bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrous oxide during the onset of the Atlantic cold tongue
Authors: Arévalo‐Martínez D. L. , Kock A. , Steinhoff T. , Brandt P. , Dengler M. , Fischer T. , Körtzinger A. , Bange H. W. 
Published: November 2016

AbstractThe tropical Atlantic exerts a major influence in climate variability through strong air‐sea interactions. Within this region, the eastern side of the equatorial band is characterized by strong seasonality, whereby the most prominent feature is the annual development of the Atlantic cold tongue (ACT). This band of low sea surface temperatures (∼22–23°C) is typically associated with upwelling‐driven enhancement of surface nutrient concentrations and primary production. Based on a detailed investigation of the distribution and sea‐to‐air fluxes of N2O in the eastern equatorial Atlantic (EEA), we show that the onset and seasonal development of the ACT can be clearly observed in surface N2O concentrations, which increase progressively as the cooling in the equatorial region proceeds during spring‐summer. We observed a strong influence of the surface currents of the EEA on the N2O distribution, which allowed identifying “high” and “low” concentration regimes that were, in turn, spatially delimited by the extent of the warm eastward‐flowing North Equatorial Countercurrent and the cold westward‐flowing South Equatorial Current. Estimated sea‐to‐air fluxes of N2O from the ACT (mean 5.18 ± 2.59 μmol m−2 d−1) suggest that in May–July 2011 this cold‐water band doubled the N2O efflux to the atmosphere with respect to the adjacent regions, highlighting its relevance for marine tropical emissions of N2O.
Seasonal variability of warm boundary layer cloud and precipitation properties in the Southern Ocean as diagnosed from A‐Train data
Authors: Mace Gerald G. , Avey Stephanie 
Published: November 2016

AbstractThe extensive cloudiness and resulting high albedo of the Southern Oceans (SO) are predominantly due to the occurrence of widespread marine boundary layer clouds. Recent work finds correlations between biogenically enhanced cloud condensation nuclei concentrations and cloud droplet number concentrations derived from passive satellite data. The active remote sensors in the A‐Train have created a unique and long‐term record of these clouds that include vertical profiles of radar reflectivity and microwave brightness temperature from CloudSat that can be combined with solar reflectances from Moderate Resolution Imaging Spectroradiometer. We examine this data record using a unique algorithm to infer warm‐topped cloud and precipitation properties. We find seasonal variations in cloud properties where summer season clouds demonstrate higher cloud droplet number concentrations on average and require higher liquid water contents to produce similar precipitation rates.
Regional Bowen ratio controls on afternoon moist convection: A large eddy simulation study
Authors: Kang Song‐Lak 
Published: November 2016

AbstractThis study examines the effect of the regional Bowen ratio β, the ratio of the domain‐averaged surface sensible heat flux (SHF) to latent heat flux (LHF), on afternoon moist convection. With a temporally evolving but spatially uniform surface available energy over a mesoscale domain under a weak capping inversion, we run large eddy simulation of the afternoon convective boundary layer (CBL). We first prescribe a small β of 0.56 (a wet surface) and then the reversed large β of 1.80 (a dry surface) by switching the SHF and LHF fields. The perturbation fields of the fluxes are prescribed with the Fourier spectra of κ− 3 (κ is horizontal wave number; strong mesoscale heterogeneity) and κ0 (homogeneity). The large β cases have strong vertical buoyancy fluxes and produce more vigorous updrafts. In the heterogeneous, large β surface case, with the removal of convective inhibition over a mesoscale subdomain of large SHF, deep convection develops. In the heterogeneous, small β surface case, convective clouds develop but do not progress into precipitating convection. In the homogeneous surface cases, randomly distributed shallow clouds develop with significantly more and thicker clouds in the large β case. (Co)spectral analyses confirm the more vigorous turbulent thermals in the large β cases and reveal that the moisture advection by the surface heterogeneity‐induced mesoscale flows makes the correlation between mesoscale temperature and moisture perturbations change from negative to positive, which facilitates the mesoscale pool of high relative humidity air just above the CBL top, a necessary condition for deep convection.
Spatial extent and temporal variability of Greenland firn aquifers detected by ground and airborne radars
Authors: Miège Clément , Forster Richard R. , Brucker Ludovic , Koenig Lora S. , Solomon D. Kip , Paden John D. , Box Jason E. , Burgess Evan W. , Miller Julie Z. , McNerney Laura , Brautigam Noah , Fausto Robert S. , Gogineni Sivaprasad 
Published: November 2016

AbstractWe document the existence of widespread firn aquifers in an elevation range of ~1200–2000 m, in the high snow‐accumulation regions of the Greenland ice sheet. We use NASA Operation IceBridge accumulation radar data from five campaigns (2010–2014) to estimate a firn‐aquifer total extent of 21,900 km2. We investigate two locations in Southeast Greenland, where repeated radar profiles allow mapping of aquifer‐extent and water table variations. In the upper part of Helheim Glacier the water table rises in spring following above‐average summer melt, showing the direct firn‐aquifer response to surface meltwater production changes. After spring 2012, a drainage of the firn‐aquifer lower margin (5 km) is inferred from both 750 MHz accumulation radar and 195 MHz multicoherent radar depth sounder data. For 2011–2014, we use a ground‐penetrating radar profile located at our Ridgeline field site and find a spatially stable aquifer with a water table fluctuating less than 2.5 m vertically. When combining radar data with surface topography, we find that the upper elevation edge of firn aquifers is located directly downstream of locally high surface slopes. Using a steady state 2‐D groundwater flow model, water is simulated to flow laterally in an unconfined aquifer, topographically driven by ice sheet surface undulations until the water encounters crevasses. Simulations suggest that local flow cells form within the Helheim aquifer, allowing water to discharge in the firn at the steep‐to‐flat transitions of surface topography. Supported by visible imagery, we infer that water drains into crevasses, but its volume and rate remain unconstrained.
Hyporheic flow and dissolved oxygen distribution in fish nests: The effects of open channel velocity, permeability patterns, and groundwater upwelling
Authors: Cardenas M. Bayani , Ford Aimee E. , Kaufman Matthew H. , Kessler Adam J. , Cook Perran L. M. 
Published: November 2016

AbstractMany fish lay their eggs in nests, or redds, which they construct in sediment. The viability of eggs depends on many factors, particularly their oxygenation. Because dissolved oxygen is typically saturated within the stream channel, the dissolved oxygen distribution within the redd depends on whether or not hyporheic flow and transport occur within the sediment. We conducted a series of flume and numerical flow and age transport modeling experiments with the aim of understanding the effects of salmonid redds on the hyporheic transport of young oxygenated water. Hyporheic flow was visualized directly through dye injections. Dissolved oxygen throughout the fish nest was measured using a planar optode. Experiments were conducted at various open channel flow velocities in order to understand their effect on dissolved oxygen, and computational simulations considered various sediment textures and ambient groundwater upwelling rates to add process‐level insight. We found that, as also shown by previous studies, the redd topography induces multiscale hyporheic flow that effectively flushes the egg pocket location with younger presumably oxygenated water; older water upwells and forms anoxic zones. This pattern persists even at the lowest channel flow rates and at small upwelling velocities of older ambient groundwater which splits the multiscale hyporheic flow cells into isolated pockets. Large groundwater upwelling rates can shut down all the hyporheic flushing. The relatively coarse texture of the redd further promotes hyporheic flushing of the redd sediment with oxygenated water. Thus, redd morphology and sediment texture optimally combine to induce hyporheic exchange flow that delivers young oxygenated water to the egg pocket.
Thermal alteration of water extractable organic matter in climosequence soils from the Sierra Nevada, California
Authors: Santos Fernanda , Russell David , Berhe Asmeret Asefaw 
Published: November 2016

AbstractIn the next decades, the influence of wildfires in controlling the cycling and composition of soil organic matter (SOM) globally and in the western U.S. is expected to grow. While the impact of fires on bulk SOM has been extensively studied, the extent at which heating of soil affects the soluble component of SOM remains unclear. Here we investigated the thermal transformations of water‐extractable organic matter (WEOM) by examining the changes in the distribution of carbon (C) functional groups in WEOM from soils heated at low and intermediate temperatures. WEOM (<0.7 µm particle size) was extracted from topsoils (0–5 cm depth) of five soil series formed from a nonglaciated granitic bedrock and sampled along a Sierra Nevada climosequence. Soils were heated in a muffle furnace at 150°C, 250°C, and 350°C for 1 h. The extracted solution was analyzed for WEOM aromaticity, mean molecular weight, organic C (OC) concentration, and major structural components by employing optical spectrophotometry and liquid‐state 1H‐NMR spectroscopy. At 150°C and 250°C, OC concentrations increased relative to the thermally unaltered samples, with losses of oxygenated functional C groups and enrichment of aliphatic C structures observed at 250°C. Conversely, OC concentration and mean molecular weight decreased as heating increased from 250°C to 350°C, whereas WEOC became more enriched in aromatic C structures. Our results suggest that low and intermediate fire intensities significantly alter the nature of dissolved organic matter exported from soils to rivers in the Sierra Nevada and beyond.
Simulating county‐level crop yields in the Conterminous United States using the Community Land Model: The effects of optimizing irrigation and fertilization
Authors: Leng Guoyong , Zhang Xuesong , Huang Maoyi , Yang Qichun , Rafique Rashid , Asrar Ghassem R. , Ruby Leung L. 
Published: November 2016

AbstractIn this study, we applied version 4.5 of the Community Land Model (CLM) at a 0.125° resolution to provide the first county‐scale model validation for simulating crop yields over the Conterminous United States (CONUS). Large bias was found in simulating crop yields against U.S. Department of Agriculture (USDA) survey data, with county‐level root‐mean‐square error (RMSE) of 42% and 38% for simulated US mean corn and soybean yields, respectively. We then synthesized crop yield, irrigation and fertilization data sets from USDA and U.S. Geological Survey (USGS) to constrain model simulations. Compared with fertilization, irrigation has limited effects on crop yields with improvements limited to irrigated regions. In most current‐generation Earth system models (ESMs), fertilizers are applied spatially uniformly with fixed amounts and timing without considering crop fertilizer demand. To address this weakness, we propose a prognostic fertilization scheme that dynamically determines the timing and rate of each fertilizer application, with the annual amounts and valid fertilization time windows constrained by surveyed data. The optimized fertilization scheme reduces RMSE to 22% and 21% of the US mean corn and soybean yields, respectively. Compared with the default CLM4.5, our fertilization scheme substantially improves crop yield simulations especially over major crop growing regions. However, to compensate for the widely documented biases in denitrification rates simulated by CLM4.5, the dynamically determined fertilization timing and rates do not match the fertilization practices of farmers exactly. Therefore, caution should be exercised when extending this method beyond the contemporary conditions.
Improved seasonal prediction using the SINTEX‐F2 coupled model
Authors: Doi Takeshi , Behera Swadhin K. , Yamagata Toshio 
Published: November 2016

AbstractThe SINTEX‐F1 Coupled General Circulation Model (CGCM) was developed within the EU‐Japan collaborative framework to study global climate variability and its predictability by use of the Earth Simulator. The seasonal prediction system based on the SINTEX‐F1 has demonstrated its outstanding performance of predicting El Niño/Southern Oscillation (ENSO) and the Indian Ocean Dipole since 2005. However, there is much room for improvement in predicting extratropical climate variations. To deal with this, a revised CGCM called SINTEX‐F2 has been developed; the new system is a high‐resolution version with a dynamical sea‐ice model. For the tropical climate variations in the Pacific and the Indian Ocean, the SINTEX‐F2 preserves the high‐prediction skill, and sometimes even shows higher skill especially for strong events, as compared to the SINTEX‐F1. In addition, it has turned out that the new system is more skillful in predicting the subtropics, particularly, the Indian Ocean Subtropical Dipole and the Ningaloo Niño. The improvement may contribute to enhancing prediction skills of the regional rainfall distributions and encourage us to develop an early warning system which may be applied for societal and industrial activities.
The tropical rain belts with an annual cycle and a continent model intercomparison project: TRACMIP
Authors: Voigt Aiko , Biasutti Michela , Scheff Jacob , Bader Jürgen , Bordoni Simona , Codron Francis , Dixon Ross D. , Jonas Jeffrey , Kang Sarah M. , Klingaman Nicholas P. , Leung Ruby , Lu Jian , Mapes Brian , Maroon Elizabeth A. , McDermid Sonali , Park Jong‐yeon , Roehrig Romain , Rose Brian E. J. , Russell Gary L. , Seo Jeongbin , Toniazzo Thomas , Wei Ho‐Hsuan , Yoshimori Masakazu , Vargas Zeppetello Lucas R. 
Published: November 2016

AbstractThis paper introduces the Tropical Rain belts with an Annual cycle and a Continent Model Intercomparison Project (TRACMIP). TRACMIP studies the dynamics of tropical rain belts and their response to past and future radiative forcings through simulations with 13 comprehensive and one simplified atmosphere models coupled to a slab ocean and driven by seasonally varying insolation. Five idealized experiments, two with an aquaplanet setup and three with a setup with an idealized tropical continent, fill the space between prescribed‐SST aquaplanet simulations and realistic simulations provided by CMIP5/6. The simulations reproduce key features of present‐day climate and expected future climate change, including an annual‐mean intertropical convergence zone (ITCZ) that is located north of the equator and Hadley cells and eddy‐driven jets that are similar to present‐day climate. Quadrupling CO2 leads to a northward ITCZ shift and preferential warming in Northern high latitudes. The simulations show interesting CO2‐induced changes in the seasonal excursion of the ITCZ and indicate a possible state dependence of climate sensitivity. The inclusion of an idealized continent modulates both the control climate and the response to increased CO2; for example, it reduces the northward ITCZ shift associated with warming and, in some models, climate sensitivity. In response to eccentricity‐driven seasonal insolation changes, seasonal changes in oceanic rainfall are best characterized as a meridional dipole, while seasonal continental rainfall changes tend to be symmetric about the equator. This survey illustrates TRACMIP's potential to engender a deeper understanding of global and regional climate and to address questions on past and future climate change.
Understanding the tropical cloud feedback from an analysis of the circulation and stability regimes simulated from an upgraded multiscale modeling framework
Authors: Xu Kuan‐Man , Cheng Anning 
Published: November 2016

AbstractAs revealed from studies using conventional general circulation models (GCMs), the thermodynamic contribution to the tropical cloud feedback dominates the dynamic contribution, but these models have difficulty in simulating the subsidence regimes in the tropics. In this study, we analyze the tropical cloud feedback from a 2 K sea surface temperature (SST) perturbation experiment performed with a multiscale modeling framework (MMF). The MMF explicitly represents cloud processes using 2‐D cloud‐resolving models with an advanced higher‐order turbulence closure in each atmospheric column of the host GCM. We sort the monthly mean cloud properties and cloud radiative effects according to circulation and stability regimes. We find that the regime‐sorted dynamic changes dominate the thermodynamic changes in terms of the absolute magnitude. The dynamic changes in the weak subsidence regimes exhibit strong negative cloud feedback due to increases in shallow cumulus and deep clouds while those in strongly convective and moderate‐to‐strong subsidence regimes have opposite signs, resulting in a small contribution to cloud feedback. On the other hand, the thermodynamic changes are large due to decreases in stratocumulus clouds in the moderate‐to‐strong subsidence regimes with small opposite changes in the weak subsidence and strongly convective regimes, resulting in a relatively large contribution to positive cloud feedback. The dynamic and thermodynamic changes contribute equally to positive cloud feedback and are relatively insensitive to stability in the moderate‐to‐strong subsidence regimes. But they are sensitive to stability changes from the SST increase in convective and weak subsidence regimes. These results have implications for interpreting cloud feedback mechanisms.
Expanded oxygen minimum zones during the late Paleocene‐early Eocene: Hints from multiproxy comparison and ocean modeling
Authors: Zhou X. , Thomas E. , Winguth A. M. E. , Ridgwell A. , Scher H. , Hoogakker B. A. A. , Rickaby R. E. M. , Lu Z. 
Published: November 2016

AbstractAnthropogenic warming could well drive depletion of oceanic oxygen in the future. Important insight into the relationship between deoxygenation and warming can be gleaned from the geological record, but evidence is limited because few ocean oxygenation records are available for past greenhouse climate conditions. We use I/Ca in benthic foraminifera to reconstruct late Paleocene through early Eocene bottom and pore water redox conditions in the South Atlantic and Southern Indian Oceans and compare our results with those derived from Mn speciation and the Ce anomaly in fish teeth. We conclude that waters with lower oxygen concentrations were widespread at intermediate depths (1.5–2 km), whereas bottom waters were more oxygenated at the deepest site, in the Southeast Atlantic Ocean (>3 km). Epifaunal benthic foraminiferal I/Ca values were higher in the late Paleocene, especially at low‐oxygen sites, than at well‐oxygenated modern sites, indicating higher seawater total iodine concentrations in the late Paleocene than today. The proxy‐based bottom water oxygenation pattern agrees with the site‐to‐site O2 gradient as simulated in a comprehensive climate model (Community Climate System Model Version 3), but the simulated absolute dissolved O2 values are low (< ~35 µmol/kg), while higher O2 values (~60–100 µmol/kg) were obtained in an Earth system model (Grid ENabled Integrated Earth system model). Multiproxy data together with improvements in boundary conditions and model parameterization are necessary if the details of past oceanographic oxygenation are to be resolved.
Phase retrieval by constrained power inflation and signum flipping
Authors: Laganà A. R. , Morabito A. F. , Isernia T. 
Published: November 2016

AbstractIn this paper we consider the problem of retrieving a signal from the modulus of its Fourier transform (or other suitable transformations) and some additional information, which is also known as “Phase Retrieval” problem. The problem arises in many areas of applied Sciences such as optics, electron microscopy, antennas, and crystallography. In particular, we introduce a new approach, based on power inflation and tunneling, allowing an increased robustness with respect to the possible occurrence of false solutions. Preliminary results are presented for the simple yet relevant case of one‐dimensional arrays and noisy data.
Innovative framework to simulate the fate and transport of nonconservative constituents in urban combined sewer catchments
Authors: Morales V. M. , Quijano J. C. , Schmidt A. , Garcia M. H. 
Published: November 2016

AbstractWe have developed a probabilistic model to simulate the fate and transport of nonconservative constituents in urban watersheds. The approach implemented here extends previous studies that rely on the geomorphological instantaneous unit hydrograph concept to include nonconservative constituents. This is implemented with a factor χ that affects the transfer functions and therefore accounts for the loss (gain) of mass associated with the constituent as it travels through the watershed. Using this framework, we developed an analytical solution for the dynamics of dissolved oxygen (DO) and biochemical oxygen demand (BOD) in urban networks based on the Streeter and Phelps model. This model breaks down the catchment into a discreet number of possible flow paths through the system, requiring less data and implementation effort than well‐established deterministic models. Application of the model to one sewer catchment in the Chicago area with available BOD information proved its ability to predict the BOD concentration observed in the measurements. In addition, comparison of the model with a calibrated Storm Water Management Model (SWMM) of another sewer catchment from the Chicago area showed that the model predicted the BOD concentration as well as the widely accepted SWMM. The developed model proved to be a suitable alternative to simulate the fate and transport of constituents in urban catchments with limited and uncertain input data.
Comment on “Estimation of composite hydraulic resistance in ice‐covered alluvial streams” by Ghareh Aghaji Zare et al.
Authors: Beltaos Spyros 
Published: November 2016

AbstractInconsistencies between basic hydraulics and hypotheses advanced by the authors are identified. They are attributed primarily to weaknesses in the analysis of velocity measurements in the ice‐controlled flow layer and suggestions for improvement are offered.