1 research outputs found
Solar Winds Driven by Nonlinear Low-Frequency Alfven Waves from the Photosphere : Parametric Study for Fast/Slow Winds and Disappearance of Solar Winds
(abridged) We investigate how the properties of the corona and solar wind in
the open coronal holes depend on the properties of the magnetic fields and
their footpoint motions at the surface, by perfoming 1D MHD simulations from
the photosphere to 0.3 or 0.1AU. We impose low-frequency (<0.05Hz) transverse
fluctuations of the field lines at the photosphere with various amplitude,
spectrum, and polarization in the open flux tubes with different photospheric
field strength, B, and super-radial expansion of the cross section, f_max. We
find that a transonic solar wind is the universal consequence. The atmosphere
is also stably heated up to >10^6K by the dissipation of the Alfven waves
through compressive-wave generation and wave reflection in the case of the
sufficient wave input with photospheric amplitude, > 0.7km/s. The density,
and accordingly the mass flux, of solar winds show a quite sensitive dependence
on because of an unstable aspect of the heating by the nonlinear Alfven
waves. A case with =0.4km/s gives ~50 times smaller mass flux than the
fiducial case for the fast wind with =0.7km/s; solar wind almost disappears
only if becomes half. We also find that the solar wind speed has a
positive correlation with B/f_max, which is consistent with recent
observations. We finally show that both fast and slow solar winds can be
explained by the single process, the dissipation of the low-frequency Alfven
waves, with different sets of and B/f_max. Our simulations naturally
explain the observed (i) anticorrelation of the solar wind speed and the
coronal temperature and (ii) larger amplitude of the Alfvenic fluctuations in
the fast winds. In Appendix, we also explain our implementation of the outgoing
boundary condition of the MHD waves with some numerical tests.Comment: 27 pages, 16 figures embedded, accepted for publication in J.
Geophys. Re