Projected disappearance of the 11-year cyclic minimum of galactic cosmic ray intensity in the antapex direction within the outer heliosphere

Details Projected disappearance of the 11-year cyclic minimum of galactic cosmic ray intensity in the antapex direction within the outer heliosphere Projected disappearance of the 11-year cyclic minimum of galactic cosmic ray intensity in the antapex direction within the outer heliosphere

Apr 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005georl..3207102v&link_type=abstract

Geophysical Research Letters, Volume 32, Issue 7, CiteID L07102

Physics

1

Interplanetary Physics: Cosmic Rays, Interplanetary Physics: Energetic Particles (7514), Interplanetary Physics: Heliopause And Solar Wind Termination, Interplanetary Physics: Solar Cycle Variations (7536)

Scientific paper

This paper reports observed galactic cosmic ray (GCR) intensity (kinetic energy T > 80 MeV/nucleon) by the University of Iowa instrument on the interplanetary spacecraft Pioneer 10 (P10) for the thirty-year period, 1972-2002, during which it moved outward from 1 to 80 AU heliocentric radial distance (r). The trajectory of P10 since 1976 was in the approximate direction of the solar antapex. Comparable data for nearly the same time period from the Applied Physics Laboratory/Johns Hopkins University instrument on the Earth-orbiting satellite Interplanetary Monitoring Platform - 8 (IMP-8), as corrected (Van Allen and Randall, 1997), have been adopted as the 1 AU reference. An important new finding is that the solar modulation of GCR intensity had dwindled markedly at P10 during the most recent (2001) cyclic intensity minimum at r ~ 78 AU relative to that at the two previous 11-year cyclic minima in 1981 and 1991. A plausible projection of the trend established by the 1991 and 2001 values of a modulation index predicts the disappearance of direct solar modulation at r = 106 (+/-10) AU in the antapex direction. A similar finding from Voyager 1 and Voyager 2 data (Webber and Lockwood, 2004a and b) in the approximate apex direction confirms the previously noted absence of a apex/antapex asymmetry (Van Allen and Webber, 2002). Several heuristic comments of a general nature are included.

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