Suprathermal electrons in high‐speed streams from coronal holes: Counterstreaming on open field lines at 1 AU

Using ACE and Genesis data, suprathermal electron measurements within high‐speed streams and their associated corotating interaction regions (CIRs) have been analyzed. Enhanced fluxes of sunward streaming suprathermal electrons are consistently observed following the passage of a corotating interaction region (CIR) over spacecraft at 1 AU. A backstreaming electron beam, produced at the CIR, is observed whether the CIRs are bounded by reverse shocks or reverse pressure waves. Because an antisunward directed electron strahl distribution is also normally present, electron counterstreaming results. Counterstreaming following CIRs can last for more than 2 days, after which time a 1 AU spacecraft is magnetically connected to a CIR at 3–5 AU. Although electron counterstreaming is frequently associated with closed field lines of interplanetary coronal mass ejections (ICMEs), electron counterstreaming associated with CIRs occurs on open field lines. Occasionally, electron counterstreaming associated with CIR‐produced suprathermal electrons is also seen within the slow wind preceding a CIR. In each such case observed the counterstreaming lasted less than 1 day.