Collaborative Research: CEDAR--A Novel Technique for Estimating Oxygen Density in the Mid-Latitude Thermosphere

该项目旨在开发一种通过将现代仪器与最先进的建模相结合来确定中纬度热层中原子氧密度的准确技术。该方法将结合光学和雷达测量来约束一个关键的热层O原子发射的正向模型，即8446A的黄昏气辉，并反过来使用该约束模型来开发适用于其他中纬度位置的[O]估计方案。由于其相对简单的发射模型，8446A的发射长期以来一直被认为是[O]遥感的理想候选者，该项目将在两个不同的中纬度设施--马萨诸塞州的米尔斯通山(MH)天文台和波多黎各的阿雷西博天文台(AO)--获取前所未有的一组在各种观测条件下的8446A光谱数据。从嵌套的非相干散射雷达、法布里-珀罗涉仪和光度计测量中获得的额外参数不仅将作为额外的正演模型约束，而且还有助于评估当前模型假设的有效性，特别是关于8446A生产的次生源的作用。结合对模式参数相关性的彻底量化，约束正演模式将被用来开发一种新的逆理论技术来从中纬度8446A的亮度测量中估计热层[O]。中性原子氧是地球200-600公里热层中的主要成分，对其进行量化具有重要意义，原因有几个。在这个区域，它与F区电离层的主要离子O的共振电荷交换在热层和电离层之间的动量和能量交换中起着至关重要的作用。同样，它与氢的电荷交换长期以来一直被认为是电离层和等离子体层之间离子传输的重要影响。由于这种强烈的化学耦合，许多基本的航空计算的准确性--例如传输系数、中性风速、能量沉积率、化学反应速率或光化学发射亮度的推导--取决于[O]的准确规范。因此，热层组成和密度方面的当前不确定性限制了对热层-电离层耦合系统的了解，既涉及其气候变异性，也涉及其对来自上方和下方的脉冲强迫的反应。开发一种新的地面测量热层[O]的能力将使NSF雪松计划的这两个核心优先事项受益。一名研究生将在该项目的支持下接受这一与空气动力学相关的领域的培训。学生将熟悉ISR光谱的获取和分析，以及光学SHS、FP I和光度计数据的获取和分析。可用于本科生研究支持的内部资金，加上AO对本科生研究经验(REU)计划的大力参与，为本科生提供了另一个向本科生介绍空气动力学的机会。

This project aims to develop an accurate technique for determining the atomic oxygen density in the mid-latitude thermosphere by combining modern instrumentation with state of the art modeling. The method will combine optical and radar measurements to constrain a forward model of a key thermospheric O-atom emission, the twilight airglow at 8446 A, and in turn use the constrained model to develop an [O] estimation scheme suitable for application at other mid-latitude locations. The 8446 A emission has long been considered an ideal candidate for [O] remote sensing owing to its relatively simple emission model, and the project will acquire an unprecedented set of 8446 A spectral data under various observational conditions at two distinct mid-latitude facilities: Millstone Hill (MH) Observatory in Massachusetts and Arecibo Observatory (AO) in Puerto Rico. Additional parameters derived from nested incoherent scatter radar, Fabry-Perot interferometer, and photometer measurements will not only serve as additional forward model constraints, but also help assess the validity of current model assumptions, specifically with regard to the role of secondary sources of 8446 A production. Together with a thorough quantification of model parameter dependencies, the constrained forward model will be used to develop a novel inverse-theoretical technique to estimate thermospheric [O] from measured 8446 A brightness at mid-latitudes. Quantification of neutral atomic oxygen, the dominant constituent in the Earth's thermosphere between 200 - 600 km, is important for several reasons. In this region, its resonant charge exchange with O+, the principle ion in the F-region ionosphere, plays a vital role in both the momentum and energy exchange between the thermosphere and ionosphere. Similarly, its charge exchange with H+ has long been recognized as an important influence on ion transport between the ionosphere and plasmasphere. Owing to this strong chemical coupling, the accuracy of many fundamental aeronomical calculations -- such as the derivation of transport coefficients, neutral wind speeds, energy deposition rates, chemical reaction rates, or photochemical emission brightnesses -- hinges on accurate specification of [O]. Thus, current uncertainties in thermospheric composition and density limit the understanding of the coupled thermosphere-ionosphere system, both with regard to its climatological variability as well as its response to impulsive forcing from above and below. The development of a new, ground-based capability of measuring thermospheric [O] will benefit both of these central priorities of the NSF CEDAR program. One graduate student will be trained in this Aeronomy-related area with support from the project. The student will gain familiarity with acquisition and analysis of ISR spectra as well as that of optical SHS, FPI, and photometer data. Available internal funds for undergraduate research support, together with the strong involvement of AO in the Research Experiences for Undergraduates (REU) program, presents another opportunity to introduce undergraduate students to aeronomy as well.