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Detailed Reference Information |
Cliver, E.W., Kamide, Y., Ling, A.G. and Yokoyama, N. (2001). Semiannual variation of the geomagnetic Dst index: Evidence for a dominant nonstorm component. Journal of Geophysical Research 106: doi: 10.1029/2000JA000358. issn: 0148-0227. |
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The geomagnetic Dst index exhibits a strong semiannual variation with amplitude of 5.3 nT (on an average baseline of -16.4 nT) for 1957--1997. If we consider the five quietest Dst days for each month during this interval, we find that while the average Dst baseline shifts from -16.4 to +4.0 nT, the amplitude of the 6-month wave remains relatively strong at 2.5 nT. Thus ~50% (2.5 nT/5.3 nT) of the seasonal variation of the Dst index results from modulation of its quiet time baseline. The seasonal modulation of Dst appears to consist of both a storm component, resulting from rapid variations of the ring current and other currents, and a slowly varying, nonstorm component. We estimate that the storm component accounts for only ~30--50% of the amplitude of the 6-month wave in Dst versus ~50--70% for the nonstorm component. The classic equinoctial effect appears to dominate the storm component, accounting for 20--40% of the amplitude of the 6-month wave in Dst versus ~10% for the combined axial/Russell-McPherron mechanisms. Candidate mechanisms for the nonstorm component of the 6-month wave in Dst include the Malin-Isikara effect (the seasonal displacement of ring/tail currents by solar wind compression) and a semiannual variation of magnetopause currents. ¿ 2001 American Geophysical Union |
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Abstract |
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Keywords
Magnetospheric Physics |
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Publisher
American Geophysical Union 2000 Florida Avenue N.W. Washington, D.C. 20009-1277 USA 1-202-462-6900 1-202-328-0566 service@agu.org |
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