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Ann. Geophys., 21, 1303-1313, 2003
www.ann-geophys.net/21/1303/2003/
© European Geosciences Union 2003
Breathing of heliospheric structures triggered by the solar-cycle activity
K. Scherer and H. J. Fahr
Institut für Astrophysik und Extraterrestrische Forschung der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
Abstract. Solar wind ram pressure
variations occuring within the solar activity cycle are communicated to the
outer heliosphere as complicated time-variabilities, but repeating its typical
form with the activity period of about 11 years. At outer heliospheric regions,
the main surviving solar cycle feature is a periodic variation of the solar
wind dynamical pressure or momentum flow, as clearly recognized by observations
of the VOYAGER-1/2 space probes. This long-periodic variation of the solar wind
dynamical pressure is modeled here through application of appropriately
time-dependent inner boundary conditions within our multifluid code to describe
the solar wind – interstellar medium interaction. As we can show, it takes
several solar cycles until the heliospheric structures adapt to an average
location about which they carry out a periodic breathing, however, lagged in
phase with respect to the solar cycle. The dynamically active heliosphere
behaves differently from a static heliosphere and especially shows a historic
hysteresis in the sense that the shock structures move out to larger distances
than explained by the average ram pressure. Obviously, additional energies are
pumped into the heliosheath by means of density and pressure waves which are
excited. These waves travel outwards through the interface from the termination
shock towards the bow shock. Depending on longitude, the heliospheric sheath
region memorizes 2–3 (upwind) and up to 6–7 (downwind) preceding solar
activity cycles, i.e. the cycle-induced waves need corresponding travel times
for the passage over the heliosheath. Within our multifluid code we also
adequately describe the solar cycle variations in the energy distributions of
anomalous and galactic cosmic rays, respectively. According to these results
the distribution of these high energetic species cannot be correctly described
on the basis of the actually prevailing solar wind conditions.
Key words. Interplanetary physics (heliopause
and solar wind termination; general or miscellaneous) – Space plasma physics
(experimental and mathematical techniques)
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