Effects of particle drift on the transport of cosmic rays. III. Numerical models of galactic cosmic-ray modulation

Journal Article · Thu Nov 15 00:00:00 EST 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/157506· OSTI ID:5637515

Jokipii, J R; Kopriva, D A

We present the first detailed numerical solutions of the steady-state modulation of galactic cosmic rays for a realistic two-dimensional model, which includes drifts. Using the recently established model of the solar-minimum heliospheric magnetic field and nominal interplanetary propagation parameters, we calculate the energy spectra, spatial density variation, and anisotropies of cosmic rays. For most runs we used diffusion coefficients k/sub parallel/=10k/sub perpendicular/=5 x 10/sup 21/P/sup 1/2/..beta.. cm/sup 2/ s/sup -1/, where P is particle rigidity in units of GV and ..beta.. is particle velocity in units of the velocity of light. In the solar equatorial plane the calculated values are similar to those observed. Moreover, these quantities are quite insensitive to the assumed size of the modulating region and to the magnitude of the particle-diffusion coefficient. The solutions are characterized by broad interior ''plateaus'' in which the radial gradient and streaming anisotropies are very small. The intensity of positive particles is substantially greater at the poles than at the equator during the present solar cycle, and substantially less at the poles than at the equator during the last (or next) solar cycle. Finally, we find large effects of drifts even at energies below approx.30 MeV per nucleon. A simple model which neglects diffusion (k/sub perpendicular/, kparallel..-->..0), but which includes drifts and adiabatic cooling, accounts for the general results of the more detailed model. We conclude that in this model diffusion plays a role secondary to that of drifts and adiabatic cooling. Increasing i/sub D'Alembertian/ and k/sub perpendicular/ by a factor of 2 above the nominal values produces small changes in the results < or approx. =5%). REsults for a factor of 10 increase show more effects of diffusion, indicating that for coefficients of this magnitude or larger, diffusion will play a more important role in comparison with drifts.

• Research Organization: Univ. of Arizona, Tucson, AZ (United States)
• OSTI ID: 5637515
• Journal Information: Astrophys. J.; (United States), Vol. 233:4
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIATION
MODULATION
COSMIC RAY PROPAGATION
STEADY-STATE CONDITIONS
ANISOTROPY
ENERGY SPECTRA
NUMERICAL ANALYSIS
SOLAR PARTICLES
SOLAR WIND
SPATIAL DISTRIBUTION
DISTRIBUTION
IONIZING RADIATIONS
MATHEMATICS
RADIATIONS
SOLAR ACTIVITY
SOLAR RADIATION
SPECTRA
STELLAR RADIATION
640101* - Astrophysics &amp; Cosmology- Cosmic Radiation