Cosmic Rays and IMF Variations and Their Implications for Long-Term Variations of the IMF

Details Cosmic Rays and IMF Variations and Their Implications for Long-Term Variations of the IMF Cosmic Rays and IMF Variations and Their Implications for Long-Term Variations of the IMF

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh51a11r&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SH51A-11

Physics

2104 Cosmic Rays, 2134 Interplanetary Magnetic Fields

Scientific paper

The variation in the aa geomagnetic index between 1964-1995 has been interpreted in terms of an increase by a factor of ~1.4 in the total magnetic flux leaving the Sun. Cosmic ray observations provide a means of inferring whether there have indeed been long-term variations in the solar magnetic field because the galactic cosmic ray density at Earth is approximately anti-correlated with changes in the intensity of the interplanetary magnetic field. Independent observations by ground-based neutron monitors and the IMP 8 spacecraft show that the GCR density has been returning to essentially similar levels at solar minimum, allowing for small intensity differences in successive minima caused by cosmic ray transport in the heliosphere. When averaged over Carrington rotations, rather than the annual means used by Lockwood et al., the IMF at 1 AU also has similar strength during every solar minimum period for which data are available. At solar maximum, the depression in the cosmic ray intensities and the increase in magnetic field strength are essentially correlated with the maximum sunspot number, which increased in cycles 20-22, but is lower again in the current cycle. Thus, we conclude that there is no evidence from solar minimum cosmic ray or magnetic field observations of a persistent increase in the solar magnetic field in recent solar cycles, while at solar maximum, the enhancement in the IMF is a function of the size of the specific solar cycle.

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