Anisotropies of Solar Energetic Electron Events Observed By Multiple Spacecraft

Abstract:

We combine energetic electron observations by the two STEREO spacecraft with ACE measurements at the Earth's longitude to investigate events with wide longitudinal spreads. We scanned the whole STEREO dataset up to mid-2013 and collected 21 of such events. To be counted as a wide-spread event, a minimum longitudinal separation angle of 80 degrees is requested between the source active region at the Sun and the magnetic footpoint of one spacecraft observing the event. Special attention is paid to anisotropies to distinguish different source and transport mechanisms leading to the unexpectedly wide particle spreads. One favorable mechanism is efficient perpendicular transport in the interplanetary medium leading to vanishing anisotropies for larger separation angles. Another scenario is a large particle spread which is performed close to the Sun either due to a coronal shock or due to coronal transport. In this case, the observations at 1 AU during the early phase of the events are expected to show significant anisotropies due to the wide injection range at the Sun and particle focusing during the outwards propagation. For both of the above scenarios we find events in our sample, which suit the expected observations and even further events, which suggest a more complex scenario.