bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Bow-Shock dynamics in response to a Quasi-Perpendicular interaction with different Solar Wind conditions
Authors: Cazzola Emanuele , Fontaine Dominique , Savoini Philippe
Published: March 2021

This work will be giving new insights into the global Quasi-Perpendicular interaction effects of the Solar Wind with a realistic three-dimensional terrestrial-like curved Bow Shock (BS) by means of hybrid computer simulations.
The Bow-Shock profoundly changes its behavior for different incoming Solar Wind conditions. For Alfvénic Mach numbers greater than a specific threshold, the Bow-Shock shows an intense rippling phenomenon propagating along its surface, as well as the formation of a set of waves in the near-Earth flanks.
A similar rippling has been observed from different independent in-situ satellite crossings, as well as studied with ad-hoc computer simulations configured with 2D-planar shocks, conclusively confirming the highly kinetic nature of this phenomenon. Yet, the possible effects of a global three-dimensional curved interaction are still poorly described.
As such, we have performed a series of 3D simulations at different Alfvénic Mach numbers, different plasma beta - ratio between the thermal to the magnetic pressures - and different incoming Interplanetary Magnetic Field (IMF) configurations with the hybrid code LatHyS, which was already successfully used for similar past analyses.
Particularly, we have found that the ripples follow a pattern not directly driven by the IMF direction as initially expected, but rather a Nose-to-Flanks propagation with the rippling onset region  being significantly displaced from the nose position. Additionally, this phenomenon seems to be mainly confined to the plane on where the IMF direction lies, with the perpendicular cross-sections showing only a slight oscillation.
Finally, we have observes a significant ions acceleration in the local perpendicular directions along the flanks modulations, which is most likely related to the local IMF-BS normal fluctuations occurring in the ripples boundary.
A new drone laser scanning benchmark dataset for characterization of single-tree and forest biophysical properties
Authors: Stefano Puliti , Pears Grant D. , Watt Michael S. , Mitchard Edward , McNicol Iain , Bremer Magnus , Rutzinger Martin , Surovy Peter , Wallace Luke , Hollaus Markus , Astrup Rasmus
Published: March 2021

Survey-grade drone laser scanners suitable for unmanned aerial vehicles (UAV-LS) allow the efficient collection of finely detailed three-dimensional information of tree structures. This data type allows forests to be resolved into discrete individual trees and has shown promising results in providing accurate in-situ observations of key forestry variables. New and improved approaches for analyzing UAV-LS point clouds have to be developed to transform the vast amounts of data from UAV-LS into actionable insights and decision support. Many different studies have explored various methods for automating single tree detection, segmentation, parsing into different tree components, and measurement of biophysical variables (e.g., diameter at breast height). Despite the considerable efforts dedicated to developing automated ways to process UAV-LS data into useful data, current methods tend to be tailored to small datasets, and it remains challenging to evaluate the performance of different algorithms based on a consistent validation dataset. To fill this knowledge gap and to further advance our ability to measure forests from UAV-LS data, we present a new benchmarking dataset. This data is composed of manually labelled UAV-LS data acquired a number of continents and biomes which span tropical to boreal forests. The UAV-LS data was collected exclusively used survey-grade sensors such as the Riegl VUX and mini-VUX series which are characterized by a point density in the range 1 – 10 k points m2. Currently, such data represent the state-of-the-art in aerial laser scanning data. The benchmark data consists of a library of single-tree point clouds, aggregated to sample plots, with each point classified as either stem, branch, or leaves. With the objective of releasing such a benchmark dataset as a public asset, in the future, researchers will be able to leverage such pre-existing labelled trees for developing new methods to measure forests from UAV-LS data. The availability of benchmarking datasets represents an important driver for enabling the development of robust and accurate methods. Such a benchmarking dataset will also be important for a consistent comparison of existing or future algorithms which will guide future method development.
Spectral Properties of Kilometer-Scale Equatorial Irregularities as Seen by the Swarm Satellites
Authors: Buchert Stephan C. , Aol Sharon , Jurua Edward
Published: March 2021

The three Swarm satellites have crossed the equator close to 80000 times each, and a large database of plasma density measurements at spatial resolution up to 500 m is available. This allows to investigate spectral properties of often seen irregularities at scale sizes of kilometers and tens of kms at heights between about 410 and 480 km above sea level. In this range of altitudes electrons are nearly completely magnetized, and ions slightly demagnetized. Therefore the irregularities could be anisotropic with a tendency to be aligned with respect to B. The satellite crossings are close to the geodetic north-south direction. Consequently the tracks of density measurement/satellite orbit have an angle with B between 0 and up to 60 deg within magnetic latitudes +/-30 degrees. Spectral properties that we have investigated are the slope of the power over wavelength, index p, and the structure function of the density. The spectral index p indicates more shallow spectra at larger angles with respect to B, in agreement with the expectation above. The spectra are also more shallow near the crests of the equatorial ionization anomaly at +/-15-20 deg magnetic latitude. This could be caused by a larger linear growth rate at these locations, which might in turn be caused by a less horizontal B.
Isotope and microbiome analysis indicates variety of N-cycle processes controlling N2O fluxes in a drained peatland forest soil
Authors: Masta Mohit , Gadegaonkar Sharvari , Sepp Holar , Espenberg Mikk , Pärn Jaan Pärn , Kirsimäe Kalle , Mander Ülo
Published: March 2021

Nitrous oxide (N2O) is a major greenhouse gas whose presence in atmosphere is continuously increasing. Hence it’s important to understand its production and consumption mechanisms. During the summer of 2020, we conducted lab experiments using heavy nitrogen tracers of Potassium Nitrate 15N 98% atom (Sigma Aldrich) and Ammonium Chloride 15N 98% atom (Sigma Aldrich) under different moisture conditions to get an insight into N2O production mechanisms and on their dependence on soil moisture. We applied the tracer to peat samples (Kärevere, Estonia) placed in 36 (12 control, 12 nitrate treatment & 12 ammonia treatment) plastic buckets (radius-10cm, height-20cm) with soil height of 10 cm and a 10 cm head space left for gas collection. We installed oxygen sensors, water table indicators and temperature sensors on all buckets. We focused on studying physical conditions (soil oxygen, temperature, water table and soil moisture), gas (N2O) emission data, soil chemistry, gas isotope 15N, soil isotope and soil microbiology to get a complete picture of the processes involved in production of N2O gas. Under the ammonia treatment, emissions increased more than ten-fold which could be due to multiple processes of the nitrogen cycle in play. N2O emissions increased as the oxygen conditions shifted from anoxic (Omg/L=0) to sub-oxic (Omg/L=0.5–6) and then decreased as oxygen conditions reached the oxic (Omg/L>6) state. Furthermore, we witnessed negative site preference and 18O values during the nitrate treatment indicating nitrifier-denitrification. Under the ammonia treatment, we recorded both negative as well as high positive site preference values indicating presence of multiple production mechanisms. This was expected as ammonia triggers multiple processes in the nitrogen cycle. In some samples, we observed N2O consumption with little change in site preference as compared to the N2O producing samples. This indicates some bacterial-denitrification along with the prevailing nitrifier-denitrification. We also observed that under both treatments, heavy oxygen increased with increasing site preference. This indicates reduction of N2O (Ostrom et al, 2007) as redox supports 15N and 18O enrichments. After these lab experiments, we conducted the same experiment at a large scale in a drained peatland forest in Agali, Estonia. In this experiment, we established 1m2 triangle-shape mesocosms using experimental draining and flooding to achieve varying oxygen conditions. Preliminary results of qPCR analysis of N-cycle control genes support the domination of ammonia oxidation and denitrification as sources of N2O.
Dynamic surface tension of xylem sap at the air-water interface
Authors: Duggireddy Reddy Prasanna , Raveh Eran , Arye Gilboa
Published: March 2021

The surface tension (ST) of xylem sap at the water-air interface is a crucial phenomenon, influencing many physiological events such as air seeding and embolism, by which xylem vessels become air-filled and cease to function. Refilling of embolized, may relies on sap’s surface activity at the interface. It is commonly assumed that the ST of xylem sap is equal to the ST of pure water (72 mN/m). However, xylem sap is a complex solution and consists of surface-active molecules that may adsorb and accumulate at the water-air interface and thereby reduce the ST of water as a function of their aqueous concentration. However, when a new water-air interface is formed, equilibrium ST is not reached instantaneously. Specifically, amphiphilic molecules are kinetically adsorbed and undergo orientation at the interface following diffusion from the bulk solution. Dynamic ST of xylem sap and liquid-solid interactions, describing the surface phenomena of the xylem of vascular plants is currently not fully understood. This is mainly due to a lack of quantitative knowledge on the rate and extent of dynamic and equilibrium ST of sap. In this regard, the main objective of this study is to quantify the dynamic and equilibrium ST of xylem sap as a function of their aqueous concentration. We extracted xylem sap from lemon trees and measured ST as a function of time using the pendant drop technique. The dynamic ST data were analyzed using empirical and diffusion-control mathematical models which adequately described the exponential-like decay of the ST as a function of time. The results showed reduced ST of water in the xylem sap, indicating significant surface activity, reaching equilibrium ST values as low as 42 mN/m. The rate of ST decay was higher in high sap concentration and reduced in diluted one. The results of dynamic and equilibrium ST and the corresponding model will be presented and their implications for xylem hydraulic functioning will be discussed.

 

Keywords: Dynamic surface tension, Equilibrium surface tension, Diffusion, Xylem sap.

 
Climate and land use change impacts on water resources in Sardinia (Italy)
Authors: Ruggiu Dario , Urru Salvatore , Deidda Roberto , Viola Francesco
Published: March 2021

The assessment of climate change and land use modifications effects on hydrological cycle is challenging. We propose an approach based on Budyko theory to investigate the relative importance of natural and anthropogenic drivers on water resources availability. As an example of application, the proposed approach is implemented in the island of Sardinia (Italy), which is affected by important processes of both climate and land use modifications. In details, the proposed methodology assumes the Fu’s equation to describe the mechanisms of water partitioning at regional scale and uses the probability distributions of annual runoff (Q) in a closed form. The latter is parametrized by considering simple long-term climatic info (namely first orders statistics of annual rainfall and potential evapotranspiration) and land use properties of basins.

In order to investigate the possible near future water availability of Sardinia, several climate and land use scenarios have been considered, referring to 2006-2050 and 2051-2100 periods. Climate scenarios have been generated considering fourteen bias corrected outputs of climatic models from EUROCORDEX’s project (RCP 8.5), while three land use scenarios have been created following the last century tendencies.

Results show that the distribution of annual runoff in Sardinia could be significantly affected by both climate and land use change. The near future distribution of Q generally displayed a decrease in mean and variance compared to the baseline.   

The reduction of  Q is more critical moving from 2006-2050 to 2051-2100 period, according with climatic trends, namely due to the reduction of annual rainfall and the increase of potential evapotranspiration. The effect of LU change on Q distribution is weaker than the climatic one, but not negligible.
Turbulence Scale in Compound Channel
Authors: Barman Jyotirmoy , Taye Jyotismita , Kumar Bimlesh
Published: March 2021

The study of turbulence in a compound channel would address the nature of sedmient transport and bank erosion activity. The study would also give insights of embankment and levee breaches at the time of high flood. Experimental investigations were conducted on two compound channels of 310 and 450 bank angle in the laboratory flume to study the turbulece scale. Velocity data were recorded with Nortek Velocimeter at seven different locations (3 locations at the upstream, 3 locations at the downstream and 1 location at the middle) of the compound channel. Turbulence scale like Taylor microscale (λT) estimates the length scale of the inertial sub- range. The Taylor scale is calculated as:

<img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.0042175ca60061700501161/sdaolpUECMynit/12UGE&app=m&a=0&c=2968072e536f82f8e38df248a26aa4a7&ct=x&pn=gepj.elif&d=1" alt="" width="199" height="148">

The Taylor microscale analysis showed dominance in the main channel for 450 bank angle as compared to 310 bank angle. In the location of slope midpoint and floodplain region of the compound channel, Taylor microscale was more dominant for 310 bank angle. Another important observation in both the compound channels (310 and 450 bank angle) is the dominance of Taylor microscale at the upstream section of the channel as compared to the downstream part of the channel. The results from the study would help us to get a better understanding of the role of turbulence in the morphological changes in a compound channel with different bank angles.
Thermal Assessment Tool: A climate service to visualize trends of risk events related to cold snaps and heatwaves
Authors: Lajarín Blas , Peña Nieves , Paz Jorge , Morris Edward P. , Vega Greta C. , Casal Estefanía , Dubuisson Martin , Teixeira Luisa , Feliu Efrén
Published: March 2021

The Thermal Assessment Tool has been developed within the framework of a Copernicus Climate Change Service (C3S) contract, titled Climate Change Dashboards for Decision Makers, to provide an interactive and informative dashboard to allow users to visualize the frequency and severity of risk events related to cold snaps and heatwaves. The tool is based on historical, seasonal forecast and long-term projections datasets, available through C3S Climate Data Store (CDS). It reduces the need for repetitive complex climate data analysis, thereby saving time and effort in the decision-making process.

Climate change has already impacted ecosystems and humans, and it is foreseeing that will lead to an increase in the number and intensity of extreme weather events, including heatwaves and cold snaps. These may bring temperatures that are significantly warmer or colder than average that may cause impacts such as thermal discomfort, lack of productivity, more energy consumption and/or health problems. To reduce or at least mitigate these impacts added-value information regarding the risks of extreme temperatures is needed to make proper decisions to prepare, protect and prevent the city and citizens.

For this purpose, the Thermal Assessment Tool provides a customized dashboard that allows users to visualize heatwaves, cold snaps and thermal comfort based on long-term projections and seasonal forecasts. The tool also presents an interactive map and a time series visualization identifying the magnitude of these three variables. This reduces the need for repetitive complex climate data analysis, thereby saving time and effort in the decision-making processes. Information on the frequency and severity of future extreme temperature events can also assist with planning.

The tool showcases how to analyze, process and simplify large volumes of data through different maps and plots that make it easier to understand climate indicators (about the past, present or future). Local governments and other decision-makers, as well as actors in housing development and management, urban planning, and insurance can refer to the tool to complement their usual information systems with additional quality-assured insights that they can act on.

Acknowledgments: We would like to thank the C3S for funding this project and the participants in the various workshops mentioned below: Ayuntamiento de Bilbao, Ihobe y la Oficina Española de Cambio Climático.
Markov modulated Poisson processes for stochastic modelling of background seismicity
Authors: Varini Elisa , Peresan Antonella , Benali Amel
Published: March 2021

We investigate the statistical properties of declustered catalogs as obtained from the application of two different data-driven declustering algorithms, namely the nearest-neighbor method and the stochastic declustering method (Benali et al., Stoch. Environ Res Risk Assess, 2020). The nearest-neighbor method partitions earthquakes into background and clustered components, based on nearest-neighbor distances between earthquakes in the space-time-magnitude domain (Zaliapin and Ben-Zion, J Geophys Res, 2013); the stochastic declustering method classifies earthquakes into background and clustered components through a probabilistic procedure based on the estimation of the space-time ETAS model (Zhuang et al., J Geophys Res, 2004).

Two Italian case studies are considered: North-Eastern Italy (data from OGS Bulletins) and Central Italy (data from ISIDe catalog). For both case studies, the time series of background seismicity are obtained from the two declustering methods. Then we investigate the general assumption according to which the temporal sequence of background seismicity is suitably modelled by the stationary Poisson model. For this purpose, several features and statistical tests are considered to verify the main properties that characterize Poisson processes (e.g. events are independent, exponential inter-arrival times, etc.). 

Whenever the Poissonian hypothesis is rejected, we get evidence of certain heterogeneity in the background sequence, which leads us to rule out the simple Poisson process for background seismicity modeling. As a simple and more suitable alternative, we consider here the Markov Modulated Poisson Process (MMPP model), which allows the Poisson seismicity rate to change over time according to a finite (unknown) number of states of the system. The MMPP model turns out suitable for identifying and quantifying heterogeneities in background seismicity, as well as for comparing them against the two considered declustering algorithms.
Current state and resilience of three main tree species in southern Germany with regard to drier and hotter weather conditions over the past 50 years
Authors: Debel Annette , Bräuning Achim
Published: March 2021

Latest drought events and their already visible damage to trees highlight the crucial need to assess the current state and resilience of forest ecosystems in southern Germany. However, commonly applied dendroclimatic approaches rarely take into account, how weather patterns affecting trees are modified by topographic conditions. For this purpose, three main tree species were studied at three low mountain ranges and three corresponding basins in the topographically complex province of Bavaria (southeast Germany). A response analysis between climate proxies and tree-ring widths was used to investigate climate-growth relationships over the past 50 years of both coniferous and deciduous tree species at each forest site. Temporal stability of tree responses to climate was compared for two 25-year periods to detect possible modifications in climate-growth correlations. A pointer year analysis was also conducted to analyze tree response to climatic extreme events. The results showed that Scots pine (Pinus sylvestris) was the most vulnerable and least drought-resistant of the investigated tree species. Although Norway spruce (Picea abies) and European beech (Fagus sylvatica) benefited from an extended growing season at high elevation sites, they showed higher drought sensitivity over the past 25 years. Beech responses were rather inhomogeneous and even differed in the optimal precipitation period. However, lower correlation coefficients for summer precipitation at the driest site may indicate the ability of beech to adapt to less summer precipitation. Nevertheless, increasing drought frequency, as predicted, poses a serious threat to all studied tree species, including even the colder and more humid sites. Hence, to more accurately estimate risk potentials under future weather conditions, we will combine dendroclimatological results with climate modelling scenarios, particularly expected future frequencies of critical weather types on the local scale.
The evolution of the tidal asymmetry in a river networks system
Authors: Zhang Wei , Bao Shiyu
Published: March 2021

Tidal asymmetry in deltas is caused by both the intrinsic asymmetry, resulting from the combination of astronomical tides, and by nonlinear tidal interactions that occur in shallow water. In recent years, nonlinear tidal interactions in deltas have become more complex due to the influence of topographic changes. The relative importance of these sources of tidal asymmetry in delta channel networks, partially due to the limitations of classical harmonic analysis (HA) in hindcasting nonstationary tides, has remained poorly studied. We take the Pearl River Delta (PRD) as an example to examine the spatial-temporal variations of tides and tidal asymmetry in deltas. For hydrological data from 14 stations in the PRD spanning the period1961-2012, the non-stationary harmonic analysis method (NS-TIDE) is used. The spatiotemporal variation of multiple sources of tidal asymmetry is quantified by a skewness metric, revealing the development of alternative sources of tidal asymmetry develop in the delta subject to study. As tides propagate into delta channel networks, analytical results show the development of tides becoming increasingly more asymmetric. In the course of the 1990s and 2000s, tidal skewness has decreased in the parts of the PRD where the water depth varies greatly, indicating that the tidal asymmetry has reduced. Our findings demonstrate that deepening of the channel system is associated with a reduction of the flood-dominant tidal asymmetry. Deeper channels tend to be more often ebb-dominant than shallow areas. Due to extensive sand excavation, the abrupt changes in bathymetry in the delta are likely to be responsible for the observed spatial variations in tidal response that reduce the flood-dominant tidal asymmetry in this region.
Seasonal Predictability of Wintertime mid-latitude Cyclonic Activity over the North Atlantic and Europe
Authors: Aranyossy Alvise , Brune Sebastian , Hellmich Lara , Baehr Johanna
Published: March 2021

We analyse the connections between the wintertime North Atlantic Oscillation (NAO), the eddy-driven jet stream with the mid-latitude cyclonic activity over the North Atlantic and Europe. We investigate, through the comparison against ECMWF ERA5 and hindcast simulations from the Max Planck Institute Earth System Model (MPI-ESM), the potential for enhancement of the seasonal prediction skill of the Eddy Kinetic Energy (EKE) by accounting for the connections between large-scale climate and the regional cyclonic activity. Our analysis focuses on the wintertime months (December-March) in the 1979-2019 period, with seasonal predictions initialized every November 1st. We calculate EKE from wind speeds at 250 hPa, which we use as a proxy for cyclonic activity. The zonal and meridional wind speeds are bandpass filtered with a cut-off at 3-10 days to fit with the average lifespan of mid-latitude cyclones. 

Preliminary results suggest that in ERA5, major positive anomalies in EKE, both in quantity and duration, are correlated with a northern position of the jet stream and a positive phase of the NAO. Apparently, a deepened Icelandic low-pressure system offers favourable conditions for mid-latitude cyclones in terms of growth and average lifespan. In contrast, negative anomalies in EKE over the North Atlantic and Central Europe are associated with a more equatorward jet stream, these are also linked to a negative phase of the NAO.  Thus, in ERA5, the eddy-driven jet stream and the NAO play a significant role in the spatial and temporal distribution of wintertime mid-latitude cyclonic activity over the North Atlantic and Europe. We extend this connection to the MPI-ESM hindcast simulations and present an analysis of their predictive skill of EKE for wintertime months.
An integrated approach for the validation of Sentinel-5P with annual observation
Authors: Ene Dragoș , Vasilescu Jeni , Boldeanu Mihai , Calcan Andreea , Ardelean Magdalena , Constantin Daniel , Merlaud Alexis , Schüttemeyer Dirk
Published: March 2021

Validation campaign for satellite missions requires efforts in terms of planning, logistics and depends on the weather for its execution. Furthermore, passive instrumentation is more sensitive at the weather, since requires special atmospheric conditions (e.g., cloud-free sky) for optimum performance. In this paper are presented activities regarding the preparation of Sentinel 5P validation in Romania, activities funded by ESA that involve ground-based (fixed and mobile – by DOAS sensors), and airborne measurements.

Research aircraft is based on a Britten-Norman BN-2 Islander platform, custom modified to accommodate, within the cabin, instrumentation for in situ measurements of aerosols (e.g., an Aerosol Particle Sizer and a nephelometer), trace gases (e.g., Picarro, and NO2 CAPS), and NO2, SO2 and H2CO column measurements (e.g., custom made DOAS whiskbroom imager for high-resolution mapping). The aircraft modification, already certified by EASA, include also the installation of an air inlet for the in-situ measurements, a nadir window for the remote sensing, and a GPS antenna for the IMU.

Measurements are planned to start in the spring of 2021 and to last until the end of the year. Region of interest is Bucharest metropolitan area, a city affected by infringement from the EU regarding poor air quality. The strategy is to perform seasonal measurements for mapping the variability of all pollution sources, e.g.: higher production from the local power plants (providers for hot water and heating for the residential population) in winter, car traffic concentrated towards the north, east or west (depending by the season).

This variability is observed also from the TROPOMI measurements, more precisely in the NO2 column concentration. During the spring and summer, the maximum is concentrated within the city centre, while for the autumn and winter, the area is more extended. Maximum values are recorded during the winter, as are shown from the 2019 and 2020 data. Moreover, the amount of S5P measurements during the winter is fewer compared with the summer, due to the presence of clouds, thus planning and execution of a campaign during wintertime being more challenging.
Detecting Transient Creep Events on the Ismetpasa Segment of the North Anatolian Fault with Continuous GNSS Time Series
Authors: Özdemir Alpay , Doğan Uğur , Jara Jorge , Jolivet Romain , Ergintav Semih , Çakır Ziyadin , Özarpacı Seda , Bilham Roger
Published: March 2021

Twenty six years after the Mw 7.3 Bolu/Gerede Earthquake of 1944, Ambraseys (1970) first recognized, in the offset of a manmade wall constructed across the fault in 1957, the signature of slow aseismic slip along the central segment of the North Anatolian Fault (NAF). Following this discovery, many studies have characterized the behaviour of this aseismic slip with land- and space-based geodetic techniques, and with creepmeters. It is now recognized that the rate of aseismic slip decreases logarithmically from more than 3 cm/yr in the years following the Gerede Earthquake to approximately 6±2 mm/yr today. Of this rate, approximately 1.2 mm/year is residual afterslip and the remainder appears to be linear creep interrupted by creep events. In the last two decades, InSAR allowed the derivation of maps of ground velocities that indicates aseismic slip extends along a 100-km-long section of the fault, with a spatially variable aseismic slip rate, reaching its peak value approximately 15-24 km east of the city of Ismetpasa. Furthermore, creepmeter measurements and InSAR time series indicate that surface aseismic slip in the region of Ismetpasa is largely episodic, alternating between quiescent periods and transient episodes of relatively rapid aseismic slip. These observations raise questions about how slip accommodates tectonic stress along the fault with significant implications in terms of hazard along the seismogenic zone.

 In July 2016, we established ISMENET (Ismetpasa Continuous GNSS Network) to monitor spatial and temporal variations in the aseismic slip rate and detect slow slip events along the fault. ISMENET stations are distributed along 120 km long segment of the fault. In order to explore the shallow, fine spatio-temporal behavior of aseismic slip, 19 stations are located within 200 m to 10 km of the fault with 30 and 1 sec sampling rate. We analysed the GNSS time series to extract the signature of aseismic slip using a principal component analysis to reduce the influence of non-tectonic noise. We compared results with creep events quantified by creepmeters.

Keywords: Ismetpasa, Aseismic slip, GNSS, PCA, Time Series Analysis, NAFZ
Assessing the effects of climate and land use land cover changes on recent carbon storage in terrestrial ecosystem using model-satellite approach over Wallonia, Belgium
Authors: Verma Arpita , Francois Louis , Jacquemin Ingrid , Tölle Merja , Zhang Huan , Lanssens Benjamin
Published: March 2021

The use of a dynamic vegetation model, CARAIB, to estimate carbon sequestration from land-use and land-cover change (LULCC) offers a new approach for spatial and temporal details of carbon sink and for terrestrial ecosystem productivity affected by LULCC. Using the remote sensing satellite imagery (Landsat) we explore the role of land use land cover change (LULCC) in modifying the terrestrial carbon sequestration. We have constructed our LULCC data over Wallonia, Belgium, and compared it with the ground-based statistical data. However, the results from the satellite base LULCC are overestimating the forest data due to the single isolated trees. We know forests play an important role in mitigating climate change by capturing and sequestering atmospheric carbon. Overall, the conversion of land and increase in urban land can impact the environment. Moreover, quantitative estimation of the temporal and spatial pattern of carbon storage with the change in land use land cover is critical to estimate. The objective of this study is to estimate the inter-annual variability in carbon sequestration with the change in land use land cover. Here, with the CARAIB dynamic vegetation model, we perform simulations using remote sensing satellite-based LULCC data to analyse the sensitivity of the carbon sequestration. We propose a new method of using satellite and machine learning-based observation to reconstruct historical LULCC. It will quantify the spatial and temporal variability of land-use change during the 1985-2020 periods over Wallonia, Belgium at high resolution. This study will give the space to analyse past information and hence calibrate the dynamic vegetation model to minimize uncertainty in the future projection (until 2070). Further, we will also analyse the change in other climate variables, such as CO2, temperature, etc. Overall, this study allows us to understand the effect of changing land-use patterns and to constrain the model with an improved input dataset which minimizes the uncertainty in model estimation.
Wide-area shrub forest map based on multi-sensor data and active learning
Authors: Rüetschi Marius , Weber Dominique , Koch Tiziana L. , Small David , Waser Lars T.
Published: March 2021

In the past few decades, the occurrence of shrub forest dominated by the two species Green alder (Alnus viridis) and Dwarf mountain pine (Pinus mugo) has increased in the Swiss Alps. Up-to-date and area-wide information on its distribution is required for countrywide forest reporting (5 % of Swiss forest consists of shrub forest) and of great interest to the forestry sector. Such information helps to better understand forest succession and supports the evaluation and management of protection forests. Until now, this information has been based on estimates from the Swiss National Forest Inventory (NFI). Due to their sampling scheme that uses a regular grid, these data are not area-wide maps. However, new developments in remote sensing techniques in combination with high spatial and temporal resolution data have facilitated the production of maps over large areas, e.g. the whole of Switzerland (41’285 km2).

To map the shrub forest areas, we developed an approach that uses a Random Forest (RF) model, active learning techniques and data from multiple remote sensing sources. The training data was produced via aerial image interpretation of areas covered by shrub forest. We used predictor data from different sensors and technologies, complementing each other by their diverse sensitivity to properties of shrub forests. These data included airborne Digital Terrain (DTM) and Vegetation Height Models (VHM), and spaceborne Synthetic Aperture Radar (SAR) backscatter from the Sentinel-1 constellation and multispectral imagery from Sentinel-2. To improve mapping quality, an iterative and semi-automatic active learning technique was used to generate further training data.

The above outlined workflow enabled the production of a shrub forest map for the whole of Switzerland with a spatial resolution of 10 m. An accuracy assessment was performed using independent validation data of a total of 7’640 regularly distributed NFI plots. Mean shrub forest cover per plot (50 m x 50 m) was slightly underestimated by 1.5 % with a root mean square error of 10 %. The influence of the active learning was observed and revealed higher accuracies after each additional iteration of training data production. The proposed approach underscores the potential of multi-sensor data combined with active learning techniques to provide cost-effective and area-wide information on the occurrence of shrub forest in a manner complementary to the NFI measurements.
Tapping the Potential of Earth Observation - Calving Front Detection in SAR Images using Deep Learning Techniques
Authors: Gourmelon Nora , Seehaus Thorsten , Davari AmirAbbas , Braun Matthias , Maier Andreas , Christlein Vincent
Published: March 2021

The calving fronts of lake or marine terminating glaciers provide information about the state of glaciers. A change in its position can affect the flow of the entire glacier system, and the loss of ice mass as icebergs calve-off and discharge into the ocean has a multi-scale impact on the global hydrological cycle. The calving fronts can be manually delineated in Synthetic Aperture Radar (SAR) images. However, this is a time-consuming, tedious and expensive task. As deep learning approaches have achieved tremendous success in various disciplines, such as medical image processing and computer vision, the project Tapping the Potential of Earth Observation (TAPE) is amongst other things dedicated to applying deep learning techniques to calving front detection. So far, all our experiments have employed U-Net based architectures, as the U-Net is state-of-the-art in semantic image segmentation. A major challenge of front detection is the class imbalance: The front has significantly fewer pixels than the remaining parts of the SAR image. Hence, we developed variants of the U-Net specifically addressing this challenge including an Attention U-Net, a probabilistic Bayesian U-Net, as well as a U-Net with a distance map-based binary cross-entropy (BCE) loss function and a Mathews correlation coefficient (MCC) as early stopping criterion. In future work, we plan to investigate multi-task learning and a segmentation of the SAR image into different classes (i.e. ocean, glacier and rocks) to enhance the quality and efficiency of the front detection.
Applying Computed Tomography (CT) scanning for segmentation of permafrost constituents in drill cores
Authors: Gadylyaev Damir , Nitzbon Jan , Schlüter Steffen , Köhne John Maximilian , Grosse Guido , Boike Julia
Published: March 2021

Computed X-ray Tomography is a non-destructive technique that allows three-dimensional imaging of soil samples' internal structures, determined by variations in their density and atomic composition. This study's objective was to develop an image processing workflow for the quantitative analysis of ice cores using high-resolution CT in order to determine the volume fraction and vertical distribution of ice, mineral, gas, and organic matter in permafrost cores. We analyzed a 155 cm permafrost core taken from a Yedoma permafrost upland on Kurungnakh Island in the Lena River Delta (northeast Siberia). The obtained results were evaluated and compared with the results of detailed, but sample-destructive laboratory analysis. The frozen permafrost core was subjected to a computerized X-ray imaging procedure with a resolution of 50 micrometers. As a result, we obtained 31000 images. Noise in the raw images is removed with a non-local means denoising filter. We chose multilevel thresholding method for the image segmentation step. Threshold values were determined based on the histograms of the images. We measured the volumetric ice content (VIC) using Java-based image processing software (ImageJ). In addition, the vertical profiles were analyzed in 1-2cm intervals. We received bulk densities and VIC by freeze-drying and standard laboratory analysis. From the top of the core and until roughly 86 cm, it mainly consists of ice and organic, with an average of 67% and 30% results, respectively. The rest of the volume is divided almost equally between air and mineral parts. Below 86 cm, it consists almost entirely of pure ice. The ice content constitutes around 97% of the composition, and air rises to roughly 3%, while mineral and organic are almost equal to zero. The difference between VIC derived through CT scan and laboratory-derived VIC lies within the range of -37% to 25%. However, the vast majority of values lie within the range of -10% to 10%. This image processing technique to quantify VIC provides a non-destructive analog to traditional laboratory analysis that could help increasing the vertical resolution for quantifying mineral, ice, gas, and organic components in permafrost cores as well as enhance the volumetric estimate.
Soil moisture as a reliable pedunculate oak (Quercus robur L.) radial growth driver
Authors: Kostić Saša , Wagner Wolfgang , Levanič Tom , Zlatanov Tzvetan , Goršić Ernest , Tsvetanov Nickolay , Stojanović Dejan
Published: March 2021

New technologies, such as satellites and sensors, provide a wealth of new information about all ecosystems. In dendrochronological studies, all drought-related factors are of great importance for a more comprehensive understanding of associations between radial growth and water loss. Soil moisture directly reflects the wetness of immediate root surroundings, which is vital to the water uptake by trees. Owing to the advances in satellite observation systems and sensors, soil moisture (SM) can be remotely measured, opening new window in dendrochronological research.

Using the pedunculate oak (Quercus robur L.) lowland SE Europe forests dataset, which count 23 stands and more than 300 tree ring width (TRW) series, we observed reliable associations between satellite-based SM and TRW. Specifically, we observed different TRW−SM patterns based on the precipitation regime. SM in the hottest months (July and August) boosted radial growth, whereas opposite results were noted in the wettest spring months oaks that growing in wetter stands. Unlike oaks from drier and wetter stands that exhibited strong response to SM, those growing on moderately wet (optimal) stands are less sensitive to SM, making these stands optimal oak surroundings.

On the other hand, by applying a Generalized Additive Mixed Model (GAMM), we noted moderate−weak interactions between TRW series and smoothed SM timescales, with stronger deviations in extreme dry/wet years. Based on the TRW sensitivity to SM findings, which were interpreted via Pearson’s correlation technique and GAMM modeling, strong relations can be inferred, and SM can be labelled as reliable pedunculate oak driver.

Keywords: Forestry, Remote sensing, Dendrochronology, Soil moisture, Pedunculate oak, GAMM

Acknowledgments: This research was supported by the Science Fund of the Republic of Serbia, PROMIS, #6066697, TreeVita.

Note: This contribution is a summary of a study by Kostić S, Wagner W, Orlović S, Levanič T, Zlatanov T, Goršić E, Kesić L, Matović B, Tsvetanov N, Stojanović DB. Different tree-ring width sensitivities to satellite-based soil moisture from drier, moderate and wetter pedunculate oak (Quercus robur L.) stands across a southeastern distribution margin (In press)
Improving the simulation of Intermediate Volatility Compounds (IVOCs) in chemical transport models
Authors: Manavi Stella-Eftychia , Pandis Spyros
Published: March 2021

Secondary organic aerosol (SOA) can be formed in the atmosphere through oxidation of volatile (VOCs), intermediate volatility (IVOCs) and semivolatile organic compounds (SVOCs), and condensation of their less volatile products to the particulate phase. While there has been a lot of progress with the simulation of the VOC chemistry, the simulation of the IVOCs remains challenging. In this study, we develop a new approach for the treatment of these compounds in chemical transport models, treating them as lumped species, similar to the VOCs. The new species are implemented in the SAPRC gas-phase chemical mechanism. We introduce four new lumped species representing larger alkanes, two species for polyaromatic hydrocarbons (PAHs) and one new lumped species representing aromatics, all in the IVOC volatility range. Their gas-phase chemistry is assumed to be analogous to that of the large alkanes and aromatics currently in the SAPRC mechanism but with appropriate parameters. The SOA yields for these additional species were estimated for low and high-NOx conditions following the Volatility Basis Set framework and using the available results of smog chamber studies. As most emission inventories do not include IVOCs, we estimated their emissions starting from road transport using existing non-methane hydrocarbons emissions and emission factors of individual IVOCs from laboratory studies. The total IVOC emissions from diesel vehicles for Europe were significantly higher than those coming from gasoline vehicles. The emissions and extended mechanism were implemented in PMCAMx and were used to simulate the EUCAARI intensive period. Cyclic alkanes, which have both high SOA yields and high emissions, were a major SOA precursor group. The contribution of the various IVOCs to SOA formation, and their overall role is discussed. Significant remaining uncertainties are summarized.
Antarctic ice sheet response to upper-bound scenarios
Authors: Sun Sainan , Pattyn Frank
Published: March 2021

Mass loss of the Antarctic ice sheet contributes the largest uncertainty of future sea-level rise projections. Ice-sheet model predictions are limited by uncertainties in climate forcing and poor understanding of processes such as ice viscosity. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) has investigated the 'end-member' scenario, i.e., a total and sustained removal of buttressing from all Antarctic ice shelves, which can be regarded as the upper-bound physical possible, but implausible contribution of sea-level rise due to ice-shelf loss. In this study, we add successive layers of ‘realism’ to the ABUMIP scenario by considering sustained regional ice-shelf collapse and by introducing ice-shelf regrowth after collapse with the inclusion of ice-sheet and ice-shelf damage (Sun et al., 2017). Ice shelf regrowth has the ability to stabilize grounding lines, while ice shelf damage may reinforce ice loss. In combination with uncertainties from basal sliding and ice rheology, a more realistic physical upperbound to ice loss is sought. Results are compared in the light of other proposed mechanisms, such as MICI due to ice cliff collapse.
Theoretical frameworks for understanding and predicting changes in hydrology and society 
Authors: Müller Marc F. , Rusca Maria , Adams Ellis , Allaire Maura , Blöschl Günter , Cabello Villarejo Violeta , Dumas Marion , Levy Morgan , Mukherjee Jenia , Rising James , Yu David J.
Published: March 2021

Coupled human water systems (CWHS) are distinctive in their diversity. Humans both affect and are affected by water across multiple, and sometimes interacting spatial, temporal, management and governance scales. These relationships pertain to multiple characteristics of both the human (e.g., culture, institutions, historical processes, power relations, and economic incentives) and water (e.g., abundance, scarcity, quality) components of CWHS. Changes in any of these characteristics might ripple through CWHSs to affect key societal outcomes, such as the distribution of hydrological risk and access to water and sanitation. The complexity of understanding and predicting hydrological and social changes lies in the fact that there are multiple, interwoven CHWS, each of which has been examined through a variety of disciplinary and theoretical perspectives. 
This chapter synthesizes existing CHWS frameworks across the social, environmental and engineering sciences. We first propose a typology for the CHWS themselves by identifying both their defining and differentiating characteristics. We then develop a typology for the frameworks used to study them, based on philosophical perspectives and methodological approaches. We then identify promising approaches (what “worked”) and outstanding gaps for future work on CHWS. Finally, we leverage the two previously defined typologies to propose a general structure around which to synthesize knowledge in the subsequent topical chapters of the book. 