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This article may be downloaded for personal use only. Any other use requires prior permission of the American Geophysical Union. This work was published in journal of Geophysical Research, v. 105 (A12) 27,147–27,156 published by American Geophysical Union. To view the published open abstract, go to http://dx.doi.org/10.1029/2000JA900056
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Journal of Geophysics Research, 105 (A12) 27147-27156