Low altitude energetic electron lifetimes after enhanced magnetic activity as deduced from SAC-C and DEMETER data

S Benck,J Cabrera,L Mazzino,M Cyamukungu,V Pierrard

doi:10.5194/angeo-28-849-2010

Abstract

Abstract. When flux enhancements of energetic electrons are produced as a consequence of geomagnetic storm occurrence, they tend to vanish gradually when the magnetic activity calms down and the fluxes decay to quiet-time levels. We use SAC-C and DEMETER low altitude observations to estimate the energetic electron lifetimes (E=0.16–1.4 MeV, L=1.6–5, B=0.22–0.46 G) and compare the decay rates to those observed at high altitude. While crossing the radiation belts at high latitude, the SAC-C and DEMETER instruments sample particles with small equatorial pitch angles (αeq<18° for L>2.5) whereas the comparison is done with other satellite data measured mainly in the equatorial plane (for αeq>75°). While in the inner belt and in the slot region no significant lifetime differences are observed from the data sets with different αeq, in the outer belt, for the least energetic electrons (<500 keV), the lifetimes are up to ~3 times larger for the electrons with the equatorial pitch-angle close to the loss cone than for those mirroring near the equator. The difference decreases with increasing energy and vanishes for energies of about 1 MeV.

Highlights

Statistical space radiation models based on averages of all measured values include variances that result from stormtime transients
We use SAC-C and DEMETER low altitude observations to estimate the energetic electron lifetimes (E=0.16–1.4 MeV, L=1.6–5, B=0.22–0.46 G) and compare the decay rates to those observed at high altitude
While crossing the radiation belts at high latitude, the SAC-C and DEMETER instruments sample particles with small equatorial pitch angles whereas the comparison is done with other satellite data measured mainly in the equatorial plane

Summary

Introduction

Statistical space radiation models based on averages of all measured values include variances that result from stormtime transients. Such models fade away the characteristics of physical processes that drive the dynamic of particle fluxes. We intend to break with classical model approaches and go beyond the existing static radiation models by introducing dynamic features based on observations of transient flux events. This approach is expected to facilitate the investigation of the physical mechanisms involved in the flux variations in the magnetosphere. Measurements of the lifetimes of energetic electrons are often considered to be the key to the understanding of the transport of these particles; for instance, they constitute key parameters in the determination of pitch angle diffusion rates (West et al, 1981)

Results

Discussion

Conclusion