Spatial structure and temporal evolution of energetic particle injections in the inner magnetosphere during the 14 July 2013 substorm event

Abstract

Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside geosynchronous orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm (Dst~À40 nT) on 14 July 2013. Van Allen Probe B, inside geosynchronous orbit, observed two energetic proton injections within 10 min, with different dipolarization signatures and duration. The first one is a dispersionless, short-timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer-timescale injection pulse accompanied by a gradual dipolarization signature. We combined ground magnetometer data from various stations and in situ particle and magnetic field data from multiple satellites in the inner magnetosphere and near-Earth plasma sheet to determine the spatial extent of these injections, their temporal evolution, and their effects in the inner magnetosphere. Our results indicate that there are different spatial and temporal scales at which injections can occur in the inner magnetosphere and depict the necessity of multipoint observations of both particle and magnetic field data in order to determine these scales.

Ion acceleration at dipolarization fronts in the inner magnetosphere

“…They showed that multiple mesoscale injections were observed throughout the storm main phase deep inside the inner magnetosphere and that these injections accounted for a large portion of plasma pressure in the storm time ring current. Gkioulidou et al [2015] reported a dispersionless ion injections at as low as L = 5.5 associated with a sharp dipolarization of magnetic field, similar to dipolarization fronts in the magnetotail. A statistical analysis of dipolarization fronts measured at Van Allen Probes [Liu et al, 2016] showed that as much as 30% of dipolarizations from the magnetotail can penetrate inside geosynchronous orbit.…”

“…As our nominal case we use an isolated injection/dipolarization event on 14 July 2013 described in Gkioulidou et al [2015]. At 11:21 UT Van Allen Probes spacecraft B observed a large dispersionless increase in the intensities of 80-300 keV protons along with a sharp ∼30 nT dipolarization in the magnetic field at L = 5.5 close to the magnetic equator at dusk.…”

“…For a quantitative analysis we conducted three-dimensional test particle simulation of energetic proton interaction with an isolated earthward propagating dipolarization front as discussed in Gkioulidou et al [2015]. Particle trajectories in the prescribed fields given by the superposition of the ambient field (Earth's dipole with a disk-shaped current sheet) and the dipolarization front were computed numerically by integrating the Lorentz equation with a symplectic adaptive stepsize Boris algorithm [e.g., Birdsall and Langdon, 2014].…”

The evolution of ring current ion energy density and energy content during geomagnetic storms based on Van Allen Probes measurements

“…Gerrard et al [2014a] showed quiet time He ion fluxes using data from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument on board the Van Allen Probes, and the observations suggest inward radial diffusive motion of He ions which were previously injected into higher L shells. Gkioulidou et al [2014Gkioulidou et al [ , 2015, also using data from the RBSPICE instrument, investigated the ion injections during the ring current buildups and concluded that the small-scale ion injections could make a substantial contribution to the augmentation of the ring current.…”

Butterfly pitch angle distribution of relativistic electrons in the outer radiation belt: Evidence of nonadiabatic scattering

“…The ion fluxes do not exhibit a similar increase, thus, the spacecraft was likely located within the electron boundary of injection but eastward relative to the ion boundary [see Birn et al, 1997b, and references therein]. The injection is observed around the midnight sector where pure electron injections without observations of an ion flux increase are not rare (see statistics in Birn et al [1997a] Gkioulidou et al [2015].…”