bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel numerical modelling of well-aquifer response induced by pressure disturbance
Authors: Xing Yixuan , Hu Rui , Gu Hongbiao , Liu Quan , Ptak Thomas
Published: March 2020

Under hydrostatic conditions, the water level observed in a well is often supposed to be equivalent to the pressure head in the surrounding aquifer. When the aquifer is subject to disturbing processes and activities, fluctuations of water level can be observed. Generally, the measured water level in the well is often considered to be less than the pressure head in the aquifer due to wellbore storage and skin effects (Ramey et al., 1972). In fact, there is another factor that can suppress or enhance the oscillating water level, which is termed the amplification effect (Cooper et al., 1965). Related studies point out that this effect is affected by well geometry (e.g. well diameter, water column height and well screen length), aquifer properties (e.g. transmissivity and storativity) and the period of the disturbed pressure head (Kipp, 1985; Liu, 1989). However, previous studies have obvious divergences in quantifying the amplification effect.

In this work, we firstly established an idealized fluid model to simplify the complex solid-fluid coupling process, aiming to discuss the influence of different well geometry parameters on the amplification factor separately, such as the well diameter, water column height and well screen length. Subsequently, we built a well-aquifer coupling numerical model to study the well-aquifer response induced by disturbed pressure based on the finite element method. Simulations of 125 scenarios showed that the amplification factor gradually increased until it reached a peak, and then decreased to 1 as the period of disturbed pressure became larger. The corresponding period of an amplification factor peak was significantly influenced by the water column height, which controlled the position of an “optimal period”. Aquifer properties can also affect the amplification factor, especially its peak value. In further numerical studies, more complicated scenarios will be investigated, considering different types of wells and aquifers.
New Heat Flux Model for Antarctica with a Machine Learning Approach
Authors: Lösing Mareen , Ebbing Jörg , Szwillus Wolfgang
Published: March 2020

Improving the understanding of geothermal heat flux in Antarctica is crucial for ice-sheet modelling and glacial isostatic adjustment. It affects the ice rheology and can lead to basal melting, thereby promoting ice flow. Direct measurements are sparse and models inferred from e.g. magnetic or seismological data differ immensely. By Bayesian inversion, we evaluated the uncertainties of some of these models and studied the interdependencies of the thermal parameters. In contrast to previous studies, our method allows the parameters to vary laterally, which leads to a heterogeneous West- and a slightly more homogeneous East Antarctica with overall lower surface heat flux. The Curie isotherm depth and radiogenic heat production have the strongest impact on our results but both parameters have a high uncertainty.

To overcome such shortcomings, we adopt a machine learning approach, more specifically a Gradient Boosted Regression Tree model, in order to find an optimal predictor for locations with sparse measurements. However, this approach largely relies on global data sets, which are notoriously unreliable in Antarctica. Therefore, validity and quality of the data sets is reviewed and discussed. Using regional and more detailed data sets of Antarctica’s Gondwana neighbors might improve the predictions due to their similar tectonic history. The performance of the machine learning algorithm can then be examined by comparing the predictions to the existing measurements. From our study, we expect to get new insights in the geothermal structure of Antarctica, which will help with future studies on the coupling of Solid Earth and Cryosphere.
CIR/HSSS-related TID activity and their interhemispheric circulation
Authors: Buresova Dalia , Habarulema John Bosco , Watermann Jurgen , Edemskiy Ilya K. , Urbar Jaroslav , Altadill David , Blanch Estefania , Segara Antoni , Katamzi Zama
Published: March 2020

The paper presents results of the analysis of the changes in the regular ionospheric variability and TID activity observed during CIR/HSSS-related storms. We analyzed main ionospheric parameters retrieved from manually scaled ionograms, plasma drift measurements and TEC data obtained from several European and African ionospheric stations and GNSS receivers. Most of the observed storm-related TIDs had periods of 60-180 min (LSTIDs). During the analyzed storms we also observed extraordinary spreads and plasma bubbles at the F region heights. The results of the analysis were compared with the TID activity during strong magnetic storms of CME origin along the European-African sector. In order to obtain quantitative information on the likeliness and morphology of interhemispheric circulation of LSTIDs at about 40 events were examined lasting between 8 and 24 hours each. We used exclusively GPS-based detection methods, specifically information on TEC, TEC deviations in space and time from a background reference (dTEC), and the Rate of TEC change in time (ROT), all inferred from GPS receiver networks in Europe and Africa. We conclude that hemispheric conjugacy of LSTID is highly probable while interhemispheric circulation rather unlikely but still occurring during some periods.
The UK Geoenergy Observatory in Glasgow, Scotland: a New Facility for Mine Water Geothermal Research
Authors: Monaghan Alison , Starcher Vanessa , Barron Hugh , Abesser Corinna , O Dochartaigh Brighid , Fordyce Fiona , Kuras Oliver , Burke Sean , Taylor-Curran Helen , Luckett Richard
Published: March 2020

Mine water geothermal heat production and storage can provide a decarbonised source of energy for space heating and cooling, however the large resource potential has yet to be exploited widely. Besides economic, regulatory and licensing barriers, the geoscientific uncertainties remain significant. A lack of detailed understanding of thermal and hydrogeological subsurface conditions and processes, resource sustainability, and the potential impacts on the subsurface-to-surface environmental impacts have so far hampered a more widespread development of this resource.

The British Geological Survey (BGS) is in the final stages of constructing the Glasgow Geothermal Energy Research Field Site on behalf of the Natural Environment Research Council with UK Government funding. As one of the two new UK Geoenergy Observatories, the Glasgow site will facilitate collaborative research to improve our understanding of subsurface processes and change. It will provide scientific infrastructure for investigating the shallow, low-temperature coal mine water geothermal energy resources available in abandoned and flooded mine workings at depths of around 50-90 m below the eastern parts of the city.

The Glasgow site was chosen due to its commonalities with other parts of the UK and beyond in terms of its coal mining history, geology and legacy of industrial land use. Mine water geothermal resources in these settings could provide sufficient heat for community-scale district heating networks.

The research infrastructure comprises arrays of mine water and environmental baseline boreholes for characterisation and monitoring, and the boreholes are instrumented with permanent geophysical sensors. Here we report on interim results from drilling the environmental baseline and mine water boreholes, and opportunities for research and innovation.

Continuous monitoring and regular sampling data will be provided for the science community to examine a dynamic subsurface geo-, hydro- and bio-sphere. The facility will also provide opportunities for researchers to undertake their own experiments, with the aim of producing high-quality scientific evidence to reduce uncertainty on mine heat energy systems and understand their environmental impacts, for schemes across the UK and beyond.
Simulating multiple wave human dispersals out of Africa
Authors: Ruan Jiaoyang , Timmermann Axel
Published: March 2020

Human fossil and archeological findings indicate that Anatomically Modern Humans (AMHs) may have migrated from Africa into Eurasia multiple times during the last glacial period. However, mtDNA-based genetic data (haplogroup L3 & its daughters M, N) appear to be more consistent with a single wave dispersal ~ 70-60 ka, coinciding with one of the driest periods in northeastern Africa. 

To reconcile this discrepancy and better understand the migration routes and interactions of different groups of AMHs, we developed a new version of the Hominin Dispersal Model (HDM, version 2). The phenomenological reaction diffusion model simulates a realistic human dispersal in a spatio-temporally varying climatic environment.  In our configuration, we introduce a group which represents individuals which dispersed into Asia prior to 60 ka and a group which migrated into Eurasia post-60 ka. An ensemble of parameter sensitivity experiments suggests that their interaction caused a characteristic east-west gradient in admixture across Eurasia, which is consistent with latest genetic datasets, which reveal a faint signal of pre-60 ka dispersal waves in Southeast Asians and individuals from Papua New Guinea. Moreover, our simulations provide new insights into possible migration routes of AMHs. Based on this analysis we propose a new hypothesis to explain the increased Neanderthal DNA percentage in present-day Asians relative to Europeans.
Linking subduction dynamics to back-arc deformation
Authors: Magni Valentina , Prada Manel
Published: March 2020

 The morphology of back-arc basins shows how complex their formation is and how pre-existing lithospheric structures, rifting and spreading processes, and subduction dynamics all have a role in shaping them. Often, back-arc basins present multiple spreading centres that form one after the other (e.g. Mariana subduction zone), propagate and rotate (e.g., Lau Basin) following trench retreat. Episodes of fast and slow trench retreat can cause rift jumps, migration of magmatism, and pulses of higher crustal production (e.g., Tyrrhenian Basin). The evolution of a back-arc basin is not only tightly linked to subduction dynamics, but it is likely that the composition and the pre-existing structure of the lithosphere play a role in shaping the basin too. In this work, we investigate the interplay between these features with numerical models of lithospheric extension with a visco-plastic rheology. We use the finite element code ASPECT to model the rifting of continental and oceanic lithosphere with boundary conditions that simulate the asymmetric type of extension caused by the trench retreat. We perform a parametric study in which we systematically change key parameters such as crustal composition and thickness, initial thermal structure and rheology of the lithosphere, and rate of extension. These models aim at understanding how pre-existing lithospheric structures affect back-arc rifting and spreading and what processes control spreading centres jumps in back-arc settings. Preliminary results show that time-dependent boundary conditions that simulate episodes of fast trench retreat, thus fast extension, play an important role into the style of lithospheric back-arc deformation. Finally, we will compare our model results with the location and timing of back-arc rifting and spreading in different active and inactive back-arc basins.
Localization of Rockfalls at Dolomieu Crater, La Réunion, through Simulation of Seismic Waves on Real Topography
Authors: Kuehnert Julian , Mangeney Anne , Capdeville Yann , Chaljub Emmanuel , Stutzmann Eleonore , Vilotte Jean-Pierre
Published: March 2020

Rockfall generated seismic signals have been shown to be of great utility in order to detect and monitor rockfall activity. Furthermore, event locations were successfully estimated using methods which rely on either arrival times, amplitudes or polarization of the seismic signal. However, strong surface topography can significantly influence seismic wave propagation and thus flaw the estimates if not taken into account correctly.

On the upside, the imprint of topography on the seismic signal can be characteristic of the source position. We show that this additional information can be used to get a more detailed rockfall location estimation. In order to do so, the seismic impulse response is modeled on a domain with 3D topography using the Spectral Element Method. Subsequently, in order to locate events, station energy ratios of the synthetic seismograms are compared with energy ratios of rockfall signals in a sliding time window.

We test the method on rockfalls which occurred at Dolomieu crater of Piton de la Fournaise, La Réunion. The sensitivity of the method on the resolution of the modeled topography and the underlying velocity model is tested. We propose that the method can be applied for monitoring rockfall activity in a specific area with multiple seismic stations after calculating once the impulse response for the corresponding topography.
Extending the Ice Watch system as a citizen science project for the collection of In-Situ sea ice observations
Authors: Hegelund Ole Jakob , Everett Alistair , Cheeseman Ted , Wagner Penelope , Hughes Nick , Pierechod Marcin , Southerland Ken , Robinson Philip , Hutchings Jennifer , Kiærbech Åshild , Lillehaug Pedersen Joakim
Published: March 2020

The Ice Watch program coordinates routine visual observations of sea-ice including icebergs and meteorological parameters. The development and use of the Arctic Shipborne Sea Ice Standardization Tool (ASSIST) software has enabled the program to collect over 6 800 records from numerous ship voyages and it is complementary to the Antarctic Sea-ice Processes and Climate (ASPeCt) in the Antarctic. These observations will enhance validation and calibration of data from the Copernicus Sentinel satellites and other Earth Observation missions where the lack of routine spatially and temporally coincident data from the Polar Regions hinders the development of automatic classification products. A critical piece of information for operations and research, photographic records of observations, is often missing. As mobile phones are nearly ubiquitous and feature high-quality cameras, capable of recording accurate ancillary timing and positional information we are developing the IceWatchApp to aid users in supplementing observations with a photographic record.

The IceWatchApp has been funded by the Citizen Science Earth Observation Lab (CSEOL) programme of the European Space Agency and the Polar Citizen Science Collective, which has successfully implemented similar observation projects within atmospherics, biology and marine geosciences, is collaborating in its development. The image database will aid the training of machine learning algorithms for automatic sea ice type classification and provide a mechanism for crowd-sourcing identification through an “ask a scientist” feedback feature. The app will also have the capability to provide near real-time satellite and Copernicus services products back to the user, thereby educating them on Earth Observation, and giving them an improved understanding of the surrounding environment.

 

Keywords: Polar regions, Arctic, Antarctic, data collection, In-Situ measurements, remote sensing, Sea Ice, user engagement, citizen science, Earth Observation.
Abstract: to session 35413

 
Free and Open Source unmanned vehicles
Authors: Delucchi Luca , Bezzi Luca
Published: March 2020

Unmanned Vehicles (UV) are used daily for different applications around the world. However, most of the software and technologies on which they are based are closed and proprietary systems. The presentation will start by introducing the history of Unmaned Vehicle technologies, with some unknown historical info, and the different types of Unmaned Vehicles that exist. The aim of the presentation is to demonstrate the integration of free and open source systems starting from the hardware, specially the autopilot component, through some payloads and finishing with the software solutions. Different software solutions for diverse aims will be showed and compared, i.e., first the different software used to configure the UV and manage the mission and later the possible software used to manage the outputs from the mission.
Eccentricity forcing of Saharan climate drives fluvial strath terrace formation in the High Atlas
Authors: Zondervan Jesse , Stokes Martin , Telfer Matt , Boulton Sarah , Buylaert Jan-Pieter , Jain Mayank , Murray Andrew , Belfoul Alaeddine , Mather Anne , Taleb Nawfal , Hann Madeleine
Published: March 2020

River strath terraces reflect changes in lateral and vertical erosion rates within mountain valleys related to changes in the sediment to water discharge ratio. In contrast to the formation of terraces in high latitude glaciated catchments, little is known about the timing and mechanisms of river valley aggradation and incision in response to climate in low latitude, non-glaciated arid regions. To investigate the timing of river strath terrace formation in North-West Africa, we developed and applied a new approach to OSL dose rate correction of gravels. We sampled terraces in the M’Goun catchment crossing the thrust front and a thrust-sheet-top basin of the south-central High Atlas in Morocco, totalling 23 dated samples. Strath surfaces are elevated 10 to 40 m above the modern river plain, depending on local valley and bedrock configuration, and are overlain by 2 to 10 m of fluvial conglomerates. Burial ages of conglomerates in the first strath terrace level span from 180 to 60 ka, with widespread abandonment and incision post 60 ka throughout the catchment. This timing coincides with an eccentricity-driven decrease in African summer insolation and a decrease in the fluvial signature of Saharan dust recorded in an offshore Atlantic sediment core. We propose enhanced precipitation from the African summer monsoon during high insolation periods led to increased sediment yield and aggradation in the southern High Atlas, whilst low insolation and dry periods led to sediment-starved incision. To our knowledge, the M’Goun river terrace record is the most detailed record of long-term landscape evolution in response to climate fluctuations in northwest Africa to date.
Application of stable isotope ratios in drinking water supply system of Ljubljana, Slovenia
Authors: Vreča Polona , Nagode Klara , Kanduč Tjaša , Bračič Železnik Branka , Jamnik Brigita
Published: March 2020

The key to understand the deterioration of the quality of urban water resources is to know the impact of urbanization on the entire waterway, which can change dramatically during the extreme climatic events. Various geochemical parameters, including stable isotope ratios of light elements (H, O, C), represent an important tool to investigate water sources, transport routes, and the mixing of individual components of the water cycle. They are indispensable in urban hydrology, both for characterizing drinking water resources and for evaluating changes within a complex water system.

In Slovenia, the majority of the population is supplied with drinking water from groundwater. In Ljubljana, the capital city of Slovenia, groundwater represents the main drinking water resource.  Therefore, the knowledge and understanding of the groundwater vulnerability is important for the protection and management of water resources. In Ljubljana, the water is supplied through the central water system (WSS), more than 1.000 km long, according to the legislation and the latest standards from five different wellfields (Kleče, Hrastje, Brest, Jarški prod and Šentvid). Despite the established water protection areas, the water supply areas are exposed to the pressures of urbanization, industry, transport, agriculture and old environmental burdens, which are often unknown.

In the past, various short-term isotopic studies have been conducted and the Ljubljansko polje and Ljubljansko barje aquifers were characterized. In addition, the sources, paths and interactions of water were determined and the obtained data were used to improve the conceptual model.

However, isotopic studies of water circulation in the drinking water supply system (WSS), which would cover the simultaneous characterization of water sources and changes within the WSS, have not been performed so far. In order to assess the usefulness of isotopes more systematically, we performed the first more detail sampling of water from WSS of Ljubljana in autumn 2018. Sampling was carried out at 103 locations that were selected according to the type of facility in the WSS (i.e. 41 wells, 7 joint exits from water pumping station, 22 water reservoirs, 2  water treatment locations, 13 fountains, and 19 taps) and according to 9 different WSS areas. Additional samples were collected on River Sava, important infiltration source of groundwater, and at outflow from Ljubljana central wastewater treatment plant. This contribution focuses on presentation of changes of different parameters (i.e. temperature, electrical conductivity, pH, total alkalinity, δ18O, δ2H and δ13C) in WSS of Ljubljana.
Serial gravity-constrained cross-sections in the Central Pyrenees validating its structural style
Authors: Soto Ruth , Clariana Pilar , Ayala Conxi , Casas-Sainz Antonio M. , Román-Berdiel Teresa , Margalef Aina , Oliva-Urcia Belén , Pueyo Emilio L. , Beamud Elisabet , Rey-Moral Carmen , Rubio Félix
Published: March 2020

Cenozoic contractional deformation in the Central Pyrenees generated several basement thrust sheets involving Paleozoic rocks and decoupled Mesozoic and Cenozoic cover units detached on the main décollement level, the Triassic evaporites. The overall geometry and structural architecture of the chain have already been established based on numerous geological and geophysical data obtained during several decades. This work aims to validate the overall accepted geometry of the Central part of the chain by the construction of six serial cross-sections constrained by gravity data and 2.5D gravity modelling. The study area comprises the southern half of the Axial Zone between La Maladeta and Andorra-Mont Louis granites and its southern leading edge as well as the northernmost part of the South-Pyrenean Zone.

New gravity data were acquired and combined with previous existing databases to obtain Bouguer anomaly and residual anomaly maps of the study area. Six serial gravity-constrained cross sections have been built using available geological maps, previous published works, new geological and gravity data and 2.5D gravity modelling. Density values for gravity modelling were derived from 231 laboratory measurements of rock samples collected in the field from non-weathered outcrops that include all rock types outcropping in the study area. The residual anomaly map shows a good correlation between basement thrust sheets and gravity highs whereas negative anomalies seem to correspond to (1) Mesozoic basins, (2) Triassic evaporites and (3) Late Variscan igneous bodies. The 2.5D gravity modelling along the six cross sections highlights: (i) strong along-strike variations on the gravity signal due to lateral differences of the surficial and subsurface occurrence of Triassic evaporites, (ii) different geometry at depth of the Late Variscan igneous bodies outcropping in the study area and (iii) geometric lateral variations of the basement thrust sheets and their relationship with the Mesozoic-Cenozoic units.
Basal conditions of Kongsvegen at the onset of surge - revealed using seismic vibroseis surveys
Authors: Smith Emma C. , Diez Anja , Eisen Olaf , Hofstede Coen , Kohler Jack
Published: March 2020

Kongsvegen is a well-studied surge-type glacier in the Kongsfjord area of northwest Svalbard. Long-term monitoring has shown that the ice surface velocity has been increasing since around 2014; presenting a unique opportunity to study the internal ice structure, basal conditions and thermal regime, all of which play a crucial role in initiating glacier surges. In April 2019, three-component seismic vibroseis surveys were conducted at two sites on the glacier, using a small Electrodynamic Vibrator source (ElViS). The first site is in the ablation area and the second near the equilibrium line, where the greatest increase in ice-surface velocity has been observed.

Initial analysis indicates the conditions at the two sites are significantly different. At the ablation area site, the ice is around 220 m thick, and the bed is relatively flat and unvaried, with no clear change in the bed reflection along the profile. The bed appears to comprise a uniform and undisturbed sediment package ~60 m thick, and there are no clear englacial reflections within the ice column. By contrast at the second site, the ice is around 390 m thick, and the internal ice structure is much more complex. Clear internal ice reflections are visible at depths between 150-250 m, and further reflections in the 100 m above the bed indicate there could be shearing or sediment entrainment in this area. Below the bed, cross-cutting layers are clearly visible and the bed reflection itself shows changing reflection polarity – suggesting water or very wet sediment is present in some areas.  The contrast between these two sites at the onset of a surge phase allows us to investigate the physical conditions that are conducive to surge initiation, both at the ice-bed interface and within the ice column.
Disentangling the relative contributions of atmospheric demand for water and soil water availability on the stomatal limitation of photosynthesis
Authors: Lavergne Aliénor , Graven Heather , Prentice Iain Colin
Published: March 2020

Plants open and close their stomata in response to changes in the environment, so they can absorb the CO2 they need to grow, while also avoid drying out. Since the activities of leaf stomata determine the exchanges of carbon and water between the vegetation and the atmosphere, it is crucial to incorporate their responses to environmental pressure into the vegetation models predicting carbon and water fluxes on broad spatial and temporal scales. The least-cost optimality theory proposes a simple way to predict leaf behaviour, in particular changes in the ratio of leaf internal (ci) to ambient (ca) partial pressure of CO2, from four environmental variables, i.e. ca, growing-season temperature (Tg), atmospheric vapour pressure deficit (Dg), and atmospheric pressure (as indexed by elevation, z). However, even though the theory considers the effect of atmospheric demand for water on ci/ca, it does not predict how dry soils with reduced soil water availability further influence ci/ca. Recent research has shown that independent of the individual effects of Tg, Dg, ca and z on ci/ca, the model tends to underestimate ci/ca values at high soil moisture and to overestimate ci/ca values at low soil moisture. Here, we will try to disentangle the relative contribution of Dg and soil moisture on changes in ci/ca and test a new implementation of soil moisture effect in the framework of the least-cost hypothesis. To achieve this goal, we will use stable carbon isotopes measurements in leaves and in tree rings at sites with different soil water availability and different evaporative demand. We will then incorporate the improved model based on the least-cost hypothesis into the UK vegetation model JULES and investigate leaf stomatal responses to recent environmental changes across regions.
Lidar measurements characterizing the thermodynamic and dynamic structure of the boundary layer up to the turbulence scale
Authors: Behrendt Andreas , Lange Diego , Späth Florian , Muppa Shravan Kumar , Metzendorf Simon , Senff Christoph , Wulfmeyer Volker
Published: March 2020

One weakness of today's weather and climate models is the inaccurate representation and parameterization of the boundary layer processes and land-atmosphere (L-A) feedback. In order to investigate these processes, scanning lidar systems allow the observation not only of wind with Doppler lidar but also of humidity and temperature. It is expected that advances in the understanding of LA feedback and boundary-layer exchange will significantly contribute to better simulations of clouds and precipitation on all temporal and spatial scales.

In this contribution, we present recent thermodynamic measurements in the surface layer, atmospheric boundary layer and free troposphere with very high resolution achieved during several field campaigns like the Land-Atmosphere Feedback Experiment (LAFE) in 2017, ScaleX in 2019, EUREC4A in 2020, and at the Land-Atmosphere Feedback Observatory (LAFO) in 2020.

University of Hohenheim (UHOH) operates besides two scanning Doppler lidars (HALO Photonics StreamlineXR), three lidars for thermodynamic profiling which have been developed within the last 15 years by the Institute of Physics and Meteorology itself. These are two scanning lidar systems which are semi-automated and a fully-automated vertical pointing lidar system.

The water vapor differential absorption lidar (DIAL) of UHOH is a mobile system with a laser power of up to 10 W at 818 nm with a pulse repetition rate of 300 Hz. The receiver consists of an 80-cm telescope. The raw resolution of the atmospheric backscatter signals is 15 m and single shot. The resolution of the data product, the water vapor number density or absolute humidity, is typically 1 to 10 s and 40 to 200 m.

The UHOH Rotational Raman Lidar measures temperature and water vapor mixing ratio. Also this system is mobile. So far, we used as transmitter a flash-lamp-pumped Nd:YAG laser with 12 W at 355 nm at 50 Hz. This laser is currently being exchanged against a similar laser with 20 W at the same pulse repetition frequency. The light backscattered from the atmosphere is received with a 40 cm telescope. Four channels detect the elastic backscatter signal, two rotational Raman signals, and the water vapor Raman signal. The signal intensities are detected in analog and photon counting mode with raw resolutions of 7.5 m and 10 s. Typical resolutions of the data products are 100 m and 10 s.

A compact and automated further development of this system, ARTHUS for Atmospheric Raman Temperature and Humidity Sounder, uses already this powerful diode-pumped laser transmitter (20 W at 355 nm, 200 Hz).

Measurement examples of all instruments will be presented and an outlook to future developments will be discussed.
Feature-based classification of European windstorms
Authors: Passow Christian , Ulbrich Uwe , Rust Henning
Published: March 2020

Scientific work on European windstorms mainly focused on local damages, location (tracks), temporal evolution or the overall severity, often measured by severity indices of different definitions. Each of the aforementioned windstorm properties is directly related to important characteristics within the windstorm itself, such as wind speed, duration, spatial extent or internal variablity. Variation or changes within these characteritics are therefore defining aspects in the spatial and temproal evolution of windstorm or their overall severity in general. As a step towards a better understanding of such variations, we intend to classify windstorms based on their characteristics. For this purpose, we categorize individual storms based on their characteristics using a K-Means clustering procedure. As a result, we get a catalog of more than 400 storm tracks, each track having properties similar to the 20 most severe storm events in the European region. In an attempt to better understand driving mechanisms behind severe European windstorms, the catalog will be further examined to find key parameters that determine the cluster characteristics, such as large-scale situations or the sequencing of clusters.
Influence of river pattern and sediment input on estuary morphology
Authors: Baar Anne , Bastianon Elena , Braat Lisanne , Parsons Daniel
Published: March 2020

Alluvial estuaries are dynamic landscapes that are very sensitive to changes in boundary conditions such as river discharge and sediment supply. A better understanding of the influence of upstream river discharge and sediment input on the development of estuaries under various scenarios requires long-term morphodynamic models, to both predict future changes and improve geological interpretations by storing the stratigraphy. Past 1D model studies have shown that upstream river discharge has a significant effect on the equilibrium bed profile of estuaries, but these studies ignore the effect of 2D bar and channel formation. Using 2D numerical models to predict the development of these systems on the scale of millennia proved to be difficult, since the modelled morphology is very sensitive to the choice in e.g. sediment transport predictor and bed slope effect. In this study, we use the knowledge of previous research that determined best parameter settings for realistic river and bar patterns to model long-term and large-scale estuary morphodynamics in Delft3D. Our objective is to quantify the effects of river discharge and sediment supply on the shape of estuaries and its deposits. Firstly, we systematically varied upstream river width and tidal amplitude to examine the relation between upstream river pattern and estuary dimensions. We quantified e.g. braiding index, bar dimensions, and tidal excursion length. Results show that flood flow velocities and tidal prism are less influenced by river discharge than suggested by 1D models, and are significantly influenced by the braiding index of the river. With relatively high tides, estuary bar patterns depend on tidal amplitude, while with lower tides estuary depth and braiding index are related to upstream river width and discharge. Next steps will include varying discharge to study the effect on the rate of adaptation of the river and estuary, and varying the grain size of the sediment input at the upstream boundary. We will input coarse sediment to explore differences between fluvial deposits and tidal currents, and fine sediment to use the model for research related to biofilm.
Investigation of droplet-mediated sensible and latent heat fluxes in a turbulent air flow over a waved water surface by direct numerical simulation
Authors: Druzhinin Oleg
Published: March 2020

The objective of the present study is to investigate sensible and latent heat transfer mediated by evaporating saline droplets in a turbulent air flow over a waved water surface by performing direct numerical simulation. Equations of the air-flow velocity, temperature and humidity are solved simultaneously with the two-way-coupled equations of individual droplets coordinates and velocities, temperatures and masses. Two different cases of air and water surface temperatures,Ta = 27 0C, Ts = 28 0C,  and Ta = -10 0C, Ts = 0 0C, are considered and conditionally termed as "tropical cyclone" (TC) and "polar low"  (PL) conditions, respectively. Droplets-mediated sensible and latent heat fluxes, QS and QL, are integrated along individual droplets Lagrangian trajectories and evaluated as distributions over droplet diameter at injection, d, and also obtained as Eulerian, ensemble-averaged fields. The results show that under TC-conditions, the sensible heat flux from droplets to air is negative whereas the latent heat flux is positive, and thus droplets cool and moisturize the carrier air. On the other hand, under PL-conditions, QS and QL  are both positive, and QL – contribution is significantly reduced as compared to QS - contribution. Thus in this case, droplets warm up the air. In both cases, the droplet-mediated enthalpy flux, QS + QL , is positive, vanishes for sufficiently small droplets (with diameters d ≤ 150 μm) and further increases with d. The results also show that the net fluxes are reduced with increasing wave slope.

This work is supported by the Ministry of Education and Science of the Russian Federation (Task No. 0030-2019-0020). Numerical algorithms were developed under the support of RFBR (Nos. 18-05-60299, 18-55-50005, 18-05-00265, 20-05-00322). Postprocessing was performed under the support of the Russian Science Foundation (No. 19-17-00209).
A weather system perspective on winter-spring rainfall variability in southeastern Australia during El Niño
Authors: Hauser Seraphine , Grams Christian M. , Reeder Michael J. , McGregor Shayne , Fink Andreas H. , Quinting Julian F.
Published: March 2020

The El Niño Southern Oscillation (ENSO) is typically associated with below-average rainfall in the winter-spring season in southeastern Australia. However, there is also a large case-to-case variability pointing to the non-linear relationship of El Niño strength and the impact on east Australian rainfall. Despite recent progress in understanding the linkage of remote climate drivers and this variability, the dynamical processes by which the drivers transmit their influence on rainfall are not fully understood. With this study, we aim to advance the dynamical understanding by relating patterns of monthly rainfall anomalies over southeastern Australia to a novel dataset of objectively identified weather systems derived from ERA-Interim reanalyses.

We find 4 rainfall anomaly patterns in the austral winter-spring season (JJASON) with above-average rainfall (Cluster 1), below-average rainfall (Cluster 2), above-average rainfall limited to the East Coast (Cluster 3) and above-average rainfall limited to the South Coast (Cluster 4) in southeastern Australia. Changes in the frequency of weather systems explain partly the rainfall anomalies in the clusters. Results indicate a significant increase of weather system activity in Cluster 1 and a weakening of weather system activity in Cluster 2. In Cluster 3, enhanced blocking favors the development of cut-off lows on its northeastern flank leading to increased rainfall along the East Coast. Positive rainfall anomalies along the South Coast are associated with frontal rainfall due to an equatorward shift of the midlatitude storm track (Cluster 4). Most of the rainfall is produced by warm conveyor belts and cut-off lows but the contributions strongly vary between the clusters. We further find that anomalies in rainfall result from changes in rainfall frequency more than in rainfall intensity. By calculating backward trajectories of warm conveyor belt and cut-off low rainfall, we point to the importance of moist air masses from the Coral Sea and the northwest coast of Australia for wet months. Air parcels, that end up in WCB or cut-off low rainfall, reach southeastern Australia from the dry remote areas to the north and not as one would expect from the Southern Ocean.
Subglacial water pressure records from a fast-flowing outlet glacier in Greenland
Authors: Doyle Samuel , Hubbard Bryn , Christoffersen Poul , Bougamont Marion , Law Robert , Chudley Tom , Prior-Jones Mike , Schoonman Charlotte
Published: March 2020

Glacier motion is resisted by basal traction that can be reduced significantly by pressurised water at the ice-bed interface. Few records of subglacial water pressure have been collected from fast-flowing, marine-terminating glaciers despite such glaciers accounting for approximately half of total ice discharge from the Greenland Ice Sheet.  The paucity of such measurements is due to the practical challenges in drilling and instrumenting boreholes to the bed, in areas that are often heavily-crevassed, through rapidly-deforming ice that ruptures sensor cables within weeks. Here, we present pressure records and drilling observations from two sites located 30 km from the calving front of Store Glacier in West Greenland, where ice flow averages ~600 m yr-1.  In 2018, boreholes were drilled 950 m to the bed near the margin of a large, rapidly-draining supraglacial lake. In 2019, multiple boreholes were drilled ~1030 m to the bed in the centre of the drained supraglacial lake, and in close proximity to a large, active moulin. All boreholes drained rapidly when they intersected or approached the ice-bed interface, which is commonly interpreted as indicating connection to an active subglacial drainage system. Neighbouring boreholes responded to the breakthrough of subsequent boreholes demonstrating hydrological or mechanical inter-connection over a distance of ~70 m. Differences in the time series of water pressure indicate that each borehole intersected a distinct component of the subglacial hydrological system. Boreholes located within 250 m of the moulin reveal clear diurnal cycles either in phase or anti-phase with moulin discharge. Pressure records from boreholes located on the lake margin, however, show smaller amplitude, and less distinct, diurnal cycles superimposed on longer-period (e.g. multiday) variability. We compare these datasets to those in the literature and investigate consistencies and inconsistencies with glacio-hydrological theory.
Atmospheric aridity and apparent soil moisture drought in European forest during heatwaves
Authors: Teuling Ryan , Lansu Eva , van Heerwaarden Chiel , Stegehuis Annemiek
Published: March 2020

Land-atmosphere feedbacks, in particular the response of land evaporation to vapour pressure deficit (VPD) or the dryness of the air, remain poorly understood. Here we investigate the VPD response by analysis of a large database of eddy-covariance flux observations and simulations using a conceptual model of the atmospheric boundary layer. Data analysis reveals that under high VPD, forest in particular reduces evaporation and emits more sensible heat. In contrast, grass increases evaporation and emits less sensible heat. Simulations show that this VPD feedback can induce significant temperature increases over forest of up to 2 K during heat wave conditions. It is inferred from the simulations that the effect of the VPD feedback corresponds to an apparent soil moisture depletion of more than 50%. This suggests that previous studies may have incorrectly attributed the effects of atmospheric aridity on temperature to soil dryness.
Drought Events and Causes in North China in 2018
Authors: Feng Jianying , Zhang Yu , Wang Suping
Published: March 2020

In 2018, severe meteorological drought occurred in the southwest of Northeast China, the  east-central of Inner Mongolia and the east of North China. Drought shows obvious regional and stage nature .In early March, mild to moderate drought appeared in North China, followed by severe drought in parts of northern and eastern of Hebe province. After the middle of April, the drought was alleviated obviously, and the drought in the southwest of Northeast China began to show signs. In  early May, there was mild to moderate drought in the central and eastern part of Inner Mongolia, and the drought in Northeast China developed. From June to early August, severe drought and above occurred in parts of Liaoning province , Inner Mongolia and North China. In mid-August, in addition to Liaoning province and North China, there were scattered light to moderate drought, drought relief in the northern China. In early September, the drought in North China increased and the range spread northward, and there were droughts of different degrees in the whole North China.In winter, there is only mild drought in North China.

The drought in this region has affected the agricultural production in different degrees. Spring sowing is blocked in the east of Inner Mongolia and the west of Northeast China, and high temperature in summer leads to the development of drought, corn and rice and other crops are adversely affected.

From spring to autumn, the precipitation in most parts of the drought disaster  area is less than 10-40%, and the temperature is higher than 1-2 ℃. The lack of precipitation and abnormal high temperature accelerated the loss of surface water, which resulted in the occurrence of drought in this area.

In spring of 2018, the middle and high latitudes are generally controlled by flat air flow, which is not conducive to the establishment of trough ridge, making the northern dry area lack of favorable precipitation conditions; in summer and autumn, the existence of Baikal Lake high-pressure ridge, resulting in circulation patterns that are not conducive to the precipitation conditions in the northern dry area. Among them, the obvious flat air flow in spring and the obvious high pressure ridge in summer are the main reasons for the outstanding drought in spring and summer in the northern arid area.
The challenge of combining initialised and uninitialised decadal projections
Authors: Murphy James
Published: March 2020

The challenge of combining initialised and uninitialised decadal projections

James Murphy, Robin Clark, Nick Dunstone, Glen Harris, Leon Hermanson and Doug Smith

During the past 10 years or so, exploratory work in initialised decadal climate prediction, using global climate models started from recent analyses of observations, has grown into a coordinated international programme that contributes to IPCC assessments. At the same time, countries have continued to develop and update their national climate change scenarios.  These typically cover the full 21st century, including the initial decade that overlaps with the latest initialised forecasts. To date, however, national scenarios continue to be based exclusively on long-term (uninitialised) climate change simulations, with initialised information regarded as a separate stream of information.

We will use early results from the latest UK national scenarios (UKCP), and the latest CMIP6 initialised predictions, to illustrate the potential and challenges associated with the notion of combining both streams of information. This involves assessing the effects of initialisation on predictability and uncertainty (as indicated, for example, by the skill of ensemble-mean forecasts and the spread amongst constituent ensemble members). Here, a particular challenge involves interpretation of the “signal-to-noise” problem, in which ensemble-mean skill can sometimes be found which is larger than would be expected on the basis of the ensemble spread. In addition to initialisation, we will also emphasise the importance of understanding how the assessment of climate risks depends on other features of prediction system design, including the sampling of model uncertainties and the simulation of internal climate variability.
Towards the estimation of DOC from space in the open ocean
Authors: Bonelli Ana Gabriela , Loisel Hubert , Vantrepotte Vincent , Jorge Daniel , Mangin Antoine , Demaria Julien
Published: March 2020

The Dissolved Organic Carbon (DOC) represents the largest pool of organic carbon and the most active carbon compartment in the ocean. Describing the spatio-temporal dynamics of the oceanic DOC in response to variation in the physical of biological forcings is therefore crucial for better understanding the global carbon cycle. The DOC distribution and its temporal dynamics is however currently not well known.

In the recent years several works have demonstrated the possibility to assess from space the DOC distribution in the coastal ocean thanks to direct relationships between DOC and the optical properties of colored dissolved organic matter (CDOM). Such CDOM-DOC relationships are not applicable for the open ocean water due making more complex the DOC estimation from space in the latter environments. Here we present first results documenting an alternative method for estimating DOC from satellite imagery which rely on the use of a neural network which combines different physical and biogeochemical input variables (SST, SSS, PAR, aCDOM and Chl-a).