Open AccessSolar winds driven by nonlinear low‐frequency Alfvén waves from the photosphere: Parametric study for fast/slow winds and disappearance of solar winds
Author(s) -
Suzuki Takeru K.,
Inutsuka Shuichiro
Publication year - 2006
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2005ja011502
Subject(s) - physics , photosphere , alfvén wave , solar wind , coronal hole , coronal mass ejection , astrophysics , sunspot , amplitude , corona (planetary geology) , magnetohydrodynamics , computational physics , field line , geophysics , magnetic field , astronomy , spectral line , optics , quantum mechanics , astrobiology , venus
We investigate how properties of the corona and solar wind in open coronal holes depend on properties of magnetic fields and their footpoint motions at the surface. We perform one‐dimensional magnetohydrodynamical (MHD) simulations for the heating and the acceleration in coronal holes by low‐frequency Alfvén waves from the photosphere to 0.3 or 0.1 AU. We impose low‐frequency (≲0.05 Hz) 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 r ,0 , and superradial expansion of the cross section, f max . We find that transonic solar winds are universal consequences. The atmosphere is also stably heated up to ≳10 6 K by the dissipation of the Alfvén waves through compressive‐wave generation and wave reflection in the cases of the sufficient wave input with photospheric amplitude, 〈 dv ⊥,0 〉 ≳ 0.7 km s −1 . The density, and accordingly the mass flux, of solar winds show a quite sensitive dependence on 〈 dv ⊥,0 〉 because of an unstable aspect of the heating by the nonlinear Alfvén waves. A case with 〈 dv ⊥,0 〉 = 0.4 km s −1 gives ≃50 times smaller mass flux than the fiducial case for the fast wind with 〈 dv ⊥,0 〉 = 0.7 km s −1 ; solar wind virtually disappears only if 〈 dv ⊥,0 〉 becomes ≃1/2. We also find that the solar wind speed has a positive correlation with B r ,0 / f max , which is consistent with recent observations by Kojima et al. On the basis of these findings, we show that both fast and slow solar winds can be explained by the single process, the dissipation of the low‐frequency Alfvén waves, with different sets of 〈 dv ⊥,0 〉 and B r ,0 / f max . Our simulations naturally explain the observed (1) anticorrelation of the solar wind speed and the coronal temperature and (2) larger amplitude of Alfvénic fluctuations in the fast wind. In Appendix A, we also explain our implementation of the outgoing boundary condition of the MHD waves with some numerical tests.