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Ann. Geophys., 24, 779-783, 2006
www.ann-geophys.net/24/779/2006/
© European Geosciences Union 2006

Long-term modulation of the cosmic ray fluctuation spectrum

S. A. Starodubtsev¹, I. G. Usoskin², A. V. Grigoryev¹, and K. Mursula^3
1Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy, SB RAS, 31 Lenin Ave., 677 980 Yakutsk, Russia
²Sodankylä Geophysical Observatory, Oulu unit, 90014 University of Oulu, Finland
³Department of Physical Sciences, 90014 University of Oulu, Finland

Abstract. Here we study the power level of rapid cosmic ray fluctuations in the frequency range of 10^-4-1.67·10^-3 Hz (periods from 10 min to about 3 h), using measurements by space-borne instruments for the period since 1974. We find that the power level of these fluctuations varies over the solar cycle, but the phase of this variation depends on the energy of cosmic ray particles. While the power level of these fluctuations in the higher energy channels (corresponding to galactic cosmic rays) changes in phase with the solar cycle, the fluctuation level for lower energy channels (predominantly of solar/interplanetary origin) is roughly in an opposite phase with the solar cycle. The results prove conclusively that these fluctuations originate in the near-Earth space, excluding their atmospheric or magnetospheric origin. We present these new results and discuss a possible scenario explaining the observed energy-dependence.

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Citation: Starodubtsev, S. A., Usoskin, I. G., Grigoryev, A. V., and Mursula, K.: Long-term modulation of the cosmic ray fluctuation spectrum, Ann. Geophys., 24, 779-783, 2006.   Bibtex   EndNote   Reference Manager