Nishino Masaki N, Fujimoto Masaki, Phan Tai-Duc, Mukai Toshifumi, Saito Yoshifumi, Kuznetsova Masha M, Rastätter Lutz
Institute of Space and Astronautical Science/Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan.
Phys Rev Lett. 2008 Aug 8;101(6):065003. doi: 10.1103/PhysRevLett.101.065003. Epub 2008 Aug 7.
Earth's magnetosphere is an obstacle to the supersonic solar wind and the bow shock is formed in the front side of it. In ordinary hydrodynamics, the flow decelerated at the shock is diverted around the obstacle symmetrically about the Earth-Sun line, which is indeed observed in the magnetosheath most of the time. Here we show a case under a very low-density solar wind in which duskward flow was observed in the dawnside magnetosheath. A Rankine-Hugoniot test shows that the magnetic effect is crucial for this "wrong flow" to appear. A full three-dimensional magnetohydrodynamics (MHD) simulation of the situation confirming this interpretation and earlier simulations is also performed. It is illustrated that in addition to the "wrong flow" feature, various peculiar characteristics appear in the global picture of the MHD flow interaction with the obstacle.
地球的磁层是超音速太阳风的一个障碍，在其前端形成了弓形激波。在普通流体动力学中，在激波处减速的气流会围绕障碍物关于地日线对称地转向，这在大多数情况下确实在磁鞘中被观测到。在这里，我们展示了一个在非常低密度太阳风情况下的案例，其中在晨侧磁鞘中观测到了向黄昏方向的气流。兰金 - 于戈尼奥检验表明，磁效应对于这种“错误气流”的出现至关重要。还对这种情况进行了全三维磁流体动力学（MHD）模拟，证实了这一解释以及早期的模拟结果。结果表明，除了“错误气流”特征外，在MHD流与障碍物相互作用的整体图像中还出现了各种奇特的特征。
