论文标题
惯性频率范围内太阳振荡理论：对流区的线性模式
Theory of solar oscillations in the inertial frequency range: Linear modes of the convection zone
论文作者
论文摘要
一方面，在太阳上观察到了几种类型的全球尺度惯性振荡模式。它们包括赤道罗斯比模式，临界纬度模式和高纬度模式。另一方面，柱状对流模式（通过模拟预测；也称为香蕉细胞或热罗斯比波）仍然难以捉摸。我们旨在研究湍流扩散率，非绝热分层，差异旋转和纬度熵梯度对旋转太阳对流区的线性全局模式的影响。我们在球形壳内部的旋转可压缩流体的特征模数求解。我们确定惯性频率范围内的模式，包括柱状对流模式以及混合字符的模式。计算相应的模式分散关系和特征函数，用于方位角订单$ m \ leq 16 $。三个主要结果如下。首先，我们发现，对于$ m \ gtrsim 5 $，赤道rossby模式的径向依赖性没有radial节点（$ n = 0 $）与传统期望（$ r^m $）的湍流差异$ \ gtrsim 10^{12} $ cm $ cm $ cm^2 $^2 $^$ s $ s $ s $ s $^1}的传统期望（$ r^m $）。其次，我们发现混合模式，即共享赤道罗斯比模式的属性的模式，其中一个径向节点（$ n = 1 $）和柱状对流模式。第三，我们表明模型中的$ M = 1 $高纬度模式与当包括对应于热风平衡的纬度熵梯度时的太阳观测（Baroclinally Undebable Mode）。据我们所知，这项工作是旋转太阳能对流区域全局模式的第一个现实征值计算。该计算揭示了惯性频率范围内的丰富模式频谱，可以将其直接与观测值进行比较。反过来，观察到的模式可以通知我们太阳对流区。
On the one hand, several types of global-scale inertial modes of oscillation have been observed on the Sun. They include the equatorial Rossby modes, critical-latitude modes, and high-latitude modes. On the other hand, the columnar convective modes (predicted by simulations; also known as banana cells or thermal Rossby waves) remain elusive. We aim to investigate the influence of turbulent diffusivities, non-adiabatic stratification, differential rotation, and a latitudinal entropy gradient on the linear global modes of the rotating solar convection zone. We solve numerically for the eigenmodes of a rotating compressible fluid inside a spherical shell. We identify modes in the inertial frequency range including the columnar convective modes, as well as modes of mixed character. The corresponding mode dispersion relations and eigenfunctions are computed for azimuthal orders $m \leq 16$. The three main results are as follows. Firstly, we find that, for $m \gtrsim 5$, the radial dependence of the equatorial Rossby modes with no radial node ($n=0$) is radically changed from the traditional expectation ($r^m$) for turbulent diffusivities $\gtrsim 10^{12}$ cm$^2$ s$^{-1}$. Secondly, we find mixed modes, i.e. modes that share properties of the equatorial Rossby modes with one radial node ($n=1$) and the columnar convective modes. Thirdly, we show that the $m=1$ high-latitude mode in the model is consistent with the solar observations when the latitudinal entropy gradient corresponding to a thermal wind balance is included (baroclinally unstable mode). To our knowledge, this work is the first realistic eigenvalue calculation of the global modes of the rotating solar convection zone. This calculation reveals a rich spectrum of modes in the inertial frequency range, which can be directly compared to the observations. In turn, the observed modes can inform us about the solar convection zone.
