Associated Research Papers
JASTP_70_2008_Lugaz_final.pdf - Lugaz et al., Observational Evidence of CMEs Interacting in the Inner Heliosphere Based on MHD Simulations
ApJL_HIs_Lugaz_et_al_2008.pdf – Lugaz et al., The Brightness of Density Structures at Large Solar Elongation Angles: What is Being Observed by STEREO/SECCHI?
Lugaz_JASTP_2007.pdf – Lugaz et al., Observational evidence of CMEs interacting in the inner heliosphere based on MHD simulations
ApJ_659_788.pdf – Lugaz et al., Numerical Investigation of the Homologous Coronal Mass Ejection Events from Active Region 9236
ApJ_627_2005_Lugaz.web.pdf - Lugaz et al., The evolution of Coronal Mass Ejection Density Structures
Research
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Read an introduction to CMEs on the CME Initiation page.
CME Cannibalism (Interaction of CMEs)
The transit of an average CME from the Sun to the Earth takes 3 days. Near solar maximum (next one around 2012), there are about 6 CMEs per day. It's just like traffic in greater LA, crashes have to happen.
Sometimes, the same active region produces a series of nearly identical CMEs. Those are referred as "homologous CMEs". The smallest delay found between two ejections from the same active region is 2 hours (January 20, 2001), but a delay of 6-10 hours is more
characteristic for homologous eruptions. The Sun rotates by about 0.6 degrees in an hour, so most successive CMEs from the same active region are separated by 4-6 degrees. However, the large spatial extent of CMEs makes the interaction of successive CMEs likely in those
cases. At Earth, only one third of the transient observed are magnetic cloud. The other have usually more complex structures and are globally referred as "complex ejecta". As many as half of these appear to be the results of the interaction of multiple CMEs or one CME with other solar wind structures. Some of the largest geomagnetic storms observed at Earth were associated with such complex ejecta.
The study of the interaction of CMEs has been an active field of research only for the past ten years. Some of the questions we, at
C2H2, try to answer are:
- What is the association between complex ejecta observed at Earth and the interaction of CME?
- How can one tell that a transient observed at Earth is the result or not of interacting CMEs?
- Can observations in the heliosphere and/or corona warn us that a geo-effective complex ejecta is coming?
- Is the sum more than the sum of its parts? Meaning does the interaction of two CMEs result in an event larger, stronger than the two isolated events would have been?
- When two CMEs collide on their way to Earth, what happens:
- Similarly to most cars in LA, does the first, slower one slows down the second, faster one?
- Similarly to some cars in LA, does the second faster one that bumps into the first one, push and accelerate it?
- Or does the fast one just pass through the slower one (not like cars)? It has been found that large SEP events seem to be associated with the interaction of CMEs. Is this real or not? If yes, what are the reasons?
Work on CME Cannibalism done by members of C2H2:
CMEs are better with traffic than people on H-1: when two CMEs collide, the first one is accelerated and compressed by the shock wave driven by the first one (Lugaz 2005b), the second one is decelerated by the presence of the first one. If the speed difference is enough, the shock waves driven by the 2 CMEs will actually merge in front of the CMEs. This merging creates a stronger shock waves: the interaction is a non-linear process and the results can be more geo-effective than the isolated CMEs. We predicted that STEREO/SECCHI Heliospheric Imagers would have the ability to detect the interaction of CMEs in the heliosphere (Lugaz 2008a). We studied the first instance of CME CME interaction obsvered by STEREO: January 24, 2007.
