bluuebunny/crossref_metadata_2025 huggingface dataset:
A historical database of key hydroclimatic variables in and across 6400 catchments around the world
Authors: Ghajarnia Navid , Kalantari Zahra , Destouni Georgia
Published: March 2020

Availability of historical hydroclimatic data for different climate regions is necessary for hydrological change modeling and analysis. Nowadays, many global products are available that provide hydrological and meteorological datasets based on direct measurements, remote sensing observations, re-analysis outputs, and model simulations. However, differences in spatial and temporal resolutions, and inconsistencies seen between observed hydrological patterns and different model results and datasets makes it difficult to choose an appropriate combination of data products for hydrological studies. This study provides a new combined historical database of five key hydroclimatic variables at monthly and daily scales, obtained from different observational and re-analysis global datasets, including runoff (R; from GSIM), precipitation (P; from GPCC-V7 and ERA5), evapotranspiration (ET; from GLEAM 3.3 and ERA5), soil moisture (SM; from ESACCI-v04.5, GLEAM 3.3 and ERA5), and temperature (T; GHCN-CAMS, ERA5). The new database combines these variables for each of 6,400 catchments of different scales around the world. In order to select the catchments, the existing nearly 35,000 streamflow time series in the GSIM database was analyzed and 8,400 catchments were selected based on the criterion of having at least 25 years of monthly runoff data available from 1980 to 2010. After further quality controls on the accuracy of catchment polygons, and reported catchment areas and stream flows, and consistency of the range, average values, and variations of variables time series, the 6,400 catchments were selected for the final development of the new catchment-related database in this study. The other hydroclimatic variables, besides runoff, are also spatially aggregated for each individual catchment and corresponding catchment-average time series are produced from 1980 to 2019. The final database thus provides a collection of long-term multi-climate and multi-catchment time series of the five key hydroclimate variables, aggregated over each of the 6,400 hydrological catchments around the world. In choosing the data sources for each variable, first priority was given to direct observational datasets (available for all variables except for the ET), and further to re-analysis outputs that many researchers regard as being close to directly observed data. The database developed in this study can be used for different types of studies on hydrology, water resources, and their changes under shifting climate and land use conditions in different parts of the world. The standardized format of this database ensures easy applicability with possibility of expansion to include more and other types of data, e.g., on land use/cover types and their changes, and on other climatic, geomorphologic, and anthropogenic conditions.
Detecting anisotropy using Distributed Acoustic Sensing and fibre-optic seismology in a fast-flowing glacier in Greenland
Authors: Booth Adam , Christoffersen Poul , Schoonman Charlotte , Clarke Andy , Hubbard Bryn , Law Robert , Doyle Sam , Chudley Tom , Chalari Athena
Published: March 2020

Material anisotropy within a glacier both influences and is influenced by its internal flow regime. Anisotropy can be measured from surface seismic recordings, using either active sources or natural seismic emissions. In the past decade, Distributed Acoustic Sensing (DAS) has emerged as a new, and potentially transformative, seismic acquisition technology, involving determining seismic responses from the deformation of optical fibres. Although DAS has shown great potential within engineering and resources sectors, it has not yet been widely deployed in studies of glaciers and ice masses.

Here, we present results from a glaciological deployment of a DAS system. In July 2019, a Solifos BRUsens fibre optic cable was installed in a 1050 m borehole drilled on Store Glacier in West Greenland. Vertical seismic profiles (VSPs) were recorded using a Silixa iDAS interrogation unit, with seismic energy generated with a 7 kg sledgehammer striking a polyethene (UHMWPE) impact plate. A three-day sequence of zero-offset VSPs (with the source located ~1 m from the borehole top) were recorded to monitor the freezing of the cable, combined with offset-VSPs in along- and cross-flow directions, and radially at 300 m offset.

P-wave energy (frequency ~200 Hz) is detectable through the whole ice thickness, sampled at 1 m depth increments. The zero-offset reflectivity of the glacier bed is low, but reflections are detected from the apparent base of a subglacial sediment layer. S-wave energy is also detectable in the offset VSP records. The zero-offset VSPs show a mean vertical P-wave velocity of 3800 ± 140 m/s for the upper 800 m of the glacier, rising to 4080 ± 140 m/s between 900-950 m. In the deepest 50 m, velocity reduces to 3890 ± 80 m/s. This variation in vertical velocity is consistent with the development of an anisotropic ice fabric in the lowermost 10% of the glacier. The full dataset also contains natural seismic emissions, highlighting the potential of DAS as both an active and passive seismic monitoring tool.

DAS offers transformative potential for understanding the seismic properties of glaciers and ice sheets. The simplicity of the typical VSP geometry makes the interpretation of seismic travel-times less vulnerable to approximations, and thus the derivation of seismic properties more robust, than in conventional surface seismic surveys. As an addition, DAS facilitates VSP recording with unprecedented vertical and temporal resolution. Furthermore, the sensitivity of the optical-fibre to both P- and S-wave particle motion means that a comprehensive suite of acoustic and elastic properties can be inferred.
Auto-tuning Hamiltonian Monte Carlo
Authors: Fichtner Andreas , Gebraad Lars , Boehm Christian , Zunino Andrea
Published: March 2020

Hamiltonian Monte Carlo (HMC) is a Markov chain Monte Carlo method that exploits derivative information in order to enable long-distance moves to independent models, even when the model space dimension is high (Duane et al., 1987). This feature motivates recent research aiming to adapt HMC for the solution of geophysical inverse problems (e.g. Sen & Biswas, 2017; Fichtner et al., 2018; Gebraad et al., 2020).

Here we present applications of HMC to inverse problems at variable levels of complexity. At the lowest level, we study linear inverse problems, including, for instance, linear traveltime tomography. Though this is not the class of problems for which Monte Carlo methods have been developed, it allows us to understand the important role of HMC tuning parameters. We then demonstrate that HMC can be used to obtain probabilistic solutions for two important classes of inverse problems: 2D nonlinear traveltime tomography and 2D elastic full-waveform inversion. In both scenarios, no super-computing resources are needed for model space dimensions from several thousand to ten thousand.

By far the most important, but also most complex, tuning parameter in HMC is the mass matrix, the choice of which critically controls convergence. Since manual tuning of the mass matrix is impossible for high-dimensional problems, we develop a new HMC flavour that tunes itself during sampling. This rests on the combination of HMC with a variant of the L-BFGS method, well-known from nonlinear optimisation. L-BFGS employs a few Monte Carlo samples to compute a matrix factorisation LLTwhich dynamically approximates the local Hessian H, while the sampler traverses model space in a quasi-random fashion. The local curvature approximation is then used as mass matrix. Following an outline of the method, we present examples where the auto-tuning HMC produces almost perfectly uncorrelated samples for model space dimensions exceeding 105.

 

References

[1] Duane et al., 1987. "Hybrid Monte Carlo", Phys. Lett. B., 195, 216-222.

[2] Sen & Biswas, 2017. "Transdimensional seismic inversion using the reversible-jump Hamiltonian Monte Carlo algorithm", Geophysics, 82, R119-R134.

[3] Fichtner et al., 2018. "Hamiltonian Monte Carlo solution of tomographic inverse problems", Geophys. J. Int., 216, 1344-1363.

[4] Gebraad et al., 2020. "Bayesian elastic full-waveform inversion using Hamiltonian Monte Carlo", J. Geophys. Res., under review.
Application of a Mise-à-la-Masse approach to detect the leak of water reservoirs
Authors: Ling Chengpeng , Revil Andre
Published: March 2020

Water reservoirs with synthetic geomembranes are widely used for storing water resources and chemical solutions in the agricultures and industries, respectively. Leakages of water reservoirs are respondible for the loss of water resources and the spread of contaminants. It is usually difficult to perceive and localize the leakage of water reseroirs. As a cheap, non-invasive, and non-destructive geophysical technique, the mise-à-la-masse method is used to detect leaks of water reservoirs. In principle, the positive (A) and negative (B) current electrodes are placed inside and outside the reservroir, respectively. A number of voltage electrodes are located around the reservoir and potentials relative to a remote reference potential electrode are measured. In the data processing, a method silimar to the self-potential inversion method is proposed to inverse the voltages recorded around the reservoir. Forward modeling was first carried out to simulate the mise-à-la-masse measurement. A kernel matrix (i.e., the collection of Green’s funstions) from forward modelings was imported to the inverse modeling. In inverse modeling, a global objective function with a data misfit term and regularization term is minimized to invert the measured voltages. An initial model based on the distribution of root mean square values between the observation and the simulation data is first given to the inversion algorithm. A weighting matrix and a minimum support function is used to strengthen the detection resolution of the leak of reservoirs. The distributions of source current density from the inverse modeling are used to provide the best estimated of the positions of leaks. Two laboratory and one field experiments are used to verify the effectiveness and reliability of the mise-à-la-masse method. The results show that the proposed method and inversion algorithm can localize a single leak. For a leak with a crack shape, the inversion algorithm detects the location of the leak with a small bias. Effects of the leak size and an undetected condutive zone on the inversion results are further analyzed. For the side leakage, the inverse algorithm overestimated the depth for a small-size leak, while is slightly underestimated the depth of big leaks. For the bottom leakage, effects of the leak size on inversion results are negligable. An undetected conductive zone could significantly distort the inversion results. This study provides an efficient approach to detect the leakage of reservoirs. In addtion, for the leakage of leachate in landfills or mine tailings, the mise-à-la-masse method is also a promising method.
Development of events detector for monitoring cryoseisms in upper soils
Authors: Afonin Nikita , Kozlovskaya Elena
Published: March 2020

In some problems of solid Earth geophysics analysis of the huge amount of continuous seismic data is necessary. One of such problems is an investigation of so-called frost quakes or cryoseisms in the Arctic caused by extreme weather events. Weather extremes such as rapid temperature decrease in combination with thin snow cover can result in cracking of water-saturated soil and rock when the water has suddenly frozen and expanded. As cryoseisms can be hazardous for industrial and civil objects located in the near-field zone, their monitoring and analysis of weather conditions during which they occur, is necessary to access hazard caused by extreme weather events. One of the important tasks in studying cryoseisms is the development of efficient data processing routine capable to separate cryoseisms from other seismic events and noise in continuous seismic data. In our study, we present an algorithm for identification of cryoseisms that is based on classical STA/LTA algorithm for seismic event detection and neural network for their classification using selected characteristics of the records.

To access characteristics of cryoseisms, we used 3-component recordings of a swarm of strong cryoseismic events with similar waveforms that were registered on 06.06.2016 by seismic station OUL in northern Finland. The strongest event from the swarm produced a fracture on the road surface and damaged basements of buildings in the municipality of Oulu. Assuming that all events in the swarm were caused by the same mechanism (freezing of water-saturated soil), we used them as a learning sample for the neural network. Analysis of these events has shown that most of them have many similarities in selected records characteristics (central frequencies, duration etc.) with the strongest event and with each other. Application of this algorithm to the continuous seismic data recorded since the end of November 2015 to the end of February 2016, showed that the number of cryoseisms per day strongly correlates with variations of air temperature.
Stock change of soil moisture under crop cultivation: A relevant and low cost indicator to assess hydrological performance of agricultural land use systems in Tigray, northern Ethiopia.
Authors: Kraaijvanger Richard
Published: March 2020

In the highlands of Tigray both crop yield and soil erosion are important concerns. At the same time the impact of climate change is felt in the form of delayed and more erratic rains. Different adaptation strategies are proposed to increase resilience. The successful implementation of most of these strategies, like for example, agroforestry, conservation tillage and water harvesting, heavily relies on improved infiltration and the amount of water stored in the root zone. In this presentation the water storage in the root zone is discussed in relation to crop productivity and hydrological performance of the local (agricultural) land use system. For this purpose measurements of (gravimetric) soil moisture content, taken at different depths in the root zone and at regular time intervals during four growing seasons in the period 2010-2013, were considered. In total 43 sites were involved, which were measured for one up to three years. In addition to soil moisture content, at selected sites also bulk density, saturation, field capacity and wilting point were determined. On the basis of the data collected, site-specific changes in soil moisture budgets were analyzed and trends observed were related to crop productivity and hydrological parameters (like rainfall and evapotranspiration). First outcomes pointed to a relatively rapid increase of soil moisture stock at the start of the growing season, followed by a more or less stable level, and ending at crop maturation with a very rapid decrease. Typical figures for gravimetric moisture content at the stable level were between 25 and 30 %. Soil depth was in most cases shallow (around 40 cm) and likely limiting moisture storage capacity. Assuming that at the start of the stable phase rainfall still is exceeding evapotranspiration, this then will point to a relatively high risk for run off at this stage. Stock change of soil moisture as such appears a relevant and low cost indicator to assess hydrological performance of land use systems in terms of infiltration capacity and soil moisture availability. In line with that, analysis of stock change of soil moisture might provide relevant clues for designing and optimizing effective land management strategies that successfully deal with erosion hazard and result in a more resilient and sustainable production of food crops.
Extreme sea levels in the context of climate change
Authors: Pineau-Guillou Lucia , Lazure Pascal , Wöppelmann Guy
Published: March 2020

The objective of this study is to investigate how extreme sea levels are changing, at a centennial time scale, in the context of climate change. We focus on Brest tide gauge (France), one of the longest time series in the world. First observations were recorded in 1701, and hourly data have been registered continuously since 1846 with little gaps. These data have been  carefully processed, in order to ensure good quality, especially regarding the datum continuity (Pouvreau, 2008) and stability (Poitevin, 2019).

Here, we investigate the evolution of the storm surges over the last 170 years. We focus on the skew surge, defined as the difference between the maximum observed water level and the maximum predicted tidal level (taking into account the mean sea level rise). This parameter is directly linked to the atmosphere variations, and may be correlated with regional climate parameters, such as the North Atlantic Oscillation (Menéndez and Woodworth, 2010). But it is also correlated with the evolution of the storminess in the North Atlantic. One of the challenges is to separate the natural interannual variability of the sea level from the long term trends at a centennial time scale.

We will discuss the variability of the storm surges, in terms of changes in the 99th percentile and the 5-year return period level. Statistical analysis will be based on extreme values theory (e.g. Generalized Extreme Value distribution, General Pareto Distribution). Correlation with other parameters such as the significant wave height (from buoys) and the wind and storm tracks (from global reanalysis, e.g. ERA5 from ECMWF) will also be investigated.

References
Menéndez M., Woodworth P. L. (2010). Changes in extreme high water levels based on a quasi-global tide-gauge dataset. J Geophys Res 115:C10011.
Poitevin (2019). Variabilité du niveau marin relatif le long du littoral de Brest (France) par combinaison de méthodes géodésiques spatiales (altimétrie radar, InSAR et GPS). PhD thesis, University of La Rochelle.
Pouvreau N. (2008). Trois cents ans de mesures marégraphiques en France : outils, méthodes et tendances des composantes du niveau de la mer au port de Brest. PhD thesis, University of La Rochelle.

 
PPP-AR with GPS and Galileo: Assessing diverse approaches and satellite products to reduce convergence time
Authors: Glaner Marcus Franz , Weber Robert , Strasser Sebastian
Published: March 2020

Precise Point Positioning (PPP) is one of the most promising processing techniques for Global Navigation Satellite System (GNSS) data. By the use of precise satellite products (orbits, clocks and biases) and sophisticated algorithms applied on the observations of a multi-frequency receiver, coordinate accuracies at the decimetre/centimetre level for a float solution and at the centimetre/millimetre level for a fixed solution can be achieved. In contrast to relative positioning methods (e.g. RTK), PPP does not require nearby reference stations or a close-by reference network. On the other hand PPP has a non-negligible convergence time. To make PPP more competitive against other high-precision GNSS positioning techniques, scientific research focuses on reducing the convergence time of PPP.

 

In this contribution, we present results of PPP with focus on integer ambiguity resolution (PPP-AR) using satellite products from different analysis centers. The resulting coordinate accuracy and convergence behaviour are evaluated in various test scenarios. In these test cases we distinguish between the use of satellite products from Graz University of Technology, which are calculated using a raw observation approach, and nowadays publicly available satellite products of different analysis centers (e.g. CNES, CODE). All those products enable PPP-AR in different approaches. To shorten the convergence time, we investigate and compare different PPP processing approaches using GPS and Galileo observations. The use of 2+ frequencies and alternatives to the classical PPP model, which is based on two frequencies and the ionosphere-free linear combination are discussed (e.g. uncombined model with ionospheric constraint). The PPP calculations are performed with the in-house software raPPPid, which has been developed at the research division Higher Geodesy of TU Vienna and is part of the Vienna VLBI and Satellite Software (VieVS PPP).
Initiation and flow conditions of contemporary flows in Martian gullies
Authors: de Haas Tjalling , McArdell Brian , Conway Susan , McElwaine Jim , Kleinhans Maarten , Salese Francesco , Grindrod Peter
Published: March 2020

Understanding the initial and flow conditions of contemporary flows in Martian gullies, generally believed to be triggered and fluidized by CO2 sublimation, is crucial for deciphering climate conditions needed to trigger and sustain them. We employ the RAMMS (RApid Mass Movement Simulation) debris flow and avalanche model to back-calculate initial and flow conditions of recent flows in three gullies in Hale crater. We infer minimum release depths of 1.0–1.5 m and initial release volumes of 100–200 m3. Entrainment leads to final flow volumes that are 2.5–5.5 times larger than initially released, and entrainment is found necessary to match the observed flow deposits. Simulated mean cross-channel flow velocities decrease from 3–4 m s-1 to ~1 m s-1 from release area to flow terminus, while flow depths generally decrease from 0.5–1 m to 0.1–0.2 m. The mean cross-channel erosion depth and deposition thicknesses are _0.1–0.3 m. Back-calculated dry-Coulomb friction ranges from 0.1 to 0.25 and viscous turbulent friction between 100–200 m s-2, which are values similar to those of granular debris flows on Earth. These results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on Earth. Using a novel model for mass-flow fluidization by CO2 sublimation we are able to show that under Martian atmospheric conditions very small volumetric fractions of CO2 of ~1% within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility.
Upper crustal velocity structure of Pearl River Delta, China, derived from dense-array observations of ambient noise
Authors: Lyu Zuoyong , Ye Xiuwei , Lyu Jinshui , Zhang Xiang , Wang Liwei , Wang Xiaona
Published: March 2020

The Pearl River Delta, located in the middle of the southeast coast of south China, is a graben basin. Although this region is considered tectonically relatively inactive, many small earthquakes still occur, and multi groups of faults with different directions are well developed. To better understand the geological structures in this region, we use about 30 days of ambient noise data from 88 portable stations and 38 permanent broadband stations to obtain a high-resolution 3D upper crustal S-wave velocity model. Over 3700 Inter-station group-velocity curves were measured in the 1-10 s period range and tomographically inverted by a direct surface wave inversion method in a 0.05°×0.05°grid. The checkerboard test shows that the tomographic final resolution is 0.1°×0.1°. Our results show that in the shallow crust of the study area, the velocity distribution corresponds to surface geology and geological features. The Huizhou-Dongguan depression and the Pearl River mouth exhibit low S-wave velocity feature, while the high S-wave velocity zone corresponds to the distribution of Mesozoic granite. Some faults are almost between low velocity and high velocity zone, which may play an important role of the channel of magmatic activity. The upper crustal structure in this area is closely related to the intense magmatic tectonic activity and crustal extension since Mesozoic.
Variation of geophysical parameters during preparation of seismic events
Authors: Jimsheladze Tamar , Kereselidze Zurab , Melikadze George , Kobzev Genadi
Published: March 2020

In terms of geodynamic life, territory of Georgia is one of the most active region. The macro structural factor here is represented by the contact with the Arabian and Eurasian tectonic plates, which in addition to the geological diversity of the area conditions the high seismicity of mentioned region. 

More the 20 year was operating a special network of hydro-geodynamical (water level, Atmosphere pressure and air temperature) observation on the territory of Georgia. Ten deep boreholes located basically on the main geo-plate and open deep aquifers. These wells as sensitive strain-meters recorded all kinds of deformation caused by exogenous (atmospheric pressure, tidal variations and season variation), as well as endogenous processes.

During observation on the territory of Georgia has observed various anomalies by water level before seismic events. Revealing of the mechanism of interrelation between the deformation processes, forestall strong earthquakes, and a hydrodynamic variation of underground waters, would allow to explain such preliminary behavior of hydrodynamic effects and to develop scientifically proven methods of the forecast of earthquakes.
Ocean surface warming in Krossfjorden, Svalbard, during the last 60 years
Authors: Guruvayoorappan Harikrishnan , Miettinen Arto , Divine Dmitry , Moros Matthias , Orme Lisa , Mohan Rahul
Published: March 2020

A high-resolution marine sediment core NP16-Kro1-MCB from Krossfjorden, Western Svalbard is studied to investigate changes in sea surface conditions in the fjord during the last 60 years (1953-2014). The diatom-based reconstruction of August sea surface temperature (aSST) demonstrates a clear warming trend of 0.6 °C through the record. As inferred from Marginal Ice Zone (MIZ) diatoms, surface warming occurs in parallel with a decline in sea ice extent (SIE) during recent decades. Factor analysis identified variations in diatom assemblages representing different water masses, showing a dominance of Arctic water diatoms throughout the period and decadal variations in the sea ice assemblage during periods of peak sea ice extent. The strong dominance of Arctic water diatoms along with increasing aSST suggest prolonged open water conditions and increased sea ice melting in the region throughout the observed period. The reconstructed ocean surface changes are in line with the background warming occurring over the Arctic region. A comparison with instrumental records from neighboring regions supports the quality of the reconstructions, including the average reconstructed aSST and the magnitude of the warming trend. We suggest that increased CO2 forcing together with ocean-atmospheric interaction have caused the increasing SST trend and decreasing sea ice presence in Krossfjorden rather than an increasing influence from Atlantic Water, which has amplified changes in many regions of Svalbard. 
Prediction of CME arrivals; differences based on stereoscopic heliospheric imager data
Authors: Hinterreiter Jürgen , Amerstorfer Tanja , Reiss Martin A. , Temmer Manuela , Möstl Christian , Bauer Maike , Amerstorfer Ute V. , Bailey Rachel L. , Weiss Andreas J.
Published: March 2020

Forecasting the arrival time and speed of CMEs is of high importance. However, uncertainties in the forecasts are high. We present the results of post-event prediction of CME arrivals using ELEvoHI (ELlipse Evolution model based on Heliospheric Imager observations) ensemble modeling. The model uses time-elongation profiles provided by HI (Heliospheric Imager) onboard STEREO (Solar TErrestrial RElations Observatory) and assumes an elliptical shape of the CME front. The drag force exerted by the ambient solar wind is an essential factor influencing the dynamic evolution of CMEs in the heliosphere. To account for this effect, ELEvoHI utilizes the modeled ambient solar wind provided by the Wang-Sheeley-Arge model. We carefully select 12 CMEs between February 2010 and July 2012, which show clear signatures in STEREO-A and STEREO-B HI images, have a corresponding in-situ signature, and propagate close to the ecliptic plane. As input to ELEvoHI, we make use of STEREO-A and STEREO-B time-elongation profiles for each CME and compare the predicted arrival times and speeds based on both vantage points with each other. We present our model results and discuss possible reasons for the differences in the arrival times of up to 15 hours.
Identifying anthropogenic effects into Doñana aquifer (SW Spain) through hydrogram clustering of piezometric database
Authors: Guardiola-Albert Carolina , Naranjo-Fernández Nuria , Aguilera Héctor , Montero-González Esperanza
Published: March 2020

Nowadays, the application of time series clustering is increasing in hydrogeology works. Groundwater level long data series provides a useful record to identify different hydrological behaviors and to validate the conceptual model of groundwater flow in aquifer systems. Piezometers also register the response to any changes that directly affect the amount of available groundwater resources (recharge or exploitation).

What are the expected variations of groundwater levels in an aquifer under high exploitation pressure? In this work, groundwater level time series from 160 piezometers in the hydrological years from 1975 to 2016 were analyzed. Especially, 24 piezometers are deeply studied. Data were preprocessed and transformed: selection of points, missing data imputation and data standardization. Visual clustering, k-means clustering and time series clustering were applied to classify groundwater level hydrographs using the available database. Six and seven groups of piezometers were identified to be associated with the different hydrofacies and extraction rates. Time series clustering was found to be the best method to analyze the studied piezometric database. Moreover, it was possible to characterize actual hydrodynamics, which will be useful for groundwater managers to make sustainable decisions.
Simulating the seasonal cycle of 13C
Authors: Lienert Sebastian , Köstler Christoph , Zaehle Sönke , Joos Fortunat
Published: March 2020

We investigate the seasonal cycle of δ13CO2 using the Earth system model of intermediate complexity Bern3D-LPX. Using a model of atmospheric transport (TM3), the spatial fields of simulated 13CO2 and CO2 exchange are translated to local δ13CO2 anomalies, which are then compared to atmospheric measurements. We discuss the ability of the model to accurately simulate the atmospheric seasonal δ13CO2 cycle, which could prove to be a valuable novel observational constraint. The coupled simulation allows us to distinguish the relative importance of the biosphere and ocean in determining the seasonal cycle of δ13CO2 at different measurement sites across the world.

The amplitude of the seasonal cycle of δ13CO2 is of particular importance to quantify land biosphere processes. The decreasing δ13CO2 of the atmosphere during the last decades (Suess effect) leads to a divergence of the δ13C signature in assimilation and heterotrophic respiration, because of the long lifetime of soil pools. This is expected to lead to a high sensitivity of the seasonal amplitude to the amount of soil respiration. The effect of changes in soil turnover times on the simulated seasonal cycle is explored with factorial simulations of the Dynamic Global Vegetation Model LPX-Bern.
A satellite era warming hole in the equatorial Atlantic Ocean
Authors: Nnamchi Hyacinth , Latif Mojib , Keenlyside Noel , Park Wonsun
Published: March 2020

Although the globally averaged surface temperature of the Earth has considerably warmed since the beginning of global satellite measurements in 1979, a warming hole, with hardly any surface warming that is most pronounced in boreal summer, has been observed in the equatorial Atlantic region during this period. The warming hole occurs in an extended area of the equatorial Atlantic that includes the cold tongue, the region of locally cooler ocean surface waters that develops just south of the equator in boreal summer, partly reflecting the upwelling of deep cold waters by the action of the southeasterly trade winds. This lack of surface warming of the cold tongue denotes an 11% amplification of the mean annual cycle of the sea surface temperature during the satellite era. The warming hole is driven by an intensification of the equatorial upwelling of cold waters into the ocean surface layers and damped by the surface heat flux. In observations, the tendency for surface cooling appears to reflect intrinsic variability of the climate system and is not unusual during the instrumental period. The warming hole is associated with wind-induced ocean circulation changes to the south and north of the northward of the equator. Coupled model ensembles forced by the observed varying concentrations of atmospheric greenhouse gases and natural aerosols as well as unforced runs were analyzed. The ensembles suggest a strong role for atmospheric aerosols in the warming hole. However, although aerosols can cause a cooling of the cold tongue, intrinsic climate variability as represented in the unforced experiment can potentially cause larger cooling than has been observed during the satellite era. This study highlights the difficulty in reconciling observations and the climate models for the attribution of the warming hole.
The extreme warm summer 2018 in Sweden - set in a historical context
Authors: Wilcke Renate , Kjellström Erik , Moberg Anders , Lin Changgui
Published: March 2020

Long-lasting high-pressure dominated weather resulting in remarkably warm and dry conditions in large parts of northern Europe during summer 2018. As a consequence, Sweden experienced a very long warm period with an unusual high number of warm days, which could be felt in many parts of the society. Groundwater shortage, many extensive forest fires (requiring assistance on European scale), health impacts on people, drought related shortage of food for livestock leading to emergency slaughter in many regions.According to SMHIs weather observations the average over Sweden for the four-month period May-August was on average 3.3K warmer than the 1961-1990 climatological mean.

Here, we evaluate climate conditions in Sweden during the summer 2018 in relation to the historical climate, reaching back to pre-industrial times. Basing the evaluation on long observation time series (150 years for some station across Sweden, and 250 years for Stockholm) as well as on 5 large ensembles from different global models, we want to assess to what extent an extreme event like the summer of 2018 may have changed as a result of global warming.

To grasp the character of summer 2018, not only daily values are considered, but also periods of heat days and heat indices describing the amplitude and length of an event.

With the extended length of the summer season, on account of an exceptional warm May, 2018 sets its record for many heat related indices and would have very unlikely been observed in pre-industrial times according to the given model data.
Crustal magnetic fields at Mars and ion escape
Authors: Dubinin Eduard , Fraenz Markus , Pätzold Marin , Woch Joachim , Fan Kai , Wei Yong , McFadden Jim , Tsareva Olga , Zelenyi Lev
Published: March 2020

Does an intrinsic field inhibits or enhances ion escape from planetary ionospheres is still an unsolved issue. Mars does not possess a global intrinsic magnetic ﬁeld but instead has the strong crustal magnetic fields localized mainly in the southern hemisphere. The crustal magnetic field significantly inﬂuences the interaction of the solar wind with Mars adding features typical for planets with a global intrinsic magnetic field. Therefore it is interesting to compare ion losses from the ionosphere regions with and without strong crustal fields. Recently such studies were performed and have shown a protective effect of the crustal field on escape of the energized (E > 30 eV) oxygen ions (e.g. Fan et al., Geophysical Review Letters, 2019). However, the main bulk of escaping ions at Mars have energy lower than 30 eV. We will present the results of influence of the crustal magnetic field at Mars on the total losses of O+ and O2+ ions. The global picture of ion escape occurs more complex. Effects of larger ionospheric areas above the crustal field sources exposed by solar wind compensate a shielding effect at lower altitudes. As a result, the ion losses from the southern ionosphere of Mars might be even higher than losses from the northern “unmagnetized” ionosphere.
Solar Type III radio bursts at Saturn’s orbit: Case study of stereoscopic observations by Cassini/RPWS and Wind/WAVES experiments
Authors: Abou el-Fadl Ahmed , Boudjada Mohammed , Galopeau Patrick H.M. , Hammoud Muhamed , Lammer Helmut
Published: March 2020

Type III radio bursts are produced by electron beams accelerated in active regions and following open magnetic field lines. Type III observed frequency is found to be nearly equal to the plasma frequency directly linked to the local electron density. The source regions of such solar bursts are the solar corona and the interplanetary medium where, respectively, higher and lower frequencies are generated. In this work, we consider specific Type III solar bursts simultaneously observed by Cassini/RPWS and Wind/WAVES experiments. Despite the distance of Cassini spacecraft to the Sun such Type III bursts have been detected at Saturn’s orbit, i.e. at about 10AU. Those considered bursts are covering a frequency bandwidth from about 10 MHz down to 100 kHz. We attempt in this study to characterize the spectral pattern, i.e. the flux density versus the observation time and the frequency range, and the visibility of the source regions to the observer (i.e. Wind and Cassini spacecraft). In this context, we analyze the evolution of the Type III bursts from the solar corona and up to Saturn’s orbit taking into consideration the Archimedean spiral which is the geometrical configuration of the solar magnetic field extension in the interplanetary medium. We principally discuss the physical parameters, i.e. solar wind speed and the electron density, which lead to constraint the location of the source region and its visibility to both spacecraft.
Distribution patterns of planted-shrubs of different restoration ages in artificial sand-fixing regions and effects on soil property in the southeastern Tengger desert
Authors: Liu Meiling
Published: March 2020

The plant density and spatial distribution in artificial vegetation is obviously initialized at the planting stage. Plants dynamics and spatial pattern may change over time as the result of interactions between individual plants and habitats, but whether this is the case for desert shrubs in artificial sand-fixing regions is largely unknown. Here we examined changes in plant density and distribution patterns of three shrubs (Artemisia ordosica Krasch., Caragana korshinskii Kom., and Hedysarum scoparium Fisch.) in different regions restored for 27, 32 and 50 years (R27, R32, R50), respectively. The vegetation analysis showed that A. ordosica were the dominated species across the 3 restoration regions. The density of A. ordosica and H. scoparium showed a significant increase from R27 to R32, then decreased in R50. However, there was no C. korshinskii survive in R27. The density of C. korshinskii was also low in R32 and R50. The variance-to-mean ratio (VMR) was used to characterize the spatial distribution patterns to ﬁt the observed frequency distributions of densities of the three shrubs. A. ordosica and C. korshinskii all showed significantly clumped distribution in three restoration regions. For H. scoparium, it showed uniform distribution in R27 and R50, however showed clumped distribution in R32. We also quantified changes in soil physio-chemical properties in different restoration regions. The proportion of sand-sized particles in the topsoil was reduced sharply; the proportion of silt and clay increased greatly from 17.3 and 4.6 to 21.4 and 10.4%, respectively. N and K contents were not significant different among R27 (0.52 and 0.93 g/kg, respectively) and R32 (0.59 and 0.98 g/kg, respectively), but has significant differences with R50 (0.78 and 1.06 g/kg, respectively). P content and soil organic matter content gradually increased with successional age. The results showed that compared to C. korshinskii and H. scoparium, A. ordosica seems to be more suitable in revegetated desert areas. Pattern analysis suggested a successive replacement of C. korshinskii, which had low proportions of survived shrubs, by the dominant A. ordosica. The soil properties were also significantly improved after restoration. This study contributes to understanding of the distribution patterns of shrubs plants and their effects to soil property in revegetation projects in arid desert area.
Intermittency of Arctic-midlatitude teleconnections: the stratospheric pathway between autumn sea ice and the winter NAO
Authors: Siew Peter Yu Feng , Li Camille , Sobolowski Stefan , King Martin
Published: March 2020

An observed relationship linking Arctic sea ice conditions in autumn to the North Atlantic Oscillation (NAO) index the following winter has potential relevance for seasonal predictions of European and North American climate. The physical pathway most often invoked to explain this particular teleconnection passes through the stratosphere. A Causal Effect Networks (CEN) approach is used to explore this stratospheric pathway between late autumn Barents-Kara sea ice and the February NAO, focusing on its seasonal evolution, timescale-dependence, and robustness. This pathway is statistically detectable in the satellite period, explaining 26% of the interannual variability in the February NAO. However, a bootstrap-resampling test reveals that the pathway is highly intermittent: the whole pathway emerges in only 15% of the bootstrapped samples. The intermittent nature of the pathway is consistent with the weak signal-to-noise ratio of the atmospheric response in the sea ice perturbation experiments, and suggests that a background state is important in determining whether the pathway is active. Higher frequency synoptic interactions between Barents-Kara sea ice and sea level pressure over Urals potentially interfere with the stratospheric pathway. Such interference likely reduces the potential for using the ice-NAO relationship for predicting midlatitude winter climate. This study helps quantify the robustness of linkages within the stratospheric pathway, and provides insight into which linkages are most subject to sampling issues within the relatively short observational record.
Volumetric soil quality modelling with machine learning in a diverse agricultural landscape in Andalusia, Spain
Authors: Rentschler Tobias , Bartelheim Martin , Díaz-Zorita Bonilla Marta , Gries Philipp , Scholten Thomas , Schmidt Karsten
Published: March 2020

Soils and soil functions are recognized as a key resource for human well-being throughout time. In an agricultural and forestry perspective, soil functions contribute to food and timber production. Other soil functions are related to freshwater security and energy provisioning. In general, the capacity of a soil to function within specific boundaries is summarised as soil quality. Knowledge about the spatial distribution of soil quality is crucial for sustainable land use and the protection of soils and their functions. This spatial knowledge can be obtained with accurate and efficient machine-learning-based soil mapping approaches, which allow the estimation of the soil quality at distinct locations. However, the vertical distribution of soil properties is usually neglected when assessing soil quality at distinct locations. To overcome such limitations, the depth function of soil properties needs to be incorporated in the modelling. This is not only important to get a better estimation of the overall soil quality throughout the rooting zone, but also to identify factors that limit plant growth, such as strong acidity or alkalinity, and the water holding capacity. Thus, the objective of this study was to model and map the soil quality indicators pH, soil organic carbon, sand, silt and clay content as a volumetric entity. The study area is located in southern Spain in the Province of Seville at the Guadalquivir river. It covers 1,000 km2 of farmland, citrus and olive plantations, pastures and wood pasture (Dehesa) in the Sierra Morena mountain range, at the Guadalquivir flood plain and tertiary terraces. Soil samples were taken at 130 soil profiles in five depths (or less at shallow soils). The profiles were randomly stratified depending on slope position and land cover. We used a subset of 99 samples from representative soil profiles to assess the overall 513 samples with FT-IR spectroscopy and machine learning methods to model equal-area spline, polynomial and exponential depth functions for each soil quality indicator at each of the 130 profiles. These depth functions were modelled and predicted spatially with a comprehensive set of environmental covariates from remote sensing data, multi-scale terrain analysis and geological maps. By solving the spatially predicted depth functions with a vertical resolution of 5 cm, we obtained a volumetric, i.e. three-dimensional, map of pH, soil organic carbon content and soil texture. Preliminary results are promising for volumetric soil mapping and the estimation of soil quality and limiting factors in three-dimensional space.
Seismological Constraints on Fault-Slip Source Models and Rupture Characteristics of Global Large Earthquakes (Mw ≥ 7.5) and Associated Tsunamis
Authors: Yolsal-Çevikbilen Seda , Taymaz Tuncay
Published: March 2020

Large and destructive earthquakes (Mw≥ 7.5) occur worldwide particularly along the major subduction zones causing extensive damage and loss of life in the hinterland of epicentral region. Source models and rupture characteristics of these earthquakes (i.e. faulting geometry, focal depth, non-uniform finite-fault slip distributions) can be precisely determined by using seismological data and multidisciplinary earth-science observations. It is also known that earthquake source parameters play key roles in the modelling of secondary events such as earthquake-induced tsunamis. There are many studies emphasizing the importance of using heterogonous slip distribution models of earthquakes in mathematical tsunami simulations to predict synthetic tsunami waves more consistent with the observed ones. In this study, we obtained double-couple source mechanisms and slip distribution models of complex large earthquakes (Mw≥ 7.5) lately occurred at different parts of the Earth. For this purpose, we used point-source teleseismic P- and SH- body waveform inversion and kinematic slip distribution inversion techniques. Besides, azimuthal distributions of P- wave first motion polarities, which are recorded by near-field and regional seismic stations, are checked to approve obtained minimum misfit source mechanism parameters of earthquakes. We essentially observed that tsunamigenic earthquakes occurred at shallow focal depths (h ≤ 70 km) with dip-slip source mechanisms and rather complex slip distributions along the fault planes. However, in some cases, tsunami waves may be unexpectedly triggered due to the secondary effects of large strike-slip earthquakes (e.g., September 28, 2018 Palu, Indonesia - Mw7.5). Here, we discuss our inversion results, which reveal the significant contributions of earthquake source studies on resolving the relationships between the faulting geometry, rupture characteristics and tsunami generation. Furthermore, the necessity of high-resolution bathymetry data in numerical tsunami simulations is highlighted for the modelling of tsunami waves, in particular, recorded at the near-field tide-gauge stations. This study is partially supported by the Turkish Academy of Sciences (TÜBA) through GEBIP program.