bluuebunny/crossref_metadata_2025 huggingface dataset:
A MODIS-based ecosystem respiration model and its application in optimizing vegetation photosynthesis and respiration model: A case study of two terrestrial ecosystems in Northern China
Authors: Hao Yong , Jiang Haimei , Ye Haotian
Published: March 2020

Turbulent flux data observed in surface layer during growing seasons at Xilinhaote National Climatic Observatory and Jinzhou Agroecosystem Observatory and remote sensing data were analyzed to acquire main environmental factors and biological factors which drive the ecosystem respiration (Reco). Then the key driven factors of Reco were selected to optimize a semi-empirical ecosystem respiration model. Based on the new ecosystem respiration model, respiration part of Vegetation Photosynthesis and Respiration Model (VPRM) was optimized and its simulation effect of net ecosystem exchange (NEE) was validated in a semi-arid grassland ecosystem and a maize cropland ecosystem.

Compared to the linear temperature model, the nocturnal Reco simulated by the new ecosystem respiration model agreed remarkably better with the observed Reco (at Xilinhaote site, R2 increased from 0.08 to 0.61 in 2010-2012; at Jinzhou site, R2 increased from 0.13 to 0.55 in 2010). And the new ecosystem respiration model showed similar performance in predicting nocturnal Reco (at Xilinhaote site, R2 increased from 0.32 to 0.57 in 2013; at Jinzhou site, R2 increased from 0.33 to 0.61 in 2011).

This study also indicates that optimization of the respiration part of VPRM can improve the simulation effect of NEE during nighttime of the growing seasons in a semi-arid grassland ecosystem and a maize cropland ecosystem, R2 between the modeled NEE and the observed NEE increased from 0.30 to 0.57 in the semi-arid grassland ecosystem and increased from 0.03 to 0.48 in the maize cropland ecosystem. However, in the whole time of the growing seasons, little difference was found between the modelled NEE by the original VPRM model and that by our modified VPRM model, probably for the reason that daytime NEE is mainly dominated by vegetation photosynthesis.
Ice-shelf and glacier changes in Northern Greenland
Authors: Mouginot Jeremie , Rignot Eric , Scheuchl Bernd , Millan Romain , Bjørk Anders , Ehrenfeucht Shivani , Derkacheva Anna
Published: March 2020

In the northern sectors of Greenland, that hold more than 2.7 m of sea level equivalent, ice drains through ice shelves similarly to Antarctica. Zachariae Isstrøm, in northeast Greenland, is retreating and accelerating, most probably because of enhanced melting at its ice-shelf bottom followed by its break- up. Nioghalvfjerdsfjorden, its neighbor, is also showing signs of thinning close to its grounding line, as is Petermann Gletscher, located 800_km more to the west. Here, we investigate dynamic and geometrical changes of all current and former ice shelves located along the northern coast of Greenland, namely Humboldt Gletscher, Steensby Gletscher, Ryder Gletscher, Ostenfeld Gletscher, Marie Sophie Gletscher, Academy Gletscher and Hagen Bræ. Using satellite and airborne-based remote- sensing sensors, we reconstruct the time series of speed, grounding-line position, submarine melt, ice thickness and surface elevation changes since the 80s. We will provide an update of the glacier ice discharges and will discuss any large-scale pattern of enhanced melting of the northern Greenlandic ice shelves . We will conclude with the possibility of actual or future destabilization -or lack thereof- of the glaciers in this sector of Greenland.
Impact of elastic material properties and discontinuities on the stress orientation
Authors: Reiter Karsten
Published: March 2020

The in-situ stress state in the upper crust is an important issue for diverse economic purposes and scientific questions as well. Several methods have been established in the last decades to estimate the present-day orientation of the maximum compressive horizontal stress (SHmax) in the crust. It has been assumed, that the SHmax orientation on a regional scale is governed by the same forces that drive plate motion too. The SHmax orientation data, compiled by the World Stress Map (WSM) project, confirmed that for many regions in the world. Due to the increasing amount of data, it is now possible to identify several areas in the world, where stress orientation deviates from the expected orientation due to plate boundary forces (first order stress sources), or the plate wide pattern. In some of this regions a gradual rotation of the SHmax orientation is observed.

Several second and third order stress sources have been identified which may explain stress rotation in the upper crust. For example, lateral heterogeneities in the crust, such as density, petrophysical or petrothermal properties and discontinuities, like faults are identified. Apparently, there are just a few studies, that deal with the potential extend of stress rotation as a function of second and third order stress sources. For that reason, generic geomechanical numerical models have been developed, consisting of up to five different units oriented at an angle of 60 degrees to the direction of contraction. These units have variable elastic material properties, such as Young’s modulus, Poisson ratio and density. In addition, an identical model geometry allows the units to be separated by contact surfaces that allow them so slide along the faults, depending on a selected coefficient of friction.

The model results indicate, that a density contrast or the variation of the Poisson’s ratio alone sparsely rotates the horizontal stress orientation. Conversely, a contrast of the Young’s modulus allows significant stress rotations. Not only areas in the vicinity of the material transition are affected by the stress rotation, but the entire blocks. Low friction discontinuities do not change the stress pattern when viewed over a wide area in homogeneous models. This also applies to models with alternating stiff and soft blocks - the stress orientation is determined solely by the boundary conditions, not the material transitions. This indicates that material contrasts are capable of producing significant stress rotation for larger areas in the crust. Active faults that separates such material contrasts have the opposite effect, they compensate for stress rotations.
Nitrate sources and sinks in oligotrophic groundwater
Authors: Herrmann Martina , Krüger Markus , Thamdrup Bo , Küsel Kirsten
Published: March 2020

Despite the high relevance of karstic aquifers as drinking water reservoirs, nitrate pollution of groundwater is posing an increasing threat on a global scale. Under anoxic conditions, nitrate can be converted to N2 by denitrification or anaerobic ammonia oxidation (anammox) and thus be removed from the system. However, in the presence of oxygen, nitrification may continue in the groundwater, supported by the activity of ammonia oxidizing bacteria (AOB), archaea (AOA), and the recently discovered complete ammonia oxidizers (comammox bacteria). We aimed to disentangle different sources and sinks of nitrate and key microbial players involved in nitrogen transformation processes in oligotrophic limestone aquifers of the Hainich Critical Zone Exploratory (CZE; Germany). Assessment of process rates using 15N-labeling techniques revealed a variance of nitrification rates by two orders of magnitude across six oxic groundwater wells. Surprisingly, wells with nitrate concentrations higher than 300 µmol L−1 showed only very low nitrification activity of less than 2 nmol NO3− L−1 d−1, pointing to surface inputs rather than in situ production. In turn, maximum nitrification activity of 127 nmol NO3− L−1 d−1 coincided with a consistently large fraction of comammox bacteria of more than 70% in the groundwater nitrifier community. Estimated per cell activities of ammonia oxidation suggested that a contribution from comammox was needed to sufficiently explain the observed nitrification rates. Anaerobic ammonia oxidation (anammox) and denitrification as potential nitrate or nitrite sinks varied within a smaller range of 1 to 5 nmol N2 L−1 d−1 across anoxic wells and were dominated by anammox, most likely linked to a low availability of organic carbon and suitable inorganic electron donors for chemolithoautotrophic denitrification. Differences in activities agreed well with 100 times higher transcriptional activity of hzsA genes involved in anammox compared to nirS genes involved in denitrification. Our findings provide strong evidence for nitrification supported by comammox bacteria in oligotrophic groundwater and for anammox as the dominating N removing process.
A field study of depletion-replenish water storage mechanism in tree stems in semi-arid region
Authors: Cheng Yiben , Wang Yunqi , Jiang Qunou
Published: March 2020

Trees in arid and semi-arid regions are faced with water shortages at most times, and the use of water storage in tree stem is an important mechanism and pathway for adaptation to drought. In this research, we have explored the tree saplings in semi-arid areas by continuous monitoring and analysis of the sap flux at stem top and stem breast, in the main growth season. A primary objective is to find out when and how trees use stem water storage as a reservoir, and more specifically if there is a difference in stem flow start time between stem top and stem breast. Our study shows that in sunny day of the growing season, the sap flow at stem top start time is later than the sap flow at stem breast, with the maximum of time lag about 60 mins, and the daily sap flow peak time of stem top is later than that of the stem breast by 1-2 hrs. The maximum daily flux at stem top is about 1.4-2.1 times greater than that at stem breast. Stem water storage increases the drought tolerance of trees. The depletion stage of stem water storage mainly occurs in early morning, and then enters the replenishing phase in the afternoon. In a sunny day, with the increase of soil water deficit with relative extractable water (REW) (or the relative effective soil water index) less than 0.43, demand for water storage of stem is more significant, and its role is mainly based on the depletion process. When the soil moisture condition is improved, the process is dominated by replenishing. From the results of continuous observations throughout the growing season, the depleting and replenishing processes can achieve equilibrium in a short period of time (like a few days). This research has advanced our understanding of the utilization mechanism of tree stem storage water in semi-arid areas.
Ecosystem services determination on an Italian urban greenspace
Authors: Busca Francesco , Vigliocco Francesca , Revelli Roberto
Published: March 2020

This paper is part of the panorama of studies on climate changes in an urban context. Starting from the concept of Ecosystem Services, we aim to underline the importance of rebalancing equally what is demanded in an urban ecosystem and what it provides people with, focusing on pollutants quantity, carbon sequestration and runoff reduction. Ecosystem services (ES) can be defined as the components of natural capital that provide direct products (food, drinking water, etc) and benefits (like biological variability and soil creation) to people. Our goal is to determinate and to quantify ES related to urban greenspaces in terms of both economic and environmental point of view.

Specifically, the study has been developed through the use of i-Tree, a suite developed in the US context, that shows on both small and large scale the economic, environmental and water-related benefits provided by a green area. Its applicability has been tested for an Italian context on a newly built park, located in “Revello Street – Turin”, with the collaboration of the Municipality of Turin, comparing past, present and future scenarios.

Eco, Hydro and Canopy tools were used for that urban greenspace, providing useful information on software usage and justifying the creation and/or the expansion of new urban green areas through economic and environmental outputs. Results show how the transition from a past residential area to an almost totally green area has led to air quality improvement, with a consequent increase in carbon storage and pollutants reduction, while in view of future improvement works in the park (intensification of arboreal and shrubby presence), the results economically justify the intervention by showing a significant water runoff reduction with consequent reduction of flood events risk.

This work aims to deepen advantages and disadvantages of i-Tree and to insert the software as an effective and innovative tool, not widely known in a European context, for the monitoring and development of methodologies to make urban spaces increasingly sustainable, within a view of smart cities.
Hydrogeochemical evidence of seawater intrusion: a case study in Venice farmland
Authors: Zancanaro Ester , Teatini Pietro , Scudiero Elia , Morari Francesco
Published: March 2020

Saltwater contamination seriously affects groundwater quality and land productivity of coastal farmland along the Venice lagoon, Italy. Characterizing seawater intrusion dynamics represents a fundamental step to better understand its effect on soil and groundwater quality and in turn, conceive mitigation strategies. To this end, a three-year study was conducted in an experimental field bounding the southern Venice Lagoon. Volumetric water content, soil matric potential and apparent electrical conductivity (ECa) were monitored by five automatic monitoring stations at four depths (0.1, 0.3, 0.5 and 0.7 m). Groundwater electrical conductivity (EC) and depth to the water table were measured at the five stations. In addition, soil pore water at the four depths and borehole groundwater samples were collected periodically and analyzed for chemical composition. Physical and chemical analyses of the soil profiles were also carried out. Relationships between Cl-, Na+, Mg2+, Ca2+, K+, SO42-, Br- ionic concentrations, EC and soil characteristics (e.g. texture, EC1:2, exchangeable cations) were calculated by Pearson and Spearman correlation. Kruskal Wallis test was performed to test the five monitoring stations. Moreover, specific molar ratios (Cl/Br, Br/Cl, Na/Cl and K/Cl) were calculated in order to identify the main drivers affecting salinity in the field. EC and ionic concentrations showed high variability across the monitoring stations and between the different sampling dates (e.g. groundwater EC ranged between 0.33 and 17.46 dS/m). Higher EC and ionic concentration values were observed during upward soil water movement, while values were lower during percolation events (e.g. maximum Cl- concentrations were 9227.3 mg/l and 3436.1 mg/l, respectively). An high correlation resulted between Na+ and Cl- ionic concentrations and EC data in four out of the five monitoring stations (r values between 0.82 and 0.92). In addition, Kruskal Wallis test showed a significant difference between EC and chemical data sampled at the five monitoring stations and different soil depths. These results allow to conclude that soil and water salinity originated from different processes such as seawater intrusion and deep brines upcoming. Understanding salinization sources would enable the definition of a mitigation strategy able to enhance land productivity and water quality.
A systematic evaluation of surface albedo prediction error in high latitude forest environments: The case of the Community Land Model (CLM)
Authors: Tang Hui , Bright Ryan , Stordal Frode
Published: March 2020

Land surface models (LSMs) employed in global climate research continue to struggle to predict  surface albedo in high latitude forests.  Persistent sources of error in LSMs may originate from one or more of the following:  a) the underlying land cover mapping and PFT classification; b) the parameterization of forest structure; c) canopy-snow dynamics and snow physical attributes; d) canopy radiative transfer.   Among the more sophisticated, the surface albedo scheme in the Community Land Model has undergone several updates over the past decade, although it remains unclear which updates – and to what extent -- they may have contributed to improved surface albedo prediction accuracy in high latitude forest environments.  Here, using Fennoscandia (Norway, Sweden, and Finland) as a case study region and a 5-year MODIS-based surface albedo time series as an empirical benchmark, we carry out a series of offline simulations using CLM versions 4.5, 5.0, and FATES (formerly ED) combined with novel land cover and structure mapping to systematically quantify errors attributable to the aforementioned sources, as well as improvements (or degradations) to predictive performance associated with incremental model developments in time.  Preliminary results using CLM v. 4.5 & 5.0 suggest that both the underlying land cover mapping and the representation of forest structure contribute equally to prediction error and outweigh the error attributable to the parameterization of canopy-snow processes.  As for canopy radiative transfer, the extent to which the multi-layer canopy radiative transfer scheme introduced in FATES reduces surface albedo prediction error over the single-layer scheme employed in all other CLM versions remains to be quantified.
Uncertainty of evapotranspiration fluxes measured with eddy covariance
Authors: Pohl Felix , Hildebrandt Anke , Werban Ulrike , Rebmann Corinna
Published: March 2020

The project MOMENT (Model Monitoring EveNTs) investigates the interplay between carbon and water cycles with special focus on the impacts of drought and heatwaves as well as their long-term trends. This project aims to investigate new monitoring and modeling methods to explain the interplay between carbon and water cycles of ecosystems on different time and spatial scales.

To achieve this goal, we need reliable information about the ecosystem and its drivers. We measure, for example, mass and energy exchange between the ecosystem and the lower atmosphere with the eddy covariance method, which allows us to obtain data on a half-hourly scale. Nevertheless, unfavorable weather conditions, as well as malfunctions of the instruments, can lead to a serious amount of data gaps. Different gap-filling methods are available, with the Marginal Distribution Sampling (MDS) by Reichstein et al. (2005) being the most common one. Here, we investigate, how different filling approaches influence the uncertainty of evapotranspiration (ET) data for a German forest. We especially focus on the imputation of evaporation from intercepted canopy water, because open-path EC systems rarely work correctly during and after rain events.

Even though the EC technique is a well-established method to measure ET at the ecosystem level, many approaches require rather the share of transpiration, such as the validation of some ecosystem models. Partitioning ET into its components is difficult due to the manifold drivers involved, and measuring ecosystem transpiration is challenging due to measurement limitations and assumptions, that have to be made. Therefore, we examine the possibility to retrieve information about the share of transpiration by using EC data only without additional measurement campaigns.

Reference:
Reichstein, M. et al.: On the separation of net ecosystem exchange into assimilation and ecosystem respiration: Review and improved algorithm, Glob. Chang. Biol., 11(9), 1424–1439, doi:10.1111/j.1365-2486.2005.001002.x, 2005.
Towards a probabilistic assessment of sediment yields in a mountainous area: the case study of Valle Camonica
Authors: Bischetti Gian Battista , Sala Paolo , Fogliata Paolo , Morlotti Emanuele , Cislaghi Alessio
Published: March 2020

Sediment production and delivery are hillslope processes characterized by significant variability and uncertainty, especially in mountain drainage catchments. Although sediments can be originated from several phenomena, such as slope instabilities, soil erosion and streambank failures, rainfall-induced landsliding, eventually turned into debris flows, is the dominant mechanism producing and conveying huge volumes of solid material to downstream areas through the channel network and therefore causing an increase of flood frequency.

Such landslide-derived mechanisms cause damage, directly and indirectly, to public and/or private properties and infrastructure on alluvial fans that are basically due to the increase of clogging probability of bridges, instream sediment accumulation, and significant geomorphological change. Identifying the sediment upstream source areas and quantifying a probability distribution of the mobilized- and delivered-sediment volume, then, is crucial for the protection of downstream areas. However, such purpose still remain extremely challenging because of scarcity, or even lack, of time-consuming direct measurements that are generally carried out at small scale and cover short time periods.

On this background, this work proposes a simplified procedure to estimate a probability distribution of the sediment yields combining: (i) rainfall intensity-duration-frequency (IDF) relationships for estimating synthetic precipitation with specific return time; (ii) a three-dimensional slope stability model to assess the rainfall-induced shallow landslides susceptibility; (iii) a connectivity index for mapping the probability of sediment delivery; and (iv) a simple hydrological model based on SCS-CN method to estimate the flood peak, and furthermore the probability distribution of sediment flux. The procedure requests low-resolution maps, usually available at the regional scale, such as digital elevation model, land cover, geology, lithology, and IDF curves, and represents a planning tool for climate and land cover change mitigation that can be extremely useful for forest managers, hydraulic engineering and watershed planners.

The procedure was tested on several small mountainous headwater catchments in Valle Camonica, located into the Central Italian Prealps, mostly covered by forests, with settlements on alluvial fans, and prone to shallow landslide, debris flood, and debris flow. It was qualitatively validated on the landslide inventory and the mapped flood areas, showing comparable results.
The large-scale tilt of the eddy divergence in the tropics
Authors: Zurita-Gotor Pablo
Published: March 2020

This work is concerned with the large-scale structure of the upper-level divergence/precipitation field in the deep tropics. Once the fine ITCZ structure is filtered out, the coarse-grained eddy divergence field is found to tilt eastward moving away from its maximum near the equator in the summer hemisphere. This robust tilt (observed for both hemispheres and seasons) is also present in the classical Gill solution.

In this presentation we show that the sign of the tilt is intimately linked to the direction of the eddy momentum flux. The observed eastward tilt is such that the momentum flux is directed towards the wave source, suggesting that the observed tilt is determined by wave propagation.

We also discuss the determination of the tilt in the simple Gill model and its sensitivity to the meridional Hadley flow. We show that the increase in the cross-equatorial momentum flux when the Hadley cell strengthens is associated with an increased tilt of the divergence field in the downstream direction of the flow, supporting the conjecture that the tilt is associated with propagation. 
Modeling mercury cycling in the marine environment
Authors: Bieser Johannes , Daewel Ute , Schrum Corinna
Published: March 2020

Five decades of Hg science have shown the tremendous complexity of the global Hg cycle. Yet, the pathways that lead from anthropogenic Hg emissions to MeHg exposure through sea food are not fully comprehended. Moreover, the observed amount of MeHg in fish exhibits a large temporal and spatial variability that we cannot predict yet. A key issue is that fully speciated Hg measurements in the ocean are difficult to perform and thus we will never be able to achieve a comprehensive spatial and temporal coverage.

Therefore, we need complex modeling tools that allow us to fill the gaps in the observations and to predict future changes in the system under changing external drivers (emissions, climate change, ecosystem changes). Numerical models have a long history in Hg research, but so far have virtually only addressed inorganic Hg cycling in atmosphere and oceans.

Here we present a novel 3d-hydrodynamic mercury modeling framework based on fully coupled compartmental models including atmosphere, ocean, and ecosystem. The generalized high resolution model has been set up for European shelf seas and was used to model the transition zone from estuaries to the open ocean. Based on this model we present our findings on intra- and inter-annual dynamics and variability of mercury speciation and distribution in a coastal ocean. Moreover, we present the first results on the dynamics of mercury bio-accumulation from a fully coupled marine ecosystem model. Most importantly, the model is able to reproduce the large variability in methylmercury accumulation in higher trophic levels.
Temperature and precipitation projections for Poland based on downscaled EuroCORDEX ensemble
Authors: Struzewska Joanna , Jefimow Maciej , Jagiełło Paulina , Kłeczek Maria , Sattari Anahita , Gienibor Aneta , Norowski Aleksander , Durka Pawel , Walczak Barłomiej , Drzewiecki Piotr
Published: March 2020

Regional climate projections are necessary to assess possible changes in the exposure and risk to allow planning the adaptation strategies.

Projections of temperature and precipitation trends were developed using a consistent methodology and homogeneous datasets to address the needs of up-to-date climate change scenarios for Poland.

The Euro-Cordex results with the resolution of 0.11deg (about 12.5km) for RCP4.5 and RCP8.5 were downscaled based on various historical gridded datasets (EOBS, ERA5, UERRA and data from IMWM).

Ensemble analysis was undertaken to assess the projection uncertainty and ensemble mean were calculated for base parameters (daily average, minimum, and maximum temperature and daily precipitation sum) as well as for the number of climate indices.

We will present spatial and temporal variability of selected climate indices over Poland for subsequent decades. Increase of the annual average temperature is due to the rise in the number of hot days and the reduction of the number of frost days. All temperature indices are characterized by statistically significant trends, strongest for RCP8.5. The most pronounced changes in the frequency and amount of precipitation occur in the north-east of Poland. The total number of days with precipitation increases slightly. The increase in the annual rainfall is due to the increase in the number of days with extreme precipitation.

Results are presented via an interactive web portal. Further analysis includes the development of projection for solar radiation, wind speed, humidity and snow cover.
Analysis of GOES-R as a Constraint in GNSS Tropospheric Tomography
Authors: Adavi Zohreh , Weber Robert
Published: March 2020

GNSS tomography is an all-weather condition remote sensing technique in the field of meteorology that is gaining considerable attention in recent years. The water vapor distribution and related parameters like wet refractivity in the troposphere can be reconstructed with reasonable Spatio-temporal resolution in this method. To achieve this goal, the troposphere is divided into a number of 3D elements (voxels). Then, the system of the observation equations is defined by a relation between the wet refractivity field and the distance traveled by GNSS rays through voxels. However, propagated signals do not pass through some of the model elements. Thereby, the reconstructed wet refractivity field suffers in terms of solution uniqueness. Consequently, additional data sources and horizontal and/or vertical constraints should be applied to avoid the singularity of the estimated field. In this presentation, the combination of wet refractivity maps computed from Geostationary Operational Environmental Satellite (GOES) sounder and refractivity fields obtained by GNSS tomography is demonstrated to achieve a unique solution. The GOES-R sounder products are provided hourly with a 10 km spatial resolution. Therefore, GOES-R wet refractivity maps are used to constrain the system of equations and consequently, the tomographic solution leads to an improved reconstructed wet refractivity field. To analyze the efficiency of the proposed data, a 3D tomographic model is defined over a regional area covered by the Continuously Operating Reference Station (CORS) Network in the United States. Moreover, radiosonde measurements in the area of interest are used to achieve the feasibility and correctness of the estimated 3D wet refractivity images.
Stable Multiscale Discretizations of L2-Differential Complexes
Authors: Simon Konrad , Behrens Jörn
Published: March 2020

Global simulations over long time scales in climate sciences often require coarse grids due to computational constraints. This leaves dynamically important smaller scales unresolved. Thus the influence of small scale processes has to be taken care of by different means. State-of-the-art dynamical cores represent the influence of subscale processes typically via subscale parametrizations and often employ heuristic coupling of scales. This, however, unfortunately often lacks mathematical consistency. The aim of this work is to improve mathematical consistency of the upscaling process that transfers information from the subgrid to the coarse scales of the dynamical core and to largely extend the idea of adding subgrid correctors to basis functions for scalar and vector valued elements discretizing various function spaces.

Discussing prototypically the issue of weighted Hodge decompositions I will show that standard techniques on coarse meshes fail to find good projections in all parts of a modified de Rham complex if rough data is involved and discuss an idea of how to construct multiscale finite element (MsFEM) correctors to scalar and vector valued finite elements and, further, how to construct stable multiscale element pairings using the theory of finite element exterior calculus (FEEC). This can be seen as a meta-framework that contains the construction of standard MsFEMs [Efendiev2009, Graham2012]. Application examples here comprise porous media, elasticity, and fluid flow as well as electromagnetism in fine-scale and high-contrast media. I will provide the necessary theoretical background in homological algebra and differential geometry, and discuss a scalable MPI based implementation technique suitable for large clusters. Several computational examples will be shown. I may, if time permits, discuss some ideas from homogenisation theory to attack the problem of a proof of accuracy.
The influence of topography of stream bed with the clogging layer on the stream-groundwater interaction and the groundwater flow patterns beneath stream bed
Authors: Lo Jui-Hsiang , Lin Hung-Yen , Chiu Yung-Chia , Lee Tsung-Yu , Tsai Yi-Zhih , Lee Jung-Dung , Hsu Shao-Yiu
Published: March 2020

Studies have indicated that the streambed with the clogging layer affects the interaction between surface water and groundwater. When the streambed covered by a clogging layer, the decrease of the groundwater table can transform the state of stream-groundwater from the connection into disconnection. When the stream-groundwater interaction reaches the state of disconnection, the infiltration rate is independent with the groundwater level beneath the streambed. In this study, we show the effects of the topography of the streambed and clogging layer on the infiltration and groundwater flow patterns beneath the streambed by numerical simulations. The results show that the clogging layer and the change of topography of streambed affect the development of the unsaturated zone, flow path, and residence time beneath the streambed.
Coastal salt-marsh sediments of the southeastern North Sea region document North Atlantic climate variability
Authors: Bunzel Dorothea , Milker Yvonne , Müller-Navarra Katharina , Arz Helge Wolfgang , Schmiedl Gerhard
Published: March 2020

Salt marshes are of substantial importance for the adaptation of coastal regions to present-day and predicted future climate changes, and accompanied sea-level fluctuations. This gives the motivation to investigate salt-marsh archives from the southern North Sea region, which provide an exceptional archive to understand the response of coastal systems to climate variability of the recent past. For this study, well-stratified sediment sequences from two different salt-marsh systems were analysed by scanning XRF spectroscopy. The study sites are affected by both natural processes and anthropogenic interventions on different time scales. To address the complex interplay between storm surges, human-induced coastal management, and coupled internally forced atmosphere-ocean mechanisms during the last century, this study focuses on the ln(Zr/Rb) ratio as proxy for the relative particle-size distribution, and the Br/Corg ratio as an indicator for the marine versus terrestrial organic matter input to the sediment. Additional information about local changes in the sedimentary organic matter quality is provided by the alteration of ln(Br/Cl) ratios. The ln(Zr/Rb) records reveal periodic fluctuations at inter-annual, inter-decadal to multi-decadal time scales, suggesting a close link of sediment accretion to the atmospheric-ocean climate oscillation over the North Atlantic and Europe, which is accompanied by variations in the wind field, precipitation and river runoff. By contrast, the Br/Corg ratios exhibit a long-term increase starting from the mid-twentieth century towards recent times, resembling the observed increasing trend in North Sea storminess. Abrupt drops in the ln(Br/Cl) records coincide with relatively coarser sand layers, indicating impacts by regional storm surges during winter, while intervals of comparable higher ln(Br/Cl) values represent times of generally calm weather conditions of periods with less frequent storm surges. Our results imply that past regional to super-regional climate changes have been transferred into the sedimentary salt-marsh archives of the southern North Sea region.
Interactive 3D visual analysis in weather forecasting
Authors: Rautenhaus Marc , Hewson Timothy , Modali Kameswar Rao , Beckert Andreas , Kern Michael
Published: March 2020

Visualization of numerical weather prediction data and atmospheric observations has always been an important and ubiquitous tool in weather forecasting. Visualization research has made much progress in recent years, in particular with respect to techniques for ensemble data, interactivity, 3D depiction, and feature-detection. Transfer of new techniques into weather forecasting, however, is slow.

In this contribution, we will discuss the potential of recent developments in 3D and ensemble visualization research for weather forecasting. We will introduce our work on 3D feature-detection methods for jet-stream and front features, which facilitate analysis of the evolution of jet-stream core lines and frontal surfaces in an (ensemble) forecast. The techniques have been integrated into the 3D visual ensemble analysis framework Met.3D (https://met3d.wavestoweather.de), in which they can be combined with traditional 2D depictions as well as further 3D visual elements and be displayed in an interactive 3D context. We will present and discuss 3D ensemble forecast products created with Met.3D based on forecast data from ECMWF and DWD, and demonstrate their use in the exploration of example cases including an extratropical transition over the North Atlantic and a European winter storm.

In addition, we will introduce new semi-operational 3D forecast products based on our techniques that we provide experimentally on the web, in order to gather user feedback and to initiate discussion about potential benefit of such products for operations.
Did a Beringian ice sheet once exist?
Authors: Zhang Zhongshi , Yan Qing , Zhang Ran , Colleoni Florence , Ramstein Gilles , Dai Gaowen , Jakobsson Martin , O’Regan Matt , Liess Stefan , Rousseau Denis-Didier , Wu Naiqing , Farmer Elizabeth J. , Contoux Camille , Guo Chuncheng , Tan Ning , Guo Zhengtang
Published: March 2020

Did a Beringian ice sheet once exist? This question was hotly debated decades ago until compelling evidence for an ice-free Wrangel Island excluded the possibility of an ice sheet forming over NE Siberia-Beringia during the Last Glacial Maximum (LGM). Today, it is widely believed that during most Northern Hemisphere glaciations only the Laurentide-Eurasian ice sheets across North America and Northwest Eurasia became expansive, while Northeast Siberia-Beringia remained ice-sheet-free. However, recent recognition of glacial landforms and deposits on Northeast Siberia-Beringia and off the Siberian continental shelf has triggered a new round of debate.These local glacial features, though often interpreted as local activities of ice domes on continental shelves and mountain glaciers on continents,   could be explained as an ice sheet over NE Siberia-Beringia. Only based on the direct glacial evidence, the debate can not be resolved. Here, we combine climate and ice sheet modelling with well-dated paleoclimate records from the mid-to-high latitude North Pacific to readdress the debate. Our simulations show that the paleoclimate records are not reconcilable with the established concept of Laurentide-Eurasia-only ice sheets. On the contrary, a Beringian ice sheet over Northeast Siberia-Beringia causes feedbacks between atmosphere and ocean, the result of which well explains the climate records from around the North Pacific during the past four glacial-interglacial cycles. Our ice-climate modelling and synthesis of paleoclimate records from around the North Pacific argue that the Beringian ice sheet waxed and waned rapidly in the past four glacial-interglacial cycles and accounted for ~10-25 m ice-equivalent sea-level change during its peak glacials. The simulated Beringian ice sheet agrees reasonably with the direct glacial and climate evidence from Northeast Siberia-Beringia, and reconciles the paleoclimate records from around the North Pacific. With the Beringian ice sheet involved, the pattern of past NH ice sheet evolution is more complex than previously thought, in particular prior to the LGM.
Towards long-term satellite root-zone soil moisture: 40-year Soil Water Index dataset from ESA CCI COMBINED Soil Moisture product.
Authors: Pasik Adam , Bauer-Marschallinger Bernhard , Preimesberger Wolfgang , Scanlon Tracy , Dorigo Wouter , Hahn Sebastian
Published: March 2020

Multiple satellite-based global surface soil moisture (SSM) datasets are presently available, these however, address exclusively the top layer of the soil (0-5cm). Meanwhile, root-zone soil moisture cannot be directly quantified with remote sensing but can be estimated from SSM using a land surface model. Alternatively, soil water index (SWI; calculated from SSM as a function of time needed for infiltration) can be used as a simple approximation of root-zone conditions. SWI is a proxy for deeper layers of the soil profile which control evapotranspiration, and is hence especially important for studying hydrological processes over vegetation-covered areas and meteorological modelling. 
Here we present the first long-term SWI dataset from ESA CCI Soil Moisture v04.5 COMBINED product, covering a 40-year period between 1978 and 2018. The ESA CCI dataset is unique because of its long-term global coverage based on merged observations from both active and passive sensors. The SWI is calculated for eight T-values (1, 5, 10, 15, 20, 40, 60, 100), where T-value is a temporal length ruling the infiltration; depending on the soil characteristics it translates into different soil depths.
Primary results show promise for pursuing development of an operational SWI product. Here, we present the results of SWI validation against data from the International Soil Moisture Network (ISMN) using the QA4SM framework, as well as results of the attempt to establish relationship between T-values and particular soil depths.
Traces of sunlight in carbon biochemistry of shallow subarctic lakes
Authors: Rantala Marttiina , Kivilä Henriikka , Meyer-Jacob Carsten , Wauthy Maxime , Rautio Milla , Lami Andrea , Luoto Tomi , Nevalainen Liisa
Published: March 2020

Sunlight fuels the drawdown and evasion of carbon in shallow northern lakes. Amplified polar warming is altering the sunlit transport and transformation of aquatic carbon at an alarming rate entailing potential for climate feedbacks. We combined experimental and retrospective approaches to explore the synoptic interlinks between underwater light, aquatic carbon biochemistry, landscape carbon cycling and climate change in two shallow subarctic lakes with divergent light and carbon regime (a clear lake low in organic carbon and a dark organic rich lake). In situ enclosures (treatments under full sunlight, sunlight without the ultraviolet [UV] spectrum, no light) were first deployed on the lakes to decipher the effect of photochemical alteration on the spectral, elemental and isotopic properties of lake water organic carbon pools under short term (four weeks) exposure. We then focused on elemental, isotopic and spectral fingerprints archived in the sediments of the lakes to trace coeval variability in aquatic primary production, terrestrial carbon transport, and underwater light under centennial climate fluctuations. We observed distinct differences in carbon biochemistry between the experimental treatments illustrating the importance of sunlight, and particularly the UV spectrum, in shaping the carbon pools of the lakes already over short time scales. Over the past centennia, sediment biogeochemical composition carried signatures of change in carbon origins (algal vs terrestrial) and shifting underwater light regime. The results shed light on how climate change and sunlight shape carbon flows in shallow northern lakes over short and long time scales.
The Latest (Dusty) Pieces in the Rosetta Story
Authors: Ivanovski Stavro Lambrov
Published: March 2020

The ESA’s Rosetta spacecraft had the unique opportunity to follow comet 67P/Churyumov-Gerasimenko (hereafter 67P) for about 2.5 years – from January 2014 to September 2016 – observing how the comet evolved while approaching the Sun, passing through perihelion and then moving back into the outer solar system. Remote sensing and in-situ instruments onboard Rosetta acquired data to study the comet’s dust environment during the entire duration of the mission, while telescopes followed the large-scale coma and tails from Earth. Here we report the latest advances of the ongoing multi-instrument approach that the Rosetta dust working group has been following in the recent years. Individual instrument data analyses have been carried on providing a first characterization of 67P dust environment. Timely, multi-instruments data analyses are now progressing a step forward in understanding how comet works and are providing critical results for a more comprehensive and unified knowledge of cometary dust environments. We will illustrate the progress we have made and the results we have reached following this constructive and collaborative approach.

We also discuss the latest achievements on the cometary dust modelling using the multi-instrument Rosetta data. In particular, what additional information these calibrated dust models provide and what we are still missing in cometary dust characterization.
The influence of loading path on fault reactivation: a laboratory perspective
Authors: Giorgetti Carolina , Violay Marie
Published: March 2020

Despite natural faults are variably oriented to the Earth's surface and to the local stress field, the mechanics of fault reactivation and slip under variable loading paths (sensu Sibson, 1993) is still poorly understood. Nonetheless, different loading paths commonly occur in natural faults, from load-strengthening when the increase in shear stress is coupled with an increase in normal stress (e.g., reverse faults in absence of the fluid pressure increase) to load-weakening when the increase in shear stress is coupled with a decrease in normal stress (e.g., normal faults). According to the Mohr-Coulomb theory, the reactivation of pre-existing faults is only influenced by the fault orientation to the stress field, the fault friction, and the principal stresses magnitude. Therefore, the stress path the fault experienced is often neglected when evaluating the potential for reactivation. Yet, in natural faults characterized by thick, incohesive fault zone and highly fractured damage zone, the loading path could not be ruled out. Here we propose a laboratory approach aimed at reproducing the typical tectonic loading paths for reverse and normal faults. We performed triaxial saw-cut experiments, simulating the reactivation of well-oriented (i.e., 30° to the maximum principal stress) and misoriented (i.e., 50° to the maximum principal stress), normal and reverse gouge-bearing faults under dry and water-saturated conditions. We find that load-strengthening versus load-weakening path results in clearly different hydro-mechanical behavior. Particularly, prior to reactivation, reverse faults undergo compaction even at differential stresses well below the value required for reactivation. Contrarily, normal faults experience dilation, most of which occurs only near the differential stress values required for reactivation. Moreover, when reactivating at comparable normal stress, normal faults (load-weakening path) are more prone to slip seismically than reverse fault (load-strengthening path). Indeed, the higher mean stress that normal fault experienced before reactivation compacts more efficiently the gouge layer, thus increasing the fault stiffness and favoring seismic slip. This contrasting fault zone compaction and dilation prior to reactivation may occur in different natural tectonic settings, affecting the fault hydro-mechanical behavior. Thus, to take into account the loading path the fault experienced is fundamental in evaluating both natural and induced fault reactivation and the related seismic risk assessment.