bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tail shortening with developing eddies in a rough‐walled rock fracture
Authors: Lee Seung Hyun , Yeo In Wook , Lee Kang‐Kun , Detwiler Russell L. 
Published: July 2015

AbstractUnderstanding fluid flow and solute transport in rough‐walled fractures is important in many problems such as geological storage of CO2 and siting of radioactive waste repositories. The first microscopic observation of fluid flow and solute transport through a rough‐walled fracture was made to assess the evolution of eddies and their effect on non‐Fickian tailing. A noteworthy phenomenon was observed that as the eddy grew, the particles were initially caught in and swirled around within eddies, and then cast back into main flow channel, which reduced tailing. This differs from the conventional conceptual model, which presumes a distinct separation between mobile and immobile zones. Fluid flow and solute transport modeling within the 3‐D fracture confirmed tail shortening due to mass transfer by advective paths between the eddies and the main flow channel, as opposed to previous 2‐D numerical studies that showed increased tailing with growing eddies.
Statistical characteristics of slow earthward and tailward flows in the plasma sheet
Authors: Zhang L. Q. , Baumjohann W. , Wang J. Y. , Rème H. , Dunlop M. W. , Chen T. 
Published: July 2015

AbstractIn this paper, we statistically analyzed and compared the earthward flow (EF) and the tailward flow (TF) in the plasma sheet. It is found that the properties of the EF/TF in the central plasma sheet (CPS) of β > 1 and the outer plasma sheet (OPS) of 0.1 < β < 1 are distinctly different. The main conclusions include that (1) the EFs occur in both the CPS and the OPS while the TFs mainly occur in the OPS, (2) both flows are dominantly convective in the CPS and parallel in the OPS, (3) in the CPS, the EF and the TF have similar characteristics, including their bulk velocities and ion densities and Ey components. Both flows tend to have isotropic temperatures; (4) in the OPS, the EFs tend to have higher ion velocity, density, and Ey than the TF. The EFs tend to have anisotropic temperatures, while the TFs tend to have more isotropic temperatures. As a whole, combined characteristics of the EF and the TF are consistent with (1) reflection at the “magnetic mirror point” near the Earth for parallel flows in the OPS and (2) bouncing off/back from the dipolar field closer to the Earth for convective flows in the CPS.
Slow and Go: Pulsing slip rates on the creeping section of the San Andreas Fault
Authors: Turner Ryan C. , Shirzaei Manoochehr , Nadeau Robert M. , Bürgmann Roland 
Published: July 2015

AbstractRising and falling slip rates on the creeping section of the San Andreas Fault have been inferred from variations of recurrence intervals of characteristically repeating microearthquakes, but this observation has not previously been confirmed using modern geodetic data. Here we report on observations of this “pulsing” slip obtained from advanced multitemporal interferometric synthetic aperture radar (InSAR) data, confirmed using continuous GPS sites of the Plate Boundary Observatory. The surface deformation time series show a strong correlation to the previously documented slip rate variations derived from repeating earthquakes on the fault interface, at various spatial and temporal scales. Time series and spectral analyses of repeating earthquake and InSAR data reveal a quasiperiodic pulsing with a roughly 2 year period along some sections of the fault, with the earthquakes on the fault interface lagging behind the far‐field deformation by about 6 months. This suggests a temporal delay between the pulsing crustal strain generated by deep‐seated shear and the time‐variable slip on the shallow fault interface, and that at least in some places this process may be cyclical. There exist potential impacts for time‐dependent seismic hazard forecasting in California and, as it becomes better validated in the richly instrumented natural laboratory of the central San Andreas Fault, the process used here will be even more helpful in characterizing hazard and fault zone rheology in areas without California's geodetic infrastructure.
Some aspects of the Coriolis‐Stokes forcing in the oceanic momentum and energy budgets
Authors: Weber Jan Erik H. , Drivdal Magnus , Christensen Kai H. , Broström Göran 
Published: July 2015

AbstractThe Coriolis‐Stokes (CS) force is a wave‐induced forcing of the Eulerian mean motion in a rotating ocean. For idealized conditions, it is demonstrated by comparison with Lagrangian results that the appropriate surface boundary condition for the Eulerian mean wave‐induced flow is that of vanishing vertical shear. The Eulerian mean current derived by applying this condition plus the inviscid Stokes drift yield the Lagrangian wave‐induced drift velocity, apart from a small boundary‐layer correction. Appreciation of the importance of the CS force in the momentum balance has led to investigations of the role of the CS force in the energy budget. The present study shows that the CS force is not a source for the rate of change of the total average energy density in the fluid, when the vertical integration is performed to the moving material surface. However, results to fourth order in wave steepness confirm earlier findings that the CS force acts to change the vertically integrated Eulerian kinetic energy of the mean flow. A new interpretation relates this effect to the fact that the mean Eulerian Coriolis force performs work in acting along the motion of the Lagrangian wave‐induced mass (caused by the divergence effect) at the surface.
Winter‐to‐summer precipitation phasing in southwestern North America: A multicentury perspective from paleoclimatic model‐data comparisons
Authors: Coats Sloan , Smerdon Jason E. , Seager Richard , Griffin Daniel , Cook Benjamin I. 
Published: July 2015

AbstractThe phasing of winter‐to‐summer precipitation anomalies in the North American monsoon (NAM) region 2 (113.25°W–107.75°W, 30°N–35.25°N—NAM2) of southwestern North America is analyzed in fully coupled simulations of the Last Millennium and compared to tree ring reconstructed winter and summer precipitation variability. The models simulate periods with in‐phase seasonal precipitation anomalies, but the strength of this relationship is variable on multidecadal time scales, behavior that is also exhibited by the reconstructions. The models, however, are unable to simulate periods with consistently out‐of‐phase winter‐to‐summer precipitation anomalies as observed in the latter part of the instrumental interval. The periods with predominantly in‐phase winter‐to‐summer precipitation anomalies in the models are significant against randomness, and while this result is suggestive of a potential for dual‐season drought on interannual and longer time scales, models do not consistently exhibit the persistent dual‐season drought seen in the dendroclimatic reconstructions. These collective findings indicate that model‐derived drought risk assessments may underestimate the potential for dual‐season drought in 21st century projections of hydroclimate in the American Southwest and parts of Mexico.
Observations of positive narrow bipolar pulses
Authors: Karunarathne Sumedhe , Marshall Thomas C. , Stolzenburg Maribeth , Karunarathna Nadeeka 
Published: July 2015

AbstractWaveforms of 226 positive narrow bipolar pulses (NBPs) were obtained with five to eight stations of E‐change meters covering an area of 70 × 100 km2. The NBPs had typical average parameters: 10–90% rise time of 2.6 μs, full width at half maximum time of 2.8 μs, zero cross time of 9.9 μs, and range‐normalized amplitude at 100 km of 11.0 V/m. Four main types of positive NBP waveforms were identified: Type A had a simple bipolar waveform with a positive peak and a negative overshoot peak (1% of NBPs), Type B had extra peak(s) superimposed on the overshoot peak (67%), Type C had extra peak(s) on or just after the main positive peak (13%), and Type D had extra peak(s) before the main positive peak (19%). Regardless of type, each NBP waveform maintained its basic shape across a range of 10 to 130 km from its origin. NBP locations, obtained with a time of arrival technique, seemed unrestricted in their horizontal distribution (except for Type C), while NBP altitudes ranged from 7 to 19 km with an average of 13 km. Estimated peak currents were 2–126 kA with an average of 30 kA. Isolation of NBPs from other lightning events was determined for both temporal (660 ms) and spatial (>10 km) quantities; 37% of NBPs were isolated, 38% occurred within 660 ms before a flash, 19% occurred within flashes, and 11% occurred within 660 ms after a flash. The total RMS power radiated by NBPs within 1 kHz–2.5 MHz bandwidth had a range of 5.0 × 106–6.1 × 108 W with an average of 7.8 × 107 W.
Increasing evaporation amounts seen in the Arctic between 2003 and 2013 from AIRS data
Authors: Boisvert L. N. , Wu D. L. , Shie C.‐L. 
Published: July 2015

AbstractThe vertical moisture flux (i.e., evaporation) plays an important role in the Arctic energy budget, the water vapor feedback, and Arctic amplification. It is one of the most uncertain variables, especially in this “new Arctic” climate system, which is dominated by large ice‐free ocean areas for a longer portion of the year. Moisture flux rates, produced using Atmospheric Infrared Sounder (AIRS) data, from the Arctic Ocean and surrounding seas were found to have increased between 2003 and 2013 by 7.2 × 10−4 g m−2 s−1 per year (equivalent to 1.79 W m−2 per year in latent heat). This is a 7% increase in the average moisture flux each year and a 0.12% increase in the yearly global ocean latent heat flux, with some months increasing more than others. The largest increases seen are in the Arctic coastal seas during the spring and fall where there has been a reduction in sea ice cover and an increase in sea surface temperatures. Increases in the moisture flux from the surface also correspond to increases in total atmospheric column water vapor and low‐level clouds, especially in the central Arctic regions. Changes in the atmospheric water vapor in the surrounding seas (e.g., East Greenland) are most likely due to lower latitude transport of moisture rather than from the surface. Yearly, the moisture flux from the surface supplies about 10% of the total column atmosphere water vapor.
Cold air incursions, δ18O variability, and monsoon dynamics associated with snow days at Quelccaya Ice Cap, Peru
Authors: Hurley John V. , Vuille Mathias , Hardy Douglas R. , Burns Stephen J. , Thompson Lonnie G. 
Published: July 2015

AbstractQuelccaya Ice Cap in the Andes of Peru contains an annually resolved δ18O record covering the past 1800 years; yet atmospheric dynamics associated with snow deposition and δ18O variability at this site are poorly understood. Here we make use of 10 years of snow pit and short core δ18O data and hourly snow‐height measurements obtained by an automated weather station deployed at the ice cap's summit to analyze linkages between snowfall, δ18O, and the South American summer monsoon (SASM). Snow accumulation peaks in December and is negative May–September. Snow δ18O values decrease gradually through austral summer from about −17 to −24‰. Surface snow δ18O is altered after deposition during austral winter from about −24 to −15‰. More than 70% of the total snow accumulation is tied to convection along the leading edge of cold air incursions of midlatitude air advected equatorward from southern South America. Snowfall amplitude at Quelccaya Ice Cap varies systematically with regional precipitation, atmospheric dynamics, midtroposphere humidity, and water vapor δD. Strongest snowfall gains correspond with positive precipitation anomalies over the western Amazon Basin, increased humidity, and lowered water vapor δD values, consistent with the “amount effect.” We discuss ventilation of the monsoon, modulated by midlatitude cold air advection, as potentially diagnostic of the relationship between SASM dynamics and Quelccaya snowfall. Results will serve as a basis for development of a comprehensive isotopic forward model to reconstruct past monsoon dynamics using the ice core δ18O record.
Vibrational‐vibrational and vibrational‐thermal energy transfers of CO2 with N2 from MIPAS high‐resolution limb spectra
Authors: Jurado‐Navarro Á. A. , López‐Puertas M. , Funke B. , García‐Comas M. , Gardini A. , Stiller G. P. , Clarmann T. von 
Published: July 2015

AbstractWe present a retrieval of several vibrational‐vibrational (V V) and vibrational‐thermal (V‐T) collisional rate coefficients affecting the populations of the CO2 levels emitting at 10, 4.3 and 2.7 μm from high‐resolution limb atmospheric spectra taken by Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). This instrument has a high spectral resolution (0.0625 cm−1) and a wide spectral coverage (from 685 to 2410 cm−1) that allow measuring and discriminating among the many bands originating the atmospheric 4.3 μm radiance. Also its high sensitivity allows measuring the atmospheric limb emission in a wide altitude range, from 20 to 170 km in its middle and upper atmosphere modes, and hence obtain information on the temperature dependence of the collisional rates. In particular, we retrieve the rate coefficients and their temperature dependence in the 130–250 K range of the following processes: with vd=2v1+v2=2,3, and 4; with and Δl = 0; and with Δvd=0 and Δl ≠ 0. In addition we have also retrieved the thermal relaxation of CO2(v3) into the v1 and v2 modes, e.g., with Δvd=2–4 and Δv3=−1 and the efficiency of the excitation of N2(1) by O(1D). All of them were retrieved with a much better accuracy than were known before. The new rates have very important effects on the atmospheric limb radiance in the 10, 4.3 and 2.7 μm spectral regions (5–8% at 4.3 μm) and allow a more accurate inversion of the CO2 volume mixing ratio in the mesosphere and lower thermosphere from measurements taken in those spectral regions.
Reconstructing a sediment pulse: Modeling the effect of placer mining on Fraser River, Canada
Authors: Ferguson R. I. , Church M. , Rennie C. D. , Venditti J. G. 
Published: July 2015

AbstractGold mining along 525 km of the Fraser River between 1858 and 1909 added an estimated 1.1 × 108 t of tailings, half gravel and the rest finer, to the river's natural sediment load. We simulate the response using a 1‐D multigrain size morphodynamic model. Since premining conditions are unknown and modern data are insufficient for tuning the process representation, we devised a novel modeling strategy which may be useful in other data‐poor applications. We start the model from a smoothed version of the modern longitudinal profile with bed grain size distributions optimized to match alternative assumptions about natural sediment supply and compare runs that include mining with control runs that can be used to quantify the effects of deficiencies in process representation and initialization. Simulations with an appropriate choice of natural supply rate closely match the best available test data, which consist of a detailed 1952–1999 gravel budget for the distal part of the model domain. The simulations suggest that the main response to mining was rapid bed fining, which allowed a major increase in bed load transport rate with only slight (~0.1 m) mean aggradation within the mining region and most of the excess sediment exported well beyond the mountain front within the mining period or soon afterward. We compare this pattern of response by a large, powerful river with previous case studies of river adjustment to sediment supply change.
Variability of rock erodibility in bedrock‐floored stream channels based on abrasion mill experiments
Authors: Small Eric E. , Blom Tevis , Hancock Gregory S. , Hynek Brian M. , Wobus Cameron W. 
Published: July 2015

AbstractWe quantify variations in rock erodibility, Kr, within channel cross sections using laboratory abrasion mill experiments on bedrock surfaces extracted from streams with sandstone bedrock in Utah and basaltic bedrock in the Hawaiian Islands. Samples were taken from the thalweg and channel margins, the latter at a height that is inundated annually. For each sample, a sequence of abrasion mill experiments was completed to quantify variations in erosion rate with erosion depth. Erosion rate data from these experiments shows two things. First, the erosion rate from channel margin samples is greater than for thalweg samples, with the greatest difference observed for the rock surface that was exposed in the stream channel. Second, erosion rate decreases with depth beneath the original rock surface, by an order of magnitude in most cases. The erosion rate becomes steady at depths of 1–3 mm for channel margin samples and 0.1–0.4 mm for thalweg samples. Because only rock properties and microtopography vary throughout the sequence of mill experiments, these results suggest that Kr of the bedrock surface exposed in stream channels is higher at the margins than near the channel center and that Kr decreases over depths of ~1 mm. The simplest explanation for these patterns is that Kr is enhanced, at the bedrock surface and along the channel margins, due to the effects of weathering on rock strength and surface roughness. We hypothesize that a balance exists between weathering‐enhanced erodibility and episodic incision to allow channel margins to lower at rates similar to the thalweg.
The relative influence of land cover, hydrology, and in‐stream processing on the composition of dissolved organic matter in boreal streams
Authors: Kothawala Dolly N. , Ji Xing , Laudon Hjalmar , Ågren Anneli M. , Futter Martyn N. , Köhler Stephan J. , Tranvik Lars J. 
Published: July 2015

AbstractLow‐order boreal streams are particularly sensitive interfaces where dissolved organic matter (DOM) is transported from soils to inland waters. Disentangling the relative influence of key environmental factors suspected to influence stream water DOM composition is highly relevant to predicting the reactivity and fate of terrestrial DOM entering inland waters. Here we examined changes to DOM composition using absorbance and fluorescence, from 17 boreal streams ranging from first to fourth orders, over 14 months, including the rarely studied winter season, and two snowmelt periods (n = 836). We also analyzed soil pore water samples from three forest soil lysimeters to a depth of 70 cm (n = 60). Of five identified fluorescing parallel factor analysis components, two (C4 and C5) expressed a clear mire wetland or forest signature, providing distinct molecular markers of dominant land cover. In fact, land cover alone explained 49% of the variability in DOM composition. In contrast, seasonal fluctuations in hydrology only contributed to minor shifts (8%) in the composition of stream water DOM, while in‐stream transformations to DOM composition were undetectable. These findings suggest that low‐order boreal streams act as a passive pipe, since in‐stream processing of DOM is restricted by short water residence times (6 h to 2 days). In addition, we demonstrated the sensitivity of optical approaches to distinguish between key terrestrial sources of DOM in the boreal landscape. By distinguishing the proportional leverage of key environmental controls on headwater stream DOM composition, we are better equipped to predict where and when key DOM transformations occur in the aquatic conduit.
Riparian vegetation, Colorado River, and climate: Five decades of spatiotemporal dynamics in the Grand Canyon with river regulation
Authors: Sankey Joel B. , Ralston Barbara E. , Grams Paul E. , Schmidt John C. , Cagney Laura E. 
Published: July 2015

AbstractDocumentation of the interacting effects of river regulation and climate on riparian vegetation has typically been limited to small segments of rivers or focused on individual plant species. We examine spatiotemporal variability in riparian vegetation for the Colorado River in Grand Canyon relative to river regulation and climate, over the five decades since completion of the upstream Glen Canyon Dam in 1963. Long‐term changes along this highly modified, large segment of the river provide insights for management of similar riparian ecosystems around the world. We analyze vegetation extent based on maps and imagery from eight dates between 1965 and 2009, coupled with the instantaneous hydrograph for the entire period. Analysis confirms a net increase in vegetated area since completion of the dam. Magnitude and timing of such vegetation changes are river stage‐dependent. Vegetation expansion is coincident with inundation frequency changes and is unlikely to occur for time periods when inundation frequency exceeds approximately 5%. Vegetation expansion at lower zones of the riparian area is greater during the periods with lower peak and higher base flows, while vegetation at higher zones couples with precipitation patterns and decreases during drought. Short pulses of high flow, such as the controlled floods of the Colorado River in 1996, 2004, and 2008, do not keep vegetation from expanding onto bare sand habitat. Management intended to promote resilience of riparian vegetation must contend with communities that are sensitive to the interacting effects of altered flood regimes and water availability from river and precipitation.
An overview of recent (1988 to 2014) caldera unrest: Knowledge and perspectives
Authors: Acocella V. , Di Lorenzo R. , Newhall C. , Scandone R. 
Published: July 2015

AbstractCalderas are among the most active and dangerous volcanoes. Caldera unrest is defined by enhanced seismicity, gravity changes, surface deformation, and degassing. Although much caldera unrest does not lead to an eruption, every eruption is preceded by an unrest episode. Therefore, the proper description of unrest and the forecast of its possible outcome is a timely and challenging task. Here we review the best known unrest at calderas from 1988 to 2014, building on previous work and proposing an updated database. Where established, the root cause for unrest is always magmatic; none was purely hydrothermal or tectonic. An interpretive classification of unrest invokes two spectra—compositional (mafic to felsic) and the state of magma conduits feeding from the magma reservoir(s) to the surface (from fully plugged, through semiplugged, to open). Magma and gas in open conduits can rise and erupt freely; magma in semiplugged conduits erupts less frequently yet still allows some gas to escape; plugged conduits allow neither magma nor gas to escape. Unrest in mafic calderas is subtler, less pronounced, and repeated, especially with open systems, ensuring the continuous, aseismic, and moderate release of magma. Plugged felsic calderas erupt infrequently, anticipated by isolated, short and seismically active unrest. Semiplugged felsic calderas also erupt infrequently and are restless over decades or centuries, with uplift, seismicity, and degassing and, on the longer‐term, resurgence, suggesting repeated stalled intrusions. Finally, the expected advances in better understanding caldera unrest are discussed.