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Ann. Geophys., 22, 2229-2238, 2004
www.ann-geophys.net/22/2229/2004/
© European Geosciences Union 2004
Perturbations of the solar wind flow by radial and latitudinal pick-up ion pressure gradients
H. J. Fahr and K. Scherer
Institut für Astrophysik und extraterrestrsiche Forschung, Universität Bonn, Germany
Abstract. It has been found that pick-up ions at their dynamical incorporation into
the solar wind modify the original conditions of the asymptotic solar wind
plasma flow. In this respect, it has meanwhile been revealed in many papers
that these type of solar wind modifications, i.e. deceleration and decrease
of effective Mach number, are not only due to the pick-up ion loading
effects, but also to the action of pick-up ion pressure gradients. Up to
now only the effects of radial pick-up ion pressure gradients were
considered, however, analogously but latitudinal pressure gradients also appear
to be important. Here we study the effects of radial and latitudinal pick-up
ion pressure gradients, occurring especially during solar minimum conditions
at mid-latitude regions where slow solar wind streams
change to fast solar wind streams. First, we give estimates of the
latitudinal wind components connected with these gradients, and then after
revealing its importance, present a more quantitative calculation of solar
wind velocity and density perturbations resulting from these pressure
forces. It is shown that the relative density perturbations near and in the
ecliptic increase with radial distance and thus may well explain the
measured non-spherically symmetric density decrease with distance. We also
show that the solar wind decelerations actually seen with
Voyager-1/2 are in conciliation with interstellar hydrogen densities of
nH∞≥0.1cm-3, in contrast to earlier claims for
nH∞=0.05cm-3.
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