Substorm injection of relativistic electrons to geosynchronous orbit during the great magnetic storm of March 24, 1991

Abstract

Abstract. The great March 1991 magnetic storm and the immediately preceding solar energetic particle event (SEP) were among the largest observed during the past solar cycle, and have been the object of intense study. We investigate here, using data from eight satellites, the very large delayed buildup of relativistic electron flux in the outer zone during a 1.5-day period beginning 2 days after onset of the main phase of this storm. A notable feature of the March storm is the intense substorm activity throughout the period of the relativistic flux buildup, and the good correlation between some temporal features of the lower-energy substorm-injected electron flux and the relativistic electron flux at geosynchronous orbit. Velocity dispersion analysis of these fluxes between geosynchronous satellites near local midnight and local noon shows evidence that both classes of electrons arrive at geosynchron0us nearly simultaneously within a few hours of local midnight. From this we conclude that for this storm period the substorm inductive electric field transports not only the usual (50-300 keV) substorm electrons but also the relativistic (0.3 to several MeV) electrons to geosynchronous orbit. A simplified calculation of the electron oe x B and gradient/curvature drifts indicates that sufficiently strong substorm dipolarization inductive electric fields ( • 10 mV/m) could achieve this, provided sufficient relativistic electrons are present in the source region. Consistent with this interpretation, we find that the injected relativistic electrons have a pitch angle distribution that is markedly peaked perpendicular to the magnetic field. Furthermore, the equatorial phase space density at geosynchronous orbit (L = 6.7) is greater than it is at GPS orbit at the equator (L = 4.2) throughout this buildup period, indicating that a source for the relativistic electrons lies outside geosynchronous orbit during this time. Earthward transport of the relativistic electrons by large substorm dipolarization fields, since it is unidirectional, would constitute a strong addition to the transport by radial diffusion and, when it occurs, could result in unusually strong relativistic fluxes, as is reported here for this magnetic storm.

Space Weather Effects Produced by the Ring Current Particles

“…There have been several studies aimed at the modeling of electron injections as they are well-known signatures of a substorm in the near-Earth space (Li et al 1998;Zaharia et al 2000;Sarris et al 2002;Gabrielse et al 2012Gabrielse et al , 2014Gabrielse et al , 2016Ganushkina et al 2013Ganushkina et al , 2014. These models give relatively good agreement with the observed dispersionless electron injections at geostationary orbit during specific events (Ingraham et al 2001;Fok et al 2001a;Li et al 2003;Mithaiwala and Horton 2005;Liu et al 2009). The substorm-associated electromagnetic fields are very complex and their proper representation is still missing from the modeling efforts for keV electrons in the inner magnetosphere.…”

Spatial spreading of magnetospherically reflected chorus elements in the inner magnetosphere

“…Figure 1 for instance shows that localized wave source around L ∼ 6-7 should produce relatively wide wave distribution at L ∼ 5 up to L ∼ 10. This localized source can mimic wave generation by transient particle injections into the inner magnetosphere (such injections often stop around L ∼ 6-7 and can penetrate up to the plasmapause; see Ingraham et al, 2001;Dubyagin et al, 2011, and references therein). Our simulations demonstrate that waves generated in a localized source fill a wide region due to the divergence of their trajectories.…”

The Electric Field and Waves Instruments on the Radiation Belt Storm Probes Mission

“…These fronts could result in the injection and energization of both ring current ions and high-energy electrons (10-700 keV), which are the dominant contribution to the particle energy density and pressure around the Earth during major geomagnetic storms. There is evidence (Ingraham et al 2001) suggesting that intense substorm injection fronts may be able to energize significant fluxes of electrons up to >1 MeV below L = 4−5 over time scales of minutes. However, our understanding of the efficiency of the mechanism is largely based on CRRES, which only saw one very large storm on the night side of the Earth.…”