CEDAR: Physics of the Hydrogen Geocorona

在威斯康星州麦迪逊附近的派恩布拉夫天文台和NM的基特峰，使用法布里-珀罗干涉仪继续对地球日冕巴尔默- α发射进行长期测量。由于低噪声图像平面检测，前所未有的仪器灵敏度允许这些地冕测量扩展到包括亚瑞利巴尔默- β发射的测量。由于来自同一源的这两种发射具有不同的光学输运性质，因此可以从上层热层提取几千公里范围内的原子氢(H)密度分布的精确值。原子H是上层电离层的中性源，可以利用电荷交换平衡来确定上层热层中原子氧(O)的密度。一旦确定，原子H高度剖面图就用于确定H的垂直通量。长期数据库还用于确定外逸层H的太阳周期变率，并探索与全大气氢物种丰度变化有关的长期变率的可能性，这种变化可能与低层大气中的甲烷沉积同时发生变化。Pine Bluff的高光谱分辨率测量也用于量化外基附近和上方的有效温度，并量化原子级联对Balmer线剖面的贡献。

Long-term measurements of the geocoronal Balmer-alpha emission are continued at the Pine Bluff Observatory near Madison, WI, and at Kitt Peak, NM using Fabry-Perot interferometers. Unprecedented instrument sensitivity due to low-noise image plane detection allows these geocoronal measurements to be extended to include measurements of the sub-Rayleigh Balmer-beta emission. Due to the dissimilar optical transport properties of these two emissions from the same source, it is possible to extract accurate values of atomic hydrogen (H) density profiles from the upper thermosphere to several thousand kilometers. That atomic H is the neutral source of the topside ionosphere, and can be used by virtue of charge exchange equilibrium to determine the density of atomic oxygen (O) in the upper thermosphere. Once determined, the atomic H altitude profiles are used to determine the vertical flux of H. The long term data base is also used to determine the solar cycle variability of exospheric H, and to explore the possibility of secular variability that relates to changes in whole-atmosphere hydrogenous species abundance that may be changing in concert with methane deposition in the lower atmosphere. High spectral resolution measurements at Pine Bluff are also used to quantify effective temperature near and above the exobase, and to quantify atomic cascade contributions to the Balmer line profiles.