bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainty quantification of continuous streamflow monitoring in high elevation Alpine catchments
Authors: Hofmeister Florentin , Rubens Venegas Brenda , Disse Markus , Chiogna Gabriele
Published: March 2020

Correct streamflow measurements are of fundamental importance for hydrology. Mountain catchments are particularly complex systems to obtain reliable discharge time series and several challenges have to be overcome. For example, turbulent flow of mountain streams leads to unstable streambed conditions by erosion and sedimentation and the irregular stream profile makes any streamflow measurements through the velocity-area method difficult. The salt dilution method provides reliable streamflow estimation for specific injection times. We can construct rating curves when these and river stage data are available. However, this relationship entails intrinsic uncertainties that derive from experimental errors as well as from extrapolation outside the measured range. In this work, we provide a rigorous quantification of the uncertainty of discharge measurement based on rating curves using error propagation techniques. During multiple field campaigns in 2019, we collected 74 streamflow measurements for nine sites over three high Alpine catchments (Horlachtal, Kaunertal and Martelltal). We then consider also continuous measurements of water level, water temperature and electrical conductivity. The aim is not only to get more information about the hydrological processes and response of these catchments but also to use this information to construct more robust and less uncertain rating curves. Our results show the high uncertainty affecting measured discharges in Alpine catchments and they are relevant for model applications as well. In fact, the uncertainty in river discharge observations affects the optimal value of the model objective function (e.g., Nash-Sutcliff Efficiency).
Low cost precipitation measurement in remote areas
Authors: Brziak Adam , Valent Peter , Kubáň Martin
Published: March 2020

Accurate measurements of atmospheric precipitation play an important role in solving a large variety of water management problems. The relatively low spatial and temporal resolution of the monitoring network in remote areas puts significant constraints on its use in small-scale studies, where a high spatial and temporal resolution is a must. Until quite recently, the high cost of the commercial devices that have to be deployed to fill in the gaps in space and time domains was very often the main factor restricting the focus of both scientific research and commercial applications on larger scales. The first decades of the 21st century brought about massive advancements in the field of low-cost electronics, sensors, and rapid prototyping techniques. Moreover, a number of open source software solutions came into existence that provides ready-to-use tools to store, analyse and transfer data. This inspired a large community of scientists and makers to build their own prototypes of measuring instruments or dataloggers, often for a fraction of the cost of the commercial devices that comply with their specific needs.

This study presents the process of the development and calibration of a low-cost rain gauge for measuring atmospheric precipitation. The prototype was designed as a two-chamber tipping-bucket rain gauge built around the Arduino open-source electronics platform. The advent of 3D printing enabled the rapid prototyping of the mechanical parts of the rain gauge, which are made of a durable ABS thermoplastic material. The study also presents the process of rain gauge calibration, with both volumetric and dynamic calibration procedures used. The rain gauge was set at a resolution of 0.5 mm with a standard deviation of  ±0.01 mm. The results of the dynamic calibration also showed that the behaviour of the rain gauge complies with that of the commercial devices.

The low cost and precision of this type of instrumentation make it ideal for applications in which there is a high risk of its being damaged or even lost. In addition, the open-source aspect of the project, its low-cost, and the relatively minor requirements for its construction make it a good candidate for use in citizen-science partnerships, which are becoming very popular, mainly due to their popularization benefits.             
Seasonal prediction of mountain snow resources: an application in the Alps
Authors: Terzago Silvia , Calì Quaglia Filippo , Bongiovanni Giulio , Palazzi Elisa , von Hardenberg Jost
Published: March 2020

The development of seasonal projections of the state of snow resources in the Alps is of particular interest for the management of water resources and tourism. We present the progress in the development of a modelling chain based on the seasonal forecast variables produced by seasonal prediction systems of the Copernicus Climate Change Service (C3S).

Seasonal forecast variables of precipitation, near-surface air temperature, radiative fluxes, wind and humidity are downscaled at three selected instrumented sites, close to five Alpine glaciers, in the North-Western Italian Alps, eventually bias-corrected and finally used as input for a physically-based multi-layer snowpack model (Snowpack; Lehning et al. 2012). A stochastic downscaling procedure is used for precipitation data in order to allow an estimate of uncertainties linked to small-scale variability in the forcing.

We evaluate uncertainties affecting the skill of the modelling chain in predicting the evolution of the winter snowpack in hindcast simulations, comparing against historical data of snow depth and snow water equivalent by automatic stations in the study areas.

The chain is tested considering seasonal forecast starting dates of November 1st, which are relevant for the snowpack processes. The sensitivity of the snow model to the accuracy of the input variables is discussed.
A multidisciplinary approach to investigate the geomorphological evolution induced by landslides in the piedmont and coastal sectors of Abruzzo region (Central Italy)
Authors: Calista Monia , Menna Valeria , Miccadei Enrico , Sciarra Nicola
Published: March 2020

According to their structural-geomorphological features, different types of landslides, with variable areal extension, largely affect the Abruzzo region (Central Italy) from the mountains to the coastal areas, contributing to the geomorphological evolution of the landscape.

In this work, we present the results of integrated investigations carried out in recent years in the Abruzzo piedmont and the coastal areas. In detail, we investigated the role of the morphostructural setting, seismic and meteorological factors in the development of piedmont landslides, and the geomorphological evolution, erosion and retreat processes widespread along clastic soft rock coasts of the region.

We investigated Ponzano landslide (Civitella del Tronto, Teramo), a large translational slide-complex landslide, affecting the Miocene–Pliocene pelitic-arenaceous bedrock, and the Castelnuovo landslide (Campli, Teramo) a complex (topple/fall-slide) landslide, which involved conglomerate rocks pertaining to terraced alluvial fan deposits of the Pleistocene superficial deposits. Both these landslides occurred in the NE Abruzzo hilly piedmont in February 2017, causing severe damage and evacuees. Regarding the coastal area, we analyzed rockfalls, topples and translational landslides which characterize the active cliffs of Torre Mucchia, Punta Lunga, Punta Ferruccio (Ortona, CH) and Punta Aderci (Vasto, CH), composed of clayey-sandy-arenaceous-conglomeratic marine sequence (Early-Middle Pleistocene) covered by continental deposits (Late Pleistocene-Holocene). These coastal areas are popular tourist destinations, included in natural reserve areas with high tourism, natural and cultural landscape value.

Through this multidisciplinary approach, the lithological, geomorphological and structural-jointing features were estimated. Focusing on their role on the stability, processes and dynamics affecting Abruzzo piedmont and coastal sectors, it was possible to analyze the triggering factors, the landslide mechanisms and types, as well as the most critical and/or failure areas.

The obtained results outline how field and remote investigations combined with FLAC3D numerical modeling provide an effective approach in the analysis of landslides, strongly improving the identification and prediction of landscape changes and supporting a new geomorphological hazards assessment.
The Atlantic Overturning Circulation: At its Weakest in a Millennium?
Authors: Rahmstorf Stefan , Caesar Levke
Published: March 2020

The Atlantic Meridional Overturning Circulation (AMOC) is a major mechanism for northward heat transport on our planet and the prime reason why the Northern Hemisphere is warmer than the Southern Hemisphere (Feulner et al. 2013). The AMOC is a sensitive non-linear system dependent on subtle thermohaline density differences in ocean water, and major AMOC transitions have been implicated e.g. in millennial climate events during the last glacial (Rahmstorf 2002).

There is evidence that the AMOC is slowing down in response to modern global warming, as predicted by climate models (Caesar et al. 2018). We will review and compile proxy evidence for AMOC changes during the past 1-2 millennia, including e.g. Sherwood et al. 2011, Thibodeau et al. 2018, Thornalley et al. 2018, Rahmstorf et al. 2015, Zanna et al. 2019. We conclude that there now is substantial and consistent evidence from multiple independent sources for a modern AMOC slowdown that is unprecedented in at least a millennium.

References

Caesar, L., S. Rahmstorf, A. Robinson, G. Feulner, and V. Saba. 2018. Nature, 556: 191-96.

Feulner, G, S Rahmstorf, A Levermann, and S Volkwardt. 2013. Journal of Climate, 26: 7136-50.

Rahmstorf, S. 2002. Nature, 419: 207-14.

Rahmstorf, S., Jason E. Box, Georg Feulner, Michael E. Mann, Alexander Robinson, Scott Rutherford, and Erik J. Schaffernicht. 2015. Nature Climate Change, 5: 475-80.

Sherwood, O. A., M. F. Lehmann, C. J. Schubert, D. B. Scott, and M. D. McCarthy. 2011. Proc Natl Acad Sci U S A, 108: 1011-5.

Thibodeau, Benoit, Christelle Not, Jiang Hu, Andreas Schmittner, David Noone, Clay Tabor, Jiaxu Zhang, and Zhengyu Liu. 2018. Geophysical Research Letters, 45: 12,376-12,85.

Thornalley, D. J. R., D. W. Oppo, P. Ortega, J. I. Robson, C. M. Brierley, R. Davis, I. R. Hall, P. Moffa-Sanchez, N. L. Rose, P. T. Spooner, I. Yashayaev, and L. D. Keigwin. 2018. Nature, 556: 227-30.

Zanna, L., S. Khatiwala, J. M. Gregory, J. Ison, and P. Heimbach. 2019. Proc Natl Acad Sci U S A, 116: 1126-31.
Determination of stress condition and friction coefficient from orientation distribution of outcrop-scale faults
Authors: Sato Katsushi
Published: March 2020

  Friction coefficients along faults control the brittle strength of the earth's upper crust, although it is difficult to estimate them especially of ancient geological faults. This study proposes to estimate the friction coefficient of faults with stress condition which activated them by the following procedure. Stress tensor inversion using fault-slip data can calculate principal stress axes and a stress ratio, which allows us to draw a normalized Mohr’s circle. Assuming that faulting occurs when the ratio of shear stress to normal stress on the fault (the slip tendency) exceeds the friction coefficient, a linear boundary of distribution of points corresponding to the observed population of faults should be found on the Mohr diagram. The slope of the boundary (friction envelope) provides the friction coefficient. Since this method has a difficulty in the graphical recognition of the linear boundary, this study automated it by considering the fluctuations of fluid pressure and differential stress. The fluctuations yield a density distribution of points representing faults on the Mohr diagram according to the friction coefficient. Then we can find the optimal value of friction coefficient so as to explain the density distribution.

  The method was applied to some examples of natural outcrop-scale faults. The first example is from the Pleistocene Kazusa Group, central Japan, which filled a forearc basin of the Sagami Trough. Stress inversion analysis showed WNW-ENE trending tensional stress with a low stress ratio. The friction coefficient was calculated to be about 0.7, which is typical value for sandstone.

  Another example is from an underplated tectonic mélange in the Cretaceous to Paleogene Shimanto accretionary complex in southwest Japan along the Nankai Trough. The stress condition was determined to be an axial compression perpendicular to the foliation of shale matrix. The friction coefficient ranges from 0.1 to 0.3, which is extremely low indicating a weak plate boundary under the accretionary wedge.
Stable isotopes evidencing microbial activity, mineral authigenesis and fluid mixing in deep interstitial fluids off South-Western Australia (IODP Leg 369)
Authors: Böttcher Michael Ernst , Brumsack Hans-Jürgen , Schmiedinger Iris , Quan Tracy
Published: March 2020

Interstitial waters extracted from long sediment cores retrieved during expedition 369 (Sites U1512-U1516) of the International Ocean Drilling Program (IODP) were analysed for the stable water isotopic (O and H isotopes) composition to constrain hydrographic changes in this region prior to modern time and possible changes due to water-rock interaction and fluid mixing. Dissolved sulfate (S and O isotopes), and sulfide (S isotopes) were analyzed to characterize, in concert with concentration measurements, diagenetic microbial and water-rock interaction processes in the sulfur cycles. The measurements demonstrate substantial downcore variations in the water oxygen isotope composition. Net microbial sulfate reduction with depth was observed at all sites, but sulfate was only found to be consumed completely, within the investigated core lengths at Site U1512, that is located off southern Australia. Whereas associated sulfur isotope fractionation is characteristic for medium range fractionation factors, the oxygen isotope composition provides evidence for a much more complex story of sulfur diagenesis at the investigated sites: At Site U1516, for instance, the oxygen isotope composition of dissolved sulfate is equilibrated with pore water, although sulfate concentrations remain above 20 mM. This indicates an intense re-oxidative sulfur cycle. At Site U1513, on the other hand, the oxygen isotope composition remains out of isotope exchange equilibrium although sulfate concentrations fall below 20 mM, indicating that the net decrease in dissolved sulfate is dominantly caused by authigenic gypsum precipitation at depth, which is further confirmed by the dissolved Ca concentration.

 
Estimation of the total wet sulfur and nitrogen deposition as a part of pollution balance in the south of the Russian Far East based on the monitoring data
Authors: Gromov Sergey A. , Galushin Dmitry A. , Zhadanovskaya Ekaterina A.
Published: March 2020

One of the main goals in the regional biogeochemical research of East Asia is to evaluate the state of acid deposition and the related pollution within EANET region (EANET, 2019). In the south of the Russian Far East there are two networks developed to monitor the content of acidic substances in atmospheric fall-out. The first one is the Russian national precipitation chemistry stations operated for more than 30 years, and the second is the international atmospheric monitoring sites supervised by EANET and WMO-GAW (Yearbook, 2019). We calculate the total deposition of airborne sulfur and nitrogen in a large region to evaluate their atmospheric balances under the transboundary influence. The present study focuses on the development and application of the spatial interpolation method to estimate wet deposition fluxes based on the monitoring data for 2013-2018. On the first step of the algorithm, we analyze the correlation of pollution monitoring results between network stations and estimate the maximum radius of representativeness for each station. On the second step, we interpolate the precipitation chemistry data for the set of meteorological stations located in the region under the study and calculate the wet deposition fluxes of sulfur and nitrogen for these sites. The flux values obtained are further interpolated for the regular grid of 10-km by 10-km cells within the region under the study. Finally, the total wet sulfur and nitrogen deposition for the region is a sum of deposition fluxes calculated for each cell. Additionally, we compared the data obtained with the correspondent flux calculated on the basis of the national snow cover chemistry network for the same region and period.

References

EANET. Fourth Report for Policy Makers (RPM4): Towards Clean Air for Sustainable Future in East Asia through Collaborative Activities. 2019. 50 p.

Yearbook. State and pollution of the environment in the Russian Federation: 2018. Moscow: RosHydroMet, 2019. 227 p. [in Russian]
Trial of continuous measurement of micro-nano bubbles in water
Authors: Aoki Shinsuke , Tamaki Masahiko , Noborio Kosuke
Published: March 2020

Micro-nano-bubbles (MNBs) are tiny bubbles with diameters ranging from tens of nanometers to several tens of micrometers. Owing to their small diameter, MNBs have some characteristics. Compared with normal bubbles, MNBs have lower rising velocity and persist for long periods in the liquid phase. MNBs technology is proposed to use for various areas such as groundwater remediation, aquaculture, mass transfer. Although MNB generation methods and applied to problems are attracted, the continuous in-situ measurement technique has not researched well. An easy, continuous, and inexpensive method is desired for more efficiently using MNBs. In previous research, the dielectric constant of MNBs water was different from that of water. Therefore we hypothesized that continuous measurement of dielectric constant could be used to estimate MNBs in the water. The purpose of this study is to investigate the attempt to continuous measurement for MNBs. To measure dielectric constant, we used time domain reflectometry (TDR). A TDR probe (0.15 m long) was used with a cable tester (Model 1502C, Tektronix Inc.) in this study. We also used GS3 sensor (METER Group, Inc.) for water temperature measurement because the dielectric constant changed with temperature. Dielectric constant and water temperature were measured every 1 min during before and after MNBs generation. We conducted experiments with several MNBs generators. Measured dielectric constant changed before and after MNBs generation. Although estimated dielectric constant from water temperature differed from measured dielectric constant, both agreed about half day. It was suggested that simultaneous measurement of temperature and dielectric constant can estimate the amount of MNB in water.
Surface and deep deformation of the great Alpine region from GNSS and seismic anisotropy measurements
Authors: Salimbeni Simone , Serpelloni Enrico , Pondrelli Silvia
Published: March 2020

The comparison of crustal and mantle shear directions can provide insights into the extent of crustal-mantle coupling and the dynamics guiding surface movements and active tectonics in continental deformation zones. Here we present a first attempt of comparing surface deformation from GNSS and deep deformation from seismic anisotropy observations for the Great Alpine Area, mainly through France, Switzerland, Italy, Germany and Slovenia. The developments of the European GNSS infrastructure, integrating public and private GNSS networks, allow now to precisely determining crustal deformation over the Alps. We present a new 3D surface velocity field obtained from a recent re-analysis of 22 years of GPS data obtained from >800 continuous GNSS stations operating across the Alps and its surroundings. Unlike the crust, the orientation of the strain field within the mantle cannot be directly measured and must be inferred from either mantle earthquakes or seismic observations, such as seismic anisotropy observations. We compiled a new map of SKS directions merging data collected during several experiments and available from different databases, deriving a new continuous mantle deformation pattern over the Great Alpine Region. Geodetically determined displacements of the Earth’s surface reflect the response to different processes acting at different spatial scales. In the comparison between crustal and mantle deformation we accounted for the intrinsic multi-scale characteristics of geodetic deformation measurements, estimating the geodetic strain-rate field using a multi-scale spherical wavelet-based method, where the velocity value at a given point of the Earth’s surface is obtained as a superposition of values obtained at different spatial scales. From the geodetic strain-rate tensors we computed the two planes of shear (or no-length-changes) directions, which are compared with the directions of SKS splitting over the study region.
Geomagnetic Virtual Observatories: Global monitoring of geomagnetic secular variation with Swarm data
Authors: Hammer Magnus , Finlay Christopher , Beggan Ciaran , Brown William , Cox Grace
Published: March 2020

The ESA Swarm DISC Geomagnetic Virtual Observatories (GVO) project aims to apply the virtual observatory concept to Swarm magnetic field measurements. The Virtual Observatory concept is a data processing method which mimics the behavior of magnetic monthly-mean time-series measured at ground observatories but at fixed locations on a uniform global grid at satellite altitude instead. Here we present several new GVO data products consisting of the average time-series of vector magnetic field values, regularly distributed in space and time which are suitable for monitoring the geomagnetic field. The GVO products consist of an equal-area grid with separation spacing of 300 km and cadence of either 1 month or 4 months. Various levels of processing are applied to remove the effects of altitude change and satellite local-time differences to produce a consistent time series. It is known that monthly time-series can have strong local-time artifacts which are removed with four-monthly averages, though with a loss of temporal resolution. The GVO products are designed to make Swarm magnetic data more accessible to researchers studying the physics of the core dynamo process, and related phenomenon such are secular variation, geomagnetic jerks and rapid core dynamics. In addition, the GVO data products also provide valuable information for investigating magnetospheric and ionospheric magnetic signals on timescales of months and longer.
Investigating the contribution of polarimetry in retrieving ice microphysical properties using Dual-Wavelength radar observations
Authors: Tetoni Eleni , Ewald Florian , Möller Gregor , Hagen Martin , Zinner Tobias , Knote Christoph , Mayer Bernhard , Li Qiang , Groß Silke
Published: March 2020

Many studies have shown that multi-wavelength radar measurements can be valuable in inferring information about the size of observed hydrometeors in the atmosphere. Dual-wavelength radar method is widely known in such retrievals as it takes advantage of the different scattering behavior of hydrometeors in Rayleigh and MIE regime. Hydrometeors with sizes much smaller than the radar wavelength, act like Rayleigh scatterers and their radar reflectivity Z is proportional to the sixth power of their size. While these particles become larger due to riming or aggregation processes, with sizes comparable or larger than the radar wavelength, MIE effects can occur and thus, Z is proportional to the second power of their size. In the framework of IcePolCKa (Investigation of the initiation of Convection and the Evolution of Precipitation using simulatiOns and poLarimetric radar observations at C- and Ka-band) project, the evolution of ice in the precipitation formation will be studied exploiting these differences in both scattering regimes. Except for the logarithmic radar reflectivity difference, known as Dual-Wavelength Ratio (DWR) or Dual-Frequency Ratio (DFR), between C-band POLDIRAD weather radar from German Aerospace Center (DLR) in Oberpfaffenhofen and the Ka-band MIRA-35 cloud radar from Ludwig Maximilian University of Munich (LMU), other measured polarimetric variables from both radars, i.e. Differential Reflectivity (ZDR), Reflectivity Difference (ZDP), Linear Depolarization Ratio (LDR) will be also used. In addition to observations, scattering algorithms, i.e. T-matrix, will provide scattering simulations for a variety of ice particles shapes, sizes and mass-size relations. Combining DWR, polarimetric measurements and simulations the shape and/or the density of the observed ice particles will be retrieved. In this presentation, we will describe the instrumentation setup as well as the measuring methods in detail. Furthermore, we will present preliminary results of the retrieval approach using T-matrix calculations and measurements. Our first dataset consist of observations during snow events over Munich in January 2019 in order to avoid strong attenuation effects in the Ka-band.
Investigation Of Pre-Earthquake Ionospheric Anomalies Before Albania 2019 Earthquake Using The Romanian Receivers Of The Vlf/Lf Infrep And Gnss Global European Networks
Authors: Moldovan Iren Adelina , Toader Victorin Emilian , Oikonomou Christina , Haralambous Haris , Biagi Pier Francesco , Muntean Alexandra , Mihai Andrei , Khadka Aakriti
Published: March 2020

The last two decades a significant effort has been invested in order to understand and interpret the link between seismic activity and ionospheric perturbations. Since not any individual seismo-ionospheric precursor can be used as an accurate stand alone for earthquake prediction it is required to integrate different kinds of precursors and analysis techniques.

To this context, the aim of this study is to investigate pre-earthquake ionospheric anomalies that occurred prior to large 6.4 Mw earthquake in Albania (26th November 2019), following a multi-instrument and multi-technique approach, using subionospheric radio VLF/LF signals obtained from the Romanian receivers of the INFREP European network and Total Electron Content (TEC) observations from GNSS global network.

To identify possible ionospheric anomalies before the earthquakes we applied the terminator time and nighttime fluctuation methods on the amplitude of subionospheric LF radio signals and spectral analysis on diurnal TEC variations several days prior the seismic event. It was found that sunrise terminator times are delayed approximately 20-40 min few days before and during the earthquake day. Intensified wave-like TEC oscillations with periods around 20 min were also revealed up to 5 days prior to the earthquake shocks in all cases that could be interpreted as possible ionospheric precursors of the impending earthquakes.      
Impact of Atmospheric Circulation on Flooding Occurrence and Type in Luxembourg (Central Western Europe)
Authors: Meyer Judith , Douinot Audrey , Zehe Erwin , Tamez-Meléndez Carol , Francis Olivier , Pfister Laurent
Published: March 2020

In the second half of the 20th century, hydrological regimes in central Western Europe were largely characterised by large-scale winter floods. This type of event was predominantly triggered by westerly atmospheric fluxes, bringing moist and mild air masses from the Atlantic Ocean to the European continent. Since the late 1990’s, major flooding events seem to have shifted in time and magnitude. Flash flood events, while being a well-known phenomenon in Mediterranean catchments, are increasingly also reported at higher latitudes. Unlike the large-scale winter flood events, flash floods are of very narrow spatial extension and triggered by rather short, but highly intense rainfall events.

Here, we focus on the specific case of rivers in Luxembourg that have experienced several flash flood events in recent years, while only small to moderate winter flood events have been reported since the late 1990’s. National hydro-meteorological monitoring and flood forecasting systems have been designed for large-scale floods and are not suited for simulating local flash flood events. Therefore, there is a need to increase our understanding of the hydro-meteorological processes underlying flash flood occurrences in our area of interest.

While increasing air temperature is known to allow a higher air moisture content that can lead to more intense rainfall events and possible flooding, we moreover hypothesize that the recent increase in flash flood occurrences in Luxembourg is reinforced by a change in atmospheric circulation patterns. To test this hypothesis, we analyse the prevailing atmospheric patterns on rainy days during summer and winter months over the period 1954 - 2019, with a particular focus on rainfall events that lead to moderate and extreme floods. In a next step, we intend to extend our findings for Luxembourg in a larger European context. This analysis should allow to better assess the current situation of hydrological extreme events in central Western Europe in order to take precaution measures and prepare for a diversifying hazard.
Atmospheric CO2 during the Late Miocene Cooling
Authors: Tanner Thomas , Guitián José , Hernández-Almeida Iván , Stoll Heather
Published: March 2020

Alkenone sea surface temperature records recently observed suggest a substantial long-term and large-magnitude ocean surface cooling during the Late Miocene. At the same time, starting about seven million years ago, both hemispheres on Earth witnessed synchronous cooling and large areas of the continents experienced drying and enhanced seasonality. Coinciding with this climatic shift were significant changes in ecology, including the rise of C4-photosynthesizing terrestrial plants and the emergence of so-called "vital effects" in oceanic coccolithophores. These changes are collectively hypothesized to be induced by declining atmospheric CO2. However, the sparse proxy data available for this time interval limits our understanding of the link between these changes and atmospheric greenhouse gas fluctuations and has let people to propose a "climate-CO2 decoupling".
In this study, the alkenone based pCO2 proxy is used to reconstruct atmospheric CO2 for the time interval between 4.5 and 8.5 Ma. Estimations are based on the carbon isotopic fractionation during photosynthesis (εp) and a new statistical multilinear regression model based on an analysis of culture and sediment data. Past coccolithophore growth rates are reconstructed using foraminiferal isotopic-based proxies, related to water column structure which favour or limit nutrient supply to the photic zone. A thorough sensitivity analysis of modern and past  εp values and its influencing factors in the Southern Ocean yield to a new, high resolution pCO2 record. Estimated pCO2 concentrations synchronously decline with the observed long-term cooling (5°C) from 6.8 to 5.9 Ma, periodically decreasing to sufficiently low values of <200 ppm, potentially inducing ephemeral Northern Hemisphere glaciation. CO2 concentrations during the Late Miocene Cooling Event are thus successfully reproduced in this study and allow a reasonable interpretation of past conditions as has not yet been previously achieved in the relevant literature. 
Modelling the flooded area extent at the downstream segment of a small basin through a coupled 1D/2D hydraulic model
Authors: Sarchani Sofia , Tsanis Ioannis
Published: March 2020

A high-resolution Digital Terrain Model 5m x 5m, land use characteristics and a validated output hydrograph from an extreme rainfall event were used as input to the coupled 1D/2D HEC-RAS hydraulic model in order to obtain the flooded area extent at the downstream segment of a small basin in the island of Crete. A spatially varying Manning’s roughness coefficient n was used to identify the differences between land coverage for the channel bed and the floodplain. Lateral structures were designed along the left and right overbanks of the stream, connecting the 1D stream flow with the 2D flow areas. The weir coefficient, used to convey the flow above the lateral structures, was also chosen for model validation in the control cross section. Detailed flood hazard mapping at the peak discharge was produced, along with the flood depths at times before and after the heavy precipitation event, in order to obtain the time evolution of the flooded area extent. The results obtained by the 1D hydraulic model are limited in their 2D lateral output that is crucial to the floodplain extent. The 1D/2D provides more detailed output concerning the flood extent at the peak discharge, as well as the maximum water depths and velocities at every grid point of the computed mesh. Defining accurate flood inundated areas is of utmost importance in civil protection agencies in order to initiate a proper early flood warning. At the same time, each EU Member State country is required to produce flood hazard maps according to EU Floods Directive at the river basin level. These 1D/2D simulation results can be beneficial in the aforementioned requirements for low probability extreme floods’ basin management.
A meshfree model for tsunami wave propagation
Authors: Zhou Zili , Lynett Patrick
Published: March 2020

The nonlinear deformation and run-up of tsunami waves on a plane beach and in a constant depth section are studied numerically and analytically based on a Meshfree Shallow Water Model. Because of the strong nonlinearity on the boundary of the propagation, issues like mesh distortion and discontinuous oscillation easily happen in the traditional mesh-based methods (e.g., FVM, FDM). But in the meshfree method, the drastic nonlinear changes can be well approximated by the high spectrum.

The study region is a rectangle, and the boundary condition is homogeneous, so the model meets the spectral expansion condition. And then, the trigonometric functions of a high order and high frequency can be used to solve mesh distortion and discontinuous oscillation problems. This means that the waves are simulated by multiple overlaid wavelets, making the simulation more similar to actual scenarios. The wave height (H) and horizontal wave speeds (U, V) are described by different trigonometrical series combinations.

Analytical methods including Fourier series expansion are used in the spatial dimension. After the expansion, we have the nonlinear partial differential equations with unknown coefficients, and they are functions of time. The Finite Difference Method is used in the time dimension. We choose the semi-implicit scheme to discretize the equations. This scheme saves much time since the model does not need to calculate the inversion matrix in every time step. Without this time-consuming task, compared to traditional mesh-based methods, the meshfree method can do less work, and the result will still be better, because the meshfree method (spectral method) can still be stable with a relatively big time step, while big time steps can cause inaccurate results in traditional mesh-based methods. Also, even though the numerical method is applied in the time dimension, time is only one dimensional, which makes the results not far away from the exact solutions. Since the series (or kernel, or basis) used to describe H, U, V is the orthogonal set. And All orthogonal sets remain continuous and smooth even when they oscillate strongly at a higher order. In this way, the leading causes of the drastic change problem are reduced to: 1. the calculation error, which means we need to try different integrations and find the optimal one; 2. the time step size is not small enough, which leads to more partial analysis on the boundary.
Taking up the challenge of identifying active faults for seismic hazard assessment of the city of Ulaanbaatar (Mongolia)
Authors: Al Ashkar Abeer , Schlupp Antoine , Ferry Matthieu , Ulziibat Munkhuu
Published: March 2020

Ulaanbaatar, capital city of Mongolia (1.5 M inhabitants, i.e. half of the country’s population), is located in Central Mongolia where seismic activity and deformation rates are low (< 1mm/yr.). In contrast, Western Mongolia has experienced four great earthquakes (M ≥ 8) between 1905 and 1957 as well as numerous moderate ones. Some (e.g. the 1957 Bogd earthquake) have been felt at the capital located more than 500 km away. During the last decades, several active faults, located 10 km to 45 km away from Ulaanbaatar, have been discovered and studied. Tectonic Geomorphology and Paleoseismology studies indicate that these faults are able to generate earthquakes of M ≥ 6 with average recurrence times ranging from 1 kyr to 10 kyr (e.g. 1195 ± 157 yr for the Sharkhai fault). Furthermore, since 2005 very dense microseismicity swarms located 10 km NW of the City have been monitored by the Seismic Observatory of Mongolia (IAG). Further studies showed the swarms are produced by the previously undetected Emeelt fault zone along three parallel branches. Due to their proximity to a key population and economic center, all these active structures contribute significantly to increasing Seismic Hazard. During the course of these studies, we documented Quaternary activity along several supplementary faults, which demonstrates that the knowledge of active faults in the region is still incomplete and suggests seismic hazard levels should be revised. Therefore, we undertook to map, as exhaustively as possible, all active tectonic structures in a radius of 300 km around Ulaanbaatar. Here we present preliminary results based on the combined analysis of multi-source and multi-sensor data from satellite images (e.g. Pleiades, Sentinel-2, Landsat8), UAV photographs, and digital elevation models (TanDEM-X and UAV photogrammetric DEMs) in order to extract the most relevant information at various scales. We performed a detailed Tectonic Geomorphology analysis of alluvial and slope landforms to identify recent deformation affecting stream channels and associated deposits (ponds, fans and terraces). On that basis, we document segmentation, deformation patterns and kinematics, as well as relationships between faults at regional scale. Finally, we identify potential sites for future paleoseismic investigations along the main structures. Though this project is in a preliminary stage, our long-term goal is to build a comprehensive database of sources of seismic hazard to the City of Ulaanbaatar and integrate these results into seismic hazard calculations.
How resolving are teleseismic forward and backscattered P to S converted waves?
Authors: Gesret Alexandrine
Published: March 2020

The Receiver Function (RF) technique, that aims to isolate P to S teleseismic converted waves, is largely used to image seismic discontinuities at depth. In particular, in subduction zones, the subducting crust has often be identified on RF as a Low Velocity Layer (LVL) embedded between the mantle of the overriding plate and the mantle of the subducting lithosphere. In several subduction zones, a high Vp/Vs ratio inside this LVL has been estimated from the arrival times of the primary and backscattered P to S converted waves at the top and at the base of the LVL. However seismograms are filtered to enhance the signal over noise ratio and this processing step can dramatically reduce the resolution of the converted waves. In order to check if the signal periods associated to common filters could lead to an overestimation of the Vp/Vs ratio, a wavelet response in conversion for primary and backscattered converted waves is developed for a LVL typical of an oceanic crust. This multiscale analysis allows to illustrate that the LVL characteristics can be misinterpreted for the common frequency range due to interferences between the converted waves at the top and at the base of the LVL. For a dominant period of about 3s, the Vp/Vs of a typical oceanic crust can be largely overestimated (about Vp/Vs=2.8 instead of Vp/Vs=1.8) and its thickness underestimated (about 5 km instead of 7 km). The characteristics of a typical oceanic crust can be reliably retrieved only in the non interaction domain that corresponds to a constant spacing between the converted waves at the top and at the base of the LVL. This non-interaction domain corresponds to dominant signal period smaller than 1 s for the primary converted waves and 3 s for the backscattered. As the Vp/Vs is generally estimated based on the interpretation of both primary and backscattered waves, the period of 1 s is required for a reliable interpretation. The multiscale approach is applied to a real data example of teleseismic events recorded at a 3-component seismometer in order to reliably constrain the Vp/Vs ratio and the thickness of the oceanic crust at the top of the Hellenic subduction.
Development of Long-Term Satellite-Based Snow Mass Records in the ESA Snow CCI Project
Authors: Luojus Kari , Takala Matias , Pulliainen Jouni , Lemmetyinen Juha , Moisander Mikko , Venäläinen Pinja , Derksen Chris , Mortimer Colleen , Nagler Thomas , Schwaizer Gabriele
Published: March 2020

Reliable information on snow cover across the Northern Hemisphere and Arctic and sub-Arctic regions is needed for climate monitoring, for understanding the Arctic climate system, and for the evaluation of the role of snow cover and its feedback in climate models. In addition to being of significant interest for climatological investigations, reliable information on snow cover is of high value for the purpose of hydrological forecasting and numerical weather prediction. Terrestrial snow covers up to 50 million km² of the Northern Hemisphere in winter and is characterized by high spatial and temporal variability making satellite observations the only means for providing timely and complete observations of the global snow cover. The ESA Snow CCI project was initiated in 2018 to improve methodologies for snow cover extent (SE) and snow water equivalent (SWE) retrieval [1] using satellite data and construct long term data records of terrestrial snow cover for climate research purposes.

The first new long term SWE data record from the ESA Snow CCI project, spanning 1979 to 2018 has been constructed and assessed in terms of retrieval performance, homogeneity and temporal stability. The initial results show that the new SWE dataset is more robust, more accurate and more consistent over the 40-year time series, compared to the earlier ESA GlobSnow SWE v1.0 and v2.0 data records [1].

The improved SWE retrieval methodology incorporates a new emission model (within the retrieval scheme), an improved synoptic weather station snow depth data record (applied to support SWE retrieval), extension of the SWE retrieval to cover the whole Northern Hemisphere.

The new Snow CCI SWE data record has been used to assess changes in the long term hemispherical snow conditions and climatological trends in Northern Hemisphere, Eurasia and North America. The general finding is that the peak hemispherical snow mass during the satellite era has not yet decreased significantly but has remained relatively stable, with changes to lower and higher SWE conditions in different geographical regions.

 

References:

[1] Takala, M, K. Luojus, J. Pulliainen, C. Derksen, J. Lemmetyinen, J.-P. Kärnä, J. Koskinen, B. Bojkov. 2011. Estimating northern hemisphere snow water equivalent for climate research through assimilation of space-borne radiometer data and ground-based measurements. Remote Sensing of Environment, 115, 12, 3517-3529, doi:10.1016/j.rse.2011.08.014.
Hidden earthquakes unveil the dynamic evolution of a large-scale explosive eruption
Authors: Garza-Giron Ricardo , Brodsky Emily , Spica Zack , Haney Matt
Published: March 2020

Volcanic eruptions progress by co-evolving the fluid and solid systems. The fluid mechanics can be observed through the evolution of plumes and ejecta. How does the solid evolve? When does the conduit open? When does it close? Seismology can potentially tell us about these processes by measuring the failure of the solid rock. However, such inferences require detection of earthquakes during an explosive eruption. Standard earthquake detection methods often fail during this time as the eruption itself produces seismic noise that obscures the earthquakes. In this work, we address this problem by applying both a supervised and unsupervised search techniques to the existing catalog of the 2008 Okmok Caldera eruption to find brittle failure signals during the continuous eruptive sequence. We were able to detect >4500 new earthquakes using the 419 events previously located by the Alaska Volcano Observatory (AVO). A spatiotemporal analysis of the occurrence of earthquakes during the eruption reveal interesting observations: Seismic bursts during the eruption are not synchronized with the exhalation of large ash and steam plumes, suggesting that the dynamics of the eruption are controlled by a clog-and-crack mechanism; most of the Caldera co-eruptive seismicity that is not located at the focus of the eruption occurs under the intra-Caldera cones, showing the activation of their hydrological system due to a system-wide pressurization; the end of the eruption is marked by a large burst of small, deep earthquakes trending SW-NE, possibly related to a propagating lateral dike similar to those observed in other basaltic calderas; the magnitude distribution of seismicity through time shows that the largest earthquakes in the bursts do not happen at the beginning of the sequence like in typical mainshock-aftershock sequences. Furthermore, high precision earthquake relocations highlight a ring-fault structure inside of Okmok Caldera which is thought to be acting as the pathway for fluids to the surface.
Heat transfer through the nappes of the Lepontine Dome
Authors: Tagliaferri Alessia , Schenker Filippo Luca , Schmalholz Stefan Markus , Seno Silvio
Published: March 2020

The heat transfer through the nappes of the Lepontine Dome (Central Alps, Ticino, Switzerland) produced metamorphic amphibolite-facies isogrades that locally dissect the tectonic contacts. This large-scale observation, suggesting a thermal amphibolite-facies event after thrusting and nappe formation, is however at odd with the extremely pervasive mineral and stretching lineation (NW-SE directed) that attests non-coaxial deformation during shearing at similar metamorphic conditions.

To solve this apparent paradox we performed 2D thermo-kinematic simulations in which we investigated the relationships between nappe geometry and the geometries of isogrades. The numerical simulations are based on the finite difference method. We evaluate the relative importance of velocity, thermal diffusion and advection, and geometry of the thrust sheets, on the geometrical relation between tectonic contacts and isogrades. We calculate the thermal evolution and peak temperatures in order to compare the numerical results with field and petrological data collected along the Simano and Cima Lunga nappes.

In the field, the alternation of lithotypes is parallel to the nappe boundaries and constant over their whole length (order of kms). Passing from the Simano to the Cima-Lunga nappe, the transition between the nappes is marked by a progressive change in the texture of gneisses, in which the porphyroblasts become more stretched from the bottom to the top, and by the change in the constituent lithotypes. In the studied area, the Simano nappe is formed mainly by metagranitoids and by minor paragneisses. The Cima Lunga nappe is made of metasediments, mainly quartz-rich gneisses intercalated with amphibolite-gneisses, peridotitic lenses and local calcschists and/or marbles. Finally, the widespread paragneisses forming both the nappes frequently contain garnets of different sizes and internal microstructure. Published and own petrological data of these garnet-bearing rocks will be used to restrict the physical parameters of the numerical results.

We intend to test multiple geological scenarios related to different sources of heat production, such as: internal heat sources (radiogenic heating); additional heat flux at the bottom of the nappes, such in the case of a magmatic underplating, slab break-off, lower crust delamination; and in situ-produced heat due to shear heating mechanisms at the tectonic boundary between the nappes (thrust surface).