We report results from calculations investigating stationary magnetic field configurations in accretion discs around magnetised neutron stars. Our strategy is to start with a very simple model and then progressively improve it providing complementary insight into results obtained with large numerical simulations. In our first model, presented here, we work in the kinematic approximation and consider the stellar magnetic field as being a dipole aligned with the stellar rotation axis and perpendicular to the disc plane, while the flow in the disc is taken to be steady and axisymmetric. The behaviour in the radial direction is then independent of that in the azimuthal direction. We investigate the distortion of the field caused by interaction with the disc matter, solving the induction equation numerically in full 2D. The influence of turbulent diffusivity and fluid velocity on the poloidal field configuration is analysed, including discussion of outflows from the top and bottom of the disc. We find that the distortions increase with increasing magnetic Reynolds number R_m (calculated using the radial velocity). However, a single global parameter does not give an adequate description in different parts of the disc and we use instead a `magnetic distortion function' D_m(r,θ) (a magnetic Reynolds number defined locally). Where D_m<<1 (near to the inner edge of the disc) there is little distortion, but where D_m>1 (most of the rest of the disc), there is considerable distortion and the field becomes weaker than the dipole would have been. Between these two regions, there is a transition zone where the field is amplified and can have a local minimum and maximum. The location of this zone depends sensitively on the diffusivity. The results depend very little on the boundary conditions at the top of the disc.
Polar Filaments Capture High Latitude Solar Poloidal Field Interactions and can Foretell the Future Sunspot Cycle Amplitude before Polar Field Precursors
Aryabhatta Research Institute of Observational Sciences（阿亚巴塔观测科学研究所）；Mahatma Jyotiba Phule Rohilkhand University（马哈特玛·乔提巴·普尔·罗希尔坎德大学）；Indian Institute of Science Education and Research Kolkata（印度科学教育与研究学院加尔各答分校）；Government of West Bengal（西孟加拉邦政府）；Institute of Science Education and Research Kolkata（科学教育与研究学院加尔各答分校）；Southwest Research Institute（西南研究所）；Indian Institute of Space Science and Technology（印度空间科学与技术学院）；Indian Institute of Astrophysics（印度天体物理研究所）；IISER Kolkata（印度科学教育与研究学院加尔各答分校）
A Three-Dimensional Babcock-Leighton Solar Dynamo Model: Initial Results with Axisymmetric Flows
介绍了STABLE（Surface flux Transport And Babcock-Leighton）太阳发电机模型。STABLE是一个3D Babcock-Leighton/Flux Transport发电机模型，其中极向场的源是双极磁区（BMR）的显式出现，扭曲和分散。在这里，我们比以前更详细地描述了稳定模型，我们通过再现2D平均场基准来验证它。我们还提出了一些有代表性的发电机模拟，侧重于特殊情况下的运动磁感应强度和轴对称流场。并非所有的溶液都是超临界的;当表面附近的湍流扩散为$\geq 10^{12}$ cm $^2$ s $^{-1}$时，BL机制维持发电机可能是一个挑战。然而，如果BMR足够大、足够深、足够多，那么就可以找到持续的、循环的、发电机的解决方案，表现出类似太阳的特征。此外，我们发现，由于表面差异旋转而产生的径向磁通量剪切可以解释每个半球的大部分净环向磁通量产生，正如Cameron & Schussler（2015）最近对太阳的论点。
