J. L. Roeder

The Magnetic Electron Ion Spectrometer (MagEIS) Instruments Aboard the Radiation Belt Storm Probes (RBSP) Spacecraft

This paper describes the Magnetic Electron Ion Spectrometer (MagEIS) instruments aboard the RBSP spacecraft from an instrumentation and engineering point of view. There are four magnetic spectrometers aboard each of the two spacecraft, one low-energy unit (20–240xa0keV), two medium-energy units (80–1200xa0keV), and a high-energy unit (800–4800xa0keV). The high unit also contains a proton telescope (55xa0keV–20xa0MeV).The magnetic spectrometers focus electrons within a selected energy pass band upon a focal plane of several silicon detectors where pulse-height analysis is used to determine if the energy of the incident electron is appropriate for the electron momentum selected by the magnet. Thus each event is a two-parameter analysis, an approach leading to a greatly reduced background.The physics of these instruments are described in detail followed by the engineering implementation. The data outputs are described, and examples of the calibration results and early flight data presented.

Timing of magnetic reconnection initiation during a global magnetospheric substorm onset

[1]xa0We have used a unique constellation of Earth-orbiting spacecraft and ground-based measurements in order to study a relatively isolated magnetospheric substorm event on August 27, 2001. Global ultraviolet images of the northern auroral region established the substorm expansion phase onset at 0408:19 (±1 min) UT. Concurrent measurements from the GOES-8, POLAR, LANL, and CLUSTER spacecraft allow us to construct a timeline which is consistent with magnetic reconnection on the closed field lines of the central plasma sheet near XGSM ∼ −18 RE some 7 minutes prior to the near-earth and auroral region times of substorm expansion phase onset. This suggests that magnetic reconnection (i.e., the substorm neutral line) in this case formed in the mid-tail region substantially before current disruption, field dipolarization near geostationary orbit, or auroral substorm onsets occurred. Thus, the magnetic reconnection process is interpreted as the causative driver of dissipation in this well-observed case.

Statistical distribution of the storm-time proton ring current: POLAR measurements

[1]xa0Equatorial proton energy densities in the ring current region have been statistically investigated by compiling data acquired with the POLAR/MICS instrument (1–200 keV) in terms of the storm phases and Dst levels. The energy density is found to increase with decreasing Dst and to exhibit strong local time dependence during the storm main phase. In particular, the energy density at noon is interestingly shown to decrease during the main phase and increase during the recovery phase. A numerical simulation, which traces drift trajectories of the plasma sheet protons in the Volland-Stern type convection electric field, gives a reasonable result in comparison with the statistically obtained distribution. Those results support the scenario that the prime source of the higher energy density of the ring current protons is the plasma sheet protons whose drift motion is governed by the large-scale convection electric field most likely driven by the solar wind and IMF.

Extreme electron fluxes in the outer zone

[1]xa0Following the work of Koons (2001), we examine the statistical properties of extremely high fluxes of MeV electrons in the outer zone. We extend the analysis to include a variety of timescales and energies using observations from Los Alamos monitors at geosynchronous orbit and to include outer zone fluxes observed from L ∼ 2–8 by spacecraft in highly elliptical Molniya orbits. We use the statistical formalism of the generalized extreme value distribution, which represents the probability distribution of the maximum value taken out of a sample of fixed size. By taking the maximum flux observed in many nonoverlapping intervals of several hours to several days, we can determine whether the maximum flux is likely to have a finite upper limit or an exponential or power law tail. Our analysis indicates that MeV electron fluxes over a broad range of energies, L shells, and timescales have a finite upper limit, a true worst case. However, the statistical estimate of this upper limit is inherently uncertain. We compare our upper limits to the internal charging specifications provided by Fennell et al. (2000). We discuss several possible physical explanations for the flux limits.

Van Allen Probes observations of direct wave‐particle interactions

Quasiperiodic increases, or “bursts,” of 17–26u2009keV electron fluxes in conjunction with chorus wave bursts were observed following a plasma injection on 13 January 2013. The pitch angle distributions changed during the burst events, evolving from sinN(α) to distributions that formed maxima at αu2009=u200975–80°, while fluxes at 90° and <60° remained nearly unchanged. The observations occurred outside of the plasmasphere in the postmidnight region and were observed by both Van Allen Probes. Density, cyclotron frequency, and pitch angle of the peak flux were used to estimate resonant electron energy. The result of ~15–35u2009keV is consistent with the energies of the electrons showing the flux enhancements and corresponds to electrons in and above the steep flux gradient that signals the presence of an Alfven boundary in the plasma. The cause of the quasiperiodic nature (on the order of a few minutes) of the bursts is not understood at this time.

First polar and 1995‐034 observations of the midaltitude cusp during a persistent northward IMF condition

We present the first observations by Polar and 1995-034 of the mid-altitude cusp. On May 29, 1996, the Polar and 1995-034 spacecraft crossed into an extended cusp region. The region was characterized by intense fluxes of solar wind like ions in the energy range 1–10 keV that had angular distributions that showed evidence of flows and trapping. The ion composition data are combined with energetic proton observations from Polar and plasma observations from 1995-034 and DMSP satellites to examine the spatial and temporal extent and plasma characteristics of the cusp during a persistent northward IMF condition. The composition data is consistent with expected solar wind composition with a source temperature of ∼1.25 × 106 K. The combined spacecraft observations show an extended cusp-like region, probably produced by northward IMF.

Tail lobe and open field line region entries at mid to high latitudes

Abstract New data from the POLAR and HEO (high earth orbit) 95-034 satellites are used in a preliminary study to estimate the position of the open/closed (OC) field line boundary using energetic particle and plasma observations. In this study, the OC boundary positions were compared in several different coordinate systems and the GSM and eccentric dipole coordinates were found to be equally effective in organizing the HEO 95-034 data. No coordinate system appeared to organize the POLAR data best. The HEO 95-034 and POLAR data were examined for interplanetary field and plasma dynamic pressure control of the dayside OC boundary. The HEO 95-034 data showed a clear response to solar wind dynamic pressure with the OC boundary being at lower latitude with increasing pressure. The HEO 95-034 data also showed some response to the IMF BZ, hinting that the OC boundary would move to lower latitude with increasingly negative BZ but be unchanged for positive BZ. The POLAR data showed no dependence on either the solar wind dynamic pressure or BZ in this initial study. The data were relatively sparse; about a month of observations for each satellite.

Polar CEPPAD/IPS energetic neutral atom (ENA) images of a substorm injection

Abstract The CEPPAD Imaging Proton Spectrometer on the POLAR spacecraft has proven to perform very well as an Energetic Neutral (ENA) atom imager, despite the fact that it was designed primarily for measuring energetic ions in-situ. ENAs emitted from the ring current can be detected during storm- as well as quiet-time conditions and can be monitored continuously for many hours at a time when Polar is situated in the polar cap. In addition, we are able to routinely detect ‘bursts’ of ENA emissions in response to substorm-associated ion injections. In this paper, we present ENA images of a single such event together with global auroral imager data from the POLAR VIS instrument. LANL geosynchronous energetic particle data, and ground magnetic Pi2 data in order to establish that such bursts are indeed caused by substorm injections.

CRRES observations of particle flux dropout events

Abstract The complete disappearance of energetic electrons was observed by CRRES in the near geosynchronous region in 7.5% of the orbits examined. These total flux dropouts were defined by the fluxes rapidly dropping to levels below the sensitivity of the MEA energetic electron spectrometer on the CRRES satellite. They were separated into those that were only energetic electron dropouts and those that were associated with energetic ion and plasma dropouts. Approximately 20% of the events showed dropouts of all particle fluxes, and these were usually coincident with large increases in the local magnetic intensity and signatures of strong current systems. The energetic particle instruments and magnetometer on CRRES provide a detailed picture of the particle and field responses to these unusual conditions. Both the local morning and dusk events were associated with strong azimuthal (eastward) and radial changes in the magnetic field indicative of a strong current system approaching and sometimes crossing the CRRES position at the time of the flux dropouts. The direction of the field changes and the details of particle observations are consistent with CRRES passing through the plasma sheet boundary layer and entering the tail lobe for a significant number of the events.

Electron plasma waves in the solar wind: AMPTE/IRM and UKS observations

Selected events of plasma wave and electromagnetic emissions in the earths electron fore-shock region have been studied. Strong emissions are observed in the plasma-wave band when the site of the satellite is magnetically connected to the bow shock. These emissions are generally highly fluctuating. Under certain conditions one observes electromagnetic radiation at the second harmonic produced locally. Electromagnetic emission generated at a position far away from the site of the spacecraft is occasionally detected giving rise to remote sensing of the bow shock. These emissions are related to energetic electron fluxes.