Shock orientations, magnetic turbulence and Forbush decreases

We have studied the effects of quasi-parallel and quasi-perpendicular shocks on the transient modulation of cosmic-ray intensity. Interplanetary magnetic field strength, its variance and solar wind velocity during their passage have also been considered for the analysis in this work. It has been demonstrated that magnetically turbulent quasi-parallel shocks are much more effective in producing Forbush decreases in cosmic-ray intensity than the non-turbulent quasi-perpendicular shocks. From these results it is inferred that turbulence in the shock environment is an important factor in causing Forbush decreases by scattering particles due to magnetic field fluctuations. Results presented in this study provide more specific information about structures responsible for Forbush decreases, physical processes mainly responsible for this phenomenon and the possibility of predicting the likely occurrence of Forbush decreases from observations in space.