Observations such as Spartan and SOHO UVCS have challenged ideas for the acceleration of the solar wind by constraining models to produce >1.5 Million K protons, several hundred km~s-1 radial outflows, and >700 km~s-1 terminal speeds in the wind emanating from polar coronal holes, with coronal electrons remaining cooler than protons. Observed properties of the solar wind at 1AU and by Ulysses provide additional constraints on these models. It was recognized some time ago that these conditions probably require adding internal energy in sufficient quantities at altitudes <1.5 R_\odot, but the origin of this energy and its method of transport and conversion to heat have remained unclear. The involvement of turbulence in this process was suggested some time ago, but various issues regarding the physics of cascade and dissipation have persisted and a wind model compatible with magnetohydrodynamic theories of turbulence, including the physics of low frequency anisotropic cascade, has not yet been presented to our knowledge. Here we suggest some simplifications and assumptions that allow a self-consistent treatment of the solar wind acceleration problem. Numerical implementation of the coupled solar wind- turbulence equations is described, and computations for a super-radially expanding coronal hole show results for wind speed, temperature, density, and cross helicity profiles that are promising in comparison with known observational constraints.

Coronal heating and solar wind acceleration by turbulence / A. Verdini;M. Velli;W. H. Matthaeus. - ELETTRONICO. - (2006), pp. SH11B-06-SH11B-06. (Intervento presentato al convegno American Geophysical Union, Fall Meeting 2006 nel 2006-#dec#).

Coronal heating and solar wind acceleration by turbulence

VERDINI, ANDREA;VELLI, MARCO;
2006

Abstract

Observations such as Spartan and SOHO UVCS have challenged ideas for the acceleration of the solar wind by constraining models to produce >1.5 Million K protons, several hundred km~s-1 radial outflows, and >700 km~s-1 terminal speeds in the wind emanating from polar coronal holes, with coronal electrons remaining cooler than protons. Observed properties of the solar wind at 1AU and by Ulysses provide additional constraints on these models. It was recognized some time ago that these conditions probably require adding internal energy in sufficient quantities at altitudes <1.5 R_\odot, but the origin of this energy and its method of transport and conversion to heat have remained unclear. The involvement of turbulence in this process was suggested some time ago, but various issues regarding the physics of cascade and dissipation have persisted and a wind model compatible with magnetohydrodynamic theories of turbulence, including the physics of low frequency anisotropic cascade, has not yet been presented to our knowledge. Here we suggest some simplifications and assumptions that allow a self-consistent treatment of the solar wind acceleration problem. Numerical implementation of the coupled solar wind- turbulence equations is described, and computations for a super-radially expanding coronal hole show results for wind speed, temperature, density, and cross helicity profiles that are promising in comparison with known observational constraints.
2006
American Geophysical Union, Fall Meeting 2006
American Geophysical Union, Fall Meeting 2006
A. Verdini;M. Velli;W. H. Matthaeus
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/865933
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