Abstract
We study the solar-activity and solar-polarity dependence of galactic cosmic-ray intensity (CRI) on the solar and heliospheric parameters playing a significant role in solar modulation. We utilize the data for cosmic-ray intensity as measured by neutron monitors, solar activity as measured by sunspot number (SSN), interplanetary plasma/field parameters, solar-wind velocity [V] and magnetic field [B], as well as the tilt of the heliospheric current sheet [Λ], and we analyze these data for Solar Cycles 20 – 24 (1965 – 2011). We divide individual solar cycles into four phases, i.e. low, high, increasing, and decreasing solar activity. We perform regression analysis to calculate and compare the CRI-response to changes in different solar/interplanetary parameters during
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i)
different phases of solar activity and
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ii)
similar activity phases but different polarity states.
We find that the CRI-response is different during negative (A<0) as compared to positive (A>0) polarity states not only with SSN and Λ but also with B and V. The relative CRI-response to changes in various parameters, in negative (A<0) as compared to positive (A>0) state, is solar-activity dependent; it is ≈ 2 to 3 times higher in low solar activity, ≈ 1.5 to 2 times higher in moderate (increasing/decreasing) activity, and it is nearly equal in high solar-activity conditions. Although our results can be ascribed to the preferential entry of charged particles via the equatorial/polar regions of the heliosphere as predicted by drift models, these results also suggest that we should look for any polarity-dependent response of solar-wind and transport parameters in modulating CRI in the heliosphere.
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Acknowledgements
We thank Station Manager Ilya Usoskin and the Sodankyla Geophysical Observatory for the online availability of Oulu neutron-monitor data. We also thank the National Science Foundation (supporting Bartol Research Institute neutron monitors) and Principal Investigator John W. Bieber for the online availability of Newark neutron-monitor data. Availability of solar and plasma/field data through the NASA/GSFC OMNI Web interface and the HCS inclination data (courtesy of J.T. Hoeksema) are also acknowledged. We also thank the reviewer for useful and constructive comments.
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Aslam, O.P.M., Badruddin Similarities and Distinctions in Cosmic-Ray Modulation During Different Phases of Solar and Magnetic Activity Cycles. Sol Phys 289, 2247–2268 (2014). https://doi.org/10.1007/s11207-013-0459-5
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DOI: https://doi.org/10.1007/s11207-013-0459-5