|
|
 |
|
|
Ann. Geophys., 21, 1275-1288, 2003
www.ann-geophys.net/21/1275/2003/
© European Geosciences Union 2003
The Ulysses fast latitude scans: COSPIN/KET results
B. Heber1, G. Sarri2, G. Wibberenz3, C. Paizis4, P. Ferrando5, A. Raviart5, A. Posner5, R. Müller-Mellin3, and H. Kunow3
1Fachbereich Physik, Universität Osnabrück, Barbarastr. 7, 49069 Osnabrück, Germany
2IASF/CNR, Milano, Italy
3Institut für Experimentelle und Angewandte Physik, Universität Kiel, D-24118 Kiel, Germany
4IASF/CNR, and Universitá di Milano, Milano, Italy
5DAPNIA/Service d’Astrophysique, C.E.Saclay, 91191 Gif-sur-Yvette, France
Abstract. Ulysses, launched in
October 1990, began its second out-of-ecliptic orbit in December 1997, and its
second fast latitude scan in September 2000. In contrast to the first fast
latitude scan in 1994/1995, during the second fast latitude scan solar activity
was close to maximum. The solar magnetic field reversed its polarity around
July 2000. While the first latitude scan mainly gave a snapshot of the spatial
distribution of galactic cosmic rays, the second one is dominated by temporal
variations. Solar particle increases are observed at all heliographic
latitudes, including events that produce >250 MeV protons and 50 MeV
electrons. Using observations from the University of Chicago’s instrument on
board IMP8 at Earth, we find that most solar particle events are observed at
both high and low latitudes, indicating either acceleration of these particles
over a broad latitude range or an efficient latitudinal transport. The latter
is supported by "quiet time" variations in the MeV electron
background, if interpreted as Jovian electrons. No latitudinal gradient was
found for >106 MeV galactic cosmic ray protons, during the solar maximum
fast latitude scan. The electron to proton ratio remains constant and has
practically the same value as in the previous solar maximum. Both results
indicate that drift is of minor importance. It was expected that, with the
reversal of the solar magnetic field and in the declining phase of the solar
cycle, this ratio should increase. This was, however, not observed, probably
because the transition to the new magnetic cycle was not completely terminated
within the heliosphere, as indicated by the Ulysses magnetic field and solar
wind measurements. We argue that the new A<0-solar magnetic modulation epoch
will establish itself once both polar coronal holes have developed.
Key words. Interplanetary physics
(cosmic rays; energetic particles; interplanetary magnetic fields)
Full Article in PDF (1634 KB) |
|
|
