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Solar and Heliospheric Physics
The IDV index: Its derivation and use in inferring long-term variations of the interplanetary magnetic field strength
Article first published online: 13 DEC 2005
DOI: 10.1029/2005JA011203
Copyright 2005 by the American Geophysical Union.
Issue
2169-9402/asset/cover.gif?v=1&s=c95aab738f9359df0f217c15befc7ccc95c58657 "Journal of Geophysical Research: Space Physics (1978–2012)")
Journal of Geophysical Research: Space Physics (1978–2012)
Volume 110, Issue A12, December 2005
Additional Information
How to Cite
, and (2005), The IDV index: Its derivation and use in inferring long-term variations of the interplanetary magnetic field strength, J. Geophys. Res., 110, A12103, doi:10.1029/2005JA011203.
Publication History
- Issue published online: 13 DEC 2005
- Article first published online: 13 DEC 2005
- Manuscript Accepted: 29 SEP 2005
- Manuscript Revised: 17 SEP 2005
- Manuscript Received: 22 APR 2005
Keywords:
- magnetic fields;
- solar activity cycle;
- solar and stellar variability;
- interplanetary magnetic fields;
- solar wind/magnetosphere interactions;
- magnetic storms
[1] On the basis of a consideration of Bartels' historical u index of geomagnetic activity, we devise an equivalent index that we refer to as the interdiurnal variability (IDV). The IDV index has the interesting and useful property of being highly correlated with the strength of the interplanetary magnetic field (B; R2 = 0.75) and essentially unaffected by the solar wind speed (V; R2 = 0.01) as measured by spacecraft. This enables us to obtain the variation of B from 1872 to the present, providing an independent check on previously reported results for the evolution of this parameter. We find that solar cycle average B increased by ∼25% from the 1900s to the 1950s and has been lower since. If predictions for a small solar cycle 24 bear out, solar cycle average B will return to levels of ∼100 years ago during the coming cycle(s).