Storm time evolution of the outer radiation belt: Transport and losses

Abstract

[1] During geomagnetic storms the magnetic field of the inner magnetosphere exhibits large-scale variations over timescales from minutes to days. Being mainly controlled by the magnetic field the motion of relativistic electrons of the outer radiation belt can be highly susceptible to its variations. This paper investigates evolution of the outer belt during the 7 September 2002 storm. Evolution of electron phase space density is calculated with the use of a test-particle simulation in storm time magnetic and electric fields. The results show that storm time intensification of the ring current produces a large impact on the belt. In contrast to the conventional D st effect the dominant effects are nonadiabatic and lead to profound and irreversible transformations of the belt. The diamagnetic influence of the partial ring current leads to expansion of electron drift orbits such that their paths intersect the magnetopause leading to rapid electron losses. About 2.5 hr after the storm onset most of the electrons outside L = 5 are lost. The partial ring current pressure also leads to an electron trap in the dayside magnetosphere where electrons stay on closed dayside drift orbits for as long as 11 hours. These sequestered electrons are reinjected into the outer belt due to partial recovery of the ring current. The third adiabatic invariant of these electrons exhibits rapid jumps and changes sign. These jumps produce localized peaks in the L*-profile of electron phase space density which have previously been considered as an observable indication of local electron acceleration.

Space Weather Effects Produced by the Ring Current Particles

“…Kim and Chan 1997), which can become a real loss of particles at the magnetopause (e.g. West et al 1972;Hudson et al 1998;Ukhorskiy et al 2006). This process has been identified as contributing rapid loss for up to 90% of the pre-existing population of both radiation belt electrons (100's keV to multi-MeV) energies and energetic ring current protons (100's keV to >1 MeV) .…”

Radial diffusion simulations of the 20 September 2007 radiation belt dropout

“…Possible resolutions include: qualitatively similar processes evaluated with better models of radial diffusion and cyclotron-resonant waves; non-diffusive radial transport (Ukhorskiy et al, 2006); non-resonant interactions with EMIC or other waves (Bortnik and Thorne, 2010); and nondiffusive wave-particle interactions (e.g., Albert, 2000;Albert et al, 2012). It has been noted in many test particle simulations that nonlinear interactions with large amplitude, resonant whistler waves lead to a preferential, rapid decrease in pitch angle, accompanied by decrease in energy (Albert, 2002;Tao et al, 2012); this could also be manifested as a loss process.…”

Radial transport of radiation belt electrons due to stormtime Pc5 waves

“…In storm recovery, however, flux levels can increase to levels greatly exceeding their pre-storm values (e.g., Reeves et al, 2003). Since flux depletions at storm main phase are most likely dominated by permanent losses (Ukhorskiy et al, 2006a), the after-storm flux increases require radial transport and subsequent heating of energetic electrons from the outer to the inner magnetospheric regions.…”