Unusual Galactic Cosmic Ray Intensity and Spectral Changes Observed by V1 Near The Heliopause
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Published version
Author(s)
Webber, WR
Quenby, JJ
Type
Journal Article
Abstract
We discuss here two unusual increases of cosmic ray intensity that were observed by V1 in the last 1.1 AU before it
crossed the heliopause in 2012 August, at 121.5 AU. These two increases are roughly similar in amplitude and
result in a total increase in ∼1 GV cosmic ray nuclei of over 50% and 0.01 GV electrons of a factor ∼2. During the
first increase the changes in the B field are small. After the first increase the B field changes become large and
during the second increase the B field variations and cosmic ray changes are correlated to within ± one day. During
these time intervals, the rigidity dependence of the increases of GCR H and He nuclei from 100–600 MeV/nuc
resemble those used to describe the solar modulation near the Earth during a large transient decrease but the ratio
between the intensity changes of H, He, and electrons are different. The magnitude of these increases at Voyager is
∼1/3 of the modulation that is required to produce the total modulation of protons, helium nuclei, and electrons
between the local interstellar intensities and those observed at the Earth at the 2009 sunspot minima. This may
imply that a significant part of the residual solar modulation at times of sunspot minima occurs near the heliopause
itself.
crossed the heliopause in 2012 August, at 121.5 AU. These two increases are roughly similar in amplitude and
result in a total increase in ∼1 GV cosmic ray nuclei of over 50% and 0.01 GV electrons of a factor ∼2. During the
first increase the changes in the B field are small. After the first increase the B field changes become large and
during the second increase the B field variations and cosmic ray changes are correlated to within ± one day. During
these time intervals, the rigidity dependence of the increases of GCR H and He nuclei from 100–600 MeV/nuc
resemble those used to describe the solar modulation near the Earth during a large transient decrease but the ratio
between the intensity changes of H, He, and electrons are different. The magnitude of these increases at Voyager is
∼1/3 of the modulation that is required to produce the total modulation of protons, helium nuclei, and electrons
between the local interstellar intensities and those observed at the Earth at the 2009 sunspot minima. This may
imply that a significant part of the residual solar modulation at times of sunspot minima occurs near the heliopause
itself.
Date Issued
2015-06-12
Date Acceptance
2015-05-03
Citation
Astrophysical Journal, 2015, 806 (1)
ISSN
1538-4357
Publisher
American Astronomical Society
Journal / Book Title
Astrophysical Journal
Volume
806
Issue
1
Copyright Statement
© 2015. The American Astronomical Society.
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
cosmic rays
diffusion
interplanetary medium
magnetic fields
Sun: heliosphere
SOLAR MINIMUM
MODULATION
Publication Status
Published
Article Number
ARTN 138