bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing the performance of flexible barrier subjected to impacts of typical geophysical flows: a unified computational approach based on coupled CFD/DEM
Authors: Kong Yong , Zhao Jidong , Li Xingyue
Published: March 2020

Flexible barriers have been increasingly used in the mitigation of destructive geophysical flows, including rock avalanches, debris avalanches, debris flood, muddy debris flows as well as muddy flows. No rigorous analytical tools are available for the design of flexible barriers to resist a wide spectrum of geophysical flows of different natures and over a broad Froude-number range. Responses of a flexible barrier to the impacts of geophysical flows are known to be exceedingly complicated, involving intricate multi-body, multi-phase interactions, mass exchange and transportation and energy transformation/dissipation which are challenging for both numerical and physical modelers. To investigate the complex interactions between channelized geophysical flows and a non-uniform flexible barrier, a unified hydro-mechanical modeling framework was developed based on the coupled computational fluid dynamics and discrete element method (CFD/DEM). Five typical geophysical flows were modeled, for instance, a muddy debris flow was considered as a mixture of a continuous viscous fluid phase and a discrete phase consisting of gap-graded frictional particles. A permeable flexible barrier consisting of deformable meshes, cables and energy dissipators was modeled by applying the DEM accounting for connections and contact in a realistic manner. The coupled CFD/DEM model was well validated by experimental data in the literature. Based on the simulations, we examined the dynamics of flow-barrier interactions, energy dissipation mechanism, regime quantification, peak-static load ratio, momentum reduction and the correlations between flow Froude number/solid fraction and the impact mechanism transitions. It was observed that the peak-static load ratio in a flexible barrier increases while the barrier-induced momentum reduction of overflow decreases with increasing flow Froude-number. The analyses of the peak-static load ratio showed that rock avalanches generate the largest one and muddy flows generate the lowest one. For the first time, the impact mechanism transitions from pile-up to run-up for five geophysical flows impacting on a non-uniform flexible barrier were quantitatively identified according to the approaching flow dynamics and solid fraction. (The study was supported by RGC/HK under T22-603/15N and GRF#16205418.​)
Capacity of bioenergy with carbon capture and storage in China consistent with the global remaining carbon budget
Authors: Wang Rong ,   BECCS group
Published: March 2020

Bioenergy with carbon capture and storage (BECCS) is one of negative-emission technologies that must be applied if we are to achieve the 1.5 °C, or even the 2 °C, warming targets of the Paris Agreement. As a start, existing coal-fired power plants could be retrofitted to co-fire with biofuel from agricultural and forestry residues, but the potential and costs of BECCS are as yet unassessed. Here, we modelled an optimal county-scale network of BECCS in China, by considering: spatial information on biofuel feedstock; power-plant retrofitting to increase the use of biofuel; biofuel transport to power stations and CO2 transport to geological repositories for carbon storage; and BECCS life-cycle emissions. BECCS at marginal costs of $100 per tonne CO2-equivalent (t CO2-eq)-1 could abate net CO2-eq emissions by up to  Gt yr-1, assuming that CO2 emitted by power plants could be captured at 90% efficiency and accounting for additional emissions of greenhouse gases from the production cycle of BECCS. Because of the huge stock of useable agricultural and forestry residues in China, this carbon price leverages 20 times more mitigation of CO2 emissions by BECCS in China than in western North America. To cap cumulative emissions over 2011-2030 from China’s power sector at 5% of the global remaining carbon budget for the 2 °C limit since 2011, BECCS would require marginal costs of $ (t CO2-eq) -1, or the equivalent of investing 0.45% of GDP to generate 1.22 PWh yr-1 of electricity by 2030; this would abate 35% more carbon emissions than the announced nationally determined contribution by China. These results clarify the economics of emission abatement by BECCS in China, suggesting that using the available domestic biofuel feedstock has the potential to make a great contribution to global carbon emission mitigation.
Sensitivity of the southern hemisphere tropospheric jet response to ozone depletion: specified versus interactive chemistry
Authors: Haase Sabine , Fricke Jaika , Matthes Katja
Published: March 2020

Southern hemisphere lower stratospheric ozone depletion has been shown to lead to a poleward shift of the tropospheric jet stream during austral summer, influencing surface atmosphere and ocean conditions, such as surface temperatures and sea ice extend. The characteristics of stratospheric and tropospheric responses to ozone depletion, however, differ among climate models largely depending on the representation of ozone in the model.

The most accurate way to represent ozone in a model is to calculate it interactively. However, due to computational costs, in particular for long-term coupled ocean-atmosphere model integrations, the more common way is to prescribe ozone from observations or calculated model fields.

Here, we investigate the difference between an interactive chemistry and a specified chemistry version of the same atmospheric model in a fully-coupled setup using a large 9-member model ensemble. In contrast to most earlier studies, we use daily-resolved ozone fields in the specified chemistry simulations to achieve a better comparability between the ozone forcing with and without interactive chemistry. We find that although the short-wave heating rate trend in response to ozone depletion is the same in the different chemistry settings, the interactive chemistry ensemble shows a stronger trend in polar cap stratospheric temperatures and circumpolar stratospheric and tropospheric zonal mean zonal winds as compared to the specified chemistry ensemble. We attribute part of these differences to the missing representation of feedbacks between chemistry and dynamics in the specified chemistry ensemble and part of it to the lack of zonal asymmetries in the prescribed ozone fields.

This study emphasizes the value of interactive chemistry for the representation of the southern hemisphere tropospheric jet response to ozone depletion.
A unified diagnostic platform to quantify the source of uncertainty in modelling global SOC dynamics
Authors: Liao Cuijuan , Chen Yizhao , Huang Yuanyuan , Lu Xingjie , Huang Xiaomeng , Liang Yishuang , Luo Yiqi
Published: March 2020

As the largest carbon reservoir in biosphere, soil organic carbon (SOC) has been extensively studied. However, the large uncertainty of modeling SOC  impedes the accurate prediction of global carbon dynamics in response to climate change. Thus, evaluating and tracing the sources of large uncertainty in predicting SOC dynamics by Earth system models are the urgently needed to improve our understanding and predicting capability. Although great efforts have been made to predict land C storage using multiple models, disentangle uncertainty sources among models are still extremely difficult. To take this challenge, we developed a Matrix-based ensemble Model Inter-comparison Platform (MeMIP). MeMIP is an integrated platform to quantify the various sources of uncertainty under a unified framework. MeMIP is embedded a new community-based ESM, Community Integrated Earth System Model (CIESM) and implemented in the super-computing cluster in Wuxi, China. Within the MeMIP, multiple SOC decomposition schemes from different land models (e.g. CLM-CENTURY, CLM-BGC, LPJ-GUESS, JULES and CABLE) have been re -constructed in a unified matrix model format. With the unified format of matrix model, the inter-model differences can be quantitatively attributed to the sources by using the traceability analysis. In this study, we analyzed how SOC decomposition schemes and the vertical resolved SOC exchange structure (VR structure) influences SOC prediction with the three-dimension parameter output (NPP, residence time and carbon storage potential) space. The results indicate that model with the VR structure result in significantly higher SOC predictions and introduced higher uncertainty than single layer models. It is mainly due to increased residence time, which is also very sensitive to future warming. The identified major uncertain components are targets for improvement via data assimilation. Overall, MeMIP provides a modeling platform that not only unifies all land carbon cycle models in the matrix form but also offers traceability analysis to identify sources of uncertainty and data assimilation to constrain multiple model ensemble prediction.
Modeling morphological changes by tsunami Induced currents
Authors: Son Sangyoung , Jung Taehwa , Kim Dae-Hong , Yoon Hyun-Doug
Published: March 2020

At the nearshore area, strong and energetic flow fields can be easily formed during the tsunami event and it is hence expected coastal morphology is significantly affected by complex tsunami-induced current. In this study, the morphological changes by tsunami impacts on the US west coasts were investigated by numerical modeling. Firstly, we introduced a developed numerical model for calculating morphological changes by the tsunami wave, which incorporates a set of sub-models; hydrodynamics, sediment transport and morphological evolution models. The fully nonlinear Boussinesq-type model was adopted in the hydrodynamics calculations aiming at the better recreation of nearshore current fields which easily develop into turbulent flows due to various types of sources (e.g., wave-breaking). Then, the benchmark tests of one-dimensional or two-dimensional sedimentation problems were performed for validation; dam-break flow over the movable bed, breaking solitary waves over a sloping beach, partially breached dam-break flow over the mobile bed, and dam-break flows over a movable bed with a sudden enlargement. Calculated results revealed good agreement with the experimental records when a reasonable parameter has been chosen for closure models. As a real-scale application of the model, the 2011 Tohoku-Oki tsunami event was attempted, which subsequently presented a good prediction of tsunami-generated scouring and deposition in harbors. It was also confirmed that strong currents were successfully generated through the model, causing severe depth changes through the sedimentation process. To provide a rough guide for prospective users, we also performed several types of sensitivity tests on many parameters involved in the model
Observations of an Electron-only Magnetic Reconnection within a macroscopic Flux Rope in the Magnetotail
Authors: Man Hengyan , Zhou Meng , Yi Yongyuan , Zhong Zhihong , Deng Xiaohua
Published: March 2020

It is widely accepted that flux ropes play important roles in the momentum and energy transport in space plasmas. Recent observations found that magnetic reconnection occurs at the interface between two counter flows around the center of flux ropes. In this presentation, we report a novel observation by MMS that reconnection occurs at the edge of a large-scale flux rope, the cross-section of which was about 2.5 Re. The flux rope was observed at the dusk side in Earth’s magnetotail and was highly oblique with its axis proximity along the XGSM direction. We found an electron-scale current sheet near the edge of this flux rope. The Hall magnetic and electric field, super-Alfvénic electron outflow, parallel electric field and positive energy dissipation were observed associated with the current sheet. All the above signatures indicate that MMS detected a reconnecting current sheet in the presence of a large guide field. Interestingly, ions were not coupled in this reconnection, akin to the electron-only reconnection observed in the magnetosheath turbulence. We suggest that the electron-scale current sheet was caused by the strong magnetic field perturbation inside the flux rope. This result will shed new lights for understanding the multi-scale coupling associated with flux ropes in space plasmas.
Highly stressed lower crust: Evidence from dry pseudotachylytes in granulites, Lofoten, Norway
Authors: Dunkel Kristina G. , Zhong Xin , Morales Luiz F. G. , Jamtveit Bjørn
Published: March 2020

Due to the high confining pressures in the lower crust, the generating mechanisms of lower crustal earthquakes, occurring below the standard seismogenic zone, are puzzling. Their investigation is difficult because the records of such earthquakes, pseudotachylytes, are typically reacted and/or deformed. Here we describe exceptionally pristine pseudotachylytes in lower crustal granulites from the Lofoten Vesterålen Archipelago, Norway. The pseudotachylytes have essentially the same mineralogical composition as their host (plagioclase, alkali feldspar, orthopyroxene) and contain microstructures indicative of rapid cooling (microlites, spherulites, ‘cauliflower’ garnet). Neither the wall rock nor the pseudotachylytes themselves contain hydrous minerals, and no mylonites are associated with the pseudotachylytes. This excludes the most commonly suggested weakening mechanisms that may cause earthquakes below the brittle-ductile transition: dehydration- or reaction-induced embrittlement, plastic instability, thermal runaway, and downward propagation of seismic rupture from shallow faults into their deeper ductile extensions. Hence, we suggest that transient stress pulses caused by shallower earthquakes are the most likely explanation for the occurrence of fossil earthquakes in the analysed rocks from Lofoten.

Earthquakes are short events, but their effects on the tectonic and metamorphic development of their host can be long-lasting. The initial deformation features related to seismic events, which potentially determine these effects, are often overprinted by metamorphism driven by fluids infiltrating the rock along the seismic fault. Because of the anhydrous conditions in the present case, those structures are preserved. The wall rocks to the investigated pseudotachylytes appear undamaged in optical and backscatter electron observation; however, cathodoluminescence imaging of feldspar and quartz reveals healed fractures and alteration zones. Those areas are further investigated with electron backscatter diffraction and transmission electron microscopy to better understand the microstructural and chemical changes during and after the seismic event.
Using the temporal distribution of noise for reference noise cancelation in sNMR surveys
Authors: Kremer Thomas
Published: March 2020

The surface Nuclear Magnetic Resonance method is gaining momentum as an efficient geophysical method for the detection and characterization of groundwater. However, the method still suffers from a low signal to noise ratio mostly due to electromagnetic noise of anthropic origin.

To solve this problem, signal processing in surface nuclear magnetic resonance surveys often relies on the reference-based noise cancellation technique. This method consists of capturing the main characteristics of the noise through a secondary loop ideally located and obtaining an estimate of the noise affecting the primary loop which can be subtracted from the noisy sNMR signal.

The main problem associated with the method occurs when the spatial distribution of the noise is heterogeneous, which can result in a low correlation between the reference loop and the primary loop, and hence in a poor noise reduction. Difficulties may also arise when the field survey location prevents the display of a reference loop for logistics or physical reasons.

To remediate these situations we have investigated the possibility of recording noise-only signals through the primary loop, prior to the sNMR measurement, and use those signals as references for subsequent calculation of the local transfer function. The correlation between a series of noise-only signal recorded on a primary loop was analyzed through the computation of the magnitude squared coherence function, and comparison was made with noise records from a secondary loop. The analysis demonstrates that temporal reference noise cancellation (TRNC) can provide more efficient noise reduction results than the classical spatial reference noise cancellation if the temporal noise-only database is large enough.

Such a technique would be particularly suited for the development of long-term sNMR monitoring systems, where noise records could be acquired for long periods without any difficulty. In addition to two field survey examples, we present a synthetic statistical analysis to estimate the minimal volume of the signal database required for optimal noise reduction.
Poroelastic effects of the damaged zone on seismic fracture reflectivity
Authors: Sotelo Gamboa Edith , Solazzi Santiago  G. , Rubino German J. , Barbosa Nicolas D. , Holliger Klaus
Published: March 2020

The presence of fractures has a predominant influence on the hydraulic and mechanical behavior of rocks. These effects are particularly pronounced and relevant for otherwise largely impermeable and stiff formations. There is widespread evidence pointing to the ubiquitous presence of damaged zones surrounding fractures and faults. The enhanced permeability associated with these zones can promote fluid pressure diffusion in the vicinity of fractures when seismic waves travel through the corresponding subsurface volume. This process, together with the inherent mechanical weakness of damaged zones, is expected to affect the seismic reflectivity of fractures and faults. We investigate these effects based on Biot’s theory of poroelasticity. To this end, we consider a 1D layered representation of the fracture and the associated damaged zone in conjunction with embedding elastic and impermeable half-spaces. We compare a fully elastic fracture-background reference model with a model consisting of a poroelastic fracture and damaged zone enclosed within an elastic background. For these two models, we compute the normal incidence seismic P-wave reflectivities at the background-fracture and at background-damaged zone interfaces, respectively. We also include a model that represents the fracture-damaged zone poroelastic system as an equivalent viscoelastic layer. We aim to test the validity of this representation since it would imply that a similar correspondence is possible to establish when more realistic descriptions of the damaged zone are considered. For this additional model, the viscoelastic layer is characterized by its frequency-dependent P-wave modulus, estimated by applying White’s classical upscaling procedure for 1D poroelastic media composed of alternating layers. We test the validity of the elastic-viscolastic model by comparing its reflectivity against the corresponding results from the elastic-poroelastic model. In doing so, we find that the simplified elastic-viscoelastic model faithfully reproduces the reflectivity of its elastic-poroelastic counterpart up to a threshold frequency, at which resonances produced within the viscoelastic layer become dominant. Overall, our results show that, in the seismic frequency range, there is a substantial increase in seismic fracture reflectivity resulting from the combined effects of fluid pressure diffusion and mechanical weakening associated with the surrounding damaged zone. This, in turn, indicates that the seismic reflectivity of a fracture may indeed be dominated by the thickness and physical properties of its surrounding damaged zone rather than by the properties of the fracture sensu stricto.
IAG Working Group on “Connectivity in Geomorphology”: Introduction and status report
Authors: Parsons Anthony , Pöppl Ronald
Published: March 2020

In 2019 a new IAG (International Association of Geomorphologists) Working Group on “Connectivity in Geomorphology” has been established. In bringing together the experience and expertise of researchers in the emerging field of connectivity in geomorphology, this IAG-WG aims to enable the transitions a) from parallel projects to concerted research (incl. a transdisciplinary framework with strong linkages to practitioners/applied aspects, e.g. management of water and sediment in catchments), b) from a plethora of case studies to more generic, comparable research, c) from a multiplicity of definitions, concepts and methodological approaches to coordinated, theory-guided research activity along agreed lines, which will provide both immediate benefit for existing projects and a springboard for the development of future research projects. The overarching aim of this WG is to form an international network of Connectivity scientists, to share expertise and develop a consensus on the definition and scientific agenda regarding the emerging field of connectivity in geomorphology. With this poster presentation we would like to communicate our mission statement to the EGU audience, further discussing about recent and future activities of the Working Group
What is the natural rhythm of temperate and boreal forest disturbances in the absence of human management?
Authors: Pugh Thomas , Senf Cornelius , Seidl Rupert
Published: March 2020

The vast majority of temperate and much of the boreal forest have been completely transformed by human activities, changing forest composition and disturbance regimes. Whilst our capability to observe this transformed state has improved dramatically in recent years, we have precious little information on the state of these forests in the absence of management. To what extent do our forests currently suffer from a surplus or a deficit of disturbance relative to their natural state? What are the implications of this for carbon turnover? Using a novel fusion of satellite observations of stand-replacing disturbances in 80 protected areas, statistical analysis and dynamic vegetation modelling, we generated wall-to-wall estimates of disturbance frequency across northern hemisphere temperate and boreal forests. Analysis of disturbance events in the protected areas revealed that the probability of disturbances from agents including fire, wind-throw and bark beetles was related to community mean functional traits and climate. We used the LPJ-GUESS dynamic vegetation model, which explicitly simulates plant functional types covering different successional stages, to simulate forest functional composition in the absence of human management. We interactively coupled this simulation to a new disturbance probability module to generate estimates of natural disturbance probability across all northern-hemisphere temperate and boreal forests. Disturbance frequency ranged from ca. one stand-replacing event per hundred years in parts of the boreal to less than one per thousand years in broadleaved temperate forests. In many regions the unmanaged disturbance frequencies differed dramatically from those observed in reality over the last two decades, with both disturbance surplus and deficits being recorded. In addition to providing the first quantitative continental-scale assessment of human impact on forest disturbance regimes, our results also provide a lightweight modelling approach for the inclusion of natural disturbances in large-scale vegetation models. They thus facilitate simulation of forest structure, a crucial driver of ecosystem function, from carbon uptake to biodiversity.
Surface denudation and soil erosion over 300 ka at the Otago upland (New Zealand) using 10Be and 239+240Pu
Authors: Raab Gerald , Scarciglia Fabio , Norton Kevin , Martin Adam , Christl Marcus , Ketterer Michael , Egli Markus
Published: March 2020

The Tor Exhumation Approach (TEA) traditionally uses large residual granitic landforms as indicators for surface lowering over time of their surrounding landscape. This study challenged the broad applicability of this approach by using large metamorphic residual landforms instead of the traditional plutonic rock formations. We applied in-situ cosmogenic nuclide techniques (10Be) along vertical landforms (schist-tors) on the Otago upland in southern New Zealand to investigate the capabilities of the TEA within another major rock type. The aim of the investigation was to decipher surface denudation models for the last ~100 ka. The experiment was coupled with fallout radionuclides (239+240Pu) in nearby soils to compare the Pleistocene / Holocene surface denudation rates with the Anthropocene (last ~60 years).

The surface ages of the eight investigated schist-tors was between ~20 ka and ~300 ka. This allowed the numerical modeling of continuous surface denudation rates with highest values near 0.16-0.20 [mm year-1] (about 140–180 [t km-2year-1]), and over a period that has not yet been achieved. The fallout radionuclide study resulted in two different mass redistribution rates. Average soil erosion along a ridge was ~400 to ~850 [t km-2year-1], whereas in an adjacent valley soil deposition rates reached ~130 to ~1,500 [t km-2year-1]. In conclusion, this study provides a new basis on how schist-tors emerge at two different landscape positions (ridges and valleys). In addition, differences between past surface denudation rates and modern ones could be revealed.
Data assimilation of oceanic proxies in the North Atlantic over the Common Era
Authors: Goosse Hugues , Gilson Gaelle , Klein François , Lenoir Guillaume , de Vernal Anne , Evans Michael N. , Saenger Casey
Published: March 2020

The mismatch between oceanic proxy data and climate model results over the past millennia has been a long-lasting challenge. Although both are valuable sources of paleoclimate information, there is a strong discrepancy in variance between models and proxies, so that they cannot be compared directly. In addition, local sea-surface temperature (SST) reconstructions are often inconsistent among proxy types. We first performed several offline data assimilation experiments with different standardized SST proxy datasets using the climate models LOVECLIM and CESM in order to investigate the effect of proxy selection on local and regional reconstructions over the Common Era (0-2000 CE). All experiments work technically at the local scale, but the spatial pattern of the reconstructions vary with the type(s), number and density of proxies, and, where there is no proxy, the choice of the model. We then developed empirical scaling factors based on independent SST observations to correct for the discrepancy between model and proxy amplitude. While it is essential to scale proxies, scaling the model leads to complications because of the biases in the sea ice extent. Data assimilation of scaled proxies results in coherent SST reconstructions at the scale of the North Atlantic, with timing and amplitude that are in agreement with those given by forced models. Finally, results are compared to online data assimilation experiments.
Tropical cyclone genesis and trajectory characteristics in the western north Pacific
Authors: Xiong Rui , Lu Mengqian
Published: March 2020

The western North Pacific (WNP) is one of the most active tropical cyclone (TC) regions, which can inflict enormous death and massive property damage to surrounding areas. Although many studies about tropical cyclone activities on multi-timescales have been done, most of them focus on the entire basin, variations within the basin deserve more investigations. Besides TC characteristics on different timescales, to investigate the impacts of environment variables on TC and provide informative factors for prediction is another concern in the research community. In this study, we adopt several data science techniques, including Gaussian kernel estimator, wavelet, cross-wavelet coherence and regression analyses, to explore the spatiotemporal variations of TC genesis and associated environmental conditions. Significant semiannual and annual variations of TC genesis have been found in the northern South China Sea (NSCS) and oceanic areas east of the Philippines (OAEP). In the southeast part of WNP (SEWNP), TC genesis shows prominent variations on ENSO time scale. With reconstructed TC series on those frequencies, we further quantify the influences of environmental variables on the primary TC signals over WNP. About 40% of the identified TC variance over NSCS and OAEP can be explained by variability in vertical shear of zonal wind and relative humidity. In the SEWNP, TC genesis reveals strong nonlinear and non-stationary relationships with vertical shear of zonal wind and absolute vorticity. Besides, A probabilistic clustering algorithm is used to describe the TC tracks in the WNP. The best track dataset from JMA is decomposed into three clusters based on genesis location and curvature. For each cluster, we analyze the relationships between TC properties, such as genesis location, trajectory and intensity, and associated environmental conditions using the self-organizing map. The spatial patterns of sea surface temperature have huge impacts on TC genesis location, while the trajectory is largely influenced by geopotential height.
A model for off-fault plastic poroelastic deformation and its effects on permeability
Authors: Yalcin Bora , Zielke Olaf , Mai P. Martin
Published: March 2020

Fractured reservoirs comprise finite or discrete fracture networks; if these are conductive, they form heterogeneously distributed high-permeability streaks. These are generally referred as fracture corridors. Unless they occur as joint swarms, fracture corridors are simply seismic or sub-seismic fault zones with connected fractures in the near-fault damage zone. Several studies document the decrease in rock-matrix permeability adjacent to the fault surface, within the damage zone. Although the damage zone creates fracture connectivity and high permeability anisotropy for reservoirs, the matrix fracture feeding mechanism is related to matrix permeability generally described by a transfer function. This transfer function accounts for fracture properties (i.e. fracture density, length and connectivity), relative fluid mobilities, imbibition and reservoir properties (i.e. matrix permeability). Commonly, the matrix permeability for all transfer functions is considered in terms of a representative rock type permeability. However, observational evidence and our numerical model show that slip induced deformation causes significant strain on matrix in vicinity to the fault surface causing a permeability decrease in the matrix.

In this study, we present a new approach to model strain in a porous medium and related permeability changes due to stress perturbation from slip around pure strike slip faults. The fault length is used to scale the amount fault slip. For given/computed dislocation (slip) the off-fault strain is then calculated to derive porosity and permeability changes. In our study we propose an off-fault plastic-poroelastic deformation model for any known fault length and known rock mechanical and petrophysical properties of the surrounding material. Our modeling technique will help to better quantify fault transmissivity in geo-reservoirs.
Development of the NIM Mass spectrometer for Exploration of Jupiter’s Icy Moons Exospheres
Authors: Föhn Martina , Tulej Marek , Galli André , Vorburger Audrey Helena , Lasi Davide , Wurz Peter , Brandt Pontus , Barabash Stas
Published: March 2020

Investigation of habitable environments is one of the main objectives in upcoming space missions. The JUICE mission will investigate Jupiter’s environment in the solar system and its icy moons Ganymede, Callisto and Europa as examples for potentially habitable worlds around a gas giant. The Particle Environment Package (PEP) on the JUICE satellite will investigate Jupiter’s icy moons and their environment. As part of PEP, the Neutral gas and Ion Mass spectrometer (NIM) will measure the chemical composition of the exospheres of the icy moons. These measurements give information about the surface composition of the moons and will set constraints on their formation processes.

NIM is a Time of Flight mass spectrometer with two entrances for neutral particles and ions. The gas enters the instrument from spacecraft ram direction. With the open source neutral particles and ions enter the ionisation region directly. With the closed source neutral particles get thermalized using an antechamber before entering the ion source. Particles entering with higher velocity are therefore easier to detect through the antechamber.

Initial performance tests with the NIM Protoflight Model (PFM) were done. The storage capability of the ion source was tested, the functionality of the antechamber was verified and we measured masses up to 642 u to demonstrate the high-mass performance of NIM. Furthermore, different subunits of the NIM instrument were successfully tested, such as the redesigned ion source and flight electronics connected with the NIM sensor head.
Strain partitioning in a collapsing hot orogeny
Authors: Temporim Filipe , Trindade Ricardo , Tohver Eric , Egydio-Silva Marcos , Valim Tiago
Published: March 2020

Large, hot orogens are characterized by an orogenic plateau supported by a zone of weak ductile flow. During the collision phase, the magnitude of the belt and the temperature increase as radioactive crustal material is accreted, buried and heated. After convergence ends, no material is added to the orogenic system and the orogen undergo gravitational (or extensional) collapse that results from the lateral flow of the hot orogenic infrastructure. In the Araçuaí-West Congo orogen (AWO), the high temperatures, slow cooling, and excessive amount of melt in the hinterland, in the northern part of the belt, imply that a high temperature was maintained for a long time. Geochronologic results suggest that this internal domain was hot for a long time, cooling at < 3°/Myr since 600 Ma until 500 Ma, and cooling through the Ar/Ar retention temperature for biotite occurred around 470 Ma. In the south the collapse of the orogen is marked by the widespread intrusion of bimodal, composite plutons at ~500 Ma. Here we use the magnetic fabric (i.e. low-field anisotropy of magnetic susceptibility) of intrusions in the north and south sectors to track the kinematics and rheological changes across the belt. In the northern part of the AWO we studied the Padre Paraíso Charnockite and the southern part of the AWO we studied the Conceição de Muqui and Santa Angélica plutons. The Padre Paraíso charnockite has a coherent magnetic fabric, with magnetic foliations trending N-S, following the general structure of the belt in that sector. In turn, Conceição de Muqui and Santa Angélica plutons show a concentric distribution of foliations and lineations, in starking contrast with the general NE-SW trend of the belt in the south. This contrasting structural pattern for coeaval plutons along the AWO belt reveal the strain partitioning at the scale of the orogenic belt during the cooling of the AWO. At 500 Ma the hot northern sector remains warm enough to allow a coherent deformation of intrusions and host rocks. At the same time, more material was being added to the margins of the hot orogen, which already cold, with the diapire-like plutons structure being dominantly controlled by the forces of magma ascent and emplacement.
Diagnosing model-structural errors with a sliding time window Bayesian analysis
Authors: Hsueh HanFang , Guthke Anneli , Woehling Eddy Thomas , Nowak Wolfgang
Published: March 2020

When a deterministic hydrological model is calibrated, parameters applied in the model are commonly assigned time-constant values. This assignment ignores that errors in the model structure lead to time-dependent model errors. Such time-dependent error occurs, among other reasons, if a hydrological process is active in certain periods or situations in nature, yet is not captured by a model. Examples include soil freezing, complex vegetation dynamics, or the effect of extreme floods on river morphology. For a given model approximation, such missing process could become visible as apparent time-dependent best-fit values of model parameters. This research aims to develop a framework based on time-windowed Bayesian inference, to assist modelers in diagnosing this type of model error.

We suggest using time-windowed Bayesian model evidence (tBME) as a model evaluation metric, indicating how much the data in time windows support the claim that the model is correct. We will explain how to make tBME values a meaningful and comparable indicator within likelihood-ratio hypothesis tests. By using a sliding time window, the hypothesis test will indicate where such errors happen. The sliding time window can also be used to obtain a time sequence of posterior parameter distribution (or of best-fit calibration parameters). The dynamic parameter posterior will be further used to investigate the potential error source. Based on Bayes rule we can also observe how influential a parameter may be for model improvement.

We will show a corresponding visualization tool to indicate time periods where the model is potentially missing a process. We provide guidance to use showing how to use the dynamic parameter posterior to obtain insights on the error source and potentially to improve the model performance. The soil moisture model (HYDRUS 1D) was applied for a pilot test to prove the feasibility of this framework.
Understanding multidecadal variability for energy system studies: can current 20th century reanalyses do the job?
Authors: Wohland Jan , Bloomfield Hannah , Brayshaw David , Pfenninger Stefan , Wild Martin
Published: March 2020

The variability of renewable power generation is often quantified based on modern reanalyses such as ERA5 or MERRA-2 which provide climatic information over the last few decades. Compared to infrastructure lifetimes, modern reanalyses cover only short periods and may consequently fail to sample relevant longer-term climate variability. While there is evidence for multi-decadal variability in wind power generation [Wohland et al. (2019), Zeng et al. (2019)], hydropower [Bonnet et al. (2017)] and solar energy [Sweerts et al. (2019)], a consistent treatment of multi-decadal variability has not been achieved. 

This knowledge barrier can potentially be overcome using 20th century reanalyses which provide internally consistent fields of energy-relevant variables (e.g., solar radiation, precipitation, temperature and wind). However, the provision of reliable climatic information on these timescales is known to be a challenge due to, for example, the evolution of measurement techniques. Some cases of spurious trends and other shortcomings of the datasets are known. It is therefore of utmost importance to quantify uncertainties prior to usage in energy system studies. To this end, we systematically compare 20CRv3, 20CRv2c, CERA20C and ERA20C with respect to variables needed in renewable energy assessments and report similarities and discrepancies accross the datasets. The focus is given to substantial differences with respect to multi-decadal solar radiation variability in Europe, also known as dimming and brightening. 

References

Bonnet, R., Boé, J., Dayon, G. & Martin, E. Twentieth-Century Hydrometeorological Reconstructions to Study the Multidecadal Variations of the Water Cycle Over France. Water Resour. Res. 53, 8366–8382 (2017).

Sweerts, B. et al. Estimation of losses in solar energy production from air pollution in China since 1960 using surface radiation data. Nat Energy 4, 657–663 (2019).

Wohland, J., Omrani, N. E., Keenlyside, N. & Witthaut, D. Significant multidecadal variability in German wind energy generation. Wind Energ. Sci. 4, 515–526 (2019).

Zeng, Z. et al. A reversal in global terrestrial stilling and its implications for wind energy production. Nat. Clim. Chang. (2019).
Is terrestrial carbon degradation in stream hyporheic zones stimulated by nutrients?
Authors: Attermeyer Katrin , Harjung Astrid , Schelker Jakob , Kainz Martin , Weigelhofer Gabriele
Published: March 2020

The stream hyporheic zone (HZ) represents the interface between streams and groundwater. Due to the mixing of organic matter and nutrients from groundwater and surface waters it is a hot spot of microbial activities and carbon processing within a stream network. The magnitude of terrestrial carbon degradation by microorganisms in the HZ influences the quantity and biochemical quality of terrestrial carbon as well as greenhouse gas concentrations in streams. One of the factors controlling microbial activities and terrestrial carbon degradation in the HZ are nutrients. However, major knowledge gaps exist regarding the control of nutrients on terrestrial carbon processing in the HZ among different streams.

We investigated the role of algal DOM (DOMalg) and phosphorus (P) on the degradation of soil DOM (DOMsoil) by hyporheic microorganisms in a lab- and a field-based experiment. In the lab-based experiment, we focused on the influence of different DOMsoil:DOMalg ratios on the DOM degradation at similar carbon concentrations in microcosms mimicking the HZ. One batch was incubated at ambient P concentrations and a second batch at increased P concentrations adapted to the highest levels found in the pure DOMalg. We assessed microbial respiration and changes in DOM optical properties to examine quantitative and qualitative changes of the DOM pool. In the field-based experiment, we determined microbial respiration rates of HZ-sediments from 20 streams in Austria with differing ambient nutrient and organic carbon concentrations. The sediments were incubated with DOMsoil, with and without additional P.

Results from the lab-based experiment show that microbial respiration in the HZ decreased with increasing soil DOM fractions. When P levels were adapted to DOMalg concentrations, microbial respiration rates were comparable between the different DOM mixtures and DOMsoil was degraded. However, in the field-based experiment, P addition only stimulated microbial respiration rates in one out of 20 HZ-sediments, suggesting that microbial respiration rates are not solely controlled by P.

In conclusion, nutrient pulses can stimulate microbial activities and thus terrestrial carbon degradation in the HZ. However, when using different stream HZ-sediments, it becomes evident that the nutrient stimulation is not a ubiquitous mechanism and terrestrial carbon degradation in the HZ is controlled by a multitude of factors.
Unraveling the contribution of the western margin of the Altiplano plateau in North Chile (20°S) to Andean mountain-building
Authors: Habel Tania , Lacassin Robin , Simoes Martine , Carrizo Daniel
Published: March 2020

The Andes are the case example of an active Cordilleran-type orogen. It is generally admitted that, in the Central Andes (~20°S), mountain-building started ~50-60 Myr ago, close to the subduction margin, and then propagated eastward. Though suggested by some early geological cross-sections, the structures sustaining the uplift of the western flank of the Altiplano have been largely dismissed, and the most common view theorizes that the Andes grow only by east-vergent deformation along its eastern margin. However, recent studies emphasize the significant contribution of the West Andean front to mountain-building and crustal thickening, in particular at the latitude of Santiago de Chile (~33.5°S). The contribution of similar structures elsewhere along the Andes to the kinematics of the orogen is still poorly solved, because not yet well synthesized nor quantified. Here, we focus on the western margin of the Altiplano at 20°S, in the Atacama desert of northern Chile. We focus our work on two sites where structures are well exposed.
Our results confirm two main structures: (1) a major west-vergent thrust placing Andean Paleozoic basement over Mesozoic strata, and (2) a west-vergent fold-and-thrust-belt involving Mesozoic units. Once restored, we calculate a minimum of ~4 km of shortening across the sole ~10 km-wide outcropping fold-and-thrust-belt. Further west, structures of this fold-and-thrust-belt are unconformably buried under slightly deformed Cenozoic units, as revealed from seismic profiles. By comparing the scale of these buried structures to those investigated previously, we propose that the whole fold-and-thrust-belt has most probably absorbed ~15-20 km of shortening, sometime between ~68 Ma (youngest folded Mesozoic layers) and ~29 Ma (oldest unconformable Cenozoic layer). Preliminary (U-Th)/He thermochronological data suggest that basement exhumation by thrusting happened at the beginning of this ~40 Ma time span. Minor shortening affecting the mid-late Cenozoic deposits indicates that deformation continued after 29 Ma along the western Andean fold-and-thrust-belt, but remained limited compared to the more intense deformation during the Paleogene. Altogether, the data presented here will provide a quantitative evaluation of the contribution of the western margin of the Altiplano plateau to mountain-building at this latitude.
River profiles from digital elevation models – limitations and new ideas
Authors: Hergarten Stefan , Robl Jörg
Published: March 2020

Longitudinal river profiles have been a central if not even the most important subject in tectonic geomorphology since the 1950s. During the last decades, considerable progress has been made in unraveling the tectonic history from river profiles. Going along with the rapidly increasing availability of DEMs, however, scientists try to derive more and more information from the topography. So the quality of the DEM is still a limiting factor in many studies. In particular, local channel slopes are strongly affected by the DEM. Several approaches have been proposed in order to reduce the errors and to distinguish specific features such as knickpoints from noise of the DEM.

In this study we use DEMs with a mesh width of 1 m obtained from airborne laser scans and reduce their resolution artificially in order to analyze the effect of the mesh width on the accuracy of river profiles systematically. Based on the results, we present an idea how the errors in channel slope could be reduced with focus on narrow valleys. Going beyond the majority of the previously published approaches, our idea does not only take into account the elevation along the river profile, but also the curvature of the topography in direction normal to the valley floor.

 