INTENSITY VARIATIONS OF GREATER-THAN-70-MEV COSMIC-RAYS MEASURED BY PIONEER-10, VOYAGER-1 AND VOYAGER-2 AND IMP IN THE HELIOSPHERE DURING THE RECOVERY PERIOD FROM 1992-1995

Citation
Wr. Webber et Ja. Lockwood, INTENSITY VARIATIONS OF GREATER-THAN-70-MEV COSMIC-RAYS MEASURED BY PIONEER-10, VOYAGER-1 AND VOYAGER-2 AND IMP IN THE HELIOSPHERE DURING THE RECOVERY PERIOD FROM 1992-1995, Geophysical research letters, 22(19), 1995, pp. 2669-2672
Citations number
7
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
00948276
Volume
22
Issue
19
Year of publication
1995
Pages
2669 - 2672
Database
ISI
SICI code
0094-8276(1995)22:19<2669:IVOGCM>2.0.ZU;2-8
Abstract
Using data from the >70-MeV channel on the Pioneer 10 and Voyager 1 & 2 spacecraft we have examined the gradients and intensities of cosmic rays in the outer heliosphere between 1992 and 1995. During this time there is a slow increase of intensity towards the next maximum in simi lar to 1997 and the radial gradient is small decreasing to similar to 0.8%/AU at the end of this period. The latitude gradient has also decr eased to only similar to 0.1-0.2%/AU but remains negative as it was in the previous Ii-year cycle. These gradients are similar to those for >70-MeV particles reported recently in the inner heliosphere but quite different from the positive gradients observed at this time throughou t the heliosphere by the Ulysses and Voyager spacecraft for anomalous cosmic rays. Overall the cosmic ray intensity is almost uniform in rad ius, azimuth and latitude at this time in the outer heliosphere - and far lower than the estimated interstellar intensity. The intensities a re, in fact, much lower than would be expected based on data from the previous cycle. This, along with the very slow increase that is observ ed, suggests that, at the same radial distance, the intensity in 1977 will be much less than in the previous cycle in 1987 - resulting in a large 22-year modulation wave. The data show some features which sugge st that large scale drift patterns, which change when the solar magnet ic polarity changes every 11 years, play a important role in the overa ll intensity distribution in the outer heliosphere - but specific deta ils, particularly in the present positive polarity cycle beginning in 1990 are not well predicted by current models.