bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Impact of Aquifer Flushing on Groundwater Arsenic Across a 35‐km Transect Perpendicular to the Upper Brahmaputra River in Assam, India
Authors: Choudhury R. , Nath B. , Khan M. R. , Mahanta C. , Ellis T. , van Geen A. 
Published: August 2018

AbstractWell testing in the floodplain of the Brahmaputra River in Golaghat and Jorhat districts of Assam, India, shows that groundwater arsenic (As) concentrations increase with distance from the river. To establish the origin of this pattern, an additional 900 wells <60‐m deep were tested for As and nine sites were drilled along a 35‐km transect perpendicular to the river. The field data show no relation between groundwater As concentrations ranging from <1 to 660 μg/L along the transect and (a) As concentrations of <1–5 mg/kg in cuttings of aquifer sand recovered while drilling or (b) the degree of reduction of iron oxides in these cuttings. The drilling indicates, however, a marked increase in the thickness of a clay layer capping the aquifer starting from <1–5 m near the river to over 60 m at the most distant site toward the base of the Naga foothills. Organic radiocarbon ages of 18–46 kyr obtained from all but one of 13 clay samples indicate pre‐Holocene deposition of the underlying sands across the entire transect. Radiocarbon ages of dissolved inorganic carbon of 0.2, 4.7, and 17.8 kyr were measured in groundwater from three monitoring wells installed to 30–60‐m depth at distances of 10, 20, and 40 km from the river, respectively. A conceptual groundwater flow model consistent with monitored heads and groundwater ages suggests that thick clay layers capping the aquifer further from the river inhibited flushing of the aquifer and, as a result, preserved higher As levels in groundwater.
Recent Acceleration of a Rock Glacier Complex, Ádjet, Norway, Documented by 62 Years of Remote Sensing Observations
Authors: Eriksen H. Ø. , Rouyet L. , Lauknes T. R. , Berthling I. , Isaksen K. , Hindberg H. , Larsen Y. , Corner G. D. 
Published: August 2018

AbstractRecent acceleration of rock glaciers is well recognized in the European Alps, but similar behavior is hardly documented elsewhere. Also, the controlling factors are not fully understood. Here we provide evidence for acceleration of a rock glacier complex in northern Norway, from 62 years of remote sensing data. Average annual horizontal velocity measured by aerial feature tracking increased from ~0.5 myr−1 (1954–1977) to ~3.6 myr−1 (2006–2014). Measured by satellite synthetic aperture radar offset‐tracking, averages increased from ~4.9 to ~9.8 myr−1 (2009–2016) and maximum velocities from ~12 to ~69 myr−1. Kinematic analysis reveals different spatial‐temporal trends in the upper and the lower parts of the rock glacier complex, suggesting progressive detachment of the faster front. We suggest that permafrost warming, topographic controls, and increased water access to deeper permafrost layers and internal shear zones can explain the kinematic behavior.
On the Limits of CALIOP for Constraining Modeled Free Tropospheric Aerosol
Authors: Watson‐Parris Duncan , Schutgens Nick , Winker David , Burton Sharon P. , Ferrare Richard A. , Stier Philip 
Published: August 2018

AbstractThe spaceborne Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument provides valuable information on the vertical distribution of global aerosol and is often used to evaluate vertical aerosol distributions in general circulation models (GCMs). Here we show, however, that the detection limit of the CALIOP retrievals mean background aerosol is not detected, leading to substantially skewed statistics that moreover differ significantly by product. In the CALIOP Level 2 product this missing low‐backscatter aerosol results in the retrieved aerosol distribution significantly overrepresenting aerosol backscatter and extinction in the middle and upper troposphere if taken to be representative of the undetected aerosol. The CALIOP Level 3 product assumes no aerosol where none is detected, which then leads to an underestimation in the aerosol extinction profile in the upper troposphere. Using the ECHAM‐HAM GCM, we estimate that the mean fraction of aerosol undetected by CALIOP daytime (nighttime) retrievals is 41% (44%) globally.
Dome Collapse Interaction With the Atmosphere
Authors: Barfucci G. , Ripepe M. 
Published: August 2018

AbstractDome collapse is a dramatic volcanic process, yet the dynamics and evolution of dome collapse still present open questions. Observational data are rare, and this limits our ability to interpret the evolution of this phenomenon in terms of risk assessment. We show how the partial dome collapse of Soufrière Hills Volcano on 2010 evolved in less than 45 min and was characterized by five main different episode of dome failure process. Time and amplitude of seismic and infrasonic records associated with successive pyroclastic density currents show a nearly quadratic temporal trend suggesting a self‐accelerating process increasing in intensity up to the failure limit. Each episode generated gravity waves in the atmosphere, representing the first evidence of internal waves formed due to propagation of density currents in stratified fluids. Finally, we use gravity waves to estimate the total erupted mass and the plume height of the Vulcanian explosions triggered by the decompression induced by the collapse.
Evidence for Predictive Skill of High‐Latitude Climate Due to Midsummer Sea Ice Extent Anomalies
Authors: He Shengping , Knudsen Erlend M. , Thompson David W. J. , Furevik Tore 
Published: August 2018

AbstractPrevious work has explored the linkages between Arctic sea ice extent (SIE) anomalies at the end of the summer melt season and high‐latitude climate. Here we show that Arctic midsummer SIE anomalies provide predictive skill on time scales of ~2–3 months for high‐latitude climate. Midsummers characterized by low SIE are associated with significant positive temperature and easterly wind anomalies throughout the high‐latitude troposphere through September and significant positive temperature anomalies at the Arctic surface into October. The inferred predictive skill for autumn climate derives from the persistence of the sea ice field. It is robust throughout the Arctic basin and is supported in climate models from the fifth phase of the Coupled Model Intercomparison Project archive and in prediction experiments from the Arctic Predictability and Prediction on Seasonal to Interannual Time scales project. It is theorized that the predictive skill derives from (1) the anomalous storage of heat in the Arctic Ocean during periods of low summertime SIE and (2) the delayed formation of sea ice during the following autumn months.
Electron Energization at a Reconnecting Magnetosheath Current Sheet
Authors: Eriksson Elin , Vaivads Andris , Graham Daniel B. , Divin Andrey , Khotyaintsev Yuri V. , Yordanova Emiliya , André Mats , Giles Barbara L. , Pollock Craig J. , Russell Christopher T. , Contel Olivier Le , Torbert Roy B. , Ergun Robert E. , Lindqvist Per‐Arne , Burch James L. 
Published: August 2018

AbstractWe present observations of electron energization within a sub‐ion‐scale magnetosheath current sheet (CS). A number of signatures indicate ongoing reconnection, including the thickness of the CS (∼0.7 ion inertial length), nonzero normal magnetic field, Hall magnetic fields with electrons carrying the Hall currents, and electron heating. We observe localized electron acceleration and heating parallel to the magnetic field at the edges of the CS. Electrostatic waves observed in these regions have low phase velocity and small wave potentials and thus cannot provide the observed acceleration and heating. Instead, we find that the electrons are accelerated by a parallel potential within the separatrix regions. Similar acceleration has been reported based on magnetopause and magnetotail observations. Thus, despite the different plasma conditions in magnetosheath, magnetopause, and magnetotail, the acceleration mechanism and corresponding heating of electrons is similar.
Impact of Short‐Term Climate Variability on Volatile Organic Compounds Emissions Assessed Using OMI Satellite Formaldehyde Observations
Authors: Stavrakou T. , Müller J.‐F. , Bauwens M. , De Smedt I. , Van Roozendael M. , Guenther A. 
Published: August 2018

AbstractA major feedback between climate and atmospheric chemistry lies in the meteorological dependence of the emissions of biogenic volatile organic compounds (BVOCs), precursors of important climate forcers, aerosols, and ozone. Whereas the short‐term response of BVOC emissions to meteorological drivers is fairly well simulated by current emission models, it is yet unclear whether models can faithfully predict their response to climate change, given the scarcity of long observation records of BVOC fluxes. Here we take advantage of the high yield of formaldehyde (HCHO) in the oxidation of VOCs and use a long‐term spaceborne record of HCHO observations in combination with model simulations to show that (i) HCHO interannual variability is primarily driven by climate through its impacts on photochemistry, vegetation fire occurrence, and above all, biogenic emissions and (ii) the HCHO record validates the interannual variability of biogenic emissions calculated by the state‐of‐the‐art Model of Emissions of Gases and Aerosols from Nature (MEGAN) emission model in vegetated regions.
Locally Enhanced Aerosols Over a Shipping Lane Produce Convective Invigoration but Weak Overall Indirect Effects in Cloud‐Resolving Simulations
Authors: Blossey Peter N. , Bretherton Christopher S. , Thornton Joel A. , Virts Katrina S. 
Published: August 2018

AbstractThe effect of aerosol emissions from an active shipping lane in the Indian Ocean is simulated using an idealized framework in a cloud‐resolving model. Increased aerosol concentrations over the modeled shipping lane lead to increased cloud droplet number, cloud liquid mass, ice hydrometeor mass, and simulated radar reflectivity. The invigoration of deep convection induces mesoscale uplift and increased precipitation over the shipping lane. A predicted increase in the prevalence of both strong updrafts and radar echoes aloft is suggestive of enhanced lightning activity over the shipping lane, as observed in a recent study. Cloud radiative effects, both shortwave and longwave, are intensified over the shipping lane, but the change in the net radiative flux at top of atmosphere is not significantly different from zero.
Distribution of Vapor and Condensate in a Hydrothermal System: Insights From Self‐Potential Inversion at Mount Tongariro, New Zealand
Authors: Miller C. A. , Kang S. G. , Fournier D. , Hill G. 
Published: August 2018

AbstractInversion of self‐potential data for source current density, js, in complex volcanic settings, yields hydrological information without the need for a prior groundwater flow model; js contains information about pH, pore saturation, and permeability, from which we infer the distribution of liquid and vapor phases. To understand the hydrothermal flow dynamics and hydraulic connectivity between surface thermal features at Mount Tongariro volcano, New Zealand, we undertook a reconnaissance scale self‐potential survey and developed an inversion routine for js, constrained by an existing 3‐D conductivity model from magnetotelluric measurements. The 3‐D distribution of js at Mount Tongariro reveals a discontinuous zero js zone interpreted as vapor or residually saturated pore space, surrounded by low to moderate js interpreted as circulating condensate liquid. Bounding faults act as conduits for down flowing groundwater or condensate, as well as barriers for the hydrothermal system. Localized small‐scale circulation associated with individual surface thermal features, rather than a single circulating system, accounts for the lack of widespread anomalous geochemical observations prior to the 2012 Te Maari eruption.
Global Freshwater Availability Below Normal Conditions and Population Impact Under 1.5 and 2 °C Stabilization Scenarios
Authors: Liu Wenbin , Lim Wee Ho , Sun Fubao , Mitchell Dann , Wang Hong , Chen Deliang , Bethke Ingo , Shiogama Hideo , Fischer Erich 
Published: August 2018

AbstractBased on the large ensembles of the half a degree additional warming, prognosis, and projected impacts historical, +1.5 and +2 °C experiments, we quantify changes in the magnitude of water availability (i.e., precipitation minus actual evapotranspiration; a function of monthly precipitation flux, latent heat flux, and surface air temperature) below normal conditions (less than median, e.g., 20th percentile water availability). We found that, relative to the historical experiment, water availability below normal conditions of the +1.5 and +2 °C experiments would decrease in the midlatitudes and the tropics, indicating that hydrological drought is likely to increase in warmer worlds. These cause more (less) people in East Asia, Central Europe, South Asia, and Southeast Asia (West Africa and Alaska/Northwest Canada) to be exposed to water shortage. Stabilizing warming at 1.5 °C instead of 2 °C would limit population impact in most of the regions, less effective in Alaska/Northwest Canada, Southeast Asia, and Amazon. Globally, this reduced population impact is ~117 million people.
Controls on Open‐Ocean North Atlantic ΔpCO2 at Seasonal and Interannual Time Scales Are Different
Authors: Henson Stephanie A. , Humphreys Matthew P. , Land Peter E. , Shutler Jamie D. , Goddijn‐Murphy Lonneke , Warren Mark 
Published: August 2018

AbstractThe North Atlantic is a substantial sink for anthropogenic CO2. Understanding the mechanisms driving the sink's variability is key to assessing its current state and predicting its potential response to global climate change. Here we apply a time series decomposition technique to satellite and in situ data to examine separately the factors (both biological and nonbiological) that affect the sea‐air CO2 difference (ΔpCO2) on seasonal and interannual time scales. We demonstrate that on seasonal time scales, the subpolar North Atlantic ΔpCO2 signal is predominantly correlated with biological processes, whereas seawater temperature dominates in the subtropics. However, the same factors do not necessarily control ΔpCO2 on interannual time scales. Our results imply that the mechanisms driving seasonal variability in ΔpCO2 cannot necessarily be extrapolated to predict how ΔpCO2, and thus the North Atlantic CO2 sink, may respond to increases in anthropogenic CO2 over longer time scales.
New High‐Pressure Forms of Al2SiO5
Authors: Zhou Y. , Irifune T. , Ohfuji H. , Kuribayashi T. 
Published: August 2018

AbstractPhase relations of Al2SiO5 have been studied by multianvil experiments at pressures of 13–23 GPa and temperatures of 2000–2900 K. Al2SiO5 kyanite was found to transform into two new high‐pressure forms of Al2SiO5 (kyanite II and III) at temperatures exceeding 2300–2500 K and pressures of 14–23 GPa: The first phase transition occurs near 14 GPa, and the second occurs near 17 GPa. The new Al2SiO5 phases have triclinic and monoclinic crystal symmetries with zero‐pressure densities of 3.876(2) and 3.982(1) g/cm3, respectively, which are significantly denser than kyanite (ρ0 = 3.666 g/cm3) but less dense than the isochemical mixture of Al2O3 corundum and SiO2 stishovite (ρ0 = 4.036 g/cm3). The exceptionally high stability temperatures of the new Al2SiO5 phases suggest that they are unlikely to form in the present mantle but may be found in some impact craters and shocked meteorites and act as important indicators of pressure and temperature for the shock events.
Two‐Dimensional Particle‐in‐Cell Simulation of Magnetosonic Wave Excitation in a Dipole Magnetic Field
Authors: Chen Lunjin , Sun Jicheng , Lu Quanming , Wang Xueyi , Gao Xinliang , Wang Dedong , Wang Shui 
Published: August 2018

AbstractThe excitation of magnetosonic waves in the meridian plane of a rescaled dipole magnetic field is investigated, for the first time, using a general curvilinear particle‐in‐cell simulation. Our simulation demonstrates that the magnetosonic waves are excited near the equatorial plane by tenuous ring distribution protons. The waves propagate nearly perpendicularly to the background magnetic field along both radially inward and outward directions. Different speeds of inward and outward propagation result in the asymmetrical distribution about the source region. The waves are accompanied by energization of both cool protons and electrons near the wave source region. The cool protons are heated perpendicularly, while the cool electrons can be heated in the parallel direction and also experience enhanced perpendicular drift at the presence of intense wave power. The implications of simulation results to the observations of magnetosonic waves and related particle heating in the inner magnetosphere are also discussed.
Generation of Lower Harmonic Magnetosonic Waves Through Nonlinear Wave‐Wave Interactions
Authors: Gao Xinliang , Sun Jicheng , Lu Quanming , Chen Lunjin , Wang Shui 
Published: August 2018

AbstractAlthough magnetosonic waves in the Earth's magnetosphere have been well understood by the linear theory, low harmonic magnetosonic waves, which often lack of free energy, can be unusually present. By employing a 1‐D particle‐in‐cell simulation model, we have investigated the generation of those unusual lower harmonic magnetosonic waves in a plasma containing a proton ring distribution. In our simulation, the higher harmonic magnetosonic waves (from~9Ωh to ~12Ωh) are firstly excited due to the unstable proton ring, which can be well explained by the linear theory. Several lower harmonic magnetosonic waves (below 5Ωh), which well separates away from the higher harmonics, soon appear in the system. Those lower harmonics, which do not have any positive linear growth rates, can be generated by a nonlinear mechanism. The bicoherence analysis demonstrates that there is a strong phase coupling among the unusual lower harmonic magnetosonic waves and the magnetosonic waves generated due to the proton ring, supporting the idea that the lower harmonic waves could be driven by the wave‐wave couplings of the generated magnetosonic waves. This wave‐wave coupling generation mechanism is further confirmed by another two simulations, where two or three pump magnetosonic waves are initially injected. The lower‐frequency waves, that is, the fundamental wave and its second harmonic, are also successfully reproduced due to the nonlinear coupling of pump magnetosonic waves. Our simulations not only propose a potential generation mechanism of unusual lower harmonic magnetosonic waves in the Earth's magnetosphere, but also give some new insights on the evolution of magnetosonic spectra.
Observations and Impacts of the 10 September 2017 Solar Events at Mars: An Overview and Synthesis of the Initial Results
Authors: Lee C. O. , Jakosky B. M. , Luhmann J. G. , Brain D. A. , Mays M. L. , Hassler D. M. , Holmström M. , Larson D. E. , Mitchell D. L. , Mazelle C. , Halekas J. S. 
Published: August 2018

AbstractOn 10 September 2017, some of the strongest solar activity occurred in association with active region 12673 (AR2673), including an X‐class solar flare and a fast coronal mass ejection. Although AR2673 was not centrally facing Mars, the activity impacted the local space weather conditions at Mars. We give an overview of observations obtained from the Mars Atmosphere and Volatile EvolutioN, Mars Science Laboratory, and Mars Express missions. Numerical results from the Wang‐Sheeley‐Arge (WSA)‐Enlil‐cone model together with Earth/L1 and STEREO‐A observations are also presented to provide some heliospheric context. We discuss the initial results on the space weather impacts at Mars, which include heating of the upper atmosphere by solar flare emissions, flare‐related enhancements of ion and neutral densities, solar energetic particles impacting the atmosphere and surface, bright emissions of a diffuse (global) aurora, deeply penetrating interplanetary magnetic fields over the Martian dayside, and enhanced atmospheric escape rates.
Impact of Aerosol‐PBL Interaction on Haze Pollution: Multiyear Observational Evidences in North China
Authors: Huang Xin , Wang Zilin , Ding Aijun 
Published: August 2018

AbstractAtmospheric aerosols have been found to influence the development of planetary boundary layer (PBL) and hence to enhance haze pollution in megacities. Previous works on aerosol‐PBL interaction were mainly based on model simulation for short‐term cases; so far, there is a lack of long‐term observational evidences. In this study, based on multiyear measurements and reanalysis meteorological data, we give observational evidences on aerosol‐PBL interaction and its impact on pollution aggravation. We found a significant heating in upper PBL with maximum temperature change about 0.7 °C on average and a substantial dimming near surface with a mean temperature drop of −2.2 °C under polluted condition. By integrating Eulerian forward simulation and Lagrangian backward trajectory calculation, we demonstrated that the atmospheric heating was mainly induced by light‐absorbing aerosols like black carbon. Then an index representing such effect was proposed, which could well characterize aerosol‐PBL interaction and its impact on air pollution.
Basal Melt and Freezing Rates From First Noble Gas Samples Beneath an Ice Shelf
Authors: Huhn Oliver , Hattermann Tore , Davis Peter E. D. , Dunker Erich , Hellmer Hartmut H. , Nicholls Keith W. , Østerhus Svein , Rhein Monika , Schröder Michael , Sültenfuß Jürgen 
Published: August 2018

AbstractA climatically induced acceleration in ocean‐driven melting of Antarctic ice shelves would have consequences for both the discharge of continental ice into the ocean and thus global sea level, and for the formation of Antarctic Bottom Water and the oceanic meridional overturning circulation. Using a novel gas‐tight in situ water sampler, noble gas samples have been collected from six locations beneath the Filchner Ice Shelf, the first such samples from beneath an Antarctic ice shelf. Helium and neon are uniquely suited as tracers of glacial meltwater in the ocean. Basal meltwater fractions range from 3.6% near the ice shelf base to 0.5% near the sea floor, with distinct regional differences. We estimate an average basal melt rate for the Filchner‐Ronne Ice Shelf of 177 ± 95 Gt/year, independently confirming previous results. We calculate that up to 2.7% of the meltwater has been refrozen, and we identify a local source of crustal helium.