bluuebunny/crossref_metadata_2025 huggingface dataset:
A simple derivation of tropical mean precipitation and circulation changes
Authors: Dacie Sally , Bao Jiawei
Published: March 2020

Using just a few simple assumptions and a widely used radiative transfer scheme, we try to explain why rainfall increases in a warming climate and predict how the tropical mean circulation changes to accommodate this. We use konrad, a 1D radiative-convective equilibrium model, in which convection is handled simply by specifying the tropospheric lapse rate and enthalpy conservation (similar to Manabe and Wetherald 1967). Considering energy balance at the surface or equivalently in the whole of the atmosphere, evaporation or condensation rates can be calculated (as in Jeevanjee and Romps 2018), giving precipitation increases of 2.0-2.7% per Kelvin increase in surface temperature. The direct radiative effect of carbon dioxide results in a decrease in precipitation, but the warming it induces leads to an overall increase in precipitation at the new equilibrium state of 1.4-2.0%/K. Thus, in agreement with global modelling studies (eg. Flaeschner et al 2016), we expect that the continual increase in atmospheric carbon dioxide in the real world is suppressing the increase in mean precipitation that will occur in the long term. To derive the convective mass flux as well as the downwelling and upwelling velocities and area fractions from our single column model output, we think of the atmosphere as two distinct regions, a saturated moist region of upward motion and a non-saturated region where adiabatic motion balances radiative cooling. The mass flux decreases in a warming climate as the increase in water vapour available for condensation is larger than the increase in condensation rate required to balance radiative cooling. Further, using our simplistic approach we find an increase in upwelling area in a warming climate. This has implications for convective aggregation and how it may change with climate change.
3D geological model of the Gråbo site from ground TEM measurements
Authors: Sopher Daniel , Wendelin Eva , Lång Lars-Ove , Öhman Johan , Lindhe Andreas
Published: March 2020

A 3D geological model was constructed for the Gråbo site to investigate its suitability for artificial groundwater infiltration, to provide drinking water. The modelling work was performed by the Geological Survey of Sweden (SGU) as part of ongoing groundwater investigations. The site is located close to the city of Gothenburg, in western Sweden. A relatively thick succession of coarse-grained glaciofluvial sediment is located at the site, which overlies a typically finer grained and more clay rich sequence. Previously, the site has been the target of several investigations, the most extensive of these was performed in 2006, where a range of geophysical (seismic refraction, ground penetrating radar and resistivity) and borehole measurements were conducted. Based on previous studies the upper course-grained layer has the best potential for infiltration. However, although these investigations improved the understanding of the site, significant uncertainty remained as to the geometry of the upper course grained layer away from borehole locations.

In order to improve the understanding of the site, additional data was collected in 2018 using a tTEM (towed transient electromagnetic) system developed by Aarhus university. The system is comprised of a transmitter and receiver coil, which are towed behind an ATV (all terrain vehicle). Using the tTEM data a 3D resistivity model of the subsurface was generated down to a depth of between 50 and 70 m at the Gråbo site. On comparison with the available borehole data, it was clear that the course-grained layer could be mapped with relatively high accuracy as a region of high resistivity. The tTEM data was combined with the pre-existing geophysical and borehole data to construct both a voxel and layer-based model of the site. These 3D models have subsequently been used as part of ongoing efforts to evaluate the suitability of the site for infiltration (for example, to decide the location of additional investigation boreholes and to provide input to hydrogeological modelling). In this study we present the tTEM data and the 3D geological model. Finally, we exemplify how the 3D model has been used in subsequent investigations and decision making.
IWV retrieval from shipborne GPS receiver on hydrographic ship Borda
Authors: Bock Olivier , Bosser Pierre , Caumont Olivier , Legouge Raphael , Laurain Nicolas
Published: March 2020

This work aims to provide a quick review of different experiments conducted in the past for the estimation of integrated water vapor content from shipborne GNSS receiver. This state of the art will be confronted with results obtained using GPS data acquired by the French Hydrographic Ship Borda on a cruise over Atlantic Ocean and Mediterranean Sea, from Brest to Toulon in August 2015; the estimated IWV are compared with satellite observations (MODIS) and outputs from numerical weather prediction models (ERAI, ERA5, Arpege, Arome); while differences between GPS and MODIS retrievals reach almost 4 kg/m2 in terms of RMS, agreement is generally much better with numerical models (2 up to 3 kg/m2 in terms of RMS). Use of real-time orbit and clocks product is also investigated in order to assess the performance of near real-time GPS-IWV estimation for NWP purposes. We will draw out the prospects in terms of possibilities and opportunities for the use of shipborne GNSS IWV for meteorology and climatology.
Glacial meltwater microbes: are there seasonal trends in exported assemblages over different catchment sizes?
Authors: Jachnická Kristýna , Kohler Tyler J. , Falteisek Lukáš , Vinšová Petra , Bulínová Marie , Wadham Jemma L. , Lamarche-Gagnon Guillaume , Tedstone Andrew J. , Hawkings Jonathan R. , Kellerman Anne M. , Cameron Karen A. , Stibal Marek
Published: March 2020

Glaciers and ice sheets host diverse microbial life within the hydrologically connected supraglacial, englacial, and subglacial habitats. Microbial cells are collected from the entire glacial ecosystem by seasonally-generated meltwater and exported by proglacial streams. Over the course of the melt season, a subglacial drainage system develops beneath outlet glaciers from the Greenland Ice Sheet (GrIS). This system evolves from an inefficient distributed network to a more efficient channelized pathway. The extent and interconnectivity of the subglacial drainage system with the surface and sediment bed is hypothesized to differ with catchment size.

In this study, we ask whether microbial export from GrIS outlet glacier systems depend on catchment size and whether they evolve with subglacial hydrology over time. We hypothesize that larger catchments will have proportionally greater subglacial drainage, which may be reflected in a greater proportion of subglacial microbes compared to smaller catchments, where the supraglacial inputs might have a higher influence on the exported meltwater. We also expect that changes in assemblage structure are likely to coincide with the evolution of the subglacial drainage system of larger catchments as the season progresses, with supraglacial inputs increasing in importance as the channelized efficient system fully develops. To test these hypotheses, we sampled three outlet glaciers of the GrIS with different catchment sizes (from biggest to smallest: Isunnguata Sermia, Leverett and Russell glaciers) over the 2018 summer. Meltwater samples were taken at the same time each day over a period of three weeks to catch temporal patterns of microbial assemblages. DNA was extracted from samples, and 16S rRNA gene amplicons sequenced to characterize assemblage structure.

This study will help us better understand the meltwater hydrology of the GrIS by describing patterns in its microbial export and the degree of influence from supra- and subglacial systems. In this current age of glacier recession, it is furthermore important to make these characterizations as we might not have opportunity in near future to investigate them in the same unchanged environment.
Seismic processing and imaging of the new 2D marine reflection seismic data in the Polish sector of the Baltic Sea
Authors: Nguyen Quang , Malinowski Michal , Krzywiec Piotr , Huebscher Christian
Published: March 2020

Geological structure and tectonics of the Phanerozoic sedimentary cover within the transition zone between the Precambrian and Paleozoic platform in the Polish sector of the Baltic Sea was imaged using new 2D high-resolution multi-channel seismic reflection data. The new seismic data were acquired in 2016 during the course of RV Maria S. Merian expedition MSM52 within the framework of the BALTEC project. Eight profiles (with the total length of ca. 850km) covered the tectonics blocks located within the Polish Exclusive Economic Zone, stretching from the East European Craton (EEC) to the Paleozoic platform across the Teisseyre-Torquist Zone (TTZ).

Our in-house seismic processing workflow focused on removing multiples contaminating this shallow-water data, both water bottom and interbed related. Various demultiple techniques such as SRME, TAU-P domain deconvolution, high resolution parabolic Radon demultiple and SWDM (Shallow water demultiple) have been tested. Combination of all those techniques at different stages of the processing with some modifications based on a particular seismic profile proved to be the most effective. Consequently, multiples obscuring seismic sections were efficiently reduced. Data were processed up to Kirchhoff pre-stack time migration.

The longest seismic profile (line BGR16-212, ca. 240 km long) crosses almost perpendicularly majority of Precambrian and Paleozoic fault systems bordering the tectonic blocks of the EEC basement, so fault systems could be easily interpreted. EEC Precambrian basement is characterized by a regional flexure towards the TTZ. Cambrian-Ordovician exhibits similar geometry and is characterized by a relatively constant thickness related to deposition on the Tornquist Ocean passive margin. Thick Silurian succession is characterized by a regional divergent pattern caused by deposition within the Caledonian foredeep basin. Structural pattern within the W part of the study area is much more complex as this area underwent Late Paleozoic extension/transtension, Variscan inversion, Permo-Mesozoic subsidence and Late Cretaceous inversion.

This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316.
Across-strike variations of fault slip-rates constrained using in-situ cosmogenic 36Cl concentrations.
Authors: Iezzi Francesco , Roberts Gerald , Faure Walker Joanna , Papanikolaou Ioannis , Ganas Athanassios , Deligiannakis Giorgios , Gheorghiu Delia-Mihaela
Published: March 2020

It is important to constrain the spatial distribution of strain-rate in deforming continental material because this underpins calculations of continental rheology and seismic hazard. To do so, it is becoming increasingly common to use combinations of GPS and historical and instrumental seismicity data to constrain regional strain-rate fields. However, GPS geodetic sites, whether permanent or campaign stations, tend to be widely-spaced relative to the spacing of active faults with known Holocene offsets. At the same time, the interpretation of seismicity data can be difficult due to lack of historical seismicity in cases where local fault recurrence intervals are longer than the historical record. This causes uncertainty on how regional strain-rates are partitioned in time and space, and hence with uncertainty regarding calculations of continental rheology and seismic hazard. To overcome this issue, we have gained high temporal resolution slip-rate histories for three parallel faults using in situ 36Cl cosmogenic dating of the exposure of three parallel normal fault planes that have been progressively exhumed by earthquakes. We study the region around Athens, central Greece, where there also exists a relatively-dense GPS network and extensive records of instrumental and historical earthquakes. This allows to compare regional, decadal strain-rates measured with GPS geodesy with strain-rates across the faults implied by slip since ~40,000 years BP. We show that faults have all had episodic behaviour during the Holocene, with alternating earthquake clusters and periods of quiescence through time. Despite the fact that all three faults have been active in the Holocene, each fault slips in discrete time intervals lasting a few millennia, so that only one fault accommodates strain at any time. We show that magnitudes of strain-rates during the high slip-rate episodes are comparable with the regional strain-rates measured with GPS (fault strain-rates are 50-100% of the value of GPS regional strain-rate). Thus, if the GPS-derived strain-rate applies over longer time intervals, it appears that single faults dominate the strain-accumulation at any given time, with crustal deformation and seismic hazard localised within a distributed network of faults.

 
Synthetic rainfall for Germany based on simulations from two stochastic models
Authors: Haberlandt Uwe , Bárdossy Andras , Birkholz Philipp , Eisele Micha , Fangmann Anne , Fuchs Lothar , Herrmann Ole-Christian , Kuchenbecker Andreas , Maßmann Stefanie , Morales Bruno , Müller Thomas , Seidel Jochen , Sympher Klaus
Published: March 2020

For planning of urban drainage systems using hydrological models, long, continuous precipi-tation series with high temporal resolution are needed. Since observed time series are often too short or not available everywhere, the use of synthetic precipitation is a common alternative.

This contribution discusses the results of a research project, providing 5-minutes continuous stochastic point rainfall data for entire Germany for urban hydrological applications. Two different stochastic rainfall models are employed: a parametric stochastic model based on Alternating-Renewal processes and a non-parametric approach based on Resampling. Using rainfall observations from about 800 stations in Germany, the parameters of the models are regionalized. Rainfall and discharge characteristics are utilised for the evaluation of the model performance using a subset of 45 stations.

The results show, that stochastic rainfall from either of the models is better suited for urban hydrologic design, compared to the common practice scenario, where data from the nearest precipitation station is used. Notably, it could be shown that a mixture of generated rainfall from both models leads to a compensation of errors and further improves results, contrasted with using only data from one single model.
The imprint of glacial and periglacial erosion processes on fluvial landscape metrics
Authors: Liebl Moritz , Robl Jörg , Egholm David Lundbek , Stüwe Kurt , Gradwohl Gerit
Published: March 2020

The emerging Pleistocene glaciations have left a distinct topographic footprint in mountain ranges worldwide. However, it is still unclear how the formation of cirques above (including the potential destruction of peak relief) and the excavation of glacial troughs below the long-term snowline altered to the large-scale topographic pattern of mountain ranges originally conditioned by fluvial processes.

Some mountain ranges such as the Eastern Alps feature a bimodal topographic pattern characterized by a transition from increasing to decreasing slope with elevation. Bimodality might be an expression of glacial reshaping, as glacial troughs with steepened valley flanks have been formed at low elevations and low relief surfaces at high elevations. On the other hand, bimodality might represent the state of fluvial prematurity as expression of ongoing landscape adjustment to an uplift event in the recent past. Despite their completely different evolution, both hypotheses lead to a bimodal landscape with a similar slope-elevation distribution.

In this study, we explore the impact of cold climate erosional processes on the mountain range scale topographic pattern. For this, we use synthetically generated and natural mountain range landscapes conditioned by fluvial processes and apply a surface process model for cold climate conditions (iSOSIA). In regions with high glacial impact, we explore an upstream migrating glacial signature represented by two frequency maxima in the slope elevation distribution at lower elevations (i.e. below the snowline, where glacial troughs formed). This is accompanied with an increase in slope on average compared to the initial topography. Above the snow line, bimodality vanishes and mean slope is similar to the initial fluvial topography. Interestingly, in the Eastern Alps, we explore a similar pattern where the transition from increasing to decreasing slope with elevation is located at about 1800 m, which is roughly at the position of the last glacial maximum (LGM) snowline of this region.
Non-linear resonant instability of short surface waves as the first stage “bag-breakup” process at the air-sea interface at high winds
Authors: Kozlov Dmitry , Troitskaya Yulia
Published: March 2020

The recent experimental study [1], [2] identify ‘‘bag breakup’’ fragmentation as the dominant mechanism by which spume droplets are generated at hurricane wind speeds. These droplets can significantly affect the exchanging processes in the air-ocean boundary layer. In order to estimate spray-mediated heat, momentum and mass fluxes we need not only reliable experimental data, but a theoretical model of this process. The “bag-breakup” fragmentation is a strongly non-linear process, and we focus only on its first stage which includes the small-scale elevation of the water surface.

Our model of the bag’s initiation is based on a weak nonlinear interaction of a longitudinal surface wave and two oblique waves propagating at equal and opposite angles to the flow as it was done in [3], [4]. All of these waves have the same critical layer where cross velocities of oblique waves become infinite making inviscid analysis invalid. So we took into account viscous effects. As a result, it has been established that for a piecewise continuous velocity profile explosive growth of wave amplitudes is possible at the wind speeds exceeding the critical one.

The present model let us find the dependency of “bag’s” transverse size on the wind speed and estimate its lifetime.

 

 Acknowledgements

This work was supported by the RSF project 19-17-00209 and the RFBR projects 19-05-00249, 19-35-90053, 18-05-00265.

References:

Troitskaya, Y. et al. Bag-breakup fragmentation as the dominant mechanism of sea-spray production in high winds. Sci. Rep. 7, 1614 (2017).

Troitskaya, Y. et al. The “Bag Breakup” Spume Droplet Generation Mechanism at High Winds. Part I: Spray Generation Function. J. Phys. Oceanogr., 48, 2167–2188 (2018).

A. Craik. Non-linear resonant instability in boundary layers// Journal of Fluid Mechanics. 50, 393-413 (1971).

A. Craik. Resonant gravity-wave interactions in a shear flow// Journal of Fluid Mechanics. 34, 531-549 (1968).
CSTools R package bringing state-of-the-arts postprocessing methods to seasonal-to-decadal forecast users
Authors: Perez-Zanon Nuria , Caron Louis-Philippe , Alvarez-Castro M. Carmen , Batté Lauriane , Corti Susanna , Dominguez Marta , Fabiano Federico , Gualdi Silvio , von Hardenberg Jost , Lledó Llorenç , Manubens Nicolau , Marson Paola , Materia Stefano , Sánchez Eroteida , Van Schaeybroeck Bert , Torralba Verónica , Terzago Silvia , Verfaillie Deborah , Volpi Danila
Published: March 2020

The availability of climate data has never been larger, as evidenced by the development of the Copernicus Climate Change Service. However, availability of climate data does not automatically translate into usability and sophisticated post-processing is often required to turn these climate data into user-relevant climate information allowing them to develop and implement strategies of adaptation to climate variability and to trigger decisions. 

Developed under the umbrella of the ERA4CS Medscope project by multiple European partners, here we present an R package currently in development, which aims to provide tools to exploit dynamical seasonal forecasts such as to provide information relevant to public and private stakeholders at the seasonal timescale. This toolbox, called CSTools (short for Climate Service Tools), contains process-based methods for forecast calibration, bias correction, statistical and stochastic downscaling, optimal forecast combination and multivariate verification, as well as basic and advanced tools to obtain tailored products. 

In addition to presenting some of the tools that are contained in the package, we also present a short overview of the development strategy adopted for this toolbox. The latter relies on a version controlling system established such as to allow scientists and developers to work within a common framework using a platform where they can exchange with other developers, test the various functionalities and discuss issues arising from the work, amongst other things. Furthermore, we will also present some vignettes, which are one of the mechanisms that allows users to understand and visualize the capabilities of CSTools. For instance, CSTools contains a step by step vignette showing how to use and visualize the output of MultivarRMSE, which gives an indication of the forecast performance (RMSE) for multiple variables simultaneously. 

While the extensive community of R users offers the opportunity of merging climate forecaster experts with final users, CSTools can also be used by other communities, such as Python users through the interface rpy. Finally, the publication of this package on CRAN (the Comprehensive R Archive Network) makes it easily accessible to interested users and ensures its proper functioning on different operational systems. 
Towards a self-consistent thermodynamic magmatic model for conduit transport processes
Authors: von der Lieth Jost , Hort Matthias
Published: March 2020

The geodynamical side of explosive volcanic eruption modelling on the one hand, as well as the petrological one on the other, have reached a high degree of sophistication and maturity independently from each other over the years. Unfortunately, adherents of one discipline often only utilize the other’s tools in a simplified and makeshift way, obscuring the full potential of their synergies. Over the past decade efforts have been made to re-integrate both approaches to the issue into a more holistic view on the sub-surface processes leading to and concurrent with explosive volcanism.
One of the difficulties encountered in that effort are conceptual and technical incompatibilities between thermo- and fluid-dynamic modelling toolboxes. While the tools perform well individually, they are often not suitable to work in combination in highly complex numerical models, due to interface problems impeding performance.
For an ongoing numerical study on transport processes within a volcanic conduit, it has been deemed necessary to re-implement an established thermodynamic model based on Holland and Powell (2011, and follow-ups) in order to a) attain the required computing performance and b) to gain sufficient petrological insight (starting from a geophysical point of view) to be able to make apt use of the tool then at hand.
The path to the intermediate goal of deriving the thermodynamic and transport properties (e.g. density, viscosity, heat capacity and conductivity) in a self-consistent and stable manner suitable for further use in a numerical fluid-dynamics model is illustrated here. The focus is on problems encountered with the petrological modelling, and on the subsequent derivation of the above properties, that are not directly available from the former results. The methods presented are general and applicable to various settings regarding volcanic chemistry and transport processes, however, they will be demonstrated on low-viscosity open-conduit systems typical for strombolian activity.
Role of friction and orography in the Asian-African monsoonal system
Authors: Dalu Giovanni , Gaetani Marco , Flamant Cyrille , Baldi Marina
Published: March 2020

The West African monsoon (WAM) originates in the Gulf of Guinea when the intertropical convergence zone (ITCZ) makes its landfall; whilst, the south Asian monsoon (SAM) originates in the Indian ocean when the ITCZ crosses the equator. The monsoonal dynamics are here studied after landfall using Gill’s tropospheric model with an implanted Ekman frictional layer (EFL). Ekman pumping increases low level convergence, making the lower monsoonal cyclone deeper and more compact that the upper anticyclone, by transferring tropospheric vorticity into the EFL. In the upper troposphere, air particles spiral-out anticyclonically away from the monsoons, subsiding over the Tropical Atlantic, the Tropical Indian ocean, or transiting into the southern hemisphere across the equator. Whilst marine air particles spiral-in cyclonically towards the WAM or the SAM, the latter appears to be a preferred ending destination in the absence of orography. The Himalayas introduced as a barrier to the monsoonal winds, strengthen the tropospheric winds by tightening the isobars. The Somali mountains (SMs), introduced as a barrier to the Ekman winds, separates the WAM and the SAM catch basins; thus, the Atlantic air particles converge towards the WAM and the Indian ocean particles converge towards the SAM. The Indian Ghats (IGs), introduced as a semi-impermeable barrier to the Ekman winds, deflect the marine air particles originated in the western Indian ocean towards the south-eastern flank of the SAM. In short, an upper single anticyclone encircles both monsoons; the Himalayas strengthen the upper-level winds by increasing the pressure gradients; the SMs split the EFL cyclone, keeping the marine air particles to the west of SMs in the WAM basin and the particles to the east of SMs in the SAM basin; the IGs guides transmit the air particles, deflecting them towards Bangladesh.
Top-down lidar characterization of exceptional dust transport event above the Annecy lake during L-WAIVE in June 2019
Authors: Totems Julien , Chazette Patrick , Baron Alexandre , Dieudonné Elsa
Published: March 2020

The L-Waive campaign took place over the Annecy lake in France in June 2019. In an effort to better understand the atmospheric structure and the water cycle over lakes, it involved an airborne Rayleigh-Mie lidar, ground-based Raman & wind lidars, as well as airborne measurements of water vapor and its isotopes, and aerosol particle size distribution.

This represented a unique opportunity to study the vertical structuring of the troposphere, which is poorly documented in mountainous regions and particularly in the Alpine valleys. Regular radio-soundings are generally not representative of the low atmospheric layers encountered above the valleys, which are influenced by relief winds. Lidar observations in Alpine valleys have been made in the past using Rayleigh-Mie instrumentation, but during L-WAIVE the ground-based Raman lidar WALI also measured the meteorological parameters of water vapour and temperature. The airborne lidar ALIAS carried by an ultra-lght aircraft complemented aerosol measurements, in a coupled top-down inversion approach, highlighting the influence of mountains on different vertical and horizontal scales.

This setup was operational when an exceptional dust transport event overpassed south-eastern France on June 14th, 2019. The origin of this event was shown by HYSPLIT back-trajectories and thermal anomalies computed from SEVIRI as laying in the Grand Erg Occidental, Algeria. An aerosol optical thickness up to 0.8 at 355 nm was measured by the lidar on this occasion, and the instrumental lidar synergy allows to completely characterize the dust plumes in terms of particle extinction, depolarization, relative humidity, and airmass velocities and potential temperature. The dust-perturbated atmosphere will be compared to the background situation where only pollution aerosols are present. The effect of the mountain aerology on the transport will thus be discussed.
Identification of droughts and heatwaves in the Western Mediterranean, variability and impacts on vegetation and wildfires using the coupled ORCHIDEE-WRF regional model
Authors: Guion Antoine , Turquety Solène , Polcher Jan , Pennel Romain , Fita Lluis
Published: March 2020

In line with what is expected in a context of global warming, droughts and heatwaves have increased both in frequency and intensity over the last century. Severe wildfires and vegetation depletion can result from those extreme weather events with considerable economic, social and environmental damages.

For the development of mitigation and adaptation strategies, there is a need for exhaustive vulnerability assessments, including the impacts of droughts and heatwaves on the Mediterranean environment.

If heatwave characteristics are well documented, similar studies about droughts are partial. Most of them are focused on meteorological droughts while agronomical ones are more complex to identify.

 

Using a coupled land surface–atmosphere regional model (ORCHIDEE-WRF) with the integration of plant phenology, we present an analysis of droughts and heatwaves occurring in the Western Mediterranean over the last 40 years. These extreme events are identified using two complementary methods: the Percentile Limit Anomalies (PLA) and the Standardized Precipitation Evapotranspiration Index (SPEI).

Impact assessment analysis show significant and dominant effect of droughts on plant phenology during summer. Evaluated using the Leaf Area Index (LAI), plant depletion can reach more than 50%. Response to drought depends on the vegetation type (long vs short root system) and biome (temperate vs semi-arid).

The impact of these extreme events on fire risk will be presented based on calculations of the wildfire meteorological risk (Fire Weather Index) and an analysis of the fire activity observed by the MODIS satellite instrument. We show that, even if extreme high temperature is the dominant cause, drought contributes to an increase of risk. Simultaneous heatwaves and droughts are the worst environmental conditions. The observed burned area can be ±4 times greater than during non-extreme conditions and the fire duration ±0.25 times longer.
Realistic estimates of floc porosity based on high resolution 3D X-Ray microtomography
Authors: Carr Simon , Lawrence Thomas , Spencer Kate , Manning Andrew , Wheatland Jonathan , Bushby Andrew
Published: March 2020

Suspended particulate matter (SPM) plays a fundamental role in the impact and eventual fate of sediment, pollutants, pathogens, nutrients and manufactured nano-materials in aquatic environments. SPM usually exists in aquatic systems as flocs; complex, fragile and loosely-bound aggregates of fine sediment particles, bacteria, organic matter and fluid-filled pore space. Floc settling velocity is widely considered to be the most important dynamic characteristic that determines SPM fate and transport, and is dependent on the size, shape, density, porosity, fractal dimension and composition of the flocs formed in suspension. Of these characteristics, floc density and porosity are thought to exert the greatest impact on settling velocity, yet neither parameter can currently be measured. As such, transport model parameters are typically estimated from Stokes’ Law, based on an assumption of a spherical shape for the floc. Due to a lack of available observational data, such assumptions cannot be validated and porosity is often omitted with flocs treated as essentially impermeable spherical entities, despite pores accounting for much of the defined ‘floc-space’ (often estimated to be > 90% within larger macro-flocs).

 

As part of a wider project exploring the 3D nature of floc structure and dynamics (NERC-3D Flocs), this study reports a first application of high-resolution 3D X-Ray microtomography on populations of flocs, offering a method that quantifies 3D floc porosity based on observation rather than assumption of floc structural properties. High resolution (3 µm voxel size) scans of both laboratory-generated and natural floc populations, from which sub-populations of different-sized micro- and macro-flocs (30 in each of 5 size categories for each floc population) are extracted. A data-processing workflow is presented which applies 3D morphological filters to systematically define a realistic expression of the total pore-space associated with individual flocs. Floc pore-space is further partitioned into isolated and effective pores, based on a 12 µm pore throat diameter threshold below which fluid flow is hydrodynamically minimal. Analysis of these realistic floc porosity data populations indicates that previous assumptions of floc porosity lack meaning in terms of settling dynamics. Substitution with meaningful, realistic floc porosity will have a significant impact on the prediction of floc settling velocity within SPM sediment transport models. 
Towards understanding heterogeneous ice nucleation on realistic silver iodide surfaces from atomistic simulation
Authors: Reischl Bernhard , Roudsari Golnaz , Turtola Siiri , Pakarinen Olli , Vehkamäki Hanna
Published: March 2020

Small particles of silver iodide (AgI) are known to have excellent ice nucleating capabilities and have been used in rain seeding applications. It is widely believed that the silver terminated (0001) surface of β-AgI acts as a template for the basal plane of hexagonal ice. However, the (0001) surface of ionic crystals with the wurtzite structure is polar and will therefore exhibit reconstructions and defects. Here, we use atomistic molecular dynamics simulations to study how the presence of defects on AgI(0001) affects the rates and mechanism of heterogeneous ice nucleation at moderate supercooling at -10 ºC. We first consider AgI(0001) surfaces exhibiting vacancies, step edges, terraces, and pits, and compare them to simulations of the corresponding ideal surface. We find that, while point defects have no significant effect on ice nucleation rates, step edges, terraces, and pits reduce both the nucleation and growth rates by up to an order of magnitude, which can be understood from the atomistic details extracted from the simulations. The reduction of the ice nucleation rate correlates well with the fraction of the surface area around the defects where perturbations of the hydration layer hinder the formation of a critical ice nucleus. Finally, we consider more realistic AgI(0001) surfaces with 5x5 surface reconstructions that cancel the surface dipole, and report on their ice nucleating abilities.
Implantation of Earth’s atmospheric ions into the nearside and farside lunar soil: implications to geodynamo evolution
Authors: Wei Yong , Zhong Jun , He Fei , zhang Hui
Published: March 2020

Earth’s present dipolar magnetic field extends into the interplanetary space and interacts with the solar wind, forming a magnetosphere filled up with charged particles mostly originating from the Earth’s atmosphere. In the elongated tail of the magnetosphere, the particles were observed to move either Earthward or tailward with different speeds at different locations, even outside the Moon’s orbit. We hypothesize that the lunar soil, on both the nearside and farside, should have been impacted by these particles during the geological history, and the impact was controlled by the size and morphology of the magnetosphere. We predict that the farside soil could also have the features similar to those in the nearside soil, e.g., 15N-enrichment. Furthermore, we may infer the evolution of the magnetosphere and atmosphere by examining the implanted particles in the lunar soil from both sides. This hypothesis could provide an alternative way to study the evolution of Earth’s dynamo and atmosphere.
Multi-decadal variability in long-range ENSO predictions (SEAS5-20C)
Authors: Weisheimer Antje , Balmaseda Magdalena , Stockdale Tim
Published: March 2020

Motivated by the high skill in predicting ENSO on seasonal time scales with ECMWF’s seasonal forecasting system SEAS5 and by previous findings of multi-decadal variability in seasonal forecast skill of extratropical dynamics, we have carried out an extensive set of 24-month long coupled hindcasts from 1901 to 2010. The hindcasts were run with SEAS5 in reduced resolution and are initialised from, and verified against, reanalyses of the 20thCentury. They allow us to analyse ENSO forecast skill beyond the first year, to study how skill varies on decadal time scales and to test sensitivities to atmospheric wind forcings and the assimilation of ocean observations in the initial conditions.

First results show a substantial amount of multi-decadal variability in both ENSO mean state and forecast skill. We find periods in the early-to-mid 20thCentury with much reduced levels of skill, in particular after the spring barrier in the first forecast year. Periods at the beginning and at the end of the Century show broadly similar good performances with substantial skill even after the first year spring barrier. Combined effects of the wind forcing and the assimilation of ocean data on the initial state seem to play a crucial role in understanding this behaviour.
Simulation experiments for studying an optimal carbon dioxide monitoring network for Osaka, Japan
Authors: Hayashida Takayuki , Oda Tomohiro , Machimura Takashi , Matsui Takanori , Kuze Akihiko , Suto Hiroshi , Shiomi Kei , Kataoka Fumie , Fukui Tetsuo , Terao Yukio , Nishihashi Masahide , Murakami Kazutaka , Sasai Takahiro , Saito Makoto , Tanimoto Hiroshi
Published: March 2020

We prototype an Observing System Simulation Experiment (OSSE) system for studying an optimal carbon dioxide (CO2) monitoring network in Osaka city, one of the populated cities in Japan (population: 8.8 million).  In the first phase of our project, we built a multi-resolution, spatially-explicit fossil fuel CO2 emissions model to better quantify CO2 emissions with an updated information and detailed geospatial information.  In the second phase, we coupled the emission model to the WRF Chem model, and developed an OSSE capability to study an optimal CO2 observation network for Osaka.  After completing an evaluation of the meteorological fields and emission fields, we have started simulating atmospheric CO2 concentration using possible emission scenarios and examined the emission change detectability by an imaginary ground-based observation networks.  We started from existing observational sites for air quality monitoring sites and the selected suitable sites based on how much useful signals can be obtained.  In order to fully examine the detectability of CO2 emission changes in the presence of potential strong local and inflow biospheric CO2 contributions, we included biospheric fluxes calculated from the BEAMS model.  We have also attempted to calculate the cost for establishing the observational sites.  Our ultimate goal is to help decision makers to design an effective observation network given their emission reduction target as well as the budget constrain.
Identification and monitoring techniques of TIDs in the H2020 TechTIDE project
Authors: Altadill David , Segarra Antoni , Blanch Estefania , Juan José Miguel , Buresova Dalia , Galkin Ivan , Belehaki Anna , Haralambous Haris , Borries Claudia
Published: March 2020

Traveling Ionospheric Disturbances (TIDs) are wave-like propagating irregularities that alter the electron density environment and play an important role spreading radio signals propagating through the ionosphere.

TechTIDE project, funded by the European Commission Horizon 2020 research and innovation program, is establishing a pre-operational system to issue warnings of the occurrence of TIDs over the region extended from Europe to South Africa based on the reliability of a set of TID detection methodologies.

This contribution aims at presenting the different methods and techniques of identification and tracking the activity of TIDs and their respective performance, that serve to feed the warning system of TechTIDE.
Structural analysis of faults related to the Late Cretaceous and Paleocene evolution of the Central Srednogorie zone, Bulgaria
Authors: Balkanska Eleonora , Georgiev Stoyan
Published: March 2020

The Panagyurishte strip of Central Srednogorie zone, Bulgaria is part of the peri-Tethyan Upper Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic arc belt and it is famous for its rich copper-porphyry and epithermal systems. The magmatic events related to the formation of the known ore systems are dated in the interval of 93–85 Ma and were followed by a period of deposition of carbonate and sandy turbidites during the latest stages of the Cretaceous and Paleocene. The main deformational event of the Central Srednogorie zone occurred after the Maastrichtian due to the closure of the arc basin and affected not only the Upper Cretaceous sequences (including the ore systems) but also the fragments of the Early Alpine edifice.

The present study is focused on the structural analysis of several regional faults that affected the Mesozoic (Triassic and Late Cretaceous) sequences in different parts of the Panagyurishte strip. The study of the post-ore deformations is important to reveal the history and current position of the ore bodies and their host rocks.

Most of the documented faults follow the main NW-SE to W-E orientation of the Panagyurishte strip. They do not represent single discrete fault surfaces but usually are segmented and the fault zones are several tens to hundreds of meters wide, often complicated by the presence of imbricate structures. Some of the faults involve rocks from the crystalline basement but most of the documented structures juxtapose different parts of the Mesozoic sequences. The deformation is brittle in almost all lithological varieties to brittle-ductile in some of the clayey limestones and turbidites at macroscopic view. Both evidence for compressional and dextral strike-slip tectonics are documented as slickenside fibres, geometry of Riedel shears and folds, lithological markers. It is difficult to distinguish them in time as no stratigraphic reference units, overprinting relationships or structural interferences between them are observed. In the different parts of the basin, either compression or strike-slip deformation are dominant. This fact, as well as the echelon configuration of the faults support the idea for their synchronous development in dextral transpressional setting and reactivation in time of the older transtenssional structures that controlled the opening of the Late Cretaceous basin.

 

Acknowledgements. The study is supported by the grant DN 04/9 funded by the National Science Fund, Ministry of Education and Science, Bulgaria.

 
Understanding the distribution of multi-model ensembles
Authors: Christiansen Bo
Published: March 2020

Ensembles of model experiments have become the standard tool both in studies of climate change and in studies of prediction on many different time-scales. When analyzing such ensembles the mean of the ensemble is often interpreted as the best estimate and the spread of the ensemble as an estimate of the uncertainty.  Naively we might argue that the error of the ensemble mean would approach zero as the size of the ensemble increases. However, this argument is based on the assumption that the ensemble is centered around the observations - the truth-plus-error interpretation. A competing assumption - the indistinguishable interpretation -- holds that the observations and the models are all drawn from the same distribution.

The rationale for the truth centered interpretation is that it is the situation that would be expected after calibration of statistical models. However, for multi-model ensembles of climate models there is an increasing amount of evidence pointing towards the indistinguishable interpretation. But why should the indistinguishable interpretation hold for an ensemble that basically is a representation of our incomplete knowledge of the climate system?

Here we analyze CMIP5 ensembles focusing on three measures that separate the two interpretations: the error of the ensemble mean relative to the error of individual models, the decay of the ensemble mean error for increasing ensemble size, and the correlations of the model errors. To get more freedom in our analysis we use a simple statistical model where observations and models are drawn from distributions with different variances and which include a bias. The two interpretations can be found as limits of this more comprehensive model  for which analytical results can be found using the simplifying properties of high dimensional space (the blessing of dimensionality).

We find that the indistinguishable interpretation becomes an increasingly better assumption when the errors are based on smaller and smaller temporal and spatial scales. Building on this, we present a simple conceptual mechanism for the indistinguishable interpretation based on the assumption that the climate models are calibrated or tuned on large scale features such as, e.g., annual means or global averages.
Characteristics and classifications of short-duration heavy precipitation in mesoscale system evolution
Authors: Ke Dan , Wang Xiaokang , Cui Chunguang
Published: March 2020

As the grid resolution continues to increase, it is essential to utilize more data to describe the occurrence and evolution of mesoscale system more precisely. Based on Local Analysis and Prediction System (LAPS), NCEP reanalysis data (FNL) is used as the background field. By improving and developing LAPS, a high spatial-temporal resolution mesoscale data is generated and a sample database is established by fusing a variety of observation data.

Moreover, the synoptic and physical variables that may affect the short- duration heavy precipitation are fully considered when establishing the diagnosis-statistical forecast model. After the calculation, three discriminant formulas of strong and weak precipitation, heavy precipitation classification I and II are obtained.

Furthermore, the grouping accuracy of the discriminant formula and Ts score were calculated, and after the independent sample test and typical case test, it can be concluded that these discriminant formulas can be used to distinguish strong and weak precipitation and heavy precipitation classification.
Chesapeake County Groundwater Problem Hands on Simulation
Authors: Newsome Kenneth
Published: March 2020

Chesapeake County Groundwater Problem

Kenneth C. Newsome Freedom High School Prince William County Virginia

Teaching students the impact of groundwater pollution and its effect on humans

This activity was modified from an activity from the Math Science Center in Richmond, Virginia.  Students construct models using six paper models of a hypothetical situation where a farmer and lighthouse keeper are having well water issues. The students are acting as a hydrogeologist and are consulting the farmer and lighthouse keeper.  This scenario is being played out on the banks of the Chesapeake Bay in Virginia.  The farmer is having trouble with his house well running dry, while his well at his barn is always supplying water.  The lighthouse keeper and his wife are wondering why their water is undrinkable, and their house plants are dying.  The lighthouse keeper claims the farmer is responsible for the undrinkable water.  The outcome is the farmer's house well is dug too shallow, while his barn well is also close to a manure pile and livestock yard.  The lighthouse keeper's well is too close to the saltwater of the Chesapeake Bay, and the intrusion of salt is making the water undrinkable.  This activity has students problem-solving water pollution issues, and this activity has them figure out the root cause of water pollution.  Students are then asked to apply this knowledge to a newly discovered planet with the same water pollution issues.       