bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐Pressure Geophysical Properties of Fcc Phase FeHX
Authors: Thompson E. C. , Davis A. H. , Bi W. , Zhao J. , Alp E. E. , Zhang D. , Greenberg E. , Prakapenka V. B. , Campbell A. J.
Published: January 2018

Face centered cubic (fcc) FeHX was synthesized at pressures of 18–68 GPa and temperatures exceeding 1,500 K. Thermally quenched samples were evaluated using synchrotron X‐ray diffraction (XRD) and nuclear resonant inelastic X‐ray scattering (NRIXS) to determine sample composition and sound velocities to 82 GPa. To aid in the interpretation of nonideal (X ≠ 1) stoichiometries, two equations of state for fcc FeHX were developed, combining an empirical equation of state for iron with two distinct synthetic compression curves for interstitial hydrogen. Matching the density deficit of the Earth's core using these equations of state requires 0.8–1.1 wt % hydrogen at the core‐mantle boundary and 0.2–0.3 wt % hydrogen at the interface of the inner and outer cores. Furthermore, a comparison of Preliminary Reference Earth Model (PREM) to a Birch's law extrapolation of our experimental results suggests that an iron alloy containing ∼0.8–1.3 wt % hydrogen could reproduce both the density and compressional velocity (VP) of the Earth's outer core.
Zircon (U‐Th)/He Thermochronometric Constraints on Himalayan Thrust Belt Exhumation, Bedrock Weathering, and Cenozoic Seawater Chemistry
Authors: Colleps Cody L. , McKenzie N. Ryan , Stockli Daniel F. , Hughes Nigel C. , Singh Birendra P. , Webb A. Alexander G. , Myrow Paul M. , Planavsky Noah J. , Horton Brian K.
Published: January 2018

Shifts in global seawater 187Os/188Os and 87Sr/86Sr are often utilized as proxies to track global weathering processes responsible for CO2 fluctuations in Earth history, particularly climatic cooling during the Cenozoic. It has been proposed, however, that these isotopic records instead reflect the weathering of chemically distinctive Himalayan lithologies exposed at the surface. We present new zircon (U‐Th)/He thermochronometric and detrital zircon U‐Pb geochronologic evidence from the Himalaya of northwest India to explore these contrasting interpretations concerning the driving mechanisms responsible for these seawater records. Our data demonstrate in‐sequence southward thrust propagation with rapid exhumation of Lesser Himalayan strata enriched in labile 187Os and relatively less in radiogenic 87Sr at ∼16 Ma, which directly corresponds with coeval shifts in seawater 187Os/188Os and 87Sr/86Sr. Results presented here provide substantial evidence that the onset of exhumation of 187Os‐enriched Lesser Himalayan strata could have significantly impacted the marine 187Os/188Os record at 16 Ma. These results support the hypothesis that regional weathering of isotopically unique source rocks can drive seawater records independently from shifts in global‐scale weathering rates, hindering the utility of these records as reliable proxies to track global weathering processes and climate in deep geologic time.
Dynamical and Thermodynamic Elements of Modeled Climate Change at the East African Margin of Convection
Authors: Giannini Alessandra , Lyon Bradfield , Seager Richard , Vigaud Nicolas
Published: January 2018

We propose a dynamical interpretation of model projections for an end‐of‐century wetting in equatorial East Africa. In the current generation of global climate models, increased atmospheric moisture content associated with warming is not the dominant process explaining the increase in rainfall, as the regional circulation is only weakly convergent even during the rainy seasons. Instead, projected wetter future conditions are generally consistent with the El Niño‐like trend in tropical Pacific sea surface temperatures in climate models. In addition, a weakening in moisture convergence over the adjacent Congo Basin and Maritime Continent cores of convection results in the weakening of near‐surface winds, which increases moisture advection from the Congo Basin core toward the East African margin. Overall confidence in the projections is limited by the significant biases in simulation of the regional climatology and disagreement between observed and modeled tropical Pacific sea surface temperature trends to date.
First Observation of Lion Roar Emission in Saturn's Magnetosheath
Authors: Píša D. , Sulaiman A. H. , Santolík O. , Hospodarsky G. B. , Kurth W. S. , Gurnett D. A.
Published: January 2018

We present an observation of intense emissions in Saturn's magnetosheath as detected by the Cassini spacecraft. The emissions are observed in the dawn sector (magnetic local time ∼06:45) of the magnetosheath over a time period of 11 h before the spacecraft crossed the bow shock and entered the unshocked solar wind. They are found to be narrow‐banded with a peak frequency of about 0.16 fce, where fce is the local electron gyrofrequency. Using plane wave propagation analysis, we show that the waves are right hand circularly polarized in the spacecraft frame and propagate at small wave normal angles (<10∘) with respect to the ambient magnetic field. Electromagnetic waves with the same properties known as “lion roars” have been reported by numerous missions in the terrestrial magnetosheath. Here we show the first evidence such emission outside the terrestrial environment. Our observations suggest that lion roars are a solar‐system‐wide phenomenon and capable of existing in a broad range of parameter space. This also includes 1 order of magnitude difference in frequencies. We anticipate our result to provide new insight into such emissions in a new parameter regime characterized by a higher plasma beta (owing to the substantially higher Mach number bow shock) compared to Earth.
Inferring Fault Frictional and Reservoir Hydraulic Properties From Injection‐Induced Seismicity
Authors: Jagalur‐Mohan Jayanth , Jha Birendra , Wang Zheng , Juanes Ruben , Marzouk Youssef
Published: January 2018

Characterizing the rheological properties of faults and the evolution of fault friction during seismic slip are fundamental problems in geology and seismology. Recent increases in the frequency of induced earthquakes have intensified the need for robust methods to estimate fault properties. Here we present a novel approach for estimation of aquifer and fault properties, which combines coupled multiphysics simulation of injection‐induced seismicity with adaptive surrogate‐based Bayesian inversion. In a synthetic 2‐D model, we use aquifer pressure, ground displacements, and fault slip measurements during fluid injection to estimate the dynamic fault friction, the critical slip distance, and the aquifer permeability. Our forward model allows us to observe nonmonotonic evolutions of shear traction and slip on the fault resulting from the interplay of several physical mechanisms, including injection‐induced aquifer expansion, stress transfer along the fault, and slip‐induced stress relaxation. This interplay provides the basis for a successful joint inversion of induced seismicity, yielding well‐informed Bayesian posterior distributions of dynamic friction and critical slip. We uncover an inverse relationship between dynamic friction and critical slip distance, which is in agreement with the small dynamic friction and large critical slip reported during seismicity on mature faults.
Plant Wax n‐Alkane and n‐Alkanoic Acid Signatures Overprinted by Microbial Contributions and Old Carbon in Meromictic Lake Sediments
Authors: Makou Matthew , Eglinton Timothy , McIntyre Cameron , Montluçon Daniel , Antheaume Ingrid , Grossi Vincent
Published: January 2018

Specific n‐alkanes and n‐alkanoic acids are commonly used as biomarkers in paleoenvironmental reconstruction, yet any individual homologue may originate from multiple biological sources. Here we improve source and age controls for these compounds in meromictic systems by measuring the radiocarbon (14C) ages of specific homologues preserved in twentieth century Lake Pavin (France) sediments. In contrast to many studies, 14C ages generally decreased with increasing carbon chain length, from 7.3 to 2.6 ka for the C14‐C30 n‐alkanoic acids and from 9.2 to 0.3 ka for the C21‐C33 n‐alkanes. Given a known hard water effect, these values suggest that aquatic microbial sources predominate and contributed to most of the homologues measured. Only the longest chain n‐alkanes exclusively represent inputs of higher plant waxes, which were previously sequestered in soils over centennial to millennial timescales prior to transport and deposition. These findings suggest that biomarker source and age should be carefully established for lacustrine settings.
Distinguishing Subauroral Ion Drifts From Birkeland Current Boundary Flows
Authors: Archer W. E. , Knudsen D. J.
Published: January 2018

The Swarm satellites regularly observe latitudinally narrow ion velocity jets exceeding 1 km/s relative to the surrounding plasma at high latitude. Two distinct categories of duskward directed flow channels are observed. The most common are situated between the Region 1 and Region 2 currents, are observed primarily during quiet geomagnetic conditions, and are called Birkeland current boundary flows. During active conditions, a second type of duskward directed ion velocity jet is observed at the equatorward edge of the Region 2 currents, colocated with a sharp poleward directed plasma density gradient, consistent with subauroral ion drifts. Pedersen current and electric field estimates from the Swarm satellites show both types of flow channel to be associated with low height‐integrated Pedersen conductivity relative to the surrounding plasma. In this study we show two cases in which the Swarm satellites passed through both types of event on the same orbit, as well as the average ion velocity, field‐aligned current, and plasma density surrounding 57 of these events. Some field‐aligned current morphologies previously associated with subauroral ion drifts suggest that they may have instead been Birkeland current boundary flows. In this study we provide a comparative description of both phenomena to facilitate their distinction in future studies.
Effects of High‐Latitude Forcing Uncertainty on the Low‐Latitude and Midlatitude Ionosphere
Authors: Pedatella N. M. , Lu G. , Richmond A. D.
Published: January 2018

Ensemble simulations are performed using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) in order to understand the role of high‐latitude forcing uncertainty on the low‐latitude and midlatitude ionosphere response to the April 2010 geomagnetic storm. The ensemble is generated by perturbing either the high‐latitude electric potential or auroral energy flux in the assimilative mapping for ionosphere electrodynamics (AMIE). Simulations with perturbed high‐latitude electric potential result in substantial intraensemble variability in the low‐latitude and midlatitude ionosphere response to the geomagnetic storm, and the ensemble standard deviation for the change in NmF2 reaches 50–100% of the mean change. Such large intraensemble variability is not seen when perturbing the auroral energy flux. In this case, the effects of the forcing uncertainty are primarily confined to high latitudes. We therefore conclude that the specification of high‐latitude electric fields is an important source of uncertainty when modeling the low‐latitude and midlatitude ionosphere response to a geomagnetic storm. A multiple linear regression analysis of the results indicates that uncertainty in the storm time changes in the equatorial electric fields, neutral winds, and neutral composition can all contribute to the uncertainty in the ionosphere electron density. The results of the present study provide insight into the possible uncertainty in simulations of the low‐latitude and midlatitude ionosphere response to geomagnetic storms due to imperfect knowledge of the high‐latitude forcing.
Exploring Wave‐Wave Interactions in a General Circulation Model
Authors: Nystrom Virginia , Gasperini Federico , Forbes Jeffrey M. , Hagan Maura E.
Published: January 2018

Nonlinear interactions involving Kelvin waves with (periods, zonal wave numbers) = (3.7d, s =− 1) (UFKW1) and = (2.4d, s =− 1) (UFKW2) and s = 0 and s = 1 quasi 9 day waves (Q9DW) with diurnal tides DW1, DW2, DW3, DE2, and DE3 are explored within a National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM) simulation driven at its ∼30 km lower boundary by interpolated 3‐hourly output from Modern‐Era Retrospective Analysis for Research and Applications (MERRA). The existence of nonlinear wave‐wave interactions between the above primary waves is determined by the presence of secondary waves (SWs) with frequencies and zonal wave numbers that are the sums and differences of those of the primary (interacting) waves. Focus is on 10–21 April 2009, when the nontidal dynamics in the mesosphere‐lower thermosphere (MLT) region is dominated by UFKW and when identification of SW is robust. Fifteen SWs are identified in all. An interesting triad is identified involving UFKW1, DE3, and a secondary UFKW4 = (1.5d, s =− 2): The UFKW1‐DE3 interaction produces UFKW4, the UFKW4‐DE3 interaction produces UFKW1, and the UFKW1 interaction with UFKW4 produces DE3. At 120 km the dynamic range of the reconstructed latitude‐longitude zonal wind field due to all of the SW is roughly half that of the primary waves, which produced them. This suggests that nonlinear wave‐wave interactions could significantly modify the way that the lower atmosphere couples with the ionosphere.
Resolving Horizontal Rupture Directivity of Moderate Crustal Earthquake in Sparse Network With Ambient Noise Location
Authors: He X. , Ni S.
Published: January 2018

Earthquake rupture directivity can remove fault plane ambiguity in earthquake moment tensor solutions; thus, it is helpful to improve reliability of shake map and understanding the seismogenic processes. In this paper, we propose an algorithm to resolve the horizontal rupture directivity of moderate crustal earthquakes in two steps. The first step is to determine the two candidate fault planes from focal mechanism inversion. Then, rupture directivity is estimated via the difference between the hypocenter and the centroid location which is constrained on the candidate fault planes. Accurate centroid location is determined with ambient noise location method, in which the noise cross‐correlation functions (NCFs) provide a stable calibration for the path effects. This technique is applied to the 2011 Oklahoma earthquake, and the estimated centroid location is about 2–4 km southwest to the hypocenter, indicating that the mainshock ruptured along the 234° plane for about 4–8 km. The result is consistent with directivity estimation using a foreshock as reference event and also agrees with early aftershock distribution as well as finite fault inversion. More applications to the 2004 Parkfield earthquake and the 2014 Napa earthquake are performed to explore the effectiveness and limitation of this method. This method is helpful for determining rupture directivity of earthquakes in sparse network but requiring one or two nearby stations. Alternatively, temporary stations can be installed in the area of high seismic hazard, then a library of NCFs and path calibrations would be available for rapidly determining rupture directivity of future earthquakes.
Magma Mixing in a Granite and Related Rock Association: Insight From Its Mineralogical, Petrochemical, and “Reversed Isotope” Features
Authors: Jiang Ding‐Sheng , Xu Xi‐Sheng , Xia Yan , Erdmann Saskia
Published: January 2018

Magma mixing commonly takes place between isotopically depleted mafic and enriched felsic magmas. Here we present isotopic evidence exhibiting the opposite behavior in the Early Cretaceous Siling complex (south China), which is composed of gabbro, quartz diorite, granodiorite, and alkali feldspar granite with locally many mafic microgranular enclaves. Field observations and zircon U‐Pb dating indicate that all of the rock units crystallized contemporaneously at ca. 127–129 Ma. Mineralogical and petrochemical analyses indicate that the Siling quartz diorite and granodiorite crystallized from hybrid magmas of temporally and spatially coexisting gabbroic and granitic melts. The Siling gabbro, characterized by variable yet enriched Sr‐Nd‐Hf isotopic compositions [(87Sr/86Sr)i = 0.70788 to 0.70833; ɛNd(t) = −7.6 to −3.5; ɛHf(t) = −6.8 to −1.9], exhibits Th/Nb, Nb/Nb*, and Sm/Yb versus εNd(t) correlations, indicating that the gabbro represents variable mixing of magmas derived from deep‐level pyroxenite and shallow‐level peridotite sources. The Siling alkali feldspar granite, which has typical A‐type characteristics, exhibits less enriched Sr‐Nd‐Hf isotopic signatures [(87Sr/86Sr)i = 0.70650; εNd(t) = −3.2 to −2.5; ɛHf(t) = −1.3] than the coexisting gabbro, indicating its derivation from the remelting of juvenile lower crust. “Reversed isotope” feature of the Siling gabbro and alkali feldspar granite means that the quartz diorite and granodiorite recorded “reversed isotope” mixing between isotopically enriched mafic and relatively depleted felsic magmas. The results indicate that the injection of mantle‐derived mafic magma does not necessarily imprint relatively depleted isotopic signatures on the host felsic melt and that the vertical growth of the continental crust by the input of isotopically enriched magma should be concerned.
Sediment Suspension by Straining‐Induced Convection at the Head of Salinity Intrusion
Authors: Zhang Qianjiang , Wu Jiaxue
Published: January 2018

The tidal straining can generate convective motions and exert a periodic modification of turbulence and sediment transport in estuarine and coastal bottom boundary layers. However, the evidence and physics of convection and sediment suspension induced by tidal straining have not been straightforward. To examine these questions, mooring and transect surveys have been conducted in September 2015 in the region of the Yangtze River plume influence. Field observations and scaling analyses indicate an occurrence of convective motions at the head of saline wedge. Theoretical analyses of stratification evolution in the saline wedge show that unstable stratification and resultant convection are induced by tidal straining. Vertical turbulent velocity and eddy viscosity at the head of saline wedge are both larger than their neutral counterparts in the main body, largely enhancing sediment suspension at the head of saline wedge. Moreover, sediment suspension in both neutral and convection‐affected flows is supported by the variance of vertical turbulent velocity, rather than the shearing stress. Finally, the stability correction functions in the Monin‐Obukhov similarity theory can be simply derived from the local turbulent kinetic energy balance to successfully describe the effects of tidal straining on turbulent length scale, eddy viscosity, and sediment diffusivity in the convection‐affected flow. These recognitions may provide novel understanding of estuarine turbidity maxima, and the dynamical structure and processes for coastal hypoxia.
Evaluation of Water Residence Time, Submarine Groundwater Discharge, and Maximum New Production Supported by Groundwater Borne Nutrients in a Coastal Upwelling Shelf System
Authors: Luo Xin , Jiao Jiu Jimmy , Liu Yi , Zhang Xiaolang , Liang Wenzhao , Tang Danling
Published: January 2018

The biogeochemical processes in the continental shelf systems are usually extensively influenced by coastal upwelling and submarine groundwater discharge (SGD). Using eastern Hainan upwelling shelf system as an example, this study fully investigates SGD and coastal upwelling and their effects on the coastal nutrient loadings to the mixing layer of eastern Hainan shelf. Based on the spatial distributions of 223Ra and 228Ra, water residence time is estimated to be 16.9 ± 8.9 days. Based on the mass balance models of 226Ra and 228Ra, the total SGD of the eastern Hainan shelf is estimated to be 0.8 × 108 and 1.4 × 108 m3 d−1, respectively. The groundwater borne dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) are estimated to be up to 1121.8 and 20.4 μM m2 d−1. The coastal upwelling delivers 2741.8 μM m2 d−1 DIN and 217.7 μM m2 d−1 DIP into the mixing layer, which are predominant in all the exogenous nutrient inputs. The groundwater borne DIN will support a maximum new production of 7.5 mM C m2 d−1, about up to 24.0% of the total new production in the study area. SGD‐derived nutrient could be significant as a missing DIN to support the new production in the mixing layer of eastern Hainan shelf. The findings contribute to a better understanding of biogeochemical processes under the influences of SGD and coastal upwelling in the study area and other similar coastal upwelling systems.
Variability of the Labrador Sea Surface Eddy Kinetic Energy Observed by Altimeter From 1993 to 2012
Authors: Zhang Weiwei , Yan Xiao‐Hai
Published: January 2018

A merged along track altimeter data set is used to study the variability of eddy kinetic energy (EKE) in the Labrador Sea from 1993 to 2012. The EKE near the west Greenland current (WGC) has strong interannual variability without long‐term trend from 1993 to 2012. The propagation direction of the Irminger Rings (IRs) originating from the WGC can be inferred from the EKE derived from altimeter, and the southward propagation of the IRs varies interannually. The central Labrador Sea EKE increases significantly from 1993 to 2012. The central Labrador Sea temperature difference between the end and the beginning of the winter convections is defined as restratification index to measure the restratification strengths. The relation between the central Labrador Sea EKE and the restratification index shows that the enhanced eddy activity originating from the west of the central Labrador Sea may cool the central Labrador Sea significantly. The interannual variability of the WGC EKE is likely to be driven by the large scale Subpolar Gyre (SPG) circulation variability and the North Atlantic Oscillation (NAO). The NAO also affects the central Labrador Sea EKE through its fingerprint in the local wind stress and surface heat flux. The NAO affects the WGC EKE by changing the SPG circulation strength, which will subsequently affect the WGC EKE through unknown physical processes.
Trends and Variability of Surface Solar Radiation in Europe Based On Surface‐ and Satellite‐Based Data Records
Authors: Pfeifroth Uwe , Sanchez‐Lorenzo Arturo , Manara Veronica , Trentmann Jörg , Hollmann Rainer
Published: January 2018

The incoming solar radiation is the essential climate variable that determines the Earth's energy cycle and climate. As long‐term high‐quality surface measurements of solar radiation are rare, satellite data are used to derive more information on its spatial pattern and its temporal variability. Recently, the EUMETSAT Satellite Application on Climate Monitoring (CM SAF) has published two satellite‐based climate data records: Surface Solar Radiation Data Set‐Heliosat, Edition 2 (SARAH‐2), and Clouds and Radiation Data Set based on AVHRR (advanced very high resolution radiometer) Satellite Measurements, Edition 2 (CLARA‐A2). Both data records provide estimates of surface solar radiation. In this study, these new climate data records are compared to surface measurements in Europe during the period 1983–2015. SARAH‐2 and CLARA‐A2 show a high accuracy compared to ground‐based observations (mean absolute deviations of 6.9 and 7.3 W/m2, respectively) highlighting a good agreement considering the temporal behavior and the spatial distribution. The results show an overall brightening period since the 1980s onward (comprised between 1.9 and 2.4 W/m2/decade), with substantial decadal and spatial variability. The strongest brightening is found in eastern Europe in spring. An exception is found for northern and southern Europe, where the trends shown by the station data are not completely reproduced by satellite data, especially in summer in southern Europe. We conclude that the major part of the observed trends in surface solar radiation in Europe is caused by changes in clouds and that remaining differences between the satellite‐ and the station‐based data might be connected to changes in the direct aerosol effect and in snow cover.
The Identification of Hail Storms in the Early Stage Using Time Series Analysis
Authors: Wang Ping , Shi Jinyu , Hou Jinyi , Hu Yan
Published: January 2018

This study investigates the characteristics of hail storms and cumulonimbus storms in China from 2005 to 2016. Ten features are proposed to identify storm cells that can produce hail, especially in the early stage of hail formation. These features describe hail storms based on three factors: the height and thickness of the cell core, the radar echo intensity, and the overhang structure and the horizontal reflectivity gradient. The 10 features are transformed into two‐dimensional comprehensive features by principal component analysis (PCA). The two comprehensive features are named the volume measurement comprehensive feature (VMCF) and the height‐gradient comprehensive feature (HGCF). Through an analysis of 49 hail cases and 35 heavy rainfall cases with S‐band radar data, the time series exhibit a distinct increase in VMCF or HGCF values in the early stage of a hail storm. However, the VMCF and HGCF values of heavy rainfall events remain relatively stable throughout the storm life cycle. An experiment involving real‐storm events, including 31 hail cases and 33 heavy rainfall cases, indicated that the probability of detection of hail storms was 93.33% and the false alarm ratio was 15.66%. In the cases that could be successfully identified as hail storms, 80.00% were detected within 18 min of reaching a hail storm reflectivity of 40 dBZ.
Generalized Dynamic Equations Related to Condensation and Freezing Processes
Authors: Wang Xingrong , Huang Yong
Published: January 2018

The generalized thermodynamic equation related to condensation and freezing processes was derived by introducing the condensation and freezing probability function into the dynamic framework based on the statistical thermodynamic fluctuation theory. As a result, the physical mechanism of some weather phenomena covered by using δ(0,1) can in turn be studied and uncovered. From the generalized dynamic equations, the tendency equation of the generalized potential vorticity (GPV) is derived. From the discussion of tendency equation of GPV, in some very thin transitional areas, GPV is found nonconserved because of the introduction of the condensation and freezing probability function, even in frictionless and moist adiabatic air motion.
On the Ability of Space‐Based Passive and Active Remote Sensing Observations of CO2 to Detect Flux Perturbations to the Carbon Cycle
Authors: Crowell Sean M. R. , Randolph Kawa S. , Browell Edward V. , Hammerling Dorit M. , Moore Berrien , Schaefer Kevin , Doney Scott C.
Published: January 2018

Space‐borne observations of CO2 are vital to gaining understanding of the carbon cycle in regions of the world that are difficult to measure directly, such as the tropical terrestrial biosphere, the high northern and southern latitudes, and in developing nations such as China. Measurements from passive instruments such as GOSAT and OCO‐2, however, are constrained by solar zenith angle limitations as well as sensitivity to the presence of clouds and aerosols. Active measurements such as those in development for the Active Sensing of CO2 Emissions over Nights, Days and Seasons (ASCENDS) mission show strong potential for making measurements in the high‐latitude winter and in cloudy regions. In this work we examine the enhanced flux constraint provided by the improved coverage from an active measurement such as ASCENDS. The simulation studies presented here show that with sufficient precision, ASCENDS will detect permafrost thaw and fossil fuel emissions shifts at annual and seasonal time scales, even in the presence of transport errors, representativeness errors, and biogenic flux errors. While OCO‐2 can detect some of these perturbations at the annual scale, the seasonal sampling provided by ASCENDS provides the stronger constraint.
Parameterization of In‐Cloud Aerosol Scavenging Due To Atmospheric Ionization: 2. Effects of Varying Particle Density
Authors: Zhang Liang , Tinsley Brian A.
Published: January 2018

Simulations and parameterization of collision rate coefficients for aerosol particles with 3 μm radius droplets have been extended to a range of particle densities up to 2,000 kg m−3 for midtropospheric (~5 km) conditions (540 hPa, −17°C). The increasing weight has no effect on collisions for particle radii less than 0.2 μm, but for greater radii the weight effect becomes significant and usually decreases the collision rate coefficient. When increasing size and density of particles make the fall speed of the particle relative to undisturbed air approach to that of the droplet, the effect of the particle falling away in the stagnation region ahead of the droplet becomes important, and the probability of frontside collisions can decrease to zero. Collisions on the rear side of the droplet can be enhanced as particle weight increases, and for this the weight effect tends to increase the rate coefficients. For charges on the droplet and for large particles with density ρ < 1,000 kg m−3 the predominant effect increases in rate coefficient due to the short‐range attractive image electric force. With density ρ above about 1,000 kg m−3, the stagnation region prevents particles moving close to the droplet and reduces the effect of these short‐range forces. Together with previous work, it is now possible to obtain collision rate coefficients for realistic combinations of droplet charge, particle charge, droplet radius, particle radius, particle density, and relative humidity in clouds. The parameterization allows rapid access to these values for use in cloud models.
Interannual and Diurnal Variability in Water Ice Clouds Observed from MSL Over Two Martian Years
Authors: Kloos J. L. , Moores J. E. , Whiteway J. A. , Aggarwal M.
Published: January 2018

We update the results of cloud imaging sequences from the Mars Science Laboratory (MSL) rover Curiosity to complete two Mars years of observations (LS=160° of Mars year (MY) 31 to LS=160° of MY 33). Relatively good seasonal coverage is achieved within the study period, with just over 500 observations obtained, averaging one observation every 2–3 sols. Cloud opacity measurements are made using differential photometry and a simplified radiative transfer method. These opacity measurements are used to assess the interannual variability of the aphelion cloud belt (ACB) for MY 32 and 33. Upon accounting for a statistical bias in the data set, the variation is found to be <30% within uncertainty. Diurnal variation of the ACB is also able to be examined in MY 33 owing to an increased number of early morning observations in this year. Although a gap in data around local noon prevents a complete assessment, we find that cloud opacity is moderately increased in the morning hours (07:00–09:00) compared to the late afternoon (15:00–17:00).
Venus Upper Clouds and the UV Absorber From MESSENGER/MASCS Observations
Authors: Pérez‐Hoyos S. , Sánchez‐Lavega A. , García‐Muñoz A. , Irwin P. G. J. , Peralta J. , Holsclaw G. , McClintock W. M. , Sanz‐Requena J. F.
Published: January 2018

One of the most intriguing, long‐standing questions regarding Venus's atmosphere is the origin and distribution of the unknown UV absorber, responsible for the absorption band detected at the near‐UV and blue range of Venus's spectrum. In this work, we use data collected by Mercury Atmospheric and Surface Composition Spectrometer (MASCS) spectrograph on board the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission during its second Venus flyby in June 2007 to address this issue. Spectra range from 0.3 μm to 1.5 μm including some gaseous H2O and CO2 bands, as well as part of the SO2 absorption band and the core of the UV absorption. We used the NEMESIS radiative transfer code and retrieval suite to investigate the vertical distribution of particles in the equatorial atmosphere and to retrieve the imaginary refractive indices of the UV absorber, assumed to be well mixed with Venus's small mode 1 particles. The results show a homogeneous equatorial atmosphere, with cloud tops (height for unity optical depth) at 75 ± 2 km above surface. The UV absorption is found to be centered at 0.34 ± 0.03 μm with a full width at half maximum of 0.14 ± 0.01 μm. Our values are compared with previous candidates for the UV aerosol absorber, among which disulfur oxide (S2O) and dioxide disulfur (S2O2) provide the best agreement with our results.
Three‐Dimensional Structures of Thermal Tides Simulated by a Venus GCM
Authors: Takagi Masahiro , Sugimoto Norihiko , Ando Hiroki , Matsuda Yoshihisa
Published: January 2018

Thermal tides in the Venus atmosphere are investigated by using a GCM named as AFES‐Venus. The three‐dimensional structures of wind and temperature associated with the thermal tides obtained in our model are fully examined and compared with observations. The result shows that the wind and temperature distributions of the thermal tides depend complexly on latitude and altitude in the cloud layer, mainly because they consist of vertically propagating and trapped modes with zonal wave numbers of 1–4, each of which predominates in different latitudes and altitudes under the influence of mid‐ and high‐latitude jets. A strong circulation between the subsolar and antisolar (SS‐AS) points, which is equivalent to a diurnal component of the thermal tides, is superposed on the superrotation. The vertical velocity of SS‐AS circulation is about 10 times larger than that of the zonal‐mean meridional circulation (ZMMC) in 60–70 km altitudes. It is suggested that the SS‐AS circulation could contribute to the material transport, and its upward motion might be related to the UV dark region observed in the subsolar and early afternoon regions in low latitudes. The terdiurnal and quaterdiurnal tides, which may be excited by the nonlinear interactions among the diurnal and semidiurnal tides in middle and high latitudes, are detected in the solar‐fixed Y‐shape structure formed in the vertical wind field in the upper cloud layer. The ZMMC is weak and has a complex structure in the cloud layer; the Hadley circulation is confined to latitudes equatorward of 30°, and the Ferrel‐like one appears in middle and high latitudes.
Linking the Modern Distribution of Biogenic Proxies in High Arctic Greenland Shelf Sediments to Sea Ice, Primary Production, and Arctic‐Atlantic Inflow
Authors: Limoges Audrey , Ribeiro Sofia , Weckström Kaarina , Heikkilä Maija , Zamelczyk Katarzyna , Andersen Thorbjørn J. , Tallberg Petra , Massé Guillaume , Rysgaard Søren , Nørgaard‐Pedersen Niels , Seidenkrantz Marit‐Solveig
Published: January 2018

The eastern north coast of Greenland is considered to be highly sensitive to the ongoing Arctic warming, but there is a general lack of data on modern conditions and in particular on the modern distribution of climate and environmental proxies to provide a baseline and context for studies on past variability. Here we present a detailed investigation of 11 biogenic proxies preserved in surface sediments from the remote High Arctic Wandel Sea shelf, the entrance to the Independence, Hagen, and Danmark fjords. The composition of organic matter (organic carbon, C:N ratios, δ13C, δ15N, biogenic silica, and IP25) and microfossil assemblages revealed an overall low primary production dominated by benthic diatoms, especially at the shallow sites. While the benthic and planktic foraminiferal assemblages underline the intrusion of chilled Atlantic waters into the deeper parts of the study area, the distribution of organic‐walled dinoflagellate cysts is controlled by the local bathymetry and sea ice conditions. The distribution of the dinoflagellate cyst Polarella glacialis matches that of seasonal sea ice and the specific biomarker IP25, highlighting the potential of this species for paleo sea ice studies. The information inferred from our multiproxy study has important implications for the interpretation of the biogenic‐proxy signal preserved in sediments from circum‐Arctic fjords and shelf regions and can serve as a baseline for future studies. This is the first study of its kind in this area.
Watershed‐Scale Drivers of Air‐Water CO2 Exchanges in Two Lagoonal North Carolina (USA) Estuaries
Authors: Van Dam Bryce R. , Crosswell Joseph R. , Anderson Iris C. , Paerl Hans W.
Published: January 2018

Riverine loading of nutrients and organic matter act in concert to modulate CO2 fluxes in estuaries, yet quantitative relationships between these factors remain poorly defined. This study explored watershed‐scale mechanisms responsible for the relatively low CO2 fluxes observed in two microtidal, lagoonal estuaries. Air‐water CO2 fluxes were quantified with 74 high‐resolution spatial surveys in the neighboring New River Estuary (NewRE) and Neuse River Estuary (NeuseRE), North Carolina, which experience a common climatology but differ in marine versus riverine influence. Annually, both estuaries were relatively small sources of CO2 to the atmosphere, 12.5 and 16.3 mmol C m−2 d−1 in the NeuseRE and NewRE, respectively. Large‐scale pCO2 variations were driven by changes in freshwater age, which modulates nutrient and organic carbon supply and phytoplankton flushing. Greatest pCO2 undersaturation was observed at intermediate freshwater ages, between 2 and 3 weeks. Biological controls on CO2 fluxes were obscured by variable inputs of river‐borne CO2, which drove CO2 degassing in the river‐dominated NeuseRE. Internally produced CO2 exceeded river‐borne CO2 in the marine‐dominated NewRE, suggesting that net ecosystem heterotrophy, rather than riverine inputs, drove CO2 fluxes in this system. Variations in riverine alkalinity and inorganic carbon loading caused zones of minimum buffering capacity to occur at different locations in each estuary, enhancing the sensitivity of estuarine inorganic C chemistry to acidification. Although annual CO2 fluxes were similar between systems, watershed‐specific hydrologic factors led to disparate controls on internal carbonate chemistry, which can influence ecosystem biogeochemical cycling, trophic state, and response to future perturbations.
Adjoint‐Based Climate Model Tuning: Application to the Planet Simulator
Authors: Lyu Guokun , Köhl Armin , Matei Ion , Stammer Detlef
Published: January 2018

The adjoint method is used to calibrate the medium complexity climate model “Planet Simulator” through parameter estimation. Identical twin experiments demonstrate that this method can retrieve default values of the control parameters when using a long assimilation window of the order of 2 months. Chaos synchronization through nudging, required to overcome limits in the temporal assimilation window in the adjoint method, is employed successfully to reach this assimilation window length. When assimilating ERA‐Interim reanalysis data, the observations of air temperature and the radiative fluxes are the most important data for adjusting the control parameters. The global mean net longwave fluxes at the surface and at the top of the atmosphere are significantly improved by tuning two model parameters controlling the absorption of clouds and water vapor. The global mean net shortwave radiation at the surface is improved by optimizing three model parameters controlling cloud optical properties. The optimized parameters improve the free model (without nudging terms) simulation in a way similar to that in the assimilation experiments. Results suggest a promising way for tuning uncertain parameters in nonlinear coupled climate models.
Zircon U‐Pb Dating of a Lower Crustal Shear Zone: A Case Study From the Northern Sector of the Ivrea‐Verbano Zone (Val Cannobina, Italy)
Authors: Langone A. , Zanetti A. , Daczko N. R. , Piazolo S. , Tiepolo M. , Mazzucchelli M.
Published: January 2018

A geochronological study was performed on zircon grains from a middle‐lower crustal shear zone exposed in the northern sector of the Ivrea‐Verbano Zone (Southern Alps, Italy) for the first time. The shear zone developed at the boundary between mafic rocks of the External Gabbro unit and ultramafic rocks of the Amphibole Peridotite unit. It is ~10–20 m wide, can be followed along a NE strike for several kilometers, and consists of an anastomosing network of mylonites and ultramylonites. Zircon grains were studied in thin sections and as separates from three representative outcrops along the shear zone. Zircon grains are more abundant in the shear zone compared to wall rocks and are generally equant, rounded to subrounded with dimensions up to 500 μm. U‐Pb data are mainly discordant, and the apparent 206Pb/238U dates show a large variation from Permian to Jurassic. Isotopic data, combined with microstructural, morphological, and internal features of zircon, reveal an inherited age component and suggest partial zircon recrystallization under high‐temperature conditions during Late Triassic to Early Jurassic. High‐temperature deformation in the shear zone, at lower crustal levels, was coeval with amphibolite to greenschist facies mylonitic deformation at upper crustal levels and is inferred to be related to Mesozoic rifting processes at the Adriatic margin.
Concentration‐Discharge Responses to Storm Events in Coastal California Watersheds
Authors: Aguilera Rosana , Melack John M.
Published: January 2018

Storm events in montane catchments are the main cause of mobilization of solutes and particulates into and within stream channels in coastal California. Nonlinear behavior of nutrients and suspended sediments during storms is evident in the hysteresis that arises in concentration‐discharge (C‐Q) relationships. We examined patterns in the C‐Q hysteresis of nutrients (
,
, DON, and
) and total suspended solids (TSS) during storms across 10 sites and water years 2002–2015 by quantifying the slope of the C‐Q relationship and the rotational pattern of the hysteresis loop. We observed several hysteresis types in the ∼400 storms included in our study. Concentrations of constituents associated with sediment transport (
and TSS) peaked during high flows. Conversely, nitrogen species had hysteretic responses such as dilution with clockwise rotation in urban sites and enrichment with anticlockwise rotation in undeveloped sites. The wide range of C‐Q responses that occurred among sites and seasons reflected the variable hydrological and biogeochemical characteristics of catchments and storms. Responses for nitrate in nested catchments differed in slope and rotation of C‐Q hysteresis. Upland undeveloped and lowland urban sites had anticlockwise rotation at the onset of the rainy season following a dry year, which implied a delay in the transport of this solute to the streams. Slopes by the middle of the rainy season showed that the urban site switched from dilution to enrichment, and then again to dilution with clockwise rotation at the end of the season, which implied high initial concentrations and proximal sources.
Nanostructured Lipid‐Based Films for Substrate‐Mediated Applications in Biotechnology
Authors: Kang Minjee , Tuteja Mohit , Centrone Andrea , Topgaard Daniel , Leal Cecilia
Published: January 2018

Amphiphilic in nature, lipids spontaneously self‐assemble into a range of nanostructures in the presence of water. Among lipid self‐assembled structures, liposomes and supported lipid bilayers have long held scientific interest for their main applications in drug delivery and plasma membrane models, respectively. In contrast, lipid‐based multilayered membranes on solid supports only recently begin drawing scientists' attention. Current studies show that the stacking of multiple bilayers on a solid support yields cooperative structural and dynamic behavior that enables new functionalities. Lipid films provide compartmentalization, templating, and enhanced release of molecules of interest. Importantly, supported lipid phases exhibit long‐range periodic nanoscale order and orientation that is tunable in response to a changing environment. Herein, the current understanding of lipid‐based film research is summarized focusing on how unique structural characteristics enable the emergence of new applications including label‐free biosensors, macroscale drug delivery, and substrate‐mediated gene delivery. The authors' recent contributions focusing on the structural characterization of lipid‐based films using small‐angle X‐ray scattering and atomic force microscopy are highlighted. In addition, new photothermally induced resonance and solid‐state nuclear magnetic resonance data are described, providing insights into drug partition in lipid‐based films as well as structure and dynamics at the molecular scale.
Hollow Spherical Nanoshell Arrays of 2D Layered Semiconductor for High‐Performance Photodetector Device
Authors: Chen Xiaoshuang , Yang Huihui , Liu Guangbo , Gao Feng , Dai Mingjin , Hu Yunxia , Chen Hongyu , Cao Wenwu , Hu PingAn , Hu Wenping
Published: January 2018

Well‐defined hollow spherical nanoshell arrays of 2D transitional metal dichalcogenide (TMDC) nanomaterials for MoSe2 and MoS2 are grown via chemical vapor deposition technique for the first time. The hollow sphere arrays display the uniform dimensions of ≈450 nm with the shell thickness of ≈10 nm. The unique hollow sphere architecture with increased active surface area is forecasted to supply more efficient route to improve light‐harvesting efficiency through repeated light reflection and scattering inside the hollow structure without decay of response and recovery speed, because exceptional “SP–SP” junction barriers conducting mechanism can facilitate carriers tunneling and transport during the electron transfer procedure within the present particular structure. The MoSe2 hollow sphere photodetector exhibits an outstanding responsivity (8.9 A W−1), which is tenfold higher than that for MoSe2 compact film (0.9 A W−1), fast response and recovery speed, and good durability under illumination wavelength of 365 nm. Meanwhile, MoSe2 hollow sphere arrays on flexible polyethylene terephthalate substrates reveal excellent bending stability. Therefore, this research indicates that unique hollow sphere architecture of 2D TMDC materials will be an anticipated avenue for efficient photodetector devices with far‐ranging capability.
Enhancing Performance Stability of Electrochemically Active Polymers by Vapor‐Deposited Organic Networks
Authors: Mao Xianwen , Liu Andong , Tian Wenda , Wang Xiaoxue , Gleason Karen K. , Hatton T. Alan
Published: January 2018

Performance stability of electrochemically active polymers (EAPs) remains one of the greatest and long‐standing challenges with regard to EAP‐based technologies for a myriad of energy, biomedical, and environmental applications. The performance instability of EAPs originates from their structural alteration under repeated charge–discharge cycling and/or flexing. In this work, a conceptually new “soft confinement” strategy to enhance EAP performance stability, including cyclic and mechanical, by using rationally designed, vapor‐deposited organic networks is presented. These chemically cross‐linked networks, when in contact with an electrolyte solution, turn into ultrathin, elastic hydrogel coatings that encapsulate conformally the EAP micro‐/nanostructures. Such hydrogel coatings allow easy passage of ions that intercalate with EAPs, while simultaneously mitigating the structural pulverization of the EAPs and/or their detachment from substrates. Fundamentally distinct from extensively studied “scaffolding” or “synthetic” approaches to stabilizing EAPs, this soft confinement strategy relies on a postmodification step completely decoupled from the EAP synthesis/fabrication, and enjoys the unique advantage of substrate‐independency. Hence, this strategy is broadly applicable to various types of EAPs. The proposed stability enhancement strategy is demonstrated to be effective for a range of EAP systems with differing chemical and morphological characteristics under various testing conditions (repeated charging/discharging, bending, and twisting).