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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Geoid anomalies in the vicinity of subduction zones

In the considered investigation, attention is given to the line source model, a surface source model, an application of the model, and a model of the thermal lithosphere associated with marginal basins. It is found that undulations in the altimetrically observed geoid of the southwest Pacific are strongly controlled by positive density anomalies in the subducting slabs of the region and the effects of elevation of the geotherm in behind arc lithosphere (corresponding to young marginal basins). Finer details of slab geometry do not obviously manifest themselves in the observed geoid. Such gravitational effects are quite attenuated at sea level and are apparently mixed with crustal effects, oceanographic noise, etc. It appears that slabs in global composite may contribute substantially to intermediate and long wavelength portions (down to spherical harmonic degree 3 or 4) of the earth's gravity field.

Mcadoo, D. C.↗
NASA NTRS1986

Global reorientation and its effect on tectonic patterns on Ganymede

The basins of Ganymede are studied in order to examine the effects of global reorientation on the grooves and furrows of the satellite. An impact basin and the global reorientation of Ganymede were modeled. The damping time, the time for relaxation of tidal bulge, and the time for isostatic adjustment of craters are significant in calculating the duration and amount of global reorientation. The regional global control of groove orientation is examined; the data reveal that the tidal despinning and furrow formation created the reactivated zones of weakness in which the groove sets were formed. It is observed that the grooved terrain emplacement caused a 15 deg shift in the paleopole.

Murchie, S. L.↗
NASA NTRS1990

Barotropic motions and the exchange of angular momentum between the oceans and solid earth

The angular momentum exchange between the earth atmosphere and the solid earth is examined with emphasis placed on the role of the ocean in the momentum transfer. Analysis of external torques such as surface wind stresses and continental torques suggest that, in general, the related angular momentum changes are mostly associated with barotropic variability in the ocean. Solutions for a midlatitude basin obtained with a shallow-water numerical model illustrate how angular momentum in a barotropic ocean is exchanged with the solid earth.

Ponte, Rui M.↗
NASA NTRS1991

The Madden-Julian oscillation and the angular momentum balance in a barotropic ocean model

The oceanic response to the Madden and Julian (1971, 1972) oscillation (MJO) wind stresses are studied with special attention given to the nature of the related angular momentum exchanges between the ocean and the solid earth for idealized 40- and 50-day fluctuations of Pacific winds. The character of these exchanges is illustrated with the use of numerical solutions of a shallow water ocean model, which were found for a constant depth basin centered on the equator and extending over 140 deg in longitude. Solutions also suggest that even small (0.5-1.5-cm) coastal sea level fluctuations can cause variations in the length of day comparable to observed values in the 40- to 50-day band.

Ponte, Rui M.↗
NASA NTRS1991

Application of TOPEX/Poseidon altimetry measurements to observational and modeling studies of the low-frequency upper ocean mass and heat circulation in the tropical Pacific

The main purpose of the proposed work is to describe the seasonal and interannual variability of the upper ocean mass and heat transport in the tropical Pacific and to understand the mechanisms responsible for these transports. This will be done through a combination of experimental and modeling approaches. Remotely sensed sea level and derived current, observed on the basin scale, will be compared, analyzed, and combined with routine and enhanced in situ measurements of thermal and current field, as well as with model solutions forced by satellite-derived estimates of momentum and heat fluxes. The practical scientific rationale for this work stems from the unique data sets collected by (or easily available to) the investigator's team and from the team members' complementary backgrounds (physical oceanography and meteorology) and expertise (in situ and satellite-observation analysis and numerical ocean modeling).

Picaut, Joel↗
NASA NTRS1993

Large floor-fractured craters and isostatic crater modification: Implications for lithospheric thickness on Venus

Several of the largest craters on Venus, including Mead, Meitner and Isabella, exhibit well-developed floor fracture patterns combining a central set of radial features with a peripheral set of concentric fractures. This pattern strongly resembles the fracture patterns observed in the largest floor-fractured craters on the Moon (e.g. Humboldt, Gauss, Petavius). Although most lunar floor-fractured craters apparently reflect crater modification by igneous intrusions and volcanism, we propose that the fractures in these larger craters represent domical flexure events in response to post-impact isostatic uplift. Since the extent of uplift and surface failure in this model depends on both the size of the basin cavity and the local lithospheric thickness, this interpretation also provides a means for constraining lithospheric thicknesses on Venus. Based on the apparent onset diameter of isostatic crater modification, we derive lithospheric thickness estimates for the Moon of approximately 80 - 100 km, and for Venus of approximately 50 - 70 km.

Wichman, R. W.↗
NASA NTRS1999

Remote Sensing May Provide Unprecedented Hydrological Data

Basic hydrological research and water resources management may reap tremendous benefits from remote sensing technology, studies are showing. Satellite coverage may allow unprecedented accuracy in the quantification of the global hydrological cycle, for example. Yet despite such benefits, few hydrologists currently use such data. This is partly because the needed tools and algorithms are not fully developed. Such development requires field experiments that combine remotely sensed data with detailed in situ observations. AGU's Remote Sensing in Hydrology Committee has constructed a Web site (http://Iand.gsfc.nasa.gov/RSHC.html) that gives an overview of many such experiments. Included on the site is information on each experiment's overall goal, the types of in situ and remotely sensed measurements taken, relevant climate and vegetation conditions, and so forth. Links to additional relevant Web sites are included. The site is designed to be a suitable starting point for those interested in learning more about remote sensing in hydrology. It lists members of the committee who can be contacted for further information. Hydrologists have recognized the potential of remote sensing technology since the 1970s. It offers a way to avoid the logistical and economic difficulties associated with obtaining continuous in situ measurements of various hydrological variables, difficulties that are particularly pronounced in remote regions. Microwave instruments in particular can potentially provide all-weather, areally averaged estimates of certain variables (such as precipitation, soil moisture, and snow water content) that have been essentially unattainable in the past. In remote sensing, the conversion of emitted and reflected radiances into useful hydrological data is a complex problem. The measured radiances, for example, reflect the integrated character of a pixel area, a scale inconsistent with the point measurements of traditional hydrology. To develop the needed algorithms, field experiments must be designed that combine relevant satellite measurements with traditional in situ measurements in regions that are al- ready well understood hydrologically. Such field experiments can lead to the development of hydrological models that are driven with remotely sensed data. Once the performance of these models is deemed acceptable in the heavily monitored basins, they can be "transported" for use in regions having little or no in situ measurement system. Author,5: Randal D. Koster, Paul R. Houser and Edwin T. Engman, Hydrological Sciences Branch, Laboratory for Hydrospheric Process, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA; William P. Kustas, Hydrology Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland, USA.

Koster, R.↗
NASA NTRS2022

Development of a “Nature Run” for Observing System Simulation Experiments (OSSEs) for Snow Mission Development

Snow is a fundamental component of global and regional water budgets, particularly in mountainous areas and regions downstream that rely on snowmelt for water resources. Land surface models (LSMs) are commonly used to develop spatially distributed estimates of snow water equivalent (SWE) and runoff. However, LSMs are limited by uncertainties in model physics and parameters, among other factors. In this study, we describe the use of model calibration tools to improve snow simulations within the Noah-MP LSM as the first step in an observing system simulation experiment (OSSE). Noah-MP is calibrated against the University of Arizona (UA) SWE product over a western Colorado domain. With spatially varying calibrated parameters, we run calibrated and default Noah-MP simulations for water years 2010–20. By evaluating both simulations against the UA dataset, we show that calibration decreases domain averaged temporal RMSE and bias for snow depth from 0.15 to 0.13 m and from −0.036 to −0.0023 m, respectively, and improves the timing of snow ablation. Increased snow simulation performance also improves estimates of model-simulated runoff in four of six study basins, though only one has statistically significant improvement. Spatially distributed Noah-MP snow parameters perform better than default uniform values. We demonstrate that calibrating variables related to snow albedo calculations and rain–snow partitioning, among other processes, is a necessary step for creating a nature run that reasonably approximates true snow conditions for the OSSEs. Additionally, the inclusion of a snowfall scaling term can address biases in precipitation from meteorological forcing datasets, further improving the utility of LSMs for generating reliable spatiotemporal estimates of snow.

Melissa L. Wrzesien↗
NASA NTRS1994

Precipitation recycling in the Amazon basin

Precipitation recycling is the contribution of evaporation within a region to precipitation in that same region. The recycling rate is a diagnostic measure of the potential for interactions between land surface hydrology and regional climate. In this paper we present a model for describing the seasonal and spatial variability of the recycling process. The precipitation recycling ratio, rho, is the basic variable in describing the recycling process. Rho is the fraction of precipitation at a certain location and time which is contributed by evaporation within the region under study. The recycling model is applied in studyiing the hydrologic cycle in the Amazon basin. It is estimated that about 25% of all the rain that falls in the Amazon basin is contributed by evaporation within the basin. This estimate is based on analysis of a data set supplied by the European Centre for Medium-range Weather Forecasts (ECMWF). The same analysis is repeated using a different data set from the Geophysical Fluid Dynamics Laboratory (GFDL). Based on this data set, the recycling ratio is estimated to be 35%. The seasonal variability of the recycling ratio is small compared with the yearly average. The new estimates of the recycling ratio are compared with results of previous studies, and the differences are explained.

Eltahir, E. A. B.↗
DOE OSTI2017

Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin

Floodplains, heavily used for water supplies, housing, agriculture, mining, and industry, are important repositories of organic carbon, nutrients, and metal contaminants. The accumulation and release of these species is often mediated by redox processes. By understanding the physicochemical, hydrological, and biogeochemical controls on the distribution and variability of sediment redox conditions we can develop conceptual and numerical models of contaminant transport within floodplains. The Upper Colorado River Basin (UCRB) is impacted by former uranium and vanadium ore processing, resulting in contamination by V, Cr, Mn, As, Se, Mo and U. Previous authors have suggested that sediment redox activity occurring within organic carbon-enriched bodies located below the groundwater level may be regionally important to the maintenance and release of contaminant inventories, particularly uranium. To help assess this hypothesis, vertical distributions of Fe and S redox states and sulfide mineralogy were assessed in sediment cores from three floodplain sites spanning a 250 km transect of the central UCRB. Our results support the hypothesis that organic-enriched reduced sediments are important zones of biogeochemical activity within UCRB floodplains. Furthermore, we found that the presence of organic carbon, together with pore saturation, are the key requirements for maintaining reducing conditions, which were dominated by sulfate-reduction products. Sediment texture was found to be of secondary importance and to moderate the response of the system to external forcing, such as oxidant diffusion. Consequently, fine-grain sediments are relatively resistant to oxidation in comparison to coarser-grained sediments. Exposure to oxidants consumes precipitated sulfides, with a disproportionate loss of mackinawite (FeS) as compared to the more stable pyrite. The accompanying loss of redox buffering capacity creates the potential for release of sequestered radionuclides and metals. Because of their redox reactivity and stores of metals, C, and N, organic-enriched sediments are likely to be important to nutrient and contaminant mobility within UCRB floodplain aquifers.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

The influence of model resolution on the simulated sensitivity of North Atlantic tropical cyclone maximum intensity to sea surface temperature

Global climate models (GCMs) are routinely relied upon to study the possible impacts of climate change on a wide range of meteorological phenomena, including tropical cyclones (TCs). Previous studies addressed whether GCMs are capable of reproducing observed TC frequency and intensity distributions. This research builds upon earlier studies by examining how well GCMs capture the physically relevant relationship between TC intensity and SST. Specifically, the influence of model resolution on the ability of a GCM to reproduce the sensitivity of simulated TC intensity to SST is examined for the MRI-AGCM (20 km), the GFDL-HiRAM (50 km), the FSU-COAPS (0.94°) model, and two versions of the CAM5 (1° and 0.25°). Results indicate that while a 1°C increase in SST corresponds to a 5.5–7.0 m s -1 increase in observed maximum intensity, the same 1°C increase in SST is not associated with a statistically significant increase in simulated TC maximum intensity for any of the models examined. However, it also is shown that the GCMs all capably reproduce the observed sensitivity of potential intensity to SST. The models generate the thermodynamic environment suitable for the development of strong TCs over the correct portions of the Nort h Atlantic basin, but strong simulated TCs do not develop over these areas, even for models that permit Category 5 TCs. This result supports the notion that direct simulation of TC eyewall convection is necessary to accurately represent TC intensity and intensification processes in climate models, although additional explanations are also explored.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Differentiable, Learnable, Regionalized Process-Based Models With Multiphysical Outputs can Approach State-Of-The-Art Hydrologic Prediction Accuracy

Predictions of hydrologic variables across the entire water cycle have significant value for water resources management as well as downstream applications such as ecosystem and water quality modeling. Recently, purely data-driven deep learning models like long short-term memory (LSTM) showed seemingly insurmountable performance in modeling rainfall runoff and other geoscientific variables, yet they cannot predict untrained physical variables and remain challenging to interpret. Here, we show that differentiable, learnable, process-based models (called δ models here) can approach the performance level of LSTM for the intensively observed variable (streamflow) with regionalized parameterization. We use a simple hydrologic model HBV as the backbone and use embedded neural networks, which can only be trained in a differentiable programming framework, to parameterize, enhance, or replace the process-based model's modules. Without using an ensemble or post-processor, δ models can obtain a median Nash-Sutcliffe efficiency of 0.732 for 671 basins across the USA for the Daymet forcing data set, compared to 0.748 from a state-of-the-art LSTM model with the same setup. For another forcing data set, the difference is even smaller: 0.715 versus 0.722. Meanwhile, the resulting learnable process-based models can output a full set of untrained variables, for example, soil and groundwater storage, snowpack, evapotranspiration, and baseflow, and can later be constrained by their observations. Both simulated evapotranspiration and fraction of discharge from baseflow agreed decently with alternative estimates. The general framework can work with models with various process complexity and opens up the path for learning physics from big data.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Effects of Shallow-Velocity Reductions on 3D Propagation of Seismic Waves

Abstract We perform 3D simulations of seismic wavefields to clarify effects of strong reductions of shallow velocities on long-period seismic waves. The simulations use a reference Community Velocity Model of southern California and a modified version with strong velocity reductions in the top 500 m of the Los Angeles basin. Differences between wavefields generated by 10 earthquakes in the reference and perturbed models are analyzed. Velocity changes are estimated by measuring relative time shifts between reference and perturbed seismograms using wavelet cross-correlation spectra. The results indicate that strong localized temporal velocity drops near the surface, such as those observed during strong ground motions, may generate regional perturbations of wavefields at periods up to 20 s. These perturbations may be misinterpreted as generated by temporal changes at seismogenic depths. The results also have important implications for waveform tomography studies.

Geochemistry & Geophysics↗
NASA NTRS1972

Two stochastic models useful in petroleum exploration

A model of the petroleum exploration process that tests empirically the hypothesis that at an early stage in the exploration of a basin, the process behaves like sampling without replacement is proposed along with a model of the spatial distribution of petroleum reserviors that conforms to observed facts. In developing the model of discovery, the following topics are discussed: probabilitistic proportionality, likelihood function, and maximum likelihood estimation. In addition, the spatial model is described, which is defined as a stochastic process generating values of a sequence or random variables in a way that simulates the frequency distribution of areal extent, the geographic location, and shape of oil deposits

Kaufman, G. M.↗
NASA NTRS1989

Calibrating the simple biosphere model for Amazonian tropical forest using field and remote sensing data. I - Average calibration with field data

Using meteorological and hydrological measurements taken in and above the central-Amazon-basin tropical forest, calibration of the Sellers et al. (1986) simple biosphere (SiB) model are described. The SiB model is a one-dimensional soil-vegetation-atmosphere model designed for use within GCMs models, representing the vegetation cover by analogy with processes operating within a single representative plant. The experimental systems and the procedures used to obtain field data are described, together with the specification of the physiological parameterization required to provide an average description of data. It was found that some of the existing literature on stomatal behavior for tropical species is inconsistent with the observed behavior of the complete canopy in Amazonia, and that the rainfall interception store of the canopy is considerably smaller than originally specified in the SiB model.

Sellers, Piers J.↗
NASA NTRS1996

Estimation of Snow Parameters Based on Passive Microwave Remote Sensing and Meteorological Information

A method to incorporate passive microwave remote sensing measurements within a spatially distributed snow hydrology model to provide estimates of the spatial distribution of Snow Water Equivalent (SWE) as a function of time is implemented. The passive microwave remote sensing measurements are at 25 km resolution. However, in mountain regions the spatial variability of SWE over a 25 km footprint is large due to topographic influences. On the other hand, the snow hydrology model has built-in topographic information and the capability to estimate SWE at a 1 km resolution. In our work, the snow hydrology SWE estimates are updated and corrected using SSM/I passive microwave remote sensing measurements. The method is applied to the Upper Rio Grande River Basin in the mountains of Colorado. The change in prediction of SWE from hydrology modeling with and without updating is compared with measurements from two SNOTEL sites in and near the basin. The results indicate that the method incorporating the remote sensing measurements into the hydrology model is able to more closely estimate the temporal evolution of the measured values of SWE as a function of time.

Tsang, Leung↗
DOE OSTI2019

Updated Groundwater Flow Simulations of the Savannah River Site General Separations Area

The groundwater flow model supporting Performance Assessments (PAs) and Composite Analyses (CAs) at the Savannah River Site was significantly revised in 2016 and 2017 using new hydrostratigraphic surfaces, updated well water level calibration targets, and semi-automated model calibration with the PEST optimization code. This model is referred to as “GSA_2016”. This report documents further refinement of the GSA_2016 model in 2018 to incorporate updates to model calibration targets, closure of the H-Area Ash Basin, construction of E-Area Slit Trench operational covers, and plume information from the Mixed Waste Management Facility and Low-Level Radioactive Waste Disposal Facility. Another objective was to lower hydraulic head residuals by adding another calibration zone. The resulting model is referred to as “GSA_2018”.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Threats to a Colorado river provisioning basin under coupled future climate and societal scenarios

Clean, reliable supplies of water are critical to the sustainability and resilience of communities, including water needed for energy and food production, industry, drinking water, and other human and ecological needs. However, water infrastructure and management in the United States are largely optimized for historic conditions—designed and operated to respond to social needs, and past mean and extreme streamflow, which may no longer apply in the future. Temperature, precipitation, ecosystem dynamics, energy and food production, and social systems are all experiencing changes, which cumulatively affect the security of water supply. Here, we examine the impact of these changes in a provisioning basin in the arid Southwest, the San Juan River, which supplies water, food, and energy to the Colorado River and the Rio Grande. Our analysis applies a multi-model framework to examine future climate and water use scenarios. Results demonstrate that the San Juan River basin could experience significant disruptions to water deliveries (-12% to -48% for the drier models) and shortages that exceed manageable thresholds (53% to 73% of water in shorted years), potentially affecting both the local basin as well as other regions that receive water and energy from the San Juan. While water stress metrics vary across the scenarios, results indicate the need for government, industry, and communities to consider options for adapting to water supply shifts. These results raise important questions regarding the resilience of water resources in basins across the West under future scenarios and implications for energy, food, and other water supply needs.

54 ENVIRONMENTAL SCIENCES↗