Distribution of energetic particles near interplanetary shocks

Abstract

The acceleration of charged particles by collisionless shocks is a process of considerable importance in astrophysics, but the physical mechanism is not yet understood in detail. Energetic particles near interplanetary shocks may be studied in situ by spacecraft, but little is known about their distribution across the shock surface because of inadequate knowledge of the location of the sampling point in relation to the whole disturbance. A ground-based method has been developed² which enables shock-associated disturbances to be mapped in three dimensions, and we have used it, in combination with near-Earth spacecraft measurements, to study how the particle flux varies for shocks travelling at different angles to the Sun–Earth line. We have observed a pronounced east–west asymmetry which indicates that the inclination of the interplanetary magnetic field to the shock surface must be a potent factor in the acceleration process.