bluuebunny/crossref_metadata_2025 huggingface dataset:
Seismic quantification of river flow depth - from the flume to the field
Authors: Bakker Maarten , Gimbert Florent , Lamb Michael P. , Recking Alain
Published: March 2021

Seismic measurements are used to study various processes that shape the Alpine landscape, including rock falls, debris flows, bedload transport and turbulent water flow. Here, we focus on the seismic quantification of turbulent flow conditions which is particularly useful for the remote monitoring of channels that are inaccessible (e.g. subglacial conduits) and/or highly dynamic (e.g. actively braiding river reaches). We test a physically-based model (Gimbert et al., 2014) to quantify force spectra generated by turbulent flow in flume experiments performed by Lamb et al. (2017) and subsequently apply the model to estimate river flow depth from continuous seismic measurements in the field.

In the flume, we assess near-bed flow velocity spectra and resulting drag and lift force spectra experienced by particles (D=0.075-0.20 m) on the cobble bed for a wide range of channel gradients (S=0.004-0.3) and submergence levels (h/D50=1-9.6). These measurements are used to test our model, and to quantify wake (interaction) effects and fluid-dynamic admittance on force spectral amplitude. Based on the conservation of turbulent energy in the Kolmogorov inertial subrange, we predict lift and drag force spectra to within ±5 dB rel. N2/Hz (frequency ~10-25 Hz) of the measured values.

We apply the calibrated model to bank-side geophone measurements from an Alpine stream (Séveraisse River, France). Using locally-derived seismic parameters, riverbed particle-size distribution and bed roughness, we can invert for water depth over a range of flow conditions, including flows with bedload transport (bedload transport dominates the seismic signal at higher frequencies). This allows us to monitor changes in flow depth during the course of a high-magnitude flood (October 2019). During the falling limb, the inferred flow depths progressively deviate from independently made water level measurements, indicating local riverbed aggradation of approximately 0.5 m, which is in agreement with post-flood observations. Through insights in near-bed turbulent flow conditions and their seismic signature, we can study flow-bedload transport interactions and the effects of extreme flow events on river morphodynamics.

References

Gimbert, F., Tsai, V. C. & Lamb, M. P. (2014). A physical model for seismic noise generation by turbulent flow in rivers. Journal of Geophysical Research: Earth Surface, 119(10), 2209-2238. http://dx.doi.org/10.1002/2014JF003201

Lamb, M. P., Brun, F. & Fuller, B. M. (2017). Direct measurements of lift and drag on shallowly submerged cobbles in steep streams: Implications for flow resistance and sediment transport. Water Resources Research, 53(9), 7607-7629. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017WR020883
Analytical approach unifying the two-regime scaling for bedload particle motions
Authors: Wu Zi , Singh Arvind , Foufoula-Georgiou Efi , Guala Michele , Fu Xudong , Wang Guangqian
Published: March 2021

Bedload particle hops are defined as successive motions of a particle from start to stop, characterizing one of the most fundamental processes describing bedload sediment transport in rivers. Although two transport regimes have been recently identified for short- and long-hops, respectively (Wu et al., Water Resour Res, 2020), there still lacks a theory explaining how the mean hop distance-travel time scaling may extend to cover the phenomenology of bedload particle motions. Here we propose a velocity-variation based formulation, and for the first time, we obtain analytical solution for the mean hop distance-travel time relation valid for the entire range of travel times, which agrees well with the measured data (Wu et al., J Fluid Mech, 2021). Regarding travel times, we identify three distinct regimes in terms of different scaling exponents: respectively as ~1.5 for an initial regime and ~5/3 for a transition regime, which define the short-hops; and 1 for the so-called Taylor dispersion regime defining long-hops. The corresponding probability density function of the hop distance is also analytically obtained and experimentally verified. 
Sediment dynamics near a sandy spit with wave-induced coastal currents
Authors: Lu Jing
Published: March 2021

    Surface gravity waves play an important role in sediment transport. Previous studies have focused on the role of bottom shear enhanced by the surface wave orbital velocity. In this study, we embedded the University of New South Wales Sediment model into the Princeton Ocean Model, which includes a three-dimensional wave module to study sediment dynamics near a sandy spit in Sanniang Bay in the South China Sea. The simulated results for the deposition rate show that wave-induced currents play a dominant role in the maintenance of the sandy spit. The spit tip was formed as a result of the separation of wave-induced coastal flow. The spit tip was shown to be a barrier to the dominant wave-induced current, and the spit base was simulated to form via sand accumulation in the shelter of the spit tip. The deposition is mainly in the low-energy region behind the tip of the spit, which can counter the erosion effect of dominant wave-induced currents. The dominant wave-induced current prompts the lateral infilling of the spit tip when both the spit tip and base are above the water surface. The sediment carried by the coastal current is deposited along the flow branch of separation and forms the spit tip, which indicates that the sediment is deposited where the longshore current changes into an offshore current. As the water depth increases along the separated flow spindle, the bottom shear stress decreases, contributing to the deposition of the spit tip.
Seasonality of precipitation extremes and their connections with large-scale climate patterns over the contiguous United States
Authors: Dhakal Nirajan , Tharu Bhikhari , Aljoda Ali
Published: March 2021

Despite the importance of seasonality of extreme precipitation events to stormwater management, there are limited number of studies examining seasonality of daily and monthly precipitation extremes over the contiguous United States. In this study, a circular statistical method was used for spatio-temporal assessment of seasonality of daily and monthly precipitation extremes and their teleconnections with large-scale climate patterns over the contiguous United States. Historic precipitation time series over the period of 64 years (1951–2014) for 1108 sites was used for the analysis. Calendar dates for extreme precipitation were used to characterize seasonality within a circular statistics framework which includes indices reflecting the mean date and variability of occurrence of extreme events. The rainfall seasonality during negative and positive phases of the El Niño–Southern Oscillation, North Atlantic Oscillation, and Pacific Decadal Oscillation were also investigated. Results showed that extreme precipitation seasonality varied across the contiguous United States with distinct spatial pattern of seasonality (strong seasonality) in the western and mid-western regions and mixed spatial pattern in the eastern region. In addition, extreme precipitation seasonality during negative and positive phases of three climate indices revealed that large-scale climate variabilities have strong influence on the mean date of occurrence of extreme precipitation but generally weak influence on the strength of seasonality in the contiguous United States. Results from our study might be helpful for sustainable water resource management, flood risk mitigation, and prediction of future precipitation seasonality.

 
Characterising recent drought events using current reanalysis and remote-sensing soil moisture products within a common framework
Authors: Hirschi Martin , Crezee Bas , Seneviratne Sonia I.
Published: March 2021

Drought events cause multiple impacts on the environment, the society and the economy. Here, we analyse recent major drought events with different metrics using a common framework. The analysis is based on current reanalysis (ERA5, ERA5-Land, MERRA-2) and merged remote-sensing products (ESA-CCI soil moisture, gridded satellite soil moisture from the Copernicus Climate Data Store), focusing on soil moisture (or agricultural) drought. The events are characterised by their severity, magnitude, duration and spatial extent, which are calculated from standardised daily anomalies of surface and root-zone soil moisture. We investigate the ability of the different products to represent the droughts and set the different events in context to each other. The considered products also offer opportunities for drought monitoring since they are available in near-real time.

All investigated products are able to represent the investigated drought events. Overall, ERA5 and ERA5-Land often show the strongest, and the remote-sensing products often weaker responses based on surface soil moisture. The weaker severities of the events in the remote-sensing products are both related to shorter event durations as well as less pronounced average negative standardised soil moisture anomalies, while the magnitudes (i.e., the minimum of the standardised anomalies over time) are comparable to the reanalysis products. Differing global distributions of long-term trends may explain some differences in the drought responses of the products. Also, the lower penetration depth of microwave remote sensing compared to the top layer of the involved land surface models could explain the partly weaker negative standardized soil moisture anomalies in the remote-sensing products during the investigated events. In the root zone (based on the reanalysis products), the drought events often show prolonged durations, but weaker magnitudes and smaller spatial extents.
Geostatistical Joint Interpretation of Gravity and Magnetotelluric Data of the US Cordillera
Authors: Shehata Mohammad , Mizunaga Hideki
Published: March 2021

Long-period magnetotelluric and gravity data were acquired to investigate the US cordillera's crustal structure. The magnetotelluric data are being acquired across the continental USA on a quasi-regular grid of ∼70 km spacing as an electromagnetic component of the National Science Foundation EarthScope/USArray Program. International Gravimetreique Bureau compiled gravity Data at high spatial resolution. Due to the difference in data coverage density, the geostatistical joint integration was utilized to map the subsurface structures with adequate resolution. First, a three-dimensional inversion of each data set was applied separately.

The inversion results of both data sets show a similarity of structure for data structuralizing. The individual result of both data sets is resampled at the same locations using the kriging method by considering each inversion model to estimate the coefficient. Then, the Layer Density Correction (LDC) process's enhanced density distribution was applied to MT data's spatial expansion process. Simple Kriging with varying Local Means (SKLM) was applied to the residual analysis and integration. For this purpose, the varying local means of the resistivity were estimated using the corrected gravity data by the Non-Linear Indicator Transform (NLIT), taking into account the spatial correlation. After that, the spatial expansion analysis of MT data obtained sparsely was attempted using the estimated local mean values and SKLM method at the sections where the MT survey was carried out and for the entire area where density distributions exist. This research presents the integration results and the stand-alone inversion results of three-dimensional gravity and magnetotelluric data.
Educational course "Creation of virtual geological outcrops of the outskirts of Lviv"
Authors: Bubniak Ihor , Tsikhon Serhiy , Tserklevych Anatoliy , Shylo Yevheniy , Oliinyk Mariia
Published: March 2021

We present a new educational course "Creation of virtual geological outcrops of the outskirts of Lviv" for students of geological specialties. Discipline "Creation of virtual geological outcrops of the outskirts of Lviv" is a selective discipline for students of 2-3 courses of various specialties, which is lectured in the amount of 3 credits (according to ECTS). The course is 32 hours of classroom classes, 16 hours of these of lectures, the rest 16 hours of practical classes and 58 hours of self-study.

The course is in three parts. First is preparatory ones. Students get acquainted with the geological structure of Lviv, prepare equipment for field work.

The field stage (the second part of the course) includes the survey of 3-4 geological objects around Lviv. These can be natural outcrops, quarries. A particularly valuable object for learning is the Honey Cave, located within the city limits. Depending on the object, we choose the type of survey— digital photogrammetry or terrestrial laser scanning. Each group of 4 students explores 2 objects.

The third cameral period includes field data processing. Students create 3D geological models and perform various measurements on them. Students compare different types of models to choose the best one. At this stage, students use a variety of software available in institutions. The final stage of the course is the preparation of a report and passing the exam.

The project war partly financed by EGU HE Teaching Award.
Variation of SO2 and CO2 in the volcanic gas plumes of Santa Ana and San Miguel volcanoes: an overview by real-time measurements 
Authors: Gutiérrez Xochilt , Bobrowski Nicole , Hoffmann Thorsten , Gutiérrez Eduardo , Dinger Florian , Montalvo Francisco , Escobar Demetrio
Published: March 2021

Volcanic degassing plays an important role in a volcano’s behavior. Going from large emissions at craters and fumaroles, to invisible degassing at vents and soil; a volcano releases H2O, CO2, SO2, HCl, HF, H2S, CO, H2, HBr, HI, Hg and noble gases.

SO2 emissions are considered a basic monitoring tool, mainly measured by remote-sensing techniques. The Differential Optical Absorption Spectroscopy (DOAS) is a well-established method currently used to regularly measure volcanic SO2 emission rates with about 80 scanning DOAS operating in 37 volcanoes within the framework of the global "Network for Observation of Volcanic and Atmospheric Change" (NOVAC) (Galle et al., 2010). Typically, SO2fluxes are often combined with in-situ gas measurements of SO2 and other volatiles (CO2, H2S), to evaluate the degassing regime. In-situ sampling can be made by collecting the gases directly in evacuated flasks or solution-filled bottles (alkaline traps), or by sampling with a multi-sensor instrument (MultiGAS) that enables real-time measurements of several gases at once (Aiuppa et al. 2005b; Shinohara 2005, Roberts et al. 2017).

Santa Ana and San Miguel are the most active volcanoes in El Salvador, with an average SO2 emission rate of 220 and 326 t/d, respectively during 2018. Both volcanoes arise along the Central American Volcanic Arc – CAVA, where the magmatism, fundamentally basaltic, is related to the convergence of the Caribbean Plate and the subducting Cocos Plate (Leeman and Carr 1995). Also, Santa Ana and San Miguel are part of the NOVAC group since 2008 with just a few published gas data (Rodriguez et al. 2004, Cartagena et al. 2004, Olmos et al. 2007, Colvin et al. 2013, Laiolo et al. 2017). The most recent studies were performed by Granieri et al. 2015 and Hasselle et al. 2019. The first, reported CO2/SO2, HCl/SO2 and HF/SO2 mass ratios (0.95, 0.13 and 0.016, respectively) measured at San Miguel volcano in early 2014; while the second, presented CO2/SO2, H2S/SO2 and H2O/SO2 ratios (<3-37.9, 0.03-0.1 and 32-205, respectively), measured in 2017-2018 at Santa Ana’s crater lake and rim.

In this study, we present an SO2 long-time data series (2008-2018) for San Miguel and Santa Ana obtained from the DOAS stations of each volcano, and complement with data collected during regular monitoring (2018-2020) and field campaigns in El Salvador (2019 and 2020) by means of MultiGAS devices. The aim of the study is to extend the characterization of these two volcanoes in El Salvador and the establishment of SO2 and CO2 baselines and inventories for them.
GemGIS – GemPy Geographic: Open-Source Spatial Data Processing for Geological Modeling
Authors: Jüstel Alexander , Endlein Correira Arthur , Wellmann Florian , Pischke Marius
Published: March 2021

Geological modeling methods are widely used to represent subsurface structures for a multitude of applications – from scientific investigations, over natural resource and reservoir studies, to large-scale analyses and geological representations by geological surveys. In recent years, we have seen an increase in the availability of geological modeling methods. However, many of these methods are difficult to use due to preliminary data processing steps, which can be specifically difficult for geoscientific data in geographic coordinate systems.

We attempt to simplify the access to open-source spatial data processing for geological modeling with the development of GemGIS, a Python-based open-source library. GemGIS wraps and extends the functionality of packages known to the geo-community such as GeoPandas, Rasterio, OWSLib, Shapely, PyVista, Pandas, NumPy and the geomodelling package GemPy. The aim of GemGIS, as indicated by the name, is to become a bridge between conventional geoinformation systems (GIS) such as ArcGIS and QGIS, and geomodelling tools such as GemPy, allowing simpler and more automated workflows from one environment to the other.

Data within the different disciplines of geosciences are often available in a variety of data formats that need to be converted or transformed for visualization in 2D and 3D and subsequent geomodelling methods. This is where GemGIS comes into play. GemGIS is capable of working with vector data created in GIS systems through GeoPandas, Pandas and Shapely, with raster data through rasterio and NumPy, with data obtained from web services such as maps or digital elevation models through OWSLib and with meshes through PyVista. Support for geophysical data and additional geo-formats are constantly added.

The GemGIS package already contains several tutorials explaining how the different modules can be used to process spatial data. It was decided against creating new data classes in case users are already familiar with concepts such as (Geo-)DataFrames in (Geo-)Pandas or PolyData/Grids in PyVista.

The GemGIS package is hosted at https://github.com/cgre-aachen/gemgis, the documentation is available at https://gemgis.readthedocs.io/en/latest/index.html. GemGIS is also available on PyPi. You can install GemGIS in your Python environment using ‘pip install gemgis’.

We welcome contributions to the project through pull requests and are open to suggestions and comments, also over Github issues, especially about possible links to other existing software developments and approaches to integrate geoscientific data processing and geomodelling.
Hydro-climatic fluctuations and their impact on Lake Abhe environments (Ethiopia & Djibouti): a lesson from the past 10,000 years
Authors: Mologni Carlo , Bruxelles Laurent , Arnaud Fabien , Sabatier Pierre , Develle Anne-Lise , Malet Emmanuel , Chaumillon Eric , Schuster Mathieu , Davtian Gourguen , Cauliez Jessie , Revel Marie , Khalidi Lamya
Published: March 2021

Throughout the last 14 ka, tropical Africa experienced significant hydrological changes that were mainly driven by the orbital precession cycle, which controls the intensity of the African monsoon. Recent studies conducted in lake and deltaic sedimentary records suggest that long-term monsoon humid oscillations (African Humid Period / AHP ~14 – ~6 ka) were punctuated by centennial-scale episodes of hyperaridity. However, the abrupt or gradual aridification modalities since the end of the AHP and the modalities of the centennial-scale episodes, as well as their impacts on past and current environments are still debated.

The Lake Abhe basin in the Central Afar region (Ethiopia & Djibouti) is the endorheic receptacle of freshwater originating in the Ethiopian Highlands, and represents a hydro-sedimentary system sensitive to hydro-climatic changes in East Africa. Today it is characterized by residual lakes (Gamari and Afambo lakes) and a hyper-arid climate, while during the AHP, the Abhe basin was occupied by a Mega-lake and by humid environmental conditions. Holocene climatic disruptions drastically changed the landscapes and ways of life along this basin.  

The aim of this study is to describe, interpret and estimate the impact of hydro-climatic oscillations on the evolution of Lake Abhe’s littoral lacustrine environments and palaeolandscapes since the AHP from different viewpoints.

Indeed, this research combines paleoclimatological and geomorphological studies based on a new set of 14C ages on two lacustrine cores and on several morpho-sedimentary outcrops spanning the Early to Late Holocene. Our results allow us to: a) refine the temporal occurrence and the hydrological modalities of the AHP including short-term arid episodes linked to Younger Dryas and 8.2 ka North Atlantic events; b) recognise some paleo-shoreline geomorphic features linked to lake level fluctuations, as well as the development littoral pedological horizons and the activation/shutdown of the perilacustrine fluvial network during humid and arid events; c) track these changes until the present day, and discuss their evolution scenario in the near future.

Comparing with other regional climatic records, we show how Lake Abhe basin was highly reactive to East African monsoonal regimes, and how current hydrological changes could impact its environments.      
Semi-structured mass movement interactions with flow-blocking mitigation
Authors: van den Bout Bastian , van Westen Cees , Jetten Victor , Dhakal Om
Published: March 2021

The development of a failure plane in the subsurface can result in movement of large volumes of solids. Depending on the type of rock and initiation mechanism, this material can partially contain cohesive structure. Such semi-structured landslides or rock avalanches feature alternate dynamics compared to debris flows and other types of granular movements. The way in which this structure influences the impact on structures, and thus the resulting hazard, remains largely unknown. Recently, a two-phase semi-structured generalized mass movement model was developed. This model implements a full stress-strain relationship for the moving mixture. In this work, this model is applied to a set of hypothetical and real mitigation measures and structures. The effect of various types of checkdams and blocking pillars is investigated. The resulting impacts are converted to impact pressures and potential damage fractions. Finally, the model results are compared with traditional unstructured debris flow and landslide runout models. Results indicate the strong increase of structural damage with increased cohesive structure. The model furthermore predicts complex interactions between the semi-structured mass movements and mitigation measures. Moving aggregates can break, after which individual rocks or particles might continue in diverging trajectories. Depending on the physical parameters of the material, fragmentation can also occur before impact, after which movement is similar to granular flows. 
Numerical determination of pressure-dependent effective thermal conductivity in Berea sandstone
Authors: Siegert Mirko , Gurris Marcel , Saenger Erik Hans
Published: March 2021

Within the scope of the present work, the pressure-dependent effective thermal conductivity of rock samples is simulated. Our workflow can be assigned to the field of digital rock physics. In a first step, a 3D micro-CT scan of a rock sample is taken. Subsequently, the resulting greyscale images are analysed and segmented depending on the occurring phases. Based on this data set, a computational mesh is created and the corresponding thermal conductivities are assigned to each phase. Finally the numerical simulations can be carried out.
For the representation of the pressure dependency we use the approach proposed by Saenger [1]. By making use of the watershed algorithm, boundaries between the individual grains of the rock sample are detected and assigned to an artificial contact phase. In the course of several simulations, the thermal conductivity of the contact phase is continuously increased. Starting with the thermal conductivity of the pore phase and ending with the thermal conductivity of the grain phase. A linear correlation is used to match the thermal conductivity of the contact phase with the pressure of a given experimental data set. This enables a direct comparison between simulation and measurement.
In a further step, the numerical model is calibrated to optimise the agreement between experimental data and simulation results. In particular, starting from two calibration points of the experimental data set, an adjustment of the thermal conductivities in the numerical model is carried out. While the thermal conductivity of the pore phase is held constant during the whole calibration process, thermal conductivities of the grain and contact phase are adjusted.

References
[1] Saenger et al. 2016. Analysis of high-resolution X-ray computed tomography images of Bentheim sandstone under elevated confining pressures. Geophysical Prospecting, 64(4), 848–859.

 
Modelling the tail behaviour of precipitation aggregates using conditional spatial extremes.
Authors: Richards Jordan , Tawn Jonathan , Brown Simon
Published: March 2021

Fluvial flooding is not caused by high intensity rainfall at a single location, rather it is caused by the extremes of precipitation events aggregated over spatial catchment areas. Accurate modelling of the tail behaviour of such events can help to mitigate the financial aspects associated with floods, especially if river defences are built within specification to withstand an n-year event of this kind. Within an extreme value analysis framework, univariate methods for estimating the size of these n-year events are well studied and cemented in asymptotic theory.

 To complement these techniques, we develop a high-resolution spatial model for extreme precipitation by providing a fully spatial extension of the conditional approach for modelling multivariate extremes. We simulate realistic precipitation fields from this model and use univariate techniques to make inference about the extremal behaviour of aggregates over specified spatial domains. The challenge of zero precipitation data is overcome and further applications of the model are discussed. The model is fit to data from a convection permitting forecast model within the 2018 UK Climate Projections (UKCP18).
Analytical modelling and joint inversion of surface displacements and gravity changes at volcanoes
Authors: Nikkhoo Mehdi , Rivalta Eleonora
Published: March 2021

Gravity change observations at volcanoes provide information on the location and mass change of intruded magma bodies. Gravity change and surface displacement observations are often combined in order to infer the density of the intruded materials. Previous studies have highlighted that it is crucial to account for magma compressibility and the shape of the gravity change and deformation source to avoid large biases in the density estimate. Currently, an analytical model for the deformation field and gravity change due to a source of arbitrary shape is lacking, affecting our ability to perform rapid inversions and assess the nature of volcanic unrest.  

Here, we propose an efficient approach for rapid joint-inversions of surface displacement and gravity change observations associated with underground pressurized reservoirs. We derive analytical solutions for deformations and gravity changes due to the volume changes of triaxial point-sources in an isotropic elastic half-space. The method can be applied to  volcanic reservoirs that are deep compared to their size (far field approximation). We show that the gravity changes not only allow inferring mass changes within the reservoirs, but also help better constrain location, shape and the volume change of the source. We discuss how the inherent uncertainties in the realistic shape of volcanic reservoirs are reflected in large uncertainties on the density estimates. We apply our approach to the surface displacements and gravity changes at Long Valley caldera over the 1985-1999 time period. We show that gravity changes together with only vertical displacements are sufficient to constrain the mass change and all the other source parameters. We also show that while mass change is well constrained by gravity change observations the density estimate is more uncertain even if the magma compressibility is accounted for in the model.
Recent seasonal changes of metal composition and size distribution of mineral particles in snow at EGRIP, Greenland
Authors: Komuro Yuki , Nakazawa Fumio , Goto-Azuma Kumiko , Hirabayashi Motohiro , Shigeyama Wataru , Nagatsuka Naoko
Published: March 2021

Seasonal changes of meteorological and ground surface conditions can cause seasonal changes of source area of mineral particles supplied to the Greenland ice sheet. Difference in metal composition and size distribution of them reflects their source area difference. To clarify seasonal changes in the source area of mineral particles, we examined the metal composition and size distribution of them in snow pit samples obtained from EGRIP (East Greenland Ice Core Project).

In summer 2017, we dug a 2.01 m snow pit at EGRIP camp. Snow samples were collected at 0.03 m intervals. The snow samples were melted, then fractions of them were analyzed for the particle size distribution (0.52-12μm) with a Coulter counter (Beckman Coulter: Multisizer 4). Other fractions of the samples were treated with a microwave acid digestion method to decompose particulates. Total concentrations of Al, Ca and Na in samples were measured by inductively coupled plasma mass spectrometry.

Total concentrations of Al (t-Al) and concentrations of non-sea-salt Ca (nssCa) showed peak values in winter to spring layers. In those layers, nssCa/t-Al ratios and volume fractions of fine particles (<4 μm) tended to be relatively high. In some of those layers, the nssCa/t-Al ratios were 2-3 times higher than the crustal average of Ca/Al ratio. This result suggests that fine Ca-rich mineral particles originated from remote desert areas were supplied to EGRIP in those seasons. In contrast, in summer to autumn layers, the nssCa/t-Al ratios and volume fractions tended to be relatively low. This result can be explained by supplies of coarse (≥ 4 μm) Ca-poor mineral particles originated from soil areas near Greenland in those seasons.
Surges of the weak magnetic field in the photosphere of the Sun
Authors: Baranov Dmitrii , Vernova Elena , Tyasto Marta
Published: March 2021

The properties of the magnetic fields of the solar photosphere are investigated, in particular, the distribution of fields of different polarity over the solar surface. As primary data, synoptic maps of the photospheric magnetic field of the Kitt Peak National Solar Observatory for 1978-2016 were used. Using the vector summation method, the non-axisymmetric component of the magnetic field is determined. It was found that the nonaxisymmetric component of weak magnetic fields B < 5 G changes in antiphase with the flux of these fields. Magnetic fields of B < 5 G constitute a significant part of the total magnetic field of the Sun, since they occupy more than 60% of the area of the photosphere. The fine structure of the distribution of weak fields can  be observed by setting the upper limit to the strength of the  fields  included in the time–latitude diagram. This allows to eliminate the contribution of the strong fields of sunspots.

On the time-latitude diagram for weak magnetic fields (B < 5 G), bands of differing colors correspond to the streams of the magnetic fields moving in the direction to the Sun’s poles.. These streams or surges show the alternation of the dominant polarity - positive or negative - which is clearly seen in all four cycles. The slopes of the bands indicate the velocity of the fields movement towards the poles. The surges can be divided into two groups. The surges of the first group belong to the so-called Rush-to-the-Poles. These are bands with the width of about three years, which begin at approximately 40° of latitude and have the same polarity as the trailing sunspots. They reach high latitudes and cause the polarity reversal of the polar field. However, in addition to these surges, for most of the solar  cycle (the descending phase, the minimum and the ascending phase), there are narrower surges of both polarities (with the width less than one year), which extend from the equator almost to the poles. These surges are most clearly visible in the southern hemisphere when the southern pole is positive. Consideration of the latitude-time diagrams separately for positive and negative polarities showed that the alternating dominance of one of the polarities is associated with the antiphase development  of the positive and negative fields of the surges. The widths of surges and the periodicity of their appearance vary significantly for the two hemispheres and from one solar cycle to the other. The mean period of the polarity alternation is about 1.5 years.
The health hazards and impacts of volcanic ash: an interdisciplinary journey towards effective mitigation, protection and communication
Authors: Horwell Claire
Published: March 2021

The eruption of Mount St. Helens in 1980 exposed a large population to volcanic ash that was found to contain cristobalite – a crystalline silica polymorph and known carcinogen. This event triggered an array of epidemiological, toxicological and geochemical studies to assess the toxicity of ash, marking the birth of a new field of research. This talk will take you on an interdisciplinary journey through the work conducted since the 1980s, which has discovered both biological mechanisms in favour of volcanic ash toxicity and inherent physicochemical characteristics of ash particles that may render the silica surfaces non-toxic. A sparsity of longitudinal clinical and epidemiological studies following eruptions means that medical evidence for chronic ash pathogenicity is lacking, but other research has shown that acute exposures to volcanic ash can exacerbate existing respiratory conditions. Additionally, a multitude of techniques and protocols have been developed for rapid, eruption-specific health hazard assessment, but conducting these assessments in a crisis is very challenging. In the absence of definitive information about the harmfulness of ash, many exposed people choose to protect themselves as a precaution, or are advised to do so by agencies, so recent research has focussed on providing them with the knowledge to do that effectively. This laboratory and community-based research, involving collaborations among geoscientists, exposure scientists, social scientists, medical ethicists, agency and community representatives, has yielded critical insight into a chain of communication from researcher, through various local ‘authorities’, to the actions taken by communities. The findings have led to changes in humanitarian and individual practice and have opened up new pathways to effective uptake of evidence-based advice through co-designed informational products.
Pliocene-Quaternary river-terrace sequences in intramontane basins in the south-eastern Alpine foreland (Slovenia): characterization of morphostratigraphy and provenance
Authors: Mencin Gale Eva , Jamšek Rupnik Petra , Bavec Miloš , Trajanova Mirka , Gale Luka , Anselmetti Flavio S. , Šmuc Andrej
Published: March 2021

This study focuses on the Pliocene-Quaternary sedimentary evolution of the fluvial systems in the Slovenj Gradec, Nazarje, Velenje, Celje, Drava-Ptuj and Krško Basins in the south-eastern Alpine foreland, Slovenia. The main aim was to determine the composition, morphostratigraphy, provenance, sedimentary environment and age of the deposits using geomorphological, sedimentological, geochemical, mineralogical and biostratigraphical methods. Pliocene-Quaternary sediments were deposited in fluvial (braided and wandering river systems) and alluvial/colluvial fan environments. The sediments are preserved in the terrace staircase sequences, formation of which is strongly controlled by tectonic activity. Based on geomorphological analyses, low-, middle- and high-level terrace groups were constrained and tentatively attributed to Late Pleistocene, Middle Pleistocene, and Plio-Early Pleistocene, respectively. The provenance analyses focused on the Plio-Early Pleistocene sediments and included lithological and microfacies analyses of the clasts. Based on the provenance analyses and published data, the long-term development of the drainage network was interpreted. Major changes occurred during the transition from Miocene-Pliocene and at the latest at Plio-Early Pleistocene the drainage network reached conformity with the present one. Overall, the spatial distribution of the Pliocene-Quaternary landforms revealed tectonic activity in intramontane basins during their development, from which the landscape evolution was deduced. 
In-season crop classification using optical remote sensing with random forest over irrigated agricultural fields in Australia
Authors: Gao Zitian , Guo Danlu , Ryu Dongryeol , Western Andrew
Published: March 2021

Timely classification of crop types is critical for agronomic planning in water use and crop production. However, crop type mapping is typically undertaken only after the cropping season, which precludes its uses in later-season water use planning and yield estimation. This study aims 1) to understand how the accuracy of crop type classification changes within cropping season and 2) to suggest the earliest time that it is possible to achieve reliable crop classification. We focused on three main summer crops (corn/maize, cotton and rice) in the Coleambally Irrigation Area (CIA), a major irrigation district in south-eastern Australia consisting of over 4000 fields, for the period of 2013 to 2019. The summer irrigation season in the CIA is from mid-August to mid-May and most farms use surface irrigation to support the growth of summer crops. We developed models that combine satellite data and farmer-reported information for in-season crop type classification. Monthly-averaged Landsat spectral bands were used as input to Random Forest algorithm. We developed multiple models trained with data initially available at the start of the cropping season, then later using all the antecedent images up to different stages within the season. We evaluated the model performance and uncertainty using a two-fold cross validation by randomly choosing training vs. validation periods. Results show that the classification accuracy increases rapidly during the first three months followed by a marginal improvement afterwards. Crops can be classified with a User’s accuracy above 70% based on the first 2-3 months after the start of the season. Cotton and rice have higher in-season accuracy than corn/maize. The resulting crop maps can be used to support activities such as later-season system scale irrigation decision-making or yield estimation at a regional scale.

Keywords: Landsat 8 OLI, in-season, multi-year, crop type, Random Forest
Prediction of future development of soil water erosion in small agricultural chatchment
Authors: Kohnová Silvia , Németová Zuzana , Sabová Zuzana
Published: March 2021

It is well known that the impact of climate change affects various areas such as hydroclimatical factors which can cause increased occurrence of heavy precipitation events, ice melting, rising temperature or sea-level as a consequence of the global warming. It is assumed that the average surface temperature on Earth has increased by more than 1° Celsius since 1880. Climate change of the Earth has changed naturally over the past 650.000 years as a result of external factors that impact the climate. Despite of this fact, over the last 100 years is global warming strongly accelerated by different kind of human activities. One of those activities represents inappropriate land use management which is directly connected with soil degradation and soil erosion as the major threat of global soil degradation. The study presents the assessment of the future development of soil water erosion processes in one small agricultural catchment located in the Slovak Republic. The calculations were done based on the long-term simulation using the event and physically-based soil erosion model and one-hour rainfall events. The model used was calibrated and validated in the previous studies. The period time analysed covers 80 years, i.e., from 2020 until 2100. From the period the years where the most intensive rainfall events have occurred were chosen. The rainfall events were determined by climate CLM model. In order to compare the suitability of land-use management, three scenarios were created. They include three different types of land cover, i.e., agricultural crops (wheat and corn) and grassland. The modelled results show development of soil erosion in the future period up to 2100 together with the comparison of land use management in the area under research. The study predicts the future development of soil water erosion where the short term extreme rainfall events play key element as a crucial factor in the soil erosion assessment processes.

 
Tracking the thickness of the A68 Iceberg using CryoSat-2 and ICESat-2
Authors: Izzard Jamie , Braakmann-Folgmann Anne , Shepherd Andrew , Lawrence Isobel
Published: March 2021

The A68 iceberg calved from the Larsen C ice shelf on the Antarctic Peninsula in July 2017 and has since been drifting northwards towards South Georgia. Originally covering an area of 5664 sq km, A68A's extent has been reduced to 2606 sq km (as of 23 December 2020) following the detachment of multiple smaller bergs. Using Satellite Altimetry data from CryoSat-2 and ICESat-2, we measure the thickness of the A68 iceberg. We use CryoSat-2 data acquired in the year before A68's calving from the Larsen C Ice Shelf in 2017 to create an initial thickness map. Following its calving, both CryoSat-2 and ICESat-2 tracks are geocoded onto the iceberg using imagery from MODIS and Sentinel-1. Comparing these measurements to the initial thickness allows us to track changes in A68's thickness. The thickness map reveals the presence of multiple 30m deep channels oriented along its narrow side, forming lines of weakness along which the iceberg shattered into multiple large fragments in December 2020. At the time of calving, its average thickness was 232m with a maximum thickness of 285m. Repeated measurements from satellite altimetry show the iceberg has thinned by an average of 32m, a thinning rate of 2.5cm per day. Combined with changes in area, we estimate that the iceberg has lost 64% of its original volume, or 941 cubic kilometres, representing a significant input of freshwater to the surrounding ocean. 
Application of information originating from spatially non-exhaustive ancillary observations in digital soil mapping
Authors: Pásztor László , Szatmári Gábor , Laborczi Annamária , Mészáros János , Takáts Tünde , Kovács Zsófia , Árvai Mátyás , László Péter , Koós Sándor , Benő András
Published: March 2021

Due to certain socio-economic processes and technical pressure, the number of potential data sources targeting the Earth’s surface increases rapidly as well as the data generated by them. Soil mapping heavily relied on these changes in the paradigm shift, which took place in the population and interpretation of spatial soil information in the last decade. In digital soil mapping practice, auxiliary, environmental co-variables, which are related to soil forming factors and processes, have been taken into account in spatially exhaustive form. However, the potential hidden in spatially non-exhaustive (most frequently point-like), ancillary information – originating from observations also targeting the soil mantle – is far from being exploited. In their thematic features, accuracy and reliability they are inferior to primary field and/or laboratory measurements collected directly, but they are generated in more facile, cheaper way, in greater volume, with denser temporal and spatial coverage and characteristically they are available in significantly easier form. Data sequences of various installed field sensors, data collections by proximal sensing techniques, information supply by farmers and land managers as well as citizen science are considered as possible information sources. Essentially, the (soft) data supplied by them don’t provide spatially exhaustive coverage, neither direct pedological reference, nevertheless they are hypothesized to be utilized as auxiliary information within DSM framework. In a recently started project we started to investigate, (i) in which way and with what efficiency these ancillary information originating from different secondary sources can be applied, furthermore (ii) in what manner their application influences (hopefully improves) the results, accuracy and reliability of goal-specific spatial predictions. The elaborated digital mapping procedures, which are based on (i) large amount of data with differing quality and (ii) integrated geostatistical and data mining methods can be absorbed in various earth and environmental science applications.

 

Acknowledgment: Our research was supported by the Hungarian National Research, Development and Innovation Office (NKFIH; K-131820) and Gábor Szatmári by the Premium Postdoctoral Scholarship of the Hungarian Academy of Sciences (PREMIUM-2019-390).
Stochastic watershed models using a logarithmic transformation of ratio residuals
Authors: Farmer William , Shabestanipour Ghazal , Lamontagne Jonathan , Vogel Richard
Published: March 2021

There is an increasing need to develop stochastic watershed models using post-processing methods to generate stochastic streamflow ensembles from deterministic watershed models (DWMs).  Stochastic streamflow ensembles are needed for a wide variety of water resource planning applications relating to both short-term forecasting and long-range simulation. Current methods often involve post-processing of ordinary, differenced residuals defined as the difference between the simulations (S) and observations (O). However, ordinary, differenced residuals from daily and sub-daily DWMs exhibit a high degree of non-normality, heteroscedasticity, and stochastic persistence leading to the need for extremely complex post-processing methods. Using deterministic simulations of daily streamflow at over 1,400 sites across the United States, we document that logarithmically transformed ratio residuals – defined as the natural log of the quotient of S divided by O –  are approximately homoscedastic, are approximately normally distributed, and can be well-represented as an autoregressive process. These characteristics make them preferable to ordinary, differenced residuals for post-processing DWMs. Though issues with seasonal fluctuation and long-term persistence are not fully resolved, this simple transformation addresses much of the stochastic complexity of the residuals from a deterministic watershed model and produces streamflow ensemble simulations that more accurately replicate essential elements of the statistical distributions of streamflow (including design events, higher-order moments and extreme values). The use of this transformation and autoregressive models demonstrates that more accurate stochastic modeling of natural resources phenomena can be achieved with relatively elegant solutions to support natural resource management in the past, present and future.