Characteristics of Forbush Decreases Measured by the PAMELA Instrument During 2006–2014

During the several decades of Forbush decrease (FD) studies the main properties of this phenomenon were established. Today is clear that Forbush decreases originate as the responses of cosmic ray particle fluxes to solar-induced processes inside interplanetary space. Moreover the profiles of FD’s are the manifestation of the complex structure of coronal mass ejections (CMEs) which are driving from the Sun and often accompanied by flares. So the investigation of FD’s is a useful tool for understanding the dynamics of CME processes and the effects they have on in the interplanetary space. Classification and theoretical interpretation of different FD’s are important for understanding the complex effect of CME’s as well as the search for new features of their behavior. Spectra of cosmic ray protons and helium nuclei obtained by the PAMELA experiment in the rigidity range between 1–15 GV were used to investigate the characteristics of Forbush decreases. Additional data on the interplanetary magnetic field and solar wind speed were taken from the ACE data center for correlation analysis. Rigidity dependences for selected Forbush decreases are also presented.