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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Dam Construction in Lancang-Mekong River Basin Could Mitigate Future Flood Risk From Warming-Induced Intensified Rainfall

Water resources management, in particular flood control, in the Mekong River Basin (MRB) faces two key challenges in the 21st century: climate change and dam construction. Herein, a large scale distributed Geomorphology-Based Hydrological Model coupled with a simple reservoir regulation model (GBHM-MK-SOP) is used to investigate the relative effects of climate change and dam construction on the flood characteristics in the MRB. Results suggest an increase in both flood magnitude and frequency under climate change, which is more severe in the upstream basin and increases over time. However, dam construction and stream regulation reduce flood risk consistently throughout this century, with more obvious effects in the upstream basin where larger reservoirs will be located. The flood mitigation effect of dam regulation dominates over the flood intensification effect of climate change before 2060, but the latter emerges more prominently after 2060 and dominates the flood risk especially in the lower basin.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Calibration of a convective parameterization scheme in the WRF model and its impact on the simulation of East Asian summer monsoon precipitation

Reasonably modeling the magnitude, south-north gradient and seasonal propagation of precipitation associated with the East Asian Summer Monsoon (EASM) is a challenging task in the climate community. In this study we calibrate five key parameters in the Kain-Fritsch convection scheme in the WRF model using an efficient importance-sampling algorithm to improve the EASM simulation. We also examine the impacts of the improved EASM precipitation on other physical process. Our results suggest similar model sensitivity and values of optimized parameters across years with different EASM intensities. By applying the optimal parameters, the simulated precipitation and surface energy features are generally improved. The parameters related to downdraft, entrainment coefficients and CAPE consumption time (CCT) can most sensitively affect the precipitation and atmospheric features. Larger downdraft coefficient or CCT decrease the heavy rainfall frequency, while larger entrainment coefficient delays the convection development but build up more potential for heavy rainfall events, causing a possible northward shift of rainfall distribution. The CCT is the most sensitive parameter over wet region and the downdraft parameter plays more important roles over drier northern region. Long-term simulations confirm that by using the optimized parameters the precipitation distributions are better simulated in both weak and strong EASM years. Due to more reasonable simulated precipitation condensational heating, the monsoon circulations are also improved. Lastly, by using the optimized parameters the biases in the retreating (beginning) of Mei-yu (northern China rainfall) simulated by the standard WRF model are evidently reduced and the seasonal and sub-seasonal variations of the monsoon precipitation are remarkably improved.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Interannual and intra-annual variability of rainfall in Haiti (1905–2005)

The interannual variability of annual and monthly rainfall in Haiti is examined from a database of 78 rain gauges in 1905–2005. The spatial coherence of annual rainfall is rather low, which is partly due to Haiti’s rugged landscape, complex shoreline, and surrounding warm waters (mean sea surface temperatures >27 °C from May to December). The interannual variation of monthly rainfall is mostly shaped by the intensity of the low-level winds across the Caribbean Sea, leading to a drier- (or wetter-) than-average rainy season associated with easterly (or westerly) anomalies, increasing (or decreasing) winds. The varying speed of low-level easterlies across the Caribbean basin may reflect at least four different processes during the year: (1) an anomalous trough/ridge over the western edge of the Azores high from December to February, peaking in January; (2) a zonal pressure gradient between Eastern Pacific and the tropical Northern Atlantic from May/June to September, with a peak in August (i.e. lower-than-average rainfall in Haiti is associated with positive sea level pressure anomalies over the tropical North Atlantic and negative sea level pressure anomalies over the Eastern Pacific); (3) a local ocean–atmosphere coupling between the speed of the Caribbean Low Level Jet and the meridional sea surface temperature (SST) gradient across the Caribbean basin (i.e. colder-than-average SST in the southern Caribbean sea is associated with increased easterlies and below-average rainfall in Haiti). This coupling is triggered when the warmest Caribbean waters move northward toward the Gulf of Mexico; (4) in October/November, a drier- (or wetter-) than-usual rainy season is related to an almost closed anticyclonic (or cyclonic) anomaly located ENE of Haiti on the SW edge of the Azores high. This suggests a main control of the interannual variations of rainfall by intensity, track and/or recurrence of tropical depressions traveling northeast of Haiti. In conclusion, during this period, the teleconnection of Haitian rainfall with synchronous Atlantic and Eastern Pacific SST is at a minimum.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Uniaxial compression of [001]-oriented CaFe 2 As 2 single crystals:the effects of microstructure and temperature on superelasticity Part I: Experimental observations

Micropillar compression experiments on [001]-oriented CaFe 2 As 2 single crystals have recently revealed the existence of superelasticity with a remarkably high elastic limit of over 10%. The collapsed tetragonal phase transition, which is a uni-axial contraction process in which As-As bonds are formed across an intervening Ca-plane, is the main mechanism of superelasticity. Usually, superelasticity and the related structural transitions are affected strongly by both the microstructure and the temperature. As such, in this study, we investigated how the microstructure and temperature affect the superelasticity of [001]-oriented CaFe 2 As 2 micropillars cut from solution-grown single crystals, by performing a combination of in-situ cryogenic micromechanical testing and transmission electron microscopy studies. Our results show that the microstructure of CaFe 2 As 2 is influenced strongly by the crystal growth conditions and by subsequent heat treatment. The presence of Ca and As vacancies and FeAs nanoprecipitates affect the mechanical behavior significantly. In addition, the onset stress for the collapsed tetragonal transition decreases gradually as the temperature decreases. These experimental results are discussed primarily in terms of the formation of As-As bonds, which is the essential feature of this mechanism for superelasticity. Our research outcomes provide a more fundamental understanding of the superelasticity exhibited by CaFe 2 As 2 under uni-axial compression.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Constraining the Influence of Natural Variability to Improve Estimates of Global Aerosol Indirect Effects in a Nudged Version of the Community Atmosphere Model 5

Natural modes of variability on many timescales influence aerosol particle distributions and cloud properties such that isolating statistically significant differences in cloud radiative forcing due to anthropogenic aerosol perturbations (indirect effects) typically requires integrating over long simulations. For state-of-the-art global climate models (GCM), especially those in which embedded cloud-resolving models replace conventional statistical parameterizations (i.e. multi-scale modeling framework, MMF), the required long integrations can be prohibitively expensive. Here an alternative approach is explored, which implements Newtonian relaxation (nudging) to constrain simulations with both pre-industrial and present-day aerosol emissions toward identical meteorological conditions, thus reducing differences in natural variability and dampening feedback responses in order to isolate radiative forcing. Ten-year GCM simulations with nudging provide a more stable estimate of the global-annual mean aerosol indirect radiative forcing than do conventional free-running simulations. The estimates have mean values and 95% confidence intervals of -1.54 ± 0.02 W/m2 and -1.63 ± 0.17 W/m2 for nudged and free-running simulations, respectively. Nudging also substantially increases the fraction of the world’s area in which a statistically significant aerosol indirect effect can be detected (68% and 25% of the Earth's surface for nudged and free-running simulations, respectively). One-year MMF simulations with and without nudging provide global-annual mean aerosol indirect radiative forcing estimates of -0.80 W/m2 and -0.56 W/m2, respectively. The one-year nudged results compare well with previous estimates from three-year free-running simulations (-0.77 W/m2), which showed the aerosol-cloud relationship to be in better agreement with observations and high-resolution models than in the results obtained with conventional parameterizations.

aerosol↗
DOE OSTI2022

Diurnal rainfall response to the physiological and radiative effects of CO 2 in tropical forests in the Energy exascale earth system model v1

Understanding how the connection between rainfall and tropical forests will respond to increasing CO$_2$ concentrations is a key element in understanding how the tropical water cycle will respond to increasing CO$_2$. The plant physiological and radiative impacts of CO$_2$ on rainfall patterns over tropical forest regions are examined in the Energy Exascale Earth System Model version 1.1 (E3SMv1.1-BGC) biogeochemistry experiments. Composite analysis reveals a dampening of the diurnal cycle of rainfall over the Amazon, Congo, and Maritime Continent in response to rising CO$_2$ levels, regardless of the sign of total rainfall change. A full factorial model experiment confirms that the CO$_2$ radiative and CO$_2$ plant physiological effects can individually or jointly reduce the magnitude of the rainfall diurnal cycle, though the physical pathway giving rise to the reduction differs between the two effects. For the physiological response, stomatal closure reduces evapotranspiration, which dries the boundary layer and raises the lifting condensation level. These effects combine to reduce deep convective rainfall during its peak occurrence in the late daytime to early nighttime period. For the radiative response, a relative reduction in daytime CAPE (consistent with a reduction in the diurnal temperature range) leads to less frequent triggering of deep convection and a reduction of rainfall diurnal amplitude. These diurnal rainfall changes are structurally similar across seasons, and show little sensitivity to representation of nutrient coupling for the land biogeochemistry. In agreement with previous findings, the physiological response has only minor impact on extreme rainfall relative to the radiative response.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

A Model of Airborne Particle Removal by a Liquid Drop Spray

The removal of airborne particles by liquid drops is an important atmospheric and industrial process. In the atmospheric science literature, it is variously referred to as “precipitation scavenging,” “wet deposition,” or “ rain out” and has been extensively studied for its role in the formation of clouds and the removal of atmospheric pollutants (Pruppacher et al. 1983; Slinn 1984; Pruppacher and Klett 2010).

42 ENGINEERING↗
DOE OSTI2020

Developing Metrics to Evaluate the Skill and Credibility of Downscaling

Major activities for this project consisted of three related elements: Comparing results using statistical downscaling to the dynamical downscaling performed by the UCLA (Dr. Alex Hall) team in the proposal Developing statistical downscaling methods for wind and near-surface humidity Evaluating differences in extremes across downscaling methods.

17 WIND ENERGY↗
DOE OSTI2025

Calibration and Validation of the SAIL Radar

Calibration of a weather radar is not a simple process, as is well described and documented in several articles (Chandrasekar, V, L Baldini, N Bharadwaj, and PL Smith. 2015. "Calibration procedures for global precipitation-measurement ground-validation radars." URSI Radio Science Bulletin 2015(355): 45–73, https://10.23919/URSIRSB.2015.7909473.). Direct hardware-based characterization is called calibration whereas indirect check with other sources such as disdrometer, or comparison with other radars or indirect means, is called validation. The validation process has its own measurement error and the comparison should fall within its limit. In the following we describe calibration and validation processes for the SAIL radar. Based on the comparison of calibration and validation, an addition of 2 dB is suggested for the SAIL radar observations, with a nuanced Z dr calibration correction, as presented. If a fixed Z dr calibration is preferred, a bias addition of 0.5 dB is suggested.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Unraveling the Age Hardening Response in U-Nb Alloys

Complicating factors that have stymied understanding of uranium-niobium’s aging response are briefly reviewed, including (1) niobium inhomogeneity, (2) machining damage effects on tensile properties, (3) early-time transients of ductility increase, and (4) the variety of phase transformations. A simple Logistic-Arrhenius model was applied to predict yield and ultimate tensile strengths and tensile elongation of U-4Nb as a function of thermal age. Lastly, fits to each model yielded an apparent activation energy that was compared with phase transformation mechanisms.

36 MATERIALS SCIENCE↗
NASA NTRS1986

Evaluation of geophysical parameters measured by the Nimbus-7 microwave radiometer for the TOGA Heat Exchange Project

The data distributed by the National Space Science Data Center on the Geophysical parameters of precipitable water, sea surface temperature, and surface-level wind speed, measured by the Scanning Multichannel Microwave Radiometer (SMMR) on Nimbus-7, are evaluated with in situ measurements between Jan. 1980 and Oct. 1983 over the tropical oceans. In tracking annual cycles and the 1982-83 E1 Nino/Southern Oscillation episode, the radiometer measurements are coherent with sea surface temperatures and surface-level wind speeds measured at equatorial buoys and with precipitable water derived from radiosonde soundings at tropical island stations. However, there are differences between SMMR and in situ measurements. Corrections based on radiosonde and ship data were derived supplementing correction formulae suggested in the databook. This study is the initial evaluation of the data for quantitative description of the 1982-83 E1 Nino/Southern Oscillation episode. It paves the way for determination of the ocean-atmosphere moisture and latent heat exchanges, a priority of the Tropical Ocean and Global Atmosphere (TOGA) Heat Exchange Program.

Liu, W. Timothy↗
NASA NTRS2003

NASA's Scientific Agenda for GPM Mission

The objectives of the Global Precipitation Measurement (GPM) Mission are to: 1) Understand the horizontal and vertical structure of rainfall, its macro- and micro-physical nature, and its associated latent heating, 2) Train and calibrate retrieval algorithms for constellation radiometers, 3) Provide sufficient global sampling to significantly reduce uncertainties in short-term rainfall accumulations, and 4) Extend scientific and societal applications. The GPM mission design consists of a core satellite, constellation satellties, precipitation validation sites for error characterization, and a precipitation processing center. This viewgraph presentation profiles the science goals of the mission, and its capability for producing climate data and weather predictions.

Smith, Eric A.↗
NASA NTRS2022

Shoshone River Water Resources: Assessing Sediment Inputs into the Shoshone River in Wyoming to Determine Areas for Protection and Restoration Practices

In 2016, a routine repair operation at the Willwood Dam released tons of built-up sediment into the Shoshone River, polluting the river and negatively impacting the ecosystem. This release greatly affected the communities that rely on the river for farming, recreation, and tourism. In partnership with the Wyoming Department of Environmental Quality (WYDEQ), Shoshone River Partners, and the United States Geological Survey (USGS) Wyoming–Montana Water Science Center, this project utilized satellite imagery and precipitation data to examine turbidity patterns in the Shoshone River between the Buffalo Bill Dam and the Willwood Dam. We used PlanetScope satellite images to assess changes in surface reflectance of the river in response to precipitation events and Global Precipitation Measurement (GPM) Integrated Multi-Spectral Retrieval (IMERG) precipitation data to estimate the lag time between rainfall events and increased turbidity. The National Land Cover Dataset (2019) was used to identify the main land cover types within each sub-basin. The end products included a turbidity analysis, land cover analysis, and precipitation analysis that provided the partners with a better understanding of sediment dynamics in the river. The results demonstrated the feasibility of using PlanetScope data to examine turbidity spatially along small rivers. Sediment plumes from tributaries were visually identified for multiple high turbidity events, and we calibrated an equation that translated reflectance to turbidity, accurately representing plume extent. Inconsistent spectral quality of PlanetScope data, however, limited our ability to assess the relative sediment contribution of the tributaries.

tributaries↗
NASA NTRSDate not supplied

Integrated Multi-Satellite Retrievals for GPM (IMERG)

The Integrated Multi-satellitE Retrievals for GPM (IMERG) product from the U.S. Science Team of the NASA-JAXA Global Precipitation Measurement (GPM) mission provides global satellite precipitation estimates for a wide range of scientific research and societal applications. By adopting a constellation approach using low-Earth orbit passive microwave and geosynchronous-orbit infrared observations from domestic and international partners, IMERG is able to achieve a high resolution of 0.1° every half-hour globally, with three Runs to cater to applications with different latency requirements. With the completion of the reprocessing of the latest version, IMERG V07 now provides improved global satellite precipitation estimates for a period of more than 20 years. This presentation summarizes background on retrievals, the IMERG algorithm, and access to the data. As well, it showcases select results from the data, which might give participants ideas about how they can analyze the data themselves. The presentation ends with a prospectus for the timeline for the upcoming Version 08 and provides a list of references.

IMERG↗
DOE OSTI2019

Nonlinear Response of Extreme Precipitation to Warming in CESM1

The response of extreme precipitation to warming varies widely among climate models, especially in the tropics. In some models, there have been indications that the rate of response increases with warming – that the response is not linear. In this work, we investigate the evolution of extreme precipitation, quantified by the maximum accumulated precipitation in a day each year, in CESM1. We find that tropical- and global-average extreme precipitation are related to global mean surface temperature quadratically. This behavior is associated with an increase in the large scale fraction of extreme precipitation, and also strengthening circulation on extreme 25 precipitation days. Compared to other CMIP5 models, the nonlinearity in CESM1 is among the largest. One implication is that the difference between CESM1 simulations with full forcing and with fixed aerosols cannot be used to isolate the response of extreme precipitation to aerosols, as the resulting climates are not equally warm.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Modeling and Validation of Irradiation Damage in Ni-based Alloys for Long-Term LWR Applications

Grizzly is a multiphysics simulation code under development at Idaho National Laboratory to simulate aging mechanisms and their effects on the integrity of critical LWR components, including Ni-Cr alloy components. Predictions of the LWR component integrity rely on the ductile-to-brittle transition temperature (DBTT) curve to determine the toughness of the alloy after a period of exposure to in-service reactor conditions. The macroscopic DBTT curve is governed by the microstructure evolution of the alloy, thus, a capability to predict the microstructure evolution in response to thermal ageing is being implemented into Grizzly. Within this report section, the implementation of the Avrami equation to estimate the phase fraction of the aged long range ordered precipitates is discussed. The initial evaluation of current crystal plasticity models within Grizzly to model these Ni-Cr alloys is also presented.

36 MATERIALS SCIENCE↗
NASA NTRS2021

The Global Satellite Precipitation Constellation: Current Status and Future Requirements

To address the need to map precipitation on a global scale a collection of satellites carrying passive microwave (PMW) radiometers has grown over the last 20 years to form a constellation of about 10-12 sensors at any one time. Over the same period, a broad range of science and user communities has become increasingly dependent on the precipitation products provided by these sensors. The constellation presently consists of both conical and cross-track scanning precipitation-capable multi-channel instruments, many of which are beyond their operational and design lifetime but continue to operate through the cooperation of the responsible agencies. The Group on Earth Observations and the Coordinating Group for Meteorological Satellites (CGMS), among other groups, have raised the issue of how a robust, future precipitation constellation should be constructed. The key issues of current and future requirements for the mapping of global precipitation from satellite sensors can be summarised as providing: 1) sufficiently fine spatial resolutions to capture precipitation-scale systems and reduce the beam-filling effects of the observations; 2) a wide channel diversity for each sensor to cover the range of precipitation types, characteristics and intensities observed across the globe; 3) an observation interval that provides temporal sampling commensurate with the variability of precipitation; and 4) precipitation radars and radiometers in low inclination orbit to provide a consistent calibration source, as demonstrated by the first two spaceborne radar/radiometer combinations on the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) mission Core Observatory (CO). These issues are critical in determining the direction of future constellation requirements, while preserving the continuity of the existing constellation necessary for long-term climate-scale studies.

Precipitation↗
DOE OSTI2013

Correlation between grain boundary misorientation and M{sub 23}C{sub 6} precipitation behaviors in a wrought Ni-based superalloy

The correlation between the grain boundary misorientation and the precipitation behaviors of intergranular M{sub 23}C{sub 6} carbides in a wrought Ni–Cr–W superalloy was investigated by using the electron backscattered diffraction (EBSD) technique. It was observed that the grain boundaries with a misorientation angle less than 20°, as well as all coincidence site lattice (CSL) boundaries, are immune to precipitation of the M{sub 23}C{sub 6} carbides; in contrast, the random high-angle grain boundaries with a misorientation angle of 20°–40° provide preferential precipitation sites of the M{sub 23}C{sub 6} carbides at the random high-angle grain boundaries with a higher misorientation angle of 55°–60°/[2 2 3] turn to retard precipitation of M{sub 23}C{sub 6} carbides owing to their nature like the Σ3 grain boundaries and retard the precipitation of M{sub 23}C{sub 6} carbides. The low-angle and certain random grain boundary segments induced by twins were found to interrupt the precipitation of the M{sub 23}C{sub 6} carbides along the high-angle grain boundaries. - Highlights: ► The low angle grain boundaries and CSL boundaries are immune to precipitation. ► M23C6 precipitate preferentially at random grain boundaries within 20°–40°. ► Some certain random grain boundary segments interrupt M23C6 precipitation.

36 MATERIALS SCIENCE↗