bluuebunny/crossref_metadata_2025 huggingface dataset:
Layered lithospheric anisotropy beneath southeastern Tibet using harmonic decomposition of receiver functions
Authors: Tiwari Ashwani Kant , Singh Arun , Saikia Dipankar , Singh Chandrani
Published: March 2021

The present research work interrogates the depth-dependent lithospheric dipping and anisotropic fabrics that characterize major fault and suture zone rheology, essential to understanding the lithospheric deformation and geodynamic process beneath southeastern Tibet. The depth-dependent anisotropic trend has been investigated via harmonic stripping of receiver functions (RFs) at 70 stations of the Eastern Syntaxis experiment, operated between 2003-2004. First, 3683 good quality P-RFs are computed from 174 teleseismic events. All the events are of magnitude ≥5.5 and recorded in the epicentral distribution of 30° to 90°. After that, the harmonic stripping technique is performed at each seismic station to retrieve the first (k = 1) and second (k =2) degree harmonics from the receiver function dataset. Our study also characterizes the type (fast or slow) of the symmetric axis. The upper crustal (0-20 km) anisotropic orientations are orthogonal to the major faults and suture zones of the area and suggest the structure-induced anisotropy. However, the anisotropic orientations in the mid-to-lower crust and uppermost mantle orientations suggest the ductile deformation due to material flow towards the east. Comparison from depth-dependent lithospheric trend and fast polarization directions obtained from the core-refracted and direct-S phases suggest the decoupled crust and lithospheric mantle beneath the area.  The distinct anisotropic trends in the Namche Barwa Metamorphic Massif (NBMM) indicate the northward indentation of the Indian crust beneath the Lhasa block. However, the lower crust and uppermost anisotropic orientation suggest the fragmented Indian lithosphere beneath the area. Our results add new constraints in understanding the type of strain and its causes in the region.
Granular effect on debris flow rheology
Authors: Yang Taiqiang
Published: March 2021

Debris flow is characterized by the multi-disperse grain composition and intergranular collision and friction, but the granular effects on rheology are often reduced to the volumetric concentration of solid (Cv), almost ignoring the specific grain size distribution (GSD). In this study, small debris flows occurring in a tributary of Jiangjia Gully were taken as the material sources for rheology experiments. From the real flows we selected slurries with different Cv and maximum grain sizes (Dm) for rheological tests under shearing rate up to 40 (s-1), which is usually the real rate for debris flows in natural conditions. The results indicate that the flows follow the Herschel-Bulkley (HB) rheology, with randomly changing consistency coefficient and relatively constant exponent of 0.45 on average. Only at high shear rate will the flow exhibit Bingham behavior. The HB rheology also reveals shear thinning behavior in surge phenomena observed in the field. Shear-thinning behavior is revealed by the viscosity-shear rate relationship: ηa=pγq, with the exponent (thinning index) dependent on shear rate. This greatly concerns the surge phenomena observed in field. Moreover, both the yield stress and the effective viscosity are found to be perfectly related to the scaling GSD parameters in power-law and exponential form, with nearly constant exponents independent of the shear rate(Figure 1). The rheology properties can be calculated from their relationships to GSD parameters (μ, Dc), which in turn can be used to infer the HB rheology for the concerned flows and then build the dynamical equations(Figure 2). This implies the presence of some interlock between the fine and coarse grains. Finally the rheology model (general in HB form) can be completely determined by the GSD parameters. This study has for the first time proposed quantitative formulas for rheology incorporating GSD parameters, which is helpful for more accurate dynamic analysis of debris flow.
Post-depositional processes visible in the integration of EGRIP high-resolution water isotope record and visual stratigraphy
Authors: Morris Valerie , Westhoff Julien , Vaughn Bruce , Weikusat Ilka , Jones Tyler , Markle Bradley , Hughes Abigail , Skorski William , Brashear Chloe , Gkinis Vasileios , Vinther Bo , White James
Published: March 2021

With recent advances in analytical techniques, water stable isotope ratios can be measured in astounding detail in ice core records (~mm scale or equivalent to subannual resolution). While this has enabled the study of past climates across a vast range of timescales, the full set of processes driving the highest frequency variability in these water isotope records remains poorly understood. In the EastGRIP ice core, we observe a strong relationship between high-frequency water isotope anomalies (sharp transitions on the scale of cms) and variability in the visual stratigraphy of the ice. The water isotope timeseries reveals these anomalies that would otherwise be missed using traditional lower resolution discrete sampling methods (5-50 cm scale).  A comparison with the dark-field imaging of stratigraphic layers (high-resolution line-scanning system; 50µm/pix) from the EGRIP ice core indicates a correlation between bubble-free ice layers and the sharp transitions observed in the isotope record.  Prior to this comparison, such anomalies in high-resolution isotope records were often dismissed as analytical artifacts. The striking correspondence to the bubble-free ice layers, which is a parameter measured independently from the isotopes, suggests the isotope variability is real. We are investigating a range of depositional and post-depositional processes that may may be able to explain the origin of this variability and its relationship to the physical properties of the ice. This study has implications for frequency analysis of the isotope data, and the related analysis of isotope diffusion and its effects on the recorded climate signal. Understanding these anomalies opens new doors to the interpretation of climate signals in ice cores.
Towards a function-first framework to make soil microbial ecology predictive
Authors: Rousk Johannes , Hicks Lettice
Published: March 2021

Soil microbial communities perform vital ecosystem functions, such as the decomposition of organic matter to provide plant nutrition. However, despite the functional importance of soil microorganisms, attribution of ecosystem function to particular constituents of the microbial community has been impeded by a lack of information linking microbial function to community composition and structure. Here, we propose a function-first framework to predict how microbial communities influence ecosystem functions.

We first view the microbial community associated with a specific function as a whole, and describe the dependence of microbial functions on environmental factors (e.g. the intrinsic temperature dependence of bacterial growth rates). This step defines the aggregate functional response curve of the community. Second, the contribution of the whole community to ecosystem function can be predicted, by combining the functional response curve with current environmental conditions. Functional response curves can then be linked with taxonomic data in order to identify sets of “biomarker” taxa that signal how microbial communities regulate ecosystem functions. Ultimately, such indicator taxa may be used as a diagnostic tool, enabling predictions of ecosystem function from community composition.

In this presentation, we provide three examples to illustrate the proposed framework, whereby the dependence of bacterial growth on environmental factors, including temperature, pH and salinity, is defined as the functional response curve used to interlink soil bacterial community structure and function. Applying this framework will make it possible to predict ecosystem functions directly from microbial community composition.
Even the low-T garnet from the iconic Barrow’s zone is tetragonal
Authors: Cesare Bernardo , Nestola Fabrizio
Published: March 2021

Common (anhydrous) Fe-Mg-Ca-Mn garnet, the archetypal cubic mineral, has been recently discovered to be tetragonal in metapelites and metabasites from low-temperature regional metamorphic terranes (Cesare et al., 2018).

Despite the differences in bulk rock composition and pressure conditions, such low-T tetragonal garnets share common chemical features, namely high grossular (>25 mol%) and low pyrope (<7 mol%) contents. Similar compositions are documented in other contexts worldwide, both in blueschists-eclogites and in phyllites, including the metapelites from the garnet zone of the iconic Barrovian metamorphism of the Scottish highlands (Viete et al., 2011).

We have analysed a garnet crystal from a chlorite-biotite schist collected at the Barrow’s garnet zone in Glen Esk. The unit cell parameters were refined using diffraction reflections between 1.20 and 0.55 Å providing a tetragonal cell with a = 11.5731(5) Å and c = 11.5887(8) Å and volume V = 1552.15(15) Å3. Systematic absences analysis on complete intensity data collected up to 2theta = 80° indicated I41/acd space group confirming the cell parameters refinement.

Therefore, the garnet is tetragonal and not cubic, as suggested by its weak birefringence under crossed polarizers.

These results show that the tetragonal structure of common Fe-Mg-Ca-Mn garnet is verified whenever this mineral displays the Ca-rich, Mg-poor composition often observed in low-T metamorphic rocks. And support the hypothesis that the lowering of symmetry is composition-dependent.

 

References

Cesare, B., et al. Garnet, the archetypal cubic mineral, grows tetragonal. Sci Rep 9, 14672 (2019).

Viete, D.R., et al. The nature and origin of the Barrovian metamorphism, Scotland: Diffusion length scales in garnet and inferred thermal time scales. J. Geol. Soc. London 168, 115–132 (2011).

 
A kinematic formalism for tracking ice-ocean mass exchange on the Earth's surface and estimating sea-level change 
Authors: Adhikari Surendra , Ivins Erik , Larour Eric , Caron Lambert , Seroussi Helene
Published: March 2021

Polar ice sheets are important components of the Earth System.  As the geometries of land, ocean, and ice sheets evolve, they must be consistently captured within the lexicon of geodesy.  Understanding the interplay between the processes such as ice-sheet dynamics, solid-Earth deformation, and sea-level adjustment requires both geodetically consistent and mass conserving descriptions of evolving land and ocean domains, grounded ice sheets and floating ice shelves, and their respective interfaces. Here we present mathematical descriptions of a generic level set that can be used to track both the grounding lines and coastlines, in light of ice-ocean mass exchange and complex feedbacks from the solid Earth and sea level. We next present a unified method to accurately compute the sea-level contribution of evolving ice sheets based on the change in ice thickness, bedrock elevation and mean sea level caused by any geophysical processes. Our formalism can be applied to arbitrary geometries and at all time scales. While it can be used for applications with modeling, observations and the combination of two, it is best suited for Earth System models, comprising ice sheets, solid Earth and sea level, that seek to conserve mass.

© 2020 California Institute of Technology. Government sponsorship is acknowledged.
Dissemination of High-Resolution Ionosphere Information from VTEC B-spline Expansions for Single-Frequency Positioning
Authors: Goss Andreas , Hernández-Pajares Manuel , Schmidt Michael , Erdogan Eren
Published: March 2021

The ionospheric signal delay is one of the largest error sources in GNSS applications and may cause in case of a single-frequency receiver a positioning error of up to several meters. To avoid such an inaccuracy some of the Ionosphere Associated Analysis Centers (IAAC) of the International GNSS Service (IGS) provide the user the Vertical Total Electron Content (VTEC) as Real-Time Global Ionosphere Maps (RT-GIM) via streaming formats. Currently, the only data format used for the dissemination of these ionospheric corrections is based on the State Space Representation (SSR) message and the RTCM standards.

Mathematically most of the RT-GIMs are based on modeling VTEC as series expansions in spherical harmonics (SH) up to a highest degree of n = 15 which corresponds to a spatial resolution of 12° in latitude and longitude and is therefore, too low for modern GNSS applications such as autonomous driving. However, the SSR VTEC message allows the dissemination of SH coefficients only up to a maximum degree of n = 16.

To avoid the drawbacks of expanding VTEC in SHs other approaches such as a voxel representation or a B-spline series expansion have been proven to be appropriate candidates for global and regional modelling with an enhanced resolution. In order to provide in these cases the significant model parameters to the user, the application of the SSR VTEC message requires a transformation of the model parameters into SH coefficients. In this contribution a methodology will be presented which describes a fast transformation of the B-spline approach into a SH representation with high accuracy by minimizing the information loss.

To test the method, a high-resolution VTEC GIM modeled as a series expansion in B-splines is transformed into SH representations of different highest degree values; the results are validated via dSTEC analysis as well as via an example of single frequency positioning and show a significantly improved accuracy compared to the IGS GIMs.
Strongly coupled data assimilation with the coupled ocean-atmosphere model AWI-CM: comparison with the weakly coupled data assimilation
Authors: Tang Qi , Mu Longjiang , Goessling Helge , Semmler Tido , Nerger Lars
Published: March 2021

We compare the results of strongly coupled data assimilation and weakly coupled data assimilation by analyzing the assimilation effect on the prediction of the ocean as well as the atmosphere variables. The AWI climate model (AWI-CM), which couples the ocean model FESOM and the atmospheric model ECHAM, is coupled with the parallel data assimilation framework (PDAF, http://pdaf.awi.de). The satellite sea surface temperature is assimilated. For the weakly coupled data assimilation, only the ocean variables are directly updated by the assimilation while the atmospheric variables are influenced through the model. For the strongly coupled data assimilation, both the ocean and the atmospheric variables are directly updated by the assimilation algorithm. The results are evaluated by comparing the estimated ocean variables with the dependent/independent observational data, and the estimated atmospheric variables with the ERA-interim data. In the ocean, both the WCDA and the SCDA improve the prediction of the temperature and SCDA and WCDA give the same RMS error of SST. In the atmosphere, WCDA gives slightly better results for the 2m temperature and 10m wind velocity than the SCDA. In the free atmosphere, SCDA yields smaller errors for the temperature, wind velocity and specific humidity than the WCDA in the Arctic region, while in the tropical region, the error are larger in general.
The analysis of splash erosion depending on the degree of soil wettability - a preliminary study
Authors: Sochan Agata , Mazur Rafał , Beczek Michał , Ryżak Magdalena , Polakowski Cezary , Bieganowski Andrzej
Published: March 2021

The soil splash phenomenon is the initial stage of the water erosion process. It occurs when a rain drop hits the soil surface and causes a few processes e.g. i) detachment of soil particles and their transport over different distances, ii) breakdown of soil aggregates, iii) surface runoff or iv) formation of a crusted surface.

The aim of the study was to carry out an analysis of the splash erosion in mineral soil in 4 variants of sample preparation: a) dry natural soil, b) wet natural soil, c) dry burnt soil, d) wet burnt soil.

In both cases (natural soil and soil modified with high temperature), full moistening was achieved by capillary rise. Fire simulation was carried out in several variants at varying temperature and duration. Variant that affected soil wettability to the greatest extent was selected for the splash analyses. "Natural" and "modified" wettability were measured using the water drop penetration time (WDPT) method. "Natural" wettability classified soil into the "wettable" group (WDPT < 5s), while the modification of the surface properties by high temperature changed the wettability group of the analyzed soil into "slightly to moderately repellent" (5 s > WDPT < 60s).

Each time, the soil material was placed in aluminum rings with an internal diameter of 36mm and a height of 10mm, and the surface was leveled without excessive compaction of the sample.

A single drop of distilled water with a diameter of 4.2 mm fell on the sample prepared in this way from a height of 1.5m. The drops were dosed with a peristaltic pump and reached the final velocity of 4.98 m/s.

Three synchronized Phantom Miro M310 cameras (Vision Research, USA) were used to register the splash phenomenon. The recorded films were used to analyze the splash phenomenon through measurements of the velocity, angle and distance of ejected particles.

A Scan3D UNIVERSE 10 MPiX structural light scanner (Smarttech 3d, Poland) was used to determine the magnitude of the surface deformation caused by the drops. The analyses made it possible to determine e.g. the depth, diameter, and volume of craters and the height of surrounding rims.

The analysis of the results showed significant differences in the size and dynamics of the emerging splash depending on the degree of soil wettability.

The study was partially funded by the National Science Centre, Poland, as part of project no. 2017/26/D/ST10/01026.
Characterization of Geometrical and Temporal Properties of Large-scale Motions in Turbulent Flows
Authors: Tsai Christina , Wu Kuang-Ting
Published: March 2021

It is demonstrated that turbulent boundary layers are populated by a hierarchy of recurrent structures, normally referred to as the coherent structures. Thus, it is desirable to gain a better understanding of the spatial-temporal characteristics of coherent structures and their impact on fluid particles. Furthermore, the ejection and sweep events play an important role in turbulent statistics. Therefore, this study focuses on the characterizations of flow particles under the influence of the above-mentioned two structures.

With regard to the geometry of turbulent structures, Meinhart & Adrian (1995) first highlighted the existence of large and irregularly shaped regions of uniform streamwise momentum zone (hereafter referred to as a uniform momentum zone, or UMZs), regions of relatively similar streamwise velocity with coherence in the streamwise and wall-normal directions.  Subsequently, de Silva et al. (2017) provided a detection criterion that had previously been utilized to locate the uniform momentum zones (UMZ) and demonstrated the application of this criterion to estimate the spatial locations of the edges that demarcates UMZs.

 

In this study, detection of the existence of UMZs is a pre-process of identifying the coherent structures. After the edges of UMZs are determined, the identification procedure of ejection and sweep events from turbulent flow DNS data should be defined. As such, an integrated criterion of distinguishing ejection and sweep events is proposed. Based on the integrated criterion, the statistical characterizations of coherent structures from available turbulent flow data such as event durations, event maximum heights, and wall-normal and streamwise lengths can be presented.
Stable isotopes as a tool for determining transformation and fate of sulphur in AMD affected water bodies in Meghalaya
Authors: Kumar Vivek , Paul Dibyendu , Kumar Sudhir
Published: March 2021

Meghalaya, also known as ‘abode of clouds’, is a state located in north-eastern part of India, blessed with abundance of water resources. In the last few decades, extensive coal mining in different parts of Meghalaya has caused detrimental changes in the environment, particularly the aquatic systems. Acid and metal loaded effluents (also known as acid mine drainage or AMD), resulting from the exposure of sulphide mineralization to oxidizing conditions from abandoned or active mining areas, are the principal environmental problems today. Sulphate (SO42-) is a major contaminant and attracts widespread attention as the dominant form of sulphur in coal mining affected aquatic systems. The increased presence of SO42- in ecosystems affected by mining activities has immense negative environmental and human health effects. Low pH and high heavy metal concentrations have been reported from streams flowing in and around the coal mining area in Meghalaya rendering the water quality to be very poor  and unfit for use as potable water.

Stable isotopes have emerged as a promising environmental tracer to understand different environmental functions and processes. Valuable information on the sources and processes can be obtained from the stable isotope ratios of chemical elements in environmental samples as the sources and processes influence history of the samples. Stable isotopes analysis combined with hydrochemical analysis enhances our understanding of transformation and environmental fate of different compounds in water bodies and can provide precise information about factors responsible for controlling water chemistry of different water bodies.

Stable isotopes of sulphur and oxygen combined with hydrochemical parameters were used as a tool for determining origin, transformation and fate of sulphur in AMD affected water bodies in Meghalaya.The study was conducted on two rivers affected by AMD, viz. Myntdu River and Lunar-Lukha River, flowing in the Jaintia Hills region of Meghalaya. The water samples collected are analysed for hydrochemical parameters and stable sulphur and oxygen isotopes (δ34S and δ18O in aqueous SO42-). The stable isotopes of sulphur and oxygen were also analysed in the coal samples from the nearby mining areas. The result provided an insight into the transformational processes of sulphur in these two AMD affected rivers and the environmental fate of sulphur.
Tropospheric ozone based on S5P-BASCOE and extension to the past based on OMI and GOME-2 observation.
Authors: Heue Klaus-Peter , Lerot Christophe , Romahn Fabian , Chabrillat Simon , Christophe Yves , Errera Quentin , Coldewey-Egbers Melanie , Loyola Diego
Published: March 2021

Ozone in the troposphere has mainly two sources, the first one is stratospheric intrusion the second one is chemical reactions following the emissions of primary pollutions such as NOx and VOCS.

We combine TROPOMI total ozone columns with Microwave Limb Sounding ozone profiles assimilated to BASCOE to retrieve tropospheric ozone columns.

Based on a first analysis we observe a decrease of tropospheric ozone during April and May 2020. The lockdown as measure against the Corona pandemic also caused an economic shutdown, and thereby a reduction of primary pollutants mainly NOx. Within the cities centres the lack of NOx caused an increase in tropospheric ozone, due to non linear effects in the ozone NOx chemistry. Outside the cities however a decrease might be expected. Thereby the tropospheric ozone reduction in April May might be caused by the lockdown due to the COVID-19.

However the natural variabilty is high caused by metrological conditions. To redcue the influnece of indiviual metrological situation the timeseries is expanded to the past by using additional sensors like GOME-2 and OMI, combined with the BASCOE reanalysis data set BRAM. The tropospheric columns are haromized using the same time and latitude depended bias added as for harmonizing the total columns. Therby we generated a typical anual mean data set, where the exceptional year of 2020 can be compared to.
The role of cloud diabatic processes in the life cycle of Atlantic-European weather regimes
Authors: Grams Christian M.
Published: March 2021

Weather regimes are quasi-stationary, persistent, and recurrent states of the large-scale extratropical circulation. In the Atlantic-European region these explain most of the atmospheric variability on sub-seasonal time scales. However, current numerical weather prediction (NWP) systems struggle in correctly predicting weather regime life cycles. Latent heat release in ascending air streams injects air into the upper troposphere, which might ultimately result in blocking. Such diabatic outflow is often linked to warm conveyor belt (WCB) activity and has been shown to be involved in upscale error growth up to the regime scale. This study systematically investigates the role of diabatic outflow in the life cycle of Atlantic-European weather regimes.

An extended definition of 7 year-round Atlantic-European weather regimes from 37 years of ERA-Interim reanalysis is used. This is based on an EOF analysis and k-means clustering of normalized low-pass-filtered 500hPa geopotential height anomalies. Furthermore an objective regime life cycle is derived. The role of cloud-diabatic processes in European weather regimes is assessed based on time lag analysis of WCB activity at specific life cycle stages.

Results indicate that the period prior to regime onset is characterized by important changes in location and frequency of WCB occurrence. Most importantly, prior to the onset of regimes characterized by blocking, WCB activity increases significantly upstream of the incipient blocking even before blocking is detectable and persists over the blocked region later. This suggests that diabatic WCB outflow helps to establish and maintain blocked regimes. Thus it is important to correctly represent cloud-diabatic processes in NWP models across multiple scales in order to predict the large-scale circulation accurately. Ongoing work now systematically investigates the representation of WCB activity in current NWP systems and how this relates to the forecast skill for weather regimes.
Hydrodynamic aspects of large river confluence with different water densities
Authors: Lyubimova Tatyana , Lepikhin Anatoliy , Parshakova Yanina , Lane Stuart , Gualtieri Carlo , Roux Bernard
Published: March 2021

River confluences are characterized by complex 3D changes in flow hydrodynamics and bed morphology and provide important ecological functions. The current literature on river confluences suggests that their hydrodynamics and morphodynamics are controlled by three aspects: (1) the geometry (planform and junction angle) of the confluence, (2) the momentum flux ratio of the tributaries and (3) the level of concordance between channel beds at the confluence entrance. However, the difference in water densities between the tributaries, and the associated stratification, potentially may impact on hydrodynamics and mixing as well, but such aspects has received less attention by far, and has not yet been subject to systematic investigation.

The objective of this study is to investigate hydrodynamics and mixing within the confluence zone of the Kama and Vishera rivers (Russia). During the warm period, the water densities in these rivers are similar due to the peculiarities of their hydrological basins. Hence density effects are negligible. However, in winter, the mineralization level of waters in the Vishera river significantly exceeds that in the Kama river. Even due to a significant decrease in the discharge of these rivers, the densimetric Froude number Fr is of the order of unity. This condition provided the motivation for investigating the effects of density differences on hydrodynamic and mixing at such river confluence.

The study of these effects was carried out on the basis of full-scale field measurements and numerical experiments in a full 3D formulation (i.e. with no hydrostatic approximation). Both the field measurements and the numerical results suggest that hydrodynamics processes at the confluence in the absence and in the presence of density stratification are fundamentally different.. At large densimetric Froude numbers (at small density differences) the waters of the Vishera and Kama rivers flow, practically without mixing, for several kilometers in the form of two parallel streams and at Fr of the order of unity, the more mineralized (more dense) waters of the Vishera river flow under the less dense waters of the Kama river leading to much more rapid mixing.

The reported study was funded by Russian Foundation for Basic Research (RFBR) and Perm Krai (grant 20-45-596028) and by RFBR (grant 19-41-590013).
Age of the Eastern Iranian oroclinal Buckling inferred from a U235/Pb207 dating on radial dikes in the Qayen Area
Authors: Rojhani Emad , Bagheri Sasan , Hinsbergen Douwe , Azizi Hossein , Ghaemi Farzin , Lom Nalan , Qayyum Abdul
Published: March 2021

The Eastern Iranian Orocline provides us several opportunities to study magmatism in relation to tectonic events. The buckling of this orocline is accompanied by an extreme extension in its Khorasan outer arc during which a calc-alkaline dike swarm, generally andesite to dacite, intruded in a radial pattern into the Paleocene-Eocene volcano-sedimentary units, belonging to the platform of the Lut block. The azimuth of these dikes shows a declination of 30 degrees, from N300o to N330o. The U235/Pb207 age of ~41±74 Ma from zircon crystals taken from the dikes represents a considerable buckling with an extension occurred during the middle-upper Eocene. In fact, this time refers to the buckling in the boundary of the inner- and outer-arc of the orocline. This could be a noticeable document of syn-orocline magmatism in the Tethyan realm in the east of the Iranian plateau. The dikes and their host rocks are also sampled for AMS analysis and paleomagnetic measurements to test the amount of the oroclinal buckling in the Qayen area.
Evaluation of the ERA5 reanalysis as a reference dataset for fine-scale hydrological modelling over alpine basins 
Authors: Shrestha Susen , Zaramella Mattia , Callegari Mattia , Greifeneder Felix , Borga Marco
Published: March 2021

The European Center for Medium-Range Weather Forecasts (ECMWF) has recently released its most advanced reanalysis product, the ERA5 dataset. It was designed and generated with methods giving it multiple advantages over the previous release, the ERA-Interim reanalysis product. Notably, it has a finer spatial resolution, is archived at the hourly time step, uses a more advanced assimilation system, and includes more sources of data. This paper aims to evaluate the ERA5 reanalysis as a potential reference dataset for hydrological modelling by considering the ERA5 precipitation and temperatures as proxies for observations in the hydrological modelling process. This is obtained by using a semi-distributed hydrological model over basins ranging from 40km2 to 6900 km2 over the Upper Adige river basin in the Eastern Italian Alps. This study shows that ERA5-based precipitation product is affected by a significant bias which translates to biased runoff at all spatial scales considered in the study. We observed that ERA5 precipitation product generally overestimate low-intensity rainfall and underestimate high rainfall intensity in the region. We analysed how this affects simulation of annual max floods over the study area. The results show that flood simulations are in general surprisingly good, as they result from the combination of two cascading errors: i) overestimation of the soil moisture conditions at the start of the event and ii) the underestimation of the event forcing rainfall. Differences between ERA5 and observation datasets are mostly linked to precipitation, as temperature only marginally influences the hydrological simulation outcomes.
The pattern of the tectonic joints and the development of the Vlychada karst show cave in Diros, Peloponnesus, Greece
Authors: Filis Christos , Skourtsos Emmanuel , Karalemas Nikolaos , Giannopoulos Vasilios , Giannopoulos Ioannis , Kotsi Evangelia , Lekkas Efthimios
Published: March 2021

The most characteristic feature of carbonate rocks is that they are prone to dissolution due to the meteoric water circulation which is enriched in CO2. One of the factors influencing this phenomenon is the existence of discontinuities within the mass of carbonate rocks. The Diros Vlychada show cave, on the peninsula of Mani in Peloponnese, Greece, has developed in marbles that belong to the Plattenkalk geotectonic unit. Most of the cave is flooded with water and its level changes depending on the external weather conditions and variations in sea level. The deformation of the marbles is represented by tectonic structures formed during the Lower Miocene metamorphism and their subsequent exhumation. The final uplift stage took place during the Pliocene-Quaternary and is still active. Five joints systems were distinguished:

A NW-SE joint system which is subdivided into a subsystem with low-angle dips, mainly towards to the NW, related to the main foliation of the marbles and a second subsystem characterized by stretching joints of the same strike (elongated joints), which have high-angle dips, also towards the NW. The latter system intersects the former but is confined between marble bedding and does not extend to more than three beds (the bedding is defined by the first subsystem).

A NW-SE striking joint system characterized by stretching joints with high-angle dips, which intersects diagonally the two previous. This system extends between more than three marble beds.

Two systems show E-W and N-S strike with the first one much better expressed. Those joints have developed diagonally to the previous ones. These are mainly shear joints that intersect the first system and are propagated within many marble beds.

The chambers of the cave have been developed along NW-SE and E-W directions. The first one is identified with the joint system that has been developed transversely to the strike of the marble foliation and the second in parallel with the main system of the shear joints. It is interesting that the bays forming the coastline of the Mani peninsula, have developed in an E-W direction, which coincides with both one of the growth directions of the cave and one of the joints systems, which correspond to shear joints developed during the folding of the marbles. Stalactites and stalagmites grow in a NE-SW direction that is identical to the elongated joints which form the system that is parallel to the foliation strike. Groundwater flow along these branches may be slower as these branches appear to be restricted between marble bedding.
Storylines of plausible past and future climates for the July 2019 European heatwave
Authors: Sánchez Benítez Antonio , Jung Thomas , Goessling Helge , Pithan Felix , Semmler Tido
Published: March 2021

Under the current global warming trend, heatwaves are becoming more intense, frequent, and longer-lasting; and this trend will continue in the future. In this context, the recent 2019 summer was exceptionally hot in large areas of the Northern Hemisphere, with embedded heatwaves, as for example the June and July 2019 European events, redrawing the temperature record map in western Europe. Large-scale dynamics (associated with blockings or subtropical ridges) play a key role in explaining these-large scale events.

Conceptually, global warming can be split into two different contributions: Dynamic and thermodynamic changes. Whereas dynamic changes remain highly uncertain, some thermodynamic changes can be quantified with higher confidence. We exploit this concept by studying how these recent European heatwaves would have developed in a pre-industrial climate and how it would develop in the future for 1.5, 2 and 4 ºC warmer climates (storyline scenarios). To do so, we employ the spectral nudging technique with AWI-CM (CMIP6 model, a combination of ECHAM6 AGCM + FESOM Sea Ice-Ocean Model). Large-scale dynamics are prescribed by reanalysis data (ERA5). Meanwhile, the model is run for different boundary conditions corresponding to preindustrial and future climates along the SSP370 forcing scenario. This approach can be useful to help understand and communicate what climate change will mean to people’s life and hence facilitate effective decision-making regarding adaptation to climate change, as we are quantifying how recent outstanding events would be modified by our climate action. 

Temperatures during the heatwaves often increase twice as much as global mean temperatures, especially in a future 4 ºC warmer climate. In this future climate, maximum temperatures can locally reach 50ºC in many western Europe countries. Nighttime temperatures would be similar to the daytime temperatures in a preindustrial world. The global warming amplification can be partly explained by a robust soil drying in the future 4 ºC warmer climate (exacerbated due to the June 2019 heatwave) which is transmitted to a robust increase in Bowen ratio. Importantly, by design of our study, this response occurs without any changes in atmospheric circulation.
Towards locally refined 3D staggered grids for the Stokes equations
Authors: Sanan Patrick
Published: March 2021

Many problems in computational geophysics can be answered by solving a discrete problem on a staggered grid - these define quantities on the elements, faces, edges, and vertices of a regular cell complex, embedded in space with an orthogonal coordinate system. A key example is the Stokes equations for creeping or highly-viscous fluid flow in Cartesian or spherical polar coordinates. These discretizations are attractive in many ways, both practically and computationally. They provide an intuitive way to pose the discrete problem, as they can be motivated as low-order finite volume methods or even as finite difference methods. They provide very regular data layout and relative easy of implementation, allowing for optimized and portable implementations in software. They couple particularly well with particle systems (as in the classical MAC scheme) which define material coefficients with arbitrary, non-grid-aligned interfaces; they provide first-order convergence with an extremely narrow stencil - in solving the discrete system, unknowns are coupled to fewer neighbors than in higher-order finite element or finite volume methods. However, especially in the context of geodynamical and seismic simulations, a severe limitation exists. Many open scientific questions relate to resolving localized features like shear bands, faults, subduction zone boundaries, and entrainment zones, and other boundary layers. With first order methods on regular grids, to resolve these fine spatial features, one must uniformly refine the entire domain (or resort to "Swiss cross" meshes, which are limited in the geometry they can resolve). These quickly becomes computationally intractable. One approach to resolving this tension is to define and use a non-uniform mesh. This is the basis for adaptive mesh refinement (AMR) methods, which are well-established in the context of finite element methods. Here, we present ongoing work in defining a stable, non-uniform, analogue to the MAC scheme for the 3D Stokes equations, attempting to retain the narrow stencil width characteristic of the uniform method while supporting arbitrary 2-to-1 refinement in a mesh described by an octree. Several researchers have made steps in this direction, so in this contribution we review those methods and discuss how they may be generalized or modified to provide a 3D scheme suitable for use in variable-viscosity Stokes flow.
On Resonant Interaction of Electrons with Falling-Tone Chorus Waves
Authors: Kuzichev Ilya , Soto-Chavez Angel Rualdo
Published: March 2021

Whistler-mode chorus waves are one of the most intense wave phenomena in the Earth’s inner magnetosphere. They are considered to be a major driver of the outer radiation belt dynamics, as they can efficiently scatter and energize electrons via resonant wave-particle interaction. These waves are observed as series of discrete coherent structures with rising or falling frequencies in the whistler frequency range (below local electron cyclotron frequency).

Such frequency variation results in a correction to the resonance Hamiltonian which describes particle dynamics in the given wave field. For a monochromatic wave, the effective potential in the resonance Hamiltonian consists of two terms. The first one corresponds to the nonlinear pendulum and describes the direct interaction of a particle with the wave. The second term accounts for plasma inhomogeneity, describing the effects of spatial gradients of plasma and wave parameters on the particle. Frequency chirping contributes to this effective inhomogeneity, producing a correction to this second term. The inhomogeneity term is of particular importance for the trapped particles that remain in resonance with the wave, this term defines their acceleration. And, as spatial inhomogeneity becomes zero at the equator (for dipole magnetic field), the wave frequency variation contribution might be the dominant one close to this region.

In this report, we present the results of test particle simulations of the electron dynamics in the field of a chirped wave. A general curvilinear relativistic code is developed to address the particle dynamics in the wave field, pre-determined from the simplified wave equations. We demonstrate that particle acceleration is affected by the competition between the effective inhomogeneity related to the wave frequency chirping and spatial inhomogeneity of the Earth’s magnetic field.

The work is supported by the National Science Foundation (NSF) grant No. 1502923. We would like to acknowledge high-performance computing support from Cheyenne (doi:10.5065/D6RX99HX) provided by NCAR’s Computational and Information Systems Laboratory, sponsored by NSF
New halogenated trace gases discovered by non-target screening of the atmosphere at the Jungfraujoch high alpine station (Switzerland)
Authors: Guillevic Myriam , Vollmer Martin K. , Hill Matthias , Schlauri Paul , Guillevic Aurore , Emmenegger Lukas , Reimann Stefan
Published: March 2021

Non-target screening consists in searching for all present substances in a sample, suspected or unknown, with very little prior knowledge about the sample. This approach has been introduced more than a decade ago in the field of water analysis or forensics, but is still very scarce in the field of indoor and atmospheric trace gas measurements, despite the urgent need for a better understanding of the composition of the atmosphere.

Recently, we have installed a novel analytical system at the Jungfraujoch high alpine station (3500 m.a.s.l., Switzerland), allowing us to conduct non-target screening of the atmosphere. The system is composed of a preconcentration unit followed by gas chromatography (GC), electron ionisation (EI), and time-of-flight high-resolution mass spectrometry (HRMS). This allows screening the air for all mass fragments from approx. 25 m/z up to 300 m/z, produced by compounds with boiling points from -128 °C (NF3, CF4) to +140 °C (e.g., CHBr3, chlorobenzene, parachlorobenzotrifluoride PCBTF).

Here, we present a new and innovative method to detect and identify unknown organic substances in ambient air using GC-EI-HRMS. We developed an algorithm combining the identification of atom assemblage for the detected fragments and the reconstruction of a pseudo-fragmentation tree, linking fragments belonging to the same substance. This supports in particular the identification of substances for which no mass spectrum is registered in databases. Moreover, we developed a quality control strategy to ensure that the compounds have been correctly identified and are separated from potential coelutants.

Finally, we present a selection of halogenated compounds newly detected in air, measured for the first time at the Jungfraujoch station.
Clumped isotope evidence for polar warmth and reduced salinity during the Early Jurassic
Authors: Letulle Thomas , Suan Guillaume , Rogov Mikhail , Daëron Mathieu , Vinçon-Laugier Arnauld , Reynard Bruno , Montagnac Gilles , Lécuyer Christophe
Published: March 2021

Greenhouse climates are periods characterized by high atmospheric CO2 levels and the absence of large continental icecaps, conditions that define most of the Phanerozoic eon. Fossil record and proxy data from the Cretaceous-Early Paleogene (145-33 My) greenhouse interval suggest increased polar warmth and reduced latitudinal gradient. Such features are challenging for most climate models. They imply either misinterpretation of paleoenvironmental data or an underestimation of climate sensitivity under greenhouse climate. Here we present a new record from polar (>80°) paleolatitudes of the Early Jurassic (~180My) global warming episode known as the Toarcian Oceanic Anoxic Event. Carbonate clumped isotope (Δ47) thermometry and stable isotope analyses (δ18Oc, δ13C) were performed on pristine aragonite bivalve shells from the Polovinnaya River succession (N Siberia) recording exceptionally low burial. Reconstructed growing season temperatures of 9.7±5.2 to 19.0±3.4 °C and water δ18Ow values of −4.6±1.2 to −2.2±0.8‰VSMOW imply increased warmth and significant freshwater contribution in the Toarcian Arctic seas, in line with coeval Siberian paleobotanical data. The unusually low δ18Ow values confirm the incorrectness of assuming a spatially uniform δ18Osw value for calculation of δ18O-derived paleotemperatures. The inferred Early Jurassic polar sea surface temperatures are in good agreement with independent high latitude proxy data from Cretaceous and Eocene warming events. Together with coeval sea surface temperatures data from the western Tethys Ocean, our new data suggest a strong reduction of latitudinal temperature gradients during the Toarcian relative to modern gradients. The reconstructed polar warmth and reduction in latitudinal temperature gradient are substantially higher than those simulated by most climate models of the Jurassic to Eocene greenhouse periods, and support the increasing amount of data and models indicating an increase of climate sensitivity with CO2 levels. Our results bring critical new constraints for model simulations of Jurassic temperatures and δ18Osw values and suggest that high climate sensitivity is the hallmark of greenhouse climates since at least 180 My.
Improving the Quality Assessment band in Landsat cloud images for the application of cloud removal  
Authors: Yang Boli , Feng Yan , Cao Ruyin
Published: March 2021

Cloud contamination is a serious obstacle for the application of Landsat data. Thick clouds can completely block land surface information and lead to missing values. The reconstruction of missing values in a Landsat cloud image requires the cloud and cloud shadow mask. In this study, we raised the issue that the quality of the quality assessment (QA) band in current Landsat products cannot meet the requirement of thick-cloud removal. To address this issue, we developed a new method (called Auto-PCP) to preprocess the original QA band, with the ultimate objective to improve the performance of cloud removal on Landsat cloud images. We tested the new method at four test sites and compared cloud-removed images generated by using three different QA bands, including the original QA band, the modified QA band by a dilation of two pixels around cloud and cloud shadow edges, and the QA band processed by Auto-PCP (“QA_Auto-PCP”). Experimental results, from both actual and simulated Landsat cloud images, show that QA_Auto-PCP achieved the best visual assessment for the cloud-removed images, and had the smallest RMSE values and the largest Structure SIMilarity index (SSIM) values. The improvement for the performance of cloud removal by QA_Auto-PCP is because the new method substantially decreases omission errors of clouds and shadows in the original QA band, but meanwhile does not increase commission errors. Moreover, Auto-PCP is easy to implement and uses the same data as cloud removal without additional image collections. We expect that Auto-PCP can further popularize cloud removal and advance the application of Landsat data.     

 

Keywords: Cloud detection, Cloud shadows, Cloud simulation, Cloud removal, MODTRAN