bluuebunny/crossref_metadata_2025 huggingface dataset:
Calibration of a superconducting gravimeter with an absolute atom gravimeter
Authors: Merlet Sébastien , Gillot Pierre , Cheng Bing , Karcher Romain , Imanaliev Almazbek , Timmen Ludger , Pereira Dos Santos Franck
Published: March 2021

Atom gravimeters based on atom interferometry offer new measurement capabilities, by combining high sensitivities and accuracies at the best level of a few tens of nm.s−2 with the possibility to perform continuous measurements. Being absolute meters, their scale factor is accurately determined and do not need calibration. Because of their high sensitivity and low drift, superconducting gravimeters are the key instruments for the continuous monitoring of gravity variations. Nevertheless, being relative meters, they need to be calibrated.

We revisit a 2015 one month long common view measurement of an absolute cold atom gravimeter (CAG) and a relative iGrav superconducting gravimeter, which we use to investigate the CAG long term stability and calibrate the iGrav scale factor. The initial measurement has already been presented at EGU 2016. Here finalized, we present how it allowed us to push the CAG long-term stability down to the level of 0.5 nm.s−2. We investigate the impact of the duration of the measurement on the uncertainty in the determination of the correlation factor and show that it is limited to about 3‰ by the coloured noise of our cold atom gravimeter. A 3-days long measurement session with an additional FG5X absolute gravimeter allows us to directly compare the calibration results obtained with two different absolute meters. Based on our analysis, we expect that with an improvement of its long term stability, the CAG will allow to calibrate the iGrav scale factor to better than the per mille level (1σ level of confidence) after only one-day of concurrent measurements during maximum tidal amplitudes.
Multiphase inversion in the Baltic sector of the North German Basin: Influence of Africa-Iberia-Europe convergence during the Late Cretaceous and Cenozoic
Authors: Ahlrichs Niklas , Noack Vera , Hübscher Christian , Seidel Elisabeth
Published: March 2021

Within the DFG project StrucFlow, we investigate the multiphase character of Late Cretaceous to Cenozoic inversion in the Baltic sector of the North German Basin based on seismic interpretation. Our analysis rests upon modern high-resolution seismic profiles in combination with data from older seismic surveys and borehole information. The resulting seismic database consists of a dense profile network with a total length of some 10.000 km. This unprecedented seismic grid allows for a detailed tectono-stratigraphic interpretation of Cretaceous and Paleogene deposits in the Baltic sector of the North German Basin. Here, basin inversion began in the Coniacian and Santonian with uplift of the Grimmen High and minor reactivation of Zechstein salt structures. Crestal faults were formed or reactivated above salt pillows in the Bays of Mecklenburg and Kiel. The onset of inversion was contemporaneous with other adjacent basins and is likewise associated with building up intraplate stress within the European foreland related to the beginning Africa-Iberia-Europe convergence. Time-isopach maps of Paleocene deposits in the study area show a slight decrease in thickness to the west. This contrasts the prevailing trend of increasing thickness towards the southwest directed basin center and indicates a changed depositional environment. In the outer eastern Glückstadt Graben, increased thicknesses and diverging strata of late Eocene and Oligocene units indicate significant remobilization of salt structures during this time. Preexisting Triassic faults above the salt pillows “Schleimünde” and “Kieler Bucht” at the eastern border of the Glückstadt Graben were reactivated and form a north-south trending crestal graben filled with Paleogene sediments. This phase of salt remobilization is contemporaneous with the reintroduction of intraplate stress triggered by the Alpine and Pyrenean orogenies in the late Eocene. In the eastern Bay of Kiel and in the Bay of Mecklenburg, Late Eocene and younger sediments are largely absent due to Neogene uplift and erosion. Deepening of rim-synclines and synchronous infill of Paleogene strata give evidence for commencing salt pillow growth. Crestal faults pierce the Paleocene and Eocene strata, indicating salt movement at least during the later Eocene. This phase of salt movement occurred contemporaneously with salt remobilization in the Glückstadt Graben, initiation of the European Cenozoic Rift System and increased activity in the Alpine realm in the Late Eocene to Oligocene. We conclude that the rise of salt pillows since the Eocene significantly exceeds the growth during late Cretaceous to Paleocene inversion phase at the northeastern North German Basin.
Coastal changes through time is the only constant: Case study of west coast of Naxos Island, Cyclades, Greece
Authors: Evelpidou Niki , Petropoulos Alexandros , Karkani Anna , Saitis Giannis
Published: March 2021

Coastal areas include various landforms, such as dunes, lagoons and wetlands, which constitutes them as areas of particular environmental and geomorphological values. Coastal lagoons and dunes are of great environmental importance, given that, among others, they provide habitat for rare species of flora and fauna, but they also contribute to the protection of the coastal zone from sea level rise, storms, etc. Although these features are unique elements for sustainable development and are of great importance to the natural environment and economy, due to their relatively small size, they are one of the most vulnerable and threatened ecosystems. Such a case is the western coast of Naxos Island, hosting several wetlands bordering with low-lying sand dunes.

Naxos island lies in the center of the Aegean Sea, being part of the Cyclades Island group. The western coasts of Naxos include a number of natural features, which have been inherited from their palaeogeographical evolution over the last 10,000 years. Typically, the western coastal zone is composed of a sandy beach, bordered by low lying sand dunes, lagoons and an alluvial plain. These systems are becoming increasingly vulnerable, due to natural processes such as intensity of waves, but also due to human interventions that have blocked sediment input to the coastal zone and the increasing touristic development. The erosion of the dunes, the intense storms, the sea level rise, extreme events such as storms or tsunamis, and the increased tourist "raid", will lead to marine flooding not only to the beach, but also to the lagoons and many acres of land (rural, residential areas).

The aim of our study is to assess the vulnerability of the western coasts of Naxos to sea level rise, considering both natural and anthropogenic pressures. For this purpose, we used a series of methodologies for the environmental and geomorphological study of the coastal zone and the shallow submarine area, which included: a) photointerpretation of aerial photographs from 1960 until today, b) systematic seasonal aerial monitoring by drone, since 2015, c) mapping of the coastal zone and topographic sections using DGPS and d) dune mapping and sampling, e) sampling of underwater beachrocks. Through our analysis we aim to better elucidate the impact of the relative sea level rise in the study area.
Soil carbon balance in Hungarian crop rotation systems
Authors: De Luca Giulia , Balogh János , Pintér Krisztina , Fóti Szilvia , Bouteldja Meryem , Malek Insaf , Nagy Zoltán
Published: March 2021

Although characteristics of the carbon balance and the organic carbon stock changes of arable lands have been the primary research focus of numerous studies, uncertainity is still a major factor in this area of research. Our aim is to determine the dynamics of carbon cycling in croplands in regards to a crop rotation consisting of different crop types and to clarify the factors driving the carbon fluxes between its main components.

A field-scale eddy covariance (EC) station was established in 2017 at a cropland site in Central Hungary in order to obtain the cropland’s annual net ecosystem exchange of CO2 (NEE). Net ecosystem carbon budget (NECB) was calculated considering vertical and lateral C fluxes as well. Soil management is a conventional management with yearly deep ploughing and mineral fertilizer application.

During the three years of our experiment the crop rotation included winter wheat, winter rapeseed, sorghum and winter wheat. The largest net CO2 uptake was observed during the sorghum season (from sowing to harvest, -309 g C m-2 yr-1). However, extreme autumnal drought resulted in the incomplete germination of rapeseed in 2018, which led to carbon loss (108 g C m-2 yr-1) during this vegetation period. Results show a significant difference between the two winter wheat seasons – sown in 2017 and 2019 – which can be explained by the differing precipitation of the two periods. Despite the strong CO2 uptake of winter wheat and sorghum, NECB ranged between negligible C gain (-18.26 g C m-2 year-1, sorghum) to C losses of up to 108 g C m-2 year-1 (rapeseed). During three years the C loss was 420 g C m-2 as C export through harvest and fallow periods counterbalanced the crops’ CO2 uptake.

As a conclusion we can state this cropland could not sequester enough carbon to maintain the soil organic carbon pool and in order to reduce the risk of the depletion of soil carbon stock further efforts are needed in the field of soil management practices.
Linking Lagrangian model simulations with stable water isotope measurements in Arctic weather systems.
Authors: Johannessen Aina , Dekhtyareva Alena , Seidl Andrew , Sodemann Harald
Published: March 2021

Transport of water from an evaporation source towards a precipitation sink is the essence of the atmospheric water cycle. However, there are significant challenges with the representation of the atmospheric water cycle in models. For example, incomplete representation of sub-grid scale processes like evaporation, mixing or precipitation can lead to substantial model errors. Here we investigate the combined use of Lagrangian and Eulerian models and in-situ observations of stable water isotopes to reduce such sources of model error. The atmospheric water cycle in the Nordic Seas during cold air outbreaks (CAOs) is confined to a limited area, and thus may be used as a natural laboratory for hydrometeorological studies. We apply Lagrangian and Eulerian models together with observations taken during the ISLAS2020 field campaign in the Arctic in spring 2020 for characterising source-sink relationships in the water cycle. During the field campaign, we observed an alternating sequence of cold air outbreaks (CAO) and warm air intrusions (WAI) over the key measurement sites of Svalbard and northern Norway. Thereby, meteorological and stable water isotope measurements have been performed at multiple sites both upstream and downstream of the CAOs and WAIs. The Lagrangian model FLEXPART has been run with the input data from the regional convection-permitting numerical weather prediction model AROME Arctic at 2.5 km resolution to investigate transport patterns. The combination of observations and model simulations allows us to quantify the connection between source and sink for different weather systems, as well as the link between large-scale transport and stable water isotopes. Findings will lead to a better understanding of processes in the water cycle and the degree of conservation of isotopic signals during transport. This study may also serve as a guideline on how to evaluate the performance of Lagrangian transport models using stable water isotope measurements, and on how to detect constraints for quantifying the transport route and evaporation source from stable water isotope measurements for future work, including an aircraft campaign planned in 2021.
A trail of crumbs: ancient geomorphological indicators of past sea-level rise in the Northern Adriatic Sea (Italy)
Authors: Ronchi Livio , Fontana Alessandro , Correggiari Annamaria
Published: March 2021

The reconstruction of timing and modes of the last marine transgression is often hampered by the scarceness of available indicators, which is caused by bad preservation, lack of formation or difficult accessibility.

This is particularly true for the first period of the Holocene, between 7 ka and 11 ka cal, when the rate of transgression was high (hence little to absent formation of possible indicators) and the sea level was placed below ca. -20 m MSL (hence scarce accessibility).

Shoreline deposits and erosional landforms have long been recognized as geomorphological indicators of past sea levels. Such indicators (e.g. beach ridges, tidal notches) can be both submerged or exposed due to RSL variations of coastal progradation.

A major group of potential indicators which, up to date, is largely underrepresented, is constituted by paleo tidal inlets. Being excavated up to several meters below the surrounding lagoon and filled during the migration or deactivation of the inlet, such landforms may represent outstanding archives with a potentially high chance of preservation from erosion. Paleo tidal inlets can be easily recognized and cataloged through shallow sub-bottom profiling methods.

The analysis of almost 7000 km of high resolution seismic profiles collected in the northern Adriatic Sea allowed to recognized almost 100 paleo tidal inlets dating to the early Holocene, which constitute the only widespread witnesses of the post-LGM marine transgression in the area. Paleo tidal inlets are essential features to the paleo-geographic and -environmental reconstruction and provide new data to constrain the position of the transgressive coastlines. The presence of widespread lagoon environments during a phase of strong RSL rise comes from the interplay between sediment dispersal operated by the main fluvial actors of the area and phases of slowdown of the RSL rise. This study sheds light on the phenomena affecting coastal plains in response to RSL rise and constitutes the first report of an extensive distribution of paleo tidal inlets on a regional scale.
Genetic Relations Between the Aves Ridge and the Grenada Back-Arc Basin, East Caribbean Sea 
Authors: Garrocq Clément , Lallemand Serge , Marcaillou Boris , Lebrun Jean-Frédéric , Padron Crelia , Klingelhoefer Frauke , Laigle Mireille , Münch Philippe , Gay Aurélien , Schenini Laure , Beslier Marie-Odile , Cornée Jean-Jacques , Mercier de Lépinay Bernard , Quillévéré Frédéric , BouDagher-Fadel Marcelle
Published: March 2021

The Grenada Basin separates the active Lesser Antilles Arc from the Aves Ridge, described as a Cretaceous-Paleocene remnant of the “Great Arc of the Caribbean.” Although various tectonic models have been proposed for the opening of the Grenada Basin, the data on which they rely are insufficient to reach definitive conclusions. We present a large set of deep-penetrating multichannel seismic reflection data and dredge samples acquired during the GARANTI cruise in 2017. By combining them with published data including seismic reflection data, wide-angle seismic data, well data and dredges, we refine the understanding of the basement structure, depositional history, tectonic deformation and vertical motions of the Grenada Basin and its margins as follows: (1) rifting occurred during the late Paleocene- early Eocene in a NW-SE direction and led to seafloor spreading during the middle Eocene; (2) this newly formed oceanic crust now extends across the eastern Grenada Basin between the latitude of Grenada and Martinique; (3) asymmetrical pre-Miocene depocenters support the hypothesis that the southern Grenada Basin originally extended beneath the present-day southern Lesser Antilles Arc and probably partly into the present-day forearc before the late Oligocene-Miocene rise of the Lesser Antilles Arc; and (4) the Aves Ridge has subsided along with the Grenada Basin since at least the middle Eocene, with a general subsidence slowdown or even an uplift during the late Oligocene, and a sharp acceleration on its southeastern flank during the late Miocene. Until this acceleration of subsidence, several bathymetric highs remained shallow enough to develop carbonate platforms.
Parameters calibration in rainfall induced landslides in the Langhe area (1994)
Authors: Evangelista Giulia , Barbero Monica , Butera Ilaria , Castelli Marta , Claps Pierluigi , Tamea Stefania
Published: March 2021

In this work we have tackled as a ‘cold case’ the prolonged rainfall and flood event occurred in the Piedmont region (Northern Italy) in November 1994, when several hundreds of shallow landslides occurred. The aim is to investigate the key trigger factors of the landslides and to put some focus on the possibility to obtain calibrated parameters thanks to the use of a regional geotechnical database.

This research has been motivated by the effort to close the methodological and conceptual gap between the use of low-detail approaches, proposed to explore wide investigation domains and that of complex ones, applied to single hillslope scale, typically relying on finite elements solutions.

To achieve the above-mentioned goals, a simple model was preferred (i.e. that of Rosso, Rulli, Vannucchi, 2006), since it allowed a better check on the sensitivity of soil parameter values to the instability condition, under the assumption that these were the main sources of uncertainty.

With reference to the 1994 event, a database of 238 observed landslide has been used, for which well-documented geometries and geotechnical parameters are available.

To address the specific aim of cohesion and permeability validation, the safety factor expression from Limit Equilibrium Analysis has been targeted to assume the value 1 for all the considered slopes subjected to the actual (measured) rainfall.

The comparison between locally calibrated cohesion and permeability and the reference ones found in the database shows some differences; in particular, in several cases, safety factors quite lower than 1 have been derived, compared to those obtained using the published parameter values. The overall uncertainty resulting from this gap has been analysed for a limited (5%) number of carefully examined landslides and it will lay the foundations for subsequent, more geometrically accurate, investigations.
Can Convection‐Permitting Models really Offer Promise of More Certain Extreme Rainfall Projections ?
Authors: Fosser Giorgia , Adinolfi Marianna , Ban Nikolina , Belusic Danijel , Berthou Ségolène , Caillaud Cécile , Cardoso Rita M. , Coppola Erika , De Vries Hylke , Dobler Andreas , Feldmann Hendrik , Goergen Klaus , Kendon Elizabeth J. , Lenderink Geert , Panitz Hans-Juergen , Pichelli Emanuela , Soares Pedro M. M. , Somot Samuel , Tölle Merja H. , Vergara-Temprado Jesus
Published: March 2021

Compared to standard regional climate models (RCMs), convection-permitting models (CPMs) provide an improved representation of sub-daily precipitation statistics and extremes thanks mainly to the possibility to switch off the deep convection parameterisation, a known source of model error and uncertainties. The more realistic representation of local processes in CPMs leads to a greater confidence in their projections of future changes in short-duration precipitation extremes. Recent literature on CPMs seems to agree on a future increase of extreme precipitation, above Clausius‐Clapeyron scaling in some cases, which is likely to have severe socio-economic impacts.

The quantification of uncertainties on future changes at this resolution has been barely touched. Using the first‐ever ensemble of CPMs run within the UK Climate Projections project, Fosser et al. (2020) found that the climate change signal for extreme summer precipitation may converge in CPMs in contrast to RCMs, thanks to a more realistic representation of the local storm dynamics.

Here we use the first multi-model CPMs ensemble over the greater Alpine region, run under the auspices of the World Climate Research Programme’s (WCRP) Coordinated Regional Downscaling Experiment Flagship Pilot Study on Convective phenomena at high resolution over Europe and the Mediterranean (Coppola et al. 2020). In our analysis we compared the uncertainties in the CPMs ensemble to the driving models following a similar method to Fosser et al. (2020). In this presentation we will show if multi-model CPMs can really provide more certain extreme rainfall projections then their parent coarser resolution models. 

 

Fosser G, Kendon EJ, Stephenson D, Tucker S (2020) Convection‐Permitting Models Offer Promise of More Certain Extreme Rainfall Projections. Geophys Res Lett 47:0–2. doi: 10.1029/2020GL088151

Coppola, E., Sobolowski, S., Pichelli, E. et al. A first-of-its-kind multi-model convection permitting ensemble for investigating convective phenomena over Europe and the Mediterranean. Clim Dyn 55, 3–34 (2020). https://doi.org/10.1007/s00382-018-4521-8
Two millennia of seasonal rainfall predictability in the neotropics with repercussions for agricultural societies
Authors: Braun Tobias , Breitenbach Sebastian F. M. , Ray Erin , Baldini James U. L. , Baldini Lisa M. , Lechleitner Franziska , Asmerom Yemame , Prufer Keith M. , Marwan Norbert
Published: March 2021

The reconstruction and analysis of palaeoseasonality from speleothem records remains a notoriously challenging task. Although the seasonal cycle is obscured by noise, dating uncertainties and irregular sampling, its extraction can identify regime transitions and enhance the understanding of long-term climate variability. Shifts in seasonal predictability of hydroclimatic conditions have immediate and serious repercussions for agricultural societies.

We present a highly resolved speleothem record (ca. 0.22 years temporal resolution with episodes twice as high) of palaeoseasonality from Yok Balum cave in Belize covering the Common Era (400-2006 CE) and demonstrate how seasonal-scale hydrological variability can be extracted from δ13C and δ18O isotope records. We employ a Monte-Carlo based framework in which dating uncertainties are transferred into magnitude uncertainty and propagated. Regional historical proxy data enable us to relate climate variability to agricultural disasters throughout the Little Ice Age and population size variability during the Terminal Classic Maya collapse.

Spectral analysis reveals the seasonal cycle as well as nonstationary ENSO- and multi-decadal-scale variability. Variations in both the subannual distribution of rainfall and mean average hydroclimate pose limitations on how reliably farmers can predict crop yield. A characterization of year-to-year predictability as well as the complexity of seasonal patterns unconver shifts in the seasonal-scale variability. These are discussed in the context of their implications for rainfall dependent agricultural societies.
A multilayer soil approach for seepage process analysis in earthen levees
Authors: Bonaccorsi Bianca , Moramarco Tommaso , Noto Leonardo Valerio , Barbetta Silvia
Published: March 2021

Earthen levees protect flood-prone areas during severe flood events. In most cases, however, flooding is the result of the collapse of the embankments due to the seepage through and under the levee body. The description of the seepage line is difficult mainly because of the uncertainty on the hydraulic parameters, first of all the soil hydraulic conductivity. Barbetta et al. (2017) proposed a practical method for the seepage analysis based on the Marchi’s equation for the estimation of the probability of occurrence of the levee seepage which provides a vulnerability index under the assumption that the groundwater level coincides with the ground. Recently, the method has been tested also considering the groundwater level below the ground pointing out that such a condition has a high impact on the levee vulnerability to seepage. However, it does not consider the interactions between seepage process in the levee body and in the foundation.

In this context, this work proposes a new approach for the analysis of the infiltration line through the body and the foundation, considering a multilayer soil and assuming a different soil hydraulic conductivity for each layer. The new equation is obtained starting from the continuity equation and the flow equation.

The saturation line estimated through the Marchi’s equation and the one derived through the new multilayer model equation are compared. The analysis is first addressed to identify a threshold of the ratio between water head and water table beyond which the Marchi’s equation is no longer applicable. Indeed, the Marchi’s equation is valid when the river water head is lower than the water table. Different values of these two variables are analyzed and a threshold ratio equal to 0.57 is identified.

Furthermore, the levee vulnerability to seepage estimated with the two approaches is compared and the levee is found more vulnerable when the new approach is applied. The results indicate that the difference between the two vulnerability approaches decreases as the distance between the groundwater table and the ground level tends to zero. The proposed approach is an attempt to quantify the seepage probability with more realistic levees characteristics, hydraulic and soil parameters.

 

Barbetta, S., Camici, S., Bertuccioli, P., Palladino, M. R., & Moramarco, T. 2017. Refinement of seepage vulnerability assessment for different flood magnitude in national levee database of Italy. Hydrology Research, 48(3), 763–775. https://doi.org/10.2166/nh.2017.101.
Tooling in engaging stakeholders in adaptive water management with Nature-based solutions: reflections from an online NGT approach through the perspectives of the water professionals
Authors: Bogatinoska Borjana , Lansu Angelique , Floor Judith , Huitema Dave , Dekker Stefan
Published: March 2021

The global water sector is changing and it is in need of more evidence-based responses of emerging global, regional, national and local challenges. Communities are seeking interventions which achieve multiple benefits and outcomes such as: improved quality of water bodies, reduced greenhouse emissions, reliably delivered water for human use but also some that are rather urgent like: flood-risk management. In order to take into account the environmental, technological, economic, institutional and cultural characteristics of river basins, we need to move from current management regimes towards more adaptive regimes with the use of Nature-based solutions (NbS) instead of traditional 'grey' engineering approaches. Quite a vast amount of tools have been developed throughout the years for achieving this transition. This paper identifies the challenges and opportunities that water professionals face when using these tools in the process of planning NbS. An online tailor-made approach, based on a modified nominal group technique (NGT) and Multi-criteria analysus (MCA) was developed and applied. The NGT-based assessment of these tools consists of two rounds during which participants were asked to reflect first individually, and then collectively about the prerequisites and implications of these tools in the process of planning NbS. The participants are water professionals from the European project Co-Adapt. Here we presented one approach where new scientific methods and practical tools are developed for participatory assessment and implementation of adaptive water management.
Using in-situ sensors to quantify spatial variability in nutrient concentrations across the Ganges river basin
Authors: Khamis Kieran ,   Team SAPTANADI
Published: March 2021

There is increasing interest in monitoring spatial variability in biogeochemical processes using field deployable sensors. Despite this, rigorous assessments of accuracy and optimal sensor configurations remain limited for such applications. We undertook a comprehensive field study, between November and December 2019 (post-monsoon), across diverse monitoring locations on the River Ganges and its tributaries in Northern India. At 81 sites, from the foothills of the Himalayas to the tidal limit at Kolkata, the following suite of routine sensor measurements were taken; dissolved oxygen (DO), electrical conductivity (EC), pH and turbidity. In addition “new” optical parameters were also measured; absorbance (190 – 360 nm) and tryptophan-like fluorescence (TLF). Parallel water samples were collected for laboratory determination of dissolved organic carbon (DOC), nitrogen species (NO3 and NH4), phosphorus fractions (SRP, TP, TDP), absorbance and fluorescence excitation emission matrices (EEMs). A series of predictive models for each laboratory derived nutrient parameter were developed based on partial least squares regression, lasso regression, and stepwise regression approaches. The predictive power of the best models (i.e. combination of sensors and model approach) were assessed using 10-fold cross validation. Residual patterns were inspected to help infer the environmental conditions under which in-situ sensors could be used reliably. The highest predictive power was apparent for NO3, DOC and SRP. This was apparent when considering models based on the routinely measured parameters (R2cv = 0.45 – 0.6; EC explained most variance) or when new optical parameters were included (R2cv = 0.6 - 0.8; absorbance <280 nm and TLF explained most variance).  No suitable surrogate model could be derived for ammonium (R2cv = 0.3) or TDP/TP (R2cv both <0.4). For DOC, changes in DOM composition from upstream – downstream influenced model fit while the nitrate model appeared robust with no spatial pattern in the residuals identified. These findings highlight clear potential for optical sensors to improve our understanding of spatial variability in nutrient concentrations and inform future development of multi-parameter sensing sondes for rapid assessment of nutrient concentration. Further research is required to assess the transferability of field calibrations across seasonal and inter-annual timescales.
Mapping irrigation efficiency in large urban green areas
Authors: Rodriguez-Sinobas Leonor , Canales-Ide Freddy , Zubelzu Sergio
Published: March 2021

This study presents a novel method for controlling and monitoring irrigation of urban green areas based on Geographical Information Systems (GIS). The proposed procedure was applied to the Spanish Valdebebas Urban Development, located in Madrid, which comprises 18 ha occupied by urban parks irrigated by subsurface drip irrigation fully automated. Its irrigation network conveys water to 67 different irrigation units, irrigating very heterogeneous plants typology. The GIS model considered the smallest irrigation unit, as the pixel size and it was fed with the information on: discharging flow, irrigated area and irrigation times of each irrigation unit. The study was performed with data from the three irrigation seasons from 2017 to 2019. Likewise, daily information from the weather station located at the urban development, used for the irrigation network operation, was also incorporated into the GIS. The results showed the spatial and temporal variability of the garden coefficients (and water needs) and the water use efficiency. The study also estimate the evolution of irrigation rates and water use efficiency indices under three different climate change forecasting scenarios (namely Representative Concentration Pathways– RCP–45, RCP 6 and RCP85). This method can assist technicians and irrigation managers to make better decisions on operating the parks’ irrigation network.
Variations in spectral reflectivity and vertical cloud structure of Jupiter’s Great Red Spot
Authors: Anguiano-Arteaga Asier , Pérez-Hoyos Santiago , Sánchez-Lavega Agustín , Irwin Patrick G.J.
Published: March 2021

The Great Red Spot (GRS) of Jupiter is a large anticyclonic vortex present in the Jovian atmosphere. First observed in the XVII century, it is almost constantly located at 22°S and it is arguably one of the main atmospheric phenomena in the Solar System. Despite having been widely studied, the nature of the chromophore species that provide its characteristic colour to the GRS’s upper clouds and hazes is still unclear, as well as its creation and destruction mechanisms.

In this work we have analysed images provided by the Hubble Space Telescope’s Wide Field Camera 3 between 2015 and 2019, with a spectral coverage from the ultraviolet to the near infrared, including two methane absorption bands. These images have undergone a photometric process of cross calibration, ensuring a consistent correlation among the images corresponding to different visits and years. From such calibrated images, we have obtained the spectral reflectivity of the GRS and its surroundings, with particular emphasis on a few, dynamically interesting regions.

We used the NEMESIS radiative transfer suite to retrieve the main atmospheric parameters (particle vertical and size distributions, refractive indices…) that are able to explain the observed spectral reflectivity of the selected regions. Here we report the spatial and temporal variations on such parameters and their implications on the GRS overall dynamics.
LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse
Authors: Ryan Aoife Maria , Gallagher Peter T. , Carley Eoin P. , Brentjens Michiel A. , Murphy Pearse C. , Vocks Christian , Morosan Diana E. , Reid Hamish , Magdalenic Jasmina , Breitling Frank , Zucca Pietro , Fallows Richard , Mann Gottfried , Kerdraon Alain , Halfwerk Ronald
Published: March 2021

The solar corona is a highly-structured plasma which can reach temperatures of more than 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations, due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120–180 MHz using baselines of up to 3.5 km (corresponding to a resolution of 1–2’) during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (0.6’) than that attainable via standard interferometric imaging (2.4’). This provides a means of studying the contribution of scattering to apparent source size broadening. This study shows that the de-occultation technique can reveal a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be 4’ using both de-occultation and standard imaging. This may be explained by increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.
The role of the prediction stategies for the reliable transformation beetween two geodetic reference systems
Authors: Perperidou Dionysia - Georgia , Moschopoulos Georgios , Ampatzidis Dimitrios , Mouratidis Antonios , Tsimerikas Alexandros
Published: March 2021

One of he most common problems of the daily surveying/geodetic/cartographic practice is reliable transformation between two geodetic reference systems. There are plenty of well-known transformation’s models (e.g. 3D Helmert transdformation, 2D silimilarity transformaton, etc) applied for this purpose. Transformation scope is to optimally absorb the systematic inconsistencies of geodetic reference systems. In many cases, the pure deterministic approach is not sufficient, as the geodetic reference systems contain systematic effects, that are not successfully eliminated or reduced. Hence, a more sophiscticated methodology should be implemented, in order to enhance transformation’s accuracy. In this paper a case study is presented, including testing of  different deterministic transformation models between the old Greek Datum and the new official 1987 Hellenic Geodetic Reference System The estimated residuals do not fullfill the present needs of accuracy, thus we further implement some specified prediction models. The final outcome reads an improvement of the transformation between these two geodetic reference systems.
Using a global tree sap flow database as ground-truth for transpiration products validation
Authors: Bittencourt Paulo , Rowland Lucy , Sitch Stephen , Poyatos Rafael , Miralles Diego , Mencuccini Maurizio
Published: March 2021

Transpiration (T) is a key driver of ecosystem energy, water and carbon flows and is tightly linked to climate and land-use change. While global models rely extensively on remotely sensed transpiration products to evaluate land-surface processes, ground-truth validation for these products does not exist. At best, data from eddy-covariance evapotranspiration is used, but the T component is partitioned based-on a set of complex assumptions, which are in themselves poorly validated for many parts of the world. Sapflow (SF) measurements allow direct quantification of tree-level T which can be used as ground-truth for T-products in forested areas. A recent global network of sapflux data, (SapFluxNet – SFN) has provided the first quality-controlled sapflow dataset at a global scale, opening up new opportunities to evaluate global T products.  Using the SFN-SF and Global Land Evaporation Amsterdam Model (GLEAM) T product, we address i) how the time course of the two products scale with one another, and ii) whether this scaling is different between days with low, median or high T/ SF within months; in addition, iii) we evaluate errors patterns of GLEAM-T in relation to SFN-SF and test whether these errors are biased by site climate or by model inputs. Our results shows GLEAM-T scales with SFN-SF, especially for days with median transpiration, but this scaling, rather than 1:1, has a slope of 0.9, which causes underestimation of SFN-SF at high GLEAM-T values. The scaling is shallower for low and high transpiration days leading to a higher bias in those days. In addition, GLEAM-T scales from SFN-SF with an offset, which compensate the shallower scaling at median values at the expense of increasing bias at extremes. Our results also show errors of GLEAM-T in relation to SFN-SF are not random but depend on the location`s climate and on the soil moisture stress factor used within GLEAM transpiration model. Our work bridges, for the first time, the scale difference between trees and pixels and shows the potential of using ground-truth SF measurements for evaluating biases and patterns in global products.
Improving Regional Rainfall Forecasts using Convolutional-Neural Networks
Authors: Barnes Andrew , McCullen Nick , Kjeldsen Thomas Rodding
Published: March 2021

Traditional weather forecasting approaches utilize numerous numerical simulations and empirical models to produce a gridded estimate of rainfall, the cells of which often span multiple regions and struggle to capture extreme events. The approach presented here combines the power of modern meteorological forecasts from the ECMWF C3S seasonal forecasts service with convolutional neural networks (CNNs) to improve the forecasting of total monthly regional rainfall in the UK. The CNN is trained using mean sea-level pressure and 2m air temperature forecasts from the ECMWF C3S service using three lead-times: one month, three months and six months. The training is supervised using the equivalent true rainfall data provided by the CEH-GEAR (Centre for Ecology and Hydrology, gridded estimates of areal rainfall). The resulting predictions are then compared with the total monthly regional rainfall values calculated from the precipitation forecasts provided by the ECMWF C3S service. The results of this comparison show the new CNN model out-performs the ECMWF model  across all three leadtimes. This performance is calculated using the root-mean square error between the predicted rainfall values for each region and the true values calculated from the CEH-GEAR dataset. The largest gap is found at a one month leadtime where the CNN model scores a root-mean square error (RMSE) 13% lower than the ECMWF model (RMSEs: 46.5 and 53.4 respectively), the smallest gap is found at a six month leadtime where the CNN scores an RMSE only 2.2% lower than the ECMWF model (RMSEs: 48.5 and 49.6 respectively). However, these differences are exacerbated at the extremes with the CNN producing errors 26% lower than the ECMWF model at a one-month leadtime, 19% lower at a three-month leadtime and 3% at a six-month leadtime. These results are then extended to show how the CNN made the predictions and by comparing the attribution patterns of North West and South East England we are able to show a reliance on both the mean sea-level pressure to the west of the UK and the 2m air temperature to the south west of the UK and over the European continent.
On the identifiability of soil hydraulic parameters in lysimeter experiments: a Bayesian perspective 
Authors: Schübl Marleen , Brunetti Giuseppe , Stumpp Christine
Published: March 2021

Groundwater recharge through the vadose zone is an important yet hard to quantify variable. It is estimated from lysimeter experiments or mathematical modelling. For the simulation of groundwater recharge rates with a physically based model soil hydraulic properties (SHPs) have to be inversely estimated because SHPs from laboratory experiments can only be poorly transferred to field conditions. Still, also the inverse estimation of SHPs, is associated with experimental and modeling uncertainties that propagate into the recharge prediction. New methods are thus required improving the inverse estimation of SHPs and reducing the uncertainty in groundwater recharge prediction. Therefore, this study aims to investigate how the assimilation of different types of soil water measurements for the inverse estimation of SHPs with the HYDRUS-1D software affects the estimated uncertainty. For this purpose, observations from a monolithic lysimeter experiment (i.e. lysimeter outflow, soil pressure head and volumetric soil water content at two different depths) have been combined in the different modeling scenarios and coupled with a Bayesian analysis to inversely estimate SHPs and assess their uncertainty. Posterior predictive checks showed that the simultaneous assimilation of outflow and soil pressure head led to the smallest uncertainty in groundwater recharge prediction. This represented a reduction in uncertainty compared to assimilating lysimeter outflow alone. Additional information provided by measurements of soil water content resulted in a reduced parameter uncertainty for residual and saturated water content, however, it did not further reduce the uncertainty in recharge prediction. Overall, this study shows the applicability of a Bayesian analysis for determining uncertainties in the inverse estimation of SHPs with lysimeter data and for the quantification of the associated uncertainty in groundwater recharge prediction. Based on our results for the investigated site, we recommend simultaneous assimilation of lysimeter outflow and soil pressure head measurements to minimize uncertainty in groundwater recharge prediction. However, a more comprehensive analysis is required to make a generally valid recommendation for other soils or climates.

 
Investigation of energy conversion processes and wave activity related to dipolarization fronts observed by MMS
Authors: Alqeeq Soboh , Le Contel Olivier , Canu Patrick , Retino Alessandro , Chust Thomas , Alexandrova Alexandra , Mirioni Laurent , Baraka Suleiman , Richard Louis , Khotyaintsev Yuri , Nakamura Rumi , Wilder Frederick , Ahmadi Narges , Wei Hanying , Argall Matthew , Fischer David , Gershman Daniel , Burch James , Torbert Roy , Giles Barbara ,   MMS Team
Published: March 2021

In the present work, we consider four dipolarization front (DF) events detected by MMS spacecraft in the Earth’s magnetotail during a substorm on 23rd of July 2017 between 16:05 and 17:19 UT. From their ion scale properties, we show that these four DF events embedded in fast Earthward plasma flows have classical signatures with increases of Bz, velocity and temperature and a decrease of density across the DF. We compute and compare current densities obtained from magnetic and particle measurements and analyse the Ohm’s law. Then we describe the wave activity related to these DFs. We investigate energy conversion processes via J.E calculations and estimate the importance of the electromagnetic energy flow by computing the divergence of the Poynting vector. Finally we discuss the electromagnetic energy conservation in the context of these DFs.
Weakly nonlinear surface gravity waves in a depth-dependent background flow
Authors: Zheng Zibo , Li Yan , Ellingsen Simen
Published: March 2021

An open ocean often has a wind driven shear-current near the surface that is able to significantly change the properties of surface waves. This work aims to investigate the effects of a vertically sheared background flow on weakly nonlinear waves with both a statistical study for irregular random waves and a deterministic study for a wave group.

We first extended the theory by Dalzell (1999) to allow for the effects of a horizontal background flow with arbitrary depth dependence. The extended theory is valid up to second order in wave steepness and is applicable for directional-spread waves of a broad bandwidth. The Direct Integration Method (Li & Ellingsen 2019) is used for the linear dispersion relation.

Using the theory, we examine the effects of an opposing and assisting shear, respectively, on the nonlinear properties of a short wave group on deep-water through comparisons to cases without a shear flow. A shear flow leads to wave crests (troughs) being either steepened or flattened, depending mainly on the direction of a shear relative to the propagation direction of the group and the strength of the depth-integrated velocity of a shear relative to the group velocity. We, furthermore, investigated skewness and kurtosis of a time record of the wave elevation for irregular waves in a background sheared flow, compared to a linear Gaussian random sea for surface waves only. We obtained the probability density function and exceedance probability for wave crests. Relevance for rogue wave formation is discussed.

Key words: waves/free-surface flow, ocean surface waves, wave-current interaction

 

References

Dalzell, J. F. "A note on finite depth second-order wave–wave interactions." Applied Ocean Research 21, no. 3 (1999): 105-111.

Li, Y., and Ellingsen, S. Å. "A framework for modeling linear surface waves on shear currents in slowly varying waters." Journal of Geophysical Research: Oceans 124, no. 4 (2019): 2527-2545.  