Solar Activity Parameters and Associated Forbush Decreases During the Minimum Between Cycles 23 and 24 and the Ascending Phase of Cycle 24

Abstract

We study the Forbush decreases in cosmic-ray intensity from January 2008 to December 2013, covering the minimum between Solar Cycles 23 and 24 and the ascending phase of Cycle 24. We performed a statistical analysis of 617 events and concentrated on three of the most important ones. We used the IZMIRAN database of Forbush effects obtained by processing the data of the worldwide neutron monitor network using the global survey method. The first event occurred on 18 February 2011 with a ${\sim}\,5~\%$ decrease of cosmic rays with 10 GV rigidity, the second on 8 March 2012 with an amplitude of ${\sim}\,12~\%$, and the third on 14 July 2012 with an amplitude of ${\sim}\,6~\%$. For these three events, we also studied the events that occurred on the Sun and the way that these affected the interplanetary space, and finally provoked the decreases of the galactic cosmic rays near Earth. We found that each neutron monitor records these decreases, which depend on the cut-off rigidity of the station. We carried out a statistical analysis of the amplitude of the cosmic-ray decreases with solar and geomagnetic parameters.