Heliospheric Observations of STEREO-Directed Events in 2008-2010: Lessons for Future Observations

From mid-2009 to early 2010, the separation between the two STEREO spacecraft was comparable to the Earth-STEREO separation from now (mid 2011) to the beginning of 2013. Investigating STEREO-impacting CME events and their remote observations by the HIs gives us a preview of years to come. To identify how the wider angular separation would affect the usual analysis techniques, we have analyzed more than two dozens CMEs which impacted one of the STEREO spacecraft from early 2008 to early 2010. This allows us to predict the accuracy of these methods for the years to come. Based on a survey of remote-sensing observations of CMEs from different viewing angles, we also discuss what is the optimal separation with the Sun-Earth line for future space weather missions.