Galactic Cosmic Ray Composition, Modulation,

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Galactic Cosmic Ray Composition,
Modulation, Radial Gradients, and Long-Term
Trends R. A. Mewaldt Caltech LWS
Radiation Workshop Washington DC April 5-6, 2004
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Solar-maximum energy spectra from B to
Ni acquired by the ACE/CRIS instrument during
2000-2002
George et al. 2004
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Solar-minimum energy spectra for B to Ni nuclei
acquired during 1997-1998
George et al. (2004)
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Solar-Minimum Energy Spectra All intensities
have been adjusted to the same solar modulation
level using neutron-monitor rates for the time of
acquisition
George et al. (2004)
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Wilson et al. (1997)
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In Davis et al. (2001) it was pointed out that
there were significant differences between the
1997-1998 solar minimum data from ACE and
standard models of the near-Earth cosmic-ray
environment. There are even greater differences
at solar maximum. The data and understanding of
cosmic ray transport processes now exist to
significantly improve these environmental models.
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The JPL/Caltech model includes cosmic-ray
acceleration, ionization energy-loss, nuclear
fragmentation, electron attachment, radioactive
decay, leakage from the Galaxy, diffusion into
the heliosphere, convection, and adiabatic
energy-loss. It does well at solar minimum, but
needs some work at solar maximum (see below).
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The GCR beam at solar maximum is more enriched in
heavy nuclei than predicted by the
models Physics-based models agree better than
semi-empirical models such as CREME, but both can
be improved.
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?????????? in heliosheath apparently x1.5 to
x3 (or more)
??????????????????? ??????70??? (x1.6 at 200
MeV/nuc)
See also Webber Lockwood (1987) Jokipii et
al. (1993) Potgieter and Le Roux
(1989) McDonald et al. (2000) Webber
Lockwood (2001)
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Cosmic Ray Gradients in the Inner Heliosphere
McDonald et al. (2003)
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Inner Heliosphere Gradients (normalized to 3 AU)
1975 1980 1985 1990
1995 2000
McDonald et al. (2003)
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Long-Term Variations of Cosmic Rays at 1
AU Measurements of Be-10 in ice-cores, and also
direct measurements, indicate that the cosmic ray
intensity was considerable higher in the past.
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Possible Opportunities Continue measuring GCR
response to Solar and Heliospheric
variations. Understand and model solar
modulation of all GCR species and energies
using models that extend from Earth to the
heliopause Improve physics-based and
semi-empirical GCR models of cosmic ray
composition and energy spectra Investigate
long-term GCR trends beyond a solar cycle
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