Abstract The spatial dependence of cosmic ray intensities in the heliosphere is slowly being revealed by intercomparisons among several spacecraft widely spread throughout interplanetary space. Up to the beginning of this year, important spacecraft included Helios 1 and 2 in to 0.3 AU, IMP 8 and ICE near 1 AU, Pioneer 11 out to 25 AU, Voyager 2 to 25 AU, Voyager 1 to 32 AU, and Pioneer 10 to 43 AU. The radial gradient has been studied most extensively, and recent determinations during the approach to solar minimum set its value from 1 to 3%/AU for integral gradients (above some threshold energy), with remarkable independence of the threshold. In the last couple of years the heliographic latitude spread of the spacecraft network has grown, with Voyager 1 climbing to 27°, Pioneer 11, 16°, Pioneer 10, 3° and Voyager 2, 0° degrees. In combination with a decline of the tilt angle of the heliospheric magnetic field, this has made it possible to obtain an unequivocal gradient with respect to heliographic latitude. When averaged over a solar rotation and expressed in %/AU, this value is near that of the radial gradient, but negative. No persistent longitudinal gradient has been identified. These spatial gradients can be variously extrapolated and interpreted to gain information regarding particle transport parameters, the predominant mechanism for modulation, and the scale size of the heliosphere.
Cosmic ray gradients in the heliosphere
Advances in Space Research ; 9 , 4 ; 209-219
1989-01-01
11 pages
Article (Journal)
Electronic Resource
English
Cosmic ray gradients in the heliosphere
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