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Ann. Geophys., 23, 1499-1504, 2005
www.ann-geophys.net/23/1499/2005/
© European Geosciences Union 2005
The heliospheric modulation of cosmic ray protons during increased solar activity: effects of the position of the solar wind termination shock and of the heliopause
U. W. Langner1,2 and M. S. Potgieter2
1Institut für Theoretische Physik IV, Ruhr-Universität Bochum, 44780 Bochum, Germany
2Unit for Space Physics and School of Physics, North-West University, 2520 Potchefstroom, South Africa
Abstract. The effects on the modulation of cosmic ray protons of
different positions for the solar wind termination shock and for the
heliopause are illustrated for moderate solar maximum conditions. This is
done with a numerical model which includes diffusive termination shock
acceleration, a heliosheath and drifts. The modulation is computed for the
heliospheric equatorial plane and at 35° heliolatitude and for both
magnetic polarity cycles of the Sun. It was found that the differences
between the modulation for the two solar polarity cycles are less
significant at a heliolatitude of 35° than in the equatorial plane. The
modulation for the different heliopause positions are qualitatively similar,
although there are clear quantitative differences which should be observable
with the two Voyager spacecraft in the outer heliosphere. It is illustrated
that the motion of the termination shock from 90 AU to 100 AU, with the
heliopause fixed at 120 AU, is not crucially important to global modulation.
What is of primary importance is the location of the heliopause. It can also
be concluded from the results that significant asymmetric modulation is to
be expected between the up-wind and down-wind directions of the heliosphere
but this may become measureable only when spacecraft move beyond the
termination shock into the heliosheath.
Keywords. Interplanetary physics (Cosmic rays; Heliopause
and solar wind termination) – Space plasma physics
(Transport processes)
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