bluuebunny/crossref_metadata_2025 huggingface dataset:
On memory and non-memory parts of surface air temperatures over China: can they be simulated by decadal hindcast experiments in CMIP5?
Authors: Xiong Feilin , Yuan Naiming , Ma Xiaoyan , Lu Zhenghui , Gao Jinhui
Published: March 2021

It has been well recognized that, for most climatic records, their current states are influenced by both past conditions and current dynamical excitations. However, how to properly use this idea to improve the climate predictive skills, is still an open question. In this study, we evaluated the decadal hindcast experiments of 11 models (participating in phase 5 of the Coupled Model Intercomparison Project, CMIP5) in simulating the effects of past conditions (memory part, M(t)) and the current dynamical excitations (non-memory part, ε(t)). Poor skills in simulating the memory part of surface air temperatures (SAT) are found in all the considered models. Over most regions of China, the CMIP5 models significantly overestimated the long-term memory (LTM) of SAT. While in the southwest, the LTM was significantly underestimated. After removing the biased memory part from the simulations using fractional integral statistical model (FISM), the remaining non-memory part, however, was found reasonably simulated in the multi-model means. On annual scale, there were high correlations between the simulated and the observed ε(t) over most regions of the country, and for most cases they had the same sign. These findings indicated that the current errors of dynamical models may be partly due to the unrealistic simulations of the impacts from the past. To improve predictive skills, a new strategy was thus suggested. As FISM is capable of extracting M(t) quantitatively, by combining FISM with dynamical models (which may produce reasonable estimations of ε(t)), improved climate predictions with the effects of past conditions properly considered may become possible.
Climate related variations in atmospheric nitrous oxide concentration during the Mid- to Late Holocene
Authors: Azharuddin Syed , Ahn Jinho , Ryu Yeongjun , Brook Ed
Published: March 2021

Nitrous oxide (N2O) is an important greenhouse gas with sources that respond to the biogeochemical processes on land and ocean. The major sources of atmospheric N2O are nitrification and denitrification occurring in terrestrial soils and the ocean. Here we present a new high-resolution atmospheric N2O record obtained from South Pole Ice (SPICE) core site covering the Mid- to Late Holocene (since ~5.5 ka). The N2O analysis was performed in a specialised wet extraction facility installed at Seoul National University that used small ice samples (<20 g) to yield a high precision (average standard deviation of ~1ppb) record. The new N2O data agree well with existing records on the millennial scale and reveal new details on the multi-centennial scale. Our results show a progressive increase in atmospheric N2O during 5.5 to 3.2 ka which correlates well with the increase of marine denitrification around the Arabian Sea (AS) and Peru-Chile Margin (PCM) as well as Indian monsoon precipitation around the same period. A local minimum in N2O is observed around 2.8 ka, possibly related to a sudden decrease in Western Tropical South (WTS) Pacific sea surface temperature and increased La-Nina like conditions which may have supressed denitrification along PCM. These conditions may have further influenced the monsoons and reduced denitrification in land soils. Our record also shows a local N2O maximum around 2.2 ka which may correspond to relaxed La-Nina like conditions around WTS Pacific. Subsequently, the N2O further dropped to attain a pronounced minimum around 1.4 ka. Similar N2O minima are also observed in Styx (Antarctica) and  NEEM (Greenland) ice core records, demonstrating the robustness of the signals.
Morphometrical analysis of Debris flow fans and torrential catchments in mountainous terrain in the northern Colombian Andes by machine learning techniques.
Authors: Castillo Cardona Emanuel , Aristizábal Edier
Published: March 2021

Debris flow fans are commonly occupied by urban and rural settlements in mountainous regions such as in the northern Colombian Andes. Those fans are originated by violent surges of high sediment concentration that are then mobilized downstream by strong currents during torrential events highly destructive. Then, characterization and understanding of the dynamics that give rise to fans in tropical and mountainous regions such as Andean zone is a fundamental tool for land use planning. This research focuses on cartography of fans and catchments using digital elevation models in the central and western mountain range of the northern part of the Andean mountain belt. The methodology considered: morphometric measurements of the catchments and fans, lithological aspects of the catchments, type of catchments (torrential or no torrential). Then the correlation between morphometric parameters of fans and catchments is carried out, including relationships with qualitative variables by multivariate statistical analysis and machine learning techniques to find patterns between quantitative and qualitative variables. The results indicate that slope of the fans has a high correlation with Melton index of the catchments and with the slope of the main stream of the catchments. About the qualitative classification of the catchments in torrential and no torrential, it is observed that there are good discriminations for slope of the fan, volume of the deposits(fans), the relationship between the relief of the catchments and other variables. On the other hand, the lithology of the catchments does not have strong influences on the morphometry of the fans.
Meshfree models for simulation of reactive transport in groundwater systems
Authors: Anshuman Aatish , Eldho t i
Published: March 2021

Groundwater is the largest source for freshwater which plays an important role in the hydrological cycle. The pollution of groundwater is on the rise due to various natural and anthropogenic sources such as landfills, agricultural lands, and underground waste storage facilities etc. These pollutants can be subjected to reactions depending on the contaminant type and the subsurface environment along with advection and dispersion processes.  As groundwater is used in various human activities such as drinking, agriculture and industrial activities, it is essential to track the contaminants in groundwater for assessing possible environmental impacts. The complex phenomena of flow and contaminant transport are represented by partial differential equations (PDEs) which are solved numerically throughout the problem domain. Although Finite Difference method (FDM) and Finite Element Method (FEM) based models are conventionally used for these simulations, these methods suffer from certain instabilities due to the presence of mesh/grid, for example, numerical dispersion and artificial oscillation for advection and reaction dominant problems. Moreover, these methods are not suitable for adaptive analysis which requires meshing and re-meshing in each simulation making the problem highly computationally expensive. Here, we present a strong form meshfree method named Radial Point Collocation Method (RPCM) for modelling flow and transport in groundwater. In contrast to mesh-based methods, the problem domain is discretised using only nodes in the proposed method. Moreover, unlike the mesh-based methods, it produces stable solutions for advection and reaction dominant problems without using special techniques such as up-winding, adaptive re-meshing or, operator splitting. The performance of the model is tested against analytical solutions, FDM and FEM based models for different reactive transport problems in groundwater involving adsorption, decay, multi-species decay network and biodegradation.
Biofilm-induced sinking of buoyant microplastics in a freshwater environment
Authors: Semcesen Patricia , Wells Mathew
Published: March 2021

The degree of microplastic dispersal and retention in lakes and oceans critically depends upon the microplastic particle’s density, which can change over time due to microbial growth (biofilm). This experiment tests the mechanism by which initially buoyant microplastics can be lost from the surface layers of a lake and become deposited in sediments. While buoyant microplastics do initially float in water, the growth of biofilm denser than water on the microplastic surface leads to an increase in particle density as a whole. This increase in density results in slower rise velocities of biofouled particles when they are mixed into the water column, and can even lead to sinking of biofouled particles. Both slower rise velocities and particle sinking would increase microplastic residence time in the water body. Through ex-situ experiments on irregularly-shaped polypropylene microplastic granules in an emulated lake environment under overcast light levels, we have found that biofouling alone is sufficient to increase microplastic particle density and lead to sinking for small particles (~125-212 µm) in 18 days and larger particles (1000-2000 µm) in 50 days. These differences in settling onset time would likely lead to size-fractionation of particle sedimentation, where smaller particles are deposited closer to their sources relative to larger particles. Using the measured values of biofilm-induced sinking rates of larger microplastics (1000-2000 µm) and lake residence times, we can describe the fraction of microplastics expected to become deposited after they enter lakes. Our results on terminal velocity change inherent to biofouling provide new information for microplastic transport modelling.
Experimental study on the deformation microstructures and crystallographic preferred orientation of glaucophane and epidote in deformed epidote blueschist at high pressure
Authors: Park Yong , Jung Sejin , Jung Haemyeong
Published: March 2021

To understand the crystallographic preferred orientation (CPO) of glaucophane and epidote and deformation microstructures at the top of a subducting slab in a warm subduction zone, deformation experiments of epidote blueschist were conducted in simple shear by using a modified Griggs apparatus. Deformation experiments were performed under high pressure (0.9–1.5 GPa), temperature (400–500 °C), shear strain (γ) in the range of 0.4–4.5, and shear strain rate of 1.5×10-5–1.8×10-4 s-1. After experiments, CPO of minerals were determined by electron back-scattered diffraction (EBSD) technique, and microstructures of deformed minerals were observed by transmission electron microscopy (TEM). At low shear strain (γ ≤ 1), the [001] axes of glaucophane were in subparallel alignment to shear direction, and the (010) poles were sub-normally aligned to the shear plane. At high shear strain (γ > 2), the [001] axes of glaucophane were in subparallel alignment to shear direction, and the [100] axes were sub-normally aligned to the shear plane. At a shear strain between 2 < γ < 4, the (010) poles of epidote were in subparallel alignment to shear direction, and the [100] axes were sub-normally aligned to the shear plane. At a high shear strain where γ > 4, the alignment of the (010) epidote poles had altered from subparallel to subnormal to the shear plane, while the [001] axes were in subparallel alignment to the shear direction. TEM observations and EBSD mapping revealed that the CPO of glaucophane was developed by dislocation creep, somewhat affected by the cataclastic flow at high shear strain. On the other hand, the CPO development of epidote is considered to have been affected by dislocation creep under a shear strain of 2 < γ < 4 but is highly affected by cataclastic flow with rigid body rotation under a high shear strain (γ > 4). Our experimental results indicate that the magnitude of shear strain and rheological contrast between component minerals plays an important role on the formation of CPOs of glaucophane and epidote.
On the vertical structure of internal solitary waves in the northeastern South China Sea
Authors: Yi Gong , Haibin Song , Zhongxiang Zhao , Yongxian Guan , Yunyan Kuang
Published: March 2021

Internal solitary waves (ISWs) make important contributions to energy cascade, ocean mixing and material transport in the ocean. However, there are few observational studies on the vertical structure of ISWs. The high-spatial resolution of seismic data enables us to obtain clear internal structure image of ISWs, so we can conduct a detailed research on their vertical structure. In this article, we report 11 ISWs near Dongsha Atoll in the South China Sea using two-dimensional seismic data.

We first extracted the amplitudes of ISW from seismic section, and obtained a series of discrete amplitude points. Then, the least-squares spline fitting was used to fit these amplitude points into a vertical structure curve. We calculated vertical structures by linear theory and first-order nonlinear theory, respectively, and compared the observed vertical structure with the two theories. We found that three ISWs conform to the linear vertical structure function, four ISWs conform to the first-order nonlinear vertical structure function, and four ISWs do not conform to the two theories. In order to figure out the reason why the observation did not conform to the theories, we decomposed the fitted vertical structures of these four ISWs by the empirical mode decomposition (EMD) algorithm, and compare the residuals of decomposition with the two theories. The results showed that the residuals of two ISWs are in agreement with the linear vertical structure function, the residual of one ISW conforms to the first-order nonlinear vertical structure function, and one residual of ISW still cannot conform to the two theories. We calculated key parameters of these ISWs to analyze the reasons for difference between observation and theory.

In summary, we found that the shape of vertical structure is mainly determined by nonlinearity. The vertical structure with low degree nonlinearity can be described by linear theory, while ISW with high degree nonlinearity conform to the first-order nonlinear theory. Besides, for an ISW with large amplitude propagating in shallow water, its vertical structure is more susceptible to be affected by the topography. Moreover, the background flow can also affect the vertical structure. We found an ISW was passing through an eddy which was trapped near seafloor, and resulted in the bottom of vertical structure decayed rapidly.
Ebysus, a Multi-Fluid Multi-Species (MFMS) code: Application to magnetic reconnection in the solar atmosphere
Authors: Wargnier Quentin , Martinez Sykora Juan
Published: March 2021

The solar atmosphere is composed of many species with a large number of ionization levels. Depending on the region considered, the plasma can be partially or fully ionized, weakly or strongly magnetized, weakly or strongly collisional, allowing for thermal non-equilibrium processes and chemical reactions. Recent observations of the IRIS mission (De Pontieu et al. 2014) have confirmed that the solar atmosphere is a complex environment involving a wide range of unsteady processes occurring at different temporal and spatial scales.

In this context, we have developed a new code Ebysus (see Martinez-Sykora et al., 2019), by expanding the state-of-the-art single-fluid radiative MHD code Bifrost (Gudiksen et al. 2011). Ebysus solves a full MultiFluid MultiSpecies (MFMS)  system of equation for any species and/or ionized/excited level as desired separately. Following Wargnier et al. 2020, an accurate description of the collisions for multicomponent plasmas in solar atmosphere conditions, consistent with the kinetic theory, has also been developed and implemented in the code. The code includes non-equilibrium (NEQ) ionization, recombination, excitation and de-excitation for any species, momentum exchange, electric forces due to velocity drift between different ionized species, thermal conduction and radiative losses. The whole numerical strategy has been tested and the modules needed for this proposal are fully implemented.

First, we will present the model and its numerical strategy. We will then focus on realistic magnetic reconnection (MR) events and perform numerical simulations in several conditions representative of different layers of the solar atmosphere. In particular, we will demonstrate the role of the drift velocities between different species on the reconnection rate and the formation of plasmoid instabilities, which leads to a high energy release. These instabilities play a significant role in the dynamics of chromospheric jets, as observed by IRIS (Rouppe et al. 2017). This strategy will be a crucial point in understanding MR events that occur during UV bursts or flares.
Importance of drivers and processes for the predictive uncertainty in vegetation dynamics change across European forests
Authors: Oberpriller Johannes , Anthoni Peter , Arneth Almut , Herschlein Christine , Krause Andreas , Rammig Anja , Hartig Florian
Published: March 2021

Model predictions about future states of ecosystems under environmental change are uncertain. Understanding which factors drive these uncertainties is of immense value for directing research, but also for their interpretations. Here, we analyse sensitivities and uncertainties of a state of the art dynamic vegetation model (LPJ-GUESS) across European forests. We found that predictions of carbon fluxes are most sensitive to structure-related and mortality-related parameters, but most uncertainty is induced by drivers, nitrogen-, water- and mortality-modules. The uncertainty induced by drivers increases with increasing temperature, decreasing precipitation and from north to south across Europe. Moreover, environmental conditions change the resulting uncertainties in other processes. In this context, we encounter that the stress-gradient hypothesis is implicitly displayed in the model processes. In conclusion, our study stresses the importance of  environmental drivers for ecosystem predictions not only due to their uncertainty contributions but also because they determine the uncertainties of other processes.  
Aeolian dust sources, transport and deposition over the Chinese Loess Plateau during 1999-2019: A study using the FLEXDUST and FLEXPART models
Authors: Haugvaldstad Ove , Tang Hui , Kaakinen Anu , Strodal Frode
Published: March 2021

The aeolian dust deposits in the Chinese Loess Plateau (CLP) contain valuable information about past environmental changes in Asia. Unlocking this information requires knowledge on the Asian dust sources and dust transport mechanisms, and how the different source regions contribute to the total dust loading and deposition over the CLP.  By studying the dust transport and deposition under present day conditions using the Lagrangian Particle Dispersion model,  FLEXPART,  and the FLEXDUST dust emission model, we aim to better understand the dust signal in the Chinese loess records to constrain their interpretation as paleoclimate proxies.  

Here we present results from a 20 year simulation of transport and deposition of aeolian dust over the CLP from 1999 until 2019, during the dust event season March until May. Both FLEXPART and FLEXDUST are driven by ERA5 ECMWF meteorological reanalysis data. FLEXPART is set up in a receptor oriented configuration, where many computational particles are released from the receptor points at each timestep. The computational particles are followed for 5 days backward in time probing for possible source regions. The end product is emission sensitivity, i.e. how sensitive the receptor is to emissions in possible source regions. The emission sensitivity establishes a linear relation between the source and receptor. Therefore, multiplying the emission sensitivity with the dust emission flux estimated by FLEXDUST produces a map of the source contribution for each receptor point. To investigate the difference in source regions between the fine and coarse dust, we include two particle sizes, 2 μm and 20 μm, in our simulation. The output from the model is compared against Asian polar vortex (APV) and Asian winter monsoon indices to identify how changes in the large scale atmospheric circulation affect the interannual variation of dust transport and deposition, and to determine whether the amount of deposited dust over the CLP is primarily governed by changes in the emission strength or by changes in the atmospheric circulation.  
Thermal sea ice classification during the MOSAiC expedition
Authors: Thielke Linda , Huntemann Marcus , Spreen Gunnar , Hendricks Stefan , Jutila Arttu , Ricker Robert
Published: March 2021

The MOSAiC expedition took place in the Arctic from September 2019 to October 2020 while having measurements under, in, and above sea ice for a complete annual cycle. Airborne thermal infrared imaging was conducted during 41 helicopter survey flights along the MOSAiC drift track. We analyze the infrared brightness temperature of snow, sea ice, and ocean water surfaces from October 2019 until May 2020 from the airborne measurements. While the snow-covered sea ice appears very cold, thin ice and open water are significantly warmer. These surface types will be considered with particular attention because they dominate the heat exchange between the ocean, ice, and atmosphere during wintertime. This influences the Arctic Climate and becomes even more important in the currently changing Arctic, where the sea ice gets thinner, moves faster, and breaks up easier. After georeferencing and merging the recorded images to a mosaic, we can provide maps of infrared brightness temperatures in a high spatial resolution of 1 m for each flight. The spatial range of the maps varies from local (~5 km) up to regional (~30 km). This data set provides a basis to study the spatial and temporal variability of sea ice characteristics in the Arctic winter. We derive the physical surface temperature from the brightness temperature, surface emissivity, and downwelling radiation from the sky or clouds. Using the surface temperature, we calculate the heat flux from a local up to a regional scale based on thermodynamic assumptions and atmospheric measurements on the ice floe. From more complex thermodynamic simulations, we estimate ice thickness and ice age based on the airborne measured surface temperatures. The model calculates for each surface temperature a specific ice thickness and heat flux based on the knowledge about the surface’s thermodynamic history. The simulated ice thickness allows a sea ice classification which is compared to our first classification approach which deals with the flight's temperature distribution only. In the future, we will investigate the sub-footprint scale variability of ice surface temperature and thin ice thickness for satellite data, e.g. MODIS and Sentinel-3.
NFDI4Earth
Authors: Thiemann Hannes , Bräsicke Peter , Reichstein Markus , Weiland Claus , Hezel Dominik , Mahecha Miguel , Bernard Lars
Published: March 2021

NFDI4Earth (www.nfdi4earth.de) is proposed as the consortium of the German NFDI (National Research Data Infrastructure) to address the digital needs of researchers in Earth System Sciences (ESS). The NFDI4Earth consortium has been created in a bottom-up process and comprises currently 58 members from German universities, research institutions, infrastructure providers, public authorities and different research organizations.

The large number and diversity of observational, analytical, and model data sets in very high spatial, temporal and thematic resolution, confronts the ESS with a strongly increasing amount of data in great heterogeneity and of inherent complexity.  Earth system processes constantly change on various time scales and strongly influence each other. Describing and evaluating these processes urgently requires efficient workflows and extremely powerful data analytic frameworks like datacubes as well as appropriate levels of harmonizing related data services and their underlying standards. Research data are currently managed by an unstructured  plethora of services that are scattered, heterogeneous and often only project-based without a long-term perspective. A variety of measures and services become bundled under the umbrella of NFDI4Earth in a one-stop service framework. With a common approach to openness and FAIRness, they form a united, sustainable and coherent solution.

In addition to existing links between German and international partners in ESS, NFDI4Earth will establish itself as a single point of contact and the voice for German Earth system scientists in both existing and emerging networks and alliances. NFDI4Earth is for example already striving to establish linkages with federative e-infrastructures like the European Open Science Cloud (EOSC) at an early stage.

 
Seismic and transient slip characteristics of frictional-viscous shear zones in subduction environments
Authors: Behr Whitney , Gerya Taras
Published: March 2021

The deep roots of subduction megathrusts exhibit aseismic slow slip events, commonly accompanied by tremor and low-frequency earthquakes. Observations from exhumed rocks suggest that the deep subduction interface is a shear zone in which frictional lenses are embedded in a weaker, distributed viscous matrix deformed under high fluid pressures and low stresses. Here we use numerical models to explore the transient slip characteristics of finite-width frictional-viscous shear zones. Our model formulation utilizes an invariant form of rate- and state-dependent friction (RSF) and simulates earthquakes along spontaneously evolving faults embedded in a 2D continuum. The setup includes two elastic plates bounding a viscoelastoplastic shear zone (subduction interface) with inclusions (clasts) of varying sizes, aspect ratios, distributions and viscosity contrasts with respect to the surrounding matrix. The entire shear zone exhibits the same velocity-weakening RSF parameters, but the low viscosity matrix in the shear zone has the capacity to switch between RSF and linear viscous creep as a function of its local viscosity and stress state. Results show that for a range of matrix viscosities near a threshold viscosity (representative of the frictional-viscous transition), viscous damping and stress heterogeneity in these shear zones both 1) sets the ‘speed limit’ for earthquake ruptures that nucleate in clasts such that they propagate at velocities similar to observed slow slip events; and 2) simultaneously permits the transmission of slow slip from clast to clast, allowing slow ruptures to propagate substantial distances over the model domain. For reasonable input parameters, modeled events have moment-duration statistics, stress drops, and rupture propagation rates that match natural slow slip events. Events resembling very low-frequency earthquakes appear to be favored at high clast densities and low matrix viscosities, whereas longer duration, higher-magnitude slow slip events are favored at intermediate clast densities and near-threshold viscosities. These model results have potential to reconcile geophysical constraints on slow slip phenomena with the exhumed geological record of the slow slip environment.
Minimal impact of model biases on northern hemisphere ENSO teleconnections.
Authors: Tyrrell Nicholas , Karpechko Alexey
Published: March 2021

Correctly capturing the teleconnection between the ENSO and Europe is of importance for seasonal prediction. Here we investigate how systematic model biases may affect this teleconnection. A two–step bias–correction process is applied to an atmospheric general circulation model to reduce errors in the climatology. The bias–corrections are applied to the troposphere and stratosphere separately and together to produce a range of climates. ENSO type sensitivity experiments are then performed to reveal the impact of differing climatologies on ENSO–Europe teleconnections.

The bias–corrections do not affect the response of the tropical atmosphere, nor the Aleutian Low, to strong ENSO anomalies. However, the anomalous upward wave flux and the response of the northern hemisphere polar vortex differs between the climatologies. We attribute this to a reduced sensitivity of waves to the strength of the Aleutian Low. Despite the differing responses of the polar vortex, the NAO response is similar between the climatologies, implying that for strong ENSO events the stratospheric response may not be the primary driver for the ENSO–North Atlantic teleconnection.
Running a new 3-D variational inversion system to assimilate isotopic observations along with CH4 observations.
Authors: Thanwerdas Joel , Saunois Marielle , Berchet Antoine , Pison Isabelle , Bousquet Philippe
Published: March 2021

Atmospheric CH4 mixing ratios resumed their increase in 2007 after a plateau during the period 1999-2006, suggesting a change of mix between sources and/or varying sinks. Exploiting observations within an inverse modeling framework (top-down estimates) is a powerful approach that reconciles observed and simulated CH4 mixing ratios using prior knowledge of CH4 sources and sinks. It is nevertheless challenging to efficiently differentiate co-located emissions from different sectors categories with CH4 observations alone. As a result, understanding CH4 burden changes and attributing these changes to specific source variations are difficult. CH4 source isotopic signatures differ between emission categories (biogenic, thermogenic and pyrogenic), and can therefore be included to disentangle overlapping sources. 

However, assimilating 13CH4 observations using inversion methods is challenging, especially with a variational framework. Here, a new 3-D variational inverse modeling framework implemented within the Community Inversion Framework [Berchet et al., 2020] and designed to assimilate 13CH4 and CH3D observations along CH4 observations is presented. This system is capable of optimizing emissions and associated source signatures of multiple emission categories independently at the pixel scale. Multiple tracers are transported by the LMDz 3-D model in order to properly simulate the clumped isotopologues of CH4. 

We present very briefly the technical implementation of such multi-constraints in the variational system and show preliminary results of long-term inversions for the period 1998-2018.

Berchet, A., Sollum, E., Thompson, R. L., Pison, I., Thanwerdas, J., Broquet, G., Chevallier, F., Aalto, T., Bergamaschi, P., Brunner, D., Engelen, R., Fortems-Cheiney, A., Gerbig, C., Groot Zwaaftink, C., Haussaire, J.-M., Henne, S., Houweling, S., Karstens, U., Kutsch, W. L., Luijkx, I. T., Monteil, G., Palmer, P. I., van Peet, J. C. A., Peters, W., Peylin, P., Potier, E., Rödenbeck, C., Saunois, M., Scholze, M., Tsuruta, A., and Zhao, Y.: The Community Inversion Framework v1.0: a unified system for atmospheric inversion studies, Geosci. Model Dev. Discuss. [preprint], https://doi.org/10.5194/gmd-2020-407, in review, 2020.
Deficit irrigation as a sustainable option for improving water productivity in Sub-Saharan Africa: the case of Ethiopia. A Critical Review 
Authors: Asmamaw Desale , Desse Mekete , Tilahun Seifu , Adgo Enyew , Nyssen Jan , Walraevens Kristine , Janssens Pieter , Cornelis Wim
Published: March 2021

Water scarcity is a major limiting factor for crop production by irrigation in sub-Saharan countries. Improved irrigation scheduling that can ensure the optimal use of the allocated water and enhance water productivity (WP) is required to address future water scarcity in the region. Maximizing WP by exposing the crop to a certain level of water stress using deficit irrigation (DI) is considered a promising strategy. To adopt DI strategies, a shred of comprehensive evidence concerning DI for different crops is required. This review aims to provide adequate information about the effect of DI on WP. We reviewed 90 research papers from Ethiopia and summarize the effect of DI on WP and yield. It is shown that DI considerably increased WP compared to full irrigation. Despite higher WP, reduced biomass yield was obtained in some of the studied DI practices compared to full irrigation. It was also found that yield reduction may be low compared to the benefits gained by diverting the saved water to irrigate extra arable land. From this review, we understood that growers must recognize specific soil management and crops before applying DI strategies. Maize revealed the highest (2.65 kg m-3) and lowest (0.50 kg m-3) WP when irrigated at only the initial stage compared with being fully irrigated in all growth stages, respectively. Also, onion showed a decreasing WP with increased irrigation water from 60% crop water requirement (ETc) (1.84 kg m-3) to 100% ETc (1.34 kg m-3). Increasing water deficit from 100 to 30% ETc led to an increase of wheat WP by 72.2%. For tomato, the highest WP (7.02 kg m-3) was found at 70% ETc followed by 50% ETc (6.98 kg m-3) and 85% ETc (6.92 kg m-3), while the water application of 100% ETc (or full irrigation) showed the least WP (6.79 kg m-3). Teff showed the lowest WP (1.72 kg m-3) under optimal irrigation, while it was highest (2.96 kg m-3) under 75% ETc throughout the growing season. The regression analysis (R2) for WP increment and yield reduction versus saved water showed higher values, indicating that DI could be an option for WP increment and increasing overall yield by expanding irrigated area and applying the saved water in water-scarce regions. In conclusion, in areas where drought stress is the limiting factor for crop production, the application of DI is feasible.

 

 

 

Keywords: Overall yield increase, water productivity, water saved, yield reduction
Can microorganisms significantly influence cast iron corrosion in a DGR?
Authors: Matschiavelli Nicole , Sushko Vladyslav , Dressler Magdalena , Neubert Tom , Kühn Luise , Schierz Ariette , Cherkouk Andrea
Published: March 2021

For the safe storage of high-level radioactive waste (HLW) in deep geological repositories (DGR), several metals could potentially act as canister material and are under investigation with respect to their properties under disposal-relevant conditions. An essential requirement for the selected metal(s) is the long-term stability which is mainly realized by the resistance to corrosion. The process of corrosion depends on the overall environment in the surrounding of the metal canister and which will change over time. Here, parameters like redox potential, pH, the presence of (pore-) water, the salinity and also the presence of metabolically active microorganisms are of relevance, among others. In order to analyze the influence of different pore waters and the natural microbial community of a Bavarian bentonite, which acts as geotechnical barrier and will be in direct contact to the canister, microcosm experiments were set up. These slurry experiments contained B25 bentonite, synthetic Opalinus Clay pore water or saline cap rock solution as well as copper- or cast iron plates in various combinations. During an incubation time of 400 days under anaerobic conditions at 37 °C, several bio-geochemical parameters (e.g. pH, redox potential and the concentration of minerals, sulfate, iron(II/III) and organic acids) were analyzed as well as the corrosion process and a potential microbial influence. The obtained results provide insights into the complex interplay between bentonite, pore water, metals and microorganisms. Different precipitates like carbonates, iron oxides and sulfides were identified on the cast iron surface, potentially accelerating or slowing down the corrosion process and, thus, affecting the long-term stability of the metal canister in a DGR.     
Current status of project SWEETS: Estimating thermospheric neutral mass densities from satellite data at various altitudes
Authors: Krauss Sandro , Suesser-Rechberger Barbara , Behzadpour Saniya , Mayer-Guerr Torsten , Temmer Manuela , Kroisz Sofia , Drescher Lukas
Published: March 2021

Within the project SWEETS (funded by the FFG Austria) it is intended to develop a forecasting model, to predict the expected impact of solar events, like coronal mass ejections (CMEs), on satellites at different altitudes between 300-800 km. For the realization, scientific data, such as kinematic orbit information and accelerometer measurements, from a wide variety of satellites are incorporated. Based on the evaluation of the impact of several hundred solar events on the thermosphere the forecasting will be realized through a joint analysis and evaluation of solar wind plasma and magnetic field data observed at the Lagrange point L1.
In this contribution we show first preliminary results of thermospheric densities estimates based on kinematic orbit information for different satellite missions (e.g., TerraSAR-X, TanDEM-X, Swarm A-C, GRACE, GRACE-FO, CHAMP). To validate the outcome, we compare the results with state-of-the-art thermospheric models as well as with densities estimated from accelerometer measurements if available. Finally, for some specific CME events we will perform a comparison between the post-processed density estimates and results from our preliminary forecasting tool.
Turbulent structure in the upper ocean during the MOSAiC drift
Authors: Fer Ilker , Baumann Till , Fang Ying-Chih , Hoppmann Mario , Koenig Zoe , Kuznetsov Ivan , Muilwijk Morven , Schaffer Janin , Schulz Kirstin , Sukhikh Natalia , Tippenhauer Sandra
Published: March 2021

Ocean turbulence measurements under the Arctic sea ice cover are sparse, especially in winter conditions. During the drift of the MOSAiC main camp, we collected vertical profiles of ocean microstructure in the upper 50-80 m using an ascending vertical microstructure profiler. Each profile terminated when the profiler hit the sea ice or broke through the surface in leads, which resolved the turbulent structure up to the ice or surface. These sporadic profile measurements were supplemented by an ice-moored system equipped with fast-response thermistors, collecting continuous time series at approximately 50 m below the ice. Both instruments are manufactured by Rockland Scientific, Canada. While the profiling was conducted from mid-February to mid-September 2020, the moored measurements were in the period between mid-December 2019 and late April 2020, spatially covering from 88°N30' to 84°N in the Amundsen Basin. From the vertical profiler, dissipation rate of turbulent kinetic energy, ε was estimated using the shear probes and the relatively standard methods applied to shear spectra. From the moored records, ε and dissipation rate of temperature variance, χ, were estimated using the high-resolution temperature records and maximum likelihood spectra fitting to the Batchelor spectrum using 75 s segments. This gives an exceptionally high time resolution of turbulence estimates, albeit from a fixed depth. Estimates ranged between 10-11 to 10-6 W/kg for ε , and 10-12 to 10-6 C2/s for χ. The vertical distribution of ε in the upper 50 m and the time variability and statistics of moored estimates will be discussed in relation to various environmental forcing conditions including storm events and convection.
Evaluation of the new irrigation implementation in CTSM
Authors: Yao Yi , Swenson Sean , Lawrence David , Lombardozzi Danica , Vanderkelen Inne , Thiery Wim
Published: March 2021

Many observational and modelling studies have highlighted the important role that irrigation plays in the terrestrial hydrological and energy cycle. Land surface models are a key tool to study these interactions, underlining the importance of an accurate representation of irrigation in these models. However, most land surface models either ignore irrigation or represent it in a crude way. Here we improve and evaluate the implementation of irrigation in the Community Terrestrial Systems Model (CTSM), the land component of the Community Earth System Model (CESM). In this improvement, we consider three irrigation techniques (flood, sprinkler and drip), which differ in the amount and way of water applied. By combining global maps of the area equipped for irrigation with the distribution of different irrigation techniques, we represent the transient spatial distribution of irrigation techniques. Subsequently, we evaluate the performance of CTSM with the improved irrigation module. Three experiments are conducted: one with irrigation switched off, the second with the original irrigation module and the third with the improved irrigation module implemented. All three outputs are evaluated against observed or remotely sensed land surface energy fluxes and near-surface climate datasets. We anticipate that the results will reveal how our new irrigation schemes improve or reduce the performance of the land surface model.
Tropical cyclone eyewall thunderstorms as a driver of upper tropospheric water vapor increases
Authors: Price Colin , Plotnik Tair , Guha Anirban , Saha` Joydeb
Published: March 2021

Tropical cyclones have been observed in recent years to be increasing in intensity due to global warming, and projections for the future are for further shifts to stronger tropical cyclones, while the changes in the number of storms is less certain in the future.  These storms have been shown to exhibit strong lightning activity in the eyewall and rainbands, and some studies (Price et al., 2009) showed that the lightning activity peaks before the maximum intensity of the tropical cyclones.  Now we have investigated the impact of these tropical storms on the upper tropospheric water vapor (UTWV) content.  Using the ERA5 reanalysis product from the ECMWF center, together with lightning data from the ENTLN network, we show that the lightning activity in tropical cyclones is closely linked to the increase in UTWV above these storms.  We find the maximum enhancement in UTWV occurs between the 100-300 mb pressure levels, with a lag of 0-2 days after the peak of the storm intensity (measured by the maximum sustained winds in the eyewall).  The lightning activity peaks before the storm reaches its maximum intensity, as found in previous studies.  The interest in UTWV concentrations is due to the strong positive feedback that exists between the amounts of UTWV and surface global warming.  Water Vapor is a strong greenhouse gas which is most efficient in trapping in longwave radiation emitted from the Earth in the upper troposphere.  Small changes in UTWV over time can result in strong surface warming.  If tropical cyclones increase in intensity in the future, this will likely result in increases in UTWV, reducing the natural cooling ability of the Earth.  Lightning may be a useful tool to monitor these changes.
Summertime dust storms over the Arabian Peninsula and impacts on radiation and atmospheric circulation.
Authors: Francis Diana , Chaboureau Jean-Pierre , Nelli Narendra , Cuesta Juan , Alshamsi Noor
Published: March 2021

This study investigates the underlying atmospheric dynamics associated with intense dust storms in summer 2018 over the Arabian Peninsula (AP); a major dust source at global scale. It reports, for the first time, on the formation of cyclone over the Empty Quarter Desert as important mechanism for intense dust storms over this source region. The dust direct and semi-direct radiative forcings are observed, for the first time over this source region, using high-resolution in-situ and CERES-SYN satellite observational data. The three-dimensional structure and evolution of the dust storms are inferred from state-of-the-art satellite products such as SEVIRI, AEROIASI and CALIPSO. The dynamics and thermodynamics of the boundary layer during this event are thoroughly analyzed using ERA5 reanalysis and ground based observations.

We found that a large dust storm by Shamal winds led up, through radiative forcing, to cyclone development over the Empty Quarter Desert, subsequent dust emissions, development of convective clouds and rain. The cyclogenesis over this region initiated a second intense dust storm which developed and impacted the AP for 3 consecutive days. The uplifted dust by the cyclone reached 5 km in altitude and altered the radiative budget at the surface, inducing both significant warming during night and cooling during day. The dust load uplifted by the cyclone was estimated by the mesoscale model Meso-NH to be in the order of 20 Tg, and the associated aerosol optical depth was higher than 3. The model simulates reasonably the radiative impact of the dust in the shortwave but highly underestimated its impact in the LW.

Our study stresses the importance of the dust radiative forcing in the longwave and that it should be accurately accounted for in models to properly represent the impact of dust on the Earth system especially near source areas. Missing the warming effect of dust aerosols would impact both the weather and air quality forecast, and the regional climate projections.

These results were published in November 2020 in the journal Atmospheric Research doi.org/10.1016/j.atmosres.2020.105364.
Ice or rock matrix? Improved quantitative imaging of Alpine permafrost evolution through time-lapse petrophysical joint inversion
Authors: Klahold Johanna , Hauck Christian , Wagner Florian
Published: March 2021

Quantitative estimation of pore fractions filled with liquid water, ice and air is one of the prerequisites in many permafrost studies and forms the basis for a process-based understanding of permafrost and the hazard potential of its degradation in the context of global warming. The volumetric ice content is however difficult to retrieve, since standard borehole temperature monitoring is unable to provide any ice content estimation. Geophysical methods offer opportunities to image distributions of permafrost constituents in a non-invasive manner. A petrophysical joint inversion was recently developed to determine volumetric water, ice, air and rock contents from seismic refraction and electrical resistivity data. This approach benefits from the complementary sensitivities of seismic and electrical data to the phase change between ice and liquid water. A remaining weak point was the unresolved petrophysical ambiguity between ice and rock matrix. Within this study, the petrophysical joint inversion approach is extended along the time axis and respective temporal constraints are introduced. If the porosity (and other time-invariant properties like pore water resistivity or Archie exponents) can be assumed invariant over the considered time period, water, ice and air contents can be estimated together with a temporally constant (but spatially variable) porosity distribution. It is hypothesized that including multiple time steps in the inverse problem increases the ratio of data and parameters and leads to a more accurate distinction between ice and rock content. Based on a synthetic example and a field data set from an Alpine permafrost site (Schilthorn, Swiss Alps) it is demonstrated that the developed time-lapse petrophysical joint inversion provides physically plausible solutions, in particular improved estimates for the volumetric fractions of ice and rock. The field application is evaluated with independent validation data including thaw depths derived from borehole temperature measurements and shows generally good agreement. As opposed to the conventional petrophysical joint inversion, its time-lapse extension succeeds in providing reasonable estimates of permafrost degradation at the Schilthorn monitoring site without a priori constraints on the porosity model.