Difference Between Magnetic Clouds and Non-cloud Ejecta in the Interplanetary Medium
Abstract
Solar cycle 23 has witnessed the accumulation of data on an unprecedented number of coronal mass ejections (CMEs) at the Sun and in the interplanetary (IP) medium, thanks to the large array of spaceborne observatories such as SOHO, Wind, and ACE. These observations have helped us make significant progress on the structure and evolution of CMEs in the inner heliosphere. One important question is whether the magnetic cloud (MC) and non-cloud ejecta have any difference in their solar origin. The ubiquitous nature of post-eruption arcades suggests that there should not be any difference. However, CMEs associated with MCs all originate from very close to the solar disk center (both in latitude and longitude). To zeroth order, the non-cloud ejecta seem to originate at larger central meridian distances (CMDs). In the extreme case of shocks without discernible ejecta, the corresponding CMEs have their solar sources near the limb. These observations suggest that whether one observes a flux rope (MC) or not depends mainly on the location of the observer with respect to the Sun-Earth line. Observations from solar cycle 23 indicate that there are significant deviations from the zeroth order picture, especially for non-cloud ejecta and the "driverless shocks": their solar sources near the disk center. The question is whether these ejecta do not have flux-rope structure by birth or they somehow got deflected away from the Sun-Earth line by other large- scale structures in the IP medium. The latter seems to be true for at least a subset of events, which seems to be affected by coronal holes located between the eruption center and the Sun-Earth line. This needs to be checked for all the events that deviate from the zeroth order picture. Charge-state signatures of MCs and non-cloud ejecta also support such a picture: the solar sources of IP CMEs with high charge states seem to originate close to the disk center, similar to the MC-associated CMEs. Another piece of evidence comes from the high correspondence between halo CMEs and MCs, both of which are highly geoeffective. Halo CMEs originating at larger CMDs produce geomagnetic storms via their sheath fields, again pointing to the importance of geometry. Contrary to importance of internal structure of CMEs for geoeffectiveness, the production of gradual solar energetic particle (SEP) should not depend on the internal structure of CMEs if the particles are accelerated by CME-driven shocks. In fact, there is a significant difference in the source distribution of SEP-producing CMEs (western sources) and MC CMEs (close to disk center). This paper illustrates these results using coronal and IP data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMSH22A..01G
- Keywords:
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- 2111 Ejecta;
- driver gases;
- and magnetic clouds;
- 2139 Interplanetary shocks;
- 7513 Coronal mass ejections (2101);
- 7514 Energetic particles (2114)