Heart Of Outer Radiation Belt Research Articles

Rapid Enhancements of the Seed Populations in the Heart of the Earth's Outer Radiation Belt: A Multicase Study

AbstractTo better understand rapid enhancements of the seed populations (hundreds of keV electrons) in the heart of the Earth's outer radiation belt (L* ~ 3.5–5.0) during different geomagnetic activities, we investigate three enhancement events measured by Van Allen Probes in detail. Observations of the fluxes and the pitch angle distributions of energetic electrons are analyzed to determine rapid enhancements of the seed populations. Our study shows that three specified processes associated with substorm electron injections can lead to rapid enhancements of the seed populations, and the electron energy increases up to 342 keV. In the first process, substorm electron injections accompanied by the transient and intense substorm electric fields can directly lead to rapid enhancements of the seed populations in the heart of the outer radiation belt. In the second process, the substorm injected electrons are first trapped in the outer radiation belt and subsequently transported into L* < 4.5 by the convection electric field. In the third process, the lower energy electrons are first injected at L* ~ 5.3 and then undergo drift resonance with ultralow‐frequency waves. These accelerated electrons by ultralow‐frequency waves are further transported into L* < 4.5 due to the convection electric field. This process is consistent with the radial diffusion. Our results suggest that these specified processes are important for understanding the dynamics of the seed populations in the heart of the outer radiation belt.

Rapid Loss of Radiation Belt Relativistic Electrons by EMIC Waves

AbstractHow relativistic electrons are lost is an important question surrounding the complex dynamics of the Earth's outer radiation belt. Radial loss to the magnetopause and local loss to the atmosphere are two main competing paradigms. Here on the basis of the analysis of a radiation belt storm event on 27 February 2014, we present new evidence for the electromagnetic ion cyclotron (EMIC) wave‐driven local precipitation loss of relativistic electrons in the heart of the outer radiation belt. During the main phase of this storm, the radial profile of relativistic electron phase space density was quasi‐monotonic, qualitatively inconsistent with the prediction of radial loss theory. The local loss at low L shells was required to prevent the development of phase space density peak resulting from the radial loss process at high L shells. The rapid loss of relativistic electrons in the heart of outer radiation belt was observed as a dip structure of the electron flux temporal profile closely related to intense EMIC waves. Our simulations further confirm that the observed EMIC waves within a quite limited longitudinal region were able to reduce the off‐equatorially mirroring relativistic electron fluxes by up to 2 orders of magnitude within about 1.5 h.

Multiple loss processes of relativistic electrons outside the heart of outer radiation belt during a storm sudden commencement

AbstractBy examining the compression‐induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP‐A/B), we find that the relativistic electrons (>2 MeV) outside the heart of outer radiation belt (L* ≥ 5) undergo multiple losses during a storm sudden commencement. The relativistic electron loss mainly occurs in the field‐aligned direction (pitch angle α < 30° or >150°), and the flux decay of the field‐aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30°–150° increase (decrease) with the decreasing (increasing) geocentric distance (|ΔL| < 0.25) of the RBSP‐B (RBSP‐A) location, and the electron fluxes in the quasi‐perpendicular direction display energy‐dispersive oscillations in the Pc5 period range (2–10 min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high‐L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850 km), and magnetic field fluctuations in the Pc5 band. The intense EMIC waves and whistler mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 h. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high‐L region with a negative electron phase space density gradient.

Energetic electron behavior in the outer radiation zone during the space weather month

The Akebono (EXOS-D) satellite made good observations of the radiation belt particles, covering an entire radiation belts in the evening sector during the space weather month (September 1999). During the campaign we had three magnetic storms; i.e. September 12–14, 22–23, and 27–28. On early September 23, the Dst index reached its minimum with −160 nT, showing a major magnetic storm, while both on September 13 and 27 the decrease of the Dst index was very gradual, having the minimum values of −70 nT and −65 nT, respectively. Even though the Dst variation was big during September 22–23, very little enhancement of MeV electrons was observed in the outer radiation belt during the storm recovery phase. On the contrary large enhancements in the intensity of MeV electrons took place for September 12–14 and 27–28, when the Dst variation were rather small. These large enhancements were made due to the prolonged magnetic activities during the storm recovery phase. The Russell-McPheron effect was evident; i.e. the 1IVIF was actually away for the cases of September 12–14 and 27–28. The increase in the intensity of MeV electrons was first seen in the heart of outer radiation belt and in lower energy. As time progressed the intensity of MeV electrons in far regions (L>5) increased, suggesting that both an internal acceleration of the electrons and an extremely large outward diffusion are taking place in the outer radiation belt.