Effects of solar flare duration on a double shock pair at 1 AU

Abstract

Numerical solutions of the time-dependent equations of motion for spherically symmetric flow are obtained to study the propagation and modification of the forward-reverse shock pair in the region between the sun and 1 AU. For cases where the duration of the disturbance is long compared to T, the shock transit time to 1 AU, a double shock pair that resembles those predicted by similarity theory occurs at 1 AU. In cases where the duration of the solar disturbance is less than about 0.45T, the shock pair structure is appreciably altered by a rarefaction, initiated at the end of the solar disturbance, which has caught up with the shock pair. In cases where the duration is less than about 0.1T, the rarefaction completely destroys the reverse shock, leaving a single shock. This analysis indicates that a forward-reverse shock pair will not be observed at 1 AU unless the time duration of the solar disturbance is greater than about 5 hours. Since solar flares that last this long are quite rare, it is concluded that observation of a flare-associated forward-reverse shock pair at 1 AU is unlikely.