Atmospheric and Hydrospheric Angular Momentum and Budgets, Climate Implications, and Earth Motions

角动量是旋转系统的基本和保守性质。在大气中，它的分布和波动基于内部变化的质量场和运动场，与在一系列时间尺度上变化的动力模式有关。大气也与其周围环境，即海洋、水圈和固体地球交换角动量。实现这一目标的两种主要方法是通过大气较低界面的扭矩，或者通过对地形特征的法向压力，或者通过对大气较低界面的切向应力。这两个力矩都是由天气和气候系统的波动引起的，它们在不同的时间尺度上以不同的幅度与其他地球物理要素相互作用。主要研究人员（pi）将研究角动量波动和再分布的细节，以及扭矩变化，以及对角动量收支、气候变化和地球运动的影响。角动量收支与描述气候变化的相关性，特别是主导的热带厄尔尼诺Niño/南方涛动（ENSO），在过去已经得到了很好的注意，尽管连接两者的所有机制尚未得到充分解释。此外，角动量变化的其他模态可能与那些对气候有重要意义的模态相似。本研究将通过统计评估来自气象分析领域的模式来扩展这些结果。除了气候模态外，角动量作为一个指标可能与其他强迫函数有关，特别是与温室气体的增加有关。pi将研究这种强迫气候波动与角动量循环的关系。除了大气本身，地球上的其他地球物理流体，包括海洋和陆基水圈，都是角动量收支的一部分。耦合模型正在考虑海洋波动。大气分析和气候模式也有水文参数，这些水库的水物质分布可以直接联系到总预算。水文场本身是基于土壤湿度、降水、径流和储存的一些模型，并在一些陆地水文模型中进行了总结。pi试图通过评估从遥感获得的场来进一步解释水文学的作用，包括新的重力测量任务，如重力恢复和气候实验。这个项目的知识价值将在于进一步综合大气的基本特性及其在周围环境中的作用。气候信号将作为由特征向量分析确定的角动量的空间模式的一部分来寻找。pi将观察各种气候模式和其他变化的气候信号如何影响全球大气，并影响固体地球的运动。此外，通过使用角动量作为诊断工具，他们将评估大气和水文建模技术的有用性。pi一直在为广泛的地球和空间科学界提供角动量数据集，包括世界各地对地球运动和自转变化的原因感兴趣的测地线学家和天文学家。这项活动在组织上是国际地球自转和参考系服务的一部分。这些信息用于评估地球的方向变化、参考系和内部结构。这些产品及其预报被国家天文台用于精确导航所需的计时操作。

Angular momentum is a fundamental and conservative property of a system in rotation. In the atmosphere its distribution and fluctuations, which are based on internally changing mass and motion fields, are related to dynamic modes that vary on a range of time scales. The atmosphere also exchanges angular momentum with its surroundings, namely the oceans, hydrosphere, and solid Earth. Two principal means of doing so are by means of torques at the atmosphere's lower interface, either through normal pressure forces against topographic features and through tangential stress forces against the atmosphere's lower interface. Each of these two torques arises from fluctuations of the weather and climate system and they interact with the other geophysical elements with different amplitudes at different temporal scales. The Principal Investigators (PIs) will investigate the details of the angular momentum fluctuation and redistribution, and torque variability, with implications for the angular momentum budget, climate variability, and Earth motions. The relevance of the angular momentum budget to describe climate variations, especially the dominant tropical El Niño/Southern Oscillation (ENSO), has been well noted in the past, though all the mechanisms linking the two have not been fully explained. Additionally, however, other modes of angular momentum variability can resemble those significant to climate. This research will expand these results by assessing statistically the modes from meteorological analysis fields. Besides the climate modes, angular momentum as an index may be related to other forcing functions, especially the increase in greenhouse gases. The PIs will investigate the relationship of such forced climate fluctuations to the angular momentum cycle. Besides the atmosphere itself, the Earth's other geophysical fluids including the oceans and the land-based hydrosphere are part of the angular momentum budget. Ocean fluctuations are being considered in the coupled models. The atmospheric analyses and climate models have hydrological parameters as well, and the distribution of the water substance in these reservoirs can have a direct link into the total budget. The hydrological fields themselves are based on a number of models of the soil moisture, precipitation, runoff and storage, and have been summarized in a number of land hydrology models. The PIs seek to explain the role of hydrology further by assessing fields obtained from remote sensing, including the novel gravity measuring missions, like the Gravity Recovery and Climate Experiment. The intellectual merit of this project will be in further synthesizing a fundamental property of the atmosphere and its role in its surroundings. Climate signals will be sought as part of the spatial patterns of the angular momentum determined by eigenvector analysis. The PIs will see how various climate modes and other changing climate signals may impact the global atmosphere, and impact the motions of the solid Earth. In addition, by using the angular momentum as a diagnostic tool, they will assess the usefulness of atmospheric and hydrologic modeling techniques. The PIs have been contributing the angular momentum datasets to the broad geo and space science community, including geodesists and astronomers worldwide who are interested in the causes of Earth motions and rotation changes. This activity is organizationally part of the International Earth Rotation and Reference Frame Service. Such information is used in assessing the Earth's orientation changes, its reference frames, and its internal structure. The products and their forecasts are used by national observatories for use in timekeeping operations necessary for exact navigation.