Statistical Analysis of Preconditioning in the Interplanetary MediumInduced by Isolated ICMEs

We investigate the effects of interplanetary coronal mass ejections (ICMEs) on the interplanetary (IP) medium, namely the solar wind (SW) and the interplanetary magnetic field (IMF). Our objective is to quantify how ICMEs alter the properties of the IP medium and to determine the degree of preconditioning. The latter occurs when ICMEs modify the IP medium in a way that enables subsequent ICMEs to propagate more efficiently, experience reduced deceleration, and retain higher energy over greater distances. This phenomenon has been proposed in the past to explain some of the shortest ICME travel times, the most intense geomagnetic storms, and the highest-energy ICME ever observed in situ.

Our analysis is based on a statistical study of a carefully curated sample of events. We examine the IP medium during 48-hour intervals before and after the passage of ICMEs. On average, the post-ICME solar wind exhibits reduced density and dynamic pressure, along with increased total velocity. Meanwhile, the trailing IMF becomes more intense and displays a stronger radial alignment. These findings indicate that even relatively moderate ICMEs can significantly precondition the IP medium, potentially influencing the behavior and impact of subsequent events.