Collaborative H-alpha and Radar Measurements of the Coupled Thermosphere, Ionosphere and Exosphere

地球最外层的大气层由最轻的气体氢组成，它是在500千米以上的高空由水蒸气和甲烷分离产生的，氢原子在自由弹道轨道上飞行，最远可到达10个地球半径的距离，然后返回。有些氢原子有足够的能量完全脱离地球，正是这样，原始地球失去了大量的氢，才有可能形成现在的富氧大气。氢提供了一种背景介质，高能电荷粒子通过它被困在地球磁场中（环电流和范艾伦带），与氢原子的碰撞是磁暴期间被困离子的主要损失过程。由这种碰撞产生的高能中性粒子沿直线轨迹运动，并且可以为合适的探测器提供环形电流的“图像”，其方式类似于进入照相机的光子。与低能离子的碰撞是非常多的低能离子的重要冷却过程，这些低能离子也分布在由地球磁场（磁层）环绕的近地空间。因此，重要的是要知道氢在地球周围的分布（地冕），以便能够模拟氢与离子的相互作用；用能量中性诠释“图像”；并量化逃逸率。这些信息可以通过法布里·佩罗干涉仪的地面观测获得，来自三所大学（威斯康星、密歇根和阿拉斯加）的一些观测者和理论家以及航空航天公司组成了一个小组，从波多黎各到斯匹茨卑尔根等地同时进行测量，以确定纬度的变化。以及氢气的高度分布。

The outermost atmosphere of the earth consists of hydrogen, the lightest gas, which is produced by the dissociation of water vapor and methane in the altitudes of above 500km, where the H atoms travel on free ballistic orbits out to distances of as much as 10 earth radii before returning. Some of the H atoms have sufficient energy to escape the earth completely, and it is in this way that the primitive earth lost the large amounts of hydrogen to make possible the present oxygen rich atmosphere. The hydrogen provides a background medium through which energetic charges particles trapped in the earth's magnetic field (the ring current and Van Allen belts) travel, and collisions with the H atoms are the main loss process for the trapped ions energized during magnetic storms. The energetic neutrals resulting from such collisions travel on straight line trajectories, and can provide, with suitable detectors, "images" of the ring current in an analogous way to photons entering a camera. Collisions with low energy ions are an important cooling process for the very numerous low energy ions that also populate the near earth space threaded by the earth's magnetic field (the Magnetosphere). Thus it is important to know the distribution of hydrogen around the earth (the Geocorona) to be able to model the interactions with the ions; interpret "images" in energetic neutrals; and quantify the escape rate. This information can be obtained by ground based observations with Fabry Perot interferometers, and a number of observers and theoreticians at three universities (Wisconsin, Michigan, and Alaska) and the Aerospace Corporation have formed a group to carry out simultaneous measurements from sites ranging from Puerto Rico to Spitzbergen, to determine the latitude variation, and the height distribution of the Hydrogen.