A multivariate study of Forbush decrease simultaneity

The distribution of the cosmic ray flux over the Earth is not uniform, but the result of complex phenomena within the Sun–Earth environment. A Forbush decrease (Fd) is a rapid decrease in the intensity of cosmic rays. A given Fd can appear in different forms at different locations of the Earth. An investigation of simultaneous observations of Fd events by a selection of cosmic ray stations remains a subject of interest among researchers and numerous methods of analysis can be found in literature. Although these studies have contributed significantly to our knowledge, the variability in the manifestations of Fds demonstrates that there are still open questions in this field. The present work suggests that multivariate analysis is a simple method that can be used to discriminate between globally simultaneous and non-simultaneous Fds.

Research Highlights
► Multivariate analysis is a simple method that can be used to discriminate between globally simultaneous and non-simultaneous Forbush decreases (Fds).
► An event that is simultaneously observed all over the Earth will be completely represented by the first principal component (PC1) whereas two or more PCs are required to account for cosmic ray intensity variations at all locations for non-simultaneous Fds.
► Strong Fds are simultaneous while weak Fds are generally non-simultaneous.