Suprathermal Electrons Bidirectionality Study inside Magnetic Clouds Observed by STEREO (2007-2014)

Magnetic clouds (MCs) are interplanetary structures with flux-rope topology, characterised by in-situ signatures, such as enhanced magnetic field magnitude, smooth magnetic field vector rotation, low proton density, low plasma beta and low temperature. Often, they also show bidirectionality in the suprathermal electron pitch-angle distribution. This bidirectionality is normally interpreted as an evidence of a continued magnetic field connection to the corona (which suggests a closed magnetic topology). For this reason, the bidirectionality can be observed due to two possible scenarios: injection from one leg and mirroring effect or an actual injection of the electrons from both footpoints. The lack of such bidirectionality also provides information about the possible erosion and reconnection processes in MCs, due to their interaction with the surrounding medium. This work presents an automated method that allows to quantify the suprathermal electrons bidirectionality using an spherical harmonic decomposition of the pitch angle distribution. The method has been applied to a set of 300 MCs observed by the twin mission STEREO between 2007 and 2014. A preliminary statistical study of the results is presented and discussed.