Heliospheric modulation of cosmic ray protons: Role of enhanced perpendicular diffusion during periods of minimum solar modulation

Details Heliospheric modulation of cosmic ray protons: Role of enhanced perpendicular diffusion during periods of minimum solar modulation Heliospheric modulation of cosmic ray protons: Role of enhanced perpendicular diffusion during periods of minimum solar modulation

Aug 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000jgr...10518295p&link_type=abstract

Journal of Geophysical Research, Volume 105, Issue A8, p. 18295-18304

Physics

29

Interplanetary Physics: Cosmic Rays, Interplanetary Physics: Energetic Particles, Heliospheric

Scientific paper

The effect of enhanced perpendicular diffusion in the polar regions of a simulated heliosphere seems required in drift models for the modulation of galactic cosmic rays in order to find a latitude dependence of cosmic ray protons in the inner heliosphere that is compatible with Ulysses observations. This effect was studied in detail to establish how important it is and to understand the role it plays in global cosmic ray modulation, particularly during minimum modulation periods. After searching through a large parameter space, it was found that enhanced perpendicular diffusion was indeed necessary to obtain compatibility with observations in the inner heliosphere, especially during A>0 magnetic field polarity epochs (e.g., from 1990 to ~2000). This approach, however, also increased the radial dependence during this epoch. Switching to A<0 epochs (e.g., from ~1981 to 1989), the same set of parameters did not fit the observed 1987 radial dependence for 200 MeV cosmic ray protons, so a completely different set of diffusion coefficients had to be used, including less enhanced perpendicular diffusion. A part from a polarity difference, minimum modulation conditions and, by implication, the diffusion tensor seem to be different during A>0 and A<0 solar minimum modulation periods.

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