Using energetic particles to probe the magnetic topology of ejecta

Abstract

Observations of energetic particles over a wide range of rigidities can provide information on the presence of ejecta, and their structure. A large fraction of ejecta produce a local, few percent depression of the cosmic ray density. The depression typically extends over the ejecta region as determined from a range of ejecta signatures, in particular plasma with abnormally low proton temperatures. At lower rigidities (less than 0.5 GV, E_proton<100 MeV), the depression can be greater than 70%. These observations suggest that ejecta are predominantly closed magnetic structures. The bidirectional particle flows present in regions of some ejecta are consistent with particle circulation/reflection within closed structures. The observation of solar particle event onsets inside some ejecta suggests that field lines in these ejecta are rooted at the Sun. These particles arrive from a range of directions, including from the east. The observations are consistent with the presence of looped magnetic field lines rooted at the Sun in many ejecta, although recent observations from the WIND spacecraft suggest that ejecta may be more complex and include regions of field lines both connected to and disconnected from the Sun. At high heliolatitudes, Ulysses observations suggest that energetic particle signatures of ejecta are slightly different. In particular, low energy (∼MeV) particle enhancements, rather than depressions, are found in ejecta, apparently because ejecta guide particles to high latitudes where the ambient particle intensity is lower than near the ecliptic.