bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation, Growth, and Failure of Debris Jams at Bridge Piers
Authors: Panici Diego , de Almeida Gustavo A. M.
Published: August 2018

The accumulation of large wood debris around bridge piers obstructs the flow, producing increased upstream water levels, large horizontal structural loadings, and flow field modifications that can considerably exacerbate scour. These effects have frequently been held responsible for the failure of a large number of bridges around the world, as well as for increased risk of flooding of adjacent areas. Yet little is currently known about the time evolution and processes responsible for the formation and growth of these debris piles. This paper is aimed at deciphering the whole life of debris accumulations through an exhaustive set of 570 experiments in which debris elements were individually introduced into a flume and accumulated at a pier model downstream. Our findings show that in all experiments, the growth of accumulations is halted at a critical stage, after which the jam is removed from the pier by the flow. This condition typically coincides with the time when the dimensions of the accumulations are maxima. The values of the accumulation maximum size display a clear dependence on flow characteristics and debris length distribution. On the other hand, other variables have shown much weaker effects on the geometry of the accumulations. For a given debris length, accumulations are wide, shallow, and long at low flow velocities but become narrower, deeper, and shorter with increasing velocities. A comparison of results of accumulations formed with debris of uniform and nonuniform size distributions has revealed that the former can be up to 2.5 times wider than the latter.
Data Assimilation in Density‐Dependent Subsurface Flows via Localized Iterative Ensemble Kalman Filter
Authors: Xia Chuan‐An , Hu Bill X. , Tong Juxiu , Guadagnini Alberto
Published: August 2018

Parameter estimation in variable‐density groundwater flow systems is confronted with challenges of strong nonlinearity and heavy computational burden. Relying on a variant of the Henry problem, we evaluate the performance of a domain localization scheme of the iterative ensemble Kalman filter in the framework of data assimilation settings for variable‐density groundwater flows in a seawater intrusion scenario. The performance of the approach is compared against (a) the corresponding domain localization scheme of the ensemble Kalman filter in its standard formulation as well as (b) a covariance localization scheme of the latter. The equivalent freshwater head, hf, and salinity, Sa, are set as the target state variables. The randomly heterogeneous field of equivalent freshwater hydraulic conductivity, Kf, is considered as the system parameter field. Density‐independent and density‐driven flow settings are considered to evaluate the assimilation results using various methods and data. When only hf data are assimilated, all tested approaches perform generally well and a localization scheme embedded in the iterative ensemble Kalman filter appears to consistently outperform the domain localized version of the standard ensemble Kalman filter (EnKF) in a density‐driven scenario; Dirichlet boundary conditions tend to show a more pronounced negative effect on estimating Kf for density‐independent than for density‐dependent flow conditions; hf data are more informative in a density‐dependent than in a density‐independent setting. The sole use of Sa information does not yield satisfactory updates of hf for the covariance localization scheme of the standard EnKF, while the sole use of hf does. The domain localization scheme leads to difficulties in the attainment of global filter convergence when only Sa data are used. A covariance localization scheme associated with a standard EnKF can significantly alleviate this issue.
Floodplain Backwater Effect on Overtopping Induced Fluvial Dike Failure
Authors: Rifai Ismail , El Kadi Abderrezzak Kamal , Erpicum Sebastien , Archambeau Pierre , Violeau Damien , Pirotton Michel , Dewals Benjamin
Published: August 2018

Fluvial dikes (i.e., levees) can be damaged by overtopping flows, leading to breach formation and severe floods. Accurate prediction of the breach geometry and outflow hydrograph is crucial to achieve sound inundation risk assessment and mitigating measures. A set of laboratory experiments were performed to study overtopping induced fluvial dike breaching. The effects of floodplain tailwater on the breach expansion and outflow were investigated. Results are compared to previous experiments under different main channel inflow discharges combined with a free floodplain. The dike breaching process follows three stages: gradual start of overtopping and slow initiation of dike erosion, fast deepening and widening of the breach with highly transient flows, and flow quasi‐stabilization with or without sustained breach expansion. Using the recorded data, a simplified regression model relating the breach stabilization time and the final breach width to the floodplain confinement and inflow Froude number in the main channel is proposed.
New Modeling Framework Improves Radiative Feedback Estimates
Authors: Sidder Aaron
Published: August 2018

A new approach offers insights into the relationship between surface temperature and top-of-atmosphere energy imbalances and improves the understanding of important climate feedbacks.
How Data Set Characteristics Influence Ocean Carbon Export Models
Authors: Bisson K. M. , Siegel D. A. , DeVries T. , Cael B. B. , Buesseler K. O.
Published: August 2018

Ocean biological processes mediate the transport of roughly 10 petagrams of carbon from the surface to the deep ocean each year and thus play an important role in the global carbon cycle. Even so, the globally integrated rate of carbon export out of the surface ocean remains highly uncertain. Quantifying the processes underlying this biological carbon export requires a synthesis between model predictions and available observations of particulate organic carbon (POC) flux; yet the scale dissimilarities between models and observations make this synthesis difficult. Here we compare carbon export predictions from a mechanistic model with observations of POC fluxes from several data sets compiled from the literature spanning different space, time, and depth scales as well as using different observational methodologies. We optimize model parameters to provide the best match between model‐predicted and observed POC fluxes, explicitly accounting for sources of error associated with each data set. Model‐predicted globally integrated values of POC flux at the base of the euphotic layer range from 3.8 to 5.5 Pg C/year, depending on the data set used to optimize the model. Modeled carbon export pathways also vary depending on the data set used to optimize the model, as well as the satellite net primary production data product used to drive the model. These findings highlight the importance of collecting field data that average over the substantial natural temporal and spatial variability in carbon export fluxes, and advancing satellite algorithms for ocean net primary production, in order to improve predictions of biological carbon export.
Nonlinear Drift Resonance Between Charged Particles and Ultralow Frequency Waves: Theory and Observations
Authors: Li Li , Zhou Xu‐Zhi , Omura Yoshiharu , Wang Zi‐Han , Zong Qiu‐Gang , Liu Ying , Hao Yi‐Xin , Fu Sui‐Yan , Kivelson Margaret G. , Rankin Robert , Claudepierre Seth G. , Wygant John R.
Published: August 2018

In Earth's inner magnetosphere, electromagnetic waves in the ultralow frequency (ULF) range play an important role in accelerating and diffusing charged particles via drift resonance. In conventional drift resonance theory, linearization is applied under the assumption of weak wave‐particle energy exchange so particle trajectories are unperturbed. For ULF waves with larger amplitudes and/or durations, however, the conventional theory becomes inaccurate since particle trajectories are strongly perturbed. Here we extend the drift resonance theory into a nonlinear regime, to formulate nonlinear trapping of particles in a wave‐carried potential well, and predict the corresponding observable signatures such as rolled‐up structures in particle energy spectrum. After considering how this manifests in particle data with finite energy resolution, we compare the predicted signatures with Van Allen Probes observations. Their good agreement provides the first observational evidence for the occurrence of nonlinear drift resonance, highlighting the importance of nonlinear effects in magnetospheric particle dynamics under ULF waves.
Intense Electric Fields and Electron‐Scale Substructure Within Magnetotail Flux Ropes as Revealed by the Magnetospheric Multiscale Mission
Authors: Stawarz J. E. , Eastwood J. P. , Genestreti K. J. , Nakamura R. , Ergun R. E. , Burgess D. , Burch J. L. , Fuselier S. A. , Gershman D. J. , Giles B. L. , Le Contel O. , Lindqvist P.‐A. , Russell C. T. , Torbert R. B.
Published: August 2018

Three flux ropes associated with near‐Earth magnetotail reconnection are analyzed using Magnetospheric Multiscale observations. The flux ropes are Earthward propagating with sizes from ∼3 to 11 ion inertial lengths. Significantly different axial orientations are observed, suggesting spatiotemporal variability in the reconnection and/or flux rope dynamics. An electron‐scale vortex, associated with one of the most intense electric fields (E) in the event, is observed within one of the flux ropes. This E is predominantly perpendicular to the magnetic field (B); the electron vortex is frozen‐in with E × B drifting electrons carrying perpendicular current and causing a small‐scale magnetic enhancement. The vortex is ∼16 electron gyroradii in size perpendicular to B and potentially elongated parallel to B. The need to decouple the frozen‐in vortical motion from the surrounding plasma implies a parallel E at the structure's ends. The formation of frozen‐in electron vortices within reconnection‐generated flux ropes may have implications for particle acceleration.
Evaluating the Contribution of Land‐Atmosphere Coupling to Heat Extremes in CMIP5 Models
Authors: Ukkola A. M. , Pitman A. J. , Donat M. G. , De Kauwe M. G. , Angélil O.
Published: August 2018

Land‐atmosphere coupling can amplify heat extremes under declining soil moisture. Here we evaluate this coupling in 25 Coupled Model Intercomparison Project Phase 5 models using flux tower observations over Europe and North America. We compared heat extremes (2.5% of the hottest days of the year) and the evaporative fraction (EF; a measure of land surface dryness) on the day the heat extremes occurred. We found a negative relationship between the magnitude of heat extremes and EF in both models and observations in transitional regions, with the hottest temperatures occurring during the driest days, with a similar but less certain relationship in dry regions. Surprisingly, many models also showed an amplification of heat extremes by low EF in wet regions, a finding not supported by observations. Many models may therefore overamplify heat extremes over wet regions by overestimating the strength of land‐atmosphere coupling, with consequences for future projections of heat extremes.
Climate Constraints on Glaciation Over High‐Mountain Asia During the Last Glacial Maximum
Authors: Yan Qing , Owen Lewis A. , Wang Huijun , Zhang Zhongshi
Published: August 2018

Reasons for restricted and nonuniform glaciation over High‐Mountain Asia (HMA) during the global last glacial maximum (LGM; ~28‐23 ka) have been intensively studied but remain elusive. Using a 1‐km‐resolution ice sheet model, we show that glaciers across HMA exhibit high region variability in glaciation. Glaciers in western and southern HMA are the most sensitive to climate change and those in the interior are the least sensitive. Our model broadly reproduces the restricted glaciation across HMA during the LGM, although it overestimates the extent of glaciation over western and southern HMA as compared with reconstructions. Modeled decreases in precipitation hampers glacier growth over northern HMA, while insufficient cooling hampers glacier advance over eastern HMA for the LGM. Both reduced precipitation and insufficient cooling inhibit large‐scale glaciation over inner HMA. Moreover, climatic conditions conducive to glaciation across the entire HMA include a reduction in temperature of ~10 °C and an increase in precipitation, unlikely to have occurred during any Quaternary glacial maximum.
Temporal Dynamics of Aerodynamic Canopy Height Derived From Eddy Covariance Momentum Flux Data Across North American Flux Networks
Authors: Chu Housen , Baldocchi Dennis D. , Poindexter Cristina , Abraha Michael , Desai Ankur R. , Bohrer Gil , Arain M. Altaf , Griffis Timothy , Blanken Peter D. , O'Halloran Thomas L. , Thomas R. Quinn , Zhang Quan , Burns Sean P. , Frank John M. , Christian Dold , Brown Shannon , Black T. Andrew , Gough Christopher M. , Law Beverly E. , Lee Xuhui , Chen Jiquan , Reed David E. , Massman William J. , Clark Kenneth , Hatfield Jerry , Prueger John , Bracho Rosvel , Baker John M. , Martin Timothy A.
Published: August 2018

Aerodynamic canopy height (ha) is the effective height of vegetation canopy for its influence on atmospheric fluxes and is a key parameter of surface‐atmosphere coupling. However, methods to estimate ha from data are limited. This synthesis evaluates the applicability and robustness of the calculation of ha from eddy covariance momentum‐flux data. At 69 forest sites, annual ha robustly predicted site‐to‐site and year‐to‐year differences in canopy heights (R2 = 0.88, 111 site‐years). At 23 cropland/grassland sites, weekly ha successfully captured the dynamics of vegetation canopies over growing seasons (R2 > 0.70 in 74 site‐years). Our results demonstrate the potential of flux‐derived ha determination for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land use change, and disturbance. The large‐scale and time‐varying ha derived from flux networks worldwide provides a new benchmark for regional and global Earth system models and satellite remote sensing of canopy structure.
Dusty Space Plasma Diagnosis Using the Behavior of Polar Mesospheric Summer Echoes During Electron Precipitation Events
Authors: Mahmoudian A. , Senior A. , Scales W. A. , Kosch M. J. , Rietveld M. T.
Published: August 2018

The behavior of polar mesospheric summer echoes (PMSEs) during an electron precipitation event is investigated by including dusty plasma effects for the first time. The observational data recorded with the very high frequency (224 MHz) and ultrahigh frequency (930 MHz) radars at the European Incoherent SCATter Scientific Association on 10 and 11 July 2012 are presented. The observed radar echoes show that the PMSEs are both correlated and anticorrelated with the increased electron density associated with electron precipitation events on the two consecutive days. The experimental observations are compared with numerical simulations of the temporal evolution of PMSE with different background dusty plasma parameters during the electron precipitation event. Specifically, the effect of dust radius, dust density, recombination/photoionization rates, photo‐detachment current, and electron density enhancement ratio on the behavior of a PMSE layer and the associated dust charging process in the course of electron precipitation events is studied. It is observed that the ratio of electron density fluctuation amplitude δne to the plasma density (ne) plays a critical role in the appearance/disappearance of the layer. The simulation results revealed that the existence of PMSE is mainly determined by dust radius and dust density. The dusty plasma parameters associated with each event are estimated. The condensation nuclei of the ice particles such as proton hydrate clusters (H+(H2O)n) or meteoric smoke particles can be determined by employing the microphysical models along with the dusty plasma simulations. This can resolve any discrepancy in the description of the observed phenomena.
Nighttime Enhancements in the Midlatitude Ionosphere and Their Relation to the Plasmasphere
Authors: Li Quanhan , Hao Yongqiang , Zhang Donghe , Xiao Zuo
Published: August 2018

In situ electron density measurements by the CHAllenging Minisatellite Payload and the Defense Meteorological Satellites Program F17 satellites show that the midlatitude ionization at altitudes of ∼350 and 850 km is enhanced in the late evening. The enhancements increase to maximum around midnight and are clearly observed till early morning as the equatorial ionization decays to minimal level. They appear in the winter hemisphere during June and December solstices and in both hemispheres during equinox. The enhancements are well confined between ±30° and ±50° magnetic latitude, with the magnetic flux tubes of L = 1.3 − 2.4 connecting to the plasmasphere. Furthermore, coincident longitudinal variations exist in both the ionospheric enhancements and the plasmaspheric total electron content, especially during the solstice months. The coincidence may suggest essential plasma transport between the ionosphere and the plasmasphere. These facts support the idea that the plasmasphere provides extra plasma to the midlatitude ionosphere through downward plasma influx along the magnetic field lines to form the nighttime ionization enhancements when the sunlight is absent.
Response of Relativistic Electron Microbursts to the Arrival of High‐Speed Solar Wind Streams and its Relation to Flux Variation of Trapped Radiation Belt Electrons
Authors: Kurita S. , Miyoshi Y. , Blake J. B. , Friedel R. H. W.
Published: August 2018

Relativistic electron microbursts are frequently observed during high‐speed solar wind stream (HSS) events. However, solar wind parameters, which are important for enhanced microburst precipitation, have not been well understood. We perform a superposed epoch analysis of microburst occurrence frequency during HSS events, considering the north/south component of the interplanetary magnetic field (IMF Bz) and solar wind speed. The IMF Bz dependence is investigated considering the Russell‐McPherron effect following the method used by Miyoshi and Kataoka (2008, https://doi.org/10.1029/2007JA012506). We find that microbursts are most frequently observed during faster (>500 km/s) solar wind speed streams with the IMF Bz shifted southward (fast SBZ‐HSS events), indicating that both fast solar wind speed and the southward IMF Bz are important for enhanced microburst precipitation. The occurrence frequency of chorus waves during the HSS events is investigated to gain an understanding of the different behavior of microburst activity in response to the HSS events. We show that relativistic electron microbursts are not always a good proxy for chorus waves, but a proxy for a subset of chorus that can resonate with MeV electrons. We also show that electron fluxes with energies from hundreds of keV to several MeV preferentially increase during the fast SBZ‐HSS events. These results indicate that observation of an enhanced occurrence of relativistic electron microbursts could be used as a proxy for the direct observation of the acceleration of MeV electrons by chorus waves in the heart of the outer radiation belt, not just a proxy for chorus wave activity in general.
Experimental Investigation of Total Bottom Shear Stress for Oscillatory Flows Over Sand Ripples
Authors: Yuan Jing , Wang Dongxu
Published: August 2018

Shoaling waves often produce vortex ripples on a sandy seabed, which significantly increases the local bottom shear stress. To improve the quantitative understanding of this phenomenon, a full‐scale experimental study is conducted using an oscillatory water tunnel. In the tests, sinusoidal oscillatory flows generate two‐dimensional uniform sand ripples from a 9‐m‐long movable bed made of coarse sand. The total bottom shear stress is estimated from the change of water pressure for driving the oscillatory flow. Flow around individual ripples is also measured using particle image velocimetry. After correction for imperfect flow generation and facility vibration, the leading three odd harmonics of total bottom shear stress are kept in the final measurements. The first harmonic is the dominant one and is generally in phase with the free‐stream velocity. Its amplitude decreases as ripples are washed‐off by increasing flow intensity. The third and the fifth harmonics are about 10–20% of the first harmonic in amplitude. Their presence makes the intraperiod variation of total bottom shear stress quite wavy with three peaks within one half period. Flow measurements suggest that these peaks are closely related to coherent vortex motions. For two selected tests, total bottom shear stress is estimated from velocity measurements via a control volume analysis. The results are in good agreement with those from the pressure‐based technique, which verifies both approaches. A new predictor for the equivalent sand grain roughness in Humbyrd's (2012, http://hdl.handle.net/1721.1/78234) formula for wave friction factor is calibrated based on the obtained measurements of maximum total bottom shear stress.
The Interannual Variability of the Breakdown of Fall Stratification on the New Jersey Shelf
Authors: Forsyth Jacob , Gawarkiewicz Glen , Andres Magdalena , Chen Ke
Published: August 2018

During the seasonal evolution of stratification on the New Jersey shelf in the fall, strong thermal stratification that was established in the preceding summer is broken down through wind‐driven processes and surface cooling. Ten years of output from a Regional Ocean Modeling Systems run and a one‐dimensional mixed layer model is used here to examine the interannual variability in the strength of the stratification and in the processes that reduce stratification in fall. Our analysis shows that the strength of the stratification at the end of the summer is not correlated with the timing of shelf destratification. This indicates that processes that occur within the fall are more important for the timing of stratification breakdown than are the initial fall conditions. Furthermore, wind‐driven processes reduce a greater fraction of the stratification in each year than does the surface cooling during the fall. Winds affect the density gradients on the shelf through both changes to the temperature and salinity fields. Processes associated with the downwelling‐favorable winds are more effective than those during upwelling‐favorable winds in breaking down the vertical density gradients. In the first process, cross‐shelf advective fluxes during storms act to decrease stratification during downwelling‐favorable winds and increase stratification during upwelling‐favorable winds. Second, there is also enhanced velocity shear during downwelling‐favorable winds, which allows for more shear instabilities that break down stratification via mixing. Observational data and model output from Tropical Storm Ernesto compare favorably and suggest that downwelling‐favorable winds act through the mechanisms identified from the Regional Ocean Modeling Systems results.
Interannual Eddy Kinetic Energy Modulations in the Agulhas Return Current
Authors: Zhu Yanan , Qiu Bo , Lin Xiaopei , Wang Fan
Published: August 2018

Interannual variability in the mesoscale eddy field in the Agulhas Return Current (ARC) of 32–42°S and 15–35°E is investigated based on satellite altimeter observations and state estimate from the Estimating the Circulation and Climate of the Ocean, Phase II from 1993 to 2016. It is found that the interannual modulation of eddy kinetic energy in the ARC region is externally mediated by the wind stress forcing that generates the westward propagating sea surface height anomalies across the South Indian Ocean subtropical gyre. The wind‐forced sea surface height anomalies influence the upstream Agulhas Current volume transports. By modulating the intensity of barotropic instability of the ARC mean flow centered around the retroflection region, the Agulhas Current inflow variability leads to the downstream interannual eddy kinetic energy fluctuations in the ARC region.
The Impact of Boreal Summer ENSO Events on Tropical Lower Stratospheric Ozone
Authors: Tweedy Olga V. , Waugh Darryn W. , Randel William J. , Abalos Marta , Oman Luke D. , Kinnison Doug E.
Published: August 2018

The interannual variability of tropical lower stratosphere ozone and its connections to sea surface temperatures in the equatorial Pacific are examined using a combination of chemistry climate model simulations, satellite observations, and reanalyses. The model simulations and observations show large differences in the magnitude of interannual variability in ozone between northern tropic (NT; EQ‐18° N) and southern tropic (EQ‐18° S) during boreal summer but small differences in winter. The interannual variability during boreal summer is highly correlated with summer sea surface temperatures in the eastern and central Pacific Ocean and El Niño–Southern Oscillation (ENSO) events. Larger variability in NT ozone is primarily due to meridional advection, connected to the changes in the onset date and strength of the Asian summer monsoon anticyclone. The Asian summer monsoon anticyclone forms earlier in a season and tends to be stronger during cold (La Niña) events leading to more isentropic transport of ozone from the extratropics into the NT, with the reverse for warm (El Niño) events.
Evaluating GPP and Respiration Estimates Over Northern Midlatitude Ecosystems Using Solar‐Induced Fluorescence and Atmospheric CO2 Measurements
Authors: Byrne B. , Wunch D. , Jones D. B. A. , Strong K. , Deng F. , Baker I. , Köhler P. , Frankenberg C. , Joiner J. , Arora V. K. , Badawy B. , Harper A. B. , Warneke T. , Petri C. , Kivi R. , Roehl C. M.
Published: August 2018

On regional to global scales, few constraints exist on gross primary productivity (GPP) and ecosystem respiration (Re) fluxes. Yet constraints on these fluxes are critical for evaluating and improving terrestrial biosphere models. In this study, we evaluate the seasonal cycle of GPP, Re, and net ecosystem exchange (NEE) produced by four terrestrial biosphere models and FLUXCOM, a data‐driven model, over northern midlatitude ecosystems. We evaluate the seasonal cycle of GPP and NEE using solar‐induced fluorescence retrieved from the Global Ozone Monitoring Experiment‐2 and column‐averaged dry‐air mole fractions of CO2 (XCO2) from the Total Carbon Column Observing Network, respectively. We then infer Re by combining constraints on GPP with constraints on NEE from two flux inversions. An ensemble of optimized Re seasonal cycles is generated using five GPP estimates and two NEE estimates. The optimized Re curves generally show high consistency with each other, with the largest differences due to the magnitude of GPP. We find optimized Re exhibits a systematically broader summer maximum than modeled Re, with values lower during June–July and higher during the fall than Re. Further analysis suggests that the differences could be due to seasonal variations in the carbon use efficiency (possibly due to an ecosystem‐scale Kok effect) and to seasonal variations in the leaf litter and fine root carbon pool. The results suggest that the inclusion of variable carbon use efficiency for autotrophic respiration and carbon pool dependence for heterotrophic respiration is important for accurately simulating Re.
Faraday Rotation, Total Electron Content, and Their Sensitivity to the Average Parallel Component of the Magnetic Field
Authors: Cushley A. C. , Noël J.‐M. , Kabin K.
Published: August 2018

A plane‐polarized electromagnetic wave that propagates through a plasma, (anti)parallel to a magnetic field, experiences a gradual rotation of its plane of polarization called Faraday rotation (FR). The FR angle depends on the integrated product of the electron density and the strength of the parallel magnetic field projection to the radio wave propagation direction. The integral is taken along the radio wave propagation direction over the entire path length. Therefore, accurate measurements or a suitable model for both the electron density and the magnetic field as well as the propagation trajectory are required for the interpretation of FR measurements. Many authors use the average value of the parallel magnetic field for estimation of FR from ionospheric total electron content measurements. Although it is known that the strength of Earth's geomagnetic field varies slowly at ionospheric altitudes, a reference height characteristic value or mean value may not always be appropriate. This work considers alternative methods to establish a characteristic value for the average parallel component of the magnetic field, particularly when independent FR and total electron content measurements are available.
Exploring Controls on Rainfall‐Runoff Events: 1. Time Series‐Based Event Separation and Temporal Dynamics of Event Runoff Response in Germany
Authors: Tarasova L. , Basso S. , Zink M. , Merz R.
Published: August 2018

Analyzing a response of catchments to rainfall inputs allows for deeper insights on the mechanisms of runoff generation at catchment scale. In this study an automated time series‐based event separation procedure consisting of available base flow separation, runoff event identification, and rainfall attribution methods and of a novel iterative procedure for the adjustment of thresholds used to identify single‐peak components of multiple‐peak events is proposed. Event runoff coefficient, time scale, rise time, and peak discharge of more than 220,000 identified rainfall‐runoff events are then used to analyze dynamics of event runoff response in 185 catchments at multiple temporal scales. In mountainous catchments with poor storage event runoff response is strongly controlled by the characteristics of rainfall and is generated by event‐fed saturation or infiltration excess. A distinct switch between saturated and unsaturated states occurs in these catchments. A weak relation between rainfall and runoff event properties is instead observed in lowland and hilly catchments with substantial storage, where a gradual transformation between functioning states occurs and the response is driven by preevent saturation. The seasonality of their event characteristics is governed by the contribution of snowmelt and the seasonality of the aridity index rather than of rainfall properties. Long‐term changes of total precipitation amount alone do not explain season‐specific long‐term changes of event characteristics that are rather consistent with changes of seasonal indicators of the wetness state. The effects of land use changes are detectable only in a few cases and display themselves mostly in the characteristic response time of catchments.
A Diagnostic Framework for Understanding Climatology of Tails of Hourly Precipitation Extremes in the United States
Authors: Papalexiou Simon Michael , AghaKouchak Amir , Foufoula‐Georgiou Efi
Published: August 2018

Hourly precipitation extremes are crucial in hydrological design. Their frequency and magnitude is encapsulated in the probability distribution tail. Traditional extreme‐analysis methods rely on theorems, like the Pickands‐Balkema‐de Haan, indicating specific type of tails assuming asymptotic convergence—a questionable assumption for real‐world samples. Moreover, popular stochastic models for hourly precipitation presume light‐tailed distributions to facilitate their mathematical formulation. In practice, limited information on hourly precipitation extremes makes identifying and quantifying their tail highly uncertain, especially on a station‐by‐station basis. Yet no comprehensive regional analysis of tails has been undertaken to quantify a climatology of tails for diagnostic and prognostic purposes. Here we undertake such an analysis for the conterminous United States. We introduce a novel Bayesian‐adjustment approach to assess the best model between power‐type and stretched‐exponential tails showing that the latter performs better. We present climatology of the tail and quantify its heaviness in over 4,000 hourly precipitation records across the United States and present three main conclusions. First, we show that hourly precipitation tails are heavier than those commonly used with important implications including underestimation of extremes. Second, we provide spatial maps of the tail behavior which reveal some strikingly coherent spatial patterns that can be used for inference in the absence of local observations. Third, we find a nonlinear increase in the tail heaviness with elevation and we formulate parametric functions to describe this law. These results can improve the accuracy of frequency analysis, probabilistic prediction, rainfall‐runoff modeling, and downscaling of historical observations and climate model projections.
U.S. Urban Water Prices: Cheaper When Drier
Authors: Luby Ian H. , Polasky Stephen , Swackhamer Deborah L.
Published: August 2018

Public water utilities are called upon to address multiple and often partially conflicting objectives, allocating potentially scarce water in an efficient and equitable manner while covering the costs of water supply. Economists typically advocate using prices to balance supply and demand of a scarce resource. But high prices necessary to balance supply and demand for scarce water may unduly burden poor households. We analyze the pricing policy of public water utilities in the major city of the 35 largest metropolitan areas in the United States. We would expect water prices to be higher in water‐stressed regions. However, we find the opposite pattern in the data: cities facing greater water scarcity tend to have lower water prices. Sacramento, Las Vegas, and Phoenix, have the lowest water prices. To address equity and ensure that all households have access to water, we would expect low prices on essential water use with higher prices for additional water beyond essential use. However, we find that the majority of cities have higher per unit water prices (average price) for low use than for high use. Such pricing may leave major urban areas in the United States ill‐prepared to meet future water shortages in an equitable manner.
In Situ and GRACE‐Based Groundwater Observations: Similarities, Discrepancies, and Evaluation in the High Plains Aquifer in Kansas
Authors: Brookfield A. E. , Hill M. C. , Rodell M. , Loomis B. D. , Stotler R. L. , Porter M. E. , Bohling G. C.
Published: August 2018

Relating Gravity Recovery and Climate Experiment (GRACE)‐derived terrestrial water storage anomaly (aTWS) variations to in situ groundwater data is important to understanding GRACE data utility. Here GRACE‐derived annual changes in aTWS (ΔTWS) from National Aeronautics and Space Administration's Jet Propulsion Laboratory and Goddard Space Flight Center are compared to annual changes in saturated groundwater volumes (ΔGW) in the High Plains aquifer (HPA) and overlying alluvial aquifers in Kansas. Regression analysis suggests that trends in ΔTWS are strongly related to trends in ΔGWalluvial and weakly related to trends in ΔGWHPA, although the magnitude of ΔTWS is much larger than ΔGWalluvial and is similar to ΔGWHPA. Unlike alluvial aquifers, a thick vadose zone overlies the HPA. Estimates of changes in vadose zone water content (ΔVZ) using GRACE products are similar in magnitude to annual variations in North American Land Data Assimilation soil moisture data, suggesting an unexpected dominance of ΔVZ in ΔTWS despite significant groundwater depletion. Results demonstrate that water storage changes in shallow alluvial aquifers, the root zone, the deep vadose zone, and the HPA itself are all significant in the HPA region of Kansas. Consequently, GRACE observations cannot, alone, be taken to reflect variations in saturated zone groundwater storage in the HPA, or other large, heavily used aquifers subject to substantial groundwater depletion, when deep unsaturated zones exist. GRACE can best provide guidance on regional aquifer storage changes where water storage changes in the vadose zone and perched or adjacent aquifers are well constrained.
Junction-based lamellipodia drive endothelial cell rearrangements in vivo via a VE-cadherin-F-actin based oscillatory cell-cell interaction
Authors: Paatero Ilkka , Sauteur Loïc , Lee Minkyoung , Lagendijk Anne K. , Heutschi Daniel , Wiesner Cora , Guzmán Camilo , Bieli Dimitri , Hogan Benjamin M. , Affolter Markus , Belting Heinz-Georg
Published: August 2018

Angiogenesis and vascular remodeling are driven by extensive endothelial cell movements. Here, we present in vivo evidence that endothelial cell movements are associated with oscillating lamellipodia-like structures, which emerge from cell junctions in the direction of cell movements. High-resolution time-lapse imaging of these junction-based lamellipodia (JBL) shows dynamic and distinct deployment of junctional proteins, such as F-actin, VE-cadherin and ZO1, during JBL oscillations. Upon initiation, F-actin and VE-cadherin are broadly distributed within JBL, whereas ZO1 remains at cell junctions. Subsequently, a new junction is formed at the front of the JBL, which then merges with the proximal junction. Rac1 inhibition interferes with JBL oscillations and disrupts cell elongation—similar to a truncation in ve-cadherin preventing VE-cad/F-actin interaction. Taken together, our observations suggest an oscillating ratchet-like mechanism, which is used by endothelial cells to move over each other and thus provides the physical means for cell rearrangements.
Ethanol facilitates socially evoked memory recall in mice by recruiting pain-sensitive anterior cingulate cortical neurons
Authors: Sakaguchi Tetsuya , Iwasaki Satoshi , Okada Mami , Okamoto Kazuki , Ikegaya Yuji
Published: August 2018

Alcohol is a traditional social-bonding reinforcer; however, the neural mechanism underlying ethanol-driven social behaviors remains elusive. Here, we report that ethanol facilitates observational fear response. Observer mice exhibited stronger defensive immobility while observing cagemates that received repetitive foot shocks if the observer mice had experienced a brief priming foot shock. This enhancement was associated with an observation-induced recruitment of subsets of anterior cingulate cortex (ACC) neurons in the observer mouse that were responsive to its own pain. The vicariously activated ACC neurons projected their axons preferentially to the basolateral amygdala. Ethanol shifted the ACC neuronal balance toward inhibition, facilitated the preferential ACC neuronal recruitment during observation, and enhanced observational fear response, independent of an oxytocin signaling pathway. Furthermore, ethanol enhanced socially evoked fear response in autism model mice.
Long-lived polarization memory in the electronic states of lead-halide perovskites from local structural dynamics
Authors: Rivett Jasmine P. H. , Tan Liang Z. , Price Michael B. , Bourelle Sean A. , Davis Nathaniel J. L. K. , Xiao James , Zou Yatao , Middleton Rox , Sun Baoquan , Rappe Andrew M. , Credgington Dan , Deschler Felix
Published: August 2018

Anharmonic crystal lattice dynamics have been observed in lead halide perovskites on picosecond timescales. Here, we report that the soft nature of the perovskite crystal lattice gives rise to dynamic fluctuations in the electronic properties of excited states. We use linear polarization selective transient absorption spectroscopy to study the charge carrier relaxation dynamics in lead-halide perovskite films and nanocrystals. We find that photo-excited charge carriers maintain an initial polarization anisotropy for several picoseconds, independent of crystallite size and composition, and well beyond the reported timescales of carrier scattering. First-principles calculations find intrinsic anisotropies in the transition dipole moment, which depend on the orientation of light polarization and the polar distortion of the local crystal lattice. Lattice dynamics are imprinted in the optical transitions and anisotropies arise on the time-scales of structural motion. The strong coupling between electronic states and structural dynamics requires a unique interpretation of recombination and transport mechanisms.
A myosin II nanomachine mimicking the striated muscle
Authors: Pertici Irene , Bongini Lorenzo , Melli Luca , Bianchi Giulio , Salvi Luca , Falorsi Giulia , Squarci Caterina , Bozó Tamás , Cojoc Dan , Kellermayer Miklós S. Z. , Lombardi Vincenzo , Bianco Pasquale
Published: August 2018

The contraction of striated muscle (skeletal and cardiac muscle) is generated by ATP-dependent interactions between the molecular motor myosin II and the actin filament. The myosin motors are mechanically coupled along the thick filament in a geometry not achievable by single-molecule experiments. Here we show that a synthetic one-dimensional nanomachine, comprising fewer than ten myosin II dimers purified from rabbit psoas, performs isometric and isotonic contractions at 2 mM ATP, delivering a maximum power of 5 aW. The results are explained with a kinetic model fitted to the performance of mammalian skeletal muscle, showing that the condition for the motor coordination that maximises the efficiency in striated muscle is a minimum of 32 myosin heads sharing a common mechanical ground. The nanomachine offers a powerful tool for investigating muscle contractile-protein physiology, pathology and pharmacology without the potentially disturbing effects of the cytoskeletal—and regulatory—protein environment.
Chemo-immunotherapy of colon cancer with focused ultrasound and Salmonella-laden temperature sensitive liposomes (thermobots)
Authors: Ektate Kalyani , Munteanu Maria Cristina , Ashar Harshini , Malayer Jerry , Ranjan Ashish
Published: August 2018

Using attenuated Salmonella that efficiently homes in solid tumors, here we developed thermobots that actively transported membrane attached low-temperature sensitive liposome (LTSL) inside colon cancer cells for triggered doxorubicin release and simultaneous polarized macrophages to M1 phenotype with high intensity focused ultrasound (HIFU) heating (40–42 °C). Biocompatibility studies showed that the synthesized thermobots were highly efficient in LTSL loading without impacting its viability. Thermobots demonstrated efficient intracellular trafficking, high nuclear localization of doxorubicin, and induced pro-inflammatory cytokine expression in colon cancer cells in vitro. Combination of thermobots and HIFU heating (~30 min) in murine colon tumors significantly enhanced polarization of macrophages to M1 phenotype and therapeutic efficacy in vivo compared to control. Our data suggest that the thermobots and focused ultrasound treatments have the potential to improve colon cancer therapy.
Chemometric Analysis of Cannabinoids: Chemotaxonomy and Domestication Syndrome
Authors: Mudge E. M. , Murch S. J. , Brown P. N.
Published: August 2018

Cannabis is an interesting domesticated crop with a long history of cultivation and use. Strains have been selected through informal breeding programs with undisclosed parentage and criteria. The term “strain” refers to minor morphological differences and grower branding rather than distinct cultivated varieties. We hypothesized that strains sold by different licensed producers are chemotaxonomically indistinguishable and that the commercial practice of identifying strains by the ratio of total THC and CBD is insufficient to account for the reported human health outcomes. We used targeted metabolomics to analyze 11 known cannabinoids and an untargeted metabolomics approach to identify 21 unknown cannabinoids. Five clusters of chemotaxonomically indistinguishable strains were identified from the 33 commercial products. Only 3 of the clusters produce CBDA in significant quantities while the other 2 clusters redirect metabolic resources toward the THCA production pathways. Six unknown metabolites were unique to CBD-rich strains and/or correlated to CBDA and 3 unknowns were found only in THC-rich strains. Together, these data indicate the domestication of the cannabis germplasm has resulted in a loss of the CBDA pathway in some strains and reallocation of resources between CBDA and THCA pathways in others. The impact of domestication is a lack of chemical diversity and loss of biodiversity in modern cannabis strains.
A fundamental catalytic difference between zinc and manganese dependent enzymes revealed in a bacterial isatin hydrolase
Authors: Sommer Theis , Bjerregaard-Andersen Kaare , Uribe Lalita , Etzerodt Michael , Diezemann Gregor , Gauss Jürgen , Cascella Michele , Morth J. Preben
Published: August 2018

The catalytic mechanism of the cyclic amidohydrolase isatin hydrolase depends on a catalytically active manganese in the substrate-binding pocket. The Mn2+ ion is bound by a motif also present in other metal dependent hydrolases like the bacterial kynurenine formamidase. The crystal structures of the isatin hydrolases from Labrenzia aggregata and Ralstonia solanacearum combined with activity assays allow for the identification of key determinants specific for the reaction mechanism. Active site residues central to the hydrolytic mechanism include a novel catalytic triad Asp-His-His supported by structural comparison and hybrid quantum mechanics/classical mechanics simulations. A hydrolytic mechanism for a Mn2+ dependent amidohydrolases that disfavour Zn2+ as the primary catalytically active site metal proposed here is supported by these likely cases of convergent evolution. The work illustrates a fundamental difference in the substrate-binding mode between Mn2+ dependent isatin hydrolase like enzymes in comparison with the vast number of Zn2+ dependent enzymes.
Short-term high glucose culture potentiates pancreatic beta cell function
Authors: Rebelato Eduardo , Santos Laila R. , Carpinelli Angelo R. , Rorsman Patrik , Abdulkader Fernando
Published: August 2018

The exposure of pancreatic islets to high glucose is believed to be one of the causal factors of the progressive lowering of insulin secretion in the development of type 2 diabetes. The progression of beta cell failure to type 2 diabetes is preceded by an early positive increase in the insulin secretory response to glucose, which is only later followed by a loss in the secretion capacity of pancreatic islets. Here we have investigated the electrophysiological mechanisms underlying the early glucose-mediated gain of function. Rodent pancreatic islets or dispersed islet cells were cultured in medium containing either 5.6 (control) or 16.7 (high-glucose) mM glucose for 24 h after isolation. Glucose-stimulated insulin secretion was enhanced in a concentration-dependent manner in high glucose-cultured islets. This was associated with a positive effect on beta cell exocytotic capacity, a lower basal KATP conductance and a higher glucose sensitivity to fire action potentials. Despite no changes in voltage-gated Ca2+ currents were observed in voltage-clamp experiments, the [Ca2+]I responses to glucose were drastically increased in high glucose-cultured cells. Of note, voltage-dependent K+ currents were decreased and their activation was shifted to more depolarized potentials by high-glucose culture. This decrease in voltage-dependent K+ channel (Kv) current may be responsible for the elevated [Ca2+]I response to metabolism-dependent and independent stimuli, associated with more depolarized membrane potentials with lower amplitude oscillations in high glucose-cultured beta cells. Overall these results show that beta cells improve their response to acute challenges after short-term culture with high glucose by a mechanism that involves modulation not only of metabolism but also of ion fluxes and exocytosis, in which Kv activity appears as an important regulator.