bluuebunny/crossref_metadata_2025 huggingface dataset:
Why is the Tuaheni Landslide Complex a spreading failure?
Authors: Urlaub Morelia , Carey Jon , Crutchley Gareth , Mountjoy Joshu
Published: March 2020

Numerous subaqueous landslides exhibit spreading failure morphologies which are typically characterized by repetitive patterns of parallel ridges and troughs oriented perpendicular to the direction of movement. Whilst these spreading failures are commonly attributed to (i) downslope removal of material causing unloading of the temporary stable slope or (ii) significant loss of shear strength of the substratum allowing blocks of overlying sediment to detach and slide downslope, their movement rates and potential triggers remain poorly constrained. Spreading appears to be a dominant failure mechanism within the Tuaheni Landslide Complex (TLC) on the Hikurangi Subduction Margin off the coast of Gisborne, New Zealand. A combination of swath bathymetric, 2D and 3D seismic data, drilling investigations and laboratory experiments on sediments recovered from the TLC indicate that this geomorphology has been generated by translational failure. Failure could occur through episodic cycles of movement-arrest in response to either elevated pore fluid pressures or undrained loading during earthquakes. We developed numerical models that integrate this unique data set to explore the processes that lead to spreading failure and determine how large shear strains can be accommodated without accelerating to catastrophic failure. The results provide a novel approach that demonstrates how seafloor morphology can, in part, be controlled by the underlying failure processes
Links between the moisture origin and isotopic signature in water vapour, snowfall and snow pack at Finse Alpine Research Center (1222m) in Southern Noway
Authors: Lanzky Mika , Touzeau Alexandra , Burkhart John F. , Filhol Simon , Weng Yongbiao , Sodemann Harald
Published: March 2020

Seasonal snow cover is a crucial resource for hydropower in Norway. Understanding water sources and processes related to inter-annual snow cover variability is therefore of fundamental societal relevance. The stable water isotope composition of precipitation provides a natural, integrated tracer of the condensation history during atmospheric water transport. The main parameters dD and d18O along with the secondary quantity d-excess give information about the origin and transport history of moisture from its source to its sink. When snow falls and deposits on the ground as a sediment, it creates a record in the form of the seasonal snow pack.

Here we utilize data acquired during a field campaign in the winter season of 2018-2019 at the Finse Alpine Research Station Center (1222m, 60.6N, 7.5E) in Norway, in order to investigate the transfer of the isotopic signal of source and transport conditions from vapour to snowfall, and to the snow pack.

Over a main period of two months, snowfall was sampled daily, while the water vapour was continuously measured from ambient air guided through a heated inlet to a Picarro L2130i infrared spectrometer, with daily calibration runs. During five periods with intense snowfall, we carried out higher frequency sampling down to 15 minute intervals. Covering the entire winter season, five snowpits were sampled for isotopic analysis as well as detailed stratigraphy. In total more than 400 snow samples where taken and analysed for their isotopic composition, accompanied by routine meteorological observations over the winter season at the site. In addition, we compare the variations in the observed isotope signal at Finse with one derived from moisture source analysis using the Lagrangian diagnostic WaterSip, based on the FLEXPART model and ERA Interim reanalysis data.

To investigate to what degree moisture source information is archived in the snow pack, and how it evolves during the season, we compare snow observations at different time resolution (daily and high frequency snowfall samples) with the record of the snow pack, aided by the snow model CROCUS. The meteorological observations supply context for understanding the snow formation conditions. In particular, deviations from isotopic equilibrium between vapour and precipitation at ambient temperature conditions provide insight into the dominant condensation regime during different intense observation periods.
Understanding changes in environmental time series with time-frequency causality analysis
Authors: Shadaydeh Maha , Guanche García Yanira , Mahecha Miguel , Denzler Joachim
Published: March 2020

Understanding causal effect relationships between the different variables in dynamical systems is an important and challenging problem in different areas of research such as attribution of climate change, brain neural connectivity analysis, psychology, among many others. These relationships are guided by the process generating them. Hence, detecting changes or new patterns in the causal effect relationships can be used not only for the detection but also for the diagnosis and attribution of changes in the underlying process.

Time series of environmental time series most often contain multiple periodical components, e.g. daily and seasonal cycles, induced by the meteorological forcing variables. This can significantly mask the underlying endogenous causality structure when using time-domain analysis and therefore results in several spurious links. Filtering these periodic components as preprocessing step might degrade causal inference. This motivates the use of time-frequency processing techniques such as Wavelet or short-time Fourier transform where the causality structure can be examined at each frequency component and on multiple time scales.

In this study, we use a parametric time-frequency representation of vector autoregressive Granger causality for causal inference. We first show that causal inference using time-frequency domain analysis outperforms time-domain analysis when dealing with time series that contain periodic components, trends, or noise. The proposed approach allows for the estimation of the causal effect interaction between each pair of variables in the system on multiple time scales and hence for excluding links that result from periodic components.

Second, we investigate whether anomalous events can be identified based on the observed changes in causal relationships. We consider two representative examples in environmental systems: land-atmosphere ecosystem and marine climate. Through these two examples, we show that an anomalous event can indeed be identified as the event where the causal intensities differ according to a distance measure from the average causal intensities. Two different methods are used for testing the statistical significance of the causal-effect intensity at each frequency component.

Once the anomalous event is detected, the driver of the event can be identified based on the analysis of changes in the obtained causal effect relationships during the time duration of the event and consequently provide an explanation of the detected anomalous event. Current research efforts are directed towards the extension of this work by using nonlinear state-space models, both statistical and deep learning-based ones.
Flux fields affect the spatial distribution of phosphorus in a tilled loamy soil
Authors: Koch Stefan , Lederer Henrike , Kahle Petra , Lennartz Bernd
Published: March 2020

Heterogenous flow pathways through the soil are a major component in the transport of water, dissolved and particle-bound nutrients like phosphorus (P) to water resources, and promote the eutrophication of water bodies. Non-uniform water flow patterns may also influence the spatial variability of the P-content in soils.

This study was designed to understand the spatial distribution of P in agriculturally used soils and the mechanism causing P accumulation and depletion at the centimeter scale. We conducted three replicate dye tracer experiments using Brilliant Blue on a loamy Stagnosol in North-Eastern-Germany. The plant-available phosphorus of stained and unstained areas was analyzed using double lactate extraction and diffusive gradients on thin films (DGT).

The DL-extractable P and the DGT-extractable P were strongly correlated (p<0.001, R²=0.63) confirming that DL-P is a good measure for the mobile phase of soil phosphorus.

The plant available P contents of the topsoil were significantly higher than those of the subsoil in all three replicates. The topsoil’s stained areas showed higher P contents than unstained areas, while the opposite was found for the subsoil. The P contents varied strongly over the soil profiles (0.4 to 11.2 mg P 100 g-1) and different categories of flow patterns (matrix flow, flow fingers, preferential flow and no flow). The P contents of these flow patterns differed significantly from each other and followed the order: Pmatrix flow > Pfinger flow > Pno flow > Ppreferential flow.

We conclude that P tends to accumulate along flow pathways in managed and tilled topsoils, while in subsoils at a general lower P level, P is depleted from the prominent preferential flow domains. It is likely, that P in the shallow groundwater origins from preferred flow zones from the subsoil.
Plant-soil-water interactions in the tropics: using isotopes to explore environmental change implications for agriculture
Authors: Geris Josie
Published: March 2020

Understanding of plant water uptake and ecohydrological interactions between plants and soil water is crucial for developing effective and sustainable water use strategies, in particular for agricultural areas. To explore these questions, isotopic analyses of plant and source water provide useful tools alongside traditional techniques. Although such studies in tropical regions are less abundant, recent meta-analyses have revealed that vegetation water generally resembles that of deeper soil water sources than in temperate and cold climate regions. However, water uptake patterns from different sources can also vary in time, especially in the tropics where seasonality in precipitation and associated water availability is strong. As the distinct wet and dry seasons are expected to become more intense, this can have important implications for ecosystems and agriculture.

This presentation will bring together results from recent isotope studies on plant-soil-water interactions in tropical climate regions across the world. In particular, it will focus on system changes at the extreme ends of hydroclimatological conditions. It will also explore the implications this might have for agriculture, e.g. in terms of the sustainability of agroforestry where competition for water between co-existing vegetation might increase during dry periods, and how additional irrigation or flooding from extreme rainfall can change runoff dynamics and recharge leading to enhanced leaching of pollutants.
Towards an European operational monitoring capacity for CO2 emissions: the CO2 Human Emission project at ECMWF
Authors: Bousserez Nicolas , McNorton Joe , Ades Melanie , Agusti-Panareda Anna , Balsamo Gianpaolo , Choulga Margarita , Engelen Richard , Flemming Johannes , Innes Antje , Kipling Zak , Massart Sebastien , Parrington Mark , Peuch Vincent-Henri , Barre Jerome
Published: March 2020

The CO2 Human Emission (CHE) project is an European initiative bringing together a consortium of 22 European partners to build a prototype global CO2 source inversion system that can provide policy-relevant information on the spatiotemporal characteristics of anthropogenic CO2 emissions. This prototype shall evolve toward a new Copernicus CO2 service, which will provide a Monitoring and Verification Support (MVS) capacity that can address the challenge of the global stocktake (GST) devised under the Paris Agreement. The global inversion system will build on existing operational infrastructures (CAMS, C3S) at the European Centre for Medium-range Weather Forecast (ECMWF) to exploit ground-based measurements as well as space-based observations from current and future satellite missions (e.g., Sentinel 5p and CO2M). We will present ongoing efforts at ECMWF to develop a source inversion capability in the current operational Integrated Forecasting System (IFS), which will serve as the basis for the future global CO2 inversion prototype. Preliminary results will be discussed, that include model transport error estimations based on Monte-Carlo ensemble simulations as well as the first chemical source optimization experiments performed with the IFS 4D-Var system.
Coupled ocean—ice shelf—ice sheet projections for the Weddell Sea Basin, Antarctica
Authors: Timmermann Ralph , Albrecht Torsten
Published: March 2020

To study Antarctica’s contribution to ongoing and future sea level rise, a coupled ice sheet – ice shelf – ocean model with an explicit representation of ice shelf cavities has been developed. The coupled model is based on a global implementation of the Finite Element Sea ice Ocean Model (FESOM) with a mesh that is substantially refined in the marginal seas of the Southern Ocean. The Antarctic Ice Sheet is represented by a regional setup of the Parallel Ice Sheet Model PISM, comprising the Filchner-Ronne Ice Shelf (FRIS) and the grounded ice in its catchment area up to the ice divides.  At the base of the FRIS, melt rates and ocean temperatures from FESOM are applied. PISM returns ice thickness and the position of the grounding line. Buildung on infrastructure developed for the Regional Antarctic and Global Ocean (RAnGO) model, we use a pre-computed FESOM mesh that is adopted to the varying cavity geometry in each coupling step, i.e. currently once per model year. Changes in water column thickness are easily accounted for by the terrain-following vertical coordinate system in the ice shelf cavity. The ice sheet model is run on a horizontal grid with 1 km resolution to ensure an appropriate representation of grounding line processes. Enhancement factors for the approximation of the stress balance, as often used in coarse-resolution ice sheet models, become obsolete at such high resolution. Ice stream flow is well captured by polythermal coupling of the ice flow and a Mohr-Coulomb yield stress criterion that accounts for properties of the till material and the effective pressure on the saturated till. We present results from model runs with a 20th-century climate forcing and projections until the end of the 22nd century. We will show that cavity hydrography, ice shelf basal melt rates and thickness evolution as well as the feedback on grounded ice  in the coupled model simulations are very sensitive to the atmospheric forcing scenario applied.

 

 
The importance of appropriate isotope reference standards for determination of the isotopic composition of C and O in atmospheric CO2
Authors: Krajnc Bor , Tamše Samo , Ogrinc Nives
Published: March 2020

      Our process-based understanding of stable isotope signals, as well as technological developments, has progressed significantly, opening new frontiers in marine interdisciplinary research. This has promoted the broad utilisation of carbon and oxygen isotope applications to gain insight into carbon cycling in marine ecosystems and their interaction with the atmosphere.

Our study was performed in the Gulf of Trieste in the N Adriatic where the influence of biological processes, riverine loads and local climate conditions on the atmosphere-water CO2 exchange and on the carbonate system equilibrium was investigated, in order to elucidate what drives the CO2 exchange and to estimate the vulnerability of the Gulf of Trieste to acidification processes. On an annual scale, the Gulf of Trieste clearly acts as a sink of CO2, strongly controlled by the seasonal variability of water temperature, biological processes, wind speed and riverine inputs. The calculated air-sea CO2 flux was estimated to be -1.47 ± 1.41 mol C m-2 yr-1. The sink was generally stronger during the winter months, whereas during early summer and autumn the CO2 fluxes were lower. It was interesting to note that the atmospheric CO2 concentrations exhibited large fluctuations on a daily basis, as well as on a seasonal time scale. The average atmospheric CO2 concentration during our study in 2013 was 438 ± 16 ppm. This is significantly higher than the global average, which, at the time was around 400 ppm. Further The isotopic composition of carbon in atmospheric carbon dioxide (δ13CCO2,air) values panned from -12.7‰ to -9.1‰ with an average value of -10.8 ± 0.9‰. This is considerably different to the “background” value of -8‰ (from NOAA/ESRL) and can most probably be attributed to the presence of fossil fuel emissions. The results are comparable with the data obtained in the Adriatic between Ravenna and Otranto.

The presented study indicate that the quality and comparability of datasets is critical to improve the estimation of processes that influence the carbon dynamics in marine environment. Thus, the implementation of the principle in our laboratory, the monitoring of our measurement quality, validation and status of newly developed gas CO2 reference materials (SIRS1, SIRS2 and SIRS3) as a part of SIRS project will be also presented.
The climate in Antarctica during the Middle Eocene: a modelling perspective
Authors: Fluteau Frederic , Tardif Delphine , Le Hir Guillaume , Donnadieu Yannick , Sepulchre Pierre , Ladant Jean-Baptiste , Poblete Fernando , Dupont-Nivet Guillaume
Published: March 2020

The Middle Eocene represents the last ice-free period of the Cenozoic. Vegetation proxy data (wood, leaves, palynomorphs) discovered in the Antarctica peninsula and neighbouring islands or hosted in sedimentary sequences deposited on the continental margin reveal the presence of paratropical rain forests which thrived along the Antarctica coast during the Early Eocene. During the Middle and Late Eocene these flora have been progressively replaced by temperate Nothofagus-dominated rainforests (Contreras et al., 2013). Jacques et al. (2012) proposed, using a physiognomic approach (CLAMP), that a warm temperate and wet climate (with a marked summer rainy season) prevails until the middle Eocene (43±2 Ma) on the tip of the Antarctica Peninsula.

            To better constrain the climate in Antarctica and understand processes governing the polar climate during the Middle Eocene, we performed a set of experiments using the IPCC-like Earth System Model (IPSL-CM5A2-VLR) forced with a Middle Eocene (~40 Ma) paleogeography reconstruction and a 4 times pre-industrial atmospheric CO2 level (1120ppm). To highlight the importance of the seasonality, we launched 6 orbital configurations exploring end-members situations. To complete the procedure, simulated sea surface temperatures and sea ice extents were then employed as boundary conditions to force the Atmospheric General circulation model LMDz6 (run at higher spatial resolution) coupled with a soil and vegetation model ORCHIDEE to simulate the corresponding vegetation over Antarctica. The 6 end-members Earth's orbital configuration allows exploring the full climatic spectrum which would have been recorded by proxy data. Simulated changes in atmospheric circulation will be discussed and the simulated climate and vegetation will be confronted to paleoclimatic indicators and vegetation data.
Stress- and temperature dependent application of joint-constitutive-models for rock-ice mechanical systems and its implementation in a comprehensive distinct element code
Authors: Pläsken Regina , Julian Groß , Michael Krautblatter , Philipp Mamot
Published: March 2020

Rock mechanics and its numerical representation alone are challenging tasks – if you add ice to that equation, it becomes an even more complex thing to do. Nevertheless, aiming for a better understanding of rock slopes in permafrost conditions and their mechanical behaviour depending on the scale and mechanisms of interest, integrating rock and joint characteristics, also including ice can become relevant. Krautblatter et al. (2013) suggests a rock-ice mechanical model, that describes the dominating effects for the stability of high-alpine rock slopes in permafrost conditions. This study aims to select ice filled rock joints as one of the relevant effects of Krautblatter et al. (2013) and combines it with findings of the laboratory test and derived temperature dependent failure criteria of Mamot et al. (2018). We present data and strategies for implementing temperature-dependent failure criteria for ice-filled rock interfaces into numerical distinct element code and their calibration by a comparison with preceding laboratory tests. Additionally, methods for temperature transfer within the model are suggested as well as for integrating stress-dependent application of different failure criteria in the numerical formulation. Here we show a benchmark joint-constitutive-model for rock-ice mechanical systems and its implementation in a comprehensive distinct element code.
Better understand mountain hydrology to enhance climate change impact assessment
Authors: Grusson Youen , Dalibard Manon , Raimonet Mélanie , Sauvage Sabine , Leroux Gaël , Begueria Santiago , Palazon Leticia , Sánchez Pérez José Miguel
Published: March 2020

Catchments of European mountains are essential because of their role to provide water to human society. Mountainous area regulate water flux through a complex system of storage and release, playing the role of water tower. Better understand the dynamic functioning of this system at the scale of each compartment and the relationships between the storage and releasing processes are important to understand the impact induced by climate change. In particular, the disappearance of snow during the winter will potentially modify the low flow water level and ecological flow in late spring and early summer, impacting the ecological services provided by e.g. ponds, peat or wetland. The presented study aims to identify the keys factors and their current role in this hydrological system of the Pyrenean Mountains, and identify critical hydrological conditions that will potentially impact the socio-ecological services related to water resources. This goal has been achieved by a development of a high resolution hydrological modeling framework at the scale of the entire Pyrenean massif, together with the study of lower scale representative systems (peatland) and the development of specific future climate scenarios, in order to suggest mitigation actions and adaptability action through water management.
Damaging effect of salt crystallization on highly porous limestone from Hungary
Authors: Rozgonyi-Boissinot Nikoletta , Khodabandeh Mohammad Ali
Published: March 2020

One of the most important weathering processes on stone-built monuments is the crystallization of salts. Since the transport material of these substances is water, the porous rock types are particularly affected. In Hungary many monuments and historic buildings have been constructed from oolithic Miocene limestone. So in this study, the effect of salt crystallization on the physical and mechanical properties of high porous limestone has been investigated. Samples were obtained from Sóskút (near to Budapest, the capital city of Hungary).

At first the petrophysical properties of the stone were determined. The porosity of the investigated stone type was 26-34 V/V%, the uniaxial compressive strength (4-5 MPa) and the Brazilian tensile strength (0,4-0,5 MPa) were very low. A special proper of this rock type is the large-pore system (2-3mm) between the ooid fragments.

Sodium chloride (NaCl) and sodium sulphate (Na2SO4) were used to investigate the effect of salt crystallization. Cylindrical rock samples were exposed to salt solutions of 14 m/m% Na2SO4 (MSZ EN 12370) and 5% NaCl solution (sea water salt content). After 15 salted water saturation- drying cycles the changes of mineralogical and petrophysical properties and indirect tensile strength of the samples were investigated. The damages on the pore walls were determined with scanning electron microscope (SEM) and the building of scaling layers on the stone surfaces were investigated with optical microscope.
Production of a High-Resolution Improved Radar Precipitation Estimation Map Using Gauge Adjustment Bias Correction Methods
Authors: Patakchi Yousefi Kaveh , Yılmaz M. Tuğrul , Öztürk Kurtuluş , Yücel İsmail , Yılmaz Koray K.
Published: March 2020

This study evaluates relative performances of different statistical algorithms to enhance radar-based quantitative precipitation estimation (QPE) accuracy using rain gauge network data. Initial investigations are implemented using observations obtained via 17 C-band radars located over different regions of Turkey. It was observed that there is an underestimation problem in radar estimations compared with the ground observations. According to the initial results, daily mean bias for radar estimations over different precipitation events is about -1.4 mm/day in average. Implemented statistical methodologies include Mean Field Bias (MFB), Local Multiplicative Bias (LMB), Local Additive Bias (LAB), Local Mixed Bias (LMIB), Multiple Linear Regression (MLR) adjustment, and Cumulative Distribution Function (CDF) Matching techniques. To test the performance of these algorithms, cross-validation methods have been used. In cross-validation, 50%, 25%, 12.5% of the station-based observations are excluded for validation while the remaining are used for the calibration in different experiments. Both the calibration and validation results obtained from all rainfall events of 2017 suggest that LMB and LAB adjustment methods perform better  both in terms of compensating the underestimation and decreasing the RMSE values. Primary results show that methods mentioned help reduce the underestimation problem by increasing the daily mean error from -1.4 mm up to -0.4 mm and decreasing the daily RMSE values from 6.2 mm/day to 0.80 mm/day in rainy days in average. Despite the fact that proposed time-independent MLR and CDF methods are shown to be compensating a large portion of radar precipitation underestimation (according to the initial results, from -1.4 mm/day into -0.5 mm/day in average), estimations obtained from these methods have higher uncertainties in estimating the precipitation amount especially in areas with higher probability of convective precipitation type (no significant increment in RMSE values). By utilizing the best methods among all bias adjustment methods, a high-resolution composite radar-based precipitation map of Turkey is currently being produced. For validating the final product, three independent networks of collocated rain-gauges will be used. Similar results are being expected from the final validation process. Nevertheless, the outputs of this validation process will help understand the relative performance of the bias correction algorithms in the areas with overlapping radar estimations.

 

Keywords — Merging, radar precipitation estimation, gauge adjustment
Transboundary Extreme Ultrafine Dust Events in East Asia under a Warmer Monsoon Climate
Authors: Choi Gwangyong
Published: March 2020

Since the late 20th century East Asia has frequently experienced unprecedented transboundary extreme ultrafine dust events (TEUDEs) due to a fast economic development based on significant amount of fossil fuel consumption. In this study, spatio-temporal patterns of the TEUDEs in East Asia and the roles of synoptic climate patterns and changing large-scale atmospheric circulation systems in exacerbating the anthropogenic atmospheric pollution events causing considerable human deaths are examined. Analyses of the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra aerosol optical depth (AOD) data (2000-2019) clearly show that the pollutants are produced mainly in northern China and move toward central Korea and southern Japanese islands during cold seasons when coals consumption soars for heating. Synoptic climatic maps drawn from the NCEP-NCAR I reanalysis data for multiple TEUDEs demonstrate that a north clockwise- south anticlockwise wind vector anomaly pattern in cold seasons formed by less southward meandering of Siberian High pressure (SH) helps the stagnation of significant amount of ultrafine dusts over East Asia. It is also notable that the long-term poleward retreating trend of cold season circumpolar vortex, which is associated with less frequent gusty wind flow from the SH, may provide a favorable condition for intense, long-lasting TEUDEs across East Asia under a warmer monsoon climate.
Communicating earthquake information to the public in Italy: ten years of INGVterremoti
Authors: amato alessandro , Casarotti Emanuele , Lauciani Valentino , Meletti Carlo , Nostro Concetta , Pignone Maurizio
Published: March 2020

Communicating earthquake scientific information is very important in countries like Italy, where seismic sequences are frequent, seismic risk is high, and people’s perception of risk is strongly affected by fear.

After the 2009 earthquake in L’Aquila (central Italy), which claimed 309 casualties and triggered a long lasting dispute among scientists, journalists, citizens, including a suite of criminal and civil trials involving scientists and civil protection officers, the scientific and risk communication in Italy (not only on earthquakes) was facing a crossroad. The first choice (feared at that time by many reporters) was to minimize or even elude public communication, in order to avoid misunderstandings and involvement in litigations. The second possibility was to increase the efforts in public communication, getting closer to citizens. INGV definitely opted for the second choice. In the past ten years the INGVterremoti platform has augmented and differentiated its activities on the web and social media, substantially increasing the number of involved people, which amounts today to several hundreds thousand. The platform consists of a coordinated suite of social media channels, including Facebook, Twitter, Youtube and a blog (on wordpress), where we publish both updating during earthquake sequences and scientific topics. Our end users are mostly citizens, but also media and authorities. Our tweets on earthquake activity are often in the first pages of web and TV news magazines.

In September 2018, we started publishing automatic locations/magnitudes for earthquakes in Italy with magnitude equal to or larger than 3, after a careful analysis of the thresholds and of the best format to use, in order to warrant message understandability and to minimize false or incorrect information. This issue is very critical both to provide the best and fastest information to citizens, and to increase people’s trust in scientific information and institutions. These are often blamed by citizens and by media when contradictory information is offered to the public. We will present an analysis of the first 18 months of this testing phase, which has been widely appreciated by the public.
The relationship between ML and Mw for small earthquakes (ML < 2-4) in Italy
Authors: Lolli Barbara , Paolo Gasperini , Biondini Emanuele , Vannucci Gianfranco
Published: March 2020

Several authors empirically observed that the scaling between local magnitude ML and moment magnitude Mw computed by spectral methods is not 1:1 for ML<2-4. In particular ML is found to be about proportional to 1.5 Mw but the exact threshold below which this occurs is argued. Such behavior was explained as due to attenuation and scattering along the path or to a minimum limit in the pulse duration or equivalently a maximum limit to the corner frequency of the observed spectra imposed by surface attenuation. The frequency-magnitude distribution of ML estimates provided by the Italian Seismic Instrumental Database (ISIDe) of INGV show a strictly linear behavior with b-value»1.0 down to about ML 1.4 at least. This implies that for Mw the b-value would be about 1.5 below magnitude 2-4 and 1 above. As the frequency magnitude relationship with b-value»1 in terms of Mw is recognized as a general characteristic of seismicity all over the world, based on both empirical and theoretical considerations, the question arises on the reasons of the observed discrepancy for small shocks. One explanation might be the assumption of incorrect seismic wave attenuation properties for the computation of ML, of spectral Mw or both.
Passive monitoring and 3D imaging of the bedrock response to the 2018 Espoo/Helsinki geothermal stimulation
Authors: Taylor George , Hillers Gregor
Published: March 2020

In recent years several deep geothermal energy projects have been forced to close following the occurrence of large seismic events associated with the stimulation of the surrounding bedrock. In 2018, an enhanced geothermal system (EGS) experiment performed in Helsinki, Finland concluded with no seismicity exceeding the threshold magnitude and thus provides an intriguing showcase for future stimulation experiments in similar environments. During the 49 days of the experiment, the five-stage injection of ~18,000 cubic meters water stimulated many thousands of earthquakes. Like in all previous stimulation cases the earthquake data constitute the primary source for the assessment of the scientific and operational aspects of the reservoir response. Here we apply ambient noise based monitoring and imaging techniques to data collected by 100 short period three-component stations that were organized in three large arrays consisting of nominally 25 stations, in addition to three small four-station arrays, and 10 single stations, during a 100 day period. We compute daily nine-component noise correlations between all stations pairs except for the intra-array pairs in a frequency range between 0.5 and 10 Hz. We measure waveform delays within our correlation functions as a function of frequency and lag time using the Continuous Wavelet Transform. We then invert these observations using a Markov chain Monte Carlo method to obtain the temporal variation in seismic velocity dv/v during the injection. By exploiting the variable spatial sensitivities of the surface- and body-wave components at different coda-wave lapse times and frequencies, we are able to image the medium response to the stimulation in both time and space. We compare the estimated seismic velocity variations to other observations such as H2/V2, as well as dv/v observations obtained from collocated borehole data. Importantly, we also compare the observed medium response to seismicity and pumping parameters. Our results suggest that we are able to resolve medium changes that are not solely associated with the induced earthquakes, but also potential signatures of fluid content or pressure changes in the bedrock. The combined observations of seismicity, pumping parameters and dv/v changes collected in this experiment can further advance passive monitoring techniques in the context of enhanced geothermal systems, and facilitate a more comprehensive analysis of fluid-rock interactions that may occur aseismically.
Mapping Antarctic sea ice albedo properties from MISR fused with MODIS
Authors: Muller Jan-Peter , Kharbouche Said
Published: March 2020

In [1] a new method is described for fusing spectral BRF and derived albedo at 1.1km within the 7 minutes that MISR acquires images of a surface point with coincident MODIS nadir spectral data processed into a 1km sea ice mask. NetCDF products were produced in polar stereographic projection and produced on daily, weekly, fortnightly and monthly from November to February each year from 2000-2016. Arctic sea ice albedo has been previously presented and in this presentation, Antarctic time series, will be presented covering the same time period. This area has less complete coverage than the Arctic due to data outages due to telecommunications issues. [2] has recently pointed out that sea ice coverage  has  reduced dramatically since 2014, mainly one quadrant centred on the Wendell sea and the spectral albedo for this area will be highlighted.

Acknowledgements: Support was provided by EU-FP7 QA4ECV (Quality Assurance for Essential Climate Variables) under Project Number 607405 for the development of the processing system.

References:
[1] Kharbouche, S.; Muller, J.-P. Sea Ice Albedo from MISR and MODIS: Production, Validation, and Trend Analysis. Remote Sens. 2019, 11, 9. doi: https://doi.org/10.3390/rs11010009

[2] Parkinson, C. A 40-y record reveals gradual Antarctic sea ice increases followed by decreases at rates far exceeding the rates seen in the Arctic. Proceedings of the National Academy of Sciences. 2019, 116 (29) 14414-14423; DOI: 10.1073/pnas.1906556116
Bringing slow slip processes into focus
Authors: Bell Rebecca
Published: March 2020

The discovery of slow slip events (SSEs) at subduction margins in the last two decades has changed our understanding of how stress is released at subduction zones. Fault slip is now viewed as a continuum of different slip modes between regular earthquakes and aseismic creep, and an appreciation of seismic hazard can only be realised by understanding the full spectrum of slip. SSEs may have the potential to trigger destructive earthquakes and tsunami on faults nearby, but whether this is possible and why SSEs occur at all are two of the most important questions in earthquake seismology today. Laboratory and numerical models suggest that slow slip can be spontaneously generated under conditions of very low effective stresses, facilitated by high pore fluid pressure, but it has also been suggested that variations in frictional behaviour, potentially caused by very heterogeneous fault zone lithology, may be required to promote slow slip.

Testing these hypotheses is difficult as it requires resolving rock properties at a high resolution many km below the seabed sometimes in km’s of water, where drilling is technically challenging and expensive. Traditional geophysical methods like travel-time tomography cannot provide fine-scale enough velocity models to probe the rock properties in fault zones specifically. In the last decade, however, computational power has improved to the point where 3D full-waveform inversion (FWI) methods make it possible to use the full wavefield rather than just travel times to produce seismic velocity models with a resolution an order of magnitude better than conventional models. Although the hydrocarbon industry have demonstrated many successful examples of 3D FWI the method requires extremely high density arrays of instruments, very different to the 2D transect data collection style which is still commonly employed at subduction zones.

 The north Hikurangi subduction zone, New Zealand is special, as it hosts the world’s most well characterised shallow SSEs (<2 km to 15 km below the seabed).  This makes it an ideal location to collect 3D data optimally for FWI to resolve rock properties in the slow slip zone. In 2017-2018 an unprecedentedly large 3D experiment including 3D multi-channel seismic reflection, 99 ocean bottom seismometers and 194 onshore seismometers was conducted along the north Hikurangi margin in an 100 km x 15 km area, with an average 2 km instrument spacing. In addition, IODP Expeditions 372 and 375 collected logging-while drilling and core data, and deployed two bore-hole observatories to target slow slip in the same area. In this presentation I will introduce you to this world class 3D dataset and preliminary results, which will enable high resolution 3D models of physical properties to be made to bring slow slip processes into focus.  
Measurement Study of Turbulence in a Tropopause Fold
Authors: Faber Jens , Gerding Michael , Lübken Franz-Josef
Published: March 2020

Tropopause folds are known as regions of intense trace gas exchange between the troposphere and the stratosphere. They occur in upper-level fronts and it is known since the 1970s that turbulence plays a major role in their formation. However, only a limited number of turbulence measurements under these conditions exist. In this study, we present a turbulence sounding in an upper-level front measured with the balloon-borne instrument LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere). This instrument infers turbulent kinetic energy dissipation rates from velocity fluctuations at the Taylor microscale. By using a radiosonde on board of the same balloon, we can observe wind fluctuations across multiple spatial scales.In the classical picture of a tropopause fold from the 1970s, we expect turbulence to occur in both shear zones above and below the tropopause jet. For the time of our measurement on 06 August 2016, a similar turbulence distribution is expected due to low Richardson numbers in the respective areas shown by the ECMWF-IFS. Our in-situ turbulence measurement with LITOS, however, shows a different picture: we find turbulence to occur in the upper shear zone above the jet but not in the lower one located in the stratospheric intrusion. In our contribution, we will examine potential reasons for this difference between theoretical expectations and the observation. Furthermore, we will discuss possible implications of the lack of turbulence in the stratospheric intrusion on the exchange of trace gases across the tropopause.
Dissolution and precipitation reactions during acidic fluid percolation through different limestone samples
Authors: Luquot Linda
Published: March 2020

CO2 sequestration in deep geological formation is considered an option to reduce CO2 emissions in the atmosphere. After injection, the CO2 will slowly dissolve into the pore water producing low pH fluids with a high capacity for dissolving carbonates. Limestone rock dissolution induces geometrical parameters changes such as porosity, pore size distribution, or tortuosity which may consequently modify transport properties (permeability, diffusion coefficient). Characterizing these changes is essential for modelling flow and CO2 transport during and after the CO2 injection. Indeed, these changes can affect the storage capacity and injectivity of the formation.

Very few published studies evaluate the transport properties changes (porosity, permeability, pore size distribution, diffusion coefficient) due to fluid-rock interactions (dissolution and/or precipitation).

Here we report experimental results from the injection of acidic fluids (some of them equilibrated with gypsum) into limestone core samples of 25.4 mm diameter and around 25 mm length. We studied two different limestone samples: one composed of 73% of calcite and 27% of quartz, and the second one of 100% of dolomite. Experiments were realized at room temperature. Before and after each acidic rock attack, we measure the sample porosity, the diffusion coefficient and the pore size distribution.

We also imaged the 3D pore network by X-ray microtomography to evaluate the same parameters. During percolation experiments, the permeability changes are recorded and chemical samples taken to evaluate calcite dissolution and gypsum precipitation. Several dissolution/precipitation-characterization cycles are performed on each sample in order to study the evolution and relation of the different parameters.

These experiments show different dissolution regimes depending of the fluid acidity and of the

limestone samples in particular the initial local heterogeneity, and pore size distribution.
Global heat uptake by inland waters
Authors: Vanderkelen Inne , van Lipzig Nicole P.M. , Lawrence Dave , Droppers Bram , Golub Malgorzata , Gosling Simon N. , Janssen Annette B. G. , Marcé Rafael , Müller Schmied Hannes , Perroud Martorie , Pierson Don , Pokhrel Yadu , Satoh Yusuke , Schewe Jacob , Seneviratne Sonia I. , Stepanenko Victor M. , Woolway Richard I. , Thiery Wim
Published: March 2020

Heat uptake is a key variable for understanding Earth system response to greenhouse gas forcing. Recent assessments highlighted that most of the excess energy is stored in the oceans, whereas the land, atmosphere and ice melt take up smaller amounts. However, despite the importance of this heat budget, heat uptake by inland waters has so far not been quantified. Here we use a unique combination of global-scale lake models, global hydrological models and Earth system models to, for the first time, quantify global heat uptake by lakes, reservoirs and rivers over the industrial period (1900-2020).

We use a total of 16 different simulations of global-scale lake models and global hydrological models driven by the same bias-corrected climate forcing from four different global climate models, conducted within the framework of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP). The model output is combined with reservoir and lake data from the Global Reservoir and Dam (GRanD) database and HydroLAKES.

Total inland water heat uptake in the industrial period amounts to 2.8 ± 4.3x1020 J by the end of the period, with the largest uptake realised after 1990. The overall uptake is dominated by warming of natural lakes (2.9 ± 2.0x1020 J, the multi-model mean and standard deviation; 103% of total inland water heat uptake), followed by reservoir warming (5.9 ± 2.7x1018 J; 2.1%). The multi-model mean heat uptake by rivers contributes negatively to the total heat uptake (-0.15 ± 4.3x1020 J; -5.3%), but encompasses a large uncertainty originating from the river storage term, simulated by the global hydrological models. The global picture of positive heat uptake by natural lakes is confirmed at the regional scale in the major lake regions by all global-scale lake model and global climate model combinations. The heat uptake by inland waters makes up ~3.2% of continental heat uptake reported in the IPCC AR5 (2013). The rapid increase in dam construction and resulting reservoir expansion in the second half of the 20th century causes a heat redistribution from ocean to land by storing extra water on land. Remarkably, this heat redistribution exceeds the anthropogenic heat uptake by inland waters by a factor of ~ 9.6, adding up to 27 ± 2.1x1020 J.

Our results overall underline the importance of inland waters for buffering atmospheric warming through enhanced anthropogenic greenhouse gas concentrations. 
The relation between the rotational and inertial modes of a triaxial planet
Authors: Rekier Jeremy , Triana Santiago , Trinh Antony , Dehant Véronique
Published: March 2020

Inertial modes are natural oscillations in the fluid parts of planets which are caused by the restoring action of the Coriolis force. The relation between these modes, as they appear in the liquid core of planets, and the well-known rotational modes – the Free (Inner) Core Nutation (FCN & FICN) and the Chandler and Inner Core Wobble (CW & IW) – is not well understood, with the FCN often being mistakenly identified to the simplest inertial mode, the Spin-Over (SO). In this work, we clarify this relation using a new formalism to compute the rotational modes of a two-layer triaxial planet with a rigid mantle and an inviscid fluid core to all order in the eccentricity. We confirm the validity of our model through comparison with the results from direct numerical integration of the equations of motion. Using this technique, we demonstrate how the SO is the only inertial mode affecting the rotation of the planet and we show how this mode identifies with the FCN only in the limit of vanishing eccentricity.