Ninety degrees pitch angle enhancements of suprathermal electrons associated with interplanetary shocks

作者：Kajdic P^*; Lavraud B; Zaslavsky A; Blanco Cano X; Sauvaud J A; Opitz A; Jian L K; Maksimovic M; Luhmann J G

来源：JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, 2014, 119(9): 7038-7060.

DOI：10.1002/2014JA020213

We report the results of the first systematic analysis of 90 degrees pitch angle (PA) enhancements or the ring distributions of suprathermal (E similar to 70 eV-2 keV) electrons at interplanetary (IP) shocks. We analyze 2 h time intervals around 232 IP shocks observed by the two STEREO spacecraft between 2007 and 2011. The ring distributions were detected downstream of 114 events (49%). In 52 (22.4%) cases they were detected at the shock ramp. We also found 90 degrees enhancements upstream of 11 (4.7%) events. Statistical analysis of basic shock properties did not reveal substantial differences between the shocks that are associated with the enhancements and those that are not. The data from the STEREO/WAVES instruments revealed that the 90 degrees PA enhancements tend to be associated with magnetic and electric field fluctuations. Although at this point we do not have a satisfactory explanation for the mechanism that produces these distributions, our findings suggest that wave-particle interactions play a role, while pure focusing and mirroring effects due to adiabatic motion of electrons across the shock fronts cannot fully account for the observations.

• 出版日期2014-9