Signatures of CMEs in HeI 1083 nm Images and Estimation of ICME Bz Direction

Details Signatures of CMEs in HeI 1083 nm Images and Estimation of ICME Bz Direction Signatures of CMEs in HeI 1083 nm Images and Estimation of ICME Bz Direction

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aas...200.3706h&link_type=abstract

American Astronomical Society, 200th AAS Meeting, #37.06; Bulletin of the American Astronomical Society, Vol. 34, p.695

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Coronal Mass Ejections (CMEs) are expulsions from the corona of material at coronal and chromospheric temperatures. Since the strength of the HeI absorption line multiplet at 1083 nm partly depends on the amount of mass in the chromosphere and overlying corona, CME signatures appear in 1083 nm observations. We examined daily time-difference images for such signatures in comparison with direct CME observations. We found that by using good spatial resolution, the time-difference images readily show disappearing filaments and sudden expansions of coronal holes which are known to be frequently associated with CMEs. The images also show the enhanced footpoints of arcades of post-flare loops as increases of line strength, and plage intensity changes. The 1083 nm changes are often spread widely over a large fraction of the solar disk, consistent with direct coronal disk observations of CMEs. These difference images will be available on NSO's web site, along with other data, as part of a transition to new a new suite of synoptic instruments called SOLIS. As an example of the utility of comparing different data, we examined contemporaneous photospheric and chromospheric magnetograms to see if the magnetic field Bz direction (north-south GSE coordinate) of the interplanetary CME (ICME) could be predicted. A southward directed Bz is associated with severe geomagnetic storms. Several predictive schemes are promising but their reliability needs improvement. A significant observational difficulty is that the detectable mass loss occurs where the magnetic field is relatively weak. This work was supported in part by ONR grant N00014-91-J-1040 and NSF grant ATM-9819842.

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