Galactic cosmic-ray intensity to a heliocentric distance of 18 AU

Journal Article · Sun Jun 01 04:00:00 EDT 1980 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/158034· OSTI ID:5097312

Van Allen, J A

An updated report is given of observations of galactic cosmic-ray intensity to heliocentric radial distance of 8.6 and 18.4 AU with Pioneer 11 and Pioneer 10, respectively. Solar activity via the magnetic structure of the interplanetary medium continues to modulate the intensity out to the greatest distance reached thus far. During the 7 year period 1972 March to 1979 March, the galactic cosmic-ray intensity E/sub p/>80 MeV as measured by detectors on Pioneers 10 and 11 exhibited aperiodic temporal variations by about a factor of 2 and on a time scale of the order of a year and quasi-persistent cyclic variations of 26 day period and amplitude a few percent. The former are attributed to overall changes in the magnetic field structure of the heliosphere, the latter to fast-slow solar wind streams in and near the ecliptic plane and not to toward-away magnetic field sectors. The apparent heliographic latitude dependence of intensity is 0( +- 1.5)% per 10/sup 0/ in the latitude range +7/sup 0/.7 to +15./sup 0/8, though it is possible that radially dependent temporal variations over the large difference in the heliocentric radial distances of the two spacecraft may make this result of limited significance. For protons of energy E/sub p/>80 MeV, there is a fairly consistent heliocentric radial gradient of +2.1( +- 0.3)% per AU integral intensity until 1978 April--May, at which time a substantial disruption of the distribution of cosmic rays in the heliosphere occurred.

• Research Organization: Department of Physics and Astronomy, University of Iowa
• OSTI ID: 5097312
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 238:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics & Cosmology-- Cosmic Radiation
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIATION
COSMIC RAY FLUX
GALAXIES
INTERPLANETARY SPACE
IONIZING RADIATIONS
MAGNETIC FIELDS
MILKY WAY
PIONEER SPACE PROBES
RADIATION FLUX
RADIATIONS
SOLAR ACTIVITY
SOLAR WIND
SPACE
SPACE VEHICLES
VARIATIONS
VEHICLES