Solar energetic particles
Solar energetic particles, formerly known as solar cosmic rays, are high-energy, charged particles originating in the solar atmosphere and solar wind. They consist of protons, electrons and heavy ions with energies ranging from a few tens of keV to many GeV. The exact processes involved in transferring energy to SEPs is a subject of ongoing study.
SEPs are relevant to the field of space weather, as they are responsible for SEP events and ground [level enhancement]s.
History
SEPs were first detected in February and March 1942 by Scott Forbush indirectly as ground level enhancements.Solar particle events
SEPs are accelerated during solar particle events. These can originate either from a solar flare site or by shock waves associated with coronal mass ejections. However, only about 1% of CMEs produce strong SEP events.Two main mechanisms of acceleration are possible: diffusive shock acceleration or the shock-drift mechanism. SEPs can be accelerated to energies of several tens of MeV within 5–10 solar radii and can reach Earth in a few minutes in extreme cases. This makes prediction and warning of SEP events quite challenging.
In March 2021, NASA reported that scientists had located the source of several SEP events, potentially leading to improved predictions in the future.