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V. B. Yurchyshyn (Big Bear Solar Obs., NJIT)
Coronal mass ejections (CMEs) are often associated with erupted magnetic fields or disappeared chromospheric filaments. The majority of CMEs headed directly toward the earth (halo CMEs) are observed at 1AU as magnetic clouds (MC). The 3D structure of a MC can be represented by a force-free flux rope. When CMEs reach the earth, they may or may not cause magnetic storms. The geoeffectiveness of CMEs depends on the orientation of the magnetic field in them.
In our previous study we showed that the direction of the axial field in a MC and its helicity are consistent with the direction of the axial field and helicity of the erupted filaments. We also suggested that geoeffectiveness of a CME can be forecasted by using daily Big Bear Solar Observatory full disk H\alpha and SOHO EIT 195Å~ images and SOHO/MDI magnetograms, as well.
Here we continue to study the orientation of magnetic fields in CMEs and its correlation with the occurrence of geomagnetic storms. The study includes 11 earth directed CMEs for which photospheric sources were reliably defined. Our results further demonstrate that the geoeffectiveness of a CME can be predicted by considering the orientation of the CME's magnetic fields.
This work was supported in part by ATM-0076602, ATM-9903515 and NASA (NAG5-9682) grants. SOHO is a project of international cooperation between ESA and NASA.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.