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.

随着遥感技术的改进和对全球成像的需求的增加，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高层大气中O/N2密度比遥感的最重要的原子和分子发射的精确（~ 15%）电子诱导发射截面。该比值是观测地磁和太阳变率引起的热层成分大尺度变化的主要工具。白天O/N2的密度比直接通过分析它们长寿命激发态的电子诱导紫外发射的强度比来确定，例如135.6 nm的OI发射和N2 lyman - birdge - hopfield （LBH）波段的发射。对于OI 135.6 nm，只有一个测量和一个理论计算的截面，都是30多年前报道的，在文献中发现，它们相差两倍。对于N2 LBH，只有20多年前发表的一种直接测量辐射截面的方法。随后基于航空观测的经验计算得出LBH的横截面大约高出1.6倍。有人认为，这种差异可能是由于在测量长寿命状态之一的排放时所使用的实验技术的局限性，或者未能适当地解释某些较高状态的级联贡献，或者两者兼而有之。为了最好地适应遥感观测，航空建模者有时会将现有的横截面调整多达200%。为了在TIMED卫星的全球紫外成像仪和经验MSIS（质谱-非相干-散射）模型的观测结果之间获得O/N2的一致性，不确定是缩放到OI 135.6 nm的截面（减小它）还是缩放到N2 LBH的截面（增加它）。由于O/N2比值在空间天气研究中起着举足轻重的作用，因此精确的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)同时测量OI 135.6和N2 LBH发射的绝对横截面，使用科罗拉多大学博尔德分校（CU）大气和空间物理实验室（LASP）和喷气推进实验室（JPL）相同的最先进的实验设施；(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观测的使用和理解。该项目的更广泛影响包括为社区提供高精度的横截面；这些横截面将使人们更好地了解地球大气层以及其他含氧和含氮的行星大气层。学生将参与研究活动，重点是紫外线光谱，这是地球轨道大天文台使用的一项重要遥感技术。