Tracking a Ulysses High-latitude ICME Event Back to Its Solar Origins

High-latitude interplanetary mass ejections (ICMEs) observed beyond 1 AU are not studied very often. They are useful for improving our understanding of the 3D heliosphere. As there are only few such events registered by the Ulysses spacecraft, the task of detecting their solar counterparts is a challenge, especially during high solar activity periods, because there are dozens coronal mass ejections (CMEs) registered by SOHO that might be chosen as candidates. We analyzed a high-latitude ICME registered by the Ulysses spacecraft on 18 January 2002. Our investigation focused on the correlation between various plasma parameters that allow the identification to be made of the ICME and its components such as the forward shock, the magnetic cloud and the reverse shock. Using a linear approach and a graphical method we have been able to track the ICME event back to the Sun and to compute the day of the occurrence of the solar CME. In order to decide among several CME candidates which one is the right solar counterpart of our event, we have performed a follow-up computation of these CMEs from the Sun to Ulysses , by using two different speed formulas. First, the computation was simply based on the initial CME velocity, while the other was based on the ICME velocity estimated from the CME initial speed (Lindsay et al. 1999 ). Differences of hours have been obtained between the arrival time predicted in these two ways, but the second one gave the best results. Both methods indicated the same two CMEs as the solar counterparts. We have found the solar source of these CMEs as being a huge polar filament that erupted in several steps. This ICME event displayed a double magnetic cloud configuration. A minimum variance analysis helped us to detect the smooth rotation of the clouds and their helicity. Both magnetic clouds show the same helicity as the filament that erupted and released them. A cylinder-shape model of both clouds gives the same helicity sign.