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Ann. Geophys., 21, 1295-1302, 2003
www.ann-geophys.net/21/1295/2003/
© European Geosciences Union 2003
Latitudinal and radial variation of >2 GeV/n protons and alpha-particles at solar maximum: ULYSSES COSPIN/KET and neutron monitor network observations
A. V. Belov1, E. A. Eroshenko1, B. Heber2, V. G. Yanke1, A. Raviart3, R. Müller-Mellin4, and H. Kunow4
1IZMIRAN, Troitsk, Moscow region, 142190, Russia
2Fachbereich Physik, Universität Osnabrück, 49069 Osnabrück, Germany
3DAPNIA/Service d’Astrophysique, C. E. Saclay, 91191 Gif-sur-Yvette, France
4Institut für Experimentelle und Angewandte Physik, Universität Kiel, 24098 Kiel, Germany
Abstract. Ulysses, launched in
October 1990, began its second out-of-ecliptic orbit in September 1997. In
2000/2001 the spacecraft passed from the south to the north polar regions of
the Sun in the inner heliosphere. In contrast to the first rapid pole to pole
passage in 1994/1995 close to solar minimum, Ulysses experiences now solar
maximum conditions. The Kiel Electron Telescope (KET) measures also protons and
alpha-particles in the energy range from 5 MeV/n to >2 GeV/n. To derive
radial and latitudinal gradients for >2 GeV/n protons and alpha-particles,
data from the Chicago instrument on board IMP-8 and the neutron monitor network
have been used to determine the corresponding time profiles at Earth. We obtain
a spatial distribution at solar maximum which differs greatly from the solar
minimum distribution. A steady-state approximation, which was characterized by
a small radial and significant latitudinal gradient at solar minimum, was
interchanged with a highly variable one with a large radial and a small –
consistent with zero – latitudinal gradient. A significant deviation from a
spherically symmetric cosmic ray distribution following the reversal of the
solar magnetic field in 2000/2001 has not been observed yet. A small deviation
has only been observed at northern polar regions, showing an excess of
particles instead of the expected depression. This indicates that the
reconfiguration of the heliospheric magnetic field, caused by the reappearance
of the northern polar coronal hole, starts dominating the modulation of
galactic cosmic rays already at solar maximum.
Key words. Interplanetary physics
(cosmic rays; energetic particles) – Space plasma physics (charged particle
motion and acceleration)
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