bluuebunny/crossref_metadata_2025_split huggingface dataset:
Representing agriculture in Earth System Models: Approaches and priorities for development
Authors: McDermid S. S. , Mearns L. O. , Ruane A. C. 
Published: August 2017

AbstractEarth System Model (ESM) advances now enable improved representations of spatially and temporally varying anthropogenic climate forcings. One critical forcing is global agriculture, which is now extensive in land‐use and intensive in management, owing to 20th century development trends. Agriculture and food systems now contribute nearly 30% of global greenhouse gas emissions and require copious inputs and resources, such as fertilizer, water, and land. Much uncertainty remains in quantifying important agriculture‐climate interactions, including surface moisture and energy balances and biogeochemical cycling. Despite these externalities and uncertainties, agriculture is increasingly being leveraged to function as a net sink of anthropogenic carbon, and there is much emphasis on future sustainable intensification. Given its significance as a major environmental and climate forcing, there now exist a variety of approaches to represent agriculture in ESMs. These approaches are reviewed herein, and range from idealized representations of agricultural extent to the development of coupled climate‐crop models that capture dynamic feedbacks. We highlight the robust agriculture‐climate interactions and responses identified by these modeling efforts, as well as existing uncertainties and model limitations. To this end, coordinated and benchmarking assessments of land‐use‐climate feedbacks can be leveraged for further improvements in ESM's agricultural representations. We suggest key areas for continued model development, including incorporating irrigation and biogeochemical cycling in particular. Last, we pose several critical research questions to guide future work. Our review focuses on ESM representations of climate‐surface interactions over managed agricultural lands, rather than on ESMs as an estimation tool for crop yields and productivity.
Evaluating the Classical Versus an Emerging Conceptual Model of Peatland Methane Dynamics
Authors: Yang Wendy H. , McNicol Gavin , Teh Yit Arn , Estera‐Molina Katerina , Wood Tana E. , Silver Whendee L. 
Published: August 2017

AbstractMethane (CH4) is a potent greenhouse gas that is both produced and consumed in soils by microbially mediated processes sensitive to soil redox. We evaluated the classical conceptual model of peatland CH4 dynamics—in which the water table position determines the vertical distribution of methanogenesis and methanotrophy—versus an emerging model in which methanogenesis and methanotrophy can both occur throughout the soil profile due to spatially heterogeneous redox and anaerobic CH4 oxidation. We simultaneously measured gross CH4 production and oxidation in situ across a microtopographical gradient in a drained temperate peatland and ex situ along the soil profile, giving us novel insight into the component fluxes of landscape‐level net CH4 fluxes. Net CH4 fluxes varied among landforms (p < 0.001), ranging from 180.3 ± 81.2 mg C m−2 d−1 in drainage ditches to −0.7 ± 1.2 mg C m−2 d−1 in the highest landform. Contrary to prediction by the classical conceptual model, variability in methanogenesis alone drove the landscape‐level net CH4 flux patterns. Consistent with the emerging model, freshly collected soils from above the water table produced CH4 within anaerobic microsites. Even in soil from beneath the water table, gross CH4 production was best predicted by the methanogenic fraction of carbon mineralization, an index of highly reducing microsites. We measured low rates of anaerobic CH4 oxidation, which may have been limited by relatively low in situ CH4 concentrations in the hummock/hollow soil profile. Our study revealed complex CH4 dynamics better represented by the emerging heterogeneous conceptual model than the classical model based on redox strata.
Stirring Up the Biological Pump: Vertical Mixing and Carbon Export in the Southern Ocean
Authors: Stukel Michael R. , Ducklow Hugh W. 
Published: August 2017

AbstractThe biological carbon pump (BCP) transports organic carbon from the surface to the ocean's interior via sinking particles, vertically migrating organisms, and passive transport of organic matter by advection and diffusion. While many studies have quantified sinking particles, the magnitude of passive transport remains poorly constrained. In the Southern Ocean weak thermal stratification, strong vertical gradients in particulate organic matter, and weak vertical nitrate gradients suggest that passive transport from the euphotic zone may be particularly important. We compile data from seasonal time series at a coastal site near Palmer Station, annual regional cruises in the Western Antarctic Peninsula (WAP), cruises throughout the broader Southern Ocean, and SOCCOM (Southern Ocean Carbon and Climate Observations and Modeling) autonomous profiling floats to estimate spatial and temporal patterns in vertical gradients of nitrate, particulate nitrogen (PN), and dissolved organic carbon. Under a steady state approximation, the ratio of ∂PN/∂z to ∂NO3−/∂z suggests that passive transport of PN may be responsible for removing 46% (37%–58%) of the nitrate introduced into the surface ocean of the WAP (with dissolved organic matter contributing an additional 3–6%) and for 23% (19%–28%) of the BCP in the broader Southern Ocean. A simple model parameterized with in situ nitrate, PN, and primary production data suggested that passive transport was responsible for 54% of the magnitude of the BCP in the WAP. Our results highlight the potential importance of passive transport (by advection and diffusion) of organic matter in the Southern Ocean but should only be considered indicative of high passive transport (rather than conclusive evidence) due to our steady state assumptions.
Machine Learning Predicts Laboratory Earthquakes
Authors: Rouet‐Leduc Bertrand , Hulbert Claudia , Lubbers Nicholas , Barros Kipton , Humphreys Colin J. , Johnson Paul A. 
Published: August 2017

AbstractWe apply machine learning to data sets from shear laboratory experiments, with the goal of identifying hidden signals that precede earthquakes. Here we show that by listening to the acoustic signal emitted by a laboratory fault, machine learning can predict the time remaining before it fails with great accuracy. These predictions are based solely on the instantaneous physical characteristics of the acoustical signal and do not make use of its history. Surprisingly, machine learning identifies a signal emitted from the fault zone previously thought to be low‐amplitude noise that enables failure forecasting throughout the laboratory quake cycle. We infer that this signal originates from continuous grain motions of the fault gouge as the fault blocks displace. We posit that applying this approach to continuous seismic data may lead to significant advances in identifying currently unknown signals, in providing new insights into fault physics, and in placing bounds on fault failure times.
The Response of the Aegean Sea (Eastern Mediterranean) to the Extreme 2016–2017 Winter
Authors: Velaoras Dimitris , Papadopoulos Vassilis P. , Kontoyiannis Harilaos , Papageorgiou Dimitra K. , Pavlidou Alexandra 
Published: August 2017

AbstractThe exceptionally cold December 2016 over the Aegean Sea—one of the most important dense water formation areas of the eastern Mediterranean Sea—resulted in winter heat loss comparable to the peak Eastern Mediterranean Transient winters (1992–1993). Hydrological data sampled in March/April 2017 showed that newly produced dense waters ventilated the North Aegean deep basins up to density horizons of σθ ~ 29.35 kg/m3. The water column ventilation was unable to reach the bottom as the present upper thermohaline circulation of the eastern Mediterranean does not favor the salinity preconditioning of the Aegean Sea. In the southwest Aegean, the Myrtoan basin was ventilated by dense waters traceable farther south to the West Cretan Straits. Export of these masses from the Aegean Sea can potentially have a broader impact on the thermohaline circulation of the eastern Mediterranean.
GOCE Gradiometer Measurements Response to Ionospheric Dynamics
Authors: Ince E. Sinem , Pagiatakis Spiros D. 
Published: August 2017

AbstractWith the launch of dedicated satellite gravity missions, starting with CHAllenging Minisatellite Payload (CHAMP) in 2000, with Gravity Recovery and Climate Experiment (GRACE) in 2002, and Gravity field and steady‐state Ocean Circulation Explorer (GOCE) in 2009, the accuracy and spatial resolution of the Earth's global gravity field models have been improved. Highly sensitive accelerometer measurements have not only been useful for gravity field modeling but have also been contributing to the studies of thermospheric dynamics. While improving the sensitivity of the accelerometer measurements, the new instrumentation used on board GOCE brings different challenges in understanding the data and developing sophisticated data processing. Our analyses reveal that the GOCE gravitational gradient measurements were affected by highly variable ionospheric dynamics that did not only degrade the quality of the GOCE Electrostatic Gravity Gradiometer (EGG) measurements but also proved that some characteristics of ionospheric dynamics can be measured by GOCE accelerometers and other Low Earth Orbiters. In this paper, we show how GOCE‐retrieved neutral winds respond to main ionospheric currents and we develop the impulse‐response relation between intense ionospheric dynamics (plasma drift) represented by Poynting energy flux and the gravity gradiometer tensor trace disturbances observed over the north geomagnetic polar region.
The Effect of Storm Driver and Intensity on Magnetospheric Ion Temperatures
Authors: Keesee Amy M. , Katus Roxanne M. , Scime Earl E. 
Published: August 2017

AbstractEnergy deposited in the magnetosphere during geomagnetic storms drives ion heating and convection. Ions are also heated and transported via internal processes throughout the magnetosphere. Injection of the plasma sheet ions to the inner magnetosphere drives the ring current and, thus, the storm intensity. Understanding the ion dynamics is important to improving our ability to predict storm evolution. In this study, we perform superposed epoch analyses of ion temperatures during storms, comparing ion temperature evolution by storm driver and storm intensity. The ion temperatures are calculated using energetic neutral atom measurements from the Two Wide‐Angle Imaging Neutral‐Atom Spectrometers (TWINS) mission. The global view of these measurements provide both spatial and temporal information. We find that storms driven by coronal mass ejections (CMEs) tend to have higher ion temperatures throughout the main phase than storms driven by corotating interaction regions (CIRs) but that the temperatures increase during the recovery phase of CIR‐driven storms. Ion temperatures during intense CME‐driven storms have brief intervals of higher ion temperatures than those during moderate CME‐driven storms but have otherwise comparable ion temperatures. The highest temperatures during CIR‐driven storms are centered at 18 magnetic local time and occur on the dayside for moderate CME‐driven storms. During the second half of the main phase, ion temperatures tend to decrease in the postmidnight to dawn sector for CIR storms, but an increase is observed for CME storms. This increase begins with a sharp peak in ion temperatures for intense CME storms, likely a signature of substorm activity that drives the increased ring current.
Sources of Ionospheric Variability at Mars
Authors: Mendillo Michael , Narvaez Clara , Vogt Marissa F. , Mayyasi Majd , Forbes Jeffrey , Galand Marina , Thiemann Edward , Benna Mehdi , Eparvier Francis , Chamberlin Phillip , Mahaffy Paul , Andersson Laila 
Published: August 2017

AbstractDuring the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's deep‐dip #2 campaign of 17–22 April 2015, spacecraft instruments observed all of the physical parameters needed to assess the photo‐chemical‐equilibrium (PCE) explanation for ionospheric variability at a fixed altitude (135 km) near the peak of the Martian ionosphere. MAVEN measurements of electron density, electron temperature, neutral CO2 density, and solar irradiance were collected during 28 orbits. When inserted into the PCE equation, the measurements of varying PCE drivers correlated with the observed electron density variations to within instrumental uncertainty levels. The dominant source of this positive correlation was the variability of CO2 densities associated with the longitudinal wave‐2 component of nonmigrating tides in the Martian thermosphere.
Fully Coupled Nonlinear Fluid Flow and Poroelasticity in Arbitrarily Fractured Porous Media: A Hybrid‐Dimensional Computational Model
Authors: Jin L. , Zoback M. D. 
Published: August 2017

AbstractWe formulate the problem of fully coupled transient fluid flow and quasi‐static poroelasticity in arbitrarily fractured, deformable porous media saturated with a single‐phase compressible fluid. The fractures we consider are hydraulically highly conductive, allowing discontinuous fluid flux across them; mechanically, they act as finite‐thickness shear deformation zones prior to failure (i.e., nonslipping and nonpropagating), leading to “apparent discontinuity” in strain and stress across them. Local nonlinearity arising from pressure‐dependent permeability of fractures is also included. Taking advantage of typically high aspect ratio of a fracture, we do not resolve transversal variations and instead assume uniform flow velocity and simple shear strain within each fracture, rendering the coupled problem numerically more tractable. Fractures are discretized as lower dimensional zero‐thickness elements tangentially conforming to unstructured matrix elements. A hybrid‐dimensional, equal‐low‐order, two‐field mixed finite element method is developed, which is free from stability issues for a drained coupled system. The fully implicit backward Euler scheme is employed for advancing the fully coupled solution in time, and the Newton‐Raphson scheme is implemented for linearization. We show that the fully discretized system retains a canonical form of a fracture‐free poromechanical problem; the effect of fractures is translated to the modification of some existing terms as well as the addition of several terms to the capacity, conductivity, and stiffness matrices therefore allowing the development of independent subroutines for treating fractures within a standard computational framework. Our computational model provides more realistic inputs for some fracture‐dominated poromechanical problems like fluid‐induced seismicity.
Spectral decomposition of internal gravity wave sea surface height in global models
Authors: Savage Anna C. , Arbic Brian K. , Alford Matthew H. , Ansong Joseph K. , Farrar J. Thomas , Menemenlis Dimitris , O'Rourke Amanda K. , Richman James G. , Shriver Jay F. , Voet Gunnar , Wallcraft Alan J. , Zamudio Luis 
Published: August 2017

AbstractTwo global ocean models ranging in horizontal resolution from 1/12° to 1/48° are used to study the space and time scales of sea surface height (SSH) signals associated with internal gravity waves (IGWs). Frequency‐horizontal wavenumber SSH spectral densities are computed over seven regions of the world ocean from two simulations of the HYbrid Coordinate Ocean Model (HYCOM) and three simulations of the Massachusetts Institute of Technology general circulation model (MITgcm). High wavenumber, high‐frequency SSH variance follows the predicted IGW linear dispersion curves. The realism of high‐frequency motions (>
) in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest‐resolution runs of each model (1/25° HYCOM and 1/48° MITgcm) with dynamic height variance frequency spectral density computed from nine in situ profiling instruments. These high‐frequency motions are of particular interest because of their contributions to the small‐scale SSH variability that will be observed on a global scale in the upcoming Surface Water and Ocean Topography (SWOT) satellite altimetry mission. The variance at supertidal frequencies can be comparable to the tidal and low‐frequency variance for high wavenumbers (length scales smaller than ∼50 km), especially in the higher‐resolution simulations. In the highest‐resolution simulations, the high‐frequency variance can be greater than the low‐frequency variance at these scales.
A Comparison of the Ocean Microbarom Recorded on the Ground and in the Stratosphere
Authors: Bowman D. C. , Lees J. M. 
Published: August 2017

AbstractThe, ocean microbarom is an acoustic signal generated via nonlinear interaction of ocean surface waves. It can propagate for thousands of kilometers and represent a significant infrasonic noise source for ground infrasound stations across the globe. However, wind noise often compromises detections at ground stations. Furthermore, the microbarom may travel in elevated acoustic ducts that do not transmit enough energy for detections on ground stations. Here the presence of the ocean microbarom on two high‐altitude balloon flights is investigated. A spectral peak consistent with the microbarom was observed on sensors in the stratosphere but not on those deployed on the ground near the flight path of the balloon. This is probably due to an elevated acoustic duct and/or a superior signal‐to‐noise ratio in the stratosphere. Thus, microbarom activity quantified solely with ground‐based sensors may underestimate the occurrence of the phenomenon. However, high levels of interference from flight system electronics and/other other payloads may have obscured other microbarom episodes during the balloon deployments.
Reactive Uptake of Sulfur Dioxide and Ozone on Volcanic Glass and Ash at Ambient Temperature
Authors: Maters Elena C. , Delmelle Pierre , Rossi Michel J. , Ayris Paul M. 
Published: August 2017

AbstractThe atmospheric impacts of volcanic ash from explosive eruptions are rarely considered alongside those of volcanogenic gases/aerosols. While airborne particles provide solid surfaces for chemical reactions with trace gases in the atmosphere, the reactivity of airborne ash has seldom been investigated. Here we determine the total uptake capacity (NiM) and initial uptake coefficient (γM) for sulfur dioxide (SO2) and ozone (O3) on a compositional array of volcanic ash and glass powders at ~25°C in a Knudsen flow reactor. The measured ranges of NiSO2 and γSO2 (1011–1013 molecules cm−2 and 10−3–10−2) and NiO3 and γO3 (1012–1013 molecules cm−2 and 10−3–10−2) are comparable to values reported for mineral dust. Differences in ash and glass reactivity toward SO2 and O3 may relate to varying abundances of, respectively, basic and reducing sites on these materials. The typically lower SO2 and O3 uptake on ash compared to glass likely results from prior exposure of ash surfaces to acidic and oxidizing conditions within the volcanic eruption plume/cloud. While sequential uptake experiments overall suggest that these gases do not compete for reactive surface sites, SO2 uptake forming adsorbed S(IV) species may enhance the capacity for subsequent O3 uptake via redox reaction forming adsorbed S(VI) species. Our findings imply that ash emissions may represent a hitherto neglected sink for atmospheric SO2 and O3.
Variability of Stratospheric Reactive Nitrogen and Ozone Related to the QBO
Authors: Park M. , Randel W. J. , Kinnison D. E. , Bourassa A. E. , Degenstein D. A. , Roth C. Z. , McLinden C. A. , Sioris C. E. , Livesey N. J. , Santee M. L. 
Published: August 2017

AbstractThe stratospheric quasi‐biennial oscillation (QBO) dominates interannual variability of dynamical variables and trace constituents in the tropical stratosphere and provides a natural experiment to test circulation‐chemistry interactions. This work quantifies the relationships among ozone (O3), reactive nitrogen (NOy), and source gas N2O, and their links to the QBO, based on satellite constituent measurements and meteorological data spanning 2005–2014 (over four QBO cycles). Data include O3, HNO3, and N2O from the Aura Microwave Limb Sounder and an NOx proxy derived from Optical Spectrograph and Infrared Imager System NO2 measurements combined with a photochemical box model (= NOx*). Results are compared to simulations from the Whole Atmosphere Community Climate Model, version 4 incorporating a QBO circulation nudged to assimilated winds. Cross correlations and composites with respect to the QBO phase show coherent 180° out‐of‐phase relationships between NOy and N2O throughout the stratosphere, with the NOx/HNO3 ratio increasing with altitude. The anomalies in NOy species propagate coherently downward with the QBO. Ozone is anticorrelated with reactive nitrogen in the middle stratosphere above ~28 km due to NOx control of ozone catalytic loss cycles. Quantitative comparisons of nitrogen partitioning and O3 sensitivity to NOx show good overall agreement between satellite observations and model results (suggesting closure of the NOy budget), although the model results show larger (up to ~20%) N2O, NOx, and O3 variations near ~35 km compared to observations. These analyses serve to assess the consistency of diverse satellite‐based data sets and also to evaluate nitrogen partitioning and NOx‐dependent ozone chemistry in the global model.
Analysis of near‐surface biases in ERA‐Interim over the Canadian Prairies
Authors: Betts Alan K. , Beljaars Anton C. M. 
Published: August 2017

AbstractWe quantify the biases in the diurnal cycle of temperature in ERA‐Interim for both warm and cold season using hourly climate station data for four stations in Saskatchewan from 1979 to 2006. The warm season biases increase as opaque cloud cover decreases, and change substantially from April to October. The bias in mean temperature increases almost monotonically from small negative values in April to small positive values in the fall. Under clear skies, the bias in maximum temperature is of the order of −1°C in June and July, and −2°C in spring and fall; while the bias in minimum temperature increases almost monotonically from +1°C in spring to +2.5°C in October. The bias in the diurnal temperature range falls under clear skies from −2.5°C in spring to −5°C in fall. The cold season biases with surface snow have a different structure. The biases in maximum, mean and minimum temperature with a stable BL reach +1°C, +2.6°C and +3°C respectively in January under clear skies. The cold season bias in diurnal range increases from about −1.8°C in the fall to positive values in March. These diurnal biases in 2 m temperature and their seasonal trends are consistent with a high bias in both the diurnal and seasonal amplitude of the model ground heat flux, and a warm season daytime bias resulting from the model fixed leaf area index. Our results can be used as bias corrections in agricultural modeling that use these reanalysis data, and also as a framework for understanding model biases.