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

地球最外层的大气层由氢组成，氢是最轻的气体，由500公里以上高度的水蒸气和甲烷解离产生，氢原子在返回之前沿着自由弹道轨道运动到地球半径10公里的距离。一些氢原子有足够的能量完全逃离地球，正是通过这种方式，原始地球失去了大量的氢，使现在的富氧大气成为可能。氢提供了一个背景介质，捕获在地球磁场(环流和Van Allen带)中的高能电荷粒子通过它运动，而与H原子的碰撞是磁暴期间被捕获的离子的主要损失过程。由这种碰撞产生的高能中性粒子沿着直线轨迹运动，并可以提供合适的探测器，以类似于光子进入相机的方式提供环电流的“图像”。与低能离子的碰撞是大量低能离子的重要冷却过程，这些离子也存在于由地球磁场贯穿的近地空间(磁层)。因此，重要的是要知道氢在地球(地冕)周围的分布，以便能够对与离子的相互作用进行建模，解释高能中性粒子的“图像”，并量化逃逸率。这些信息可以通过使用法布里·佩罗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)和航空航天公司的一些观察员和理论家组成了一个小组，从波多黎各到斯皮茨卑尔根进行同步测量，以确定氢的纬度变化和高度分布。

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.