A Novel Faraday Filter-based Spectrometer for Studying the Sodium Airglow and Measuring the Atomic Oxygen Mixing Ratio in the Upper Mesosphere

该项目将开发和部署一种新的光学仪器--紧凑型光谱仪，它将能够对中层钠夜光进行新的测量。主要目标之一是确定两条钠发射线D2和D1的比率。早期的研究预测，由于化学作用，D2/D1比率可能不同于其量子统计值2。然而，三十年前使用法布里-珀罗仪器进行的测量报告的值为1.98±0.1；从那时起，在没有进一步调查的情况下，2被认为是正确的值。最近，T·G·斯兰格、J·M·C·普兰和其他人搜索了凯克望远镜8年来的天空光谱，得出结论：根据大气条件，nard=i(D2)/i(D1)介于1.2和1.8之间。也注意到这一比率具有明显的季节依赖性，在春分时的值较高，在冬至时的值较低。他们提出了一种改进的查普曼机制，认为NAO-O反应的竞争路径会产生Na的夜光发射。经过实验室实验的证实，他们得出结论，nard比率是测量[O]/[O2]比率的可靠指标。由于原子氧可能是决定中间层和低热层(MLT)化学和动力学的最重要的物种，即使是间接实时测定[O]/[O2]也可以极大地促进我们对MLT能量平衡的理解，特别是因为没有直接的地面方法来观测原子氧浓度[O]。通过这个项目，将设计一种新型的紧凑型光谱仪，基于一对改进的钠蒸气法拉第滤光片，用于测量钠的夜辉和测定钠的发光强度。除了NARD外，该方法还可以确定改进的查普曼过程中两个可能反应的路径分数。NARD光谱仪将部署在科罗拉多州立大学激光雷达基地进行初始测试和校准。该项目涉及一名研究科学家作为合作伙伴，以及一名研究生撰写他的博士论文。这项研究将导致开发一种廉价的紧凑型光谱仪，可以在其他天文台上使用简单的钠激光雷达。随着未来从不同地点收集更多数据，该项目将为研究中层顶区域的原子氧做出贡献。这样的测量将提高对气辉过程的大气学的理解，其中大部分涉及与O。

This project will develop and deploy a new optical instrument, a compact spectrometer, that will enable new measurements of the mesospheric sodium nightglow. One of the primary aims is to determine the ratio of two sodium emission lines, the D2 and D1. Early studies predicted that the D2/D1 ratio might differ from its quantum statistical value of 2 due to chemical interactions. However, measurements taken three decades ago using a Fabry-Perot instrument reported a value of 1.98±0.1; since then, 2 has taken to be the correct value without further investigation. Recently, T. G. Slanger, J. M. C. Plane and others have searched through sky spectra from Keck telescopes taken over 8 years, and deduced that depending on atmospheric conditions, the value NaRD = I(D2)/I(D1) lies between 1.2 and 1.8. A clear seasonal dependence of this ratio, with higher values in equinox and lower values in solstice, was noted as well. They proposed a modified Chapman mechanism which suggests competing pathways of NaO+O reactions produce Na nightglow emission. Substantiated by laboratory experiments, they concluded that the ratio NaRD is a reliable proxy for the measurement of the [O]/[O2] ratio. Since atomic oxygen is probably the most important species in determining the chemistry and dynamics of the mesosphere and lower thermosphere (MLT), even an indirect real-time determination of [O]/[O2] could greatly advance our understanding of the MLT energy balance, especially since there is no direct ground-based method for observing the atomic oxygen concentration, [O]. Through this project, a novel, compact spectrometer, based on a pair of modified Na vapor Faraday filters, will be designed to measure Na nightglow and to determine NaRD. In addition to NaRD, the method can also determine the pathway fractions of the two possible reactions in the modified Chapman process. The NaRD spectrometer will be deployed at the Colorado State University lidar site for intitial testing and calibration. The project involves a research scientist as Co-PI and a graduate student for his Ph.D thesis. The research would lead to the development of an inexpensive compact spectrometer that could be used at other observatories with a simple sodium lidar. The project will contribute to studies of atomic oxygen in the mesopause region as more data are gathered from various sites in the future. Such measurements will improve the understanding of the aeronomy of airglow processes, most of which involve interactions with O.