bluuebunny/crossref_metadata_2025 huggingface dataset:
Combination of stress-controlled erosion and tensile failures during development of piping conduits in locked sand
Authors: Vojtisek Jan , Bruthans Jiri , Slavik Martin
Published: March 2020

Piping is an erosion process in which cracks and macropores extend into channels with a diameter of cm or more. This process is important for the formation of highly permeable porosity, failure of the levees, formation of gullies and intense erosion of agricultural soil. In this research we studied the evolution of conduits in Střeleč locked sand (SLS). This material composes mainly of quartz and resembles friable sandstone. Study was done in Střeleč quarry (Czech Republic), where depression in the regional water table (decrease of water table by ~20 m) due to the water pumping causes fast flow (up to 40 cm/s) through fractures in the SLS body. Large conduit systems developed along fracture zones that divide the SLS body into subvertical blocks with a width of cm to tens of cm in each fracture zone. Erosion starts at water table and blocks bordered by fractures are eroded by the fast water flow, especially the parts that are in stress shadows due to inefficient loading from the surrounding sandstone mass. Blocks whose base is eroded tend to collapse, which leads to the creation of free space above the water table and also possibly destabilization of the sides. Empty space propagates upward mostly meters but sometimes tens of meters toward ground surface. Experiments showed that the SLS is prone to erosion when it is under low gravity induced stress. In addition to observation of the existing conduits, the experiments focused on the evolution of transversal section of conduits in SLS were performed. Experimental erosion was done on fracture systems exposed in quarry by the flow of water from the hose. Sequence of photos of fracture zones evolving into conduit during experiments was taken and the evolution of the transverse section of conduits was observed. By this method the blocks were eroded to a depth of several decimeters. Based on field experiments and time-laps photos two erosion mechanisms are responsible for conduits evolution. While the less thick blocks are eroded mainly by rapid water flow, thicker blocks are eroded by tension failures (gravity driven wasting). The tension failure dominates, forming about 65 % of total erosion.

Many thanks to the management of Střeleč Quarry for enabling of the field documentation and experiments. The research was supported by Charles University Grant Agency (GAUK #1292119).
High-resolution pan-European multi-model simulations of hydrologic states and fluxes
Authors: Naz Bibi S , Sharples Wendy , Goergen Klaus , Kollet Stefan
Published: March 2020

 High-resolution large-scale predictions of hydrologic states and fluxes are important for many regional-scale applications and water resource management. However, because of uncertainties related to forcing data, model structural errors arising from simplified representations of hydrological processes or uncertain model parameters, model simulations remain uncertain. To quantify this uncertainty, multi-model simulations were performed at 3km resolution over the European continent using the Community Land Model (CLM3.5) and the ParFlow hydrologic model. While Parflow uses a similar approach as CLM in simulating the snow, vegetation and land-atmosphere exchange processes, it simulates three-dimensional variably saturated groundwater flow solving Richards equation and overland flow with a two-dimensional kinematic wave approximation. The CLM3.5 uses a simple groundwater model to account for groundwater recharge and discharge processes. Both models were driven with the COSMO-REA6 reanalysis dataset at 6km resolution for the time period from 2000 to 2006 at an hourly time step, and both used the same datasets for the static input variables (such as topography, vegetation and soil properties). The performance of both models was analyzed through comparisons with independent observations including satellite-derived and in-situ soil moisture, evapotranspiration, river discharge, water table depth and total water storage datasets. Overall, both models capture the interannual variability in the hydrologic states and fluxes well, however differences in performance between models showed the uncertainty associated with the representation of hydrological processes, such as groundwater flow and soil moisture and its control on latent and sensible heat fluxes at the surface.
Connecting data streams with On-Demand Services in the Alpine Environmental Data Analysis Centre
Authors: Munke Johannes , Götz Alexander , Heller Helmut , Hachinger Stephan , Laux Dominik , Goussev Oleg , Handschuh Jana , Wüst Sabine , Bittner Michael , Mair Roland , Wittmann Bianca , Rehm Till , Beck Inga , Neumann Markus
Published: March 2020

The AlpEnDAC (Alpine Environmental Data Analysis Center) platform (www.alpendac.eu) aims to collect scientific data measured on different high-altitude research stations in the alpine region and beyond. It provides research data management, analysis and simulation services and supports the research activities of the VAO (Virtual Alpine Observatory) community.

With funding from the Bavarian State Ministry of the Environment and Consumer Protection, a new development cycle of the platform was launched in 2019. Novel components for Computing on Demand (CoD), Service on Demand (SoD) and Operating on Demand (OoD) will be integrated into the system. These will help to implement a near-real-time (NRT) decision support for the scientist during measurement processes and a better control of the measurement process.

In this work, the authors present a stream processing architecture to couple the new CoD, SoD and OoD components. Data from measurements (or also simulations) are normally ingested via a representational state transfer application programming interface (REST API) into the AlpEnDAC system. Before such data are stored in the data base, they will be run through a central stream processing engine, based on a message queue (e.g. Apache Kafka) and a series of specialized workers to process the data. A rule engine and analytics tools are connected to this engine and allow the automatic triggering of, e.g., measurements, HPC simulations, or evaluation and notification services in NRT. The services will be usable and configurable, as much as possible, via the AlpEnDAC web portal where also certain measurement device settings can be adjusted. With these developments, we want to make environmental scientists profit from NRT data collection and processing, as it is already an everyday tool, e.g., in the Internet-of-Things sector and in commercial applications.
Effect of trees on street canyon ventilation
Authors: Fellini Sofia , De Giovanni Alessandro , Marro Massimo , Ridolfi Luca , Salizzoni Pietro
Published: March 2020

Due to the overall growth of the world population and to the progressive shift from rural to urban centres, 70% of the world population is expected to live in urban areas in 2050. This trend is alarming when related to the constant decline of urban air quality at the global level. To cope with this rapid urbanization, solutions for sustainable cities are extensively sought. In this framework, the mitigation of air pollution in street canyons plays a crucial role. The street canyon (a street flanked by high buildings on both sides) is the fundamental unit of the urban tissue, as well as a vital public and residential space. Street canyons are particularly vulnerable to air pollution due to traffic emissions, low ventilation conditions, and the number of citizens exposed. Tree planting in street canyons is often used as a pollution mitigation strategy, due to the filtering effect of vegetation on airborne pollutants. However, from the aerodynamic point of view, trees can obstruct the wind flow thus reducing canyon ventilation and leading to higher pollutant concentrations. In this framework, we present the results of an experimental study aimed at evaluating how tree planting influences the flow and concentration fields within a street canyon. The study was carried out in a recirculating wind tunnel. An idealised urban district was simulated by an array of square blocks, whose orientation with respect to the incident wind was varied. Within this urban geometry, two rows of model trees were arranged at the sides of a street canyon. Three configurations with different spacing between the trees were considered. A passive scalar was injected from a line source placed at ground level to simulate traffic emissions. Concentration and flow field measurements were performed in several cross-sections of the street canyon. Results showed the effect of trees on the spatial distribution of pollutants. Moreover, a characteristic exchange velocity between the street canyon and the overlying atmosphere was estimated to quantify the overall canyon ventilation under several wind directions and different planting densities. These preliminary results provide city planners with first recommendations for the sustainable design of urban environments. Moreover, the experimental dataset is valuable in validating numerical simulations of air pollution in cities accounting for urban vegetation.
Early to Late Pliocene climate change in the mid-latitude North Atlantic
Authors: Voelker Antje H. L. , Sierro Francisco J. , Naafs B. David A. , Andersen Nils , Kuhnert Henning
Published: March 2020

The early Pliocene, with atmospheric CO2 concentrations at levels similar to today, is seen as a case study for Earth’s future climate evolution. During this period the progressive closing of the Central American Seaway led to increased poleward heat and salt transport within the Atlantic with North Atlantic Deep Water (NADW) becoming warmer and saltier and resulting in an enhanced Atlantic Meridional Overturning Circulation (AMOC). In order to evaluate how stable the Pliocene AMOC really was, we are producing surface and deep-water records for IODP Site U1313 (41°N, 33°W, 3412m) for the interval from 3.3 to 4.1 Ma. This site is ideally located to monitor past AMOC changes with North Atlantic Drift waters at the surface and NADW, exported by the deep western boundary current, in the deep. Surface water conditions are reconstructed based on the stable isotope data of planktonic foraminifer species Globigerinoides ruber (white) or Globigerinoides extremus with centennial-scale resolution and on sea-surface temperatures (Uk37' alkenone thermometer) with an average 4 ky resolution. Stable isotope records of the benthic foraminifer genus Cibicidoides reveal changes in the deep water.

Besides the interglacial/glacial cycles, higher frequency oscillations are recorded in both the planktonic and benthic foraminifer stable isotope records. Varying surface water conditions, especially during Late Pliocene interglacial periods, are reflected in the Globigerinoides isotope data and appear to be linked to salinity changes since they are not recorded in the sea-surface temperature data. The high-frequency oscillations in the planktonic isotope records are related to precession (insolation) forcing, especially its harmonics in the 5.5 ky and 11 ky ranges. The benthic δ13C values indicate nearly continuous NADW presence and confirm a strong AMOC throughout the studied interval, also during most of the glacial periods. Excluding the pronounced M2 glacial, glacial stage Gi 6 had a stronger impact on the AMOC, as revealed by cooler, less ventilated surface waters and a less ventilated NADW, than Gi 2 and Gi 4. Overall, the AMOC was strong throughout, but experienced high frequency oscillations at a level similar to the middle Pleistocene interglacial periods.
Indian Ocean impact on ENSO evolution 2014-2016 in a set of seasonal forecasting experiments
Authors: Mayer Michael , Alonso Balmaseda Magdalena
Published: March 2020

In 2014 the scientific community and forecasters were expecting a major El Nino event, which was suggested by physical indicators and predicted by several seasonal forecasting systems. However, only moderately warm El Nino – Southern-Oscillation (ENSO) conditions materialized in 2014, but one year later in boreal winter 2015/16, one of the strongest El Ninos on record occurred. Moreover, the 2015/16 El Nino exhibited very unusual energetics: Despite warm conditions in the tropical Pacific in 2014 and especially 2015, its ocean heat content (OHC) did not decrease during that period, which usually is the case during El Nino events. Overall, the 2014-16 evolution of the tropical Pacific was quite different from the evolution during the 1997/98 El Nino, which exhibited exceptionally strong Pacific OHC discharge. This discrepancy was attributed at least partly to the anomalously warm Indian Ocean and the exceptionally weak Indonesian Throughflow transports during 2015-16 that kept Pacific OHC at high levels.

This contribution aims to elucidate the role of the Indian Ocean in the tropical Pacific Ocean evolution during ENSO for the two periods February 1997-1999 and February 2014-2016. For this purpose, we perform initialized two-year predictions using the ECMWF seasonal forecasting system. To isolate the role of the Indian Ocean, we carry out hindcasts with unperturbed ocean initial conditions and hindcasts with swapped Indian Ocean initial conditions, where the 2014 (1997) hindcasts use Indian Ocean initial conditions from 1997 (2014). We first investigate the impact of the Indian Ocean on the strength of the Indonesian Throughflow and the evolution of the tropical Pacific heat budget. Second, we seize these experiments to explore the impact of the Indian Ocean state on two-yearly ENSO evolution, especially on the probability of extreme events, and which role the atmospheric bridge plays versus the oceanic bridge.
Towards a neural network approach for automated recognition of lichen-covered prehistoric carvings at Stonehenge
Authors: Leong Gavin , Brolly Matthew
Published: March 2020

Petroglyphs (rock carvings) are a form of tangible cultural heritage that have been used to investigate cultural change and understand the origins of art and belief. However, many sites with rock carvings are accompanied by lichen. They often obscure these panels of rock art, rendering the cultural artefacts inaccessible to study, documentation and public enjoyment. Above all, lichen-covered rock carving is under the threat of lichen-attributed physical and chemical erosion. But evidence of a simultaneous protective role played by lichen has prompted concern that the removal of lichen may result in more rapid deterioration of the rock art.

Stonehenge, a UNESCO World Heritage site, provides a strong case study as dense lichen covers roughly a quarter of its above-ground stone surfaces, rendering it inaccessible to examination. 72 Early Bronze Age carvings have recently been found on the bare stone surfaces prompting concerns that lichen may be obscuring prehistoric rock art.

As a first step towards creating a technique for revealing carvings beneath lichen, an interdisciplinary approach was implemented. Photogrammetry-derived 3-D modelling and machine learning code written in Python were combined to create a method for identifying repeating carving motifs on bare stone surfaces. This code, a neural network classifier called MeshNet, “learns” 3-D shape representation from mesh-based 3-D models and was adapted to capture features of the rock carvings. After training on 150 models (75 carving and non-carving areas of the rock surface each) and testing on 38 models (19 carvings and non-carvings each), our method achieved 84.2% accuracy.

In previous work, we have shown that it is possible to recover indications of carvings covered by digitally simulated lichen. Thus, it will be possible to repeat our method on the same carvings with coverage of simulated lichen to compare accuracies. If successful, it will be the first demonstration of a technique capable of revealing carvings obscured by lichen using only a surface imaging technique.

Our current methodology for identifying rock carvings can be adopted by conservators and rock art site managers. It serves as a tool for non-rock art specialists to discover and digitally record repeating rock carving motifs. With further development using simulated lichen, it will partially alleviate the need to remove lichen from panels of rock carvings.

As our method is scale invariant, it could also be adapted for use in airborne and UAV platforms for discovering e.g. repeating natural landforms hidden by forest cover and buried Roman roads in 3-D terrain maps.
India can't Wait to Act upon Climate Change as Heatwaves Claim Life
Authors: Sudharsan Naveen , Singh Jitendra , Ghosh Subimal , Karmakar Subhankar
Published: March 2020

In the recent past, India has experienced an increase in daily maximum and minimum temperature by 0.8 to 1 °C and 0.2 to 0.3 °C, respectively, along with an increased number of heatwave days. Human fatality, morbidity and discomfort are often reported due to the frequent heatwaves in India. To understand the effect of humidity in heatwaves over India, here in this study, we have classified the heatwaves into oppressive (high temperature and high humidity) and extreme (high temperature and low humidity) using excess heat factor approach. The rate of increase in oppressive heatwave days is exceeding that of the extreme heatwave days, even though the total number of oppressive heatwave days is fewer than the extreme heatwave days in the considered period (1953 to 2013). Moreover, the oppressive heatwave days are found to be the fatal one, as it is well correlated with the heat-related deaths in India.

As per COP 21 agreement, countries pledged to maintain the global temperature well below a 2 °C above the pre-industrial levels while attempting to limit the same to 1.5 °C. Taking these two warming scenarios, we have identified the heatwave events in near-future (2035 to 2065) and far-future (2070 to 2100). The number of oppressive heatwave days is expected to show an alarming five-fold increase at 2 °C warming (comparing to the period 1976 to 2005) by the end of the century. Limiting the warming to 1.5 °C from the proposed 2 °C results in a 67% reduction in oppressive heatwave days. A substantial jump in the number of oppressive heatwave days when compared with extreme heatwave days proposes that the Indian population is expected to be severely affected by heatwaves in the future amidst inadequate adaptive measures.
Interpreting erosion frequency and magnitude from luminescence profiles in boulders
Authors: Brown Nathan , Moon Seulgi
Published: March 2020

Exposed bedrock is ubiquitous on terrestrial and planetary landscapes, yet little is known
about the rate of bedrock erosion at a granular scale on timescales longer than the
instrumental record. As recently suggested, using the bleaching depth of luminescence
signals as a measure of bedrock erosion may fit these scales. Yet this approach assumes
constant erosion through time, a condition likely violated by the stochastic nature of erosional
events. Here we simulate bleaching in response to power-law distributions of removal
lengths and hiatus durations. We compare simulation results with previously measured
luminescence profiles from boulder surfaces to illustrate that prolonged hiatuses are unlikely
and that typical erosion scales are sub-granular with occasional loss at mm scales,
consistent with ideas about microflaws governing bedrock detachment. For a wide range of
erosion rates, measurements are integrated over many removal events, producing
reasonably accurate estimates despite the stochastic nature of the simulated process. We
hypothesize that the greater or equal erosion rates atop large boulders compared to rates at
ground level suggest that subcritical cracking may be more influential than aeolian abrasion
for boulder degradation in the Eastern Pamirs, China.
Lithospheric structure of the Pannonian Basin using Rayleigh wave ambient noise tomography – preliminary results
Authors: Timkó Máté , Wiesenberg Lars , El-Sharkawy Amr , Wéber Zoltán , Meier Thomas ,   AlpArray Working Group
Published: March 2020

We used Rayleigh wave ambient noise tomography to investigate the crust and uppermost mantle structure of the Pannonian Basin. The Pannonian Basin and the surrounding orogens are located within the arcuate Alpine–Carpathian mountain chain in Central Europe. It is a back-arc basin characterized by a thinned lower crust and an updoming mantle. Benath the basin both the crust and the lithosphere have smaller thickness than the continental average. Imaging the velocity structure of the crust and upper mantle may help us to better understand the structure and formation of the Carpathian–Pannonian region.

We used data from the permanent seismological stations of the broader Central European region together with the AlpArray Seismic Network (AASN) and analysed one-year seismic data from 2017. More than 18 thousand vertical component noise cross-correlation functions were calculated and Rayleigh wave inter-station phase velocity curves were determined using an automated measuring algorithm. Anisotropic phase velocity tomographic imaging were carried out for the whole Pannonian Basin between 2 and 40s periods (~5-60 km).

The locations of the retrieved phase-velocity anomalies consistent with the well-known geologic and tectonic structure of the area (deep basins and orogenic belts) and are comparable to recent tomographic models published in the literature.
Thermal energy pattern related with the temperature increasing due to intraplate and induced seismicity, Southern Norway, 2017-2018
Authors: Estay Rodrigo
Published: March 2020

Small seismological events recorded in southern Norway in the period of 2017-2018 were used to calculate the sudden co-seismic temperature increase using a simple stress-drop model. In order to estimate the net production of thermal energy, both, industry explosions and natural events were included.  The range of resultant average temperature rise, with a maximum of ~ 143 ° C for a Mw =3.5, is proposed as an additional constituent that explain the weakness areas related to the high amount of intracrustal seismicity, mainly regarding the anisotropic thermal expansion of rocks and the flash heating thermal process produced by historical earthquakes with magnitudes over . The temperature values were subsequently used to estimate the thermal energy in 2D and 3D cumulative patterns in the area, as well as the total amount of energy that is available regarding seismic activity. The results were correlated with existing geological information, considering lineaments and heat flux data. Areas with high values of thermal energy seems to be spatially linked with both high heat flux zones and high density of lineaments, mainly to the south of the Trøndelag Platform as well as to the south of the Møre basin.
What urban streamflow can tell us about changes in water storage and streamflow due to development
Authors: Thomas Brian
Published: March 2020

The urbanization of a watershed radically impacts how watersheds store, transmit and discharge water. Although urbanization’s effects on floods, droughts, and water supply have been explored in recent decades through land-use modeling, hydrological modeling, remote sensing, and empirical approaches, clarification of these effects remains a challenge due to limited availability and accessibility of useful data. Streamflow records for three neighboring watersheds in Baltimore, an urbanized watershed, an urbanizing watershed and a natural watershed, provide a unique opportunity to study the influence of urbanization on watershed function.  The 5-minute instantaneous discharge records span an increase in residential development of the urbanizing watershed.  Coupling the streamflow and development records allows direct comparison of hydrologic changes with spatial patterns of land use change.  Recession analysis was used to evaluate altered hydrologic response, particularly relationships between watershed storage and streamflow that may occur during urbanization.  Recession approaches were applied using variable time steps to estimate the time derivative of streamflow (dQ/dt) to avoid known issues in parameter estimation driven by the time derivative of a noisy time series. Several hypotheses are tested, including comparisons to conceptual models of hydrologic change that would be expected in urbanizing watersheds.  Preliminary results suggest that hydrologic changes are notable during periods of intense development, with recession plot characteristics markedly variable in urbanizing and urban watersheds as compared to the natural watershed. Analysis of streamflow records during the process of urbanization reveals groundwater-surface water interactions driven by urban development previously only observed over relatively shorter time periods. These findings can inform implementation of sustainable design of storm water management and future development planning.
Implementing FAIR Principles in the IPCC Assessment Process
Authors: Juckes Martin , Pirani Anna , Pascoe Charlotte , Matthews Robin , Stockhause Martina , Chen Bob , Xiaoshi Xing
Published: March 2020

The Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC) have provided the scientific basis underpinning far reaching policy decisions.The reports also have a huge influence on public debate about climate change. The IPCC is not responsible either for the evaluation of climate data and related emissions and socioeconomic data and scenarios or for the provision of advice on policy (reports must be “neutral, policy-relevant but not policy-prescriptive”). These omissions may appear unreasonable at first sight, but they are part of the well-tested structure which enables the creation of authoritative reports on the complex and sensitive subject of climate change. The responsibility for evaluation of climate data and related emissions and socioeconomic data and scenarios remains with the global scientific community. The IPCC has the task of undertaking an expert, objective assessment of the state of scientific knowledge as expressed in the scientific literature. The exclusion of responsibility for providing policy advice from the IPCC remit allows the IPCC to stay clear of discussions of political priorities. 

These distinctions and limitations influence the way in which the findable, accessible, interoperable, and reusable (FAIR) data principles are applied to the work of the IPCC Assessment. There are hundreds of figures in the IPCC Assessment Reports, showing line graphs, global or regional maps, and many other displays of data and information. These figures are put together by the authors using data resources which are described in the scientific literature that is being assessed. The figures are there to illustrate or clarify points raised in the text of the assessment. Increasingly, the figures also provide quantitative information which is of critical importance for many individuals and organisations which are seeking to exploit IPCC knowledge. 

This presentation will discuss the process of implementing the FAIR data principles within the IPCC assessment process. It will also review both the value of the FAIR principles to the IPCC authors and the IPCC process and the value of the FAIR data products that the process is expected to generate.
The effects of climate warming inferred from an Adamello Glacier (Italy) ice core
Authors: Festi Daniela , Jenk Theo , Schwikowski Margit , Maggi Valter , Oeggl Klaus
Published: March 2020

Glacier ice cores from mid latitude are capable of retaining essential information on past climate and anthropic activities at high time resolution. However, Alpine glaciers are also highly sensitive to the current atmospheric warming, which is seriously compromising the quality of the signal preserved in the ice and threatens the very persistence of these ice bodies.

In this context, we present new chronological and palynological results from a 46 m deep ice core extracted from the Adamello glacier in the locality Pian di Neve (3100 m a.s.l.). The glacier is situated in northern Italy and it is the most extened (16,3 km²) and deepest (257 m) glacier of the Southern European Alps. Ice core chronological results obtained from Cs-137, Pb- 210 isotopic analyses, black carbon and pollen annual layer counting will be discussed in the frame of the effects of the ongoing climate warming on Alpine glaciers. Furthermore, we will discuss the palynological data gained from the ice in terms of vegetation changes driven by the combined effect of intensive human activities and alarming climate change in the post World War II period.
Defining the Green’s function derivative for imaging & inversion without the Born approximation
Authors: Cummings Dominic , Curtis Andrew
Published: March 2020

The goal of most seismic experiments is to use data readily available at the surface of the Earth to characterise the inaccessible interior. In order to solve this inverse problem, we generally make a number of assumptions about either the data or the Earth to simplify the physics. For example, we often assume that the Earth is an acoustic medium rather than an elastic medium, which for data without S-waves makes the problem far more tractable computationally than the full elastic problem.

One of the most common assumptions made about the data is the single-scattering assumption, widely known as the Born approximation. Clearly this is invalid in the presence of multiple scattering, which occurs in all seismic experiments. Despite this, the majority of imaging and inversion methods applied to seismic data are dependent on this assumption, including most full waveform inversion algorithms. As a consequence, seismic data processing requires a great deal of effort to remove multiply scattered waves from data.

A key justification for making this assumption is that a priori we can only estimate a relatively smooth Earth model that does not predict multiply scattered waves. However, with the recent emergence of so-called Marchenko methods, we now have access to full Green’s functions between sources and receivers at the Earth’s surface and virtual source or receiver locations inside the Earth’s interior, Green’s functions which can be estimated using only recorded reflection data and an estimate of the direct (non-scattered) wavefield travelling into the subsurface. As Marchenko methods become more commonplace, our justification for the single-scattering assumption diminishes, and hence we require new methods to use this information.

By iterating the Lippmann-Schwinger equation, we define a new compact form of the Frechét derivative of the Green’s function that involves all orders of scattering. In combination with Green’s functions obtained by a Marchenko method, these may be used for imaging and inversion of seismic data. We will describe an example of such a scheme, which we call “Marchenko Lippmann-Schwinger Full-Waveform Inversion”, to demonstrate how our redefined Green’s function derivative may be applied to solve seismic inverse problems for the Earth’s subsurface structure.
Lagrangian Data Assimilation of Surface Drifters to Support Ocean and Coupled Model Initialization
Authors: Sun Luyu
Published: March 2020

The air-sea interface is one of the most physically active interfaces of the Earth's environments and significantly impacts the dynamics in both the atmosphere and ocean. In this study, we discuss the data assimilation of surface drifters, of which the dynamic motions are highly relevant to the instant change of both surface wind field and underlying ocean flow fields. We intend to take advantage of this relationship and improve the estimation of the model initialization in both ocean and coupled atmosphere-ocean systems.

The assimilation of position data from Lagrangian observing platforms is underdeveloped in operational applications because of two main challenges: 1) nonlinear growth of model and observation error in the Lagrangian trajectories, and 2) the high dimensionality of realistic models. In this study, we first propose an augemented-state Lagrangian data assimilation (LaDA) method that is based on the Local Ensemble Transform Kalman Filter (LETKF). The algorithm is tested with “identical twin” approach of Observing System Simulation Experiments (OSSEs) using the ocean model. Examinations on both of the eddy-permitting and the eddy-resolving Modular Ocean Model of the Geophysical Fluid Dynamics Laboratory (GFDL) are tested, which is intended to update the ocean states (T/S/U/V) at both the surface and at depth by directly assimilating the drifter locations. Results show that with a proper choice of localization radius, the LaDA can outperform conventional assimilation of surface in situ temperature and salinity measurements. The improvements are seen not only in the surface state estimate, but also throughout the ocean column to deep layer. The impacts of localization radius and model error in estimating accuracy of both fluid and drifter states are further investigated. In the second section, we investigate the LaDA within a Strongly Coupled Data Assimilation (SCDA) system using the simplified Modular Arbitrary-Order Ocean-Atmosphere Model (MAOOAM), a three-layer truncated quasi-geostrophic model. Results show that assimilating the surface drifter locations directly is capable of improving not only the ocean states but also the atmosphere states as well. We then compare it to the conventional approach to assimilate the approximated velocities instead of the direct drifter locations and it shows that the assimilating drifter locations outperforms the other approach.
Counterstreaming strahls and dropouts observed in pitch angle distributions of suprathermal electrons as possible signatures of local particle acceleration in the solar wind
Authors: Khabarova Olga , Zharkova Valentina , Xia Qian , Malandraki Olga
Published: March 2020

We present multi-spacecraft observations of pitch-angle distributions (PADs) of suprathermal electrons at ~1 AU which cannot be easily interpreted within the classical paradigm that all suprathermal electrons originate in the solar corona. We suggest that suprathermal electrons accelerated locally in the solar wind are mixed up with the well-known population of electrons of solar origin. Using PIC simulations, we show that key PAD features such as (i) heat flux dropouts and vertical PAD stripes encompassing reconnecting current sheets (RCSs), (ii) bi-directionality of strahls, and (iii) dramatically different PAD patterns observed in different energy channels can be explained by the behavior of electrons accelerated up to hundreds eV directly in the solar wind while thermal particles pass through local RCSs and/or dynamical 3D plasmoids (or 2D magnetic islands).
Defining the most suitable source of irrigation water for farmers and communities: a socio-agricultural model
Authors: Vico Giulia , Tamburino Lucia , Rigby James R , Di Baldassarre Giuliano
Published: March 2020

Supplemental irrigation is critical to ensure high and stable crop yields in many regions. Water needs for irrigation will increase in the future, because of higher demands for food, feed and biofuels, and warmer, more extreme, climates. Water withdrawals for irrigation has led to plummeting water tables in many aquifers. Water harvesting like on-farm ponds can be a more sustainable approach to meet water requirements for irrigation. Nevertheless, whether groundwater or on-farm pond is the most suitable source of irrigation water for a single farmer and the whole community depends not only on the crop water demands and the unpredictability of rainfall, but also on the farmers’ preferences, in terms of risk aversion and long/short-view orientation and how they evolve in time. Here we couple the dynamics of crop development to that of soil water availability and water stored in on-farm ponds and aquifers. For a community of farmers, we also consider each farmer’s short/long-view orientation, and how it evolves in time. While general, the model is applied to the case of the Lower Mississippi River Basin, in the south-eastern USA, where irrigation has already led to a significant decline in groundwater levels. Results show that, for a single farmer, production maximization and risk of low yield minimization are often irreconcilable criteria when sizing the on-farm pond. Moreover, on farm ponds as source of irrigation can be more advantageous as source of water for the community, leading to a higher and more stable income. Yet, this choice is beneficial for the individual farmer only under extreme climates and in communities where the use of on-farm ponds is common.
Optimizing Ensemble-Based Inversions for Non-unique Volcanic Systems
Authors: Albright John , Gregg Patricia
Published: March 2020

In recent years, the advent of ensemble-based methods in volcanology has greatly facilitated the use of numerical models within data assimilation frameworks that had previously been limited, either computationally or mathematically, to simpler analytical models. Because numerical models can simulate stress conditions throughout the model space, recent inversions based on assimilated volcanic deformation data are able to track not only the basic parameters of a magma reservoir, but also how those parameters affect the overall mechanical stability of the system. Although this approach has produced successful forecasts and hind-casts of volcanic eruptions, much work remains to be done in assessing its full capabilities and limitations. In particular, non-uniqueness in how source parameters are reflected in surface deformation can significantly impair the inversion’s ability to resolve the magma system’s true state and, by extension, the likelihood of eruption. While this problem is nearly intractable for deep reservoirs, for which changes in pressure and size are indistinguishable from deformation alone, preliminary synthetic tests at shallower systems have demonstrated a limited ability to resolve the main inflation mechanism. In this study, we investigate how the performance of an Ensemble Kalman Filter (EnKF) data assimilation framework varies under a wider range of experimental conditions than used in these initial investigations. In particular, we test how different mathematical implementations of the filter and how different levels of data availability affect the EnKF’s ability to distinguish inflation drivers and to accurately resolve reservoir parameters. To implement this experiment, two time series of synthetic GPS and InSAR data are generated, one in which deformation is driven by excess pressure and another in which it is driven by lateral expansion of the reservoir. For each filter implementation these datasets are down-sampled and given random noise prior to inversion, and after assimilation the resulting model is compared to the original synthetic conditions. We find that newer deterministic formulations of the EnKF are more accurate and consistent than the original stochastic implementation, although the improvement is relatively small. Moreover, some amount of parameter inflation is required to avoid model collapse, but more sophisticated adaptive inflation schemes do not produce better results than more basic formulations. Finally, we show that while increased data sampling does improve performance, this effect is subject to diminishing returns. In particular, data resolution near the center of inflation is more important than overall range of coverage. As new inversion techniques are developed or adapted from other fields, rigorous testing as demonstrated here will be a key step in being able to interpret future results and develop new forecasting frameworks for volcanic eruptions.
Using WRF-Chem Volcano to model the in-plume halogen chemistry of Etna’s 2018 eruption
Authors: Surl Luke , Warnach Simon , Wagner Thomas , Roberts Tjarda , Bekki Slimane
Published: March 2020

Volcanic eruptions emit halogen-containing species in varying quantities, with their emission ratio to tracer species such SO2 varying between volcanoes, eruptions, and even phases of an eruptive event.

The bromine explosion is known to occur within volcanic plumes, converting bromine from HBr – the primary form in which it is emitted – to other forms, including the spectroscopically detectable BrO. Measurements of BrO have been made in the plumes of many volcanoes from both ground-based and satellite-based instruments. There also exist a small number of measurements of OClO.

We present results from WRF-Chem Volcano (WCV), a modified version of the three-dimensional regional atmospheric chemistry and transport model WRF-Chem and associated utilities. We have simulated the Christmas 2018 eruptive event of Mount Etna using a nested implementation the model at maximum lateral resolution of 1km, as well as a weaker emission plume representing Etna’s more common quiescent degassing state. The plume of this 2018 eruption was observed remotely by the TROPOMI instrument.

WCV is able to model the transport and dispersion of the plume. We compare these model outputs to the satellite observations and use this to estimate the volcanic emission column height.

In terms of chemistry, WCV is able to reproduce the bromine explosion and the major features of the satellite observation – including a cross-plume variation in the BrO/SO2 column ratio. We find that variations in the BrO/SO2 ratio are primarily caused by variations in the concentration of ozone. Ozone is consumed by bromine chemistry and is replenished by the mixing in of ozone-rich background air. This creates a zone of low ozone in the core of the plume which is consequently low in BrO and surrounded by a higher-ozone edge with a higher BrO/SO2 ratio.

For the temporal evolution of the plume, we find that the bromine-chemistry of a concentrated emission plume can be divided into four phases, also governed by ozone availability. In the last phase ozone limitation is minimal and the proportion of bromine in the form of BrO (and the BrO/SO2 ratio) is approximately stable. We find this stable regime also with a simulation of a weaker emission plume. These results could facilitate the use of remote-sensing BrO measurements as a means of quantifying total bromine emissions from volcanoes.

Oxidized forms of chlorine are modelled to be formed within the plume due to the heterogenous reaction of HOBr with HCl, forming BrCl that photolyzes and produces Cl radicals. We also investigate the extent to which mercury could be oxidized by halogens within the plume.
Nature-Based Solutions: Dependency of Effectiveness on Spatial Configuration
Authors: Pattison Ian
Published: March 2020

Several recent large flood events have had severe economic and social impacts. The winter 2015-16 UK floods resulted in 16,000 properties flooding and damage to critical infrastructure. It is increasingly being recognised that traditional approaches of flood defence are not sustainable due to the pressures of climate change and economic constraints. The solution to the flood risk problem in cities is no longer seen as being just on-site, and thinking is shifting upstream and to the catchment/landscape scales, known as Nature-Based Solutions or Natural Flood Management (NFM). The approach consists of measures that “Work with Natural Processes”, such as storing water in ponds, and slowing the flow in rivers. The evidence for the impacts is strong at the local scale, but the larger spatial scale impact is highly uncertain due to the cumulative impacts resulting from amplifying/mitigating effects of different interventions, controlled by spatial location and storm-track interaction.

To date, Nature-Based Solution schemes have proceeded on an opportunistic basis, without a clear design strategy (which measure and where to implement it). However, if schemes are implemented without clear understanding of their impacts, they may, at best, fail to achieve the optimum flood reduction benefit downstream, or, at worst, make flooding more severe (if implemented in inappropriate locations, when tributaries’ flows are synchronised).  

Impacts of NFM measures are spatially and temporally dependent i.e. the same intervention in two locations will have different effects on flows, and the same intervention will have different impacts during different storm events. Therefore, it is essential that when strategically designing NFM schemes for catchments, that WHERE? and WHAT? are answered together to optimise the impact, as it is possible that whilst upstream NFM may be beneficial locally it may make tributary peaks coincide and make flood magnitudes worse downstream. Here we demonstrate the importance of the spatial configuration of Nature-Based Solutions on their catchment scale effectiveness in reducing flood risk.
Testing the improved Integral Suspension Pressure method ISP+ with the PARIO™ device
Authors: Durner Wolfgang , Miller Alina , Gisecke Madita , Iden Sascha C.
Published: March 2020

The integral suspension pressure method (ISP) uses pressure measurements in a soil suspension to derive the particle size distribution (PSD) in the silt range in high resolution. The sedimentation process is mathematically simulated and the simulated suspension pressure at a fixed depth in the sedimentation cylinder is fitted to an observed time series. The PSD is determined by numerically solving the inverse problem. The methodology is implemented in a commercial apparatus named PARIO that is produced by METER AG, Munich.

Practical experiments with PARIO indicated that the accuracy of the method to determine the clay fraction was not as high as expected from theory, which may partly be caused by the error propagation from the independently determined sand fractions. Durner and Iden (2019) thus proposed an extension of the experimental protocol called ISP+, which makes the inverse problem better-posed and allows shorter experimental time. After a sedimentation time of few hours, a part of the suspension is drained laterally from the sedimentation cylinder through an outlet, collected and oven-dried. The resulting dry mass of the soil particles is integrated into the objective function of the inverse problem. This markedly reduces the uncertainty of the identified PSD towards the finest particles. We present experimental results from PARIO measurements evaluated by the ISP+ method and illustrate the new experimental design and the improvement of accuracy for the clay fraction.

Reference: Durner, W., & Iden, S. C. (2019, January). ISP+: improving the Integral Suspension Pressure method by an independent measurement of clay content. In Geophysical Research Abstracts (Vol. 21).