The evolution of interplanetary shocks

Abstract

Unambiguous identification of the solar events associated with 48 interplanetary (IP) shocks has been facilitated by the observation of radio emission generated by the shocks. This identification makes possible an investigation of the way in which these shocks evolve and of the relationship between solar event 'strength' and shock velocity. All but two of the 48 solar events associated with IP type II radio emission included long-duration soft X-ray events (LDE's). In addition, it is shown that all intense LDE's are associated with IP shocks. A weak correlation between the integral flux of soft X-rays and the average velocity of the associated shock is suggested. However, for two events all of the usual flare signatures were absent, and the events are associated with the disappearance of solar filaments. It is shown that the shocks propagate isotropically over about 50 deg from the source site. Beyond 50 deg the shocks weaken particularly on their eastern flanks. As a consequence, shocks originating on the west limb cannot reach the earth. IP type II radio emission is dependent on shock velocity with faster shocks producing more intense emission. The study shows that radio intensities provide information about the evolution of IP shocks.