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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Gridded Hourly Text Products: A TRMM Data Reduction Approach

The quantity of precipitation data from satellite-based observations is a blessing and a curse. The sheer volume of the data makes it difficult for many researchers to use in targeted applications. This volume increases further as algorithm improvements lead to the reprocessing of mission data. In addition to the overall volume of data, the size and format complexity of orbital granules contribute to the difficulty in using all the available data. Finally, the number of different instruments available to measure rainfall and related parameters further contributes to the volume concerns. In summary, we have an embarrassment of riches. The science team of the Tropical Rainfall Measuring Mission (TRMM) recognized this dilemma and has developed a strategy to address it. The TRMM Science Data and Information System (TSDIS) produces, at the direction of the Joint TRMM Science Team, a number of instantaneous rainfall products. The TRMM Microwave Imager (TMI), the Precipitation Radar and a Combined TMI/PR are the key "instruments" used in this production. Each of these products contains an entire orbit of data. The algorithm code computes not just rain rates but a large number of other physical parameters as well as information needed for monitoring algorithm performance. That makes these products very large. For example, a single orbit of TMI rain rate product is 99 MB, a single orbit of the combined product yields a granule that is 158 MB, while the 80 vertical levels of rain information from the PR yields an orbital product of 253 MB. These are large products that are often difficult for science users to electronically transfer to their sites especially if they want a large period of time. Level 3 gridded products are much smaller, but their 5 or 30 day temporal resolution is insufficient for many researchers. In addition, TRMM standard products are produced in the HDF format. While a large number of user-friendly tools are available to hide the details of the format (including a toolkit developed at TSDIS for the TRMM science team), many potential users shy away

Stocker, Erich↗
DOE OSTI2019

Microstructural Stability During Creep Exposure of 9Cr-1Mo Steel Treated at Different Normalization Temperatures

A modified 9Cr-1Mo steel has been exposed to three separate austenitization temperatures, i.e., at 950, 1025, and 1100 °C for normalization. After subsequent tempering at 750 °C, the normalized and tempered samples were creep-tested at temperatures of 550, 600, and 650 °C. The creep strength of the investigated samples was evaluated in terms of minimum creep strain rate and time to rupture. The effects of microstructure, precipitate and boundary misorientation on the creep behavior of the samples have been studied with TEM and EBSD analyses. Further, the evolution of crystallographic texture after creep tests has also been studied. The presence of an intermediate size of martensitic microstructural units (i.e., prior-austenite grain, martensitic packets, etc.) and combination of fine coherent and incoherent Nb(C,N) precipitates has provided superior creep strength for the samples normalized at 1025 °C, when these are subsequently subjected to low-temperature (i.e., 550 °C) and high-temperature (i.e., 650 °C) creep tests, as compared to other conditions of normalizing heat treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Mechanisms causing east Australian spring rainfall differences between three strong El Niño events

Strong El Niño events have had significant impacts on society through their association with extreme events, such as droughts and floods. However, questions remain as to the robustness of strong El Niño events in forcing regional climate variability. The strong 1982, 1997 and 2015 El Niño events were of similar type and strength, but in eastern Australia they were associated with differing spring rainfall anomaly magnitudes and patterns. To understand these differences, we first determined the most important processes for teleconnecting the El Niño signal to east Australian spring rainfall using historical relationships with winds and sea level pressure. Then, using a 60-member atmospheric model ensemble, we estimated the influence of sea surface temperatures (SSTs) on Australian atmospheric circulation and rainfall during these three El Niño events relative to internal variability. We found that the different east Australian spring rainfall anomalies for each of the three El Niño events are best explained by differences in the strength of the meridional wind component of the regional circulation. All three El Niño events exhibited a positive sea level pressure anomaly to the south of Australia, which was associated with rainfall deficits along the southeast Australian coast. The experiments indicate the regional atmospheric circulation and rainfall differences were forced by SSTs during spring of 1982 and 1997, with their influence on the circulation in 2015 remaining unclear. We also show that SSTs adjacent to Australia further contributed to the modelled rainfall differences mainly by regulating moisture availability.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Soil carbon stocks across tropical forests of Panama regulated by base cation effects on fine roots

We report that tropical forests are the most carbon (C)- rich ecosystems on Earth, containing 25–40% of global terrestrial C stocks. While large-scale quantifi- cation of aboveground biomass in tropical forests has improved recently, soil C dynamics remain one of the largest sources of uncertainty in Earth system models, which inhibits our ability to predict future climate. Globally, soil texture and climate predict B 30% of the variation in soil C stocks, so ecosystem models often predict soil C using measures of aboveground plant growth. However, this approach can underestimate tropical soil C stocks, and has proven inaccurate when compared with data for soil C in data-rich northern ecosystems. By quantifying soil organic C stocks to 1 m depth for 48 humid tropical forest plots across gradients of rainfall and soil fertility in Panama, we show that soil C does not correlate with common predictors used in models, such as plant biomass or litter production. Instead, a structural equation model including base cations, soil clay content, and rainfall as exogenous factors and root biomass as an endogenous factor predicted nearly 50% of the variation in tropical soil C stocks, indicating a strong indirect effect of base cation availability on tropical soil C storage. Including soil base cations in C cycle models, and thus emphasizing mechanistic links among nutrients, root biomass, and soil C stocks, will improve prediction of climate-soil feedbacks in tropical forests.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

A Thermodynamic Model to Estimate the Formation of Complex Nitrides of Al{sub x}Mg{sub (1–x)}N in Silicon Steel

A complex nitride of Al{sub x}Mg{sub (1−x)}N was observed in silicon steels. A thermodynamic model was developed to predict the ferrite/nitride equilibrium in the Fe-Al-Mg-N alloy system, using published binary solubility products for stoichiometric phases. The model was used to estimate the solubility product of nitride compound, equilibrium ferrite, and nitride compositions, and the amounts of each phase, as a function of steel composition and temperature. In the current model, the molar ratio Al/(Al + Mg) in the complex nitride was great due to the low dissolved magnesium in steel. For a steel containing 0.52 wt pct Al{sub s}, 10 ppm T.Mg., and 20 ppm T.N. at 1100 K (827 °C), the complex nitride was expressed by Al{sub 0.99496}Mg{sub 0.00504}N and the solubility product of this complex nitride was 2.95 × 10{sup −7}. In addition, the solution temperature of the complex nitride increased with increasing the nitrogen and aluminum in steel. The good agreement between the prediction and the detected precipitate compositions validated the current model.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Inclusion Precipitation, Partition Coefficient, and Phase Transition on Microsegregation for High-Sulfur Steel Solidification

A microsegregation model coupled with inclusion precipitation, variable partition coefficient, and diffusion coefficient of the solute was developed to investigate solute microsegregation for high-sulfur steel solidification. The effects of the solidification path and phase transition on solute microsegregation were explored. The results showed that the solute concentration predicted by the variable partition coefficient was quite different from the solute concentration predicted by the constant partition coefficient, and the percentage differences of solutes Si, P, and S were − 35.5, − 25.0, and 43.0 pct, respectively. For high-sulfur steel solidification, the concentrations of solutes Mn and S would be reduced by 88.3 and 74.9 pct, respectively, due to the precipitation of MnS. The solidification path and phase transition has a significant effect on the solute partition coefficient and microsegregation. With the increase in C content, the fraction of δ-phase decreased while the fraction of the γ-phase increased, and the microsegregation ratio of solutes C and Si decreased while the microsegregation ratio of solute P increased. To predict microsegregation more accurately, all influencing factors of the partition coefficient, inclusion precipitation, and phase transition should be comprehensively considered.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Integrated modeling of second phase precipitation in cold-worked 316 stainless steels under irradiation

The current work combines the Cluster Dynamics (CD) technique and CALPHAD-based precipitation modeling to address the second phase precipitation in cold-worked (CW) 316 stainless steels (SS) under irradiation at 300–400 °C. CD provides the radiation enhanced diffusion and dislocation evolution as inputs for the precipitation model. The CALPHAD-based precipitation model treats the nucleation, growth and coarsening of precipitation processes based on classical nucleation theory and evolution equations, and simulates the composition, size and size distribution of precipitate phases. We benchmark the model against available experimental data at fast reactor conditions (9.4 × 10 –7 dpa/s and 390 °C) and then use the model to predict the phase instability of CW 316 SS under light water reactor (LWR) extended life conditions (7 × 10 –8 dpa/s and 275 °C). The model accurately predicts the γ' (Ni 3 Si) precipitation evolution under fast reactor conditions and that the formation of this phase is dominated by radiation enhanced segregation. The model also predicts a carbide volume fraction that agrees well with available experimental data from a PWR reactor but is much higher than the volume fraction observed in fast reactors. We propose that radiation enhanced dissolution and/or carbon depletion at sinks that occurs at high flux could be the main sources of this inconsistency. The integrated model predicts ~1.2% volume fraction for carbide and ~3.0% volume fraction for γ' for typical CW 316 SS (with 0.054 wt% carbon) under LWR extended life conditions. Finally, this work provides valuable insights into the magnitudes and mechanisms of precipitation in irradiated CW 316 SS for nuclear applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Role of refractory inclusions in the radiation-induced microstructure of APMT

Kanthal APMT is a promising FeCrAl-based alloy for accident-tolerant fuel cladding because of its excellent high-temperature oxidation resistance. In this study, powder metallurgy Kanthal APMT alloy, neutron irradiated to 1.8 dpa at nominally 382 °C, was characterized. On-zone STEM imaging revealed that radiation-induced dislocation loops with Burgers vectors of a/2 <111 > or and black dots tended to agglomerate in the vicinity of refractory inclusions. The densities and sizes of these loops decreased with distance from the inclusion-matrix interfaces. In addition, high-resolution energy-dispersive X-ray spectroscopy mapping was used to determine the inclusions to be either yttrium- or silicon-rich, as well as to detect the radial distribution of radiation-enhanced α' phase near these inclusions. A high density of randomly distributed Cr-rich α' phase was found, regardless of the presence of inclusions. Here, the results from this study provide insights into how microstructural features can locally tailor the radiation-induced defects in FeCrAl-based alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of grain-boundary θ-Al 2 Cu precipitates on tensile and compressive creep properties of cast Al–Cu–Mn–Zr alloys

Tensile and compressive creep tests were performed at 300 °C on high-temperature Al–Cu–Mn–Zr (ACMZ) alloys with 6 wt% Cu (6Cu) and 9 wt% Cu (9Cu) to evaluate the effect on creep properties of micron-size θ-Al 2 Cu intergranular precipitates. For compressive creep, the increased volume fraction of θ-precipitates at grain boundaries (from ~0.7% in 6Cu to ~ 6% in 9Cu) does not affect deformation rates across the investigated stress range of 15–110 MPa, consistent with creep being controlled by submicron θ'-Al 2 Cu precipitates within grains, whose size and fractions are the same in both alloys. In contrast, for tensile creep, 9Cu creeps faster than 6Cu at stresses above 20 MPa, and this difference increases with the stress level. Additionally, this discrepancy between tensile and compressive creep behavior is explained by cavitation during tensile creep, which is favored by higher volume fraction and larger size of intergranular θ precipitates in 9Cu. Conversely, larger precipitates impede cavity linkage resulting in improved creep ductility of 9Cu as compared to 6Cu at 300 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The Effects of Secondary Mineral Precipitates on 90Sr Mobility at the Hanford Site, USA

The effects of secondary precipitates on 90Sr transport at the Hanford Site were investigated using quartz column experiments with simulated caustic tank waste leachates (STWL). Significantly enhanced retardation of Sr transport was observed in the column contacted with STWL due to Sr sorption and co-precipitation with neo-formed nitratecancrinite. However, the column results also suggest that neo-formed secondary precipitates could behave like native mobile colloids that can enhance Sr transport. Initially immobilized Sr within secondary precipitates could remobilize given a change in the porewater background conditions. The mobility of the neo-formed Sr-bearing precipitates increased with increased solution flow rate. In the field, porewater contents and flow rates can be changed by snowmelt (or storm water) events or artificial infiltration. The increased porewater flow rate caused by these events could affect the mobility of 90Sr-containing secondary precipitates, which can be a potential source for facilitated Sr transport in Hanford Site subsurface environments.

Effects Secondary Mineral Precipitates Mobility Ha↗
DOE OSTI2021

Connections Between Mean North Pacific Circulation and Western US Precipitation Extremes in a Warming Climate

Abstract Extreme precipitation has widespread impacts over the western US (WUS), which are expected to be exacerbated in the future given thermodynamically driven increases in atmospheric moisture and shifts in atmospheric circulation patterns. However, internal climate variability complicates how these factors affect future projections of precipitation changes. In this study, we investigate late 21st‐century changes in mean‐state responses over the North Pacific Ocean and associated WUS precipitation extremes using the Multi‐Model Large Ensemble Archive, which is a recent and valuable resource to disentangle the effects of model structural differences from internal variability. We found that inter‐model differences in precipitation extremes over the WUS are large: from south to north (here, from California to Washington), models show different levels of increases for both the frequency and intensity of heavy precipitation. In general, the Pacific Northwest sees a more consistent signal than California. We show that wet‐season mean circulation influences extreme precipitation, by using a decomposition of the relative contributions of thermodynamic (atmospheric humidity) and dynamic (large‐scale circulation) driven changes. The thermodynamic contribution dominates, however, the dynamic contribution varies with latitude and differs substantially between model ensembles. Inter‐model differences affect the spread in not only the magnitude, but also the sign of the dynamic contribution. This implies that mean circulation changes contribute to uncertainty in quantifying the regional structure of concentrated moisture flux and future extreme events. This result highlights the need to more accurately constrain projected North Pacific coupled circulation changes to narrow the spread in projections of future precipitation extremes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Blowing Snow at McMurdo Station, Antarctica During the AWARE Field Campaign: Surface and Ceilometer Observations

Blowing snow (BLSN) is an impactful process in cold climates, affecting regional thermodynamics, radiation properties, and the surface mass balance of snow. Though it has significant climatic impacts, the process is still poorly understood and not widely included in weather and climate models. In 2016, the AWARE Field Campaign saw the deployment of a large suite of in situ and remote sensing instruments to McMurdo Station, Antarctica allowing for investigation of BLSN. A ceilometer–based BLSN detection algorithm used elsewhere in Antarctica is applied to data from AWARE, yielding a BLSN frequency of 14.1% compared to 8.2% as detected by human observers. To increase confidence in detections, the algorithm is updated to have shorter temporal averaging and to include a variety of meteorological thresholds to limit false detections due to fog. Efforts to incorporate a laser disdrometer into the algorithm were unsuccessful. An unphysical dependence of particle size distributions on wind speed is found suggesting observations are problematic at wind speeds greater than 10 m s –1 . The revised algorithm detected a BLSN frequency of 7.4%, increasing agreement with human observations and confidence that the process is actively occurring at the observation site. Furthermore, these observations are put into context of a climatology of human observations of BLSN at McMurdo station from 2002–2018. An annual average of 8.0%–14.0% is estimated, with a total annual range of 3.4%–21.3%. Regardless of whether BLSN is observed by humans or instrument, the majority of cases at this location are associated with ongoing precipitation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Contributions of Climate Change and ENSO Variability to Future Precipitation Extremes Over California

The El Niño/Southern Oscillation (ENSO) affects the occurrence frequency and intensity of extreme precipitation through modulations of regional heat and moisture fluxes. California experiences particularly strong ENSO influences and models project different to its extreme precipitation. It remains unclear how diverse projections of future precipitation extremes relate to inter-model differences for those changing signals. Here, we use “large ensemble” simulations with multiple climate models along with the Coupled Model Intercomparison Project Phase 5 to investigate the range of precipitation extreme changes over California and the influences from ENSO-related teleconnections. We found that precipitation amount increases are much larger during El Niño relative to La Niña years, mainly caused by the differences in frequency of extreme events during different phases. The ENSO-driven effect is even larger than the overall climate change signal for the most extreme events, implying uncertainties from inter-model differences in ENSO-related SST variability for extreme precipitation changes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

New Particle Formation Events Over the Southeast Atlantic Coincide With the African Biomass Burning Season

Abstract We investigated the occurrence and evolution of new particle formation (NPF) events over the southeast Atlantic. The studied region is under the influence of the long‐range transport of aerosols and gases during the southern African biomass burning season, from June to October every year. Interestingly, NPF was observed to coincide with the African biomass burning season, although wet removal of pre‐existing aerosols is needed during these NPF events. Surface and airborne measurements show that these NPF events likely occurred in the upper region of the marine boundary layer, and the newly formed aerosols were further transported to the surface via vertical air motions. Using a box model, we predicted that a large fraction of these particles could grow to sizes related to cloud condensation nuclei. Our study shows that NPF can occur over the southeast Atlantic, and the African biomass‐burning plume likely contributed to the NPF occurrence.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Deforestation size influences rainfall: Biosphere–atmosphere interactions

We report that changes to the land surface, such as land clearing and logging of forest areas, impacts moisture cycling. Now a shift from small-scale to large-scale deforestation in the southern Amazon is found to modify the mechanisms and patterns of regional precipitation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Duplex precipitates and their effects on the room-temperature fracture behaviour of a NiAl-strengthened ferritic alloy

Duplex precipitates are presented in a NiAl-strengthened ferritic alloy. They were characterized by the ultra-small angle X-ray scattering and transmission electron microscope. Fine cooling precipitates with the size of several to tens of nanometres harden the matrix considerably at room temperature. Cracks are likely to initiate from precipitates, and coalesce and propagate quickly through the matrix due to the excessive hardening effect of cooling precipitates, which lead to the premature fracture of NiAl-strengthened ferritic alloys.

36 MATERIALS SCIENCE↗