Preconditioning of the Interplanetary Medium Due To Isolated ICMEs

We perform a systematic study of the preconditioning of the interplanetary (IP) medium due to isolated IP coronal mass ejections (ICMEs). Preconditioning is highly relevant when ICMEs, ejected in close succession and direction, modify the IP medium to allow subsequent ICMEs to propagate more freely, decelerate less, and retain higher kinetic energy at larger distances. We base our study on a sample of carefully selected events. The IP medium is analyzed during time intervals of 48 hr before and after the ICMEs in order to statistically quantify their impact on the properties of the solar wind (SW) and interplanetary magnetic field (IMF). We find that the SW behind ICMEs on average exhibits reduced density ($-$41%) and dynamic pressure ($-$29%), and increased total velocity (+15%), while the trailing IMF is more intense (+14%) and more radially aligned (13$°$). The results suggest that even relatively low speed ICMEs can significantly precondition the IP medium. The results are relevant for better understanding of CME propagation and SW interaction, and hold implications for heliospheric models and applied research of space weather.