Space Science Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, 8 College Road, Durham, New Hampshire 03824, USA.
Department of Physics, University of New Hampshire, Durham, New Hampshire 03824, USA.
Nat Commun. 2016 Oct 3;7:13001. doi: 10.1038/ncomms13001.
The interaction between Earth's magnetic field and the solar wind results in the formation of a collisionless bow shock 60,000-100,000 km upstream of our planet, as long as the solar wind fast magnetosonic Mach (hereafter Mach) number exceeds unity. Here, we present one of those extremely rare instances, when the solar wind Mach number reached steady values <1 for several hours on 17 January 2013. Simultaneous measurements by more than ten spacecraft in the near-Earth environment reveal the evanescence of the bow shock, the sunward motion of the magnetopause and the extremely rapid and intense loss of electrons in the outer radiation belt. This study allows us to directly observe the state of the inner magnetosphere, including the radiation belts during a type of solar wind-magnetosphere coupling which is unusual for planets in our solar system but may be common for close-in extrasolar planets.
当地球磁场与太阳风相互作用时，会在我们星球的上游 6 万至 10 万公里处形成一个无碰撞的弓形激波，只要太阳风的快磁声马赫数（以下简称马赫数）超过 1 即可。在这里，我们展示了一个极其罕见的例子，即 2013 年 1 月 17 日，太阳风马赫数连续几个小时稳定在<1。在近地环境中，十多艘航天器的同步测量揭示了弓形激波的消失、磁层顶的向日运动以及外辐射带中电子的极其快速和强烈的损失。这项研究使我们能够直接观察到内磁层的状态，包括在一种对太阳系内行星来说不寻常但对外太阳系近地行星可能很常见的太阳风-磁层耦合状态下的辐射带。
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