bluuebunny/crossref_metadata_2025 huggingface dataset:
Settling behaviour of particles in Rayleigh-Benard convection
Authors: Patocka Vojtech , Calzavarini Enrico , Tosi Nicola
Published: March 2020

Our numerical study evaluates the settling rate of solid particles, suspended in a highly 
vigorous, finite Prandtl number convection of a bottom heated fluid. We explore a broad 
range of model parameters, covering particle types appearing in various natural systems, 
and focus in particular on crystals nucleating during the cooling of a magma ocean. The 
motion of inertial particles within thermal convection is non-trivial, and under idealized 
conditions of spherical shaped particles with small Reynolds number it follows the 
Maxey-Riley equation (Maxey and Riley, 1983). Two scaling laws exist for the settling 
velocities in such system: for particles with small but finite response time, the Stokes' 
law is typically applied. For particles with a vanishing response time, a theoretical model 
was developed by Martin and Nokes (1989), who also validated their prediction with analogue 
experiments. 

We develop a new theoretical model for the settling velocities. Our approach describes 
sedimentation of particles as a random process with two key constituents: i) transport 
from convection cells into slow regions of the flow, and ii) the probability of escaping 
slow regions if a particle enters them. By quantifying the rates of these two processes, 
we derive a new equation that bridges the gap between the above mentioned scaling laws. 
Moreover, we identify four distinct regimes of settling behaviour and analyze the lateral 
distribution of positions where particles reach the bottom boundary. Finally, we apply our 
results to the freezing of a magma ocean, making inferences about its equilibrium vs 
fractional crystallization. The numerical experiments are performed in 2D cartesian geometry 
using the freely available code CH4 (Calzavarini, 2019).

References:
Maxey, M. R. and Riley, J. J.(1983): Equation of motion for a small rigid sphere in a nonuniform flow. 
Physics of Fluids, 26(4), 883-889.

Martin, D and Nokes, R (1989): A fluid-dynamic study of crystal settling in convecting magmas. 
Journal of Petrology, 30(6), 1471-1500.

Calzavarini, E (2019): Eulerian–Lagrangian fluid dynamics platform: The ch4-project. Software Impacts, 1, 100002.
Study of Tropical Cyclones in the North Indian Ocean basin using Percolation in Climate Networks
Authors: Gupta Shraddha , Kurths Jürgen , Pappenberger Florian
Published: March 2020

Every point on the Earth’s surface is a dynamical system which behaves in a complex way while interacting with other dynamical systems. Network theory captures this feature of climate to study the collective behaviour of these interacting systems giving new insights into the problem. Recently, climate networks have been a promising approach to the study of climate phenomena such as El Niño, Indian monsoon, etc. These phenomena, however, occur over a long period of time. Weather phenomena such as tropical cyclones (TCs) that are relatively short-lived, destructive events are a major concern to life and property especially for densely populated coastlines such as in the North Indian Ocean (NIO) basin. Here, we study TCs in the NIO basin by constructing climate networks using the ERA5 Sea Surface Temperature and Air temperature at 1000 hPa. We analyze these networks using the percolation framework for the post-monsoon (October-November-December) season which experiences a high frequency of TCs every year. We find significant signatures of TCs in the network structure which appear as abrupt discontinuities in the percolation-based parameters during the period of a TC. This shows the potential of climate networks towards forecasting of tropical cyclones.

 

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 813844.
A Rockfall inventory: Ötztal Alps, Tyrol, Austria
Authors: Knoflach Bettina , Tussetschläger Hannah , Sailer Rudolf , Meißl Gertraud , Stötter Johann
Published: March 2020

Climate change has serious implications for the cryosphere and a close relationship between the instability of rock faces and the changes in high mountain permafrost is suspected. Although, the number of rockfall events in Alpine areas is increasing, detailed analyses of the frequency and runout distances in high altitudes are rare. This study gives an insight into the rockfall activity in the Ötztal Alps in Tyrol, Austria. A systematic observation utilizing bi-temporal ALS-DTMs in combination with orthoimages revealed a total of 93 rockfalls over an area of 637 km² in the period from 2006 to 2010. Since more than 90 % of the rockfall release areas were mapped in potential permafrost areas, a correlation between rockfall activity and climatically driven degradation of permafrost in bedrock is very likely. 18 rockfall events, ranging in volume from 69 to 8420 m³, were suitable for runout assessments. To estimate the maximum range of future rockfalls with empirical models, values of 30 ° (Fahrböschung) and 26 ° (minimum shadow angle) can be proposed for risk assessment at a regional scale (1:25,000 – 1:100,000). Rockfalls occurring on snow or ice may also go below these values.

Keywords: Rockfall, Permafrost, digital elevation model; runout distance, Fahrböschung, minimum shadow angle, Ötztal Alps
Simulating vortices and jets in deep atmospheres of gas giant planets
Authors: Yadav Rakesh , Bloxham Jeremy , Heimpel Moritz
Published: March 2020

Decades of observations have painted a dynamic and rich picture of the atmosphere on Saturn and Jupiter. Both planets have a dominant prograde equatorial jet, and strong zonal flows that alternate in direction at higher latitudes, with Saturn also having a mysterious hexagon shape embedded in one of the polar jets. Both planets also have numerous vortices or storms of different sizes scattered on their surface. All these features are striking examples of turbulent self-organization. While observations abound, the physics behind the formation of these dynamical features is still uncertain. Two interpretations have emerged over time: In one, the surface features are shallow, extending to depths ranging from 10s to 100s of kilometers, while, in the other, they extend to 1000s of kilometers. Here we utilize the deep interpretation and investigate the properties of rotating convection in deep spherical shells. We present three cases: In the first case a giant polar cyclone, alternating zonal flows, and a high latitude eastward jet having polygonal patterns form simultaneously; The second case generates alternating zonal flows as well as numerous cyclones and anticyclones on various latitudes; And, the third case exclusively generates anticyclones with few being as large as Jupiter's great red spot. We discuss what drives these features in these turbulent simulations, and what can we learn from these cases about the interior and surface dynamics of Saturn and Jupiter. 
Germination potential of Sesbania cannabina in 2 Chromium (Cr) spiked growth media
Authors: Ibne Kamal Abdul Kadir , Batty Lesley , Bartlett Rebecca , Suleiman Suleiman , Chustecki Joanna
Published: March 2020

Sediments of the banks of the Buriganga River, Bangladesh, are contaminated with heavy metals from industrial activity, especially Chromium (Cr). These carcinogens pose a serious risk to human and environmental health (Nargis et al., 2018). Sesbania cannabina, a leguminous fodder crop with rapid growth and high biomass production, is found to be naturally growing in these areas (Sarwar et al., 2015) and may have phytoremediation potential (Varun et al., 2017). This study aims to determine whether Sesbania cannabina can be grown from seed under chromium stressed conditions to establish this species as a possible phyto-extractor.

In this experiment toxicity testing of Chromium (K2Cr2O7) on seed germination was carried out using two growth media: Murashige and Skoog basal medium (MS0); and filter paper (Whatman Grad 1), by top of media or top of paper method respectively. In all cases, seeds were germinated under controlled conditions; 12 h full spectrum light at temperature 28°C ± 1°C and relative humidity of ~ 75% for 5 days. Seeds were pre-treated with H2O2 (6% v/v) for 5 minutes and primed with 65°C water for 5 minutes, before the addition of Cr. Under low Cr concentrations (0 to 50 ppm) there was no significant effect observed in germination or root length. Under high Cr concentrations 98-100% of seeds germinated in both growth media, but root length decreased to almost half that of controls in ≥ 500 ppm Cr, and root elongation was negligible or stopped in ≥ 1000 ppm Cr. Confocal micrographs (stained with propidium iodide) indicate that damage to the cell wall of lateral root tips of germinated seeds increased with the concentration of Cr. There was no significant difference observed between the two growth media.

Thus it can be concluded that Sesbenia cannabina can tolerate Cr contamination, and is able to germinate and grow in up to 500 ppm Cr. Given the ability of SC to grow in semi-arid to sub-humid climates, and a range of environmental conditions including seasonally submerged soils, there is great potential for SC to be adopted as a tool for phytoremediation of Cr contaminated soils in Bangladesh and elsewhere.
Nature-based solutions for urban resilience
Authors: Kalantari Zahra , Gadnert Andrea , Ferreira Carla Sofia Santos
Published: March 2020

Nature-based solutions have the potential to provide a wide range of essential ecosystem services as well as water management goals. As the majority of the global population lives in cities, NBS for addressing water management in urban areas is of great importance. Despite the recent advances and growing experiences with the implementation of NBS, there is still below 1% of the total investment in water resource management infrastructure that is dedicated to NBS in urban areas? One of the current obstacles for implementation is the lack of knowledge, data and information about the design and implementation of NBS for water management. Although there has been a growing interest in NBS in recent years, there are still a large need for a comprehensive evidence based on the effectiveness of NBS. Therefore, there is also a need for monitoring both the process of implementing NBS as well as the outcomes, including the final benefits of the NBS, how the NBS is perceived and how it responds to the challenge for which it was implemented.  The aim of this study is to assess the effectiveness of nature-based solutions (NBS) for urban resilience in particular for water management in different climate zones, focusing on cities that have worked or are planning to work extensively with NBS. This study explores which opportunities and barriers current regulatory frameworks and management practices imply and how the former can be reaped and the latter overcome, for implementation of effective NBS. The study focuses on the analysis of available data bases of NBS in different cities This study also creates an inventory of indicators used to assess the NBS effectiveness, covering a range of social, economic and technical aspects.
Interannual variability in North American ecosystems
Authors: Byrne Brendan , Liu Junjie , Bloom A. Anthony , Bowman Kevin , Butterfield Zachary , Joiner Joanna , Keppel-Aleks Gretchen , Parazoo Nicholas , Yin Yi
Published: March 2020

Semi-arid ecosystems have been recognized as an important driver of interannual variability (IAV) in the growth rate of atmospheric CO2. However, the importance of these ecosystems for IAV in gross primary productivity (GPP) and net ecosystem exchange (NEE) over North America is not well characterized. In this study, we examine IAV over temperate North America using NEE constrained by surface-based and space-based atmospheric CO2 measurements over 2010–2015 and upscaled GPP from FluxSat over 2001–2017. We show that the arid west of North America provides a larger contribution to IAV in GPP and NEE than the more productive eastern half of North America. This occurs because flux anomalies in western North America are temporally coherent across the growing season leading to an amplification of GPP and NEE for wet years. In contrast, IAV in eastern North America shows seasonal compensation effects, wherein positive anomalies during April–June are compensated for by negative anomalies during July–September.
Climate change impact on terrestrial water balance components at continental and global scales
Authors: Nasonova Olga , Gusev Yeugeniy , Kovalev Evgeny
Published: March 2020

This work is a continuation of our previous investigations performed within the framework of the International Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) on a regional scale when hydrological projections and their uncertainties were obtained for 11 large-scale river basins using the physically based land surface model Soil Water – Atmosphere – Plants (SWAP) driven by meteorological projections from five Global Climate Models (GCMs). In the present work, we decided to spread our investigations to continental and global scales. The main goals are as follows: (i) projecting changes in terrestrial water balance components in the 21st century due to possible climate change for different continents and for the whole globe, (ii) evaluation of uncertainties in the obtained projections sourced from application of different GCMs and different climatic scenarios, (iii) studying the patterns of spatial distribution of changes in the water balance components and their uncertainties.

Simulations of the water balance components (evapotranspiration and runoff) for the entire land surface of the globe (with the exception of Antarctica) were performed by the SWAP model with a spatial resolution of 0.5o×0.5o for the period of 1961-2099. The model was driven by daily meteorological outputs from five GCMs (including GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-LR, MIROC-ESM-CHEM, and NorESM1-M) obtained for each of four Representative Concentration Pathway (RCP) scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5). As a result, 20 variants of daily values of evapotranspiration, runoff, and precipitation were obtained for each calculational grid cell. Then, the climatic annual values of the water balance components for four periods (historical and three prognostic ones: 2006-2036, 2037-2067, 2068-2099) were obtained and their changes for different prognostic periods compared to historical values were calculated. Besides, uncertainties in the projected changes of the water balance components resulted from application of different GCMs and RCP scenarios were estimated. The obtained results were mapped and averaged over the continents, latitudinal zones, and the globe that allowed us to identify spatio-temporal patterns of changes in the water balance components and their uncertainties due to possible climate changes.
Investigating the seasonal response of precipitation extremes to global warming using observations and large-ensembles of coupled climate models
Authors: Williams Andrew , O'Gorman Paul
Published: March 2020

Changes in extreme precipitation are amongst the most impactful consequences of global warming, with potential effects ranging from increased flood risk and landslides to crop failures and impacts on ecosystems. Thus, understanding historical and future changes in extreme precipitation is not only important from a scientific perspective, but also has direct societal relevance.

However, while most current research has focused on annual precipitation extremes and their response to warming, it has recently been noted that climate model projections show a distinct seasonality to future changes in extreme precipitation. In particular, CMIP5 models suggest that over Northern Hemisphere (NH) land the summer response is weaker than the winter response in terms of percentage changes.

Here we investigate changes in seasonal precipitation extremes using observations and simulations with coupled climate models. First, we analyse observed trends from the Hadley Centre’s global climate extremes dataset (HadEX2) to investigate to what extent there is already a difference between summer and winter trends over NH land. Second, we use 40 ensemble members from the CESM Large Ensemble to characterize the role played by internal variability in trends over the historical period. Lastly, we use CMIP5 simulations to explore the possibility of a link between the seasonality of changes in precipitation extremes and decreases in surface relative humidity over land.
Factors Leading to Increased Algal Production in Mountain Lakes: A Paleolimnological Perspective from the Uinta Mountains, Utah, USA
Authors: Moser Katrina A. , Hundey Elizabeth J , Sia Maria E. , Doyle Rebecca M. , Dunne Holly , Longstaffe Fred J.
Published: March 2020

Mountain lakes are often remote, located in environments that experience cold temperatures, high incident solar and ultraviolet radiation, and prolonged ice and snow cover. They are, therefore, frequently dilute and oligotrophic. Together these factors can aﬀect mountain lake ecosystem structure, diversity, and productivity. However, distant human activities resulting in atmospheric pollution, as well as more local disturbances, such as fish stocking, potentially increase nutrient inputs and alter mountain lake ecosystems. Our research addresses how these human activities have altered algal production in Uinta Mountain (Utah, USA) lakes. Sedimentary chlorophyll a and its derivatives were measured using visible reflectance spectroscopy in short sediment cores from a total of 12 lakes, including both alpine and subalpine lakes, to determine trends in algal production. All sediment cores were dated using 210Pb and 14C dating, and the records were shown to extend back 300 to 500 years. Our results show that regardless of whether lakes were stocked or not, algal production remained virtually unchanged until 1950 when it increased dramatically in most lakes. The widespread distribution of the sites points to a regional stressor, such as atmospheric deposition of nutrients, as being the main cause for increased algal production. Additional analyses, including diatoms and C and N isotopes, measured in sediments from some lakes support this finding. The few lakes where algal production trends differed showed either that algal production had changed little overtime or that it was variable throughout the record. Although speculative, the lake that showed unchanged algal production is surrounded by a wetland that may have contributed nitrogen to the lake throughout the record meaning that additional nitrogen had little effect on algal production. Lakes with more variable algal production were subalpine lakes. The variable trend may point to more complex pathways and transport of nitrogen from the catchment to the lakes at lower elevation sites. Our findings show that remote mountain lakes, which typically are important water resources and biodiversity hotspots, are rapidly changing as a result of human activities, but not all of these lakes are responding in the same way. To effectively protect mountain lakes it will be important to identify and quantify influential factors affecting lake response to anthropogenic stressors.  
The role of fluids in the seismicity of the Western Gulf of Corinth (Greece)
Authors: Michas Georgios , Kapetanidis Vasilis , Kaviris George , Vallianatos Filippos
Published: March 2020

The present study focuses on the Western Gulf of Corinth (WGoC), which is one of the most seismically active sites in Europe and also the region where the Corinth Rift Laboratory (CRL) Near Fault Observatory (NFO) has been installed. The WGoC exhibits high extension rates and intense microseismicity, with frequent occurrence of clustered seismicity, as in the cases of the 2001 Agios Ioannis swarm, the seismic sequences of 2003-2004 and 2006-2007 in the central part of the Gulf and the 2013 Helike swarm. These outbreaks of seismicity, lasting a few days to months, are characterized by a high frequency and density of earthquakes, with magnitudes generally not exceeding 4.5, with the strongest ones usually occurring in the middle or towards the end of the sequence. These short-lived seismic crises often exhibit patterns of spatio-temporal migration in their hypocentral distribution, which has been associated with the effects of diffusion and circulation of fluids to the seismogenic crust of the WGoC. Fluids appear to play an important role in both triggering and evolving seismic sequences. In the framework of the present study, earthquake hypocenters, relocated with high resolution by employing waveform cross-correlation and the double difference-method, are used to perform an upper crust Shear-Wave Splitting (SWS) study at the WGoC area. The temporal variation of the SWS is investigated, in relation with the temporal evolution of seismicity, to possibly identify patterns related to changes of the stress-field due to fluid migration, or before the occurrence of moderate to strong earthquakes. In addition, the relocated catalogue is analyzed using nonlinear statistical physics for the definition of the spatio-temporal scaling properties of clustered seismicity, as well as for the quantification and modeling of seismic diffusion phenomena associated with fluid circulation at the upper crust of the WGoC.

Acknowledgements

We would like to thank the personnel of the Hellenic Unified Seismological Network and the Corinth Rift Laboratory Network (https://doi.org/10.15778/RESIF.CL) for the installation and operation of the stations used in the current article. The present work was co-funded by the European Union (ESF) and Greek national funds through the Operational Program "Human Resources Development, Education and Lifelong Learning", project title “Τhe effect of fluids on the seismicity of the Western Gulf of Corinth” (project code MIS: 5048127).
Continental Crust formation in the Archean vs modern times
Authors: Jagoutz Oliver , Klein Benjamin , Schmidt Max W , Küter Nico
Published: March 2020

When subduction initiated and contributed to formation of Continental crust is uncertain. A crucial difference between subduction zones magma and e.g. plume related magmatism is the role of H2O in the magma formed. Subduction zones magma are frequently wet and follow a liquid line of descent (LLD) that differs from dry plume related magmas. We developed a qualitative hygrometer based on major elements that allow to distinguish between LLD formed at water saturated condition from those that formed at dry conditions. While arc magmas can by dry at times, plume related magmas are generally dry. So wet LLD are a hall mark of subduction. In this talk we will compare the modern arc record with the Archean rock record to investigate if Archean rocks formed due to a wet or dry LLD. 
Poroelastic relaxation in thermally cracked and fluid-saturated glass
Authors: Ògúnsàmì Abdulwaheed , Borgomano Jan , Fortin Jérôme , Jackson Ian
Published: March 2020

To test theoretical models of modulus dispersion and dissipation in fluid-saturated rocks, we have investigated the broadband mechanical properties of four thermally cracked glass specimens of simple microstructure with complementary forced-oscillation (0.004 -100 Hz) and ultrasonic techniques (~1MHz). Strong pressure dependence of moduli (bulk, Young’s, and shear), axial strain, and ultrasonic wave speeds for dry conditions, attests to essentially complete crack closure at a confining pressure of 15 MPa – indicative of ambient-pressure crack aspect ratios mainly < 2 ´ 10-4.Oscillation of the confining pressure reveals bulk modulus dispersion and a corresponding dissipation peak, near 2 mHz only at the lowest effective pressure (2.5 MPa) – attributed to the transition with increasing frequency from the drained to saturated-isobaric regime. The observations are consistent with Biot-Gassmann theory, with dispersion and dissipation adequately represented by a Zener model.  Above the draining frequency, axial forced-oscillation tests show dispersion of Young’s modulus and Poisson’s ratio, and an associated broad dissipation peak centred near 0.3 Hz, thought to reflect local ‘squirt’ flow and adequately modelled with a continuous distribution of relaxation times over two decades. Observations of Young’s and shear modulus dispersion and dissipation from complementary flexural and torsional oscillation measurements for differential pressure ≤ 10 MPa provide supporting evidence of the transition with increasing frequency from the saturated-isobaric to the saturated-isolated regime – also probed by the ultrasonic technique. These findings validate predictions from theoretical models of dispersion in cracked media and emphasize need for caution in the seismological application of laboratory ultrasonic data for cracked media.
Scaling and anisotropic heterogeneities of ocean SST images from satellite data
Authors: Schmitt Francois , Yahia Hussein , Sudre Joel , Garçon Véronique , Charria Guillaume
Published: March 2020

Oceanic fields display a large variability over large temporal and spatial scales. One way to characterize such variability, borrowed from the field of turbulence, is to consider scaling regimes and multi-scaling properties.

He we use 2D power spectral analysis as well as 2D structure functions <X(M)-X(N)q>=F(q,d(M,N)), between tow points M and N belonging to the region of interest. By performing statistics with respect to the distance d(M,N), one may extract the scaling property of the 2D field, for a range of distances Lmin<d<Lmax, of the form F(q,d)=dζ(q). This approach can be used even for irregular images (having missing values due to cloud coverage) or for part of images in order to estimate the statistical heterogeneity of different zones of a given image.

In the framework of the French CNRS/IMECO project, we consider MODIS Aqua SST images, in France (English Channel versus Gascogne Golf) and in Chili (Eastern Boundary Upwelling System). We illustrate the use of the 2D structure function analysis for different part of these images and also different times. Scaling ranges and also scaling exponents are compared. To take into account the anisotropy of some of these zones, an anisotropic version of the 2D structure functions is also used.
Chemical and structural analysis of proposed ca. 3.7 Ga stromatolites from the Isua Supracrustal Belt (West Greenland) - a reappraisal
Authors: Zawaski Mike , Kelly Nigel , Orlandini Omero Felipe , Nichols Claire , Allwood Abigail , Mojzsis Stephen
Published: March 2020

The biogenicity of proposed stromatolites from deformed greenschist/amphibolite facies Eoarchean (ca. 3.71 Ga) rocks of the Isua Supracrustal Belt (ISB) in West Greenland, is debated  [1,2; cf. 3]. To assess their promise as primary sedimentary structures – as opposed to artefacts of strain localization in layered ductile rocks – we report new field mapping at the discovery site of Nutman et al. (2016) to guide micro- and macro-structural investigations and geochemical sampling. Discontinuous field relations preclude confident assignment of these outcrops as being structurally overturned as originally argued. The structures are not deformed conical stromatolites, but instead linear inverted ridges aligned with azimuths of local and regional fold axes, and parallel to linear structures. Combined major element (e.g., Ca, Mg, Si) scanning μXRF maps, and electron back-scattered diffraction (EBSD) patterns on fresh surfaces cut perpendicular and parallel to the ridges show that the structures lack any internal laminae. Seeming internal layering previously inferred for these features instead arises from variable weathering of outcrop surfaces that otherwise conceal structureless quartz ± dolomite granoblastic cores. These asymmetric boudins sit between semi-continuous competent layers of enveloping quartzite in a calc-silicate schist. Boudinage fabrics reflect viscosity contrasts of the different ductile layers during deformation, and are thus not of primary origin. Collectively, our results show that such structures were probably never stromatolites, but are instead the expected result of a tectonic fabric that preserves no fine-scale primary sedimentary structure.

[1] Nutman, A.P. et al. 2016, Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures: Nature, v. 537, p. 535–538; [2] Nutman, A.P. et al., 2019, Cross-examining Earth’s oldest stromatolites: Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ∼3700 Ma sedimentary rocks: Precambrian Research, v. 331, p. 105347; [3] Allwood, A.C. et al. 2018, Reassessing evidence of life in 3,700-million-year-old rocks of Greenland: Nature, doi: 10.1038/s41586-018-0610-4.
New insights on bottom water flows crossing a marine sill under periodic or impulsive perturbations: an application to the Sicily Channel sill (Central Mediterranean Sea)
Authors: Falcini Federico , Di Paolantonio Marco , Salusti Ettore
Published: March 2020

We here discuss the remarkable uplift of the Eastern Mediterranean bottom waters that flow westward, over the Malta Escarpment, and cross the sill of the Channel of Sicily (Astarldi et al., 2001; Iudicone et al., 2003; Falcini & Salusti 2015); a dynamics that is rather similar to the one occurring at the Strait of Gibraltar (Mediterranean Sea) and Bab el Mandab (Red Sea) (Siddall et al., 2002). This classical uplift, which usually occurs under a three layer system dynamics, is mostly explained by the Bernoulli suction effect (Lane-Serff et al., 2000). However, the real filed analyses suggest that this dynamics are significantly perturbed by tidal effects and or large scale storms (Smeed et al., 2004). Here consider a novel, theoretical approach to obtain a rather realistic view of natural perturbations that affect these deep flow dynamics. Our insights on uplift processes, in addition, give a contribution to the general understanding of the Mediterranean Sea deep water circulation and, on climatological grounds, heat storage dynamics. We finally remark that similar phenomena happens in several marine straits and/or in semi-enclosed, peripheral basins of particular importance for local and large-scale processes.

 

References

Astraldi, M., Gasparini, G. P., Gervasio, L., & Salusti, E. (2001). Dense water dynamics along the Strait of Sicily (Mediterranean Sea). Journal of Physical Oceanography, 31(12), 3457-3475.

Falcini, F., & Salusti, E. (2015). Friction and mixing effects on potential vorticity for bottom current crossing a marine strait: an application to the Sicily Channel (central Mediterranean Sea). Ocean Science, 11(3), 391-403.

Iudicone, D., Buongiorno Nardelli, B., Santoleri, R., & Marullo, S. (2003). Distribution and mixing of intermediate water masses in the Channel of Sicily (Mediterranean Sea). Journal of Geophysical Research: Oceans, 108(C9).

Lane-Serff, G. F., Smeed, D. A., & Postlethwaite, C. R. (2000). Multi-layer hydraulic exchange flows. Journal of Fluid Mechanics, 416, 269-296.

Siddall, M., Smeed, D. A., Matthiesen, S., & Rohling, E. J. (2002). Modelling the seasonal cycle of the exchange flow in Bab el Mandab (Red Sea). Deep Sea Research Part I: Oceanographic Research Papers, 49(9), 1551-1569.

Smeed, D. A. (2004). Exchange through the Bab el Mandab. Deep Sea Research Part II: Topical Studies in Oceanography, 51(4-5), 455-474.
Low-temperature thermochronology of fault zones
Authors: Tagami Takahiro
Published: March 2020

Thermal signatures as well as timing of fault motions can be constrained by thermochronological analyses of fault-zone rocks (e.g., Tagami, 2012, 2019).  Fault-zone materials suitable for such analyses are produced by tectocic and geochemical processes, such as (1) mechanical fragmentation of host rocks, grain-size reduction of fragments and recrystallization of grains to form mica and clay minerals, (2) secondary heating/melting of host rocks by frictional fault motions, and (3) mineral vein formation as a consequence of fluid advection associated with fault motions.  The geothermal structure of fault zones are primarily controlled by the following three factors: (a) regional geothermal structure around the fault zone that reflect background thermo-tectonic history of studied province, (b) frictional heating of wall rocks by fault motions and resultant heat transfer into surrounding rocks, and (c) thermal influences by hot fluid advection in and around the fault zone.  Geochronological/thermochronological methods widely applied in fault zones are K-Ar (40Ar/39Ar), fission-track (FT), and U-Th methods.  In addition, (U-Th)/He, OSL, TL and ESR methods are applied in some fault zones, in order to extract temporal information related to low temperature and/or recent fault activities.  Here I briefly review the thermal sensitivity of individual thermochronological systems, which basically controls the response of each method against faulting processes.  Then, the thermal sensitivity of FTs is highlighted, with a particular focus on the thermal processes characteristic to fault zones, i.e., flash and hydrothermal heating.  On these basis, representative examples as well as key issues, including sampling strategy, are presented to make thermochronological analysis of fault-zone materials, such as fault gouges, pseudotachylytes and mylonites, along with geological, geomorphological and seismological implications.  Finally, the thermochronological analyses of the Nojima fault are overviewed, as an example of multidisciplinary investigations of an active seismogenic fault system.

 

References:

Tagami, 2012. Thermochronological investigation of fault zones. Tectonophys., 538-540, 67-85, doi:10.1016/j.tecto.2012.01.032.

Tagami, 2019. Application of fission track thermochronology to analyze fault zone activity. Eds. M. G. Malusa, P. G. Fitzgerald, Fission track thermochronology and its application to geology, 393pp, 221-233, doi: 10.1007/978-3-319-89421-8_12.
Microbial impact assessment of the 2018 European drought on groundwater quality in the Republic of Ireland: An opportunistic field study
Authors: O'Dwyer Jean , Weatherill John , Chique Carlos , Hynds Paul
Published: March 2020

Global climate change models predict an increase in both the frequency and severity of extreme weather events, including prolonged drought conditions, thus posing a unique set of challenges for regions traditionally unaccustomed to severe climate phenomena. This is particularly significant for the occurrence of severe drought events in areas characterised by temperate maritime climates, such as the Republic of Ireland (ROI). While numerous studies have explored the impacts of drought on groundwater levels and chemical contamination, few studies have sought to investigate the impacts of sporadic drought events on the microbial quality of groundwater for human consumption. Accordingly, the 2018 (June-August) European drought event represented a unique opportunity to investigate the effects of prolonged low rainfall and elevated temperature (relative to seasonal means) on the incidence of faecal indicator organisms (FIOs) among unregulated domestic groundwater supplies in the ROI.

A dual-sampling fieldwork regime (during and post-event) of private wells (n=74) and subsequent risk factor (logistic regression) and bivariate analyses were used to evaluate the potential role of meteorological and site specific (hydrogeology, contaminant sources etc.) conditions on the incidence of microbial contamination. During absolute drought conditions (≥15 days characterised by no measureable precipitation, June 2018), the sampled cohort exhibited a significantly decreased risk of microbial contamination (OR: 0.356, p = 0.024) with 12.2% (n = 9/74) of supplies contaminated with Escherichia coli (E. coli), increasing to 28.4% (n = 21/74) upon abatement of drought conditions (October 2018). No analysed risk factors were associated with E. coli presence at the 95% confidence level, although, the presence of onsite domestic wastewater treatment systems (U = 1.03 p = 0.057) approached statistical significance during the drought. Findings suggest that the 2018 European drought served to decrease background levels of FIO within private wells in the ROI, likely due to reduced hydraulic loading from the surface, soil moisture deficits and consequently, significantly decreased bacterial survival. Results would seem to reiterate the significance of onsite domestic wastewater treatment systems as a source of subsurface contaminants in Ireland. The presented opportunistic field study provides a critical characterization of the impacts of unprecedented drought events on microbiological water quality in domestic groundwater supplies in temperate regions, and may be used by sanitary/environmental engineers, hydrologists, hydrogeologists, policy-makers, planners and healthcare practitioners to safeguard against the future human health effects of climate change and extreme weather events.   
Sea-state dependency of air-sea fluxes for high winds in ECMWF Earth System Model
Authors: Bidlot Jean
Published: March 2020

The global analyses and medium range forecasts from the European Centre for Medium range Weather Forecasts rely on a state-of-the-art Numerical Weather Prediction (NWP) system. To best represent the air-sea exchanges, it is tightly coupled to an ocean wave model.  As part of ECMWF approach to Earth System Model, it is also coupled to a global ocean model for all its forecasting systems from the medium range up to the seasonal time scale.

Because the feedback from and to the ocean can be significant, it is only in the fully coupled system that parameterisation for air-sea processes should be revisited. For instance, it is now accepted that the drag coefficient should generally attained maximum values for storm winds but should level or even decrease for very strong winds, namely in tropical cyclones or intense mid-latitude wind storms.

A modification of the wind input source was tested, whereby the Charnock coefficient estimated by the wave model and therefore the drag coefficient sharply reduce for large winds (> 30 m/s). As a consequence, ECMWF tendency to under predict strong tropical cyclones was sharply alleviated, in better agreement with observational evidence. This change is now planned for operational implementation with the next model cycle (CY47R1, June 2020).

Experimental evidences also point to a sea state/wind dependency of the heat and moisture fluxes.  Following an extension of the wind wave generation theory, a sea state dependent parameterisation for the roughness length scales for heat and humidity has been tested. Again, a proper assessment of the different parameterisations warrants the fully coupled system. Experimentations so far indicate the benefit of such change. Ongoing work aims at future operational implementation.
Locality and dynamics shaping the global scaling pattern of hourly precipitation extremes
Authors: Moustakis Yiannis , Onof Christian J , Paschalis Athanasios
Published: March 2020

According to thermodynamics, as the climate gets warmer under climate change the water holding capacity of the air increases at a rate of 7%/oC (Clausius-Clapeyron; CC). This implies that in the absence of severe changes in relative humidity, precipitation extremes (PEx) will increase likewise. Would this relationship prove to be globally robust, then ground temperature predictions could be used as an indicator for predicting future PEx intensification under climate change. This could be a helpful tool, given the well-documented discrepancies of climate models in simulating PEx and the increased confidence in temperature projections. However, studies based on observational and modelled data have revealed contradicting behaviours regarding the scaling rate of PEx with ground temperature. In this study we use hourly data from weather stations (1,461 sites), two convection permitting models and 40 years of climate reanalysis in order to reveal the global scaling pattern of PEx with ground air and dewpoint temperature at fine spatial and temporal scales based on a robust methodology. Our results suggest that a robust ~CC scaling with both air temperature and dew temperature occurs in high- and mid-latitudes. In the tropics and extra-tropics scaling with temperature ranges from negative up to >CC rates, while scaling with dewpoint is strongly positive with >CC values. An investigation of the emerging global pattern reveals that exhibited divergence from CC is linked to the dynamics of deep atmospheric convection in the tropics and extra-tropics. Topography, larger-scale weather patterns and their associated mechanisms shape the scaling pattern in high- and mid- latitudes and seem to disengage ground measurements from activity at the cloud level. In this study we also prove that non-convection permitting models fail to capture the observed behaviour in regions with strong topographic features and/or distinct deep convection. We show that in such regions convection permitting models which capture those features make more reliable estimations.
EUREC4A: First Impressions
Authors: Stevens Bjorn , Bony Sandrine , Farrell David , Blyth Alan , Fairall Chris , Karstensen Johannes , Quinn Trish , Speich Sabrina , Eurec4a Team
Published: March 2020

The EUREC4A field campaign took place during January and February 2020, in the lower trades of the northern tropical Atlantic, over and in the seas windward of Barbados.  The initial purpose of the campaign was to test hypothesized cloud responses underpinning large positive radiative feedbacks from the desiccation of marine shallow convection with warming. To do so EUREC4A built on a long-standing cooperation with the Caribbean Institute for Meteorology and Hydrology to collect long-term cloud observations. Its scope was subsequently expanded by the addition of many partners, with funding from a variety of additional EU and UK projects, and US participants through ATOMIC, to address many additional questions. These ranged from the role of fine-scale eddies and fronts on air-sea coupling, to the effects of meso-scale organization on cloud radiative effects, to the strength of aerosol cloud interactions, among others. Hundreds of scientists from nearly a dozen nations -- incorporating measurements from four large Research Vessels and five Research Aircraft, an advanced remote sensing ground station and a large number of autonomous vehicles in the air and sea -- combined their expertise  to develop an unusually comprehensive picture of the processes relevant to the lower atmosphere and the upper ocean in the lower trades. We share our first impressions from EUREC4A, its surprises, and its prospects for answering some of the riddles that motivated this tremendous and coordinated effort.
Nonlinear components in global climate teleconnections
Authors: Mikšovský Jiří
Published: March 2020

Among the sources of temporal variability in the climate system, an important role belongs to internal variability modes – phenomena with oscillatory behavior ranging from predominantly sub-annual (e.g. North Atlantic Oscillation) or inter-annual (e.g. Southern Oscillation) to decadal or multidecadal variations (e.g. Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation). These oscillations manifest themselves not only within their particular geographical areas of origin, but their effects are typically also transmitted through long-range teleconnections, affecting weather and climate patterns worldwide. Analysis of these relationships is often done assuming their linearity – but rarely is such assumption explicitly verified.

In this presentation, presence and magnitude of nonlinear components in long-range teleconnections associated with selected climate variability modes are studied through various time series analysis methods. Several nonlinearity-quantifying statistics, ranging from simple measures of asymmetry in the regression coefficients to outcomes of more formal surrogate data-based tests, are employed to investigate the teleconnection-related responses of local temperatures across the globe. It is shown that substantial variations exist in degree of manifested nonlinearity, subject to both the target location and type of the variability mode(s) considered. Potential of individual nonlinearity-sensitive techniques for more realistic capture of the teleconnection-related response patterns is also discussed, with an ultimate goal of construction of a more accurate model of variability transfer in the climate system.
Tropical forest CH4: from flux chambers to micrometeorological tower measurements
Authors: van Asperen Hella , Warneke Thorsten , Carioca de Araújo Alessandro , Rider Forsberg Bruce , Ramos de Oliveira Leonardo , de Lima Xavier Thiago , de Oliveira Sá Marta , Ricardo Teixeira Paulo , Azevedo de Oliveira Robson , Sousa de Moura Veber , do Socorro Monteiro Leal Leila , Botia Santiago , Lavrič Jošt , Komiya Shujiro , Frumau Arnoud , Hensen Arjan , van den Bulk Pim , van Dinther Danielle , Notholt Justus
Published: March 2020

Methane (CH4) is the second most important long-lived anthropogenic atmospheric greenhouse gas. Despite its importance, natural sources of methane, such as tropical wetlands, are still not well understood and a large source of uncertainty to the global CH4 budget. The Amazonian rain forest is estimated to hold 90-120 Pg of carbon, which is approximately 14-27% of the carbon stored in vegetation worldwide. The region is characterized by high precipitation rates and large wetlands, and it has been estimated that the Amazon basin emits 7% of the annual total CH4 emissions. Due to its remote location, micro-meteorological measurements are rare and absent for other gases than CO2.

The 50 m high K34 tower (field site ZF2) is located in a pristine tropical forest region 60 km northwest of Manaus (Brazil), and is located next to a waterlogged valley, a possible location for anaerobic CH4 production. In October 2018, in addition to the existing EC CO2 system, a Relaxed Eddy Accumulation (REA) system was set up at this tower, connected to an in-situ FTIR-analyzer. This set up continually measures fluxes and concentration profiles of CO2, CO, CH4, N2O and δ13CO2. In addition, CH4, CO2, and N2O uptake and emission processes were studied by flux chamber measurements in the footprint of the REA tower, focusing on different possible sources (soil, stream, trees and termites). In this presentation, an overview of the measured CH4 and N2O forest concentrations and fluxes will be shown.