Origin of the MeV energy nucleon flux associated with CIRs
Measurements of recurrent enhancements of interplanetary nucleon flux in the MeV energy range, detected at widely separated points in the heliosphere by charged particle instruments on board the Pioneer 10 and 11, IMP 7 and 8, and Mariner 10 spacecraft, are presented and interpreted. These features recur at the solar rotation period in association with stream-stream plasma interaction regions corotating with the sun (CIRs) and are not directly produced by solar flaring activity. At distances from the sun r<1 AU, the maximum intensities of the hydrogen (H) and helium (He) components in these flux enhancements increase with increasing r at the same rate, usually between 300 %/AU and 600 %/AU. The nucleon abundance ratio H/He and the slopes of H and He differential energy spectra are relatively constant with r. One of the models proposed to explain these enhanced fluxes predicts the acceleration of nuclei from keV plasma energies to MeV energies via the transit time damping of magnetosonic waves as solar wind plasma flows from the sun. The predicted acceleration rates of H and He different in this model. We compute numerical solutions of the transport equation to show that this model does not reproduce the radial variations of the H and He fluxes observed with nearly identical University of Chicago instruments. Flux associated with one of the relatively rare CIR shocks at 1 AU is shown to be similar to the flux in other corotating enhancements. Direct estimates of the radial diffusive mean free path lambda/sub r/ ranging from 0.03 AU to 0.11 AU, are evaluated by using the sunward diffusive anisotropies obtained at 1 AU and the simultaneous increase of intensity with r. These values of lambda/sub r/ are consistent with those derived in studies of solar flare related particle flux and other corotating nucleon flux enhancements at higher rigidities. The observations are consistent with nucleon acceleration at the CIR shocks beyond 1 AU with subsequent diffusion inward.
- Research Organization:
- Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637
- OSTI ID:
- 5873552
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 86:A11
- Country of Publication:
- United States
- Language:
- English
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GENERAL PHYSICS
SOLAR ALPHA PARTICLES
PLASMA ACCELERATION
SOLAR PROTONS
DIFFUSION
ENERGY SPECTRA
INTERPLANETARY MAGNETIC FIELDS
MEAN FREE PATH
MEV RANGE
NUMERICAL SOLUTION
PLASMA WAVES
SOLAR WIND
ACCELERATION
ALPHA PARTICLES
BARYONS
CHARGED PARTICLES
ELEMENTARY PARTICLES
ENERGY RANGE
FERMIONS
HADRONS
MAGNETIC FIELDS
NUCLEONS
PROTONS
RADIATIONS
SOLAR ACTIVITY
SOLAR PARTICLES
SOLAR RADIATION
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STELLAR RADIATION
640104* - Astrophysics & Cosmology- Solar Phenomena