CEDAR: A Theoretical and Modeling Study of Global Change in the Mesosphere and Thermosphere

研究人员将研究一些与全球变化对中间层和热层的影响有关的科学问题。这项理论研究需要与最近对过去几十年长期卫星拖曳观测所得出的热层密度下降的估计进行比较。这将需要将三维光谱中间层/低热层模式(SMLTM)扩展到外基，并纳入相关的物理过程，包括主要物种的交互扩散分离。初步工作表明，全球热层响应可以进行分析，这将提供对高层大气工作的更深层次的了解。该项目的第二个重点将是调查在以前的数值模拟中发现的反应的稳健的普遍空间结构，并将以开发适当的分析模型为基础，结合全球平均的SMLTM一维版本。对现有长期观测记录的非决定性、有时自相矛盾的分析大体上与中间层、热层和电离层(MTI)的温室冷却概念一致。这种冷却是由于二氧化碳等温室气体从低层大气输送到MTI区域的数量增加，导致向太空发射更有效的红外辐射。它通常表现为MTI温度较低，热层密度明显下降，以及各种电离层向下移动。这些变化的幅度预计将大大大于低层大气，它们很可能成为整个陆地大气系统全球变化的预报器。到目前为止进行的一些模拟研究已经阐明了各种机制的作用，提供了不确定性估计，并解释了一些观察到的特征，例如，冷却的季节-纬度相关性。然而，悬而未决的科学问题仍然需要通过合适的数字模型来解决。将计算机模拟的诊断与适当的分析模型相结合，并将它们与数据分析直接比较，可以更全面地理解MTI对热力强迫的响应。对MTI中可能的人为变化进行更好的估计和预测、更深入的理解和更充分的模型，将大大加强基础设施，并为不仅在高层大气而且在整个地球大气系统中更广泛的气候变化领域进行研究提供新的工具。

The investigators will study a number of science questions related to global change effects on the mesosphere and thermosphere. The theoretical study entails comparisons with recent estimates of a thermospheric density decline from long-term satellite-drag observations over the last few decades. This will require extension of a three-dimensional Spectral Mesosphere/Lower Thermosphere Model (SMLTM) to the exobase and incorporation of relevant physical processes, including interactive diffusive separation of the main species. Preliminary work shows that the global thermospheric response is amenable to analytical analysis, which will provide a deeper insight into the workings of the upper atmosphere. The second thrust of this project will be investigation of robust universal spatial structures of the response found in previous numerical simulations and will be based on development of appropriate analytical models in conjunction with a global mean one-dimensional version of the SMLTM. Inconclusive and sometimes-contradictory analyses of available long-term observational records are generally consistent with the notion of greenhouse cooling in the mesosphere, thermosphere, and ionosphere (MTI). The cooling is caused by increasing amounts of greenhouse gases, such as carbon dioxide, transported from the lower atmosphere into the MTI region and resulting in more efficient emission of infrared radiation into space. It typically manifests in colder MTI temperatures, a noticeable thermospheric density decline, and a downward displacement of various ionospheric layers. The magnitude of these changes is expected to be substantially greater than in the lower atmosphere and they may well serve as predictors of global change in the whole terrestrial atmosphere system. Several modeling studies performed to date have elucidated the role of various mechanisms, provided uncertainty estimates, and explained some of the observed features, for example, the seasonal-latitudinal dependence of the cooling. Outstanding science issues still remain, however, to be addressed by suitable numerical models. Fuller understanding of the MTI response to thermal forcing may be achieved in combination of diagnostics of computer simulations with appropriate analytic models and their direct comparison with data analyses. Better estimates and forecasts, deeper understanding, and more adequate models of possible anthropogenic changes in the MTI will substantially enhance the infrastructure and provide new tools for research not only in the upper atmosphere but in the wider area of climate change in the whole Earth atmosphere system.