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: 0850396
• 负责人: Richard Eastes
• 金额: $ 11.44万
• 依托单位: The University of Central Florida Board of Trustees
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2015-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0850396&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全球成像需求的增加，远紫外线(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/N密度比的最重要的原子和分子发射的准确(~15%)电子诱导发射截面。这一比率是观察地磁和太阳变化引起的热层组成大范围变化的主要工具。通过分析它们的长寿命激发态，如135.6 nm的OI发射和N_2的Lyman-Birge-Hopfield(LBH)带的电子诱导紫外光发射的强度比，直接确定了白天O/N_2的密度比。对于OI 135.6 nm，文献中只有一次测量和一次理论计算横截面，这两种方法都是在30多年前报道的，而且它们相差两倍。对于N2LBH，只有一种直接测量排放截面的方法，这是在二十多年前发表的。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某一长寿命状态的排放时所使用的实验技术的局限性，或者是未能适当地考虑到一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，空气动力学模型师有时会将现有的横截面调整高达200%。为了在定时卫星的全球紫外线成像仪的观测结果与经验的质谱计非相干散射(MSIS)模型之间获得O/N_2的一致性，目前还不确定是尺度到OI的135.6纳米(减小它)还是N_2LBH的横截面(增大它)。由于O/N_2比在空间气象研究中起着举足轻重的作用，准确的O_I和LBH绝对发射截面是非常重要的。因此，该项目将承担两项任务：(1)使用科罗拉多大学博尔德分校大气和空间物理实验室和喷气推进实验室的相同最先进的实验设施，同时测量大气层135.6和氮气LBH排放的绝对截面；(2)在佛罗里达空间研究所与计算物理公司协作进行的分析中使用新的截面，以改进对大气层135.6 nm和氮气LBH观测的使用和了解。该项目的更广泛影响包括向社区提供高精度的横截面；横截面将使人们能够更好地了解地球大气层以及其他含氧和含氮的行星大气。学生将参加研究活动，重点是紫外线光谱，这是一种重要的遥感技术，由地球轨道大天文台使用。