论文标题
天王星磁层的物理模型在求解时间
A physical model for the magnetosphere of Uranus at solstice time
论文作者
论文摘要
天王星是太阳系中唯一的行星，其旋转轴和轨道平面几乎彼此平行。天王星也是旋转轴和磁性偶极子方向之间最大角度的行星（大约$ 59^\ circ $）。因此，其磁层尾巴的形状和结构与所有其他季节都可以考虑的所有其他行星的形状和结构都大不相同。我们提出了一个在求解时天气的磁性尾巴的磁性水力动力学模型。该模型的主要结论之一是，从行星的表面出现从它们出现的时间开始，所有磁场线形成延伸的磁性尾巴均遵循相同的定性进化，以及在行星下游几次伸展和扭曲后的后期演变的时间。在行星框架中，这些场线在磁性表面上移动，从而形成龙卷风形的涡流，在行星上有两个脚（一个在每个磁性半球）。涡旋（龙卷风之眼）的中心是一个简单的双螺旋螺旋，带有螺旋音高（沿对称轴$ z $）$λ=τ[v_z+b_z/（μ_0ρ）^{1/2}]流体速度和$ b_z $的磁场必须在涡流中心进行本地评估。总而言之，在行星框架中，延伸的Uranian磁性尾巴的典型磁场的运动是一种涡旋运动，无论该线在行星表面上的出现点如何，它渐近地收敛于单个双螺旋。
Uranus is the only planet in the Solar System whose rotation axis and orbital plane are nearly parallel to each other. Uranus is also the planet with the largest angle between the rotation axis and the direction of its magnetic dipole (roughly $59^\circ$). Consequently, the shape and structure of its magnetospheric tail is very different to those of all other planets in whichever season one may consider. We propose a magnetohydrodynamic model for the magnetic tail of Uranus at solstice time. One of the main conclusions of the model is that all magnetic field lines forming the extended magnetic tail follow the same qualitative evolution from the time of their emergence through the planet's surface and the time of their late evolution after having been stretched and twisted several times downstream of the planet. In the planetary frame, these field lines move on magnetic surfaces that wind up to form a tornado-shaped vortex with two foot points on the planet (one in each magnetic hemisphere). The centre of the vortex (the eye of the tornado) is a simple double helix with a helical pitch (along the symmetry axis $z$) $λ=τ[v_z+B_z/(μ_0ρ)^{1/2}],$ where $τ$ is the rotation period of the planet, $μ_0$ the permeability of vacuum, $ρ$ the mass density, $v_z$ the fluid velocity, and $B_z$ the magnetic field where all quantities have to be evaluated locally at the centre of the vortex. In summary, in the planetary frame, the motion of a typical magnetic field of the extended Uranian magnetic tail is a vortical motion, which asymptotically converges towards the single double helix, regardless of the line's emergence point on the planetary surface.
