With the diffusion approximation, we study the cascade and damping of Alfvén-cyclotron fluctuations in solar plasmas numerically. Motivated by wave-wave couplings and nonlinear effects, we test several forms of the diffusion tensor. For a general locally anisotropic and inhomogeneous diffusion tensor in the wave vector space, the turbulence spectrum in the inertial range can be fitted with power-laws with the power-law index varying with the wave propagation direction. For several locally isotropic but inhomogeneous diffusion coefficients, the steady-state turbulence spectra are nearly isotropic in the absence of damping and can be fitted by a single power-law function. However, the energy flux is strongly polarized due to the inhomogeneity that leads to an anisotropic cascade. Including the anisotropic thermal damping, the turbulence spectrum cuts off at the wave numbers, where the damping rates become comparable to the cascade rates. The combined anisotropic effects of cascade and damping make this cutoff wave number dependent on the wave propagation direction, and the propagation direction integrated turbulence spectrum resembles a broken power-law, which cuts off at the maximum of the cutoff wave numbers or the $^4$He cyclotron frequency. Taking into account the Doppler effects, the model can naturally reproduce the broken power-law wave spectra observed in the solar wind and predicts that a higher break frequency is aways accompanied with a greater spectral index change that may be caused by the increase of the Alfvén Mach number, the reciprocal of the plasma beta, and/or the angle between the solar wind velocity and the mean magnetic field. These predictions can be tested by future observations.
Solar off-limb line widths: Alfven waves, ion-cyclotron waves, and preferential heating
阿尔芬波和离子回旋吸收高频波经常被纳入模型致力于日冕加热和快速太阳风加速。已经在太阳风（HELIOS航天器）和最近在上部日冕（UNOPS/SOHO遥感结果）中现场观测到了离子回旋共振的特征。我们提出了一种方法来约束阿尔芬波的振幅和离子回旋共振引起的优先加热，上面的一个部分开发的极冕洞观察与SUMER/SOHO光谱仪。首先从光谱中减去仪器杂散光的贡献。假设非热速度与阿尔芬波振幅有关，通过密度诊断和Mg X 625 A谱线宽度梯度来约束非热速度。几个日冕离子的温度，作为肢体以上的距离的函数，然后确定通过减去非热分量所观察到的线宽。杂散光的影响解释了几条谱线的宽度随高度明显减小的现象，这种减小通常从临边上方约0.1-0.2 Rs处开始。这一结果排除了任何直接的证据阻尼的阿尔芬波，往往建议由其他作者。我们还发现，具有最小荷质比的离子是在固定高度处最热的离子，并且与其他离子相比，它们在肢体上方57”和102”之间受到更强的加热。这构成了离子回旋优先加热的重要线索。
The role of damped Alfven waves on magnetospheric accretion models of young stars
我们研究阿尔芬波阻尼加热等离子体中的磁漏斗的年轻恒星的磁层吸积模型的作用。我们研究了四种不同的阻尼机制的阿尔芬波：非线性，湍流，粘性阻力和碰撞。讨论了阿尔芬波的两种可能起源：1）由下落物质产生的激波在恒星表面产生的阿尔芬波; 2）由Kelvin-Helmholtz不稳定性在漏斗中局部产生的阿尔芬波。我们发现，在一般情况下，阻尼长度小于管长。由于管中的热传导效率不高，仅在恒星表面产生的阿尔芬波无法将管加热到适合观测所需的温度。只有当阿尔芬波的频率很低时（约为离子回旋频率的10^{-5}），粘阻阻尼长度才大于管长。在这种情况下，在恒星表面产生的阿尔芬波能够加热整个管。否则，当地生产的阿尔芬波需要解释的意见。湍流水平计算不同频率的光学薄和厚介质。结果表明，不同阻尼机制下湍流速度变化很大，小频率波的碰撞阻尼可达100 km s^{-1}.
