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Abstract: Here we investigate the contribution of surface Alfven wave damping to theheating of the solar wind in minima conditions. These waves are present inregions of strong inhomogeneities in density or magnetic field e. g., theborder between open and closed magnetic field lines. Using a 3-dimensionalMagnetohydrodynamics MHD model, we calculate the surface Alfven wave dampingcontribution between 1-4 solar radii, the region of interest for bothacceleration and coronal heating. We consider waves with frequencies lower thanthose that are damped in the chromosphere and on the order of those dominatingthe heliosphere. In the region between open and closed field lines, within afew solar radii of the surface, no other major source of damping has beensuggested for the low frequency waves we consider here. This work is the firstto study surface Alfven waves in a 3D environment without assuming a priori ageometry of field lines or magnetic and density profiles. We determine thatwaves with frequencies >2.8x10^-4 Hz are damped between 1-4 solar radii. Inquiet sun regions, surface Alfven waves are damped at further distancescompared to active regions, thus carrying additional wave energy into thecorona. We compare the surface Alfven wave contribution to the heating by avariable polytropic index and find that it an order of magnitude larger thanneeded for quiet sun regions. For active regions the contribution to theheating is twenty percent. As it has been argued that a variable gamma acts asturbulence, our results indicate that surface Alfven wave damping is comparableto turbulence in the lower corona. This damping mechanism should be includedself consistently as an energy driver for the wind in global MHD models.



Author: R. M. Evans, M. Opher, V. Jatenco-Pereira, T. I. Gombosi

Source: https://arxiv.org/







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