http://arxiv.org/abs/1601.07835
Two of the central problems in our understanding of the solar chromosphere are how the upper chromosphere is heated and what drives spicules. Estmates of the required chromospheric heating, based on radiative and conductive losses suggest a rate of $\sim 0.1 \mathrm{\:erg\:cm^{-3}\:s^{-1}}$ in the lower chromosphere dropping to $\sim 10^{-3} \mathrm{\:erg\:cm^{-3}\:s^{-1}}$ in the upper chromosphere (\citet{Avrett1981}). The chromosphere is also permeated by spicules, higher density plasma from the lower atmosphere propelled upwards at speeds of $\sim 10-20 \mathrm{\:km\:s^{-1}}$, for so called Type-I spicules (\citet{Pereira2012,Zhang2012}, reaching heights of $\sim 3000-5000 \mathrm{\:km}$ above the photosphere. A clearer understanding of chromospheric dynamics, its heating and the formation of spicules, is thus of central importance to solar atmospheric science. For over thirty years it has been proposed that photospheric driving of MHD waves may be responsible for both heating and spicule formation. This letter presents results from the first high-resolution, self-consistent MHD treatment of photospheric driven Alfv\’en waves propagating upwards into an expanding flux tubes in a realistic chromospheric atmosphere. We show that the ponderomotive coupling from Alfv\'{e}n waves into slow modes generates shocks which both heat the upper chromosphere and drive spicules. These simulations show that Alfv\'{e}n wave driving of the solar chromosphere can give a local heating rate which matches observations and drive spicules consistent with Type-I observations all within a single coherent model.
C. Brady and T. Arber
Fri, 29 Jan 16
30/52
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