The 22-Year Hale Cycle in Cosmic Ray Flux - Evidence for Direct Heliospheric Modulation

Abstract

The ability to predict times of greater galactic cosmic ray (GCR) fluxes is important for reducing the hazards caused by these particles to satellite communications, aviation, or astronauts. The 11-year solar cycle variation in cosmic rays is highly correlated with the strength of the heliospheric magnetic field. Differences in GCR flux during alternate solar cycles yield a 22-year cycle, known as the Hale Cycle, which is thought to be due to different particle drift patterns when the northern solar pole has predominantly positive (denoted a qA>0 cycle) or negative (qA<0) polarities. This results in the onset of the peak cosmic ray flux at Earth occurring earlier during qA>0 cycles than for qA<0 cycles and hence the peak being more domed for qA>0 and more sharply peaked for qA<0. In this study, we demonstrate that properties of the large-scale heliospheric magnetic field are different during the declining phase of the qA<0 and qA>0 solar cycles, when the difference in GCR flux is most apparent. This suggests that particle drifts may not be the sole mechanism responsible for the Hale Cycle in GCR flux at Earth. However, it is also demonstrated that these polarity-dependent heliospheric differences are evident during the space-age but much less clear in earlier data: using geomagnetic reconstructions, it is shown that for the period of 1905 - 1965, alternate polarities do not give as significant a difference during the declining phase of the solar cycle. Thus we suggest that the 22-year cycle in cosmic ray flux is at least partly the result of direct modulation by the heliospheric magnetic field and that this effect may be primarily limited to the grand solar maximum of the space-age.

16 pages, 7 figures

References in corpus (2)

• The Solar Cycle
• A History of Solar Activity over Millennia

Cited by in corpus (11)

• The behaviour of galactic cosmic ray intensity during solar activity cycle 24
• Study of Cosmic-Ray Modulation during the Recent Unusual Minimum and Mini Maximum of Solar Cycle 24
• Variations of the Galactic Cosmic Rays in the Recent Solar Cycles
• Cosmic Ray Intensity Variation Lags Sunspot number: Implications of Late Opening of Solar Magnetic Field
• First results from the LUCID-Timepix spacecraft payload onboard the TechDemoSat-1 satellite in Low Earth Orbit
• An ACE/CRIS-observation-based Galactic Cosmic Rays heavy nuclei spectra model II
• Solar Energetic Particle Ground-Level Enhancements and the Solar Cycle
• The Sun's magnetic (Hale) cycle and 27 day recurrences in the $aa$ geomagnetic index
• Hemispheric asymmetry in the sunspot cycle as a nonextensive phenomenon
• The Instantaneous Response of Geomagnetic Field, near-Earth IMF and Cosmic-Ray Intensity to Solar Flares
• Extracting Hale Cycle Related Components from Cosmic-Ray Data Using Principal Component Analysis