Discrete energetic(～50-200 keV) electron events in the high-altitude cusp/polar cap/lobe

We identified 28 discrete electron events(DEEs) with enhanced fluxes at ~50-200 keV in the high-altitude cusp/polar cap/lobe,using the electron measurements by the BeiDa Image Electron Spectrometer(BD-IES) instrument onboard an inclined(55°)geosynchronous orbit(IGSO) satellite from October 2015 to January 2016. We find that among the 28 DEEs, 22 occur in the nightside and mostly in the northern cusp/polar cap/lobe, while 6 occur in the dayside and all in the southern cusp; 24 events correspond to an average interplanetary magnetic field(IMF) component B_z>0, 3 correspond to an average IMF B_z<0, and 1 has no OMNI IMF data. In these DEEs, the observed average omnidirectional electron differential flux generally fits well to a power-law spectrum, J^E^(-γ), with the spectral index y ranging from 2.6 to 4.6, while the average electron flux varies over three orders of magnitude from event to event. The spectral index of these cusp DEEs are(strongly) larger than the spectral index of solar wind superhalo electrons(radiation belt electrons) observed by the WIND 3 D Plasma & Energetic Particle instrument(the BD-IES). At^110 keV,the electron flux of DEEs in the cusp/polar cap/lobe shows a weak positive correlation with the solar wind superhalo electron flux but no obvious correlation with the radiation belt electron flux. These results suggest that these DEEs probably originate from transient processes acting on the solar wind superhalo electrons, e.g., the mid/high-latitude reconnection.

Radial propagation of magnetospheric substorm-injected energetic electrons observed using a BD-IES instrument and Van Allen Probes

In cases where substorm injections can be observed simultaneously by multiple spacecraft,they can help elucidate the potential mechanisms of particle transport and energization,of great importance to understanding and modeling the magnetosphere.In this paper,using data returned from the BeiDa-IES（BD-IES） instrument onboard a satellite in an inclined（55°） geosynchronous orbit（IGSO）,in combination with two geo-transfer orbiting（GTO） satellite Van Allen Probes（A and B）,we analyze a substorm injection event that occurred on the 16 th of October 2015.During this substorm injection,the IGSO onboard BD-IES was outbound,while both Van Allen Probe satellites（A and B） were inbound,a configuration of multiple trajectories that provides a unique opportunity to simultaneously investigate both the inward and outward radial propagation of substorm injection.Indicated by AE/AL indices,this substorm was closely related to an IMF/solar wind discontinuity that showed a sharp change in IMF Bz direction to the north.The innermost signature of this substorm injection was detected by Van Allen Probes A and B at L-3.7,while the outermost signature was observed by the onboard BD-IES instrument at L-10.These data indicate that the substorm had a global,rather than just local,effect.Finally,we suggest that electric fields carried by fast-mode compressional waves around the substorm injection are the most likely candidate mechanism for the electron injection signatures observed in the inner- and outermost inner magnetosphere.

Particle acceleration and transport in the inner heliosphere

In the solar system, our Sun is Nature's most efficient particle accelerator. In large solar flares and fast coronal mass ejections(CMEs), protons and heavy ions can be accelerated to over ~GeV/nucleon. Large flares and fast CMEs often occur together. However there are clues that different acceleration mechanisms exist in these two processes. In solar flares, particles are accelerated at magnetic reconnection sites and stochastic acceleration likely dominates. In comparison, at CME-driven shocks,diffusive shock acceleration dominates. Besides solar flares and CMEs, which are transient events, acceleration of particles has also been observed in other places in the solar system, including the solar wind termination shock, planetary bow shocks, and shocks bounding the Corotation Interaction Regions(CIRs). Understanding how particles are accelerated in these places has been a central topic of space physics. However, because observations of energetic particles are often made at spacecraft near the Earth,propagation of energetic particles in the solar wind smears out many distinct features of the acceleration process. The propagation of a charged particle in the solar wind closely relates to the turbulent electric field and magnetic field of the solar wind through particle-wave interaction. A correct interpretation of the observations therefore requires a thorough understanding of the solar wind turbulence. Conversely, one can deduce properties of the solar wind turbulence from energetic particle observations. In this article I briefly review some of the current state of knowledge of particle acceleration and transport in the inner heliosphere and discuss a few topics which may bear the key features to further understand the problem of particle acceleration and transport.