期刊
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
卷 111, 期 A6, 页码 -出版社
AMER GEOPHYSICAL UNION
DOI: 10.1029/2005JA011502
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[ 1] 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 Alfven waves from the photosphere to 0.3 or 0.1 AU. We impose low-frequency (less than or similar to 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,B- 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 greater than or similar to 10(6) K by the dissipation of the Alfven waves through compressive-wave generation and wave reflection in the cases of the sufficient wave input with photospheric amplitude, [d nu(perpendicular to, 0)] greater than or similar to 0.7 km s(-1). The density, and accordingly the mass flux, of solar winds show a quite sensitive dependence on [d nu(perpendicular to, 0)] because of an unstable aspect of the heating by the nonlinear Alfven waves. A case with [d nu(perpendicular to, 0)] = 0.4 km s(-1) gives similar or equal to 50 times smaller mass flux than the fiducial case for the fast wind with [d nu(perpendicular to,0)] = 0.7 km s(-1); solar wind virtually disappears only if [d nu(perpendicular to,0)] becomes similar or equal to 1/2. We also find that the solar wind speed has a positive correlation with B-r,B-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 Alfven waves, with different sets of [d nu(perpendicular to,0)] and B-r,B-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 Alfvenic 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.
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