bluuebunny/crossref_metadata_2025 huggingface dataset:
Plant communities on fertile soils of drained thermokarst lakes in Western Siberia
Authors: Kuzmina Darya , Loiko Sergey , Lim Artem , Raudina Tatyana , Klimova Nina
Published: March 2021

Climate warming and increased precipitation and permafrost thaw in the Arctic are accompanied by an increase in the frequency of a full or partial drainage of thermokarst (thaw) lakes. After lake drainage, abundant plant communities on nutrient-rich sediments may develop, but the specific features of this process remain extremely poorly known across the Arctic. Here, we examine case studies of lake basins located in the continuous permafrost zone of the largest peatland in the world, the Western Siberia Lowland (WSL). We characterize the vegetation and biological productivity of the drained thermokarst lake basins (khasyreys) located in the southern tundra of the WSL. The biological productivity of the khasyrey vegetation is a factor of two to nine higher than that in the surrounding tundra and the khasyreys may provide substantial contribution to observed greening of the northern part of the WSL (65 to 70°N). In the early successional stage, during the first years after the drainage, the seasonally thawed layer has maximal thickness. These wet mesotrophic ecotopes are rich in nutrients. The plant communities are represented by a dense herb layer of a hydrophilic species of sedges, grasses, and cotton grasses, covering 60–70% of the area, whereas mosses cover < 1%. In the mid successional stage, from 50 years after drainage, as plant litter is accumulated, and the nutrients are leached from the soil, the abundance of herbs decreases to 25–40%, the abundance of mosses increases to 40–60%, and the overall productivity of the plant communities decreases. The late stage of the succession khasyreys lasts several hundred years. The ecotopes are characterized by an accumulation of peat, which reaches a thickness of up to 40 cm on the soil surface. Among the vascular plants, which cover between 10% and 60% of the area, the abundance of herbaceous species is minimal, and dwarf shrubs prevail. The moss and lichen have continuous coverage. At this stage, the plant communities consist of mesotrophs and mesooligotrophs of a very low productivity, and the phytocoenoses are similar to the surrounding polygonal bogs. Overall, the main driving factor of the vegetation succession in the khasyreys is the accumulation of peat on the soil surface and microtopography of the lake bottom. The soil nutrient depletion occurs simultaneously with a decrease in the thickness of the active layer and an increase in the thickness of peat. The succession rate in different parts of the lake bottom varies, depending on the nutrient reserves in the initial sediment, the microlandscape, permafrost aggradation, and the content of redeposited peat.

This research was funded by the Russian Science Foundation (RSF) (project № 18-77-10045).
Advancing the Geosciences through Open Standards
Authors: Khalsa Siri Jodha
Published: March 2021

Data is the lifeblood of the geosciences. Furthermore, the acquisition, processing and interpretation of data all depend on established specifications describing the systems and procedures that were used in producing, describing and distributing that data. It can be said that technical standards underpin the entire scientific endeavour. This is becoming ever truer in the era of Big Data and Open, Transdisciplinary Science. It takes the dedicated efforts of many individuals to create a viable standard. This presentation will describe the experiences and status of standards development activities related to geoscience remote sensing technologies which are being carried out under the auspices of the IEEE Geoscience and Remote Sensing Society (GRSS).

A Standards Development Organization (SDO) exists to provide the environment, rules and governance necessary to facilitate the fair and equitable development of standards, and to assist in the distribution and maintenance of the resulting standards. The GRSS sponsors projects with the IEEE Standards Association (IEEE-SA), which, like other SDOs such as ISO and OGC, has well-defined policies and procedures that help ensure the openness and integrity of the standards development process. Each participant in a standards working group typically brings specific interests as a producer, consumer or regulator of a product, process or service. Creating an environment that makes it possible to find consensus among competing interests is a primary role of an SDO. I will share some of the insights gained from the six standards projects that the GRSS has initiated which involve hyperspectral imagers, the spectroscopy of soils, synthetic aperture radar, microwave radiometers, GNSS reflectometry, and radio frequency interference in protected geoscience bands.
Evaluation of shortwave radiation fluxes in the multi-layer SPARTACUS-Urban scheme using DART
Authors: Stretton Megan , Morrison William , Hogan Robin , Grimmond Sue
Published: March 2021

The heterogenous structure of cities impacts radiative exchanges (e.g. albedo and heat storage). Numerical weather prediction (NWP) models often characterise the urban structure with an infinite street canyon – but this does not capture the three-dimensional urban form. SPARTACUS-Urban (SU) - a fast, multi-layer radiative transfer model designed for NWP - is evaluated using the explicit Discrete Anisotropic Radiative Transfer (DART) model for shortwave fluxes across several model domains – from a regular array of cubes to real cities .

SU agrees with DART (errors < 5.5% for all variables) when the SU assumptions of building distribution are fulfilled (e.g. randomly distribution). For real-world areas with pitched roofs, SU underestimates the albedo (< 10%) and shortwave transmission to the surface (< 15%), and overestimates wall-plus-roof absorption (9-27%), with errors increasing with solar zenith angle. SU should be beneficial to weather and climate models, as it allows more realistic urban form (cf. most schemes) without large increases in computational cost.
Viability study of ice nucleating active bacteria (Pseudomonas Syringae) in freezing cloud droplets
Authors: Kiselev Alexei , Wieber Corina , Zoheir Amer Ahmed Eid , Rabe Kersten
Published: March 2021

The plant pathogenic bacteria Pseudomonas syringae are capable of inducing ice nucleation at low supercooling due to the presence of INA proteins on the outer cell membrane. Moreover, P. Syringae was shown to survive long-range transport in cold airmasses and redeposition to the earth’s surface with rain and snow. Thus, the life cycle of P. syringae is tightly coupled to the water cycle in the Earth's ecosystem. Understanding the survival mechanism of P. Syringae exposed to atmospheric cloud conditions is a prerequisite for characterization of bacteria as atmospheric ice nucleating particles, describing its dissemination paths and potential role in the spread of plant-pathogenic disease.

In this contribution we report on the viability study of ice nucleating active bacteria in freezing cloud droplets. To investigate the bacterial viability, water droplets containing several bacterial cells with low and high concentration of INA proteins are levitated in an electrodynamic balance (EDB) and cooled down to a temperature of -25°C. After freezing, the droplets are extracted from the EDB and the survival probability of the bacteria is determined by colony counting. A fluorescence stain and a high-speed video camera were used to visualize individual bacteria in the levitated droplets and to study their behavior during freezing.

The results have shown that the survival of bacteria depends on the freezing dynamics of bacteria-containing droplets (growth rate of ice in supercooled water). The P. syringae bacteria with high concentration of INA proteins are capable of inducing freezing at low supercooling and thus inhibit the growth rate of ice crystals, resulting in higher chance to survive the freezing. If high supercooling is achieved, the ice growth rate immediately after nucleation is very high and the survival probability is dramatically reduced.
The diurnal cycle can trigger convective self-aggregation 
Authors: Jensen Gorm Gruner , Fiévet Romain , Haerter Jan O.
Published: March 2021

Convective self-aggregation (CSA) is an established modelling paradigm for large-scale thunderstorm clusters, as they form in mesoscale convective systems, the Madden-JulianOscillation or tropical cyclo-genesis [1]. The onset of CSA is characterized by the spontaneous formation of persistently dry patches with suppressed deep convective rainfall. Recently another type of spatio-temporal pattern formation was observed in simulations where the diurnal cycle was mimicked by a sinusoidally varying surface temperature [2]. This diurnal aggregation (DA) is characterized by clusters of intense rain that correlate negatively from one day to the next. 

Here we demonstrate that the diurnal cycle can also act as a trigger of persistently dry patches resembling the early stages of CSA. When the surface temperature is held constant, CSA has been shown to occur within simulations of coarse horizontal model resolution, but not when the resolution was increased [3]. We show that, when a temporally periodic surface temperature forcing is imposed, persistently convection free patches occur even faster when the spatial resolution is increased. The failure to achieve CSA at high horizontal resolution has so far been attributed to the more pronounced cold pool effects at such resolution. In our simulations these cold pools in fact play a key role in promoting CSA. Our results have implications for the origin of persistent convective organization over continents and the sea — and point a path towards achieving such clustering under realistic conditions.

[1]  Christopher S Bretherton, Peter N Blossey, and Marat Khairoutdinov.  An energy-balance analysisof deep convective self-aggregation above uniform SST.Journal of the Atmospheric Sciences, 62(12):4273–4292, 2005.
[2]  J. O. Haerter, B. Meyer, and S. B. Nissen.  Diurnal self-aggregation.npj Climate and AtmosphericScience, 3:30, 2020.
[3]  Caroline  Muller  and  Sandrine  Bony.   What  favors  convective  aggregation  and  why?GeophysicalResearch Letters, 42(13):5626–5634, 2015.  doi:  https://doi.org/10.1002/2015GL064260.
Sensitivity of segmentation of GNSS IWV time series and trend estimates to data properties
Authors: Nguyen Khanh Ninh , Quarello Annarosa , Bock Olivier , Lebarbier Emilie
Published: March 2021

Homogenization is an important step to improve the quality of long-term observational data sets and estimate climatic trends. In this work, we use the GNSSseg/GNSSfast segmentation packages that were developed by Quarello et al., 2020, for the detection of abrupt changes in the mean of Integrated Water Vapour (IWV) data derived from GNSS measurements. The method works on the difference of the IWV time series (GNSS – reference) in order to cancel out the common climatic variations and enhance the discontinuities due to the inhomogeneities in the GNSS series. This segmentation method accounts for changes in the variance on fixed intervals (monthly) and a periodic bias (annual) due to representativeness differences between GNSS and the reference (in our case, a global atmospheric reanalysis). 
The goal of this study is to analyze the sensitivity of the segmentation method to the data properties, particularly the GNSS data processing method. Two reprocessed GNSS solutions are considered: IGS repro1, covering the period 1995-2010, and CODE REPRO2015 + OPER, covering the period 1994-2018. Next, the impact of the length of time series and missing data are investigated. Finally, the use of two different reference series is considered (ERA-Interim and ERA5 reanalyses).
The segmentation results are screened for outliers (multiple detections occurring within a distance of 80 days) and validated with respect to known equipment changes (from GNSS metadata). The impact of the data properties is analyzed by comparing the number and position of detected change-points and the fraction of validated change-points. The influence of the variance of the IWV difference series and the magnitude of the periodic bias is examined. Finally, the results are compared in terms of estimated linear trends taking the detected change-points into account.
From the multiple comparisons, we found that about 30 % of change points are similar when the GNSS processing method changed, while 60 % are similar when the CODE series is shortened to match the length of the repro1 series. These tests highlight that the segmentation results are processing-dependent and are affected by the length of the series. The impact of the data properties on the IWV trends and associated uncertainties are also quantified. Besides, it is important to note that the best segmentation result is found when the ERA5 reanalysis is used as a reference.
The comparative analysis of the Hungarian and European methodology of discharge measurement
Authors: Keve Gábor , Sziebert János , Koch Dániel , Tamás Enikő Anna , Varga György , Majer Fruzsina , Krikovszky Sándor , Ficsor Johanna , Fekete Árpád
Published: March 2021

According to the climate change and Water Framework Directive 2000/60/EC (WFD) the analysis od the status of waterbodies and their continuous monitoring has to be carried out based on unified methodologies and standards. Individual prescriptions have to be in harmony with national and international standards, in order to ensure equal scientific value and comparability of the data. The international standard EN ISO 748 entitled „Hydrometry - Measurement of liquid flow in open channels using current-meters or floats” was issued in 2008. This standard is based on the discharge measurement methods in the European Union (EU) and it differs in some aspects from the Hungarian standard (ME-10-231-16:2009). The goal of our study was to identify and answer the questions related to the introduction of this standard into Hungarian practice. The issue is crucial for the hydrometry units of Hungarian Water Directorates, as if the introduction of a new standard is not correctly substantiated the consequences can include avoidable economical burdens and/or changes in the quality of data. The research was initiated and financed by the Hungarian General Directorate of Water management and targeted at the comparative analysis of the measurement and calculation methodologies of the two standards, carried out on watercourses in Hungary. Thus we have executed a series of measurements in 31 cross-sections on 18 different watercourses in Hungary. Based on our results we can state that the difference between the results of the different methodologies generally does not exceed the uncertainties originating from the measurements themselves. Under specific circumstances (e.g. very low flow velocities) the effect of the chosen methodology can be significant.
Detection and quantification method intercomparison of methane emission from natural gas distribution network leaks in Hamburg, Germany
Authors: Maazallahi Hossein , Delre Antonio , Buth Lena , Fredenslund Anders Michael , Nagler Ina , Scheutz Charlotte , Schwietzke Stefan , Denier van der Gon Hugo , Röckmann Thomas
Published: March 2021

On October 14, 2020 the European Commission adopted the EU methane strategy[1]. Measurement-based reporting of methane emissions will be crucial and may become legally binding. A variety of different methods are in use to quantify methane emissions from natural gas distribution networks, some attempting to quantify the pipeline leak under the ground, others attempting to quantify the emissions to the atmosphere. Comparisons between these methods are essential, as each method has its own advantages and limitations. In August and September 2020, we conducted an extensive campaign to compare three different methods, the mobile survey method, the tracer release method, and the suction techniques, to quantify emission rates of leaks from the natural gas distribution network in Hamburg, Germany. The mobile measurement technique employed two different cavity ringdown analyzers to identify and quantify methane, ethane and carbon dioxide using a moving vehicle. The tracer release technique measured methane and the tracer gas acetylene also with fast laser methods during driving or stationary deployment in a vehicle at an identified leak location. The suction method deployed soil sondes around an identified leak and measured methane in a stream of air pumped out of the soil until an equilibrium was reached.  In total, we targeted 20 locations that had been identified by mobile measurements or by the routine leak detection of the local gas utility, GasNetz Hamburg. For numerous locations we detected several emission outlets from e.g., cavities, cracks or drains and we used measurements of the ethane to methane ratio to identify possible mixture of fossil and microbial sources. We will compare the different quantification methods, including their suitability for routine application and precision and accuracy in emission quantification.

[1] https://ec.europa.eu/energy/sites/ener/files/eu_methane_strategy.pdf
Seasonal to sub-seasonal hydrological forecast in Central Asia to improve water management and mitigate hydrometeorological risks
Authors: Gafurov Abror , Kalashnikova Olga , Adkhamov Uktam , Gafurov Akmal , Mamaraimov Adkham , Niyazov Djafar
Published: March 2021

Central Asia is facing a water shortage due to the negative impacts of climate change and demographic development. Water resources in this region originate mainly in the mountains of Pamir and Tian-Shan due to snow-and glacier melt. However, a limited observation network is available in these mountain systems and many are malfunctioning. Thus, the region needs new innovative methods to forecast seasonal and sub-seasonal water availability to ensure better water resources management and mitigate hydro-meteorological risks.

In this study, we present the results of our efforts for many years to develop a forecasting tool and implementation in the region. Since the region has limited observed meteorological data, we use primarily remote sensing data on snow cover for this purpose. We apply the MODIS snow cover data that is processed, including cloud removal, using the MODSNOW-Tool. We have applied this tool, which can be used to monitor snow cover in an operational mode and forecast water availability for the vegetation period but also for the monthly scale using the multiple linear regression method.

Our results show that snow is important in most of the river basins and can also be used as a single predictor to forecast seasonal water availability. Especially, in remote areas with limited observations, this approach gives a possibility of forecasting water availability for different time period. Besides seasonal hydrological forecast, the MODSNOW-Tool was also used to forecast water availability for upcoming months. The validity of forecasts were tested against observed discharge for the last 20 years and mostly above 70 % verification was achieved. Additionally to remote sensing based snow cover data, observed meteorological information was also used as predictors and improved the validity of forecast models in some river basins.

The implementation of the MODSNOW-Tool to improve the hydrological forecast was done for 28 river basins in Central Asia that are located in the territories of five post-Soviet countries Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan.  The MODSNOW-Tool was also implemented at the National Hydrometeorological Services (NHMS) of each post-Soviet country.
Climate contributions to Arctic coastal sea level change
Authors: Ludwigsen Carsten Ankjær , Rose Stine Kildegaard , Andersen Ole Baltazar
Published: March 2021

The Arctic Ocean is at the frontier of the fast changing climate in the northern latitudes. As the first study, we assessthe different mass and steric components of the observed sea level trend from both absolute sea level (ASL) from altimetryand tide gauges, without using gravimetric observations from GRACE. This approach permits a longer time series and avoidsproblems with errors from leakage effects in GRACE-products. ASL is equal to mass-driven sea level added with steric sealevel, while tide gauge based sea level are also corrected with novel estimates of vertical land movement. Calculations of the5mass component from present-day deglaciation, shows that deglaciation rises Arctic sea level with more than 1 mm y−1, whilethe steric contribution is between -5 and 15 mm y−1 with large spatial variability, with the halosteric signal dominating thepattern. A dynamic mass contribution is derived from the Estimating Circulation and Climate of the Oceans (ECCO)-model(version 4 release 4), which varies between -1 and 2 mm y−1. The combined mass and steric product agrees (within uncertainty)with ASL-trends observed from altimetry in 99% of the Arctic, although large uncertainties originate from poor data coverage in the steric data and large variability in the dynamic product. A comparison with ASL trends observed at tide gauges agreeswith mass+steric at 11 of 12 tide gauge sites.
High resolution mapping of the Arctic Ocean deepest area: Molloy Hole
Authors: Ivaldi Roberta , Demarte Maurizio , Nannini Massimiliano , Aquino Giuseppe , Brancati Cosimo , Ercolani Massimo , Fares Agnese , Guideri Matteo , Labella Luca , Marro Mauro , Maurantonio Federica , Nardini Roberto , Niccolini Alberto
Published: March 2021

New hydro-oceanographic data were collected in the Arctic Ocean during HIGN NORTH20 marine geophysical campaign performed in July 2020, in a COVID-19 pandemic period. HIGH NORTH20 was developed as part of the IT-Navy HIGH NORTH program, a Pluriannual Joint Research Program in the Arctic devoted to contribute to oceans knowledge in order to ensure ocean science improving conditions for sustainable development of the Ocean in the aim of United Nations Decade of Ocean Science for Sustainable development and the GEBCO - SEABED 2030 project. In order to contribute in exploration and high-resolution seabed mapping new data was collected using a multibeam echosounder (EM 302 - 30 kHz). The particular sea ice environmental condition with open-sea allowed to survey and mapping the Molloy Hole, the deepest sector of the Arctic Ocean, a key area in the global geodynamics and oceanographic context. A 3D model of the Molloy Hole (804 km2) and the detection of the deepest seafloor (5567m - 79° 08.9’ N 002° 47.0’ E) was obtained with a 10x10m grid in compliance to the IHO standards.
A Three-Dimensional Version of the Free Surface Capturing Discretization for Staggered Grid Finite Difference Schemes: Implementation into StagYY
Authors: Tackley Paul
Published: March 2021

In order to treat a free surface in models of lithosphere and mantle dynamics that use a fixed Eulerian grid it is typical to use "sticky air", a layer of low-viscosity, low-density material above the solid surface (e.g. Crameri et al., 2012). This can, however, cause numerical problems, including poor solver convergence due to the huge viscosity jump and small time-steps due to high velocities in the air. Additionally, it is not completely realistic because the assumed viscosity of the air layer is typically similar to that of rock in the asthenosphere so the surface is not stress free.  

In order to overcome these problems, Duretz et al. (2016) introduced and tested a method for treating the free surface that instead detects and applies special conditions at the free surface. This avoids the huge viscosity jump and having to solve for velocities in the air. They applied it to a two-dimensional staggered grid finite difference / finite volume scheme, a discretization that is in common use for modelling mantle and lithosphere dynamics. Here I document the application of this approach to a three-dimensional spherical staggered grid solver in the mantle simulation code StagYY. Some adjustments had to be made to the two-dimensional scheme documented in Duretz et al. (2016) in order to avoid problems due to undefined velocities for certain boundary topographies. The approach was applied not only to the Stokes solver but also to the temperature solver, including the implementation of a mixed radiative/conductive boundary condition applicable to surface magma oceans/lakes.

References

Crameri, F., H. Schmeling, G. J. Golabek, T. Duretz, R. Orendt, S. J. H. Buiter, D. A. May, B. J. P. Kaus, T. V. Gerya, and P. J. Tackley (2012), A comparison of numerical surface topography calculations in geodynamic modelling: an evaluation of the ‘sticky air’ method, Geophysical Journal International,189(1), 38-54, doi:10.1111/j.1365-246X.2012.05388.x.

Duretz, T., D. A. May, and P. Yamato (2016), A free surface capturing discretization for the staggered grid finite difference scheme, Geophysical Journal International, 204(3), 1518-1530, doi:10.1093/gji/ggv526.
New Analog Experiment for Convergent Regime an example of planet Mercury
Authors: Özeren Sinan , Şengör A. M. Celal , Acar Dursun , Postacıoğlu M. Nazmi , Klimczak Christian , Byrne Paul K. , Öner Tayfun
Published: March 2021

We conduct a series of experiments to understand the nature of thrust faulting as a result of global thermal contraction in planetary bodies such as Mercury. The spatial scales and patterns of faulting due to contraction are still not very well understood. However, the problem is complicated even for the homogeneous case where the crustal thickness and material properties do not vary spatially. Previous research showed that the thrust faulting patterns are non-random and are arranged in long systems. This is probably due to the regional-scale stress patterns interacting with each other, leading to the creation of coherent structures. We first conduct 1-Axis experiments where we simulate the contraction of the substratum using an elastic ribbon. On top of this we place the material for which the friction, cohesion and thickness can be controlled for each experiment. The shared interface between the frictional-cohesive material and the shortening elastic substratum dictates undulations and finally the generation of slip planes in the upper layer. We discuss the spatial distribution of these patterns spatially. We then speculate the interaction of such patterns on a 2D plane.

 

 
Investigating the seismic imaging of faults using PS data from the Snøhvit field, Barents Sea, and forward seismic modelling 
Authors: Cunningham Jennifer , Weibull Wiktor , Cardozo Nestor , Iacopini David
Published: March 2021

PS seismic data from the Snøhvit field are compared with forward seismic modelling to understand the effect of azimuthal separation and incidence angle on the imaging of faults. Two faults, one oriented oblique to the survey and one approximately parallel to the survey were chosen. Azimuthally separated W (source is W relative to receivers) and E (source E relative to receivers) data demonstrate that fault imaging is more affected by azimuth when the faults are oblique to the survey orientation, and W data image the faults better. Partial stack data show that with increasing incidence angle there is a systematic improvement in the quality of fault imaging in both the E and W data. In addition, the frequency content of seismic waves back-scattered from within and around fault zones is analysed in the Snøhvit data. Low-medium frequencies are dominant within fault zones, compared with higher frequencies in adjacent areas and haloes of medium frequencies surrounding the faults. Two synthetic experiments support the azimuth, incidence angle and frequency observations. In the first experiment, the fault is modelled as a planar discontinuity and the data were processed in the same way as the Snøhvit data (into separate azimuths and incidence angle stacks). The first experiment confirms a strengthening in the seismic signal from faults in the W data. This is due to the interaction of specular waves and diffractions which are more abundant in the W data. The second experiment had three parts modelling the fault zone with different layering complexity. It proved that frequencies in the fault and adjacent areas increase with fault zone complexity, and that the internal architecture of faults can impact the frequencies in the data adjacent to faults. 
Characterizing ground water salinity in Coastal Bangladesh by using observations and perception-based information
Authors: Rahman Mohammed Mofizur , Nauditt Alexandra
Published: March 2021

Salinity intrusion has become a serious threat to coastal areas worldwide, with severe effects on human health, agricultural production and ecosystem services. Coastal populations of Bangladesh, as with many other countries, are living with and experiencing rising salinity in drinking water on a daily basis. Water quality management requires reliable data based on continuous monitoring of freshwater at any abstraction source. However, such monitoring is costly and unavailable in most of the coastal areas of Bangladesh. Several perception studies based on semi-structured interviews have shown a strong potential to support environmental monitoring but inadequate for decision-making. Therefore, we attempted to capture state of water salinity through people’s experiences lenses, self-reported perception, and measured salinity. The overall objective of this study is therefore to evaluate if the perception of coastal inhabitants in Bangladesh adequately describes salinity loads in drinking water in space and time. In this paper, we are going to describe spatial and temporal variation of drinking water salinity in a coastal delta of Bangladesh. In addition, to present the analysis of self-reported perception on salinity in drinking water in compassion to measured actual salinity of tube-well water. Our initial analysis shows that there is a large spatial variation of salinity in drinking water but no seasonal variation. In addition to that, we found that salinity loads are differing with tube-well depths. The majority of the interviewed people were able to report salinity in drinking water when it was also measured, although with some mismatch between measured and perceived salinity. This might influenced by taste adaptation to salt and other socio-cultural factors.

The results suggest that our interdisciplinary approach is useful to explore the state of drinking water salinity in coastal areas, water consumption practices of the coastal community and we concluded that regular water quality monitoring along with people´s perception studies could better support the decision-making related to coastal water management.
Controls on the space-time variability of raindrop size distributions
Authors: Uijlenhoet Remko
Published: March 2021

It has been stated that "the study of drop-size distributions, with its roots in both land-surface processes [e.g. interception, erosion, infiltration and surface runoff] and atmospheric remote sensing [e.g. radar meteorology], provides an important element to an integrated program of hydrometeorological research" (Smith, 1993). Although raindrop size distributions have been studied from a scientific perspective since the early 20th century, it was not until the mid-1990s that researchers realized that all parameterizations for the drop size distribution published until then could be summarized in the form of a scaling law, which provided "a general phenomenological formulation for drop size distribution" (Sempere Torres et al., 1994). The main implication of the proposed expression is that the integral rainfall variables (such as rain rate and radar reflectivity) are related by power laws, in agreement with experimental evidence. The proposed formulation naturally leads to a general methodology for scaling all raindrop size data in a unique plot, which yields more robust fits of the drop size distribution. Here, we provide a statistical interpretation of the law’s scaling exponents in terms of different modes of control on the space-time variability of drop size distributions, namely size-control vs. number-control, inspired by the work of Smith and De Veaux (1994). Also, an attempt will be made toward interpreting the values of the scaling exponents and the shape of the scaled drop size distribution in terms of the underlying (micro)physical processes.

REFERENCES

Smith, J. A., 1993: Precipitation. In Maidment, D. R., editor, Handbook of Hydrology, pages 3.1–3.47. McGraw-Hill, New York.

Sempere Torres, D., J.M. Porrà, and J.-D. Creutin, 1994: A general formulation for raindrop size distribution. J. Appl. Meteor., 33, 1494–1502.

Smith, J.A. and R.D. De Veaux, 1994: A stochastic model relating rainfall intensity to raindrop processes. Water Resour. Res., 30, 651–664.
Seasonal flow variations of Ross Ice Shelf (Antarctica): from observations to modeling
Authors: Mosbeux Cyrille , Padman Laurence , Klein Emilie , Bromirski Peter , Springer Scott , Fricker Helen A
Published: March 2021

Ice mass loss from both Antarctic Ice Sheet is increasing, accelerating its contribution to global sea level rise. Interactions between the ice shelves (the floating portions of the ice sheet) and the ocean are key processes in this mass loss. The large Ross Ice Shelf is presently stable but buttresses grounded ice equivalent to about 12 m of global sea level, and geological evidence points to large and sometimes rapid past changes. Recent ocean modeling and observations show that seasonal inflows of warmed upper-ocean water under a thin-ice corridor from Ross Island to Minna Bluff and at the ice front can produce locally high melt rates each summer, suggesting that future increases in summer upper-ocean ocean warming north of the ice front could accelerate ice-shelf flow speeds and mass loss. Recent GPS observations of Ross Ice Shelf velocity have shown seasonal flow variations of several meters per year over a large part of the ice shelf, accelerating in summer and decelerating in winter. A similar seasonal variability has been observed over the floating extension of Byrd glacier (one of the major tributary glaciers of Ross Ice Shelf) by processing Antarctic image pairs in the ITS_LIVE dataset. However, ice-sheet simulations driven by realistic annual cycles of basal melt rates near the ice front produce much smaller seasonal variations than observed, suggesting that other processes could be at play. Here, we investigate a new potential mechanism for a seasonal signal in ice flow: variations of sea surface height (SSH) driven by seasonal changes in thermodynamic and atmospheric forcing of ocean state under the ice shelf. Model annual cycle of SSH under Ross Ice Shelf has an amplitude of up to ~20 cm, with substantial spatial variability. These variations of sea level, similarly to tidal signal but with a longer period, can lead to changes in driving stress over the ice shelf as well as a migration of the grounding line due to hydrostatic adjustment and visco-elastic bending of the ice shelf in the grounding zone. By simulating these SSH variations in an ice-sheet model, we more accurately reproduce the variations observed at GPS stations on Ross Ice Shelf.
Infra-AUV project: Metrology for low-frequency sound and vibration
Authors: Ceranna Lars , Bruns Thomas , Koch Christian , Rodrigues Dominique , Robinson Stephen , Winther Jacob Holm , Larsonnier Franck , Barham Richard
Published: March 2021

Infra-AUV is a new EU project that will establish primary measurements standards for low frequency phenomena across the fields of airborne and underwater acoustics and vibration (seismology). Combining expertise from the national measurement institutes and geophysical monitoring station operators, it will develop both high-precision laboratory-based methods of calibration and methods suitable for field use. Infra-AUV will also address requirements for reference sensors that link laboratory calibration capabilities to field requirements for measurement traceability.

To establish standards in the three technical areas, a variety of calibration principles will be employed, including extension of existing techniques such as reciprocity and optical interferometry, and development of new methods. There will also be an investigation of the potential for in-situ calibration methods, including use of both artificially generated and naturally occurring stimuli such as microseisms and microbaroms. The influence of calibration uncertainties on the determination of the measurands required by the monitoring networks will also be studied.

The project was strongly motivated by the CTBTO strategy to drive new metrology capability to underpin IMS data. The intention is to maintain interaction with stakeholders, not only in connection with the IMS, but with the broad range of users of low frequency acoustic and vibration data. 
Exploring causes of hydrological alterations and the relative contributions of climate change and human activities in the Isser catchment, Algeria
Authors: Kadir Mokrane , Vanclooster Marnik
Published: March 2021

The water resources of Mediterranean countries are strongly affected by climate change and anthropogenic activities, which exert considerable pressure on the overall water security.  Understanding the relative contributions of each of the possible causal factors to the hydrological alteration is pivotal to design sustainable water resources management strategies. In this study, the hydrological alteration of the Isser catchment in Algeria is assessed and explained in terms of possible explanatory factors. A long term hydro-meteorological dataset was reconstructed and the nonparametric Mann-Kendall test was used to detect the alteration of streamflow and the possible causal factors. To identify the role of causal factors in the hydrologic alterations, two techniques were used.  First, Convergent Cross Mapping (CCM), which is an advanced data-based nonlinear time-series analysis tool, was used to identify causality in time-series. Second, a Fuzzy Analytical Hierarchical Process (FAHP) expert-based model was applied to assess the possible underlying causes for hydrologic alterations and to quantify the potential influences of human activities and climate change. The results of the trend analysis show a significant downward trend for streamflow (pvalue< 0.05) for the period 1971-2010. The CCM method shows that the streamflow alteration is unidirectionally caused by changes in precipitation, temperature, irrigation, evapotranspiration, and NDVI patterns and that there is little feedback from streamflow alteration to these causing factors.  The FAHP suggests that climate change is dominating the decreasing trend in streamflow, being responsible for 60 % of the alterations as compared to 40 % of the alterations caused by changes in the land use patterns and intensive water extraction.
Long-term Surface Temperature (LoST) Database as a Complement for Transient and Control Preindustrial Simulations
Authors: Cuesta-Valero Francisco José , García-García Almudena , Beltrami Hugo , Zorita Eduardo , Jaume Santero Fernando
Published: March 2021

Estimates of climate sensitivity from Atmosphere-Ocean Coupled General Circulation Model (GCM) simulations present a large spread despite the continued improvements in climate modeling since the 1970s. This variability is partially caused by the dependence of several long-term feedback mechanisms on the reference climate state. However, it is difficult to provide a reference to assess the climatology of preindustrial control simulations as there are no long-term preindustrial observations.
In the ground, recent changes in ground surface temperature are observed at shallow depths as perturbations to the quasi-steady state geothermal regime. However, if undisturbed by recent surface temperature changes, the deep ground temperatures vary linearly as a function of depth, and the extrapolation of this linear behavior to the surface can be interpreted as the past long-term surface temperature climatology.

We assemble a new gridded database of past long-term ground surface temperatures (LoST database) obtained from 514 borehole temperature profiles measured across North America, and we explore its use as a potential reference for the evaluation of GCM preindustrial control simulations and past millennium simulations. All temperature profiles are truncated at 300 m depth, allowing to estimate the ground surface climatology for the period 1300-1700 of the common era. We compare the LoST database with observations from the CRU database, as well as with five past millennium simulations and five preindustrial control simulations from the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3) and the fifth phase of the Coupled Model Intercomparison Project (CMIP5) archives. Our results suggest that LoST temperatures could be employed as a reference to narrow down the spread of surface temperature climatologies on GCM preindustrial control and past millennium simulations.
GERI – The emerging Global Ecosystem Research Infrastructure
Authors: Bäck Jaana , Kutsch Werner , Mirtl Michael
Published: March 2021

Ecosystem Research Infrastructures around the world have been designed, constructed, and are now operational as a distributed effort. The common goal is to address research questions that require long-term ecosystem observations and other service components at national to continental scales, which cannot be tackled in the framework of single and time limited projects.  By design, these Research Infrastructures capture data and provide a wider range of services including access to data and well instrumented research sites. The coevolution of supporting infrastructures and ecological sciences has developed into new science disciplines such as macrosystems ecology, whereby large-scale and multi-decadal-scale ecological processes are being explored. 

Governments, decision-makers, researchers and the public have all recognized that the global economy, quality of life, and the environment are intrinsically intertwined and that ecosystem services ultimately depend on resilient ecological processes. These have been altered and threatened by various components of Global Change, e.g. land degradation, global warming and species loss. These threats are the unintended result of increasing anthropogenic activities and have the potential to change the fundamental trajectory of mankind.  This creates a unique challenge never before faced by society or science—how best to provide a sustainable economic future while understanding and globally managing a changing environment and human health upon which it relies.

The increasing number of Research Infrastructures around the globe now provides a unique and historical opportunity to respond to this challenge. Six major ecosystem Research Infrastructures (SAEON/South Africa, TERN/Australia, CERN/China, NEON/USA, ICOS/Europe, eLTER/Europe) have started federating to tackle the programmatic work needed for concerted operation and the provisioning of interoperable data and services. This Global Ecosystem Research Infrastructure (GERI) will be presented with a focus on the involved programmatic challenges and the GERI science rationale.
Towards SI-traceable Isotope Ratios of Greenhouse Gases
Authors: Flierl Lukas , Nwaboh Javis , Rienitz Olaf , Werhahn Olav , Ebert Volker
Published: March 2021

The emission of greenhouse gases and the resulting global warming is one of the most important and challenging issues of the 21st century. Carbon dioxide is one of the major contributors to the greenhouse eﬀect and its atmospheric abundance has growing constantly since the beginning of the industrialization. The isotope ratios n(13C)/n(12C) and n(18O)/n(16O) are important tools for studying the impact of anthropogenic CO2. Usually, isotopic compositions of CO2 are reported as δ-values, that express isotope ratios relative to an artifact based on a fossil calcite called VPDB. This relative VPDB scale was necessary, since absolute and SI-traceable isotope ratios of CO2 are currently not available, neither by isotope ratio mass spectrometry (IRMS) nor by optical isotope ratio spectroscopy (OIRS). In this study we present a potential way of deriving absolute carbon and oxygen isotope ratios of carbon dioxide via IRMS based on the gravimetric mixture approach. Besides practical improvements like an air buoyancy correction scheme for masses of gases, we show first results applying our method which demonstrate its feasibility, limitations, and achievable uncertainties. Also, we show the mathematics behind our approach and discuss further improvements and applications. Furthermore, we show how these absolute ratios can be used in field applications by OIRS methods including a new approach on OIRS uncertainty assessments according to the GUM. For this contribution we report on our recent results within in the European metrology research projects SIRS (16ENV06). and STELLAR (19ENV05).
Numerical simulation of kinetic interface sensitive tracers in two-phase flow in porous media applied in two-dimensional experimental setups
Authors: Abdullah Hiwa , Gao Huhao , Sauter Martin , Tatomir Alexandru
Published: March 2021

The newly developed kinetic interface sensitive (KIS) tracers have been the focus of research in the past decade, as a new method to determine the mobile interfacial area between immiscible fluids in porous media. An accurate and reliable interfacial area determination is crucial to several industrial applications and the geoscientific research.

In this work we investigate the relationship between the concentration breakthrough curves of the KIS tracer, consequently the specific interfacial area and the evolution of the mobile non-wetting-phase front.

Up to now, such laboratory experiments have been conducted only in columns, quasi-one-dimensional systems. In this study we consider two-dimensional domains filled with porous material where immiscible displacement of water by oil takes place. The presence of heterogenous inclusions leads to perturbations in the fluid interface and causes fingers. By means of numerical modelling we investigate these effects and the results will help as a basis in the design of a new two-dimensional flume setup.

An analysis is performed for different viscosity ratios, capillary numbers corresponding to different capillary pressure-saturation relationships, injection rates and geometrical heterogeneity. We found that the presence of higher or lower permeability inclusions have a significant but clearly distinct impact on the destruction and/or production of the fluid-fluid interfacial area. Lower permeability inclusions increase the overall area of the front, compared to a decrease in the overall area for higher permeability inclusions. By increasing the interfacial area an increase of the reactive tracer concentration is observed. The mobile interfacial area is evaluated at the front of the saturation profile by using a cut-off value from the saturation profile, and then the area of the mobile concentration of the reactive tracer is calculated.