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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. Mursula3
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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