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Galactic cosmic ray intensity from 1 to 9 A.U.
Author(s) -
Van Allen James A.
Publication year - 1976
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl003i008p00425
Subject(s) - physics , cosmic ray , astrophysics , amplitude , astronomy , interplanetary medium , intensity (physics) , interplanetary magnetic field , heliosphere , variation (astronomy) , interplanetary spaceflight , solar wind , nuclear physics , plasma , optics
The galactic cosmic ray intensity at Pioneer 10 has been compared to that at Pioneer 11 over the respective ranges of heliocentric radial distances 3.9 < r 10 < 9.0 and 1.0 < r 11 < 5.0 astronomical units (A.U.) during the period April 1973 — January 1976. The dominant variation is a coherent temporal one with a peak‐to‐peak amplitude of about 35 percent of the mean. A further cyclic variation of about 8 percent peak‐to‐peak has a 26‐day period and is attributed to solar‐corotating interplanetary magnetic field structures. After detailed time‐lag analysis the ratios of intensities at the two spacecraft yield a radial gradient G = +2.0 (± 0.5) percent per A. U., integral above a particle energy E = 80 MeV/nucleon and over the differential radial distance range 1.2 < (r 10 ‐ r 11 ) < 5.3 A.U.