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This grant supported several observational and modeling activities as reviewed in the final report. Overall, over 20 papers (published, in press or still in preparation) acknowledge support from this grant; see the complete list in the final report (uploaded in this system).
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Engineering the precipitation of calcium carbonate, which can co-precipitate trace metal contaminants, is a proposed strategy for remediating toxic or radioactive metals in subsurface environments. Engineering precipitation of multi-component minerals will involve injection of chemical amendments that must be mixed at a molecular level to supersaturated conditions that are sufficient to promote rapid mineral precipitation relative to natural systems. In subsurface systems this often means reactant mixing zones will be formed that are characterized by gradients in solute concentrations, saturation state, and solute activity ratios. To better understand the effect of ion activity ratios on CaCO{sub 3} precipitation kinetics and Sr{sup 2+} co-precipitation we experiments were conducted under constant composition conditions where the supersaturation state ({Omega}) with respect to calcite was held constant at 9.4, but the ion activity ratio (r = a{sub co{sub 3}{sup 2-}}/a{sub Ca{sup 2+}}) ranged from 0.003 to 4.15. Results: Under the chosen experimental conditions the CaCO{sub 3} phase formed was calcite and initial precipitation rates varied from a maximum rate of 84.7 {mu}mol/ m{sup 2}/min for a carbonate to calcium activity ratio of (0.21). However, precipitation rates were found to vary with time which could be indicative of variations in precipitation mechanisms that are related to the ion activity ratio. The observed trends in the distribution coefficients for co-precipitated Sr2+ (D{sup P}{sub Sr}{sup 2+}) relative to the calcite precipitation rate (i.e. a positive correlation) indicate that increasing calcite precipitation rates increase the incorporation of Sr{sup 2+}. Conclusion: The observed variation between the rate maxima and minima based on the ion activity ratio could have great deal of implication for sequestering radionuclides (e.g. {sup 90}Sr) and other toxic metals in engineered systems at contaminated sites. Extending our data plot range allowed us to have clues about the differences in mechanism calcite precipitation, which would have significance in our understanding of mineral precipitation modes in subsurface remediation strategies. The positive correlation between D{sup P}{sub Sr}{sup 2+} and calcite precipitation rate could be indicative of the impact calcite precipitation would have on sequestering toxic metals in subsurface environment.
Abstract Background Precipitation plays an important role in crop production and soil greenhouse gas emissions. However, how crop yield and soil nitrous oxide (N 2 O) emission respond to precipitation change, particularly with different background precipitations (dry, normal, and wet years), has not been well investigated. In this study, we examined the impacts of precipitation changes on corn yield and soil N 2 O emission using a long-term (1981–2020, 40 years) climate dataset as well as seven manipulated precipitation treatments with different background precipitations using the DeNitrification-DeComposition (DNDC) model. Results Results showed large variations of corn yield and precipitation but small variation of soil N 2 O emission among 40 years. Both corn yield and soil N 2 O emission showed near linear relationships with precipitation based on the long-term precipitation data, but with different response patters of corn yield and soil N 2 O emission to precipitation manipulations. Corn yield showed a positive linear response to precipitation manipulations in the dry year, but no response to increases in precipitation in the normal year, and a trend of decrease in the wet year. The extreme drought treatments reduced corn yield sharply in both normal and wet years. In contrast, soil N 2 O emission mostly responded linearly to precipitation manipulations. Decreases in precipitation in the dry year reduced more soil N 2 O emission than those in the normal and wet years, while increases in precipitation increased more soil N 2 O emission in the normal and wet years than in the dry year. Conclusions This study revealed different response patterns of corn yield and soil N 2 O emission to precipitation and highlights that mitigation strategy for soil N 2 O emission reduction should consider different background climate conditions.
Changes in precipitation amount, intensity and frequency in response to global warming are examined using global high‐resolution (16 km) climate model simulations based on the European Centre for Medium‐range Weather Forecasts (ECMWF) Integrated Forecast System (IFS) conducted under Project Athena. Our study shows the increases of zonal‐mean total precipitation in all latitudes except the northern subtropics (15°–30°N) and southern subtropics‐to‐midlatitudes (30°–40°S). The probability distribution function (PDF) changes in different latitudes suggest a higher occurrence of light precipitation (LP; ≤1 mm/day) and heavy precipitation (HP; ≥30 mm/day) at the expense of moderate precipitation reduction (MP; 1–30 mm/day) from Tropics to midlatitudes, but an increase in all categories of precipitation in polar regions. On the other hand, the PDF change with global warming in different precipitation climatological zones presents another image. For all regions and seasons examined, there is an HP increase at the cost of MP, but LP varies. The reduced MP in richer precipitation zones resides in the PDF peak intensities, which linearly increase with the precipitation climatology zones. In particular in the Tropics (20°S to 20°N), the precipitation PDF has a flatter distribution (i.e. HP and LP increases with MP reduction) except for the Sahara Desert. In the primary precipitation zones in the subtropics (20°–40°) of both hemispheres, precipitation over land switches toward higher intensity (HP increases, but MP and LP decrease) in both winter and summer, while precipitation over ocean in both seasons shows a flattening trend in the intensity distribution. For the major precipitation zones of the mid‐to‐high latitude belt (40°–70°), PDF of precipitation tends to be flatter over ocean in summer, but switches toward higher intensities over land in both summer and winter, as well as over ocean in winter.
Current climate model resolution cannot accurately describe the complex topography over the Tibetan Plateau, which limits our understanding of past and future precipitation over this region. This study investigates the daily precipitation characteristics and its future changes over the Tibetan Plateau, especially for the southern slope of Tibetan Plateau (SSTP), by 14-km Nonhydrostatic ICosahedral Atmospheric Model (NICAM) with explicitly calculated convection for historical and future 30-years period. By comparing with the satellite Global Precipitation Measurement (GPM), NICAM well reproduces the historical precipitation spatial pattern, seasonal cycle, and the extreme precipitation belt over SSTP, but overestimates precipitation amount by~35%. It is found that heavy precipitation probability decreases as elevation becomes higher while the light precipitation generally shows the opposite. For the precipitation changes during June to September from 1979–2008 to 2075–2104, NICAM predicts that mean precipitation will decrease over low-level SSTP but increase over high-level SSTP. Nonprecipitation and heavy precipitation probability will increase while light precipitation probability will decrease in the future over SSTP. The extreme precipitation probability and intensity will increase ~50%/°C and ~8%/°C over SSTP, and this increase is more obvious as elevation becomes higher. The robust increase of extreme precipitation along the SSTP topography is unique and has not been identified by the climate model simulations before. The strong meridional gradient of specific humidity over SSTP is found to be further enhanced under global warming, and this gradient enhancement is suggested to be responsible for the increase in the extreme precipitation over SSTP.
The present study investigates the impact of horizontal resolutions on heavy‐precipitating storms using the Energy Exascale Earth System Model version2 (E3SMv2) at low (∼100 km, LR) and high (∼25 km, HR) resolutions through short‐range hindcasts. The short‐range hindcast approach ensures a faithful comparison of model resolution in simulating the same storm events under a controlled large‐scale environment. Using a phenomenon‐based framework, we attribute precipitation to specific storm types: tropical cyclones (TCs), extratropical cyclones, atmospheric rivers, and mesoscale convective systems (MCSs). Our findings show that E3SM hindcasts with both HR and LR configurations significantly underestimate storm‐associated precipitation intensity but overestimate precipitation from other sources. Furthermore, both HR and LR hindcasts face significant challenges in accurately simulating extreme precipitation events, particularly over MCS hotspots. Nevertheless, HR simulations capture more detailed and intense precipitation patterns with an improved representation of storm dynamics. HR hindcasts produce 16% more storm precipitation compared to LR. For precipitation extremes, HR simulates a 33% higher 99th percentile precipitation magnitudes compared to LR, and most of the increment comes from these four heavy‐precipitating storm types. The increase in precipitation mainly comes from stratiform precipitation rather than convective precipitation. The improvement in HR simulations varies across different storm types with TC showing the largest improvement. The phenomenon‐based approach provides important insights into precipitation simulations especially for extremes. Our results emphasize the need for further refinement in high‐resolution models to improve the accuracy of precipitation predictions, which is crucial for better understanding and mitigating climate change impacts.
In situ irradiations with 1 MeV Kr ions at 50~613 K up to a fluence of 6.25 × 10 14 ions/cm 2 (~1.25 displacements per atom, dpa) have been performed on pre-aged dilute Cu-0.9%Co, Cu-0.9%Fe and Cu-0.8%Cr alloys containing uniform matrix dispersions of coherent precipitates in order to study the effects of initial precipitate sink strength, damage dose and irradiation temperature on radiation-induced coherency loss of precipitates. Coherent precipitates with different point defect sink strengths (2πNd, where N and d are the precipitate density and diameter) were used in this work to examine potential differences in atomic relaxation during absorption of point defects. In all cases, irradiation to low doses (<~1 dpa) was very effective at inducing loss of precipitate coherency. At low sink strengths (~10 13 m -2 ), loss of precipitate coherency could be induced for doses ~0.01 dpa. This suggests there might be an efficient preferential medium-range strain-induced bias for absorption of interstitial defects due to tensile strains emanating from the undersized precipitates, which induces relatively rapid loss of coherency at low precipitate sink strengths. High precipitate sink strength (~10 14 m -2 ) conditions were relatively resistant to the radiation-induced loss of coherency (requiring higher doses approaching ~1 dpa) and this might be due to nearly equal numbers of interstitial and vacancy defects arriving at the precipitate interface for such high sink strength conditions. The precipitate coherency loss was observed to have a weak dependence on irradiation temperature. Molecular dynamics simulations confirm a strong effect of precipitate sink strength on the probability of interstitial absorption at precipitates.
In this study, we apply an efficient sampling approach and conduct a large number of simulations to explore the sensitivity of the simulated Asian summer monsoon (ASM) precipitation, including the climatological state and interannual variability, to eight parameters related to the cloud and precipitation processes in the Beijing Climate Center AGCM version 2.1 (BCC_AGCM2.1). Our results show that BCC_AGCM2.1 has large biases in simulating the ASM precipitation. The precipitation efficiency and evaporation coefficient for deep convection are the most sensitive parameters in simulating the ASM precipitation. With optimal parameter values, the simulated precipitation climatology could be remarkably improved, e.g. increased precipitation over the equator Indian Ocean, suppressed precipitation over the Philippine Sea, and more realistic Meiyu distribution over Eastern China. The ASM precipitation interannual variability is further analyzed, with a focus on the ENSO impacts. It shows the simulations with better ASM precipitation climatology can also produce more realistic precipitation anomalies during El Niño decaying summer. In the low-skill experiments for precipitation climatology, the ENSO-induced precipitation anomalies are most significant over continents (vs. over ocean in observation) in the South Asian monsoon region. More realistic results are derived from the higher-skill experiments with stronger anomalies over the Indian Ocean and weaker anomalies over India and the western Pacific, favoring more evident easterly anomalies forced by the tropical Indian Ocean warming and stronger Indian Ocean-western Pacific tele-connection as observed. Our model results reveal a strong connection between the simulated ASM precipitation climatological state and interannual variability in BCC_AGCM2.1 when key parameters are perturbed.
Ice-nucleating particles (INPs) influence the formation of ice crystals in clouds and many types of precipitation. This study reports unique properties of INPs collected from 42 precipitation samples in the Texas Panhandle region from June 2018 to July 2019. We used a cold stage instrument called the West Texas Cryogenic Refrigerator Applied to Freezing Test system to estimate INP concentrations per unit volume of air (nINP) through immersion freezing in our precipitation samples with our detection capability of >0.006 INP L -1 . A disdrometer was used for two purposes: (1) to characterize the ground-level precipitation type and (2) to measure the precipitation intensity as well as size of precipitating particles at the ground level during each precipitation event. While no clear seasonal variations of n INP values were apparent, the analysis of yearlong ground-level precipitation observation as well as INPs in the precipitation samples showed some INP variations, e.g., the highest and lowest n INP values at -25°C both in the summer for hail-involved severe thunderstorm samples (3.0 to 1130 INP L -1 ), followed by the second lowest at the same temperature from one of our snow samples collected during the winter (3.2 INP L -1 ). Furthermore, we conducted bacteria community analyses using a subset of our precipitation samples to examine the presence of known biological INPs. In parallel, we also performed metagenomics characterization of the bacterial microbiome in suspended ambient dust samples collected at commercial open-lot livestock facilities (cattle feedyards hereafter) in the Texas Panhandle (i.e., the northernmost counties of Texas, also known as “West Texas”) to ascertain whether local cattle feedyards can act as a source of bioaerosol particles and/or INPs found in the precipitation samples. Some key bacterial phyla present in cattle feedyard samples appeared in precipitation samples. However, no known ice nucleation active species were detected in our samples. Overall, our results showed that cumulative n INP in our precipitation samples below -20°C could be high in the samples collected while observing > 10 mm h -1 precipitation with notably large hydrometeor sizes and an implication of cattle feedyard bacteria inclusion.
An integrated experimental characterization and molecular dynamics (MD) simulation approach was used to explore the dislocation-precipitate interactions in a dilute Magnesium–Neodymium (Mg–Nd) precipitation hardened alloy. In situ indentation in a transmission electron microscope (TEM) and postmortem TEM characterization of deformed samples and MD simulations revealed that basal < a > type dislocations interacted differently with β 1 (Mg 3 Nd) and β"(Mg 3-7 Nd) precipitates. For β" precipitates, the basal dislocations directly shear the precipitates. For β 1 precipitates, such shearing becomes much more difficult because it requires the creation of antiphase boundaries in the ordered lattice of β 1 precipitates. Screw dislocations were observed to cross-slip from basal to the prismatic plane, which could be parallel to the broad facet of β 1 precipitates. It is postulated that double cross-slip (basal to prismatic to basal) via the Hirsch mechanism may enable screw dislocations to overcome the β 1 precipitates. MD simulations also revealed that an edge dislocation is unable to bypass the precipitate via the generation of screw dislocation segments plus the double cross-slip mechanism. The edge dislocation can bow around the precipitate, and the segment that adopts a screw character can cross-slip to the prismatic plane but with increasing applied stress, cross-slips back to the original basal plane to continue glide via precipitate shearing. Finally, the implication of glide dislocation - β 1 -precipitate interaction mechanisms on the strength and ductility of β 1 precipitate dominant microstructures is discussed.
Here, we analyze the past (1900–2015) temperature and precipitation changes in nine separate US climate regions. We find that the temperature increased in a statistically significant (95% confidence level equivalent to alpha level of 0.05) manner in all of these regions. However, the variability in the observed precipitation was much more complex. In the eastern US (east of Rocky Mountains), the precipitation increased in all five climate regions and the increase was statistically significant in three of them. In contract, in the western US, the precipitation increased in two regions and decreased in two with no statistical significance in any region. The CMIP5 climate models (an ensemble mean) were not able to capture properly either the large precipitation differences between the eastern and the western US, or the changes of precipitation between 1900 and 2015 in eastern US. The statistical regression model explains the differences between the eastern and western US precipitation as results of different significant predictors. The anthropogenic greenhouse gases and aerosol (GHGA) are the major forcing of the precipitation in the eastern part of US, while the Pacific Decadal Oscillation (PDO) has the major influence on precipitation in the western part of the US. This analysis suggests that the precipitation over the eastern US increased at an approximate rate of 6.7%/K, in agreement with the Clausius-Clapeyron equation, while the precipitation of the western US was approximately constant, independent of the temperature. Future precipitation over the western part of the US will depend on the behavior of the PDO, and how it (PDO) may be affected by future warming. Low hydrological sensitivity (percent increase of precipitation per one K of warming) projected by the CMIP5 models for the eastern US suggests either an underestimate of future precipitation or an overestimate of future warming.
This campaign, entitled Sea Ice Effect on Arctic Precipitation, started in January 2010 and ended in December 2016. The campaign involved sampling precipitation, storm by storm, within the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility observatory at Barrow, Alaska. Before the ARM Atqasuq, Alaska site was closed in September, 2014, precipitation samples were also collected at Atqasuq. The objective of this campaign was to study how sea ice retreat under warming conditions affects the arctic hydrological cycle, namely evaporation and precipitation, using oxygen and hydrogen isotopic measurements in precipitation. One of the roles of sea ice in the arctic climate system is to influence evaporative fluxes from the sea surface. When sea ice melts, the evaporation is promoted from the newly opened sea surface, which increases the moisture supply, and precipitation. Reduction of sea ice cover may feed back to the climate system in several ways. First, it affects the latent heat flux from the sea surface. Second, the increased precipitation in the Arctic may change the surface albedo. For example, if the increased precipitation falls as snow, it would increase the albedo in spring due to delayed melting. Both mechanisms would affect the radiation balance of the Arctic and thus induce additional climate change. Stable isotopic ratios in precipitation record meteorological conditions from the moisture source through the transport path and to the precipitation site. If moisture from the arctic sea surface increases, the average transport distance would decrease. This would result in an enrichment of oxygen-18 and deuterium in precipitation. Samples collected at Barrow allow us to track the moisture source areas for each sampled storm and analyze if the sea ice change is associate with systematic shift of hydrological conditions. Between July 2011 and December 2014, Barrow was one of the sites in a network of pan-Arctic precipitation observations in the project called iisPacs, standing for Isotopic Investigation of Precipitation in Sea ice in the Arctic Climate System. The project included eight stations where precipitation was collected following the protocols developed in Barrow and Atqasuq. These stations included Barrow and Atqasuq, Alaska, Cambridge Bay, Canada, Ny Ålesund, Norway, Ikerasaarsuk and Summit, Greenland, and Chersky and Tiksi, Russia. Currently, synthesizing data from all of these stations is in progress.
The ferritic Fe-Ni-Al-Cr-Mo steel (FBB8) has good creep properties up to 700 °C due to B2-NiAl nanoscale precipitates and its creep resistance can be further improved by additions of 2 or 4 wt.% Ti, as a result of sub-precipitates within the main precipitates. We report the hierarchical structure of the precipitates is studied in the light of phase separation via transmission electron microscopy (TEM) and atom probe tomography (APT). For FBB8-2Ti (with 2% Ti added) exhibiting B2-NiAl precipitates with L2 1 -Ni 2 AlTi sub-precipitates, APT analysis shows strong partitioning of Ni, Al and Ti from the ferritic matrix into the B2/L2 1 precipitates and, within the precipitates, partitioning of Ti and Fe within the L2 1 sub-precipitates. Based on the published pseudo-binary phase-diagram between (Ni,Fe)Al and (Ni,Fe)Ti, this hierarchical precipitate microstructure is discussed based on the known miscibility gap between the B2 and L2 1 phases, due to partitioning of Ti into the L2 1 phase and ordering of Al and Ti on the Al sub-lattice of the B2 structure. For FBB8-4Ti (with 4% Ti added), by contrast, the L2 1 precipitates exhibit bcc sub-precipitates rich in Fe and Cr, with a composition close to that of the matrix; the absence of the B2 structure is consistent with an increase of Ti and Fe concentrations, to 18.2 and 19.3 at.% respectively, as measured via APT, in the L2 1 precipitates.
Abstract Cold-season precipitation statistics in simulations from the storm-resolving WRF Model at 6-km and 1-h resolution over western North America are analyzed. Pseudo–global warming future simulations for the 2041–80 period, constrained by GCMs under the RCP8.5 scenario, are compared to the 1981–2020 historical simulation. The analysis focuses on the dynamical properties of precipitation time series at subdaily scales and on the morphology of storms. The statistical distribution of precipitation intensities in each pixel of the simulation domain is characterized through nonparametric statistical indicators: frequency of wet hours, mean wet-hour precipitation intensity, and Gini coefficient as a measure of the temporal concentration of the precipitation volume. Additionally, the temporal and spatial Fourier power spectra of precipitation time series and precipitation fields are analyzed. The half-power period (HPP) and half-power wavelength (HPW) are defined as spectral measures of the characteristic scales of precipitation’s temporal and spatial patterns. The results show statistically significant increases in the mean wet-hour precipitation intensity and in the Gini coefficient in 99% of the pixels, indicating that the seasonal precipitation volume becomes more concentrated within a smaller number of hours with higher precipitation intensity. The statistics of change in the frequency of wet hours are more contrasted across the simulation domain. The changes are also reflected in the power spectra, which show the spatial and temporal variability increasing proportionally more with finer spatial and temporal scales and the HPW and HPP decreasing. These projected changes are expected to have consequences, not only in terms of hydrologic impacts but also in terms of the predictability of precipitation patterns. Significance Statement The precipitation characteristics of winter storms over the western United States and southwestern Canada are analyzed in future climate simulations for the 2041–80 period. As compared to present-day climate, the most intense parts of the storms are projected to produce a higher rainfall volume, with increased concentration over smaller areas and shorter time intervals. The propensity of rainfall intensity to vary rapidly over time will be enhanced in the future according to the simulations. These model predictions imply an increased risk of rapid flooding in small basins. They also suggest that predicting several hours ahead the time and location at which a storm will produce maximum rainfall may become more challenging in the future.
Precipitation and nitrogen (N) fertilization are the two most important drivers for soil nitrous oxide (N 2 O) emission. However, the effects of changes in N fertilization and precipitation patterns (i.e., precipitation intensity and frequency) on N 2 O emissions in agricultural fields are still unclear. In this study, we simulated soil N 2 O emission under different precipitation patterns (6 precipitation intensities, and 12 precipitation frequencies by either merging or splitting precipitation events) and N fertilization rates (low, typical, and high N fertilization) in a cornfield using the DeNitrification-DeComposition model. The model was parameterized and validated using meteorological data and N experimental measurements in Nashville, Tennessee, USA. Results showed that soil water filled pore space (WFPS) and simulated soil N 2 O emission increased as precipitation intensity increased. Less frequent but high intensity precipitation treatments reduced the soil WFPS by 25.2% and stimulated soil N 2 O emission by 45.3%, while more frequent but low intensity precipitation treatments increased soil WFPS by 9.0% and reduced soil N 2 O emission by 23.9%. Compared to typical N fertilization, the sensitivity of soil N 2 O emission to precipitation was higher under high N than low N fertilization treatments, and the response ratios were 50.0% and 40.1%, respectively. There was significant interactive effect of precipitation intensity and N fertilization on soil N 2 O emission. Furthermore, these findings improved our understanding of precipitation and N impacts on soil N 2 O emissions and provided useful knowledge for irrigation and N fertilizer management in agriculture to mitigate greenhouse gas emissions.
The goal of the present investigation is to explain the obviously different appearances of Ti-rich precipitates in vanadium alloy and in steels. To achieve the goal, the formation and evolution of the precipitates in the as-cast and the heat treated V–4Cr–4Ti samples were investigated using optical and electron microscopies. The precipitates were found to be rare in the as-cast samples, and a high density of the precipitates occur in the samples subjected to isothermal holding at 600–1300 °C. The precipitates preferentially distribute within the grains rather than at the grain boundaries. All of the precipitates are platelet-like, with NaCl structure, in three-dimensional space. The further observation using high-resolution electron microscopy (HREM) reveals that a high density of twins occurs in the growth front of the precipitates, whereas the middle of the precipitates is twin-free. Meanwhile, enrichment of titanium atoms was observed in the middle of the precipitates. These results indicate that the precipitates form by a displacive transformation, followed by a diffusional process to enrich titanium further and eliminate the twined structure. - Highlights: • Precipitates in the V–4Cr–4Ti alloy are Ti-(CN) with NaCl structure. • The Ti-rich precipitates are platelet-like in three dimensional space. • Twins occur in both ends of the precipitates and the midst of these is twin-free. • Twinning and its elimination is explained by displacive followed by diffusion.