Heliospheric Observations of STEREO-Directed Coronal Mass Ejections in 2008 – 2010: Lessons for Future Observations of Earth-Directed CMEs
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We present a study of coronal mass ejections (CMEs) which impacted one of the STEREO spacecraft between January 2008 and early 2010. We focus our study on 20 CMEs which were observed remotely by the Heliospheric Imagers (HIs) onboard the other STEREO spacecraft up to large heliocentric distances. We compare the predictions of the Fixed-Φ and Harmonic Mean (HM) fitting methods, which only differ by the assumed geometry of the CME. It is possible to use these techniques to determine from remote-sensing observations the CME direction of propagation, arrival time and final speed which are compared to in-situ measurements. We find evidence that for large viewing angles, the HM fitting method predicts the CME direction better. However, this may be due to the fact that only wide CMEs can be successfully observed when the CME propagates more than 100∘ from the observing spacecraft. Overall eight CMEs, originating from behind the limb as seen by one of the STEREO spacecraft can be tracked and their arrival time at the other STEREO spacecraft can be successfully predicted. This includes CMEs, such as the events on 4 December 2009 and 9 April 2010, which were viewed 130∘ away from their direction of propagation. Therefore, we predict that some Earth-directed CMEs will be observed by the HIs until early 2013, when the separation between Earth and one of the STEREO spacecraft will be similar to the separation of the two STEREO spacecraft in 2009 – 2010.
KeywordsCoronal mass ejections STEREO Heliospheric imagers Methods
The authors would like to thank the anonymous referee for useful comments and suggestions, which helped improve the clarity of the manuscript. N.L. was supported during this work by NSF grants AGS-0819653, AGS-1239699 and AGS-1239704 and NASA grants NNX-07AC13G, NNX-08AQ16G and NNX-12AB28G. P.K. performed research for this work under a Research Experience for Undergraduates (REU) position at the University of Hawaii’s Institute for Astronomy and funded by NSF. L.K.J.’s work was funded by NASA’s SMD as part of the STEREO project, including the IMPACT investigation. This work was also partially supported by NASA STEREO program through grant NAS5-03131 to UC Berkeley and UNH and has received funding from the European Union Seventh Framework Programme (FP7/2007 – 2013) under grant agreement 263252 [COMESEP]. C.M. was supported by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (PIOF-GA-2010-272768 [WILISCME]). SOHO and STEREO are projects of international cooperation between ESA and NASA. The SECCHI data are produced by an international consortium of Naval Research Laboratory, Lockheed Martin Solar and Astrophysics Lab, and NASA Goddard Space Flight Center (USA), Rutherford Appleton Laboratory, and University of Birmingham (UK), Max-Planck-Institut für Sonnensystemforschung (Germany), Centre Spatiale de Liege (Belgium), Institut d’Optique Théorique et Appliquée, and Institut d’Astrophysique Spatiale (France).