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| Titel |
Reproducing the Solar Wind proton temperature profile via DNS of MHD turbulence |
| VerfasserIn |
Victor Montagud-Camps, Roland Grappin, Andrea Verdini |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250144447
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| Publikation (Nr.) |
 EGU/EGU2017-8273.pdf |
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| Zusammenfassung |
| Context: The Solar Wind proton temperature Tp shows a radial profile R−0.9 significantly
shallower than the adiabatic R−4∕3 profile [Totten et al 1996]. This temperature profile
has been attributed to turbulent heating, which requires a dissipation rate equal to
Q = 3.610−5TpU∕R[J∕(kg s)] (1) [Vasquez et al 2007]. The possibility of a turbulent
heating large enough to modify the radial profile of the temperature has not been verified yet
via direct numerical simulations.
Aim: We want to test if MHD turbulence developing in the range [0.2,1] AU is able to
reproduce the observed R−0.9 temperature profile.
Method: We use the expanding box model (EBM) [Grappin & Velli 1996] which incorporates
the effects of expansion into the compressible MHD equations, and so allows to
follow the evolution of the plasma advected by the solar wind between 0.2 and 1
AU. In the absence of turbulence, the R−4∕3 temperature profile is obtained. We
start at 0.2 AU with mean field almost aligned with the radial and k⊥−1 spectrum
perpendicular to the mean field [Verdini, Grappin 2016]. Simple phenomenology
(Kolmogorov) suggests that the ratio between turbulent heating and the required heating (1)
is close to M2∕ε, where M is the Mach number of the large eddies and ε is the
nonlinear time normalized by the transport time of the plasma by the wind. We thus
explore the (M,ε) parameter space and examine whether a large enough value of
M2∕ε indeed allows to recover the temperature profile observed by Totten et al
(1996).
Results: We have obtained significant slowing down of the adiabatic cooling by
considering increasing Mach numbers and/or decreasing ε and approach in some cases
the R−0.9 temperature profile. The role of the compressibility in the cascade is
examined. |
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