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| Titel |
Heliospheric pick-up ions influencing thermodynamics and dynamics of the distant solar wind |
| VerfasserIn |
H. J. Fahr  , D. Rucinski |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 9, no. 3/4 ; Nr. 9, no. 3/4, S.377-386 |
| Datensatznummer |
250006552
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| Publikation (Nr.) |
 copernicus.org/npg-9-377-2002.pdf |
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| Zusammenfassung |
| Neutral interstellar
H-atoms penetrate into the inner heliosphere and upon the event of
ionization are converted into pick-up ions (PUIs). The magnetized solar
wind flow incorporates these ions into the plasma bulk and enforces their
co-motion. By nonlinear interactions with wind-entrained Alfvén waves,
these ions are then processed in the comoving velocity space. The complete
pick-up process is connected with forces acting back to the original solar
wind ion flow, thereby decelerating and heating the solar wind plasma. As
we show here, the resulting deceleration cannot be treated as a pure
loading effect, but requires adequate consideration of the action of the
pressure of PUI-scattered waves operating by the PUI pressure gradient.
Hereby, it is important to take into proper account the stochastic
acceleration which PUIs suffer from at their convection out of the inner
heliosphere by quasi-linear interactions with MHD turbulences. Only then
can the presently reported VOYAGER observations of solar wind
decelerations and heatings in the outer heliosphere be understood in view
of the most likely values of interstellar gas parameters, such as an
H-atom density of 0.12 cm-3 . Solar wind protons (SWPs) appear
to be globally heated in their motion to larger solar distances. Ascribing
the needed heat transfer to the action of suprathermal PUIs, which drive
MHD waves that are partly absorbed by SWPs, in order to establish the
observed SWP polytropy, we can obtain a quantitative expression for the
solar wind proton pressure as a function of solar distance. This
expression clearly shows the change from an adiabatic to a quasi-polytropic
SWP behaviour with a decreasing polytropic index at increasing distances.
This also allows one to calculate the average percentage of initial
pick-up energy fed into the thermal proton energy. In a first order
evaluation of this expression, we can estimate that about 10% of the
initial PUI injection energy is eventually transfered to SWPs independent
of the PUI injection rate. |
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