Is the Interplanetary shock wave evolution self-similar in the Inner Heliosphere?

Abstract In situ observations of interplanetary (IP) coronal mass ejections (ICMEs) and IP shocks are important to study as they are the main components of the solar activity. Hundreds of IP shocks have been detected by various space missions at different times and heliocentric distances. Some of these are followed by an ICME while not for others. In this study, we carry out a statistical analysis of the distributions of plasma and magnetic parameters of the IP shocks. We classify the shocks according to the heliocentric distance, namely from 0.29 to 0.99 au (Helios-1/2); near 1 au (Wind, ACE and STEREO-A/B); and from 1.35 to 5.4 au (Ulysses). We also differentiate the IP shocks into two populations, those with a detected ICME and those without it. We find, as expected, that there are no significant difference in the results from spacecraft positioned at 1 au. Moreover, the distributions of shock parameters, as well as the shock normal have no significant variations with the heliocentric distance. Additionally, we investigate how the number of shocks associated to stream interaction regions (SIRs) increases with distance in proportion of ICME/shocks. From 1 to 5 au, SIRs/ shock occurrence increases slight from 21% to 33%, in contrast ICME/shocks occurrence decreases from 47% to 17%. We find also no indication of an asymmetry induced by the Parker spiral.