Observations of suprathermal electron conics in an interplanetary coronal mass ejection

Abstract

Solar wind suprathermal electron velocity distributions measured by the SWEPAM experiment aboard ACE were studied to determine the internal magnetic structure of the coronal mass ejection (CME) that passed 1 AU on 4-5 February, 1998. Pitch-angle distributions range from symmetric counter-streaming to complex distributions that include conics. Identification of suprathermal electron conics in interplanetary CMEs (ICMEs) is reported here for the first time. The origin of these conics is highly uncertain. We suggest, however, that the conics may originate in transient electron heating associated with magnetic reconnection within the magnetic legs of the CMEs. Such reconnection generates large, complex magnetic loops that have enhanced anti-solar electric fields at their solar edge to maintain charge neutrality. This field must be sufficiently strong to bind electrons with high pitch angles to the bottom of the loops as they propagate away from the Sun.