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Abstract
The recovery of cosmic ray He nuclei of energy ~150-250 MeV/nuc in solar
cycle #23 from 2004 to 2010 has been followed at the Earth using IMP and ACE
data and at V2 between 74-92 AU and also at V1 beyond the heliospheric
termination shock (91-113 AU). The correlation coefficient between the
intensities at the Earth and at V1 during this time period is remarkable
(0.921), after allowing for a ~0.9 year delay due to the solar wind propagation
time from the Earth to the outer heliosphere. To describe the intensity changes
and to predict the absolute intensities measured at all three locations we have
used a simple spherically symmetric (no drift) two-zone heliospheric transport
model with specific values for the diffusion coefficient in both the inner and
outer zones. The diffusion coefficient in the outer zone, assumed to be the
heliosheath from about 90 to 120 (130) AU, is determined to be ~5 times smaller
than that in the inner zone out to 90 AU. This means the Heliosheath acts much
like a diffusing barrier in this model. The absolute magnitude of the
intensities and the intensity changes at V1 and the Earth are described to
within a few percent by a diffusion coefficient that varies with time by a
factor ~4 in the inner zone and only a factor of ~1.5 in the outer zone over
the time period from 2004-2010. For V2 the observed intensities follow a curve
that is as much as 25% higher than the calculated intensities at the V2 radius
and at times the observed V2 intensities are equal to those at V1. At least
one-half of the difference between the calculated and observed intensities
between V1 and V2 can be explained if the heliosphere is squashed by ~10% in
distance (non-spherical) so that the HTS location is closer to the Sun in the
direction of V2 compared to V1.