Study of the 27-day variations in GCR fluxes during 2007-2008 based on PAMELA and ARINA observations

TL;DR

This study analyzes 27-day variations in galactic cosmic ray fluxes during 2007-2008 using PAMELA and ARINA data, revealing complex rigidity dependence and implications for heliospheric modulation models.

Contribution

First direct space-based analysis of 27-day GCR flux variations across a wide rigidity range using PAMELA and ARINA data, with insights into their energy dependence and heliospheric implications.

Findings

Rigidity dependence of GCR variations differs at low and high energies.

Identified a flat rigidity interval with a near-zero power-law index.

Discussed the relationship between GCR variations and solar wind parameters.

Abstract

Using measurements from the PAMELA and ARINA spectrometers onboard the RESURS DK-1 satellite, we have examined the 27-day intensity variations in galactic cosmic ray (GCR) proton fluxes in 2007-2008. The PAMELA and ARINA data allow for the first time a study of time profiles and the rigidity dependence of the 27-day variations observed directly in space in a wide rigidity range from ~300 MV to several GV. We find that the rigidity dependence of the amplitude of the 27-day GCR variations cannot be described by the same power-law at both low and high energies. A flat interval occurs at rigidity R = <0.6-1.0> GV with a power-law index gamma = - 0.13+/-0.44 for PAMELA, whereas for R >= 1 GV the power-law dependence is evident with index gamma = - 0.51+/-0.11. We describe the rigidity dependence of the 27-day GCR variations for PAMELA and ARINA data in the framework of the modulation potential concept using the force-field approximation for GCR transport. For a physical interpretation, we have considered the relationship between the 27-day GCR variations and solar wind plasma and other heliospheric parameters. Moreover, we have discussed possible implications of MHD modeling of the solar wind plasma together with a stochastic GCR transport model concerning the effects of corotating interaction regions.