Spacecraft measurements of ions and electrons (>40 KeV) near and far upstream of the earthʹs bow shock Original Research Article

Two classes of proton enhancement can be recognised in the particle populations recorded upstream of the Earthʹs bow shock by the LION instrument onboard SOHO during a uniquely quiet period on the Sun in early 1996. These kinds of enhancement are, herein, defined to be events of Class 1 and Class 2 respectively. The flux profiles and characteristic features of Class 1 events suggest that they may be composed of particles accelerated at the bow shock. Class 2 events, which have different characteristics and co-relate with a high value of the geomagnetic index might, on the other hand, be associated with leakage from inside the magnetosphere, These possibilities of origin require further detailed study. On May 4, 1998 a population of particles accelerated up to ∼600 keV was identified in Interball and POLAR data at the Earthʹs (quasi-parallel) bow shock. Due to a lack of good magnetic connectivity, this population was not observed far upstream on SOHO (at L1) or onboard WIND. Records of relativistic electrons detected at SOHO and at Interball during a very active episode on the Sun in May 1998 are also presented and interpreted to have been associated with solar processes. These particles (unlike protons) were not dependent on the configuration of the interplanetary field to allow them to reach particular upstream locations. Such energetic electrons constitute a particular hazard to spacecraft.