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D.A. Biesecker, W. Murtagh, D.J. Zezula (NOAA/SEC), C.N. Arge (AFRL/Hanscom AFB)
Many sectors of our technology infrastructure have identified the importance of accurate and timely predictions of hazardous space weather. Organizations react to space weather warnings by taking important mitigating actions to protect vulnerable systems. Geomagnetic storms in particular can impact spacecraft operations, the electric power grid, communications, and navigation systems. Virtually all geomagnetic storms are caused by coronal mass ejections (CME's) or high speed solar wind streams. High speed streams typically originate from coronal holes which are easily identified on a variety of solar imaging wavelengths. The recurrent nature of coronal holes generally results in accurate predictions of the associated geomagnetic storms.
The prediction of CME's, which account for almost all of the strongest storms, is considerably more difficult, but they can be detected almost immediately upon initiation. It usually takes 1-3 days for a CME to transit from the Sun to the Earth, which gives forecasters plenty of time to predict its arrival. Gopalswamy et al. (2000,2001) showed that it is possible to use the measured plane-of-the-sky speed of CME's to predict their transit time. Gopalswamy et al. noted that the transit time depends on the CME acceleration (deceleration) terminating when the CME achieves the background solar wind speed. Accounting for the actual speed of the solar wind at the time of the CME, we find that transit time predictions can be improved. Further work, accounting for the average background wind speed encountered by the CME, will be presented here and is expected to provide additional improvement. Since the transit time also depends on which part of the CME intersects the Earth's magnetosphere, accounting for the source location, which is a proxy for the launch direction, is expected to provide even more improvement.
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Bulletin of the American Astronomical Society, 36 #2
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