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At least 199 records · Page 11

Analysis of short‐ and long‐term system response during gas production from a gas hydrate deposit at the UBGH2‐6 site of the Ulleung Basin in the Korean East Sea

Abstract This study is a continuation of an investigation into the feasibility of long‐term production from a marine hydrate accumulation that has the properties and conditions of the UBGH2‐6 (UBGH2, Ulleung Basin Gas Hydrates 2; 2 is the number of the scientific expedition) site at the Ulleung Basin in the Korean East Sea. The 12.7 m‐thick system is in deep water (2157 m), but at 140 m below the seafloor. It is characterized by alternating hydrate‐free clays and muds and hydrate‐rich sand layers. The layered stratigraphy and the presence of mud layers favours the use of vertical wells rather than horizontal wells for production. The analysis indicates that production from such a hydrate accumulation is technically feasible, but the gas production rates are generally low. Water production accompanying gas production from this deposit appears manageable under all the scenarios investigated in this study, however, the water‐to‐gas ratio is high. Subsidence at the ocean floor at the end of a 14 day test is quite limited. However, there is significant uncertainty in the predictions of the geomechanical system's behaviour because they are not based on measured system properties but only on estimates/assumptions from analogues. The long‐term production potential of the reservoir at the site investigated here appears challenging because of the limited effectiveness of dissociation and large water production, in addition to substantial subsidence.

Moridis, George J.↗

The impact of coupled air–sea interaction on extreme East Asian summer monsoon simulation in CMIP5 models

Abstract In this study, the relationship between the ability to simulate air–sea interactions over the western North Pacific (WNP), and to reproduce the extreme East Asian summer monsoon (EASM), were investigated by comparing the performances of several global climate models (GCMs). High ranked in air–sea interaction simulation (HRA) and low ranked in air–sea interaction simulation (LRA) models were selected, according to their performance in simulating relations between sea surface temperature (SST) and precipitation over the WNP, from the ensemble of models that participated in the third and fifth phases of the Coupled Model Intercomparison Project (CMIP3, CMIP5). Compared with CMIP3 models, CMIP5 models exhibited improved simulations of the distinctive air–sea interaction over the WNP, namely, the strong atmospheric forcing on the ocean. Among CMIP5 models, HRA models, which reproduced intrinsic negative correlations between precipitation and SST over the WNP, could simulate the extreme EASM better than LRA models. In particular, HRA models generated a more realistic spatial distribution of the extreme EASM compared with LRA models. The defects of the LRA models resulted from distorted synoptic fields, including underestimated geopotential height and overestimated low‐level wind over the WNP, inducing unrealistic moisture supply and convection due to the exaggerated SST forcing. In contrast, reasonable air–sea interactions represented in HRA models lead to realistic synoptic fields over the WNP, and proper simulation of the extreme EASM.

Kim, Taehyung↗

Projected increase of the East Asian summer monsoon ( Meiyu ) in Taiwan by climate models with variable performance

Abstract The active phase of the East Asian summer monsoon (EASM) in Taiwan during May and June, known as Meiyu , produces substantial precipitation for water uses in all sectors of society. Following a companion study that analysed the historical increase in the Meiyu precipitation, the present study conducted model evaluation and diagnosis based on the EASM lifecycle over Taiwan. Higher and lower skill groups were identified from 17 Couple Model Intercomparison Project Phase 5 (CMIP5) models, with five models in each group. Despite the difference in model performance, both groups projected a substantial increase in the Meiyu precipitation over Taiwan. In the higher skill group, weak circulation changes and reduced low‐level convergence point to a synoptically unfavourable condition for precipitation. In the lower skill group, intensified low‐level southwesterly winds associated with a deepened upper level trough enhance moisture pooling. Thus, the projected increase in Meiyu precipitation will likely occur through the combined effects of (1) the extension of a strengthened North Pacific anticyclone enhancing southwesterlies; and (2) more systematically, the Clausius–Clapeyron relationship that increases precipitation intensity in a warmer climate. The overall increase in the Meiyu precipitation projected by climate models of variable performance supports the observed tendency toward more intense rainfall in Taiwan and puts its early June 2017 extreme precipitation events into perspective.

Tung, Yu‐Shiang↗

Statistical framework to assess long-term spatio-temporal climate changes: East River mountainous watershed case study

Abstract Evaluation of long-term temporal and spatial climatic change in mountainous regions is a critical challenge because of the interactive effects of multiple land and climatic factors and processes. Here we present the application of the statistical framework to the assessment of changes of climatic conditions, using data from 17 meteorological stations across the East River watershed near Crested Butte, Colorado, USA, and spanning the period from 1966 to 2021. The framework is developed based on (1) a time-series analysis of daily, monthly, and yearly averaged meteorological parameters (temperature, relative humidity, precipitation, wind speed, etc.), (2) evaluation and time series analysis of potential evapotranspiration (ET o ), actual evapotranspiration (ET), aridity index (AI), standard precipitation index (SPI) and standard precipitation-evapotranspiration index (SPEI), and (3) a temporal-spatial climatic zonation of the studied area based on the hierarchical clustering and PCA analysis of the SPEI, because the SPEI can be considered an integrative characteristic of the changes of climatic conditions. The Budyko model, with the application of the Penman–Monteith equation for the estimation of ET o , was used to determine the ET. The time series analysis of the AI is used to identify the periods with energy limited and water limited conditions. Hierarchical clustering of site locations for the three temporal segments of the SPEI showed a significant temporal-spatial shifts, indicating that dynamic climatic processes drive zonation patterns. Therefore, the watershed climatic zonation requires periodic re-evaluation based on the structural time series analysis of meteorological and water balance data.

54 ENVIRONMENTAL SCIENCES↗

3D Modelling of the Lithium Injection Experiment in H-Mode Plasma of EAST

Investigations of lithium transport in H-mode plasma of EAST tokamak have been performed by the three-dimensional fluid code EMC3-EIRENE. The simulation results show that the toroidally-localized lithium injection at the low field side (LFS) leads to a toroidally non-axisymmetric distribution of the Li 1+ and Li 2+ ions. The field line tracing approach is utilized to carry out a detailed study on the distributions of the Li 1+ and Li 2+ ions. It is found that Li 1+ ions mainly reside at the LFS while Li 2+ ions can transport from LFS to the high field side. The relationship between mean free path and connection length for Li 1+ and Li 2+ ions has been discussed. Here, the 3D line-integration images of deuterium and lithium emission spectra modelled by EMC3-EIRENE are in qualitative consistency with the experiment results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Role of E × B Drift in Divertor Detachment Control via Boron Powder Injection on EAST

Here, the effects of B powder injection on plasma detachment about EAST discharge were studied by using SOLPS-ITER code package with the effects of E × B drifts considered. The simulation results show that plasma detachment occurs at the inner target in favourable toroidal magnetic field (B t ) direction at a relatively low B powder flow rate, one order of magnitude lower than that at the outer target. In a similar scenario with unfavourable B t , it is found that the detachment thresholds of B flow rate for both the inner and outer targets are close and of the same order as that for the outer target with favourable Bt. In favourable B t direction at B powder flow rate of 1.2 × 10 21 atoms/s, a localized, broadened high-density region is formed near the inner target benefitted by the injection location and the E × B drift, and a radiation-intensified zone, mostly contributed by B 1+ and B 2+ , occurs there. The E × B drift facilitates plasma detachment at the inner target and simultaneously amplifies the in–out divertor asymmetry. In addition, the simulation results with three different injection locations show that the injection from outer strike point leads to the lowest Z eff inside the separatrix and has an intermediate flow rate for detachment at the outer target, comparing with the X-point and upstream locations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Real-time gas cooling of flowing liquid lithium limiter for the EAST

A novel continuously flowing liquid lithium limiter (FLiLi) which employs an in-vessel electro-magnetic pump to drive liquid Li flowing on the surface of limiter has been successfully designed and tested in the experimental advanced superconducting tokamak (EAST) device in 2014. In order to better control the surface temperature, an upgraded design and the real-time gas cooling were performed in 2016. Two kinds of cooling gas, helium (He) and argon (Ar) were tested on the FLiLi system prior to the experiment. It was found that the cooling rates of He and Ar at 2.5 MPa are 34.2 °C/min, 10.2 °C/min or 31.7 °C/kL and 28.1 °C/kL, respectively. The cooling performance of He is more effective than Ar. Experimental results show that the real-time He cooling could effectively contain the FLiLi surface temperature increase and prevent the strong passive evaporation of lithium during plasma discharges. Limiter heat flux up to 0.2 MW/m2 was removed during ohmic discharge with 2.5 MPa He gas. Finally, Because of the upgraded design and real-time gas cooling, the surface of FLiLi was not damaged by heat flux after entire plasma discharge.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Quasi-optical beam tracing module development for millimeter-wave high-wavenumber collective scattering on the NSTX-U and EAST tokamaks

A Python3-based beam tracing code utilizing Quasi-Optics has been developed to track both incident and receiving beams in high-k collective millimeter wave scattering systems within magnetic fusion plasmas. In contrast to existing ray tracing codes that solely consider refraction, this beam tracing code incorporates diffraction phenomena, providing a more comprehensive calculation. Here, this enhanced capability allows for a more accurate calculation of the scattering volume and spatial resolution in high-k collective scattering systems, crucial for evaluating system performance and facilitating data analysis. Unlike Geometrical Optics, Quasi-Optics employs the complex eikonal method, representing a Gaussian beam as a collection of coupled rays to accurately preserve diffraction characteristics. The developed code is intended for application in NSTX-Upgrade and EAST high-k beam tracing analyses, targeting frequencies of 693 GHz and 270 GHz, respectively. The high-k system's primary objective is the observation of electron-scale instabilities. Employing a symplectic integrator, the code ensures numerical accuracy, assessed through the conservation of the Hamiltonian. With its precision and efficiency, the code facilitates rapid inter-shot analyses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Renewable hydrogen horizon: Geospatial techno-economic feasibility and life cycle greenhouse gas analysis in the Middle East and North Africa

Renewable hydrogen is receiving increasing attention for its potential as a flexible energy carrier in sectors such as transportation and industry. Specific cost and carbon intensity (CI) of renewable hydrogen production vary largely based on the location, owing to differences in renewable energy resources, as well as the supply chain dynamics. This study maps the techno-economic and life cycle greenhouse gas emissions of renewable hydrogen production in the Middle East and North Africa region, leveraging abundant solar and wind resources. The work investigates the variability in hydrogen costs and CI, optimally sizing proton-exchange membrane (PEM) electrolyzers to account for partial and cyclic loading, and explores standalone versus grid-connected systems. PEM capacity ratios of 52 %–63 % for photovoltaic (PV) systems and 28 %–82 % for wind systems were identified as optimal, with hydrogen production costs ranging from $\$3.8$-$\$4.8$/kg for PV and $2.0-$7.0/kg for wind. CIs span from 1.9 to 3.7 kg CO 2 ,eq /kg H 2 for PV and 0.4–7.7 kg CO 2,eq /kg H 2 for wind systems. The study highlights significant cost and CI reductions achievable with technological advancements and co-product revenue from oxygen and excess electricity sales.

Carbon Intensity↗

Variation in natural attenuation rates of polychlorinated biphenyls (PCBs) in fish from streams and reservoirs in East Tennessee observed over a 35-year period

Environmental contamination due to human activities is a major concern, particularly for persistent chemicals. Within catchments, persistent chemicals linked to negative health outcomes such as polychlorinated biphenyls (PCBs) have great potential to be transported, through adsorption or biological uptake, with downstream locations acting as sinks for accumulation. Here we present long-term trends in PCB bioaccumulation in fish found in lower-order tributaries on the Oak Ridge Reservation, an impacted US Department of Energy property in East Tennessee, USA, and a large reservoir system adjacent to it composed of parts of the Clinch and Tennessee Rivers. Given that the reservoir system has experienced no direct PCB mitigation activities, this record offers an opportunity to explore potential natural attenuation of PCBs within a large lotic ecosystem. Additionally, attenuation rates ranged from 0% to 8% yr -1 in minnows and sunfish at stream sites and 5.4–11.3% yr -1 in catfish at reservoir sites. These rates are comparable to findings from similar studies in other regions, suggesting a consistency in responses since the banning of PCB production in 1979. Further, results suggest that PCB sources from discharge outfalls are important locally but are not primarily responsible for sustaining PCB contamination in downstream reservoirs.

54 ENVIRONMENTAL SCIENCES↗

Numerical simulation study of impurity B transport during real-time B powder injection in EAST

To understand the beneficial effects of impurity boron (B) on the plasma, the transport of B species in both atomic and ionic states in the edge plasma and the ensuing evolution of the background plasma are simulated during real-time B powder injection by using two-dimensional fluid code SOLPS-ITER. The initial background plasma profiles for the simulation are reconstructed based on an EAST upper-single null discharge (shot No. 70601). With the injection rate of B atoms, 4.0 × 10 21 atoms/s, the simulation shows that effective charge number is less than 1.1 at the inner boundary R - R sep = -5.2 cm (background plasma density, 5.1 × 10 19 m -3 ) at the outer mid-plane indicating that the B impurity does not have much influence on the energy confinement. The present work finds that the impurity B exhibits very specific features in the edge plasma, mostly present in the narrow region just outside the separatrix. The particular distribution pattern can reduce the heat flux greatly, leading to the divertor detachment. The divertor detachment can be achieved easily under an injection rate of B powder in a reasonable range. This study suggests that the impurity B has a promising potential application in future tokamaks.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Pore Structure and Wettability of Bossier Shale, East Texas, United States: Insights from Integrated Porosimetry, Scattering, and Imbibition Approaches

In this study, ascertaining the pore geometry and wettability characteristics of tight shales is of great significance for revealing the mechanisms of occurrence, migration, and production of shale resources. Taking the Bossier Shale collected from Well A, East Texas, USA, as an example, the pore geometry and wettability behavior in a broad nm-& μm scale pore spectrum were quantified based on integrated techniques, including water immersion porosimetry (WIP), mercury intrusion porosimetry(MIP), (ultra)small-angle X-ray scattering [(U)SAXS], contact angle, and liquid spontaneous imbibition (SI). Mainly owing to differences in the sample sizes used, data interpretation, as well as the detectable pore type (e.g., connected or not) and pore diameter ranges among different methods, sample porosities derived from WIP, MIP, and (U)SAXS were quite different, which range from 7.70 to 13.34%, 5.12 to 9.52%, and 2.48 to 6.44%, respectively. Therefore, a comparison of the porosities derived from different methods must be handled with utmost care. Additionally, although (U)SAXS is an effective technique for detecting both connected and non-connected pores, the fraction of non-connected pores could be underestimated by directly comparing the pore size distribution derived from (U)SAXS and MIP tests. This is because the sample sizes used for and pore information reflected by these two methods are different. Furthermore, the studied Bossier Shales exhibited various contact angle values and imbibition behaviors when using differently polarized liquids, revealing their mixed-wet characteristics. Comprehensively considering the differences in contact angle, imbibition slope, and imbibed liquid volume, three sub-categories of wettability behavior, with respect to more oil-wet, more water-wet, and intermediate mixed-wet, were qualitatively identified.

(U)SAXS↗

Atmospheric Research Over the Extended Western North Atlantic Ocean Region and North American East Coast: A Review of Past Work and Challenges Ahead

Decades of atmospheric research have focused on the extended Western North Atlantic Ocean (WNAO) region, including the East Coast of North America and the island of Bermuda, because of its unique location that offers accessibility, gradients in important atmospheric parameters, and a range of meteorological regimes leading to diverse conditions that are poorly understood. This work reviews decades of scientific investigations for the extended WNAO region. Approximately 40 combined field campaigns and long-term monitoring programs, in addition to 563 peer-reviewed publications between 1950 and 2019 have provided a firm foundation of knowledge for the extended WNAO region. Of particular importance in this region has been extensive work at the island of Bermuda that is host to important time series records of oceanic and atmospheric variables. Our review categorizes WNAO research into eight major categories, with some studies fitting into multiple categories (relative %): Aerosols (26%), Gases (23%), Development/Validation of Techniques, Models, and Retrievals (17%), Meteorology and Transport (10%), Air-Sea Interactions (9%), Wet Deposition (6%), Clouds/Storms (6%), and Aerosol-Cloud Interactions (3%). These extensive works have revealed a series of major knowledge gaps. For instance, a disproportionately low number of studies have been devoted to aerosol-cloud interactions, which is identified here as one of the most pressing research needs for the extended WNAO region. Recommendations for future research are provided in the categories highlighted above. Part 2 of this paper series will summarize major spatial and temporal features for the extended WNAO region.

Sorooshian, Armin↗

Soil Respiration Response to Rainfall Modulated by Plant Phenology in a Montane Meadow, East River, Colorado, USA

Soil respiration is a primary component of the terrestrial carbon cycle. However, predicting the response of soil respiration to climate change remains a challenge due to the complex interactions between environmental drivers, especially plant phenology, temperature, and soil moisture. In this study, we use a 1-D diffusion-reaction model to calculate depth-resolved CO 2 production rates from soil CO 2 concentrations and surface efflux observations in a subalpine meadow in the East River watershed, CO. Modeled rates are compared to in situ soil temperature and moisture conditions and MODIS satellite enhanced vegetation index (EVI) representing plant phenology across three hydrologically distinct growing seasons from 2016-2018. While soil respiration correlated with temperature on diel timescales (p<0.05), seasonal variability was dominated by soil moisture and plant phenology (p<0.05). We observed significant respiration increases in response to precipitation events; however, magnitude and duration were significantly higher in 2017 than 2016 despite similar wetting characteristics. Based on MODIS EVI, we suggest the respiration response to rainfall is controlled by plant phenology, which in turn reflects the capacity of plants to respond to precipitation via increased photosynthesis and autotrophic respiration, behavior that is not captured in typical soil respiration pulse models. Projected changes in montane climate such as earlier snowmelt and prolonged fore-summer drought may decrease soil respiration fluxes by decreasing the overlap between peak productivity and the summer monsoon. Lastly, we observed significant late-season CO 2 fluxes from the deep sub-soil (>165 cm) that support growing evidence for the importance of sub-soil processes in driving integrated respiration fluxes.

54 ENVIRONMENTAL SCIENCES↗

Convection-permitting hindcasting of diurnal variation of Mei-yu rainfall over East China with a global variable-resolution model

Two sets of 48-hr hindcast experiments for Mei-yu season using non-hydrostatic global variable-resolution model (MPAS-Atmosphere) with regional refinement at 4km resolution (V4km) and uniform 60km resolution (U60km) are first-time conducted to attempt at simulating the Mei-yu rainfall in 2015 over East China. The analysis focuses on the seasonal average of diurnal variation of precipitation amount (PA), intensity (PI), and frequency (PF). Both simulations reasonably reproduce the spatial distribution of PA. V4km is more skillful in simulating the spatial distributions and magnitudes of PF and PI. The diurnal cycle of Mei-yu rainfall shows a major early morning peak and a minor afternoon peak, contributed by precipitation during two sub-periods with distinct synoptic circulations. With strong Mei-yu in the first sub-period, the diurnal variation of PA is controlled by nocturnal southwesterly jet. V4km overestimates the morning peak mainly due to its bias in simulating boundary layer inertial oscillation. Although differences in PA between the simulations are small, U60km overestimates PF and underestimates PI. With weak Mei-yu in the second sub-period, the diurnal variation of PA is controlled by both synoptic circulation and local convection. At both resolutions, deviations in the large-scale circulation modulated by a few typhoons lead to positive biases in the morning peak of PA. After removing the typhoon impacts, V4km captures the observed diurnal cycle of PA well, while U60km significantly underestimates PA and PI particularly in the afternoon. Future studies focusing on advancing modeling of southwesterly jet and typhoons may further improve convection permitting simulation of Mei-yu rainfall.

Xu, Mingyue↗

Hyporheic Oxygen Dynamics in the East River, Colorado: Insights From an In–Situ, High Frequency Time Series During Two Distinct Flow Seasons

Dissolved oxygen (DO) is critical for aquatic ecosystems, however, few studies have focused on the long-term DO dynamics in hyporheic zones, which are a function of both transport (hydrologic exchange between river and hyporheic zone) and uptake by biogeochemical reactions or respiration. We explore the dynamics of temperature and DO at 10, 20, and 35 cm depth beneath the East River, Colorado, from July–October 2017 (relatively normal water year) and April to October 2018 (comparatively low flow year), enabled by distinctive, in-situ, high frequency (Δt = 5 min) sensors that provided continuous time-series from the undisturbed study site over 14 months. We expect that hyporheic DO, which has a regular daily fluctuation pattern, is supplied by the surface water (at all times we estimate downwelling) and that diurnal hyporheic DO temporal patterns should be aligned with diurnal hyporheic temperature patterns. However, this was not found to be the case. Hyporheic DO becomes depleted briefly at 20 and 35 cm depths in 2017, and at all three hyporheic depths for extended periods in 2018. Whereas diurnal temperature fluctuations have consistent timings of maxima and minima, hyporheic DO rarely has as regular a pattern, and daily ranges are inconsistent. Rainfall events caused some of these changes to diurnal hyporheic DO patterns without repeatable effects. Antecedent snowpack conditions influence streamflow dynamics and therefore hyporheic DO dynamics in this alpine river. These results also point to the strong and variable influence of hyporheic microbial communities regulating hyporheic DO.

54 ENVIRONMENTAL SCIENCES↗

Shift in Peaks of PAH-Associated Health Risks From East Asia to South Asia and Africa in the Future

Lung cancer risk from exposure to ambient polycyclic aromatic hydrocarbons (PAHs) is expected to change significantly by 2050 compared to 2008 due to changes in climate and emissions. Integrating a global atmospheric chemistry model, a lung cancer risk model, and plausible future emissions trajectories of PAHs, we assess how global PAHs and their associated lung cancer risk will likely change in the future. Benzo(a)pyrene (BaP) is used as an indicator of cancer risk from PAH mixtures. From 2008 to 2050, the population-weighted global average BaP concentrations under all RCPs consistently exceeded the WHO-recommended limits, primarily attributed to residential biofuel use. Peaks in PAH-associated incremental lifetime cancer risk shift from East Asia (4 × 10 –5 ) in 2008 to South Asia (mostly India, 2–4 × 10 –5 ) and Africa (1–2 × 10 –5 ) by 2050. In the developing regions of Africa and South Asia, PAH-associated lung cancer risk increased by 30–64% from 2008 to 2050, due to increasing residential energy demand in households for cooking, heating, and lighting, the continued use of traditional biomass use, increases in agricultural waste burning, and forest fires, accompanied by rapid population growth in these regions. Due to more stringent air quality policies in developed countries, their PAH lung cancer risk substantially decreased by ~80% from 2008 to 2050. Climate change is likely to have minor effects on PAH lung cancer risk compared to the impact of emissions. Future policies, therefore, need to consider efficient combustion technologies that reduce air pollutant emissions, including incomplete combustion products such as PAH.

54 ENVIRONMENTAL SCIENCES↗

Contrasting Climatic Trends of Atmospheric River Occurrences Over East Asia

Atmospheric rivers (ARs) are increasingly recognized as a major driver of hydrological cycles, and are projected to increase around the world under a changing climate. However, the long-term trends of ARs over East Asia (EA) remains less elucidated. Here we fill the gap by developing a longest-ever archive of EA ARs, and examine its role in determining spatiotemporal precipitation variability over EA. We find contrasting changes in AR occurrences, with more frequent ARs in low latitudes but less in high latitudes during the period 1950-2020. The “dipole” pattern of decadal changes in AR occurrences is dictated by atmospheric dynamics (i.e., winds) in the north but thermodynamics (i.e., moisture) in the south. The reduced AR occurrences explain 49% of decreased annual precipitation in northern China, while more AR-related precipitation is observed in southern China. Furthermore, our results provide new insights into regional hydroclimate over EA by connecting it with large-scale weather systems.

54 ENVIRONMENTAL SCIENCES↗