Variation of the PSD slopes of cosmic rays in 1953-2016
Abstract
The flux of cosmic rays observed at the Earth is modulated by the Sun and the heliosphere. Modulation of the galactic cosmic rays (GCR) is mostly caused by scattering on the inhomogeneities of the heliospheric magnetic field (HMF). Sporadic solar events like coronal mass ejections and merged interaction regions affect the HMF and scatter GCR. Turbulent variations are another source of inhomogeneities of the, causing scattering at different scales. The variability of the cosmic ray flux as measured ground-based neutron monitors (NMs) can serve as a probe for heliospheric turbulence and its scaling. Turbulent phenomena are often characterized by a power-law type power spectral density (PSD) of the measured variable. Using 1-hour resolution data from the global NM network in 1953-2016, we have studied the power-law slope in the frequency range between 5.56*10^{-6} and 2.14*10^{-6} Hz, corresponding to time scales of 50 and 130 hours. The mean power-law slope was found to be -1.81±0.02. We have studied the temporal variation of this power-law slope and found that the slope values differ for different solar cycles and different cycle phases, with steeper slopes observed usually during the ascending and maximum phases, and less steep slopes during the declining and minimum phases. This implies that the scaling of HMF turbulence varies in the course of the solar cycle, reflecting different physical processes affecting GCR modulation.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3483V