bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tracking the Strength of the Walker Circulation With Stable Isotopes in Water Vapor
Authors: Dee Sylvia G. , Nusbaumer Jesse , Bailey Adriana , Russell James M. , Lee Jung‐Eun , Konecky Bronwen , Buenning Nikolaus H. , Noone David C. 
Published: June 2018

AbstractGeneral circulation models (GCMs) predict that the global hydrological cycle will change in response to anthropogenic warming. However, these predictions remain uncertain, in particular, for precipitation (Intergovernmental Panel on Climate Change, 2013, https://doi.org/10.1017/CBO9781107415324.004). Held and Soden (2006, https://doi.org/10.1175/JCLI3990.1) suggest that as lower tropospheric water vapor concentration increases in a warming climate, the atmospheric circulation and convective mass fluxes will weaken. Unfortunately, this process is difficult to constrain, as convective mass fluxes are poorly observed and incompletely simulated in GCMs. Here we demonstrate that stable hydrogen isotope ratios in tropical atmospheric water vapor can trace changes in temperature, atmospheric circulation, and convective mass flux in a warming world. We evaluate changes in temperature, the distribution of water vapor, vertical velocity (ω), advection, and water isotopes in vapor (δDV). Using water isotope‐enabled GCM experiments for modern versus high‐CO2 atmospheres, we identify spatial patterns of circulation change over the tropical Pacific. We find that slowing circulation in the tropical Pacific moistens the lower troposphere and weakens convective mass flux, both of which impact the δD of water vapor in the midtroposphere. Our findings constitute a critical demonstration of how water isotope ratios in the tropical Pacific respond to changes in radiative forcing and atmospheric warming. Moreover, as changes in δDV can be observed by satellites, our results develop new metrics for the detection of global warming impacts to the hydrological cycle and, specifically, the strength of the Walker circulation.
Impacts of Synoptic Weather Patterns and their Persistency on Free Tropospheric Carbon Monoxide Concentrations and Outflow in Eastern China
Authors: Han Han , Liu Jane , Yuan Huiling , Jiang Fei , Zhu Ye , Wu Yue , Wang Tijian , Zhuang Bingliang 
Published: June 2018

AbstractThe relationship between synoptic weather patterns (SWPs) and variability of air pollution has not been fully understood. In this study, we assess the sensitivity of carbon monoxide (CO) concentrations and outflow in the free troposphere over eastern China to SWPs and their persistency, using daily CO data from the spaceborne Atmospheric Infrared Sounder (AIRS) instrument from 2003 to 2015. The SWPs over eastern China are classified into eight patterns following the Kirchhofer approach. On a regional average over the 13 years, distinct differences are observed in CO distributions and outflows among the eight SWPs. CO concentrations tend to increase under three SWPs that are characterized with anticyclonic circulations and downdrafts in all or part of eastern China. In contrast, three SWPs related to the East Asian summer monsoon (EASM) tend to reduce CO concentrations. The remaining two SWPs, dominant in winter and autumn, respectively, tend to bring more clean episodes. CO outflow from eastern China is sensitive to the influence of the SWPs on zonal winds. CO outflow is enhanced under two SWPs that prevail in winter and spring. Under the other SWPs, CO outflow decreases or changes only slightly. CO concentrations either increase or decrease by 5–15% under the persistent control of a SWP for two to seven days. In most cases, the anomalies of CO concentrations and CO outflow tend to be amplified if a SWP persists for several days. This study statistically illustrates the synoptic influences on the regional distribution and transport of air pollutants.
Geometric Controls on Tidewater Glacier Retreat in Central Western Greenland
Authors: Catania G. A. , Stearns L. A. , Sutherland D. A. , Fried M. J. , Bartholomaus T. C. , Morlighem M. , Shroyer E. , Nash J. 
Published: June 2018

Glacier terminus changes are one of the hallmarks of worldwide glacier change, and thus, there is significant focus on the controls and limits to retreat in the literature. Here we use the observational record of glacier terminus change from satellite remote sensing data to characterize glacier retreat in central West Greenland with a focus on the last 30 years. We compare terminus observations of retreat to glacier/fjord geometry from available bed and bathymetry data and find that glacier retreat accelerates through wide, overdeepened parts of the bed characterized by retrograde bed slopes. We find that the morphology of the overdeepening can be used as a predictive measure for the length of retreat and that short regions (less than twice the seasonal change in terminus position) of the bed with prograde bed slopes are not sufficient to stop a retreating terminus. Even narrow overdeepenings can control glacier retreat, likely because they focus subglacial runoff, which entrains warm water in the fjords when it emerges at the grounding line and melts the terminus, creating enhanced local retreat. Future retreat of these glaciers is assessed given upstream fjord geometry.
Long‐Term Evolution of Sand Transport Through a River Network: Relative Influences of a Dam Versus Natural Changes in Grain Size From Sand Waves
Authors: Topping David J. , Mueller Erich R. , Schmidt John C. , Griffiths Ronald E. , Dean David J. , Grams Paul E. 
Published: June 2018

AbstractTemporal and spatial nonuniformity in supplies of water and sand in a river network leads to sand transport that is in local disequilibrium with the upstream sand supply. In such river networks, sand is transported downstream as elongating waves in which coupled changes in grain size and transport occur. Depending on the magnitude of each sand‐supplying event and the interval between such events, changes in bed‐sand grain size associated with sand‐wave passage may more strongly regulate sand transport than do changes in water discharge. When sand transport is controlled more by episodic resupply of sand than by discharge, upstream dam construction may exacerbate or mitigate sand‐transport disequilibria, thus leading to complicated and difficult‐to‐predict patterns of deposition and erosion. We analyzed all historical sediment‐transport data and embarked on a 4‐year program of continuous sediment‐transport measurements to describe disequilibrium sand transport in a river network. Results indicate that sand transport in long river segments can evolve over ≥50‐year timescales following rare large sand‐supplying events. These natural changes in sand transport in distal downstream river segments can be larger than those caused by an upstream dam. Because there is no way to know a priori whether sand transport in a river has changed in response to changes in the upstream sand supply, contemporary continuous measurements of sand transport are required for accurate sand loads and budgeting. Analysis of only historical sediment‐transport measurements, as is common in the literature, may lead to incorrect conclusions with respect to current or future sediment‐transport conditions.
In situ Raman Quantitative Detection of the Cold Seep Vents and Fluids in the Chemosynthetic Communities in the South China Sea
Authors: Du Zengfeng , Zhang Xin , Luan Zhendong , Wang Minxiao , Xi Shichuan , Li Lianfu , Wang Bing , Cao Lei , Lian Chao , Li Chaolun , Yan Jun 
Published: June 2018

AbstractBased on the previously developed deep‐sea hybrid Raman insertion probe for cold seeps, the in situ detection of a cold seep vent and geochemistry analysis of fluids in chemosynthetic communities were conducted at the Formosa Ridge in the northern South China Sea. Three different methods were used to measure the components of the fluids erupting from the cold seep vent. The in situ Raman spectra of the cold seep fluids indicated the presence of gaseous CH4, C3H8, and H2S. The results indicate that the gases at this site are of biogenic origin; however, the presence of C3H8 suggests that thermogenic methane should not be excluded. The conclusion is also supported by the results of gas chromatography and stable carbon isotope analysis. More significantly, we found that the concentration of SO42− decreases with increasing depth, while the concentrations of CH4 and S8 increase in fluids in chemosynthetic communities, but without H2S. This finding indicates that the methane is oxidized by sulfate and that elemental sulfur is formed. This process usually occurs in marine sediments as the anaerobic oxidation of methane. Overall, the findings in this work provide a new insight into the geochemical analysis of cold seep fluids and in situ evidence of the oxidation of methane in the chemosynthetic communities near cold seeps.
Interdecadal Sea Level Variations in the Pacific: Distinctions Between the Tropics and Extratropics
Authors: Merrifield M. A. , Thompson P. R. 
Published: June 2018

AbstractLong tide gauge records from Fremantle and San Diego are used to examine interdecadal sea level fluctuations and their relationship to Pacific climate variability. The sea level difference between the tide gauges and the Southern Oscillation Index (SOI) provide a consistent depiction of trade wind variations along the equator over the past century. The sea level difference and SOI exhibit weak interdecadal variability prior to the late 1970s, followed by an extended 40‐year period of high levels at San Diego and low at Fremantle, and low SOI levels signifying weakened equatorial trade winds. By referencing the tide gauge records to global mean sea level, we infer that Pacific trade winds exhibited weak departures from mean conditions on interdecadal time scales prior to the late 1970s and that a prolonged El Niño‐like lull dominated the tropics at the end of the century. A recent shift suggests that the trades are reverting back to the El Niño‐like state. These tropical interdecadal variations have counterparts in the extratropical North Pacific after the 1970s, as captured by the Pacific Decadal Oscillation, but the early twentieth century quiescent phase in the tropical Pacific is not reflected in the extratropics, which exhibits more energetic oscillatory behavior over the same time span.
Ion Trapping and Acceleration at Dipolarization Fronts: High‐Resolution MHD and Test‐Particle Simulations
Authors: Ukhorskiy A. Y. , Sorathia K. A. , Merkin V. G. , Sitnov M. I. , Mitchell D. G. , Gkioulidou M. 
Published: June 2018

AbstractMuch of plasma heating and transport from the magnetotail into the inner magnetosphere occurs in the form of mesoscale discrete injections associated with sharp dipolarizations of magnetic field (dipolarization fronts). In this paper we investigate the role of magnetic trapping in acceleration and transport of the plasma sheet ions into the ring current. For this purpose we use high‐resolution global magnetohydrodynamic (MHD) and three‐dimensional test‐particle simulations. It is shown that trapping, produced by sharp magnetic field gradients at the interface between dipolarizations and the ambient plasma, affects plasma sheet protons with energies above approximately 10 keV, enabling their transport across more than 10 Earth radii and acceleration by a factor of 10. Our estimates show that trapping is important to the buildup of the ring current plasma pressure of injected particles; depending on the plasma sheet temperature and energy spectrum, trapped protons can contribute between 20% and 60% of the plasma pressure. It is also shown that the acceleration process does not conserve the particle first invariant; on average protons are accelerated to higher energies compared to a purely adiabatic process. We also investigate how trapping and energization vary for deferent ions species and show that in accordance with recent observations, ion acceleration is proportional to the ion charge and is independent of its mass.
X‐ray Emissions in a Multiscale Fluid Model of a Streamer Discharge
Authors: Lehtinen Nikolai G. , Østgaard Nikolai 
Published: June 2018

AbstractWe use a three‐specie fluid model of electric discharge in air to simulate streamer evolution from the avalanche‐to‐streamer transition to the collision of opposite‐polarity streamers. We estimate the upper limit on the production of thermal runaway electrons, which is dominant during the second of these processes. More thermal runaways are produced if the ionization due to natural background and photoionization is reduced, due to possibility of creation of higher electric fields at streamer tips. The test‐particle simulation shows, however, that these thermal runaway electrons have insufficient energies to become relativistic runaways. The simulations are done in constant uniform background fields of E0=4 and 6 MV/m. A simulation was also performed in E0=2 MV/m after formation of streamers in 4‐MV/m field, in order to approximate the average background field created by ∼1‐MV voltage over a ∼1‐m electrode gap used in laboratory spark experiments. We conclude that the used fluid model is insufficient to explain X‐ray observations during such experiments. We discuss the possible role of mechanisms which were not included in this or previous modeling but may play the deciding role in the electron acceleration and X‐ray production during a streamer collision.
Identification of Extreme Ultraviolet Emission Lines of the Io Plasma Torus Observed by Hisaki/EXCEED
Authors: Hikida R. , Yoshioka K. , Murakami G. , Kimura T. , Tsuchiya F. , Yamazaki A. , Yoshikawa I. , Iwagami N. 
Published: June 2018

AbstractThe sulfur and oxygen ions in the Io plasma torus (IPT), which is located at a distance of ~6 RJ from Jupiter, emit light in various wavelength regions. In particular, radiative cooling in the ultraviolet wavelength range plays an important role in the energy balance of the Io torus, and it is important to explore the detailed spectral structure in the ultraviolet region. The ultraviolet spectrum of the IPT in the wavelength range 52.0–148.0 nm with a resolution of 0.3–0.4 nm was obtained by Extreme Ultraviolet Spectroscope for Exospheric Dynamics on the Hisaki satellite. Owing to its instrument performance and long integration time, 10 emission lines from the IPT were detected for the first time. By summarizing previous observations and using the results obtained by Extreme Ultraviolet Spectroscope for Exospheric Dynamics, we updated the term diagrams for S II, S III, and S IV emissions from the IPT. Four excited levels in the IPT were detected for the first time. Detection of the emission lines may improve the estimation accuracy of the fraction of hot electron density using the atomic data.
Reply to Comment by Sookhak Lari, K. and Davis, G. B. on “ ‘Large Eddy Simulation of Turbulence and Solute Transport in a Forested Headwater Stream’: Invalid Representation of Scalar Transport by the Act of Diffusion”
Authors: Khosronejad A. , Sotiropoulos F. 
Published: June 2018

AbstractBased on the molecular diffusion coefficient used in the large eddy simulation (LES) (equation (3) of the article), one can easily infer that a molecular Schmidt number of 700 was adopted for the solute. It should be acknowledged that in the published article we omitted to include the value used for the molecular diffusion and did not mention that is the reciprocal of the turbulent Schmidt number. Although these details should have been included, these omissions do not change well‐established facts that in turbulent flows the mixing of the solute by the molecular diffusion is many orders of magnitude less important than that induced by the turbulence. As we mentioned in our article, the viscous sublayer in the Eagle Creek stream was not resolved in our simulations as the first node off the solid boundaries in wall units was (on average) equal to 45 (see Table 3 of the article). This implies that all of the computational nodes are located well outside of the viscous sublayer, where molecular diffusion becomes dominant. Moreover, since we carry out LES, we do not resolve the Kolmogorov scales in the flow the rate of dissipation of which is governed by molecular viscosity. Rather, the subgrid scale eddy viscosity of the LES acts as the model for the effect of the unresolved scales of motion. Even though all these are well‐known facts from fundamental theory of turbulent mixing, we include in this response additional simulations to address the concerns raised in this commentary.
Environmental Controls, Emergent Scaling, and Predictions of Greenhouse Gas (GHG) Fluxes in Coastal Salt Marshes
Authors: Abdul‐Aziz Omar I. , Ishtiaq Khandker S. , Tang Jianwu , Moseman‐Valtierra Serena , Kroeger Kevin D. , Gonneea Meagan Eagle , Mora Jordan , Morkeski Kate 
Published: June 2018

AbstractCoastal salt marshes play an important role in mitigating global warming by removing atmospheric carbon at a high rate. We investigated the environmental controls and emergent scaling of major greenhouse gas (GHG) fluxes such as carbon dioxide (CO2) and methane (CH4) in coastal salt marshes by conducting data analytics and empirical modeling. The underlying hypothesis is that the salt marsh GHG fluxes follow emergent scaling relationships with their environmental drivers, leading to parsimonious predictive models. CO2 and CH4 fluxes, photosynthetically active radiation (PAR), air and soil temperatures, well water level, soil moisture, and porewater pH and salinity were measured during May–October 2013 from four marshes in Waquoit Bay and adjacent estuaries, MA, USA. The salt marshes exhibited high CO2 uptake and low CH4 emission, which did not significantly vary with the nitrogen loading gradient (5–126 kg · ha−1 · year−1) among the salt marshes. Soil temperature was the strongest driver of both fluxes, representing 2 and 4–5 times higher influence than PAR and salinity, respectively. Well water level, soil moisture, and pH did not have a predictive control on the GHG fluxes, although both fluxes were significantly higher during high tides than low tides. The results were leveraged to develop emergent power law‐based parsimonious scaling models to accurately predict the salt marsh GHG fluxes from PAR, soil temperature, and salinity (Nash‐Sutcliffe Efficiency = 0.80–0.91). The scaling models are available as a user‐friendly Excel spreadsheet named Coastal Wetland GHG Model to explore scenarios of GHG fluxes in tidal marshes under a changing climate and environment.
Structure and Evolution of Mesoscale Convective Systems: Sensitivity to Cloud Microphysics in Convection‐Permitting Simulations Over the United States
Authors: Feng Zhe , Leung L. Ruby , Houze Robert A. , Hagos Samson , Hardin Joseph , Yang Qing , Han Bin , Fan Jiwen 
Published: June 2018

AbstractRegional climate simulations over the continental United States were conducted for the 2011 warm season using the Weather Research and Forecasting model at convection‐permitting resolution (4 km) with two commonly used microphysics parameterizations (Thompson and Morrison). Sensitivities of the simulated mesoscale convective system (MCS) properties and feedbacks to large‐scale environments are systematically examined against high‐resolution geostationary satellite and 3‐D mosaic radar observations. MCS precipitation including precipitation amount, diurnal cycle, and distribution of hourly precipitation intensity are reasonably captured by the two simulations despite significant differences in their simulated MCS properties. In general, the Thompson simulation produces better agreement with observations for MCS upper level cloud shield and precipitation area, convective feature horizontal and vertical extents, and partitioning between convective and stratiform precipitation. More importantly, Thompson simulates more stratiform rainfall, which agrees better with observations and results in top‐heavier heating profiles from robust MCSs compared to Morrison. A stronger dynamical feedback to the large‐scale environment is therefore seen in Thompson, wherein an enhanced mesoscale vortex behind the MCS strengthens the synoptic‐scale trough and promotes advection of cool and dry air into the rear of the MCS region. The latter prolongs the MCS lifetimes in the Thompson relative to the Morrison simulations. Hence, different treatment of cloud microphysics not only alters MCS convective‐scale dynamics but also has significant impacts on their macrophysical properties such as lifetime and precipitation. As long‐lived MCSs produced 2–3 times the amount of rainfall compared to short‐lived ones, cloud microphysics parameterizations have profound impact in simulating extreme precipitation and the hydrologic cycle.
Microbiome niche modification drives diurnal rumen community assembly, overpowering individual variability and diet effects
Authors: Shaani Yoav , Zehavi Tamar , Eyal Stav , Miron Joshuah , Mizrahi Itzhak 
Published: June 2018

Abstract
Niche modification is a process whereby the activity of organisms modifies their local environment creating new niches for other organisms. This process can have a substantial role in community assembly of gut microbial ecosystems due to their vast and complex metabolic activities. We studied the postprandial diurnal community oscillatory patterns of the rumen microbiome and showed that metabolites produced by the rumen microbiome condition its environment and lead to dramatic diurnal changes in community composition and function. After feeding, microbiome composition undergoes considerable change in its phylogenetic breadth manifested as a significant 3–5-fold change in the relative abundance of methanogenic archaea and main bacterial taxa such as Prevotella, in a manner that was independent of individual host variation and diet. These changes in community composition were accompanied by changes in pH and methane partial pressure, suggesting a strong functional connection. Notably, cross-incubation experiments combining metabolites and organisms from different diurnal time points showed that the metabolites released by microbes are sufficient to reproduce changes in community function comparable to those observed in vivo. These findings highlight microbiome niche modification as a deterministic process that drives diurnal community assembly via environmental filtering.