Solar winds driven by nonlinear low‐frequency Alfvén waves from the photosphere: Parametric study for fast/slow winds and disappearance of solar winds
Solar winds driven by nonlinear low‐frequency Alfvén waves from the photosphere: Parametric study for fast/slow winds and disappearance of solar winds
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DOI：
10.1029/2005ja011502
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发表时间：
2005-10
影响因子：
--
通讯作者：
T. Inutsuka
中科院分区：
文献类型：
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作者：
T. Inutsuka
[1]我们调查的日冕和太阳风的性质在开放的冕洞取决于磁场的性质和他们的脚点运动在表面。利用一维磁流体动力学（MHD）方法模拟了从光球层到0.3或0.1 Au的低频Alfven波对冕洞的加热和加速。我们施加低频（约0.05 Hz）的横向波动的磁力线在光球与不同的振幅，频谱和偏振在开放的通量管具有不同的光球场强度，Br，0，和超径向膨胀的横截面，fmax。我们发现跨音速太阳风是普遍的结果。在光球振幅为0.7km s−1的足够波输入的情况下，通过压缩波的产生和波的反射，阿尔芬波的耗散，大气也被稳定地加热到106 K。由于非线性阿尔芬波加热的不稳定性，太阳风的密度和相应的质量通量对Δ dv Δ，0 Δ有相当敏感的依赖性。在风速为0.4 km s−1的情况下，太阳风的质量通量比风速为0.7 km s−1的基准情况下的质量通量小50倍;只有当风速为0.7 km s−1时，太阳风才会消失。我们还发现，太阳风速度与Br，0/fmax之间存在正相关关系，这与Kojima等人最近的观测结果相一致。在此基础上，我们发现，无论是快太阳风还是慢太阳风，都可以用低频Alfven波的耗散这一单一过程来解释。我们的模拟自然地解释了观测到的（1）太阳风速度和日冕温度的关系和（2）在快风中较大的阿尔文波动幅度。在附录A中，我们还解释了我们的MHD波的出射边界条件的实现与一些数值试验。
[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 (≲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, Br,0, and superradial expansion of the cross section, fmax. We find that transonic solar winds are universal consequences. The atmosphere is also stably heated up to ≳106 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, 〈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 Alfven 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 Br,0/fmax, 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 〈dv⊥,0〉 and Br,0/fmax. 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.