Distant heliospheric results on interplanetary shock propagation

Solar wind plasma data from Pioneers 10 and 11 and the Pioneer Venus Orbiter for 1978 to mid-1981 have been examined for forward shock signatures, and associations have been made with solar flares. (IMP 8 shocks from early 1978 have similarly been included for completeness). The numbers of flare-associated shocks observed at the various heliocentric distances of the spacecraft (ranging from 0.7 to 24 AU) are deduced, and the shock strengths and energies are given. Significantly fewer shocks associated with flares are observed at the greater distances, presumably because more cases have decreased below the threshold for inclusion. Three cases in which the same shock was probably detected by spacecraft at different heliocentric distances indicate deceleration and weakening at the greater distances.