bluuebunny/crossref_metadata_2025 huggingface dataset:
Microphysical Sensitivity of Superparameterized Precipitation Extremes in the Contiguous United States Due to Feedbacks on Large‐Scale Circulation
Authors: Charn Alexander B. , Collins William D. , Parishani Hossein , Risser Mark D. , O'Brien Travis A.
Published: April 2020

Superparameterized (SP) global climate models have been shown to better simulate various features of precipitation relative to conventional models, including its diurnal cycle as well as its extremes. While various studies have focused on the effect of differing microphysics parameterizations on precipitation within limited‐area cloud‐resolving models, we examine here the effect on contiguous U.S. (CONUS) extremes in a global SP model. We vary the number of predicted moments for hydrometeor distributions, the character of the rimed ice species, and the representation of raindrop self‐collection and breakup. Using a likelihood ratio test and accounting for the effects of multiple hypothesis testing, we find that there are some regional differences, particularly during spring and summer in the Southwest and the Midwest, in both the current climate and a warmer climate with uniformly increased sea surface temperatures. These differences are most statistically significant and widespread when the number of moments is changed. To determine whether these results are due to (fast) local effects of the different microphysics or the (slower) ensuing feedback on the large‐scale atmospheric circulation, we run a series of short, 5‐day simulations initialized from reanalysis data. We find that the differences largely disappear in these runs and therefore infer that the different parameterizations impact precipitation extremes indirectly via the large‐scale circulation. Finally, we compare the present‐day results with hourly rain gauge data and find that SP underestimates extremes relative to observations regardless of which microphysics scheme is used given a fixed model configuration and resolution.
Seismic Wave‐Based Constraints on Geodynamical Processes: An Application to Partial Melting Beneath the Réunion Island
Authors: Franken T. , Armitage J. J. , Fuji N. , Fournier A.
Published: April 2020

The inversion of seismic observations leads to maps of the interior of the Earth that can be interpreted. Regions of low seismic velocity have historically been interpreted to be due to factors related to high‐temperature and high‐melt retention. Subsequently, geodynamic models can be used to test such interpretations. However, the inversions are nonunique, and arguably, it would be best to test geodynamic scenarios against observations rather than interpretations. Here we make a first attempt at this. At depths greater than 80 km below Réunion, a low shear‐wave velocity zone is imaged. Rather than interpret this inverted model, we test a forward model of melt generation and retention against seismic observations. Geodynamic model solutions are converted with a mineral parameter database to P wave and S wave velocity profiles from various initial temperatures T, upwelling velocities
, and permeabilities k0. By embedding these velocity profiles, synthetic seismograms are generated. For a range of k0, T, and
, we generate synthetic traces for 21 teleseismic events registered at a receiver on Réunion island. We measure the traveltime difference between observed and synthetic waveforms and the interphase differential travel times for 210 scenarios for several phase arrivals of three components, filtered between 0.01 and 0.2 Hz. The results indicate that upper mantle temperatures beneath Réunion lie within 1400–1450 °C, with permeability coefficients of 10−5–10−6 m2. These conditions are associated with porosities of <0.28% and high‐melt extraction rates of 8.37–18.35 m·year−1. This study demonstrates the potential for fully comparing geodynamic scenarios with seismic observations.
Morphotectonic Evolution of Passive Margins Undergoing Active Surface Processes: Large‐Scale Experiments Using Numerical Models
Authors: Beucher R. , Huismans R. S.
Published: April 2020

Extension of the continental lithosphere can lead to the formation of rifted margins with contrasting tectonic and geomorphologic characteristics. Many of these characteristics depend on the manner extension spatially distributed. Here we investigate the feedback between tectonics and the transfer of material at the surface resulting from erosion, transport, and sedimentation and discuss how they influence the rifting process. We use large‐scale (1,200×600 km), high‐resolution (1 km) numerical experiments coupling a 2‐D upper‐mantle‐scale thermo‐mechanical model with a planform 2‐D surface processes model. We test the sensitivity of the coupled models to varying crust‐lithospheric rheology and erosional efficiency. We confirm that the development and long‐term support of topography is dependent on the strength of the coupling between the crust and the mantle lithosphere. Strong coupling promotes high topography as the integrated strength of the lithosphere is sufficient to support the additional stress. Weak coupling results in the stress being relaxed via viscous flow in the middle/lower crust and leads to more subdued topography. Erosion and transport of sediment modulates this behavior but has only minor effect on the overall structure of the rift. High erosion efficiency counters the development of high topography and creates complex landscape morphologies while low erosion efficiency allows for longer standing high topography and results in more simple landscape morphologies. The transfer of mass between the continent and the basin alters the stress field at the onshore‐offshore transition and facilitates the development of faults, increasing their offsets and keeping them active over a longer period.
Raytracing Study of Source Regions of Whistler Mode Wave Power Distribution Relative to the Plasmapause
Authors: Maxworth A. S. , Gołkowski M. , Malaspina D. M. , Jaynes A. N.
Published: April 2020

A comprehensive numerical raytracing study of whistler mode wave power with the inclusion of finite background electron and ion temperature is performed in order to investigate wave power distribution in relation to the plasmapause. Both Landau damping and linear growth of whistler mode waves are taken into account using a bi‐Maxwellian hot electron distribution as well as an isotropic hot electron distribution. Isotropic and bi‐Maxwellian distributions yield similar results of statistical spatial wave power for frequencies below 500 Hz. The effect of finite background temperature of ∼1 eV for electrons and ions are secondary in terms of the spatial distribution of whistler mode waves relative to the plasmapause. Three primary equatorial source locations at L=2, Lpp and L=5, corresponding to within the plasmasphere, at the plasmapause and outside the plasmapause, are investigated for MLT values of 00, 06, 12, and 18. At each location, waves are launched with a range of initial wave normal angles (−70° to 20°). The simulated wave power distributions are compared with observations from the EMFISIS instrument on Van Allen Probe A. Correspondence between the simulated distribution and the observations requires a weighting of the source regions. Results suggest that the majority of whistler mode power in the plasmasphere is sourced from within the plasmasphere itself and near the plasmapause. Only at noon (MLT 12) is wave power sourced primarily from at and outside the plasmapause.
Simultaneous Observations of Electromagnetic Ion Cyclotron (EMIC) Waves and Pitch Angle Scattering During a Van Allen Probes Conjunction
Authors: Sigsbee K. , Kletzing C. A. , Faden J. B. , Jaynes A. N. , Reeves G. D. , Jahn J.‐M.
Published: April 2020

On 22 December 2015, the two Van Allen Probes observed two sets of electromagnetic ion cyclotron (EMIC) wave bursts during a close conjunction when both Probe A and Probe B were separated by 0.57 to 0.68 RE. The EMIC waves occurred during an active period in the recovery phase of a coronal mass ejection‐driven geomagnetic storm. Both spacecraft observed EMIC wave bursts that had similar spatial structure within a 1–2 min time delay. The EMIC waves occurred outside the plasmasphere, within ΔL ≈ 1–2 of the plasmapause and within a few degrees in magnetic latitude of the equatorial plane. The spatial structure of the EMIC wave bursts may have been related to the proton drift paths outside the plasmasphere and influenced by total magnetic field strength variations associated with solar wind pressure enhancements. The EMIC waves were observed in a narrow L shell region from L ≈ 4.55–5.32 between 10 and 11 magnetic local time (MLT) on the outbound halves of the spacecraft orbits and from L ≈ 4.82–5.51 between 13 and 14 MLT on the inbound halves of the spacecraft orbits. However, Pc1 pulsations were observed on the ground over a broad range of local times. The anisotropy of the proton pitch angle distributions was enhanced when the EMIC waves were observed. Although the overall radiation belt response during this storm was dominated by acceleration and transport processes, the EMIC waves produced local pitch angle scattering of 13–15 keV protons and 2.1–2.6 MeV electrons, consistent with calculations of the expected resonant energies.
On the Transition Between the Inner and Outer Plasma Sheet in the Earth's Magnetotail
Authors: Miyashita Yukinaga , Seki Kanako , Sakaguchi Kaori , Hiraki Yasutaka , Nosé Masahito , Machida Shinobu , Saito Yoshifumi , Paterson William R.
Published: April 2020

We have statistically studied the average structure and properties of the plasma sheet in the Earth's magnetotail at radial distances between R∼8 and 32 RE on the basis of ion, electron, and magnetic field data from the Geotail spacecraft. Here we discuss the transition between the inner plasma sheet and the outer plasma sheet near the equatorial plane. The ion and electron number densities, pressures, and energy fluxes at high energies, as well as the magnetic field, generally decrease with increasing radial distance from the Earth. The characteristics of the flux changes are reflected in the radial pressure gradients. If the transition between the inner and outer plasma sheet is determined by the radial pressure gradient change, the ion and electron transitions are located, on average, at R∼11 to 13 RE and R∼11 to 17 RE, respectively, at the midnight meridian. It is possible that the ion transition is located earthward of the electron transition. Furthermore, we have estimated the electric field, the electric and diamagnetic drift velocities, and the κ parameter (the square root of the ratio of the minimum curvature radius of the magnetic field line to the maximum gyroradius), which differ between the ion inner and outer plasma sheet.
Survey of Ion Properties in Jupiter's Plasma Sheet: Juno JADE‐I Observations
Authors: Kim Thomas K. , Ebert R. W. , Valek P. W. , Allegrini F. , McComas D. J. , Bagenal F. , Connerney J. E. P. , Livadiotis G. , Thomsen M. F. , Wilson R. J. , Bolton S. J.
Published: April 2020

This study presents a survey of ion flow speed, density, temperature, and composition observed by the Jovian Auroral Distributions Experiment Ion (JADE‐I) sensor on Juno from 10–40 RJ in the dawn to midnight sector of Jupiter's magnetosphere. The survey covers Juno orbits 5–22, and the observations are separated by equatorial (|zmag[RJ]| ≤ 1.5) and off‐equator (|zmag[RJ]|>1.5) regions. Plasma parameters for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ are derived by forward modeling JADE‐I's energy‐per‐charge versus time‐of‐flight spectra using omni‐directional averaged convected kappa distributions and modeled instrument responses. O+ and S2+ are resolved via a ray‐tracing simulation based on carbon‐foil effects. The ion flow speed increases with radial distance and is comparable to rigid corotation speed out to ∼20 RJ. Ion number densities decrease with radial distance, the primary species being H+, O+, and S2+. The relative contribution of H+ and S2+ increases and decreases, respectively, in the off‐equator regions, supporting the interpretation that the latitudinal distribution of ions is mass dependent. The O+ to S2+ and ΣOn+ to ΣSn+ number density ratios are variable, the 5 RJ bin averages for O+ to S2+ ranging from ∼0.75–1.5 (equator) and ∼1.1–1.8 (off‐equator) and ΣOn+ to ΣSn+ from ∼0.6–0.9 (equator) and ∼0.8–1.1 (off‐equator). Both proton and heavy ion temperatures show order of magnitude increases between 10 and 20 RJ and range from ∼100 eV to 10 keV and 1 keV to a few tens of keV, respectively.
Hybrid Simulations of Solar Wind Proton Precipitation to the Surface of Mercury
Authors: Fatemi S. , Poppe A. R. , Barabash S.
Published: April 2020

We examine the effects of the interplanetary magnetic field (IMF) orientation and solar wind dynamic pressure on the solar wind proton precipitation to the surface of Mercury using a hybrid‐kinetic model. We use our model to explain observations of Mercury's neutral sodium exosphere and compare our results with MESSENGER observations. For the typical solar wind dynamic pressure at Mercury our model shows a high proton flux precipitates through the magnetospheric cusps to the high latitudes on both hemispheres on the dayside, centered near the noon meridian with ∼11° latitudinal extent in the north and ∼21° latitudinal extent in the south, which is consistent with MESSENGER observations. We show that this two‐peak pattern is controlled by the radial component (Bx) of the IMF and not the Bz. Our model suggests that the southward IMF and its associated magnetic reconnection do not play a major role in controlling plasma precipitation to the surface of Mercury through the cusps. We found that the total precipitation rate through both of the cusps remain constant and independent of the IMF orientation. We also show that the solar wind proton incidence rate to the entire surface of Mercury is higher when the IMF has a northward component and nearly half of the incidence flux impacts the low latitudes on the nightside. During extreme solar events (e.g., coronal mass ejections), our model suggests that over 70 nPa solar wind dynamic pressure is required for the entire surface of Mercury to be exposed to the solar wind plasma.
Global ENA Imaging and In Situ Observations of Substorm Dipolarization on 10 August 2016
Authors: Goldstein J. , Valek P. W. , McComas D. J. , Redfern J. , Spence H. , Skoug R. M. , Larsen B. A. , D. Reeves G. , Nakamura R.
Published: April 2020

This paper presents the first combined use of data from Magnetospheric Multiscale (MMS), Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS), and Van Allen Probes (RBSP) to study the 10 August 2016 magnetic dipolarization. We report the first correlation of MMS tail observations with TWINS energetic neutral atom (ENA) images of the ring current (RC). We analyze 15‐min, 1° TWINS 2 images in 1–50 keV energy bins. To characterize the high‐altitude RC we extract peak ENA flux from L= 2.5 to 5 in the postmidnight sector. We estimate peak low‐altitude ion flux from ENAs near the Earth's limb. For a local perspective, we use spin‐averaged proton fluxes from the RBSP A Helium Oxygen Proton Electron (HOPE) spectrometer. We find that the 1000 UT dipolarization triggered an abrupt and significant increase in low‐altitude ions and a gradual but modest increase in the high‐altitude RC. The relative strength and timing of the low versus high‐altitude flux indicate that the dipolarization isotropized the injected ions and initially filled the loss cone. The substorm injection brought cooler ions in from the magnetotail, reducing the peak energy at both low and high altitudes. The post‐dipolarization low‐altitude flux exhibited a decay rate dispersion favoring longer decay times at lower energies, possibly caused by growth of the low energy RC providing enhanced flux into the loss cone. A variety of finer scale local injection structures were observed in the high‐altitude RC both before and after the dipolarization, and the average system level RC intensity increased after 1000 UT.
Distinct Mechanisms Underlying Interannual to Decadal Variability of Observed Salinity and Nutrient Concentration in the Northern North Sea
Authors: Pätsch Johannes , Gouretski Viktor , Hinrichs Iris , Koul Vimal
Published: April 2020

The influence of large‐scale oceanic circulation on salinity in the northern North Sea has lead to the hypothesis that nutrient concentrations in this region are also driven by remote oceanic anomalies. Here, using a newly established biogeochemical data set of the North Sea, we show that interannual to decadal variability in winter nutrient concentrations exhibits distinct phase deviations from salinity. The variability in salinity is explained by zonal shifts in the position of the subpolar front (SPF) in the eastern North Atlantic and the associated advective delay. However, the high correlation and absence of advective delay between the position of the SPF and winter nutrient concentrations in the Shetland region (59–61°N, 1°W to 3°E) point to the role of atmospheric variability in driving concurrent changes in winter nutrient concentrations and the SPF position. Our analysis suggests that the prevailing wind direction and local distribution of winter nutrient concentrations together determine the interannual to decadal variability in winter nutrient concentrations in this region. In the analyzed observations, we find a strong spatial gradient in mean winter nutrient concentrations northwest of the Shetland region, which is absent in salinity. The horizontal shift of this spatial gradient, forced by changes in wind direction, has a larger influence on winter nutrient concentration in the Shetland region than the nutrient signal in oceanic anomalies originating from the eastern subpolar North Atlantic. Overall, we conclude that interannual to decadal variability in the observed nutrient concentrations is mainly driven by atmospheric variability here expressed as wind direction.
Impact of Cloud Physics on the Greenland Ice Sheet Near‐Surface Climate: A Study With the Community Atmosphere Model
Authors: Lenaerts Jan T. M. , Gettelman Andrew , Van Tricht Kristof , van Kampenhout Leo , Miller Nathaniel B.
Published: April 2020

The Greenland Ice Sheet (GrIS) is losing mass in an accelerated fashion, which is for ~60% dominated by an increase in surface melting. Clouds exhibit an important control on the GrIS surface energy balance and surface melt. Therefore, to better simulate present and future GrIS climate, it is essential to represent clouds correctly in climate models. Here we use ground (at Summit Station) and satellite remote sensing (from CloudSat‐CALIPSO) observations to evaluate GrIS cloud characteristics in several versions of the Community Atmosphere Model (CAM) over the period 2007–2012. Cloud cover, phase, water path, and radiative effects over the GrIS vary widely across the atmosphere models. Thanks to the inclusion of new cloud physical parameterizations, that is, ice nucleation and prognostic precipitation, in the most recent CAM version (CAM6), this model, amongst the various CAM versions, is best able to represent GrIS clouds, summer temperatures, and surface melting. However, CAM6 shows excessive rainfall over the ice sheet, which is an important outstanding model bias. Our study demonstrates the importance of simulating realistic cloud properties to improve climate model simulations of GrIS climate and climate change.
Climate State Dependence of Arctic Precipitation Variability
Authors: Bogerd L. , van der Linden E. C. , Krikken F. , Bintanja R.
Published: April 2020

Arctic precipitation is projected to increase more rapidly than the global mean in warming climates. However, warming‐induced changes in the variability of Arctic precipitation, which are related to surface evaporation and poleward moisture transport (PMT), are currently largely unknown. This study compares the precipitation variability in different quasi‐equilibrium climates simulated by a global climate model (EC‐Earth) and studies the underlying mechanisms. Five quasi‐equilibrium simulations of 400 years length forced with a broad range of CO2 concentrations (0.25, 0.5, 1, 2, and 4 times the current global mean) were analyzed. PMT is the dominant source of Arctic precipitation variability in colder climates when the ocean in the Arctic basin is completely covered by sea ice year‐round. Arctic precipitation variability increases from colder to warmer climates, primarily in summer. In summer, the increasingly stronger relation between Arctic sea level pressure variability and precipitation variability toward warmer climates enhances variability. In winter, the severe increase in mean precipitation (due to enhanced evaporation) exerts a comparatively small increase in variability, and precipitation variability is modulated by both PMT and evaporation, which oppose each other as they both affect the vertical and meridional moisture gradients.
A Model‐Based Investigation of Terrestrial Plant Carbon Uptake Response to Four Radiation Modification Approaches
Authors: Duan Lei , Cao Long , Bala Govindasamy , Caldeira Ken
Published: April 2020

A number of radiation modification approaches have been proposed to counteract anthropogenic warming by intentionally altering Earth's shortwave or longwave fluxes. While several previous studies have examined the climate effect of different radiation modification approaches, only a few have investigated the carbon cycle response. Our study examines the response of plant carbon uptake to four radiation modification approaches that are used to offset the global mean warming caused by a doubling of atmospheric CO2. Using the National Center for Atmospheric Research Community Earth System Model, we performed simulations that represent four idealized radiation modification options: solar constant reduction, sulfate aerosol increase (SAI), marine cloud brightening, and cirrus cloud thinning (CCT). Relative to the high CO2 state, all these approaches reduce gross primary production (GPP) and net primary production (NPP). In high latitudes, decrease in GPP is mainly due to the reduced plant growing season length, and in low latitudes, decrease in GPP is mainly caused by the enhanced nitrogen limitation due to surface cooling. The simulated GPP for sunlit leaves decreases for all approaches. Decrease in sunlit GPP is the largest for SAI which substantially decreases direct sunlight, and the smallest for CCT, which increases direct sunlight that reaches the land surface. GPP for shaded leaves increases in SAI associated with a substantial increase in surface diffuse sunlight, and decreases in all other cases. The combined effects of CO2 increase and radiation modification result in increases in primary production, indicating the dominant role of the CO2 fertilization effect on plant carbon uptake.
A Laboratory Dust Generator Applying Vibration to Soil Sample: Mineralogical Study and Compositional Analyses
Authors: Qu Z. , Trabelsi A. , Losno R. , Monna F. , Nowak S. , Masmoudi M. , Quisefit J.‐P.
Published: April 2020

A laboratory study was carried out using a vibrating system (SyGAVib) to produce aerosols from four soils collected in the central Tunisian region around Sfax. The aim of this device is to mimic dust emission by natural wind erosion. Using compositional analysis, the dust produced was compared to (i) dust generated in a wind tunnel by the same soils, (ii) fine sieved and (iii) original bulk soils, and (iv) naturally occurring aerosol samples collected in the same area. The relative quartz content strongly decreases from bulk to fine soils, and again from fine soils to both wind tunnel and vibration‐generated aerosols. Compositional data analysis (CoDA) clearly shows (i) a silica dilution effect in bulk soils, and (ii) that if silica is removed from the composition, the elemental compositions of fine soils and generated aerosols are similar but differ from bulk soils. Both aerosol generation methods produce material with chemical compositions that are also close to those measured in field‐sampled aerosols, and the fine soil composition is much closer to that of field and laboratory aerosols than to the parent soil. Aerosols generated from soils in the laboratory, either using a vibrating system or a wind tunnel, can be used as surrogates of the particles collected directly in the field.
Multilevel Nitrogen Additions Alter Chemical Composition and Turnover of the Labile Fraction Soil Organic Matter via Effects on Vegetation and Microorganisms
Authors: Chen Qiuyu , Niu Bin , Hu Yilun , Wang Jian , Lei Tianzhu , Xu‐Ri  , Zhou Jizhong , Xi Chuanwu , Zhang Gengxin
Published: April 2020

Global nitrogen (N) deposition greatly impacts soil carbon sequestration. A 2‐yr multiple N addition (0, 10, 20, 40, 80, and 160 kg N·ha−1·yr−1) experiment was conducted in alpine grassland to illustrate the mechanisms underlying the observed soil organic matter (SOM) dynamics on the Qinghai‐Tibet Plateau (QTP). Labile fraction SOM (LF‐SOM) fingerprints were characterized by pyrolysis‐gas chromatography/tandem‐mass spectrometry, and microbial functional genes (GeoChip 4.6) were analyzed in conjunction with LF‐SOM fingerprints to decipher the responses of LF‐SOM transformation to N additions. The significant correlations between LF‐SOM and microbial biomass, between organic compounds in LF‐SOM and compound degradation‐related genes, and between LF‐SOM and net ecosystem exchange implied LF‐SOM were the main fraction utilized by microorganisms and the most sensitive fraction to N additions. The LF‐SOM increased at the lowest N addition levels (10 and 20 kg N·ha−1·yr−1) and decreased at higher N addition levels (40 to 160 kg N·ha−1·yr−1), but the decrease of LF‐SOM was weakened at 160 kg N·ha−1·yr−1 addition. The nonlinear response of LF‐SOM to N additions was due to the mass balance between plant inputs and microbial degradation. Plant‐derived compounds in LF‐SOM were more sensitive to N addition than microbial‐derived and aromatic compounds. It is predicted that when the N deposition rate increased by 10 kg N·ha−1·yr−1 on the QTP, carbon sequestration in the labile fraction may increase by nearly 170% compared with that under the current N deposition rate. These findings provide insight into future N deposition impacts on LF‐SOM preservation on the QTP.
The Influence of Lithospheric Mantle Scars and Rheology on Intraplate Deformation and Orogenesis: Insights From Tectonic Analog Models
Authors: Santimano Tasca , Pysklywec Russell
Published: April 2020

Structural heterogeneities in the deep lithosphere have been identified as an important factor in crustal tectonics, particularly where inherited deep zones of weakness may initiate orogenesis in continent interiors. Aside from structural heterogeneity, the rheological strength of the lithosphere may also have a primary role affecting the kinematics of deformation in the lithosphere. To investigate the interplay of rheology and preexisting structures, we designed a set of physical scaled analog experiments for a convergent setting that tests (a) the presence and absence of a preexisting weak zone in the lithospheric mantle and (b) the effects of the rheological strength of the lithospheric mantle. Tectonic evolution of the model is recorded to acquire a time series data set of the velocity field and subsequently strain in the model. Results show that a weak zone in the lithospheric mantle allows deformation to be accommodated by displacement along this zone and into the overlying lower and upper crust, regardless of lithosphere strength. In contrast, a model absent of a weak zone accommodates deformation by folding and thickening of the viscous layers. The viscous lithosphere in models with a strong lithospheric mantle tends to buckle creating a sequence of brittle faulting in the upper crust. Specifically, the rheology of the lithosphere dictates the distribution of strain. Our results are considered in the context of the formation of the Eurekan fold and thrust belts in an intraplate setting on Ellesmere Island, where deformation may be related to the influence of deep lithosphere structure(s) and deep lithosphere strength.
A Dynamic Water Balance/Nonlinear Reservoir Model of a Perched Phreatic Aquifer–River System With Hydrogeologic Threshold Effects
Authors: O'Reilly Andrew M. , Holt Robert M. , Davidson Gregg R. , Patton Austin C. , Rigby James R.
Published: April 2020

Heterogeneity in the hyporheic zone or near‐field geology can impart a threshold effect on groundwater‐surface water (GW‐SW) exchange. Variations in the texture of riverbed sediments and lithologic variations in adjacent and underlying geology are examples of common heterogeneities. Hydrologic interaction with these heterogeneities leads to distinct types of “behavior” that “switch” when surface water or groundwater levels rise above or fall below the interface of the layers of differing lithology. A dynamic water balance/nonlinear reservoir model incorporating threshold effects was developed for a perched phreatic aquifer–river system. Four conceptualizations of the system were modeled, each of which simulates a perched aquifer as a dynamical system that receives recharge from the riverbank and loses water to an underlying regional aquifer, using combinations of zero, one, or two thresholds representing layered heterogeneity in riverbank and/or aquifer lithology. Application of the model code was demonstrated at a location in the Lower Mississippi River Valley, USA. Models were run using hourly river gage measurements, calibrated to a 382‐day period of corresponding measurements in a nearby well, and further assessed for a 3.5‐yr period representing varied hydrologic conditions. The best performance was demonstrated by the model incorporating threshold effects, which elucidated four modes of GW‐SW system behavior controlled by both riverbank (riverbed hydraulic conductivity) and aquifer (hydraulic conductivity and storage coefficient) properties. The dynamical system modeling approach incorporates the salient hydrologic processes of a GW‐SW system with layered heterogeneity. Based upon fundamental mass conservation concepts, the simple dynamic water balance/nonlinear reservoir model has broad applicability to many hydrogeologic settings.
Hyper‐Resolution Continental‐Scale 3‐D Aquifer Parameterization for Groundwater Modeling
Authors: de Graaf Inge , Condon Laura , Maxwell Reed
Published: April 2020

Groundwater is the world's most important freshwater resource. Despite this importance, groundwater flow and interactions between groundwater and other parts of the hydrological cycle are often neglected or simplified in large‐scale hydrological models. One of the challenges in simulating groundwater flow and continental to global scales is the lack of consistent globally available hydrogeological data. These input data are needed for a more realistic physical representation of the groundwater system, enabling the simulation of groundwater head dynamics and lateral flows. A realistic representation of the subsurface is especially important as large‐scale hydrological models move to finer resolutions and aim to provide accurate and locally relevant hydrologic information everywhere. In this study, we aim at improving and extending on current available large‐scale data sets providing information of the subsurface. We present a detailed aquifer representation for the continental United States and Canada at hyper resolution (250 × 250 m). We integrate local hydrogeological information, including observations of aquifer layer thickness, conductivity, and vertical structure, to obtain representative aquifer parameter values applicable to the continental scale. The methods used are simple and can be expanded to other parts of the world. Hydrological simulations were performed using the integrated hydrological model ParFlow and demonstrated improved model performance when using the new aquifer parameterization. Our results support that more detailed and accurate aquifer parameterization will advance our understanding of the groundwater system at larger scales.
An Example of Augmenting Regional Sensitivity Analysis Using Machine Learning Software
Authors: Spear Robert C. , Cheng Qu , Wu Sean L.
Published: April 2020

Regional sensitivity analysis, RSA, has been widely applied in assessing the parametric sensitivity of environmental and hydrological models, in part because of its inherent simplicity. In that spirit, this paper reports an example of an augmented approach to improve its utility in ranking parameter importance, beyond reliance solely on the univariate marginal distributions, to include parametric interactions. Both a deterministic and a stochastic model of the transmission of dengue, an important mosquito‐borne disease, were used to explore the effect of interactions to parameter importance ranking using random forests, a commonly used method based on decision trees. The importance ranking based on random forests was generally consistent with the ranking computed from earlier methods that only examined marginal distributions, but with increased importance shown by several interacting parameters. In addition, and building on an earlier application of tree‐structured density estimation, recently developed software was used to map the regions of the parameter space supporting good fits to calibration data. These methods were also found useful in revealing the scale dependence of sensitivity analysis as well as providing a means of identifying alternative explanations for the observed behavior of the system that remain consistent with calibration criteria, a phenomenon known as equifinality.
The Drivers of River Temperatures Below a Large Dam
Authors: Daniels Miles E. , Danner Eric M.
Published: April 2020

Temperature is a fundamental aspect of water quality in rivers, controlling the rate of many ecological processes. By disrupting the flow of water, large reservoirs and dams can fundamentally alter downstream temperature regimes by resetting the water temperature and flow boundary conditions at the dam release point. Therefore, it is critically important to understand how the volume and temperature of these releases interact with meteorological conditions to influence downstream temperature dynamics. In this study, we modeled temperature dynamics in a large regulated river (Sacramento River, CA, USA) to better understand how heat fluxes, and ultimately river temperatures, responded to different physical drivers connected to meteorology and the upstream boundary conditions established by dam operations. We used a quantitative process‐based model of river temperature (RAFT), combined with sensitivity analysis, to identify the dominant physical drivers of temperature in the Sacramento River, and explored how these drivers varied over space and time. The physical drivers that had the greatest influence on temperature dynamics were dam discharge temperature, air temperature, and solar radiation. The primary controlling factors were dam discharge temperature in the most upstream reaches and air temperature in the most downstream reaches. When isolating the effect of boundary conditions on downstream river temperature, we observed that temperatures closer to the dam under all but low flow conditions responded more to changes in dam discharge temperature than dam discharge volume. Understanding the spatial and temporal extents of drivers of heat flux and their relative importance is critical when managing for river temperature.
An Automated Seepage Meter for Streams and Lakes
Authors: Solomon D. Kip , Humphrey Eric , Gilmore Troy E. , Genereux David P. , Zlotnik Vitaly
Published: April 2020

We describe a new automatic seepage meter for use in soft bottom streams and lakes. The meter utilizes a thin‐walled tube that is inserted into the streambed or lakebed. A hole in the side of the tube is fitted with an electric valve. Prior to the test, the valve is open and the water level inside the tube is the same as the water level outside the tube. The test starts with closure of the valve, and the water level inside the tube changes as it moves toward the equilibrium hydraulic head that exists at the bottom of the tube. The time rate of change of the water level immediately after the valve closes is a direct measure of the seepage rate (q). The meter utilizes a precision linear actuator and a conductance circuit to sense the water level to a precision of about ±0.1 mm. The meter can also provide an estimate of vertical hydraulic conductivity (K

v
) if data are collected for a characteristic time. The detection limit for q depends on the vertical hydraulic head gradient. For K

v
 = 1 m/day, q of about 2 mm/day can be measured. Results from a laboratory sand tank show excellent agreement between measured and true q, and results from a field site are similar to values from calculations based on independent measurements of K

v
and vertical head gradients. The meter can provide rapid (30 min) q measurements for both gaining and losing systems and complements other methods for quantifying surface water groundwater interactions.
Huntsville Alabama Marx Meter Array 2: Upgrade and Capability
Authors: Zhu Yanan , Bitzer Phillip , Stewart Michael , Podgorny Scott , Corredor David , Burchfield Jeff , Carey Lawrence , Medina Bruno , Stock Michael
Published: April 2020

The Córdoba Argentina Marx Meter Array (CAMMA), consisting of 10 second‐generation Huntsville Alabama Marx Meter Array (HAMMA 2) sensors, operated at Córdoba, Argentina, during the Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign in late 2018. Initial results obtained from the campaign demonstrate that the new sensor is able to provide a significantly more detailed depiction of various lightning processes than its first generation. The lightning flashes mapped by the CAMMA and a colocated Lightning Mapping Array (LMA) were compared. The overall flash structures mapped by the CAMMA and the LMA look similar for most of the flashes. However, comparisons at smaller time scale show that the majority of CAMMA and LMA sources are not concurrent, indicating that unmatched sources were possibly due to different physical processes in leader propagation dominating different frequencies and differences in data processing and location techniques.
Electron Pitch‐Angle Distribution in Earth's Magnetotail: Pancake, Cigar, Isotropy, Butterfly, and Rolling‐Pin
Authors: Liu C. M. , Fu H. S. , Liu Y. Y. , Wang Z. , Chen G. , Xu Y. , Chen Z. Z.
Published: April 2020

Electron pitch‐angle distributions, including isotropy, pancake, cigar, butterfly, and recently discovered rolling‐pin distributions, are crucial to understanding electron dynamics in the magnetotail. However, occurrence rates of these distributions remain unclear. Here, for the first time, we reveal the occurrence rates of these distributions in the magnetotail by using Cluster data during 2001–2009, with special focus on the newly reported rolling‐pin distribution. We find that percentages of these distributions are 44.7% (isotropy), 31.3% (pancake), 17.5% (cigar), 4.9% (rolling‐pin), and 1.6% (butterfly), respectively. We find that in the XYGSM plane, occurrence rates of these PADs peak near: [XGSM ≈ −11 RE, YGSM ≈ −5 RE] (isotropy), [XGSM ≈ −15 RE, YGSM ≈ −11 RE] (pancake), [XGSM ≈ −11 RE, YGSM ≈ −5 RE] (cigar), [XGSM ≈ −11 RE, YGSM ≈ −3 RE] (rolling‐pin), and [XGSM ≈ −11 RE, YGSM ≈ −4 RE] (butterfly), respectively; and along the r direction, where r is the distance to the center of the Earth in the XYGSM plane, their occurrence rates peak near: −18 RE < r < −12 RE (isotropy), −20 RE < r < −12 RE (pancake), −16 RE < r < −10 RE (cigar), r ≈ −13 RE (rolling‐pin), and −14 RE < r < −10 RE (butterfly), respectively. Such rates indicate that the rolling‐pin and cigar distributions have similar occurrence rates, supporting previous studies suggesting that rolling‐pin distributions arise from cigar distributions. All distributions have maximum occurrences near the equator but at different subregions. We cannot find any statistical correlation between magnetic structures and the rolling‐pin distributions, different from previous studies suggesting a close connection between them.
Influence of Dynamic Ozone Dry Deposition on Ozone Pollution
Authors: Clifton O. E. , Paulot F. , Fiore A. M. , Horowitz L. W. , Correa G. , Baublitz C. B. , Fares S. , Goded I. , Goldstein A. H. , Gruening C. , Hogg A. J. , Loubet B. , Mammarella I. , Munger J. W. , Neil L. , Stella P. , Uddling J. , Vesala T. , Weng E.
Published: April 2020

Identifying the contributions of chemistry and transport to observed ozone pollution using regional‐to‐global models relies on accurate representation of ozone dry deposition. We use a recently developed configuration of the NOAA GFDL chemistry‐climate model—in which the atmosphere and land are coupled through dry deposition—to investigate the influence of ozone dry deposition on ozone pollution over northern midlatitudes. In our model, deposition pathways are tied to dynamic terrestrial processes, such as photosynthesis and water cycling through the canopy and soil. Small increases in winter deposition due to more process‐based representation of snow and deposition to surfaces reduce hemispheric‐scale ozone throughout the lower troposphere by 5–12 ppb, improving agreement with observations relative to a simulation with the standard configuration for ozone dry deposition. Declining snow cover by the end of the 21st‐century tempers the previously identified influence of rising methane on winter ozone. Dynamic dry deposition changes summer surface ozone by −4 to +7 ppb. While previous studies emphasize the importance of uptake by plant stomata, new diagnostic tracking of depositional pathways reveals a widespread impact of nonstomatal deposition on ozone pollution. Daily variability in both stomatal and nonstomatal deposition contribute to daily variability in ozone pollution. Twenty‐first century changes in summer deposition result from a balance among changes in individual pathways, reflecting differing responses to both high carbon dioxide (through plant physiology versus biomass accumulation) and water availability. Our findings highlight a need for constraints on the processes driving ozone dry deposition to test representation in regional‐to‐global models.
Synthesis of Mn3O4 nanozymes from structurally characterized phenoxazinone synthase models based on manganese(iii) Schiff base complexes
Authors: Mandal Arnab , Dasgupta Sanchari , Adhikary Amit , Samanta Debabrata , Zangrando Ennio , Das Debasis
Published: April 2020

Mn3O4 nanozymes of phenoxazinone synthase have been prepared from the manganese(iii) based mimicking models of the enzyme.
Enhancing the structural durability of Ni-rich layered materials by post-process: washing and heat-treatment
Authors: Lee Wontae , Lee Donghyun , Kim Yunok , Choi Woosung , Yoon Won-Sub
Published: April 2020

Post-process (i.e., heat-treatment after washing) enables Ni-rich layered materials to have an enhanced structural durability in addition to a surface stabilization, consequently improving the electrochemical performances.
Inkjet printing a small-molecule binary emitting layer for organic light-emitting diodes
Authors: Mu Lan , He Mengjiao , Jiang Congbiao , Wang Juanhong , Mai Chaohuang , Huang Xiaolan , Zheng Hua , Wang Jian , Zhu Xu-Hui , Peng Junbiao
Published: April 2020

Inkjet printing a synthesized small-molecule host material and its blend for OLEDs with a single solvent.
Feature cognitive model combined by an improved variational mode and singular value decomposition for fault signals
Authors: Chen Jinxiang , Zhu Zhu , Zhang Xiaoda
Published: April 2020

A feature cognitive model combined with an improved variational mode and singular value decomposition is presented to recognise the characteristics of the fault signals from vibration signals of mechanical equipment in this study. Specifically, the variational mode model is constructed firstly to decompose the known fault signals for mechanical equipment with the same load. Singular value decomposition approach is applied to recognise further the inherent modal features of the fault signals and construct the feature set. The supervised learning‐support vector machine and the unsupervised learning‐fuzzy c‐means clustering are used to verify the effectiveness of the presented method. Finally, the provided feature cognitive model is used to recognise the bearing faults to verify its effectiveness. From simulation results, it can be seen that compared to the complete integration empirical mode decomposition method, the feature cognitive model combined by an improved variational mode and singular value decomposition can obtain more higher accuracy and larger evaluation coefficients. It is worth mentioning that the presented method can also be applied to recognise the key characteristics of the other signals.
Iterative maximum likelihood estimation of the compound inverse Gaussian clutter parameters
Authors: Belhi K. , Soltani F. , Mezache A.
Published: April 2020

This Letter aims at proposing a cost‐effective method for estimating the parameters of the compound inverse Gaussian distributed clutter. Under the assumption of the absence of thermal noise, an iterative maximum likelihood estimator (IMLE) is proposed and compared with existing MLE, the [zlog(z)] estimator, the non‐integer order moments estimator and the higher order moment estimator. The results obtained show that the IMLE method outperforms all the other methods and has similar estimation performance than the MLE method but requires lower computational time.
Investigations on pulse compression favourable thermal imaging approaches for characterisation of glass fibre‐reinforce polymers
Authors: Rani A. , Mulaveesala R.
Published: April 2020

Active infrared imaging is one of the promising remote and whole field characterisation techniques for non‐destructive testing and evaluation of various solids irrespective of their electrical and magnetic prosperities. This technique relies on a mapping of thermal response for a predefined incident heat flux over the test object to detect the presence of surface and subsurface anomalies. Due to its fast, non‐contact, safe and quantitative testing capabilities, infrared thermography has gained significant importance in the testing of fibre reinforced polymers. This Letter highlights testing and evaluation of glass fibre‐reinforced polymer (GFRP) specimen for detection of subsurface hidden defects using pulse compression favourable thermal wave imaging techniques (for an imposed digitised chirp as well as a 7‐bit Barker coded modulated heat fluxes over the test specimen). Further depth scanning capabilities of the proposed schemes have been compared using a time‐domain pulse compression based approach. Proposed analytical, as well as simulation studies, have been validated with the experimental results on GFRP material having flat bottom holes as defects.