spase://NASA/Catalog/ACE/Counterstreaming_Electrons

Solar wind electrons at 1 AU are observed to stream through the solar wind at speeds in excess of the solar wind speed. This is not the case for thermal ions. Electrons are observed to move away from the sun and along magnetic field lines. At some times electrons are observed to stream in both directions along the magnetic field. It is widely held that at these times either both ends of the magnetic field line are connected to the sun, producing an expanding bubble-like intrusion into the interplanetary medium, or both ends of the field line were recently connected to the sun and reconnected to form a closed structure. Such periods are said to exhibit counterstreaming electrons and the SWEPAM instrument on ACE is capable of measuring such distributions. Periods of prolonged counterstreaming electrons are frequently associated with interplanetary observations of Coronal Mass Ejections (CMEs). For the counterstreaming electrons events listed here the counterstreaming is not always, or even generally, continuous throughout the event, but is almost always intermittent over the prolonged period that marks the duration of the observation.
Interplanetary, in-situ observations of coronal mass ejections are measurements of solar ejecta. These in-situ observations have now been correlated with remote optical observations of solar ejecta (see SOHO/LASCO CME list from remote optical observations).
Magnetic clouds are sometimes, but not always, observed within the CME or counterstreaming electron event. Comparison of this list with the cloud list will reveal those periods when both are present.
Magnetic field lines connected to downstream disturbances, such as shocks, may also produce counterstreaming electrons; although generally these events are of shorter duration than those listed here. For a spacecraft that is upstream of the Earth, as is ACE, such a downstream shock source could also include the Earth's bow shock.