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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on KFeTc2 by Materials Project

KTc2Fe crystallizes in the cubic F-43m space group. The structure is three-dimensional. K1+ is bonded in a distorted body-centered cubic geometry to ten Tc2- and four equivalent Fe3+ atoms. There are four shorter (2.74 Å) and six longer (3.16 Å) K–Tc bond lengths. All K–Fe bond lengths are 2.74 Å. There are two inequivalent Tc2- sites. In the first Tc2- site, Tc2- is bonded to four equivalent K1+ and four equivalent Tc2- atoms to form distorted edge-sharing TcK4Tc4 tetrahedra. All Tc–Tc bond lengths are 2.74 Å. In the second Tc2- site, Tc2- is bonded in a 4-coordinate geometry to six equivalent K1+, four equivalent Tc2-, and four equivalent Fe3+ atoms. All Tc–Fe bond lengths are 2.74 Å. Fe3+ is bonded in a distorted body-centered cubic geometry to four equivalent K1+ and four equivalent Tc2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaSiTc2 by Materials Project

BaTc2Si crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ba2+ is bonded to ten Tc3- atoms to form distorted BaTc10 tetrahedra that share corners with six equivalent BaTc10 tetrahedra, corners with twelve equivalent TcBa4Tc4 tetrahedra, faces with four equivalent TcBa4Tc4 tetrahedra, and faces with twelve equivalent BaTc10 tetrahedra. There are four shorter (2.94 Å) and six longer (3.39 Å) Ba–Tc bond lengths. There are two inequivalent Tc3- sites. In the first Tc3- site, Tc3- is bonded in a 8-coordinate geometry to six equivalent Ba2+, four equivalent Tc3-, and four equivalent Si4+ atoms. All Tc–Tc bond lengths are 2.94 Å. All Tc–Si bond lengths are 2.94 Å. In the second Tc3- site, Tc3- is bonded to four equivalent Ba2+ and four equivalent Tc3- atoms to form distorted TcBa4Tc4 tetrahedra that share corners with twelve equivalent BaTc10 tetrahedra, edges with twelve equivalent TcBa4Tc4 tetrahedra, and faces with four equivalent BaTc10 tetrahedra. Si4+ is bonded in a 4-coordinate geometry to four equivalent Tc3- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Rb5Tc3S7 by Materials Project

Rb5Tc3S7 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are seven inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded to six S2- atoms to form RbS6 octahedra that share corners with six TcS5 square pyramids. There are a spread of Rb–S bond distances ranging from 3.10–3.42 Å. In the second Rb1+ site, Rb1+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Rb–S bond distances ranging from 3.19–3.66 Å. In the third Rb1+ site, Rb1+ is bonded in a 2-coordinate geometry to six S2- atoms. There are a spread of Rb–S bond distances ranging from 3.12–3.61 Å. In the fourth Rb1+ site, Rb1+ is bonded in a 3-coordinate geometry to four S2- atoms. There are a spread of Rb–S bond distances ranging from 3.18–3.78 Å. In the fifth Rb1+ site, Rb1+ is bonded in a 4-coordinate geometry to four S2- atoms. There are a spread of Rb–S bond distances ranging from 3.18–3.45 Å. In the sixth Rb1+ site, Rb1+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Rb–S bond distances ranging from 3.25–3.76 Å. In the seventh Rb1+ site, Rb1+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Rb–S bond distances ranging from 3.20–3.77 Å. There are four inequivalent Tc3+ sites. In the first Tc3+ site, Tc3+ is bonded to five S2- atoms to form TcS5 square pyramids that share a cornercorner with one RbS6 octahedra and edges with four TcS5 square pyramids. The corner-sharing octahedral tilt angles are 7°. There are a spread of Tc–S bond distances ranging from 2.42–2.44 Å. In the second Tc3+ site, Tc3+ is bonded to five S2- atoms to form TcS5 square pyramids that share a cornercorner with one RbS6 octahedra and edges with four TcS5 square pyramids. The corner-sharing octahedral tilt angles are 1°. There are a spread of Tc–S bond distances ranging from 2.42–2.44 Å. In the third Tc3+ site, Tc3+ is bonded to five S2- atoms to form TcS5 square pyramids that share a cornercorner with one RbS6 octahedra and edges with four TcS5 square pyramids. The corner-sharing octahedral tilt angles are 11°. There are a spread of Tc–S bond distances ranging from 2.42–2.46 Å. In the fourth Tc3+ site, Tc3+ is bonded to five S2- atoms to form TcS5 square pyramids that share a cornercorner with one RbS6 octahedra and edges with four TcS5 square pyramids. The corner-sharing octahedral tilt angles are 5°. There are a spread of Tc–S bond distances ranging from 2.40–2.48 Å. There are ten inequivalent S2- sites. In the first S2- site, S2- is bonded in an octahedral geometry to five Rb1+ and one Tc3+ atom. In the second S2- site, S2- is bonded in a 5-coordinate geometry to four Rb1+ and one Tc3+ atom. In the third S2- site, S2- is bonded in a 7-coordinate geometry to four Rb1+ and three Tc3+ atoms. In the fourth S2- site, S2- is bonded in a 8-coordinate geometry to three Rb1+ and three Tc3+ atoms. In the fifth S2- site, S2- is bonded in a 6-coordinate geometry to three Rb1+ and three Tc3+ atoms. In the sixth S2- site, S2- is bonded in a 6-coordinate geometry to five Rb1+ and one Tc3+ atom. In the seventh S2- site, S2- is bonded in a 7-coordinate geometry to four Rb1+ and three Tc3+ atoms. In the eighth S2- site, S2- is bonded in a 6-coordinate geometry to three Rb1+ and three Tc3+ atoms. In the ninth S2- site, S2- is bonded in a 6-coordinate geometry to three Rb1+ and three Tc3+ atoms. In the tenth S2- site, S2- is bonded in a 6-coordinate geometry to five Rb1+ and one Tc3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al3Tc by Materials Project

TcAl3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tc is bonded to twelve Al atoms to form TcAl12 cuboctahedra that share corners with four equivalent TcAl12 cuboctahedra, corners with eight equivalent AlAl8Tc4 cuboctahedra, edges with eight equivalent TcAl12 cuboctahedra, edges with sixteen equivalent AlAl8Tc4 cuboctahedra, faces with four equivalent TcAl12 cuboctahedra, and faces with fourteen AlAl8Tc4 cuboctahedra. There are four shorter (2.71 Å) and eight longer (2.78 Å) Tc–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded to four equivalent Tc and eight Al atoms to form AlAl8Tc4 cuboctahedra that share corners with twelve equivalent AlAl8Tc4 cuboctahedra, edges with eight equivalent TcAl12 cuboctahedra, edges with sixteen AlAl8Tc4 cuboctahedra, faces with four equivalent TcAl12 cuboctahedra, and faces with fourteen AlAl8Tc4 cuboctahedra. There are four shorter (2.71 Å) and four longer (2.78 Å) Al–Al bond lengths. In the second Al site, Al is bonded to four equivalent Tc and eight equivalent Al atoms to form distorted AlAl8Tc4 cuboctahedra that share corners with four equivalent AlAl8Tc4 cuboctahedra, corners with eight equivalent TcAl12 cuboctahedra, edges with twenty-four AlAl8Tc4 cuboctahedra, faces with six equivalent TcAl12 cuboctahedra, and faces with twelve AlAl8Tc4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TcGe3 by Materials Project

TcGe3 is alpha bismuth trifluoride structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tc is bonded to twelve Ge atoms to form TcGe12 cuboctahedra that share corners with four equivalent TcGe12 cuboctahedra, corners with eight equivalent GeTc4Ge8 cuboctahedra, edges with eight equivalent TcGe12 cuboctahedra, edges with sixteen equivalent GeTc4Ge8 cuboctahedra, faces with four equivalent TcGe12 cuboctahedra, and faces with fourteen GeTc4Ge8 cuboctahedra. There are eight shorter (2.80 Å) and four longer (2.88 Å) Tc–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four equivalent Tc and eight Ge atoms to form GeTc4Ge8 cuboctahedra that share corners with twelve equivalent GeTc4Ge8 cuboctahedra, edges with eight equivalent TcGe12 cuboctahedra, edges with sixteen GeTc4Ge8 cuboctahedra, faces with four equivalent TcGe12 cuboctahedra, and faces with fourteen GeTc4Ge8 cuboctahedra. There are four shorter (2.80 Å) and four longer (2.88 Å) Ge–Ge bond lengths. In the second Ge site, Ge is bonded to four equivalent Tc and eight equivalent Ge atoms to form GeTc4Ge8 cuboctahedra that share corners with four equivalent GeTc4Ge8 cuboctahedra, corners with eight equivalent TcGe12 cuboctahedra, edges with twenty-four GeTc4Ge8 cuboctahedra, faces with six equivalent TcGe12 cuboctahedra, and faces with twelve GeTc4Ge8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on InTc3 by Materials Project

Tc3In is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Tc1- sites. In the first Tc1- site, Tc1- is bonded to eight Tc1- and four equivalent In3+ atoms to form TcIn4Tc8 cuboctahedra that share corners with twelve equivalent TcIn4Tc8 cuboctahedra, edges with eight equivalent InTc12 cuboctahedra, edges with sixteen TcIn4Tc8 cuboctahedra, faces with four equivalent InTc12 cuboctahedra, and faces with fourteen TcIn4Tc8 cuboctahedra. There are four shorter (2.74 Å) and four longer (2.87 Å) Tc–Tc bond lengths. All Tc–In bond lengths are 2.87 Å. In the second Tc1- site, Tc1- is bonded to eight equivalent Tc1- and four equivalent In3+ atoms to form distorted TcIn4Tc8 cuboctahedra that share corners with four equivalent TcIn4Tc8 cuboctahedra, corners with eight equivalent InTc12 cuboctahedra, edges with twenty-four TcIn4Tc8 cuboctahedra, faces with six equivalent InTc12 cuboctahedra, and faces with twelve TcIn4Tc8 cuboctahedra. All Tc–In bond lengths are 2.74 Å. In3+ is bonded to twelve Tc1- atoms to form InTc12 cuboctahedra that share corners with four equivalent InTc12 cuboctahedra, corners with eight equivalent TcIn4Tc8 cuboctahedra, edges with eight equivalent InTc12 cuboctahedra, edges with sixteen equivalent TcIn4Tc8 cuboctahedra, faces with four equivalent InTc12 cuboctahedra, and faces with fourteen TcIn4Tc8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga3Tc by Materials Project

TcGa3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tc is bonded to twelve Ga atoms to form TcGa12 cuboctahedra that share corners with four equivalent TcGa12 cuboctahedra, corners with eight equivalent GaGa8Tc4 cuboctahedra, edges with eight equivalent TcGa12 cuboctahedra, edges with sixteen equivalent GaGa8Tc4 cuboctahedra, faces with four equivalent TcGa12 cuboctahedra, and faces with fourteen GaGa8Tc4 cuboctahedra. There are four shorter (2.72 Å) and eight longer (2.80 Å) Tc–Ga bond lengths. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded to four equivalent Tc and eight Ga atoms to form GaGa8Tc4 cuboctahedra that share corners with twelve equivalent GaGa8Tc4 cuboctahedra, edges with eight equivalent TcGa12 cuboctahedra, edges with sixteen GaGa8Tc4 cuboctahedra, faces with four equivalent TcGa12 cuboctahedra, and faces with fourteen GaGa8Tc4 cuboctahedra. There are four shorter (2.72 Å) and four longer (2.80 Å) Ga–Ga bond lengths. In the second Ga site, Ga is bonded to four equivalent Tc and eight equivalent Ga atoms to form GaGa8Tc4 cuboctahedra that share corners with four equivalent GaGa8Tc4 cuboctahedra, corners with eight equivalent TcGa12 cuboctahedra, edges with twenty-four GaGa8Tc4 cuboctahedra, faces with six equivalent TcGa12 cuboctahedra, and faces with twelve GaGa8Tc4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Using radiochemistry to diagnose fuel-ablator mix in inertial confinement fusion studies at the National Ignition Facility: measurement of Tc/Mo isotopic ratios for the Pushered Single Shell campaign

The development of radiochemical measurement techniques as a diagnostic for fusion experiments at the National Ignition Facility enables a new method for assessing fuel-ablator mix and the impact of this mix on capsule performance. Diagnosing capsule mix in internal confinement fusion studies is difficult due to the small spatial scales (10s of µm) and short-time frames (100s of ps) over which the mix typically evolves in these experiments. For the Pushered Single Shell campaign, radiochemical measurements on debris collected from fusion experiments can be used to determine isotopic ratios of activation products, particularly 96g Tc/ 99 Mo and 95g Tc/ 99 Mo, to provide vital information on nuclear reactions in the burning plasma that can inform simulations that seek to understand the degree of capsule-fuel mix and the impact on the capsule performance. These radiochemical measurements have been conducted regularly since November 2023 providing data on a range of capsule designs and neutron yields. Data from eight NIF experiments is presented, the measured 96g Tc/ 99 Mo and 95g Tc/ 99 Mo range from (0.5–5) × 10 –4 to (0.3–3) × 10 –4 , respectively. The development of radiochemical diagnostics aids in understanding and optimizing the design of fusion experiments, providing unique and valuable insights into capsule behavior and directly measuring fuel-ablator mix.

and nuclear chemistry↗
DOE OSTI2024

Tuning the Superconducting Transition Temperature of Co-sputtered Iridium and Platinum Films

A superconducting film with a tunable low transition temperature (Tc) is required in high-resolution Transition-Edge Sensor (TES) detectors, which have applications including dark matter detection, low threshold coherent elastic neutrino nucleus scattering measurement, and X-ray spectroscopy. We have been investigating a new approach to tune the Tc of superconducting thin films fabricated by co-sputtering Iridium and Platinum. The effects of Pt concentration and deposition parameters on the films' structural, electrical, and superconducting properties have been studied. AFM and XRD techniques and low temperature resistance measurements have been utilized for film characterization. By varying the Pt concentration and deposition parameters when co-sputtering, we have successfully achieved controllable tuning of Tc in the range of 30-200 mK. The experimental results demonstrate co-sputtering as a viable method for controlling the Tc of Ir-based thin films that can be applied to fabricating high-resolution TESs.

Yefremenko, V. G.↗
DOE OSTI2020

Radionuclide incorporation in negative thermal expansion α-Zr(WO 4 ) 2 : A density functional theory study

The incorporation of uranium, plutonium and technetium in the negative thermal expansion (NTE) α-Zr (WO 4 ) 2 has been investigated within the framework of density functional theory (DFT). It is found that the vacancy formation energies of the charged vacancies are overall larger than that of its counterpart neutral Frenkel defects and Schottky defects. DFT calculations suggest that U and Pu substitutions for the Zr site are preferred in α-Zr (WO 4 ) 2 . In case of Tc substitution, both Tc(IV) for the Zr site and Tc(VII) for the W site are considered under oxygen-poor and oxygen-rich conditions, while Tc(VII) substitution can be improved significantly by including Y 2 O 3 (charge compensation).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Quantifying the effect of late bombardment on terrestrial zircons

The first 500 million years of Earth history is thought to be a period of intense planetary bombardment, but the timing and flux of this meteorite bombardment is poorly understood. In particular, on the basis of an inferred lunar impact history, some workers have hypothesized a ~3.9 Ga terminal cataclysm (TC) in which there was marked increase in the impact flux affecting the Moon, the Earth and possibly other terrestrial planets. Minerals that survived this enigmatic period offer a way to test early planetary bombardment models as they may contain telltale micro- to nanoscale shock features. Here, we present results from a numerical modeling calculation that assesses the probability that a zircon residing in the crust would escape shock melting or shock deformation during a TC bombardment event. Even with conservative pressure estimates for zircon shock deformation and intermediate bombardment intensities, we find that only ~6% of ≥4.0 Ga crust would be expected to survive a 3.9 Ga cataclysm without experiencing either complete melting or zircon shock metamorphism. In this study, we couple this modeling with a search for shock effects in the oldest zircons from the Acasta Gneiss Complex, which would have been present in the Earth's crust during a putative 3.9 Ga TC. Spatially correlated electron and NanoSIMS ion microscopy of 4.02 Ga igneous zircons from Acasta reveals no evidence of ancient shock. These data, together with similar results from other Hadean zircon suites, confirm that a post-Hadean TC is unlikely to have occurred. We suggest that the dearth of pre-3.9 Ga terrestrial crust and zircons is instead best explained by endogenic processes related to the mechanisms of early crust formation. Our modeling allows us to evaluate bombardment scenarios from the terrestrial zircon record by applying probabilistic interpretations to zircon shock deformation data. This approach will be valuable for other planetary bodies, allowing broader conclusions to be drawn from geographically limited datasets.

58 GEOSCIENCES↗
DOE OSTI2020

Epsilon Metal: A Waste Form for Noble Metals from Used Nuclear Fuel

Epsilon metal (e-metal) is the metallic phase that forms as inclusions at the grain boundaries in the UO2 fuel during reactor operation. This metal is composed of Pd, Mo, Rh, Ru, and Tc. These metallic inclusions are insoluble in strong acid and remnants of these metallic inclusions have been found in the UO2 matrix that remains from the natural reactors in Gabon that were active 1.8 billion years ago, therefore e-metal should be an excellent waste form for the immobilization of the long-lived isotopes 107Pd (6.5 ? 106 a) and 99Tc (2.13 ? 105 a), with 99Tc being the isotope of interest for repository performance. Therefore, the chemical durability of this potential waste form is assessed in this study. Typically, corrosion rates for metallic materials are measured electrochemically because they are quick, inexpensive, and can reveal the mechanism by which a metal corrodes, at least initially. However, in a repository the waste form would be subjected to slowly flowing water without an applied electrical potential over long time periods. Therefore, the corrosion rates of e-metal specimens were measured with both electrochemical tests and the single-pass flow-through test (SPFT). Potentiodynamic and potentiostatic polarization results suggest that a thin passive film exists on the alloy surface, which seems to be responsible for its high corrosion resistance. Additionally, X-Ray photoelectron spectroscopic results suggest that Pd oxides are significantly enriched in the passive film Results from the SPFT show that the dissolution rates were weakly dependent on pH. Only Mo and Re were found in solution and were used for the calculation of the dissolution rates. In general, the electrochemically determined corrosion rates agree reasonably well with the initial dissolution rate measured with the SPFT test, but they are about one or two orders of magnitude higher than the steady state rates. The causes for this discrepancy are discussed.

epsilon-metal, nuclear waste form, corrosion, sing↗
DOE OSTI2023

Evaluation of the critical behavior near ferromagnetic to paramagnetic phase transition in CrTe 1-x Se x alloys: An experimental study

For this study, we used the conventional solid-state reaction method to prepare stoichiometric samples of CrTe 1-x Se x , where 0 ≤ x ≤ 0.10, and investigated the structural and critical behavior of the prepared samples. Room temperature powder X-ray diffraction, along with Rietveld refinement, revealed the emergence of the NiAs structure with P6 3 /mmc (194) space group with increasing Se substitution. The high-temperature linear fit to inverse of the dc-susceptibility versus temperature for the mother sample resulted in an effective moment of 3.65μ B Cr with Curie-Weiss temperature near 335K, which is slightly higher than the Tc of ~332K obtained from the inflection point of magnetization versus temperature. Magnetization isotherms were employed to investigate the critical behavior of ferromagnetic CrTe 1-x Se x with 0.0 ≤ x ≤ 0.10 near their Curie temperatures (Tc). The magnetic behavior near Tc was found to follow 3D mean-field critical exponents with a second-order phase transition in all samples investigated. We fine-tuned the critical exponents (β, γ, and δ) using a combination of an iteration technique, the Kouvel-Fisher method, and modified Arrott plots. All samples follow a mean field behavior, with Tc ranging from 298 to 340K. The acquired values exhibit self-consistency, as indicated by the results from the Widom scaling relation. Furthermore, the magnetization isotherms exhibit a universal scaling behavior, providing additional credence to the calculated critical exponents.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

RuAl 6 —An Endohedral Aluminide Superconductor

Superconductivity is reported in an endohedral aluminide compound, RuAl6, with Tc = 1.21 K. The normalized heat capacity jump at Tc, ΔC/γTc = 1.58, confirms bulk superconductivity. The Ginzburg-Landau parameter of κ = 9.5 shows that RuAl6 is a type-II superconductor. Electronic structure calculations for RuAl6 are explored in comparison to its structural analogue ReAl6 (Tc = 0.74 K). The stability of the phases is discussed in terms of the crystal orbital Hamilton population (-COHP) analysis. The difference in Tc in the two materials is caused by the significantly stronger electron-phonon coupling found in RuAl6, which is a result of significantly stronger antibonding interactions. The presence of superconductivity in yet another compound made of aluminum clusters possibly expands the correlation of critical temperature and the structure shown for Ga-built clusters.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Tropical Cyclone Frequency

Abstract The frequency with which tropical cyclones (TCs) occur controls all other aspects of tropical cyclone risk since a storm that does not occur can do no harm. Yet this frequency is poorly understood. There is no accepted theory that explains the average number of TCs that occur each year on the Earth, nor how that number will change with global warming. Arguments based on global budgets of heat or moisture do not yet appear helpful, nor does a detailed understanding of the physical processes of TC genesis. Empirical indices that predict TC frequency as a function of large‐scale environmental variables can explain some of its relative variations in space and time, but not its absolute value. Global numerical models with horizontal grid spacings on the order of 25–50 km have allowed much improved simulations of TC activity, however. Many such models project a decrease in frequency with warming, but some project an increase. Idealized simulations, including those at higher resolutions, offer promise by allowing a systematic, deductive investigation of the roles of individual environmental factors. In addition to the larger‐scale environmental modulation of genesis likelihood, precursor disturbances, or “seeds”, may exert an independent influence on TC frequency.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Observed Global Increases in Tropical Cyclone-Induced Ocean Cooling and Primary Production

Tropical cyclones (TC) provide an important source of mixing for the upper ocean, bringing cold, nutrient-rich water to the surface and triggering phytoplankton blooms. TCs are changing in response to global warming, yet the impacts of those changes on the upper ocean are poorly known. Here we show a significant increasing trend in global TC-induced sea surface temperature (SST) cooling of 0.054oC per decade since 1982. The enhanced cooling has been driven primarily by an increase in the intensity of strong TCs (maximum wind speed > 33 m s-1) and associated strengthening of TC-induced mixing. Consistent with the enhanced mixing and SST cooling, we find a significant increase in TC-induced surface chlorophyll-a concentration of 3.7 x 10-3 mg m-3 per decade in oligotrophic areas. This enhancement of oceanic primary production by TCs is expected to partially offset its projected global decline under climate change.

Dac Da, Nguyen↗
DOE OSTI2023

Climate Change Signal in Atlantic Tropical Cyclones Today and Near Future

This manuscript discusses the challenges in detecting and attributing recently observed trends in the Atlantic tropical cyclone (TC) and the epistemic uncertainty we face in assessing future risk. We use synthetic storms downscaled from five CMIP5 models by the Columbia HAZard model (CHAZ), and directly simulated storms from high-resolution climate models. We examine three aspects of recent TC activity: the upward trend and multi-decadal oscillation of the annual frequency, the increase in storm wind intensity, and the decrease in forward speed. Some data sets suggest that these trends and oscillation are forced while others suggest that they can be explained by natural variability. Projections under warming climate scenarios also show a wide range of possibilities, especially for the annual frequencies, which increase or decrease depending on the choice of moisture variable used in the CHAZ model and on the choice of climate model. The uncertainties in the annual frequency lead to epistemic uncertainties in TC risk assessment. Here, we investigate the potential for reduction of these epistemic uncertainties through a statistical practice, namely likelihood analysis. We find that historical observations are more consistent with the simulations with increasing frequency than those with decreasing frequency, but we are not able to rule out the latter. We argue that the most rational way to treat epistemic uncertainty is to consider all outcomes contained in the results. In the context of risk assessment, since the results contain possible outcomes in which TC risk is increasing, this view implies that the risk is increasing.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

The Effects of African Easterly Wave Suppression by Wave Track on Atlantic Tropical Cyclones

Abstract It is well established that African easterly waves (AEWs) can serve as seedling disturbances for Atlantic tropical cyclones (TCs). However, research has shown that AEWs are not necessary to maintain specifically basin‐wide TC frequency. Here, we for the first time investigate the effects of AEW suppression by wave track on Atlantic TC activity. Regional model simulations were performed, where AEWs were either prescribed or suppressed from the eastern lateral boundary condition. We found that without AEWs, there was an increase in TC frequency and strength, with the most pronounced increases occurring when the waves were suppressed in the south track. These changes coincided with more favorable environmental conditions and disturbances associated with increased convective activity over the Atlantic. Our results indicate that AEWs are not a limiting factor for TCs, and that AEW suppression, specifically in the south track, can affect the large‐scale environment to enhance favorability for TC genesis.

54 ENVIRONMENTAL SCIENCES↗