies near a few MeV, electron intensity levels are different between noon and midnight. Furthermore, when Cassini was inbound to Saturn, electron fluxes dropped precipitously before the spacecraft reached the main rings. Outbound, electron fluxes returned to high levels when the spacecraft moved outward of the main rings. In this paper, we suggest that electron flux level asymmetries are due in part to the presence of local time stationary particles in Saturn's inner magnetosphere. We also consider possible mechanisms to account the drop off of electrons near the ring edge on the dayside. © 2010 by the American Geophysical Union.

Cooper J.F.,NASA | King J.H.,NASA | Papitashvili N.E.,NASA | Lal N.,NASA | And 16 more authors.
AIP Conference Proceedings | Year: 2012

Space weathering by the plasma and energetic particle radiation environment of the heliosphere contributes to the physical and chemical evolution of exposed surfaces on airless bodies such as the Moon, asteroids, comets, and icy bodies of the outer solar system. The Multi-Source Spectral Plot (MSSP) service of the NASA Virtual Energetic Particle Observatory (VEPO) enables enhanced access and comparative global heliospheric analysis of ion flux spectra from the past and present fleet of interplanetary spacecraft for modeling of space weathering effects. Commonly red colors of low-inclination Classical Kuiper Belt Objects may be the result of specific compositional origin and spectral irradiation effects in the outer heliosphere. VEPO also enables easy comparison of flux spectra to check intercalibration issues. © 2012 American Institute of Physics.

O'Brien T.P.,The Aerospace Corporation | Claudepierre S.G.,The Aerospace Corporation | Looper M.D.,The Aerospace Corporation | Blake J.B.,The Aerospace Corporation | And 11 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

We describe a method for using drift echo signatures in on-orbit data to resolve discrepancies between different measurements of particle flux. The drift period has a well-defined energy dependence, which gives rise to time dispersion of the echoes. The dispersion can then be used to determine the effective energy for one or more channels given each channel's drift period and the known energy for a reference channel. We demonstrate this technique on multiple instruments from the Van Allen Probes mission. Drift echoes are only easily observed at high energies (100 s keV to multiple MeV), where several drift periods occur before the observing satellite has moved on or the global magnetic conditions have changed. We describe a first-order correction for spacecraft motion. The drift echo technique has provided a significant clue in resolving substantial flux discrepancies between two instruments measuring fluxes near 2 MeV. Key Points The drift echo period in a static magnetic field is a function of particle energy All channels on the same spacecraft must give consistent energy versus drift period Knowing only one channel's energy, it is possible to infer all others' energies ©2015. American Geophysical Union. All Rights Reserved.

Shi R.,Wuhan University | Shi R.,Memorial University of Newfoundland | Summers D.,Memorial University of Newfoundland | Ni B.,Wuhan University | And 3 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2016

A statistical study of ring current-energy proton pitch angle distributions (PADs) in Earth's inner magnetosphere is reported here. The data are from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on board the Van Allen Probe B spacecraft from 1 January 2013 to 15 April 2015. By fitting the data to the functional form sinnα, where α is the proton pitch angle, we examine proton PADs at the energies 50, 100, 180, 328, and 488 keV in the L shell range from L = 2.5 to L = 6. Three PAD types are classified: trapped (90° peaked), butterfly, and isotropic. The proton PAD dependence on the particle energy, magnetic local time (MLT), L shell, and geomagnetic activity are analyzed in detail. The results show a strong dependence of the proton PADs on MLT. On the nightside, the n values outside the plasmapause are clearly lower than those inside the plasmapause. At higher energies and during intense magnetic activity, nightside butterfly PADs can be observed at L shells down to the vicinity of the plasmapause. The averaged n values on the dayside are larger than on the nightside. A maximum of the averaged n values occurs around L = 4.5 in the postnoon sector (12–16 MLT). The averaged n values show a dawn-dusk asymmetry with lower values on the dawnside at high L shells, which is consistent with previous studies of butterfly PADs. The MLT dependence of the proton PADs becomes more distinct with increasing particle energy. These features suggest that drift shell splitting coupled with a radial flux gradient play an important role in the formation of PADs, particularly at L > ~ 4.5. ©2016. American Geophysical Union. All Rights Reserved.

Mitchell D.G.,Johns Hopkins University | Lanzerotti L.J.,New Jersey Institute of Technology | Kim C.K.,Johns Hopkins University | Stokes M.,Johns Hopkins University | And 17 more authors.
Space Science Reviews | Year: 2013

The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on the two Van Allen Probes spacecraft is the magnetosphere ring current instrument that will provide data for answering the three over-arching questions for the Van Allen Probes Program: RBSPICE will determine "how space weather creates the storm-time ring current around Earth, how that ring current supplies and supports the creation of the radiation belt populations," and how the ring current is involved in radiation belt losses. RBSPICE is a time-of-flight versus total energy instrument that measures ions over the energy range from ∼20 keV to ∼1 MeV. RBSPICE will also measure electrons over the energy range ∼25 keV to ∼1 MeV in order to provide instrument background information in the radiation belts. A description of the instrument and its data products are provided in this chapter. © 2013 The Author(s).

Korotova G.I.,Russian Academy of Sciences | Sibeck D.G.,NASA | Tahakashi K.,JHU APL | Dai L.,University of Minnesota | And 7 more authors.
Annales Geophysicae | Year: 2015

We present Van Allen Probe B observations of azimuthally limited, antisymmetric, poloidal Pc 4 electric and magnetic field pulsations in the pre-midnight sector of the magnetosphere from 05:40 to 06:00 UT on 1 May 2013. Oscillation periods were similar for the magnetic and electric fields and proton fluxes. The flux of energetic protons exhibited an energy-dependent response to the pulsations. Energetic proton variations were anticorrelated at medium and low energies. Although we attribute the pulsations to a drift-bounce resonance, we demonstrate that the energy-dependent response of the ion fluxes results from pulsation-associated velocities sweeping energy-dependent radial ion flux gradients back and forth past the spacecraft. © Author(s) 2015.

Morgado B.,Portuguese Laboratory of Instrumentation and Experimental Particle Physics | Morgado B.,University of Porto | Maia D.J.F.,University of Porto | Lanzerotti L.,New Jersey Institute of Technology | And 2 more authors.
Astronomy and Astrophysics | Year: 2015

Aims. We show that the Heliosphere Instrument for Spectra Composition and Anisotropy at Low Energies (HISCALE) on board the Ulysses spacecraft and the Electron Proton Alpha Monitor (EPAM) on board the Advance Composition Explorer (ACE) spacecraft can be used to measure properties for ion populations with kinetic energies in excess of 1 GeV. This previously unexplored source of information is valuable for understanding the origin of near relativistic ions of solar origin. Methods. We model the instrumental response from the low energy magnetic spectrometers from EPAM and HISCALE using a Monte Carlo approach implemented in the Geant4 toolkit to determine the response of different energy channels to energies up to 5 GeV. We compare model results with EPAM observations for 2012 May 17 ground level solar cosmic ray event, including directional fluxes. Results. For the 2012 May event, all the ion channels in EPAM show an onset more than one hour before ions with the highest nominal energy range (1.8 to 4.8 MeV) were expected to arrive. We show from Monte Carlo simulations that the timing at different channels, the ratio between counts at the different channels, and the directional fluxes within a given channel, are consistent with and can be explained by the arrival of particles with energies from 35 MeV to more than 1 GeV. Onset times for the EPAM penetrating protons are consistent with the rise seen in neutron monitor data, implying that EPAM and ground neutron monitors are seeing overlapping energy ranges and that both are consistent with GeV ions being released from the Sun at 10:38 UT. © 2015 ESO.

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