Study of Cosmic-Ray Modulation During the Recent Unusual Minimum and Mini-Maximum of Solar Cycle 24
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After a prolonged and deep solar minimum at the end of Cycle 23, the current Solar Cycle 24 is one of the lowest cycles. These two periods of deep minimum and mini-maximum are separated by a period of increasing solar activity. We study the cosmic-ray intensity variation in relation with the solar activity, heliospheric plasma and magnetic field parameters, including the heliospheric current sheet, during these three periods (phases) of different activity level and nature: (a) a deep minimum, (b) an increasing activity period, and (c) a mini-maximum. We use neutron monitor data from stations located around the globe to study the rigidity dependence on modulation during the two extremes, i.e., minimum and maximum. We also study the time lag between the cosmic-ray intensity and various solar and interplanetary parameters separately during the three activity phases. We also analyze the role of various parameters, including the current sheet tilt, in modulating the cosmic-ray intensity during the three different phases. Their relative importance and the implications of our results are also discussed.
KeywordsGalactic cosmic rays Solar modulation Deep solar minimum Solar wind
We thank the station managers of the neutron monitors whose data have been used in this study. Availability and use of solar and plasma and field data from the NASA/GSFC OMNI Web interface and the HCS inclination data the Wilcox Solar Observatory, Stanford, are also acknowledged. We also thank the referees, whose comments and suggestions helped us to improve the article.