Rapid Cosmic Ray Fluctuations: Evidence for Cyclic Behaviour
Abstract
We study rapid cosmic-ray fluctuations using 5-min resolution data from eight neutron monitors with different cutoff rigidities as well as from the ACE satellite. We define a proxy index of rapid cosmic-ray fluctuations as the mean power of the cosmic-ray power spectrum in the frequency range 10−4 −1.67 × 10−3 Hz (10 min to about 3 h). A dominant 11-year periodicity in the index is found in all neutron monitors. We also report on intermittent, short-term periodicities in the power of rapid cosmic-ray fluctuations. A strong mid-term periodicity of about 1.6 - 1.8 years, possibly related to a recently found similar periodicity in IMF, appears in CR fluctuation power since the 1980s. Another strong periodicity is found at 1 year, which is likely related to the relative position of the Earth in the heliosphere. These results also provide new challenge to test the cosmic-ray modulation theory.
- Publication:
-
Solar Physics
- Pub Date:
- October 2004
- DOI:
- 10.1007/s11207-005-4178-4
- Bibcode:
- 2004SoPh..224..335S
- Keywords:
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- Power Spectrum;
- Relative Position;
- Modulation Theory;
- Resolution Data;
- Cyclic Behaviour