[Heber 1996 a]
Spatial variation of > 40 MeV/n nuclei fluxes observed
during the Ulysses rapid latitude scan
B. Heber, W. Dröge, P. Ferrando, L. J. Haasbroek,
H. Kunow, R. Müller-Mellin, C. Paizis,
M. S. Potgieter, A. Raviart, and G. Wibberenz.
Spatial variation of > 40 MeV/n nuclei fluxes observed during the
Ulysses rapid latitude scan.
Astronomy and Astrophysics 316, 538-546. 1996.
Contents
The authors present fluxes of galactic cosmic ray nuclei
with energies above 40 MeV/n observed by the Kiel Electron Telescope
on board the Ulysses spacecraft during the fast scan from the south
pole (September 1994) to the north pole (July 1995). This part of the
Ulysses orbit gives the unique opportunity to investigate spatial
modulation of cosmic rays under solar minimum conditions. The authors
show that during this period temporal variations are well ordered with
particle rigidity using 1 AU data from the University of Chicago
particle instrument on board IMP-8. The
latitudinal variation is particularly strong for 38-125 MeV/n helium
nuclei und decreases with increasing energy. In contrast, the spatial
variation for protons is most dominant in the energy range of a few
hundred MeV. Spatial effects are very small for some ten to one hundred
MeV protons. The proton results are compared with predictions of a
steady-state modulation model which takes into account modifications of the
large scale heliospheric magnetic field and an increased level of cosmic
ray scattering over the poles. The authors opinion is that
the model is in excellent agreement with the latitudinal variations
of > 2 GeV protons, whereas it does not reproduce the behaviour at
low rigidities. They conclude that either the assumed rigidity dependence
for the diffusion coefficients at low energies has to be modified
or that time-dependent modulation effects dominate at low energies.
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