Collaborative Research: Determination of Crucial Space Weather Component O/N2 by Laboratory Measurements of O and N2 Absolute Electron-Induced Emission Cross Sections

合作研究：通过实验室测量 O 和 N2 绝对电子感应发射截面来确定关键空间天气成分 O/N2

• 批准号: 0850348
• 负责人: Joseph Ajello
• 金额: --
• 依托单位: National Aeronautics and Space Administration
• 依托单位国家: 美国
• 项目类别: Interagency Agreement
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2012-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0850348&HistoricalAwards=false
• 关键词: Collaborative; Research; Determination; Crucial; Space

As remote sensing techniques have been refined and the desire for global imaging has increased, spectroscopic observations of atomic oxygen (O) and molecular nitrogen (N2) in the far ultraviolet (FUV) have assumed an important role. The central objective of this project is to determine accurate (~ 15%) electron-induced emission cross-sections for the most important atomic and molecular emissions used for remote sensing of the O/N2 density ratio in the upper atmosphere. This ratio is a primary tool for observing the large scale changes in thermospheric composition that result from geomagnetic and solar variability. The density ratio of O/N2 during the daytime is determined directly from analysis of the intensity ratio of electron-induced ultraviolet emissions of their long-lived excited states, such as the OI emission at 135.6 nm and those from the N2 Lyman-Birge-Hopfield (LBH) bands. For OI 135.6 nm only one measurement and one theoretical calculation of cross-section, both reported more than 30 years ago, are found in the literature and they differ by a factor of two. For N2 LBH there is only one direct measurement of the emission cross-sections, published more than two decades ago. Subsequent empirical calculations based on aeronomical observations gave LBH cross-sections approximately 1.6 times higher. It was suggested that this difference could be due to either limitations in the experimental techniques used when measuring the emissions from one of the long-lived states or a failure to properly account for the cascade contributions of some of the upper states or both. To best fit remote sensing observations, aeronomy modelers have sometimes adjusted the existing cross-sections by as much as 200%. It is uncertain whether to scale to the cross-section of OI 135.6 nm (decreasing it) or to the cross-section of N2 LBH (increasing it) in order to obtain agreement for O/N2 between observations from the TIMED satellite's Global Ultraviolet Imager instrument and the empirical MSIS (Mass-Spectrometer-Incoherent-Scatter) model. As the ratio O/N2 plays a pivotal role in Space Weather studies, accurate absolute emission cross-sections of OI and LBH are important. The project will therefore undertake two tasks: (1) To simultaneously measure the absolute cross-sections of both the OI 135.6 and N2 LBH emissions using the same state-of-the-art experimental facilities at the Laboratory for Atmospheric and Space Physics (LASP) of University of Colorado at Boulder (CU) and the Jet Propulsion Laboratory (JPL); and (2) To use the new cross-sections in an analysis to be performed at the Florida Space Institute (FSI in collaboration with Computational Physics Inc. (CPI), in order to improve use and understanding of OI 135.6 nm and N2 LBH observations. The broader impacts of the project include the provision of high-accuracy cross-sections to the community; the cross sections will enable improved understanding of Earth's atmosphere as well as other oxygen- and N2-bearing planetary atmospheres. Students will participate in the research activities which focus on UV spectroscopy, an important remote sensing technique used by the Earth-orbiting Great Observatories.

随着遥感技术的不断完善以及对全球成像的需求不断增加，远紫外 (FUV) 中原子氧 (O) 和分子氮 (N2) 的光谱观测发挥了重要作用。 该项目的中心目标是确定用于遥感高层大气中 O/N2 密度比的最重要原子和分子发射的精确（约 15%）电子诱导发射截面。 该比率是观察地磁和太阳变化引起的热层成分大规模变化的主要工具。 白天 O/N2 的密度比直接通过分析其长寿命激发态的电子诱导紫外线发射的强度比来确定，例如 135.6 nm 处的 OI 发射和来自 N2 Lyman-Birge-霍普菲尔德 (LBH) 乐队。 对于 OI 135.6 nm，文献中仅发现了 30 多年前报道的一种横截面测量值和一种理论计算值，且相差两倍。 对于 N2 LBH，只有一种发射截面的直接测量方法，是二十多年前发表的。 随后基于航空观测的经验计算得出 LBH 横截面大约高出 1.6 倍。 有人认为，这种差异可能是由于测量长寿命状态之一的排放时所使用的实验技术的限制，或者未能正确解释某些较高状态的级联贡献，或两者兼而有之。 为了最好地适应遥感观测，航空建模者有时会将现有横截面调整多达 200%。 不确定是缩放到 OI 135.6 nm 的横截面（减小它）还是缩放到 N2 LBH 的横截面（增大它），以便获得 TIMED 卫星全球紫外线成像仪观测值之间 O/N2 的一致性仪器和经验 MSIS（质谱仪-非相干散射）模型。由于 O/N2 比率在空间天气研究中起着关键作用，因此准确的 OI 和 LBH 绝对发射截面非常重要。 因此，该项目将承担两项任务：(1) 使用大气与空间物理实验室 (LASP) 相同的最先进的实验设施，同时测量 OI 135.6 和 N2 LBH 排放的绝对截面。 ）科罗拉多大学博尔德分校 (CU) 和喷气推进实验室 (JPL)； (2) 在佛罗里达空间研究所 (FSI 与计算物理公司 (CPI) 合作进行的分析中使用新的横截面，以提高对 OI 135.6 nm 和 N2 LBH 观测结果的使用和理解该项目的更广泛影响包括向社区提供高精度横截面；这些横截面将有助于更好地了解地球大气以及其他含氧和氮的行星大气。学生将参加以紫外光谱为重点的研究活动，这是地球轨道大天文台使用的一种重要遥感技术。