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J. Zhang, W. Poomvises (George Mason University)
We address the issues in observing and understanding the chain Sun-Earth connection activities that result in major geomagnetic storms, one of severe space weather phenomena. From 1996 to 2004, there are 77 major geomagnetic storms (defined as Dst <= -100). A systematic multi-step process is carried out to identify the event chain for each of the major events. It is found that a major geomagnetic storm event could be driven by three types of solar sources (1) S type, a single halo CME, (2) M-type, multiple halo CMEs, or (3) C-type, CIR (corotating interaction region) originated from coronal hole. Throughout the solar cycle 23rd, there are more major events originated from western solar hemisphere than from eastern hemisphere, probably due to the spiral interplanetary magnetic field connecting the western hemisphere and the geo-space. Before solar polar field reversal in 2001, a significant number of events originate from the northern hemisphere. However, after the polar field reversal, events predominantly originate from the southern hemisphere. This effect indicates that the global solar field plays an important role in determining the geo-effective southward magnetic field in the solar wind disturbances. It is recognized that the lack of observations in the inner heliosphere makes it difficult to unambiguously determine the solar sources of geo-effective space weather events.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.