Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh31a..04r&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH31A-04
Physics
2104 Cosmic Rays, 2114 Energetic Particles, Heliospheric (7514), 2134 Interplanetary Magnetic Fields, 2162 Solar Cycle Variations (7536)
Scientific paper
We investigate the relationship between the evolution of the solar magnetic field and cosmic ray modulation at 1 AU on time-scales of ~1~year using the concept that changes in the solar magnetic field propagate from the Sun and cause a change in the radial diffusion coefficient, assumed to scale as an inverse power of the IMF magnitude (K~ B-n). Increases in the IMF cause a reduction in the cosmic ray density in the inner heliosphere. The subsequent recovery is represented by a time scale τ , related to particle entry into the depleted regions of the heliosphere by drift and diffusion processes. The concept is examined by numerical integration of the spherically symmetric equation representing this process, incorporating observations of the magnetic field intensity, solar wind speed, radial particle intensity gradient, tilt-angle and mean field of the Sun. The concept is able to account for the variations in cosmic ray intensity observed by neutron monitors or spacecraft during solar cycles 20-23, assuming that (a) n ~1-2, consistent with the n ~2 expected for high-energy particles on the basis of quasi-linear theory and the n ~1 often used in modulation studies; (b) inferred recovery times are shorter (τ ~50 days at neutron monitor energies) during epochs when the direction of the solar global magnetic field (A)>0 than when A<0 (τ > ~100 days), consistent with faster particle inflows into the inner heliosphere from over the poles in A>0 epochs than along the heliospheric current sheet when A<0 and (c) recovery times are long, suggesting weak inflows into the inner heliosphere, during a period around solar maximum, consistent with Ulysses observations of the disappearance of latitudinal intensity gradients at solar maximum. Despite the simplicity of the concept, we suggest that it provides insights into the relationships between the solar magnetic field, interplanetary parameters and cosmic ray modulation which merit further exploration using full modulation models.
Cane Hilary V.
Richardson Ian G.
Wibberenz Gerd
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