22 Year Patterns in the Relationship of Sunspot Number and Tilt Angle to Cosmic-Ray Intensity

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Abstract
A comparison of 27 day averages of the sunspot number with the Galactic cosmic-ray intensity observed at Climax reveals a 22 yr pattern. The 11 yr cosmic-ray cycle appears to lag the sunspot cycle by ~1 yr for odd-numbered cycles such as 19 and 21. During even-numbered cycles the sunspot number and cosmic-ray intensity curves are essentially in phase. A similar pattern is apparent in a comparison of the tilt angle of the heliospheric current sheet (HCS) with cosmic-ray intensity for the last three solar cycles (21-23). The tilt angle evolution on the rise of the last three cycles was remarkably similar, while the decline of the tilt angle from high values at the maximum of cycle 21 (~1980) was more gradual than that observed following the maximum of cycle 22 (~1990) or that inferred from coronal hole areas for cycle 20 (~1970). The reduced responsiveness of cosmic rays to sunspot or tilt angle increases on the rise of odd-numbered solar cycles is consistent with a drift effect. A difference in the evolution of large-scale fields on the decay of even- and odd-numbered cycles may contribute to more gradual recovery of cosmic-ray intensity following the maxima of odd-numbered cycles. The onset of modulation in odd-numbered cycles, and of diffusion/convection-dominated modulation in even-numbered cycles, appears to begin when the tilt angle of the HCS exceeds ~50°.