bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the pre-eruptive processes of the 2014/15 Holuhraun eruption based on extracted volcanic tremor signals
Authors: Zali Zahra , Eibl Eva , Ohrnberger Matthias , Scherbaum Frank
Published: March 2021

During volcanic unrest, multiple subsurface processes can happen simultaneously and may lead to an eruption. The analysis of seismic records in an unrest period before an eruption reveals information about the pre-eruptive processes and might be able to provide hints for a possible future eruption.

The 2014–2015 Holuhraun eruption was the largest one in Iceland in 230 years. It was extensively monitored and studied in a variety of multidisciplinary research approaches. Intense seismicity and ground deformation were interpreted as magma propagation from Bárðarbunga volcano 48 km laterally at ∼6 km depth over two weeks before an eruption started at Holuhraun. Different processes including vertical and lateral magma migration, dike propagation, caldera subsidence, and subglacial eruptions happened in this period and some models linking these processes are suggested. In the two-week interval preceding the eruption, there is still no clear connection between the observed tremor and pre-eruptive processes. Both the tremor source location and tremor generation process are not well understood yet. While cauldrons as a sign of subglacial eruptions were identified on the glacier surface from aerial photos, these cauldrons might have been formed earlier and there is hence an uncertainty of a few days. A tremor location might help to constrain these dates. However, the simultaneous occurrence of intense seismicity and tremor hinders the study and location of tremor. Here, we use a recent volcanic tremor extraction algorithm (Zali et al., 2020) and extract pre-eruptive tremor signals in order to better locate them using the Seismic Amplitude Ratio Analysis (SARA) method. Furthermore, the occurrence of the tremor could open new insights into ascending magma and fluid migration as well as the timing and duration of the subglacial eruptions.

We also observed short-lived tremors before the eruptions on August 29 and 31, which could be considered as eruption precursors. The primary investigation on the extracted tremor signals is promising while further analysis is on-going.
Multiscale Natural Gas Emissions Observations of the San Juan, NM Coal Mine: Inversion Using Plume and Neural Network Models
Authors: Meyer Aaron , Lindenmaier Rodica , Travis Bryan , Heerah Sajjan , Dubey Manvendra
Published: March 2021

Methane (CH4) is a potent greenhouse gas; therefore, accurate measurement of its sources is important for climate research. Because of the diversity of methane sources, identifying and apportioning different sources is essential.  We demonstrate our ability characterize a specific source using top-down atmospheric observations downwind of a coal mine vent shaft, a large natural gas source, in San Juan, NM. To facilitate a field campaign in December of 2020, a mobile platform was developed to make simultaneous in situ observations of methane and ethane (C2H6) with an Aeris mid-IR spectrometer and wind velocities with a Trisonica mini 3-D anemometer. Total column methane was also measured during the campaign using an EM27/SUN mobile solar Fourier transform spectrometer (FTS) and compared with column methane and ethane measured in March of 2013 using higher resolution FTS instruments at a TCCON station near the site1. Our in situ data shows a unique and stable C2H6:CH4 ratio of 1-2% in the vent plume that agrees well with the 1.5% ratio measured by the TCCON FTS instruments in 2013, demonstrating that consistent attribution can be made using both in situ and remote methods. Furthermore, we infer the mass flux of methane and ethane from the vent shaft using a simple plume dispersion model and multiple measurements around the vent shaft. This direct source inversion is compared to results from a trained neural network code we have developed for source location and quantification (ALFaLDS)2. Our results demonstrate how multiscale measurements, inverse modeling, and machine learning can be used to better attribute and constrain methane emissions.

1 Lindenmaier, R.  et al.: Multiscale observations of CO2, 13CO2, and pollutants at Four Corners for emission verification and attribution, Proc. Natl. Acad. Sci., 111 (23), 8386-8391, https://doi.org/10.1073/pnas.1321883111, 2014.

2 Travis, B., Dubey, M. and Sauer J.: Neural networks to locate and quantify fugitive natural gas leaks for a MIR detection system, Atmos. Environ: X, 8, (2020) 100092, https://doi.org/10.1016/j.aeaoa.2020.100092, 2020.
Fluvial Seismology: Case Study of the Contagem River (Brasilia), Brazil
Authors: Havenith Hans-Balder , Hussain Yawar , Maciel Susanne
Published: March 2021

Rainfall-induced landslides may pose a significant risk to communities and infrastructures. Such landslides are substantially impacted by the fluvial systems, therefore the continuous monitoring of the seasonal erosive potentials of these rivers are crucial. However, such environmental conditions the direct in-situ investigation is often a challenging task. Therefore, the present study aims at providing a brief overview of the use of ambient seismic noise for the dynamic monitoring of fluvial systems and a discussion about the preliminary results obtained from a Brazilian case study.

Data were acquired with single short-period (2 Hz) seismometers, REFTEK-130 data-logger and GPS lock, in dry and rainy days installed within a seasonal streams in Ribeirão Contagem watershed of the Federal district of Brazil. The pre-processing of ambient noise records include conversion from REFTEK to mini-seed format and saving data in units of velocity after removing the instrumental response. Then, the frequency content (spectrograms, percentiles), waveform characteristics (envelope) and polarization attributes of changes in ambient noise wave-fields induced by bed-load transport and water flow in dry and flooding days are analyzed.

A prominent increase in mean probabilistic power spectral density (PPSD) values are observed during rainy days within a frequency range of 10 Hz to 100 Hz. The polarization analysis shows that most of the recorded energy arrived from the river side. It is concluded that seismic attributes have their relation with the river generated ambient noise and can be used for the remote monitoring of such fluvial systems. Future studies dedicated to the dense surficial and geodetic surveying (also with UAV) are recommend for the detailed quantification of these seasonal river dynamics.

Keywords: Seismic records; bed-loads; spectrograms; percentile; envelope
Autogenic knickpoints initiation related to downstream river width dynamic: Experimental approach.
Authors: de Lavaissière Léopold , Bonnet Stéphane , Davy Philippe
Published: March 2021

Upward propagation of knickpoints is known to reflect landscape disequilibrium in response to changes in boundary conditions such as tectonics, climate or base-level. However, it is suggested that some knickpoints may also form autogenically, solely from river system intrinsic process. Genesis and dynamics of such autogenic knickpoints were explored here through basin-scaled experimental modeling. The experiment consists on a 1.00 x 0.55 m box filled with silica grains, where one of the short sides goes down steadily as constant base-level fall while homogenous precipitation is applied on top of the surface.  The experimental topography is digitized on a 5 min step basis to produce 1 mm squared grid DEMs thereafter used to extract hydraulic information such as water depth, water discharge and shear stress with the hydrodynamic model Floodos (Davy et al., 2017).

We present here results from three experiments performed with similar precipitation rate but different rates of base-level fall. For the three experiments, knickpoints regularly initiate near catchment’s outlet and propagate through landscapes throughout the duration of experiments, despite steady boundary conditions. We show that their initiation near the outlet occurs from cycles in river narrowing/widening. River narrowing leads to an increase in shear stress and a knickpoint initiation. Once the knickpoint propagate upward, the river widens and the shear stress decreases, down to a new cycle of river narrowing, increasing shear stress and knickpoint initiation. We also show that the propagation rate of such autogenic knickpoints is not consistent with a stream power-based model, as it does not decrease monotonously through the experimental landscape.  We propose a new model of knickpoints generation and propagation related to downstream river width dynamic that highlights the need to better consider and understand autogenic processes in landscapes and surface process models.

Davy, P., Croissant, T., Lague, D., 2017. A precipiton method to calculate river hydrodynamics, with applications to flood prediction, landscape evolution models, and braiding instabilities: A Precipiton Method for River Dynamics. Journal of Geophysical Research: Earth Surface 122, 1491–1512.
Exploring the relationship between organic deposition resulting from marshes and autogenic scales in deltaic stratigraphy
Authors: Silvestre Jose , Sanks Kelly , Zapp Sam , Ripul Dutt , Shaw John , Straub Kyle
Published: March 2021

Many deltas contain extensive marshes, typically defined as laterally extensive, low energy settings tied to a narrow elevation window around sea level. Biological activity in marshes results in in-situ organic sediment accumulation that has the potential to be stored in the sedimentary record. However, it is unclear how marshes interact with channels that transport the clastic sediment and typically control autogenic stratigraphic architecture. We present results from a physical experiment designed to explore the coupled evolution of marshes and deltas over geologic timescales. In the experiment, deltaic channels self-organized due to constant input rates of water and clastic sediment that experience constant long-term accommodation production through sea-level rise. A low bulk density kaolinite clay was deposited on the delta-top following rules developed by the ecology community for in-situ organic production. The kaolinite clay serves as a proxy for the in-situ organic sediments in overbank regions. As such, the autogenic processes of the clastic transport system, which influence elevation relative to sea-level, also exert a control on the scales of preserved organic-rich strata. We quantify the fraction of the organic sediment proxy in the fluvio-deltaic deposit to define a transfer function between the accumulation of organic sediment and its preservation beneath the morphodynamically active layer. We also use synthetic stratigraphy and images of the preserved strata to characterize the spatial arrangements of organic strata, and the influence of marshes on the resulting arrangement of channel bodies. Initial findings suggest that the thickest seams are located near the mean shoreline but extend significant distances from this location due to autogenic shoreline transgressions and regressions. Quantifying these trends will inform our understanding of how in-situ organic sediment accumulation influences clastic transport systems and the structure of deltaic stratigraphy.
Investigation of β parameter used in Haverkamp 1D-analytical infiltration equation 
Authors: Yılmaz Deniz , Lassabatere Laurent , Moret-Fernández David , Latorre Borja
Published: March 2021

For heterogeneous soils, accurate water modeling in unsaturated soil conditions is a very important prerequisite since activation of macropore during the flow process is directly linked to the bulk saturation of the soil matrix. Indeed, macropores activate and begin to infiltrate when they receive the runoff from saturated matrices. To this point, the accurate estimation of the matrix hydraulic properties is of uttermost importance. We then focus on the accuracy of estimates for hydraulic parameters, by fitting to the well-know Haverkamp 1D analytical infiltration equation, that is widely used for Beerkan type infiltration. This equation involves an infiltration constant called β that is fixed to a by-default value of 0.6. This value is considered for relatively dry condition and for all type of soils, including fine matrices (silt, clay, etc.) but also coarse soils which are prone to preferential flows. However, the values of β have already been questioned by several authors. In this study, we performed a numerical study to investigate the value of β. Several cumulative infiltrations were numerically generated and fitted to Haverkamp’s model to derive the parameter β. This was then plotted as a function of initial water content and the type of soil. We proved that β is not constant. Especially for lower permeable soils, previous studies point that β value must be over 1 which is in contradiction with the domain of definition of β and the usual ranges considered for this parameter. Therefore, using β equal to 0.6 leads to an overestimation of Ks, leading to an overestimation of the soil capability to infiltrate and the prediction of the water budget. Numerical investigations of β show that this parameter is also a function of the degree of saturation. As defined by Haverkamp (1994), it varies from 1 for dry soil conditions to zero for saturated conditions. The hypothesis of the constancy of β allows easy integration of Richards 1D equation, leading to the formulation proposed by Haverkamp et al. However, it conducts for low permeable of soils to overestimate Ks. In this study, we demonstrate that the use of the adequate function for describing β in function to the degree saturation and the soil type improves significantly the accuracy of Haverkamp’s model.
Synchronous climate change between the Arctic and the Asian and Indo-Australian summer monsoon domains at the Younger Dryas termination
Authors: Drysdale Russell , Griffiths Michael , Hellstrom John , Corrick Ellen , Woodhead Jon , Sniderman Kale , Rasmussen Sune , Mueschler Raimund , Capron Emilie
Published: March 2021

The end of the Younger Dryas (YD) was Earth’s last major abrupt climate event and is most vividly preserved in the water-isotope (ice δ18O), calcium (Ca2+) and methane-concentration (CH4) series of Greenland ice cores. Although numerous palaeoclimate records span this transition, surprisingly few have the dating precision necessary to test whether or not abrupt warming in Greenland was accompanied by synchronous climate changes beyond the Arctic. Speleothems, with their exceptional absolute chronologies, are well placed to conduct such a test.

Here we apply a change-point detection algorithm to new and published speleothem δ18O records of the YD from the Indo-Australian summer monsoon and Asian summer monsoon domains to compare the synchronicity of hydroclimate changes across the YD termination. The algorithm, which identifies the age (and its uncertainty) of a regime shift in a time series, was applied to the 13 - 11 ka interval of each speleothem record. The results yield an error-weighted mean YD-termination age of 11.55 ± 0.02 ka BP (2σ), supporting the hypothesis of a closely coupled monsoon seesaw. Analysis of the Greenland NGRIP ice-core δ18O and Ca2+ records on the GICC05 chronology for the same interval produces a YD-termination age of 11.63 ± 0.10 ka BP. Although the NGRIP and speleothem ages overlap within uncertainties, this hints at a possible Arctic lead over the tropics. However, if we apply a correction to the GICC05 chronology based on recent ice-core 10Be and tree-ring 14C synchronisation, the change-point analysis gives a NGRIP termination age of 11.57 ± 0.02 ka BP. This revised timing is consistent with the Cariaco Basin greyscale record (11.56 ± 0.02 ka BP). It also brings the NGRIP and Antarctic WAIS Divide ice-core CH4 records into perfect alignment across the transition. This assemblage of ages from geographically dispersed regions suggests that hydroclimate changes associated with the YD termination were synchronous, at least to within a couple of decades. It also calls for a revision to the onset age of the Greenlandian Stage (the Pleistocene-Holocene boundary).
Spatio-temporal variability of snow accumulation on the Biafo and Hispar glaciers in the central Karakoram
Authors: Groos Alexander Raphael , Mayer Christoph , Lambrecht Astrid , Erlwein Sabrina , Schwikowski Margit
Published: March 2021

The Karakoram is an extensively glacierised mountain range in the western part of High Mountain Asia and constitutes an important source of fresh water for millions of people in the Indus Basin. Over the last years, the Karakoram has attracted increasing attention due to an anomalous glacier stability, which contrasts the progressing ice mass loss across the Himalaya. Decreasing summer temperatures and increasing winter precipitation have been proposed as potential causes for the anomaly. However, the lack of snow accumulation studies and long-term meteorological measurements above 3,000 m a.s.l. hampers the corroboration of this hypothesis. To quantify the spatial and temporal variability of snow accumulation in the central Karakoram, we followed the track of a Canadian research expedition from 1986. We reinvestigated eight sites between ca. 4,400 and 5,200 m a.s.l. in the connected accumulation zone of the Biafo and Hispar glaciers in 2019. Density measurements were performed in each snow pit down to the summer horizon of the previous year to quantify the elevation-dependent amount of annually accumulated snow. In addition, snow samples were collected from three selected pits for the analysis of rare earth elements and stable water isotopes to constrain the origin and seasonality of the deposited snow. Finally, we compared our recent measurements with the 30-year-old results from the Canadian research expedition as well as independent meteorological data.  In doing so we aim to evaluate the hypothesised increase in winter precipitation in this region.
Linking Large-scale Circulation Descriptors to Precipitation Variability in the Northern French Alps
Authors: Blanc Antoine , Blanchet Juliette , Creutin Jean-Dominique
Published: March 2021

This work analyses the link between Western Europe large-scale circulation and precipitation variability in the Northern French Alps from 1950 to 2017. We consider simple descriptors characterizing the daily 500hPa geopotential height fields. They are the Maximum Pressure Difference - representing the range of geopotential heights over Western Europe -, and the singularity - representing the mean distance between a geopotential shape and its closest analogs, i.e. the way this geopotential shape is reproduced in the climatology. These descriptors are compared to the occurrence of different atmospheric influences - Atlantic, Mediterranean, Northeast, Anticyclonic - and to the leading mode of large-scale circulation variability over Europe - the North Atlantic Oscillation (NAO) - for explaining precipitation variability in the Isère River catchment from one day to 10 years. We show that the Maximum Pressure Difference and the singularity of geopotential shapes explain a significant part of precipitation variability in the Northern French Alps from 10 days to 10 years, especially in winter (correlation values of 0.7). These descriptors provide much better performance than NAO and the same performance as the occurrence of the Atlantic influence, which is the best performing atmospheric influence. This means that simple characteristics of large-scale circulation - that are easy to implement - provide as much information as weather pattern classification to explain precipitation variability in the Northern French Alps.
The fate of chromium in soils
Authors: Magalhães M. Clara F. , Sarabando Cândida , Santos Teresa M. , Abreu Maria Manuela
Published: March 2021

The large industrial utilization of chromium compounds originates heavy environmental and health risks concerns. Chromium has a double behavior, as Cr(III), is an essential element to living beings but also a very harmful carcinogenic as Cr(VI). Hexavalent chromium is a powerful oxidant easily reduced to chromium(III). The fact of the compounds of chromium(III) being considered kinetically inert induces their environmental abandon without any concerns about their real final fate. Nowadays there is an increasing interest on chromium bioremediation in soils.

Depending on soils composition, the interaction between the chromium(III) compounds and both organic and inorganic soil components can originate an increase of the solubility of the chromium(III) compounds together with acid-base and redox reactions. The change on the solubility of chromium compounds can be monitored from the composition of the soil solutions from where plants can have access to the ionic species of chemical elements. The presence of organic matter is usually associated to the existence of reducing environments, while the presence of manganese oxides is associated to oxidizing environments. Here is analysed the influence of these two environments in the composition of soil solutions and the consequent availability to plants, as well as the design of the soil remediation programs.
Tracking the sources of water isotopes in water vapor and monsoon precipitation over India using iCESM1.2 simulations
Authors: Tharammal Thejna , Bala Govindasamy , Nusbaumer Jesse
Published: March 2021

Stable isotopes of water are common proxies used to reconstruct the past precipitation in the tropics, based on the climate-dependent fractionation of the water molecule. Hence, an investigation of the factors affecting the present-day isotope ratios in precipitation in the tropical monsoon regimes could aid the interpretation of the paleo-proxies. Along with the degree of rainouts and strength of convection, the isotope ratios in precipitation over a region depend on the source of water vapor. We use the water vapor-isotope tagging capabilities in the isotope-enabled earth system model iCESM1.2 to estimate the relative contribution of different oceanic sources and regional land water recycling to the present-day distribution of precipitation and isotope ratios in precipitation in the Indian land region. We choose two major precipitation seasons for our study – the Southwest monsoon [SW, June to September], the major contributor of annual precipitation in the region, and the Northeast monsoon [NE, October to December] that is important for the annual precipitation in the southern Indian region. It is expected that these two monsoon seasons should have different major sources of water vapor because of the reversal in monsoon circulation between these two seasons. Preliminary results suggest that the model can reproduce the seasonal distribution of precipitation and water isotopes in precipitation in the Indian region. The water-tagging method successfully identifies the sources of precipitation in the Indian region. The detailed results of this study will be presented at the meeting.
Tracking signal propagation through landscapes using a granular avalanching system
Authors: Griffin Chloe , Higham Jonathan , Duller Robert , Straub Kyle
Published: March 2021

Landscapes have the ability to transmit environmental signals or inhibit them. The mechanisms by which landscapes do this are largely unquantified, but is probably due to the ability of landscapes to transiently store and release sediment which acts as a medium for energy to propagate. Previous experiments using 1D avalanching rice piles suggest that stochastic collapses can overprint, or shred, periodic sedimentary signals (Jerolmack and Paola (2010), as measured using mass efflux from the experimental rice pile. Jerolmack and Paola (2010) defined a threshold for successful surface signal propagation: Tx, where signals with a period less than Tx are shredded, unless the magnitude of the signal is sufficiently large. We aim to utilise the rice pile to further investigate signal propagation across a landscape, and the thresholds for this, by quantifying inter-particle interactions and the mechanics of how signals propagate using a quasi-2D rice pile model, built using MFiX-DEM code. This open source, physics model utilises individual particles which compose the solid phase whilst treating the fluid as a continuum. The rice grains in the model are represented by spherical particles, where each individual particle, or cluster of particles, can be tracked through each time step using a coordinate axis system, allowing internal dynamics, such as avalanche sizes and sediment residence times, to be quantified. To certify the model replicates the self-organised nature of an experimental rice pile, sensitivity tests were performed by systematically changing two key parameters controlling grain interactions: the friction coefficient and the coefficient of restitution, alongside the sediment flux. To calibrate the results of the sensitivity analysis, mass efflux through time and the corresponding power spectra are compared to real experimental rice pile results and statistical rice pile models. It is hoped this work will provide fundamental insights into how a signal propagates through a landscapes, and how they are shredded in the process.   
Looking for the present in the past: Paleoenvironmental analyses and Social-ecological memory to explore changes in the mangroves of the Ciénaga Grande de Santa Marta - Colombia
Authors: Gutierrez-Cala Lina , Zúñiga Andrés C. , Gonzalez Catalina , Salgado Jorge , Saavedra-Díaz Lina M. , Ricaurte Constanza , Zipper Samuel C. , Jaramillo Fernando
Published: March 2021

Compound anthropogenic pressures are driving critical mangrove degradation worldwide, threatening the wellbeing of coastal human populations historically associated with these systems. The Ramsar and Biosphere Reserve, Ciénaga Grande de Santa Marta (CGSM) is located in the northern of Colombia and is the largest coastal lagoon-delta in the Caribbean. It is inhabited by stilt communities that have developed intricate livelihood and cultural relationships with the mangroves. The CGSM has experienced sustained social and ecological degradation during the last six decades, triggered by land-use change and disruption of hydrological connections. This study integrates Social-ecological Memory from fishing communities and Paleoenvironmental frameworks to develop a historical perspective of the biophysical and social dimensions of environmental change in the CGSM. Integrating X-ray fluorescence (XRF) geochemical sediment analysis, C14 radiocarbon dating, and demographic inferences from archaeological evidence revealed three distinct periods over the last ~5000 years where sea-level rise and hydroclimatic variability shaped the transition between freshwater to prevailing marine conditions and modulated human occupation patterns in the area. Specifically, the period with the highest hydroclimatic variability and precipitation minima (4000 – 2500 yr BP) is consistent with the lowest human population estimates, whereas sea-level increase (~ 2000 yr BP) corresponds with a sustained increase in estimated population growth. In connection, participatory oral reconstructions conducted in the stilt-house communities of Buenavista and Nueva Venecia, offered nuanced descriptions about the spatial, temporal, and contextual aspects generating and reinforcing hypersalinization of the system, and their profound social-ecological consequences over the past several decades. The interdisciplinary approach of this study indicates that the CGSM is a highly dynamic socio-ecological system that has been changing and reconfiguring across different time scales in response to both natural and human-induced processes. Finally, it reveals the relative effects of biophysical and social drivers on driving social-ecological change on millennial to decadal time scales.
Scanning 10-W Water Vapor DIAL for the Investigation of Atmospheric Turbulence and Land-Atmosphere Feedback
Authors: Behrendt Andreas , Spaeth Florian , Wulfmeyer Volker
Published: March 2021

We will present recent measurements made with the water vapor differential absorption lidar (DIAL) of University of Hohenheim (UHOH). This scanning system has been developed in recent years for the investigation of atmospheric turbulence and land-atmosphere feedback processes.

The lidar is housed in a mobile trailer and participated in recent years in a number of national and international field campaigns. We will present examples of vertical pointing and scanning measurements, especially close to the canopy. The water vapor gradients in the surface layer are related to the latent heat flux. Thus, with such low-elevation scans, the latent heat flux distribution over different surface characteristics can be monitored, which is important to verify and improve both numerical weather forecast models and climate models.

The transmitter of the UHOH DIAL consists of a diode-pumped Nd:YAG laser which pumps a Ti:sapphire laser. The output power of this laser is up to 10 W. Two injection seeders are used to switch pulse-to-pulse between the online and offline signals. These signals are then either directly sent into the atmosphere or coupled into a fiber and guided to a transmitting telescope which is attached to the scanner unit. The receiving telescope has a primary mirror with a dimeter of 80 cm. The backscatter signals are recorded shot to shot and are typically averaged over 0.1 to 1 s.
Effective hydraulic properties of virtual stony soils: Forward 3D simulations evaluated by 1D inverse modeling
Authors: Naseri Mahyar , C. Iden Sascha , Durner Wolfgang
Published: March 2021

Measuring hydraulic properties of stony soils and interpretation of the measured data is a challenge in vadose zone hydrology. The reason is not only the problem of installing suitable sensors but also the systematic measurement errors when sensors are only located in the background soil. A common approach to calculate the hydraulic properties of stony soils is by scaling the properties of the background soil according to the rock fragment content. Such modeling approaches are primarily developed for saturated flow conditions and only consider the amount of rock fragments as an input parameter. However, there is still a gap in knowledge regarding the effective properties of stony soils under unsaturated flow conditions.

Recently, 3D numerical simulation has become a convenient alternative tool to study the transport properties of heterogeneous porous media. The generation of data by numerical models is fast, measurements are repeatable and the simulation of the system under different initial and boundary conditions is easily achievable. We simulated three-dimensional unsaturated water flow in laboratory columns with stony soil material using the Hydrus 2D/3D software. Geometries were generated by assuming different volume fractions of impermeable rock fragments with spherical, cylindrical, or prolate shapes embedded in sandy loam soil. Time series of mean water contents, local pressure heads, and fluxes across the upper boundary were generated in an evaporation experiment, and a multi-step unit gradient simulation was applied to obtain values of hydraulic conductivity near saturation.

The synthetic measurement data were evaluated by inverse modeling, assuming a homogeneous system, and the effective hydraulic properties of stony soils were identified. The results were used to evaluate the scaling approaches for different volumes of rock fragments. A non-linear reduction in hydraulic conductivity by the increase of rock fractions was visible. The results also highlighted the effects of the orientation and shape of rock fragments. The orientation of rock fragments towards flow has a significant effect on the flow reduction, and in the case of prolate spheroids oriented along the flow direction, the reduction in conductivity was less significant. 
How useful is experimental hydrology in understanding overland flow and associated transport processes?
Authors: de Lima João L.M.P.
Published: March 2021

During the last decades, more and more researchers have concentrated their work on the study of overland flow and associated transport processes: new developments, innovative techniques and breakthroughs are being presented year after year, which is noteworthy. Whilst experimental hydrology has played an important role in many of these studies, it is not always acknowledged the main difficulties, limitations, challenges, but also advantages and opportunities in this study approach.

 

Bearing on personal involvement in three decades of experimental work in surface hydrology that contributed to improve our understanding of several hydrological processes (e.g. overland flow, sediment transport, rill and interrill erosion, infiltration), this presentation addresses shortly main issues related to the experimental part of that work, conducted in two continents. The work used experimental setups that focused mainly in the study of rainfall-runoff, overland flow and associated transport processes, namely water erosion. Experiments were conducted in natural, agricultural and urban surfaces, both in disturbed and undisturbed conditions or samples. Special attention has been given to mulching, wind-driven rain, and on the use of thermal tracers. The input in field-based studies was natural rainfall, whereas simulated rainfall simulators and/or run-on have been applied within laboratory-based experiments. In fact, the adaptability of rainfall simulators to different temporal and spatial scales allowed many experimental designs to suit specific research objectives.

 

This presentation highlights the inherent problems and difficulties in conducting studies to encompass such diverse situations as observed in natural and human-modified surfaces. However, the main objective is to stimulate the discussion and enhance understanding of the requirements of experimental research, both in the laboratory and in the field, since that can contribute to achieve further clarifications in surface hydrology. For example, runoff responses of urban, rural and periurban areas are still not well understood. Experimental research is also essential in multidisciplinary approaches aiming at further improving our knowledge on transports associated with runoff (e.g. litter, virus, microbial contaminants, emerging chemicals found in pharmaceuticals, personal care products, pesticides, industrial and household products, surfactants, metals).
Effects of topsoil removal on greenhouse gas exchange of fen paludicultures
Authors: Köwitsch Philipp-Fernando , Tiemeyer Bärbel
Published: March 2021

Drainage is necessary for conventional agriculture on peatlands, but this practice causes high emissions of the greenhouse gases (GHG) carbon dioxide and nitrous oxide. Paludiculture is an option to mitigate these adverse environmental effects while maintaining productive land use. Whereas the GHG exchange of paludiculture on rewetted bog peat, i.e. Sphagnum farming, is relatively well examined, data on GHG emissions from fen paludicultures is still very scarce. As typical fen paludiculture species are all aerenchymous plants, the release of methane is of particular interest when optimising the GHG balance of such systems. Topsoil removal is, on the one hand, an option to reduce methane emissions as well as phosphorus release upon rewetting, but on the other hand, nutrient-rich topsoils might foster biomass growth.

In this project, Typha angustifolia, Typha latifolia, and Phragmites australis are grown at a fen peatland formerly used as grassland. Water levels will be kept at the surface or slightly above it. In parts of the newly created polder, the topsoil will be removed. To be able to separate the effects of topsoil removal and water level, four smaller sub-polders will be installed. Greenhouse gas exchange will be measured with closed manual chambers for all three species with and without topsoil removal as well as at a reference grassland site close by.
Ripples in the Heliospheric Current Sheet: Dependence on Latitude and Transient Outflows
Authors: Laker Ronan , Horbury Timothy , Matteini Lorenzo , Woolley Thomas , Woodham Lloyd , Stawarz Julia , Bale Stuart , Davies Emma , Eastwood Jonathan , O'Brien Helen , Evans Vincent , Angelini Virginia , Richter Ingo , Heyner Daniel , Owen Chris , Louarn Philippe , Fedorov Andrei
Published: March 2021

The recent launches of Parker Solar Probe (PSP), Solar Orbiter (SO) and BepiColombo, along with several legacy spacecraft, have provided the opportunity to study the solar wind at multiple latitudes and distances from the Sun simultaneously. We take advantage of this unique spacecraft constellation, along with low solar activity between May and July 2020, to investigate how latitude affects the solar wind and Heliospheric Current Sheet (HCS) structure. We use ballistic mapping to compare polarity and solar wind velocity between several spacecraft, showing that fine scale ripples in the HCS can be resolved down to several degrees in longitude. We show that considering solar wind velocity is also useful when investigating the HCS structure, as it can reveal times when the spacecraft is within slow, dense streamer belt wind without changing magnetic polarity. We measured the local orientation of planar magnetic structures associated with HCS crossings, finding that these were broadly consistent with the shape of the HCS but at much steeper angles due to compression from stream interaction regions. We identified several transient magnetic clouds associated with HCS crossings, and have shown that these can disrupt the local HCS orientation up to four days after their passage, but did not significantly affect the position of the HCS. This work highlights that the heliosphere should always be treated as three-dimensional, especially at solar minimum, where a few degrees in latitude can create a considerable difference in solar wind conditions.
Mixtures of (skewed) Gaussian distributions for statistical post-processing
Authors: Taillardat Maxime
Published: March 2021

The implementation of statistical post-processing of ensemble forecasts is increasingly developed among national weather services. The so-called Ensemble Model Output Statistics (EMOS) method, which consists in generating a given distribution whose parameters depend on the raw ensemble, leads to significant improvments in forecast performance for a low computational cost, and so is particularly appealing for reduced performance computing architectures. However, the choice of a parametric distribution has to be sufficiently consistent so as not to lose information on predictability such as multimodalities or asymmetries.

Different distributions are applied to the post-processing of the ECMWF ensemble forecast of surface temperature. More precisely, mixture of Gaussian and skew-Normal distributions are tryed from 3 up to 360h lead time forecasts. For this work, analytical formulas of the continuous ranked probability score have been derived. We will discuss the first results obtained judging both overall performance and tolerance to mispecification.
Using BOSS to learn microphysical process rate information from polarimetric radar observations
Authors: Reimel Karly , van Lier-Walqui Marcus , Kumjian Matthew , Morrison Hugh , Prat Olivier
Published: March 2021

Representing microphysics within weather and climate models is challenging because we lack fundamental understanding of microphysical processes and are limited by the computational inability to track each hydrometeor within a cloud system.  Microphysics schemes parameterize rates for specific processes such as drop evaporation, collision-coalescence, or collisional-breakup, but their inherent assumptions lead to uncertainty in model solutions which are often difficult to understand and quantify. Observations such as those from polarimetric radar provide insight into the microphysical evolution of clouds, but alone they are unable to provide quantitative information about the process rates that lead to this evolution. The Bayesian Observationally Constrained Statistical-Physical Scheme (BOSS) is a recently-developed bulk microphysics scheme designed to bridge the gap between observations and the processes acting on individual drops, such that process rate information can be directly learned from polarimetric radar observations. BOSS operates with no predefined drop size distribution (DSD) shape and makes few assumptions about the process rate formulations. Because there is no prescribed DSD shape, a new moment-based polarimetric forward operator is used to relate model prognostic moment output to polarimetric radar variables.  Process rates are written as generalized power functions of the prognostic DSD moments (related to bulk quantities such as mass concentrations), with flexibility to choose the number and order of the prognostic DSD moments and number of power terms in the process rate formulations.  The corresponding process rate parameters are constrained directly with observation using Markov chain Monte Carlo in a Bayesian inference framework, allowing BOSS to learn microphysical information directly from observations while simultaneously quantifying parametric uncertainty. The process rate formulations in BOSS can be made systematically more complex by adding more terms and/or more prognostic DSD moments, which allows us also to track down sources of structural uncertainty. In this study, we use a detailed bin microphysics scheme as “truth” to generate the constraining observations synthetically, which include profiles of polarimetric radar variables (ZH, ZDR, KDP) and vertical fluxes of prognostic DSD moments at the surface. An error analysis shows that BOSS produces process rate profiles similar to those of a bin scheme when only provided polarimetric rain profiles and surface prognostic moment fluxes. We also display initial results where BOSS is used to estimate microphysical process rate information from real polarimetric radar observations.  
The impacts of hot-dry compound extremes on US Soybean yields
Authors: Hamed Raed , Van Loon Anne , Aerts Jeroen , Coumou Dim
Published: March 2021

The US agriculture system supplies more than one third of globally traded soybean, of which 90% is produced under rainfed agriculture. This makes the commodity particularly sensitive to weather and climate variability. Previous research has shown that annually averaged climate conditions explain about a third of global crop yield variability. Additionally, although less studied so far, crops are sensitive to specific short-term weather conditions, isolated or co-occurring at key moments throughout the growing season. Here we aim to identify key within-season weather and climate variables that can explain soybean yield variability in the US while exploring synergies between drivers that can have compounding impacts. The study combines weather data from reanalysis and satellite-based evapotranspiration and root-zone soil moisture with sub-national crop yield estimates using statistical methods that account for interaction effects. We also analyze the historic changes in identified key driving conditions in order to explore the effects of current climatic trends on yields. Our preliminary results indicate positive yield response to higher minimum temperature early and late in the season whereas the largest effect on soybeans is driven by the harmful co-occurrence of high temperature and low moisture levels during the summer flowering period significantly reducing yields on average in the US  by one standard deviation. The magnitude of the response to climate drivers varies across the spatial domain highlighting the need to focus on local and season specific management strategies. On the bright side, recent trends in temperature have not increased the likelihood of low yields. This is because the overall warming conditions reduce the risk of frost early and late in the season. Conversely, a peculiar cooling trend during the summer period attributed to agricultural land use is beneficial for yields when crops are most sensitive to high temperatures. Our study provides a detailed understanding of the current relationship between climate and soybean yields in the US. This is particularly relevant for adaptation and mitigation strategies aimed at avoiding low yields in a context of increasing food demand and climate change.
Ground-based lidar observations of vertical aersosol and water vapor profiles within the boundary layer over heterogeneous terrain
Authors: Speidel Johannes , Vogelmann Hannes , Perfahl Matthias , Mauder Matthias , Wanner Luise
Published: March 2021

Connecting the earth's surface with the free troposphere, the planetary boundary layer (PBL) comprises complex dynamics of turbulent behavior. This especially applies for areas with heterogeneous terrain. Relevant near-ground processes such as released energy fluxes and the emission of aerosols and trace gases directly interact with the atmosphere. Therefore, the PBL's physical state is determined both by the near-ground processes as well as entrainment of air parcels from higher layers. The mainly turbulence-driven transport of particles and properties throughout the PBL constrain a comprehensive understanding of the PBL's behavior. Hence, the energy balance closure problem as well as errors in precipitation forecast in long-term numerical weather predictions, amongst others, remain unresolved challenges. Here, ground-based lidar profiling is a well suitable method for observing the PBL, as data sampling allows for high temporal and vertical resolutions (Here: Sampling rate of 100\,Hz and 7.5\,m). During the CHEESEHEAD campaign, carried out in summer 2019, our newly developed ATMONSYS lidar performed measurements over complex terrain in northern Wisconsin. There, our lidar system was embedded in a dense network of multiple in-situ and remote sensing instruments. The central aim of this campaign was to further contribute to solve the energy balance closure problem. With the ATMONSYS lidar, vertical columns of aerosol backscatter coefficients, water vapor and temperature have been recorded. The presented work shows what the data is suitable for in terms of resolution and temporal extent in the first place. As a second point, focus is given on structure and variability of aerosol backscatter coefficient distributions and water vapor concentrations as well as their implications on the prevailing state of the PBL. Based on the presented findings, we discuss the potential and suitability of this experimental data for deriving transport processes within the PBL.