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

Atmospheric And Environmental Research Inc, Lexington MA

Investigators

Abstract

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.