bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal, Kp and IMF dependence of hemispheric asymmetry in ionospheric horizontal and field-aligned currents 
Authors: Workayehu Abiyot , Vanhamäki Heikki , Aikio Anita , Shepherd Simon
Published: March 2021

We present statistical investigation of the seasonal, geomagnetic activity and interplanetary magnetic field (IMF) dependence of  hemispheric asymmetry in the auroral currents. Magnetic data from the Swarm satellites has been analyzed by applying the spherical elementary current system (SECS) method. Bootstrap resampling has been used to remove the difference in the number of samples as well as activity and IMF conditions between the local seasons and the hemispheres. In general, the currents are larger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Asymmetry is larger during low (Kp<2) than high Kp (Kp≥2) and during local winter and local autumn than local summer and local spring. Averaging over all Kp and IMF conditions, we find larger currents flowing in the NH than in the SH with the NH/SH ratio for FACs: 17­±5%, 14±5%,7±4% and 2±4% in winter, autumn spring and summer, respectively.  When making the statistical analysis for different IMF directions, we find that the orientation of IMF By has strong influence on the hemispheric asymmetry in the auroral currents, but this influence depends on local season. When IMF By is positive in NH (negative in SH), on average FACs as well as ionospheric horizontal currents are stronger in NH than inSH in most local seasons under both signs of IMF Bz. Conversely, when IMF By is negative in NH (positive in SH), the hemispheric differences of auroral currents during most local seasons are small except in local winter. Overall, comparing the hemispheres for opposite signs of IMF By, we find larger hemispheric asymmetry when IMF By is positive in  NH (negative  in SH) than vice versa.

The factors causing the observed hemispheric asymmetries in the auroral currents are not understood at the moment. Background conductances from the IRI model and cross polar cap potential values from SuperDARN dynamic modelsuggest that solar induced ionospheric conductances and convection electric field cannot explain all the observed features of the hemispheric asymmetry in auroral currents. The role of conductance enhancements due to auroral particle precipitation and possible asymmetries in the energy  flux of precipitating particles need to be investigated in future studies.
Prediction of Dansgaard-Oeschger events using machine learning
Authors: Moniz Nuno , Barbosa Susana
Published: March 2021

The Dansgaard-Oeschger (DO) events are one of the most striking examples of abrupt climate change in the Earth's history, representing temperature oscillations of about 8 to 16 degrees Celsius within a few decades. DO events have been studied extensively in paleoclimatic records, particularly in ice core proxies. Examples include the Greenland NGRIP record of oxygen isotopic composition.
This work addresses the anticipation of DO events using machine learning algorithms. We consider the NGRIP time series from 20 to 60 kyr b2k with the GICC05 timescale and 20-year temporal resolution. Forecasting horizons range from 0 (nowcasting) to 400 years. We adopt three different machine learning algorithms (random forests, support vector machines, and logistic regression) in training windows of 5 kyr. We perform validation on subsequent test windows of 5 kyr, based on timestamps of previous DO events' classification in Greenland by Rasmussen et al. (2014). We perform experiments with both sliding and growing windows.
Results show that predictions on sliding windows are better overall, indicating that modelling is affected by non-stationary characteristics of the time series. The three algorithms' predictive performance is similar, with a slightly better performance of random forest models for shorter forecast horizons. The prediction models' predictive capability decreases as the forecasting horizon grows more extensive but remains reasonable up to 120 years. Model performance deprecation is mostly related to imprecision in accurately determining the start and end time of events and identifying some periods as DO events when such is not valid.
Does the lack of root hairs alter root system architecture of Zea mays?
Authors: Schlüter Steffen , Lippold Eva , Phalempin Maxime , Vetterlein Doris
Published: March 2021

Root hairs are one root trait among many which enables plants to adapt to environmental conditions. How different traits are coordinated and whether some are mutually exclusive is currently poorly understood. Comparing a root hair defective mutant with its corresponding wild-type we explored if and how the mutant exhibited root growth adaption strategies and as to how far this depended on the substrate.

Zea mays root hair defective mutant (rth3) and the corresponding wild-type siblings were grown on two substrates with contrasting texture and hence nutrient mobility. Root system architecture was investigated over time using repeated X-ray computed tomography.

There was no plastic adaption of root system architecture to the lack of root hairs, which resulted in lower uptake in particular in the substrate with low P mobility. The function of the root hairs for anchoring did not result in different depth profiles of the root length density between genotypes. Both maize genotypes showed a marked response to substrate. This was well reflected in the spatiotemporal development of rhizosphere volume fraction but especially in the strong response of root diameter to substrate, irrespective of genotype.

The most salient root plasticity trait was root diameter in response to substrate, whereas coping mechanisms for missing root hairs were less evident. Further experiments are required to elucidate whether observed differences can be explained by mechanical properties beyond mechanical impedance, root or microbiome ethylene production or differences in diffusion processes within the root or the rhizosphere.
Initial effective stress controls the nature of earthquakes 
Authors: Passelegue Francois , Almakari Michelle , Dublanchet Pierre , Barras Fabian , Fortin Jerome , Violay Marie
Published: March 2021

  Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures. Despite geodetical, seismological, experimental and field observations, the origin of this variation of the rupture velocity in nature, as well as the physics behind it, is still debated. Here, we first discuss the scaling relationships existing for the different types of fault slip observed in nature and we highlight how they appear to stem from the same physical mechanism. Second, we reproduce at the scale of the laboratory the complete spectrum of rupture velocities observed in nature. Our results show that when the nucleation length is within the fault length, the rupture velocity can range from a few millimetres to kilometres per second, depending on the available energy at the onset of slip. Our results are analysed in the framework of linear elastic fracture mechanics and highlight that the nature of seismicity is governed mostly by the initial stress level along the faults. Our results reveal that faults presenting similar frictional properties can rupture at both slow and fast rupture velocities. This combined set of field and experimental observations bring a new explanation of the dominance of slow rupture fronts in the shallow part of the crust and in areas presenting large fluid pressure, where initial stresses are expected to remain relatively low during the seismic cycle.
Evaluating simulated linear kinematic features in high-resolution sea-ice simulations of the FAMOS Sea Ice rheology experiments (SIREx)
Authors: Hutter Nils , Bouchat Amélie , Dupont Frédéric , Dukhovskoy Dmitry , Koldunov Nikolay , Lee Younjoo , Lemieux Jean-François , Lique Camille , Losch Martin , Maslowski Wieslaw , Myers Paul G. , Olason Einar , Rampal Pierre , Rasmussen Till , Talandier Claude , Tremblay Bruno , Wang Qiang
Published: March 2021

Simulating sea-ice drift and deformation in the Arctic Ocean is still a challenge because of the multi-scale interaction of sea-ice floes that compose the Arctic sea ice cover. The Sea Ice Rheology Experiment (SIREx) is a model intercomparison project formed within the Forum of Arctic Modeling and Observational Synthesis (FAMOS) to collect and design skill metrics to evaluate different recently suggested approaches for modeling linear kinematic features (LKFs) and provide guidance for modeling small-scale deformation. In this contribution, spatial and temporal properties of LKFs are assessed in 33 simulations of state-of-the-art sea ice models (VP/EVP,EAP, and MEB) and compared to deformation features derived from RADARSAT Geophysical Processor System (RGPS).
All simulations produce LKFs, but only very few models realistically simulate at least some statistics of LKF properties such as densities, lengths, lifetimes, or growth rates. All SIREx models overestimate the angle of fracture between conjugate pairs of LKFs pointing to inaccurate model physics. The temporal and spatial resolution of a simulation and the spatial resolution of atmospheric forcing affect simulated LKFs as much as the model's sea ice rheology and numerics. Only in very high resolution simulations (≤2km) the concentration and thickness anomalies along LKFs are large enough to affect air-ice-ocean interaction processes.
A hybrid CAI/IMU solution for higher navigation performance 
Authors: Tennstedt Benjamin , Weddig Nicolai , Schön Steffen
Published: March 2021

Atom Interferometers as inertial sensors were getting quite some interest in the last decade. Several attempts have been made to combine the two sensors (i.e. classical inertial measurement units IMU and cold atom interferometers), mainly with the goal to use the atom interferometer as main sensor, and support it with different conventional sensors in order to suppress noise and achieve maximum sensitivity and long-term stability.
We present a quite promising combination of both sensors in an error state extended Kalman Filter framework aimed especially on further improving the performance of a conventional high end IMU. While the full potential of the cold atom interferometer is not yet entirely exploited in this combination, first simulations in terrestrial applications with small and even larger change of inertial forces show an increase of the navigation solution precision by a factor of 20 and more.
Quantifying gas, ash and aerosols in volcanic plumes using emission OP-FTIR measurements
Authors: Smekens Jean-François , Mather Tamsin , Burton Mike
Published: March 2021

Monitoring of volcanic emissions (gas, ash and aerosols) is crucial to our understanding of eruption mechanisms, as well as to developing mitigation strategies during volcanic eruptions. Ultraviolet (UV) spectrometers and cameras are now ubiquitous monitoring tools at most volcano observatories for quantifying sulphur dioxide (SO2) emissions. However, because they rely on scattered UV light as a source of radiation, their use is limited to daytime only, and measurement windows are often further restricted by unfavourable weather conditions. On the other end of the spectrum, Open Path Fourier Transform Infrared (OP-FTIR) instruments can be used to measure the concentrations of a series of volcanic gases, and they allow for night-time operation. However, the retrieval methods rely on the presence of a strong source of IR radiation in the background - either natural (lava flow, crater rim, the sun) or artificial – restricting their use to very specific observation geometries and a narrow range of eruptive conditions. Here we present a new approach to derive quantities of SO2, ash and aerosols from measurements of a drifting volcanic plume. Using the atmosphere as a background, we measured self-emitted IR radiation from plumes at Stromboli volcano (Italy) capturing both passive degassing and ash-rich explosive plumes. We use an iterative approach with a forward radiative transfer model (the Reference Forward Model – RFM) to quantify concentrations of sulphur dioxide (SO2), aerosols and ash in the line of sight of the spectrometer. This new method could significantly enhance the scientific return from OP-FTIR instruments at volcano observatories, ultimately expanding their deployment as part of permanent scanning networks (an alternative to DOAS instruments) to provide continuous data on the emissions of gas, ash and aerosols. 
Relationships between wood anatomical traits and climate conditions at three beech forest sites in Slovenia
Authors: Arnič Domen , Gričar Jožica , Jevšenak Jernej , Božič Gregor , von Arx Georg , Prislan Peter
Published: March 2021

It is uncertain how European beech (Fagus sylvatica L.) will perform under climate change. Several dendroclimatological studies suggest that increasing temperature will positively affect radial increments at sites optimal for its growth. However, it is not entirely clear how changing growth conditions will affect wood anatomy and thus wood properties. The aim of this study was therefore to analyse the relationships between climate conditions (temperature and precipitation) and wood anatomical traits in beech trees growing at optimal beech forest sites in Slovenia. Three forest sites representing the main Slovenian beech provenances were selected (Idrija, Javorniki, and Mašun). At each site, 16 increment cores were collected in 2016 and subsequently prepared for observation under the light microscope. Image analysis software (Image Pro-Plus and Roxas) were used for quantitative wood anatomy. Mean vessel area, vessel density, and relative conductive area were analysed in tree rings between 1960-2016. Furthermore, tree rings were divided into four quarters to assess the intra-annual variability in vessel features also in relation to weather conditions. The preliminary results indicated that there was a significant difference in tree-ring widths as well as in vessel features among the selected forest sites. Idrija, the late flushing provenance, had the narrowest tree rings, the highest vessel density and relative conductive area, and smallest mean vessel area. The other two sites had a similar mean vessel area, while the widest tree-ring width and the smallest vessel density and relative conductive area were observed at Mašun (the mid-flushing provenance). The response of tree-ring width and vessel features to changing climate conditions differed among sites/provenance. Tree-ring widths at Idrija and Javornik were positively affected by late winter temperature, while tree-ring widths at Mašun were mostly affected by summer precipitation. In the case of vessel features, the highest correlations with climate data were observed in the fourth quarter of the rings with late summer temperature and precipitation. In conclusion, early spring temperatures and summer precipitation proved to be the most important climatic factors affecting beech growth and vessel features.
Wave climate change in the Gulf of Bothnia
Authors: Björkqvist Jan-Victor , Särkkä Jani , Kanarik Hedi , Tuomi Laura
Published: March 2021

Wave climate change in the Gulf of Bothnia in 2030–2059 was investigated using regional wave climate projections. For the simulations we used wave model WAM. As the atmospheric forcing for the wave model we had three global climate scenarios (HADGEM2-ES, MPI-ESM, EC-EARTH) downscaled with RCA4-NEMO regional model. The ice concentration for the wave model was obtained from NEMO ocean model simulations using the same atmospheric forcing. We used both RCP4.5 and RCP8.5 greenhouse gas scenarios. The spatial resolution of the simulation data was 1.8 km, enabling detailed analyses of the wave properties near the coast. From the simulation data we calculated statistics and return levels of significant wave heights using extreme value analysis, and assessed the projected changes in the wave climate in the Gulf of Bothnia. The projected increase in the significant wave heights is mainly due to the decreasing ice cover, especially in the Bothnian Bay. Projected changes in the most prevalent wind direction impacts the spatial pattern of the wave heights in the Bothnian Sea.
Mineral chemistry, P-T pseudosection and in-situ U-Th-Pbtotal monazite geochronology of Banded Iron Formation from Bundelkhand craton North-Central India, and its geodynamic significance
Authors: Raza Mohd Baqar , Nasipuri Pritam , Hifzurrahman
Published: March 2021

The Banded Iron Formation (BIF) in Bundelkhand craton (BuC) occurred as supracrustals associated with TTG’s, amphibolites, calcsilicate rocks, and quartzite within the east-west trending Bundelkhand tectonic zone (BTZ). The BIFs near Mauranipur do not show any prominent iron-rich and silica-rich layer band and are composed of garnet, amphibole, quartz, and magnetite. The volumetrically dominant monoclinic-amphiboles are grunerite in composition. XMg of grunerite varies between 0.39-0.37. The garnets are Mn-rich, the XSpss of garnet ranges from 0.26-0.20, XPyp and XGrs vary between 0.10-0.06 and 0.07-0.05, respectively. P-T pseudosection analysis indicates that by destabilizing iron-silicate hydroxide phases through a series of dehydration and decarbonation reactions, amphibole and garnet stabilized in BIF at temperature 400-450°C and pressure 0.1-0.2 GPa.

Massive type BIFs have monazite grains that vary from 10 to 50 µm in size, yield three distinct U-Th-Pbtotal age clusters. 10-20 µm sized monazite grains yield the oldest age, 3098±95 Ma. 2478±37 Ma average age is obtained from the second group, which is relatively larger and volumetrically predominant. The third age group of Monaiztes gives an age of 2088±110 Ma. ~3100 Ma monazite suggests the older supracrustal rocks of Bundelkhand craton, similar to those obtained from Singhbhum and the Dharwar craton. The 2478±37 Ma age is constrained as the timing of metamorphism and stabilization of BuC. The third age group, 2088±110 Ma probably associated with renewed hydrothermal activities, leading to rifting and emplacement of mafic dykes in BuC.
Rocky tidal pools: carbonate chemistry, diurnal variability and calcifying organisms in future high-CO2 conditions
Authors: Dorey Narimane , Martin Sophie , Kwiatkowski Lester
Published: March 2021

Understanding the coastal ocean variability and quantifying its significance in the global biogeochemical cycles is crucial to our ability to project future changes. In the shallow coastal waters, the contribution of the biological activity to water chemistry can be high locally, and responsible for seasonal and diurnal variations. These variations are not yet well-understood: they are often under-estimated and the general lack of observations means that they are seldom integrated into global predictive models such as those used by the IPCC.
    In this presentation, we will present results on the natural carbonate chemistry diurnal variability in tidal rock pools in Brittany (France), during emersion times. We chose tidal rock pools as to represent "mini-coastal seas": realistic small mesocosms that simulate coastal environments with extreme variability. These have the advantage to be closed systems containing a range of calcifying organisms such as coralline encrusting and non-encrusting algae, that influence and are influenced by the carbonate chemistry. We calculated calcification of the pools community by using the alkalinity anomaly method and estimated the community photosynthesis/respiration. We also compared night-time dissolution and day-time calcification. Finally, we manipulated the pools chemistry at emersion by adding CO2 to mimick future acidification changes, and explored the impact of seawater acidification on the calcification of the tidal pools' communities.
Machine Learning Based Surface Velocimetry
Authors: Ansari Saber , Rennie Colin D. , Jamieson Elizabeth C. , Seidou Ousmane , Clark Shawn P.
Published: March 2021

Streamflow measurement is of great importance in hydrological research, water management and water infrastructure design. Traditional measurement methods typically employ intrusive techniques, and under certain conditions, obtaining accurate streamflow data with these techniques can be challenging because of safety concerns, especially in some critical circumstances, such as during flood flows. The advent of new instrumentation and technologies, and in particular advances in digital imagery, has led to the emergence of non-intrusive novel image-based technologies that can be used to estimate surface velocity, which in turn can be used to estimate streamflow. Image based technologies, most of which are based on correlation between consecutive images, have the potential for remote and on demand measurements and can provide data when the application of other traditional methods are not possible, reliable or safe. In this study, we present a novel machine learning based optical flow algorithm for streamflow surface velocimetry estimation. The developed algorithm is tested in different flow conditions and using drone and fixed photogrammetry. This method appears to outperform all the other available image-based surface velocimetry approaches (i.e. correlation based and classical optical flow methods). Moreover, this method requires the least user involvement for velocity estimation and thus reduces the impact or arbitrary choices linked to user expertise.
The Impact of Global Ice Sheet Evolution on North Sea Glacial Isostatic Adjustment during the Last Interglacial
Authors: Pollard Oliver , Barlow Natasha , Gregoire Lauren , Gomez Natalya , Cartelle Víctor
Published: March 2021

The Last Interglacial (LIG) period (130 - 115 ka) was the last time in Earth’s history that the Greenland and Antarctic ice sheets were smaller than those of today due, in part, to polar temperatures reaching 3 - 5 °C above pre-industrial values. Similar polar temperature increases are predicted in the coming decades and the LIG period could therefore help to shed light on ice sheet and sea level mechanisms in a warming world.

The North Sea region is a promising study site for the reconstruction of both the magnitude and rate of LIG sea-level change as well as the identification of relative, individual ice sheet contributions to sea level. The impact of glacial isostatic adjustment (GIA) is particularly significant for the North Sea region due to its proximity to the former Eurasian ice sheet, which deglaciated during the penultimate deglaciation leading into the LIG. The evolution of the local Eurasian and global ice sheets during the penultimate glacial cycle has left a complex spatio-temporal pattern of GIA during the LIG, both regionally and globally. In addition, interpretation of the LIG record is further complicated by uncertainties in ongoing earth deformation and sea level evolution since the LIG. However, there are large uncertainties in the geometry and evolution of global ice sheets before the Last Glacial Maximum and, in particular, a major source of uncertainty for North Sea LIG records is the geometry and evolution of the Eurasian ice sheet during the Penultimate Glacial Maximum (PGM).

We produce a range of plausible global ice sheet histories spanning the last 400 thousand years that vary in penultimate deglaciation characteristics including glacial maximum ice sheet volume, deglaciation timing, and the ice volume distribution of the Eurasian ice sheet. This novel PGM Eurasian component is constructed with the use of a simple ice sheet model (Gowan et al. 2016) enabling systematic variation in the thickness of each ice sheet region within known uncertainty ranges. We then employ a gravitationally consistent sea level model (Kendall et al. 2005) with a range of viscoelastic Earth structure models to calculate the global GIA response to each ice history and to infer which input parameters the North Sea LIG signal is most sensitive to. This work will improve our understanding of the GIA effects on near field relative sea level during previous interglacials and will enable a systematic quantification of uncertainties in LIG sea level in the North Sea.
Quantification of the relation between dynamical properties of meteorological variables and their predictability
Authors: Krouma Meriem , Yiou Pascal , Faranda Davide , Thao Soulivanh , Déandréis Céline
Published: March 2021

Local properties of chaotic systems can be summarized by dynamical indicators, that describe the recurrences of all states in phase space. Faranda et al. (2017) defined such indicators with the local dimension (d, approximating the local number of degrees of freedom of the system) and the inverse of persistence (θ, approximating the time it takes to leave a local state). It has been conjectured that such indicators give access to the local predictability of systems. The aim of this study is to evaluate how the predictability of climate variables such as temperature and precipitation is related to dynamical properties of the atmospheric flow.

The predictability of a chaotic system can be evaluated through ensembles of simulations, with probability scores (e.g. Continuous Rank Probability Score, CRPS). In this work, we consider ensembles of climate forecasts with a stochastic weather generator (SWG) based on analogs of atmospheric circulation (Yiou and Déandréis, 2019). We are interested in relating predictability scores of European temperatures and precipitation, obtained with this SWG, and the local dynamical properties of the synoptic atmospheric circulation, obtained from the NCEP reanalysis. We show experimentally that the CRPS of local climate variables can be predicted from large-scale (d, \ θ) values of geopotential height fields, for time leads of 5 to 10 days. A practical application is that the predictability of local variables (in Europe) can be anticipated from large-scale dynamical quantities, which can help to dimension the size of ensemble forecasts.

References

Faranda, D., Messori, G., Yiou, P., 2017. Dynamical proxies of North Atlantic predictability and extremes. Sci. Rep. 7, 41278. https://doi.org/10.1038/srep41278

Caby, T. Extreme Value Theory for dynamical systems, with applications in climate and neuroscience. Mathematics [math]. Université de Toulon Sud; Universita dell’Insubria, 2019. English.tel-02473235v1

Yiou, P., Déandréis, C., 2019. Stochastic ensemble climate forecast with an analogue model. Geosci. Model Dev. 12, 723–734. https://doi.org/10.5194/gmd-12-723-2019

 

Acknowledgments

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 813844.

 
Comparison of different infiltration schemes in the regional climate model REMO
Authors: Abel Daniel , Ziegler Katrin , Pollinger Felix , Paeth Heiko
Published: March 2021

The European Regional Development Fund-Project BigData@Geo aims to create highly resolved climate projections for the model region of Lower Franconia in Bavaria, Germany. These projections are analyzed and made available to local stakeholders of agriculture, forestry, and viniculture as well as general public. Since regional climate models’ spatiotemporal resolution often is too coarse to deal with such local issues, the regional climate model REMO is improved within the frame of the project in cooperation with the Climate Service Center Germany (GERICS).

Accurate and highly resolved climate projections require realistic modeling of soil hydrology. Thus, REMO’s original bucket scheme is replaced by a 5-layer soil scheme. It allows for the representation of water below the root zone. Evaporation is possible solely from the top layer instead of the entire bucket and water can flow vertically between the layers. Consequently, the properties and processes change significantly compared to the bucket scheme. Both, the bucket and the 5-layer scheme, use the improved Arno scheme to separate throughfall into infiltration and surface runoff.

In this study, we examine if this scheme is suitable for use with the improved soil hydrology or if other schemes lead to better results. For this, we (1) modify the improved Arno scheme and further introduce the infiltration equations of (2) Philip as well as (3) Green and Ampt. First results of the comparison of these four different schemes and their influence on soil moisture and near-surface atmospheric variables are presented.
OBLIMAP parallelization and optimization toward high resolution climate model - ice sheet model coupler
Authors: Raffin Erwan , Guibert David , Reerink Thomas
Published: March 2021

Within the ESiWACE2 project we parallelized and optimized OBLIMAP. OBLIMAP is a climate model - ice sheet model coupler that can be used for offline and online coupling with embeddable mapping routines. In order to anticipate future demand concerning higher resolution and/or adaptive mesh applications, a parallel implementation of OBLIMAP's fortran code with MPI has been developed. The data intense nature of this mapping task, required a shared memory approach across the processors per compute node in order to prevent that the node memory is the limiting bottleneck. Besides, the current parallel implementation allows multi node scaling and includes parallel netcdf IO in addition with loop optimizations. Results show that the new parallel implementation offers better performance and scales well. On a single node, the shared memory approach allows now to use all the available cores, up to 128 cores in our experiments on Antarctica 20x20km test case where the original code was limited to 64 cores on this high-end node and it was even limited to 8 cores on moderate platforms. The multi node parallelization offers on Greenland 2x2km test case a speedup of 4.4x on 4 high-end compute nodes equipped with 128 cores each compared to the original code which was able to run only on 1 node. This paves the way to the establishment of OBLIMAP as an candidate ice sheet coupling library candidate for large-scale, high-resolution climate modeling.
Examining the accuracy of satellite retrievals of trace-gas emissions and lifetimes using high-resolution plume modelling.
Authors: Davis Zoe , Griffin Debora , Jia Yue , Tegtmeier Susann , Loria Mallory , McLinden Chris A
Published: March 2021

A recent method uses satellite measurements to estimate lifetimes and emissions of trace-gases from point sources (Fioletov et al., 2015). Emissions are retrieved by fitting measured vertical column densities (VCDs) of trace-gases to a three-dimensional function of the wind speed and spatial coordinates. In this study, a plume model generated “synthetic” satellite observations of prescribed emissions to examine the accuracy of the retrieved emissions. The Lagrangian transport and dispersion model FLEXPART (v10.0) modelled the plume from a point source over a multi-day simulation period at a resolution much higher than current satellite observations. The study aims to determine how various assumptions in the retrieval method and local meteorological conditions affect the accuracy and precision of emissions. These assumptions include that the use of a vertical mean of the wind profile is representative of the transport of the plume’s vertical column. In the retrieval method, the VCDs’ pixel locations are rotated around the source based on wind direction so that all plumes have a common wind direction. Retrievals using a vertical mean wind for rotation will be compared to retrievals using VCDs determined by rotating each altitude of the vertical profile of trace-gas using the respective wind-direction. The impact of local meteorological factors on the two approaches will be presented, including atmospheric mixing, vertical wind shear, and boundary layer height. The study aims to suggest which altitude(s) of the vertical profile of winds results in the most accurate retrievals given the local meteorological conditions. The study will also examine the impact on retrieval accuracy due to satellite resolution, trace-gas lifetime, plume source altitude, number of overpasses, and random and systematic errors. Sensitivity studies repeated using a second, “line-density”, retrieval method will also be presented (Adams et al., 2019; Goldberg et al., 2019).
Morphoecological characteristics of grasses used to restore degraded semi-arid African rangelands
Authors: Mganga Kevin
Published: March 2021

Progressive loss of productivity and plant diversity is a major in global rangelands. In African rangelands ecosystems, this process is partly attributed to heavy and uncontrolled grazing by livestock and wildlife, leading to land degradation. Therefore, restoring such degraded rangelands is critical for enhancing ecosystem health and securing the livelihoods of millions of people. Active restoration strategies, e.g. reseeding using indigenous perennial grasses has been identified as a viable ecological solution for restoring degraded African rangelands. Grass species indigenous to African rangelands Cenchrus ciliaris L. (African foxtail grass), Eragrostis superba Peyr. (Maasai love grass), Enteropogon macrostachyus (Hochst. Ex A. Rich.) Monro ex Benth. (Bush rye grass), Chloris roxburghiana Schult. (Horsetail grass) and Chloris gayana Kunth. cv Boma (Rhodes grass) were established in a semi-arid rangeland in Africa under natural conditions to compare their morphoecological characteristics and suitability for use in ecological restoration. Biomass dry matter yields, plant densities, basal cover, seed production, tiller densities and plant height were measured. Chloris gayana cv Boma and E. superba produced significantly higher dry matter biomass yields and seed production than other species. High biomass and seed production demonstrate their suitability to support livestock production and replenish depleted soil seed banks, respectively. Enteropogon macrostachyus and C. ciliaris displayed significantly higher values for plant densities, tiller densities and basal cover, also a component of establishment and ecological restoration success. Chloris roxburghiana ranked lowest in all the measured morphoecological characteristics. This may be a strong indicator of ecological site-specific characteristic of C. roxburghiana. Successful restoration of degraded African semi-arid rangelands using indigenous grass reseeding can best be achieved through careful selection of grasses to take advantage of their specific morphoecological characteristics. This selection should primarily be informed by the intended use of the rangeland.
Changes in peatland hydrology alter organic matter chemical composition in ombrotrophic Finnish mires: a comparative Py-GCMS depth profile study
Authors: Klein Kristy , Groβ-Schmölders Miriam , Alewell Christine , Leifeld Jens
Published: March 2021

From a carbon sequestration perspective, peatland restoration projects could be considered successful when net primary productivity exceeds decomposition, resulting in net peat growth in the ecosystem. To demonstrate the effectiveness of peatland restoration projects with a carbon storage aim, analytical techniques are needed that can distinguish between natural/restored ecosystems undergoing (or transitioning to) net peat growth and degraded ecosystems experiencing increased rates of aerobic decomposition (carbon loss). Molecular analysis techniques able to relate changes in organic matter (OM) chemical composition to changes in degradation status occurring on the mechanistic level are especially needed.

This study combined a molecular biomarker and chemical compound class approach to conduct a depth-based molecular comparison of natural (ON) and drained (OD) ombrotrophic peatland sites in Lakkasuo Finland. To explore how changes in hydrology impacted peat OM chemical composition, the relative abundance of various molecular biomarkers (Sphagnum marker p-isopropenylphenol, lignin vascular plant markers) and chemical compound classes (phenolics, polysaccharides, aromatics, N-containing compounds, lipids) was determined with depth from three replicate cores per site using pyrolysis gas chromatography tandem mass spectrometry (Py-GCMS). Py-GCMS results were compared with onsite vegetative assemblages and bulk elemental analysis conducted on the same cores. ON and OD were matched by age using radiocarbon dating at three depths per core.

For OD relative to ON, significant reductions in average relative percent abundance were observed for p-isopropenylphenol, phenolics and polysaccharides, and corresponding increases in abundance were observed for lignin, aromatics, N-containing compounds, and lipid sterols. Differences in compound classes between sites were greatest in the drainage-affected upper acrotelm, and diminished with depth. Samples consistently below the depth of the water table (>20 cm) followed similar trends in both ON and OD, suggesting that deeper horizons remained unaffected by the onsite drainage activities. An increasing trend in the relative abundance of lignin-derived compounds was observed with depth - particularly in ON. As the plant macrofossil assessment did not suggest previous dominance of vascular plants, this trend was considered evidence for preservation of lignin in anaerobic conditions in organic soils. Overall, these findings indicate that differences in chemical composition between the two sites can be directly correlated to OM transformation occurring on a mechanistic level, and that observed shifts in chemical composition reflect the effect of altered hydrology in peatland ecosystems.
Strong activity of the Orinoco Low-Level Jet and its association with moisture transport in northern South America
Authors: Builes-Jaramillo Alejandro , Yepes Johanna , Hernán D. Salas
Published: March 2021

We classified events of extreme Orinoco Low-Level Jet (OLLJ) activity using the ERA5 time series of daily winds at 925 hPa averaged over the 6°S–8°N/67°W–69°W area for the period 1981-2019. This area exhibits an overall mean of 3.7 m/s easterly wind speed and an overall standard deviation of 3.5 m/s. Then, during December-January-February (June-July-August), the season of strong (weak) OLLJ activity, we defined the events below (above) one standard deviation from the overall mean. Hence, days with easterly wind speeds higher than 7.2 m/s are considered events with strong activity during DJF. In contrast, days with westerly wind speed higher than 0.2 m/s are the events with weak activity during JJA. A composite analysis of precipitation from CHIRPS dataset during the days classified as strong or weak OLLJ activity showed that during the most active period (DJF), daily precipitation values are close to 0 mm/day; except for increased precipitation in the border between Colombia, Ecuador, Peru, and Brazil. In contrast, precipitation composites during the period of non-activity of the OLLJ (JJA), showed that precipitation increases in the range 5–10 mm/day along the OLLJ corridor. A detailed analysis of the precipitation time series used for composite analysis indicates that the probability of precipitation during DJF (JJA) is less (more) than 20% (80%) over Venezuela and the Guianas. In terms of advective water transport (qV) during the most active events of the OLLJ water is transported from the Tropical Atlantic towards northern South America through the OLLJ corridor, whilst during the less active events water transport along the OLLJ corridor comes from the north Amazon basin towards northern South America. In conclusion, during DJF the OLLJ is associated with the northerly cross-equatorial flow and dry season, whereas during JJA the southerly cross-equatorial flow from the Amazon river basin predominates, which contributes to the rainy season over the Orinoco region.
Identifying exposure biases in early instrumental data
Authors: Wallis Emily , Osborn Timothy , Taylor Michael , Lister David , Jones Philip
Published: March 2021

Long observational records of land surface air temperature are vital to our understanding of climate variability and change, as well as for testing predictions of climatic trends. However, of the relatively few long observational records which exist, many contain inhomogeneities or biases resulting from changing instrumentation, station location/surroundings and/or observing practises. One of the most significant issues is the exposure bias. Prior to the widespread adoption of louvered Stevenson-type screens in the late-19th century, various (often insufficient) approaches were used to shield thermometers. Each approach exposed the thermometer to differing levels of solar radiation, thus introducing inhomogeneities into individual station records and biases across regions, if similar approaches were used. Poorly shielded thermometers, for example, tended to read higher during the summer half year than those in Stevenson-type screens. Despite a number of studies documenting the presence of the exposure bias in early instrumental data, relatively few corrections have been applied or incorporated into global temperature datasets. This is largely due to the pervasive nature of the bias and a lack of observational metadata impeding bias identification or estimation of the appropriate correction.

In this work we explore a range of datasets to identify the potential for exposure bias in early instrumental data. We analyse historical data, corrections applied to homogenized datasets, as well as the small number of parallel measurements from differentially-shielded thermometers, in order to better define the characteristics of the exposure bias. These characteristics are then used to identify potential instances of exposure bias in early instrumental temperature records. We consider differences in seasonal anomalies, which is a key feature of many exposure biases, as well as their geographical variation (focussing mostly, but not solely, on Europe). We analyse how these behave at stations where it is known that exposure bias has already been adjusted for (though perhaps not completely) versus those that have not been. We also make comparisons with proxy reconstructions of temperature as an independent reference that is not susceptible to the same biases as the early instrumental data.

This work forms part of the NERC-funded GloSAT project which is developing a global surface air temperature dataset starting in 1781. The ultimate aim of the work reported here is to refine the error associated with these biases, in order to improve the representation of the exposure bias in error models used for gridded instrumental temperature datasets.
Basal Shear-Zone of the Lower allochthon in the Morais complex (Portugal): microstructural and neutron diffraction constraints.
Authors: Malecki Jeremie , Gómez Barreiro Juan , Durán Oreja Manuela , Martínez Catalán José Ramón , Tettamanti Magdalena , Barrios Sánchez Santos , Sánchez Migallón Juan Morales , Puente Orench Inés
Published: March 2021

The NW Iberian Massif represents a segment of the Variscan Belt, where several allochthonous complexes crop out: : Cabo Ortegal, Ordenes and Malpica-Tuy, in Spain, and Bragança and Morais in Portugal. These allochthonous complexes comprise allochthonous units, overthrusting parautochthonous and autochthonous units. The suture zone of the Variscan orogeny in the NW Iberia preserves the testimony of the collisional dynamics between Gondwana and Laurussia during the Carboniferous. The stacking of allochthonous units into an accretion wedge, and their subsequent incorporation by thrusts into the continental margin of Gondwana, resulted in polyphasic tectonothermal evolution. Different units record valuable information about the deformation mechanisms, rheological behaviour and the configuration of plates during the Palaeozoic.

The kinematic and deformational evolution of major tectonic boundaries of the Variscan Allochthonous units, as well as their mutual relationship in Iberia is critical, in order to constrain their regional meaning and correlation with similar units along the European Variscan Belt. In shear-zones, plastic deformation of polycrystalline aggregates result into microstructural and textural fingerprints that need to be interpreted. Quantitative analyses of fabrics has been crucial in untangling complex tectonothermal evolutions. In this case neutron diffraction experiments have been conducted in transmission mode in the Institute Laue-Langevin (ILL) (France), to characterize mylonites from the basal shear zone of the Lower Allochthon in Morais Complex. Two different experimental sets have been tested in D1B and D20 beamlines, comparing textural standards and new vanadium sample holders in order to optimize the procedure. Diffraction data were refined with Rietveld software MAUD to obtain quantitative texture information and orientation distribution functions (ODF) for main phases. Afterward, pole figures of relevant planes were interpreted in terms of slip-system activity to understand deformation conditions. Overall, microstructural data and fabric analysis points to a top-to-the SE shearing with a pure-shear component in the mylonitic flow.

Keywords: Shear zones, texture analysis, neutron diffraction, Rietveld method, Variscan orogeny, Morais complex.
 Analysis of soil oxygen dynamics as a diagnostic tool of the soil oxygen status in-situ
Authors: Shenker Moshe , Yalin David
Published: March 2021

Soil oxygen has been recognized as a potential limiting factor in plant production second only to water and nutrients. While it is widely accepted that soil gaseous oxygen levels below 10% V/V are detrimental to plant production, there are currently no accepted indices to quantify the effect of different agricultural practices on soil oxygen supply and availability. To address this challenge, a new approach is introduced, whereby indices describing the soil oxygen dynamics are determined using data from continuous in-situ soil oxygen measurements. To give the measurements a mechanistic interpretation, we developed a conceptual model describing the soil oxygen dynamics as a simplified mass balance between oxygen supply rate and oxygen consumption rate. The approach was applied to analyze field measurements of soil oxygen and water tension at 35 cm depth in avocado orchards irrigated with either Fresh Water (FW) or Treated Wastewater (TWW) in clay soil (~60% clay). The reliability of the method was shown, as soil respiration rates equivalent to 1-2 g O2m-2 d-1 were established, in line with previous reports for evergreen trees. The model defines the soil water tension at which oxygen supply to the measurement depth after irrigation surpasses the oxygen consumption rate as the critical soil water tension, and a value of ~50 mbar was established for the experiment site, again within the range described in the literature for soils with similar properties using other methodologies. Using the new approach, it was established that more hypoxic conditions occur in TWW irrigated plots as compared to FW irrigated plots due to a difference in the time required to reach the critical soil water tension – TWW irrigated plots took nearly 50% longer to reach a soil water tension of 50 mbar after each irrigation in the height of the irrigation season. This delay in TWW irrigated plots was directly related to the soil drying rate, which was lower in the TWW irrigated soils in both night and day periods, indicating both a hindering of drainage and of plant water uptake. In a second study site, the values describing the soil oxygen dynamics were found to relate to the soil stone content (particles>2mm), a known effector of soil aeration. By utilizing in-situmeasurements, the method aims to represent the intricate interrelations occurring in the field which may be missed using methods focusing on the individual factors affecting soil oxygen. The insights gained can provide the basis for designing management techniques to resolve unfavorable low oxygen levels in agriculture, as well as in natural environments where hypoxia affects soil carbon turnover, the evolution of greenhouse-gasses, and the fate of toxic elements in soils.