The amount of solar wind produced continuously by the sun is not constant due to changes in solar activity. This unsteady nature of the solar wind seems to be responsible for galactic cosmic ray flux modulation, hence the flux of incoming galactic cosmic rays observed at the top of the Earth's atmosphere varies with the solar wind reflecting the solar activity. The aforementioned reasons have lead to attempts by several researchers to study correlations between galactic cosmic rays and the solar wind. However, most of the correlation studies carried out by authors earlier are based on the analyses of observational data from neutron monitors. In this context, we study the effects of solar wind on galactic cosmic ray flux observed at r ≈ 1 AU, using a theoretical approach and found that the solar wind causes significant decreases in galactic cosmic ray flux at r ≈ 1 AU. A short time variation of the calculated flux is also checked and the result is reflected by exposing a negative correlation of the solar wind with the corresponding galactic cosmic ray flux. This means that the higher the solar wind the lower the galactic cosmic rays flux and vice-versa. To obtain a better understanding, the calculated flux and its short time variation at 1 AU are compared to data that shows a good fit to the model making it possible to establish a statistically significant negative correlation of −0.988 ± 0.001 between solar wind variation and galactic cosmic rays flux variation theoretically.

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The relationship between galactic cosmic rays and solar wind is investigated using an extended time-dependent and anisotropic force field model, where galactic cosmic rays flux is found to be related to the solar wind speed through the local interstellar spectrum and a modulation parameter. Galactic cosmic ray flux calculated at 1AU within the energy range (0.2-88)GeV using the model is also presented, the flux variation with time calculated at 1AU at a fixed energy range using the model is also presented and the solution is used to predict the flux variation at earth. The mechanism of cosmic rays transport considered here are only the diffusion and convection, other processes such as particle drifts, energy losses and magnetic irregularities among others are not considered in this work.

The flux of Galactic cosmic rays (GCRs) can undergo a Forbush decrease (FD) during the passage of a shock, sheath region, or magnetic flux rope associated with a coronal mass ejection (CME). Cosmic-ray observations during FDs can provide information complementary to in situ observations of the local plasma and magnetic field, because cosmic-ray distributions allow remote sensing of distant conditions. Here we develop techniques to determine the GCR anisotropy before and during an FD using data from neutron monitors worldwide. For example, for the FD starting on 2013 April 13, we find that at times with strong magnetic fluctuations and strong cosmic-ray scattering, there were spikes of high perpendicular anisotropy and weak parallel anisotropy. These results, along with the near constancy of parallel anisotropy across magnetic field reversals, are consistent with diffusive barriers causing the decrease in GCR flux before the arrival of the flux rope. In contrast, within the CME flux rope there was a strong parallel anisotropy in the direction predicted from a theory of drift motions into one leg of the magnetic flux rope and out the other, confirming that the anisotropy can remotely sense a large-scale flow of GCRs through a magnetic flux rope.