Solar and interplanetary particle acceleration

The nature and location of energetic particle acceleration (excluding planetary magnetospheres) in the inner heliosphere (<6 A.U.) is controversial. A likely reason for this controversy is that some acceleration occurs in the interplanetary medium, some occurs at the site of solar flares and some occurs in the solar corona. Relativistic electrons are certainly accelerated at the Sun and they manifest themselves readily through the microwave and non-thermal X-ray emissions they produce. Electron acceleration also occurs in the corona near the Sun, and when this happens it is sometimes in association with fast coronal mass ejections. The role of strong shocks accompanying very fast (> 1000 km/sec) coronal mass ejections is examined, but we find that they are not normally associated with relativistic energetic particle acceleration, although they may enhance the energy of particles already present in the vicinity of the shock. There is no evidence that relativistic electron acceleration occurs in the interplanetary medium, except possibly for a very few isolated cases. A similar situation exists for the relativistic ions, although in this case the only electromagnetic signature they produce is gamma ray emission through nuclear interactions, which is not measured currently with high sensitivity. The extent of particle acceleration in the interplanetary medium in corotating interaction regions is only to sub-relativistic energies. Evidence to support these claims is reviewed. (C) 2003 COSPAR. Published by Elsevier Science Ltd. All rights reserved.