Diffusion of cosmic rays in heliosphere, observations from GRAPES-3

Abstract

The large area (560m2) GRAPES-3 tracking muon telescope has been operating at Ooty, India uninterruptedly from 2001. It records 4 × 109 muons of energy > 1GeV with an angular resolution of ∼4° every day. The high statistical accuracy of this instrument helps in measuring the variations of galactic cosmic rays (GCRs) with a statistical precision of < 0.01% every hour. Here a study of solar modulation of GCR using GRAPES-3 is presented. We analysed uninterrupted GRAPES-3 data for six years (2005-2010) after applying the detector efficiency, pressure, and temperature corrections on this data to remove the effects of instrumental and atmospheric variations. Muon intensity, after applying these corrections shows an anti-correlation with the interplanetary magnetic field (IMF) from ACE/WIND spacecrafts. This anti-correlation of muon intensity with the IMF indicates that the solar modulations of GCRs may be caused by variations in the IMF. The dependence of GCR intensity variation and IMF is estimated. Further calculations were performed to study these variations by assuming the diffusion of GCRs through the turbulent magnetic field. The results show that the solar modulations of GCRs are largely due to the diffusion of GCRs though turbulent IMF in the heliosphere.