bluuebunny/crossref_metadata_2025 huggingface dataset:
Tsunami Resonance Characterization and Response in Japan Due to Transpacific Sources
Authors: Wang Yuchen , Zamora Natalia , Quiroz Marco , Satake Kenji , Cienfuegos Rodrigo
Published: March 2020

Tsunami resonance in the bays/harbors and the continental shelf leads to amplification of the wave heights and extends the duration of wave activity. Therefore, for the early warning systems and emergency response, it is important to understand the resonance behavior and mechanism. Tsunami resonance is caused by reflection and interference of tsunami waves from the edge of a harbor or continental shelf. The resonance over continental shelf is controlled by the bathymetry characteristics, and the bay/harbor resonance is mostly due to the features of the coastline. However, quantifying the impact in Japan from transpacific sources has not been systematically conducted. In this study, we assess the tsunami resonance processes from transoceanic and local sources in the ports of Japan. We first analyze the characteristics of the resonance behavior based on past events and also generate a set of ruptures like the 1730 Valparaiso earthquake to forecast these effects in Japan for a future event along the central Chilean margin. With the synthetic earthquake sources, we are able to further characterize the area using a larger number of tsunami events.
Stalagmite geochemical proxy-inferred precipitation records over the past 800 years in northern Italy
Authors: Shen C.-C. (River) , Hu Hsun-Ming , Michel Véronique , Valensi Patricia , Mii Horng-Sheng , Spötl Christoph , Starnini Elisabetta , Zunino Marta , Watanabe Takaaki , Watanabe Tsuyoshi , Tsai Hsien-Chen , Sung Wen-Hui , Chien Wei-Yi
Published: March 2020

We here present new 230Th-dated stalagmite multi-proxy records from Toirano cave (44˚ N, 8˚E), northern Italy, characterized by a semi-arid Mediterranean climate with humid winters and dry summers. Eleven U-Th ages was used to build the regional hydroclimate evolution over the past 800 years. Sr/Ca and Ba/Ca records show a similar pattern with an increasing trend at the end of Medieval Warm Period (MWP; 950-1250 C.E.) and a decreasing trend at the inception of Little Ice Age (LIA; 1300 to 1800 C.E). The temperature effect on the Sr partition coefficient in calcite is negligible and no significant influence of deposition rate on Sr/Ca and Ba/Ca is observed. The high degree of co-variation between the two records (r = 0.91; n = 212) suggest the variation should be mainly governed by prior calcite precipitation (PCP). Dry conditions lead to a longer water residence time in the epikarst, enhanced CO2 degassing and decreasing drip rate, resulting in high Sr/Ca and Ba/Ca ratios due to the preferential removal of Ca during PCP. Our results suggest a dry period during the transition of MCA and LIA in our region.
Atlantic Zonal Mode-Monsoon teleconnection in CMIP6 Models
Authors: Cherumadanakadan Thelliyil Sabeerali , Ajayamohan Ravindran , Veluthedathekuzhiyil Praveen
Published: March 2020

Atlantic Zonal Mode (AZM) and Indian summer monsoon rainfall (ISMR) are known to have an inverse relationship, which means that the cold (warm) phases of AZM result in strong (weak) ISMR. The realistic simulation of AZM and its teleconnection with ISMR in coupled models is important for the better seasonal prediction of ISMR. Here, we evaluated the performance of 26 CMIP6 models in simulating the AZM-ISMR teleconnection using 40 years of historical simulations. The skill of most CMIP6 models in simulating the teleconnection between AZM and ISMR is poor. Out of the 26 models analyzed, only 10 models show the correct sign of AZM related rainfall response over central India. The underlying mechanism responsible for the models' failure in capturing AZM-teleconnection is studied using the large-scale dynamical/thermodynamical variables. By choosing a set of good and bad models we unravel the common biases responsible for the wrong teleconnection between AZM-ISMR. This study highlights the importance of correcting AZM‐ISMR teleconnection in climate models for better seasonal monsoon prediction.
Atlantic influence on content of freshwater in upper layer of the Arctic Ocean
Authors: Alekseev Genrikh , Pnyushkov Andrey , Smirnov Alexander , Vyazilova Anastasia , Glok Natalia
Published: March 2020

The interdecadal changes in layer of the Atlantic water (AW) and the fresh water content (FWC)  in the  Arctic Basin  (AB) are traced for the 1960s - 2010s  in order to assess the influence of the influx from the Atlantic on the FWC changes. The results showed that the upper boundary of the AB layer, identified on zero isotherm, everywhere rose in the 1990s - 2010s by several tens of meters relative to its position before the start of the warming in the 1970s. The lower boundary of the layer, also determined by the depth of the zero isotherm, fell. Such displacements of the layer boundaries indicate an increase in the volume of the AW in the AB. A reduction in the volume of the upper freshened layer it is necessary to maintain balance. Our calculations confirmed that in the 1990s, the FWC in the layer 0–100 m decreased to 2 m or more in the Eurasian part of the Arctic Basin west of 180 °E and increased to east of 180 °E closer to the shores of Alaska and the Canadian archipelago,. This trend intensified in the 2000s and in the 2010s. A comparison of the distributions of the FWC and the position of the upper boundary of the AB layer over different decades by the method of spatial correlation confirmed a close relationship between both distributions. The response on changes of water temperature in the tropical region of the Atlantic is traced in the Barents Sea and in the Arctic basin.  That indicates the influence of low latitude SST on changes in AW layer and serves as an indicator of tropical effect on the Arctic processes. The study is supported by the RFBR grant 18-05-60107.
Long-profile evolution of transport-limited gravel-bed rivers: Implications for sediment and landscape dynamics
Authors: Wickert Andrew , Schildgen Taylor
Published: March 2020

Gravel-bed rivers cross and sculpt Earth's upland regions. Field, flume, and theoretical studies together provide governing equations for these rivers. Building upon this rich background, we quantitatively link catchment-scale hydrology, sediment transport, and morphodynamics into a model of river long-profile change over time. We focus on the transport-limited case (i.e., alluvial rivers), as most rivers around the world expend the majority of their geomorphic work by moving sediment rather than eroding the underlying substrate. Morphologically, this "transport-limited" category includes all alluvial rivers as well as those bedrock rivers for which bedrock erosion is easy relative to sediment transport. This model provides predictions for how such systems respond to changes in water supply, sediment supply, and base level – which are often linked to climate, land use, and tectonics. After deriving the central equation for long-profile evolution, we demonstrate that river concavity is strongly determined by the attrition rate of gravel, which can occur by either hillslope weathering or downstream fining. This dependency creates the potential for significant feedbacks between climate, tectonics, lithology, and river morphology. Furthermore, the equation predicts that oscillations in sediment and water supply will lead to net river incision when compared to steady means of both quantities. If true, this theoretical prediction could help to explain the near-ubiquitous presence of river terraces around the world.
Progress in observational geodynamics from the analysis of geological hiatus surfaces across Africa in the Cenozoic
Authors: Bunge Hans-Peter , Carena Sara , Friedrich Anke M.
Published: March 2020

Geological maps contain crucial information to constrain geodynamic models, but they remain underutilized by the geodynamic community. Particularly significant are unconformable geologic contacts at continental scales: what is usually perceived as a lack of data (material eroded or not deposited) becomes instead part of the signal of dynamic topography variation over geologic time.

 

 Here we show how we were able to use geological maps to constrain the dynamic processes in the mantle beneath Africa by understanding its Cenozoic elevation history, and by using it to distinguish between different uplift and subsidence scenarios. This was accomplished by using geological maps at the continent scale to map the spatiotemporal patterns of geological contacts, under the assumption that continental-scale unconformable contacts are proxies for vertical motions and paleotopography.

 

We found that significant differences exist in interregional-scale hiatus surfaces at the level of geologic series. The total unconformable area at the base of the Miocene expands significantly compared to the base of the Oligocene, strongly suggesting that most of Africa underwent uplift in the Oligocene. In southern Africa there are no marine Oligocene or Pleistocene sediments, suggesting that this region reached a high in the Oligocene, subsided in the Miocene and Pliocene, and has been high again since late Pliocene to Pleistocene. Our results therefore support a dynamic origin for the topography of Africa. Specifically, the time-scale of geologic series (at most a few tens of millions of years) is comparable to the spreading-rate variations in the south Atlantic, which have been linked to African elevation changes through pressure-driven upper mantle flow.
Simulating co-existence of functionally diverse trees in European natural forests with LPJmL-FIT
Authors: Thonicke Kirsten , Billing Maik , von Bloh Werner , Sakschewski Boris , Niinemets Ülo , Penuelas Josep , Cornelissen J.Hans C. , van Bodegom Peter , Shaepman Michael E. , Schneider Fabian D. , Walz Ariane
Published: March 2020

We adopted the flexible trait Dynamic Global Vegetation Model LPJmL-FIT for European natural forests by eliminating bioclimatic limits of Plant Functional Types (PFTs) and replacing prescribed values of functional traits with flexible individual traits. Vegetation dynamics are simulated with permafrost and fire disturbance being considered in the simulation domain. Leaf and stem-economic traits are assigned to individual trees at establishment which then determine plant competition for light and water in a forest patch. We simulate vegetation dynamics in selected natural forests sites and at the Pan-European scale. We quantified functional richness (FR), functional divergence (FDv) and functional evenness (FE) from combinations of functional and structural traits of the simulated individual trees.

We find good agreement with observed productivity, biomass and tree height, and spatial PFT and local trait distributions. The latter is compared against TRY observations. We find site-specific trait distributions and spatial gradients of the simulated LES and SES traits to coincide with environmental and competitive filtering for light and water in environments with strong abiotic stress. Where deciduous and needle-leaved trees co-occur in a forest patch, functional richness (potential niche space) is high, and extreme ends of the niche space are occupied resulting in high FDv. Functional divergence declines where the performance of deciduous trees decreases due to increasing environmental stress as simulated along altitudinal and latitudinal gradients. When climate gets cooler, needle-leaved trees become dominant, occupying the extreme ends of the niche space. Under Mediterranean climate conditions, drought increasingly limits tree growth thus niche differentiation becomes more important.

Co-existence of functionally diverse trees within and across PFTs emerges from alternative life history strategies, disturbance and tree demography.
Does a comprehensive evaluation increase confidence in the hydrological model intended for climate impact assessment?
Authors: Gelfan Alexander , Kalugin Andrei , Krylenko Inna , Nasonova Olga , Gusev Yeugeniy , Kovalev Evgeny
Published: March 2020

The objective of the study is to verify a hypothesis that the hydrological model that successfully passed a comprehensive evaluation test is more suitable for impact study than the other model that failed the test. The hypothesis verification is carried out on an example of the physically-based hydrological models ECOMAG and SWAP, which are set up for the two great Arctic basins: the Lena and the Mackenzie rivers. Three versions of every model are compared: (1) the model with a priori assessed parameters (without any calibration); (2) the model calibrated against the streamflow observations at the basin outlets only, and (3) the model calibrated against the streamflow observations at several sites within the basins. The comprehensive evaluation procedure, which includes enhanced tests of model performance and robustness, is applied for all the versions of every model. The performance of the models is compared at multiple sites within the catchments and for multiple hydrological indicators of interest (high flow, low flow, multi-year trends). The robustness of the models is compared through statistical significance of the differences in the performance criteria of the model for climatically contrasting periods composed from the historical meteorological data. From the evaluation results, we identified the preferable (in terms of the assigned criteria) models and established the limits of the models applicability. Then all the compared models, being forced by the Global Climate Model ensemble data, were applied to simulate flow projections for the 21st century and assess the projection uncertainty. The experiment demonstrates that the basin outlet flow projections simulated by the non-calibrated models differ from the projections of the calibrated models in terms of the mean ensemble trajectories and their uncertainty. Thus, under the study conditions (used models, studied basins), we answer "yes" to the question posed in the title of the presentation.       
Reconstruction of Complex Dynamical Systems Using Stochastic Differential Equations
Authors: Hassanibesheli Forough , Boers Niklas , Kurths Jürgen
Published: March 2020

A complex system is a system composed of highly interconnected components in which the collective property of an underlying system cannot be described by dynamical behavior of the individual parts. Typically, complex systems are governed by nonlinear interactions and intricate fluctuations, thus to retrieve dynamics of a system, it is required to characterize and asses interactions between deterministic tendencies and random fluctuations. 

For systems with large numbers of degrees of freedom, interacting across various time scales, deriving time-evolution equations from data is computationally expensive. A possible way to circumvent this problem is to isolate a small number of relatively slow degrees of freedom that may suffice to characterize the underlying dynamics and solve the governing motion equation for the reduced-dimension system in the framework of stochastic differential equations(SDEs).  For some specific example settings, we have studied the performance of three stochastic dimension-reduction methods (Langevin equation(LE), generalized Langevin Equation(GLE) and Empirical Model Reduction(EMR)) to model various synthetic and real-world time series. In this study corresponding numerical simulations of all models have been examined by probability distribution function(PDF) and Autocorrelation function(ACF) of the average simulated time series as statistical benchmarks for assessing the differnt models' performance. 

First we reconstruct the Niño-3 monthly sea surface temperature (SST) indices averages across (5°N–5°S, 150°–90°W) from 1891 to 2015 using the three aforementioned stochastic models. We demonstrate that all these considered models can reproduce the same skewed and heavy-tailed distributions of Niño-3 SST, comparing ACFs, GLE exhibits a tendency towards achieving a higher accuracy than LE and EMR. A particular challenge for deriving the underlying dynamics of complex systems from data is given by situations of abrupt transitions between alternative states. We show how the Kramers-Moyal approach to derive drift and diffusion terms for LEs can help in such situations. A prominent example of such 'Tipping Events' is given by the Dansgaard-Oeschger events during previous glacial intervals. We attempt to obtain the statistical properties of high-resolution, 20yr average, δ18O and Ca+2 collected from the same ice core from the NGRIP on the GICC05 time scale. Through extensive analyses of various systems, our results signify that stochastic differential equation models considering memory effects are comparatively better approaches for understanding  complex systems.

 
Soil moisture dynamics under Caragana korshinskii shrubs of different ages in Wuzhai County on the Loess Plateau, China
Authors: Li Zongshan , Liang Haibin
Published: March 2020

Soil moisture is a key factor affecting vegetation growth and survival in arid and semi-arid regions. Knowledge of deep soil moisture dynamics is very important for guiding vegetation restoration and for improving land management practices on the water-limited Loess Plateau. Temporal changes and vertical variations in deep soil moisture (at soil depths of 0–600 cm) combined with soil moisture availability were monitored in situ under Caragana korshinskii shrubs of different ages (named CK-10a, CK-20a and CK-35a) in the Loess hilly region during the growing season of 2013. The soil moisture content (SMC) under C. korshinskii shrubs of different ages was highly consistent with the seasonal precipitation variations and generally decreased as follows: CK-10a > CK-20a > abandoned land > CK-35a. The SMC varied greatly over time during the growing season (P < 0.01), decreasing from April to May and then slowly increasing with some fluctuation from June to October. The SMC drastically decreased with depth from 0–300 cm and then gradually increased with some fluctuation from 300–600 cm. A critical turning point and transition zone connecting the shallow and deep soil moisture occurred at 200–300 cm. Therefore, the soil profile was divided into active, secondary active and relatively steady soil layers in terms of soil moisture. The SMC fluctuated at depths of 0–100 cm and 300–400 cm and was relatively stable in the deeper soil layers. The amount of available soil moisture gradually decreased as the forest stand age increased, especially at CK-35a, where most of the soil moisture was unavailable for plant use. In addition, our study indicates that a large-scale restoration strategy with pure shrubland or woodland may not be suitable for soil moisture recovery in arid environments.
Quartz inclusions in garnet from high-temperature metamorphic rocks change their shape
Authors: Cesare Bernardo , Parisatto Matteo , Mancini Lucia , Peruzzo Luca , Franceschi Matteo , Tacchetto Tommaso , Reddy Steven M. , Spiess Richard , Marone Welford Federica
Published: March 2020

Trapped and sheltered inside other crystals, mineral inclusions preserve fundamental and otherwise lost information on the geological history of our planet. In the last decade, quartz inclusions in garnet have become a fundamental tool to estimate pressure and temperature of metamorphic rocks at the time of inclusion entrapment. In these approaches, as well as in all other applications, inclusions are regarded as immutable objects and the possibility of a change in their shape has never been considered.

With a detailed characterization of samples from greenschist and granulite facies, performed by optical and electron microscopy, EBSD, X-ray tomographic microscopy, laser Raman spectroscopy and FIB serial slicing, we show that after being trapped with irregular (“scalloped”) shape in low-temperature rocks, quartz inclusions in garnet from granulites formed at 750-900 °C and various pressures acquired a polyhedral “negative crystal” shape imposed by the host garnet, and almost exclusively defined by the facets of dodecahedron and icositetrahedron. A similar behaviour is also observed in biotite inclusions. The 3-fold and 4-fold morphological symmetry axes of the polyhedral negative crystals are parallel to corresponding crystallographic axes in the host garnet.

The systematic presence of a fluid film at the quartz-garnet boundary is not supported by Raman and FIB investigation.

Strengthened by microstructures indicating the process of “necking down” of polycrystalline quartz inclusions, our data support that - like in fluid inclusions changing shape to negative crystals - shape maturation of mineral inclusions occurs by temperature-assisted dissolution-precipitation via grain boundary diffusion. This process tends to minimize the surface free energy of the host-inclusion system by forming energetically favored facets and by decreasing the inclusion surface/volume and aspect ratios.

Optical investigation of numerous samples of worldwide provenance suggests that the negative crystal shape of quartz inclusions in garnet from granulites is a widespread microstructure that underpins a systematic phenomenon so far overlooked.
WRF forecast sensitivity to spatial resolution
Authors: Tagaris Efthimios , Stergiou Ioannis , Sotiropoulou Rafaella-Eleni
Published: March 2020

The Weather Research and Forecasting (WRF) model dynamically downscales NCEP FNL Operational Global Analysis data in order to assess the grid size resolution effect on the simulated variables. Simulations where conducted over Europe for the year 2015 using 36km, 12km and 4km grid size resolutions. The sensitivity analysis assesses the grid size resolution effect on the simulated mean, maximum and minimum daily temperatures as well as precipitation. The simulated data are evaluated using reanalysis dataset. The statistical variables used are the bias, mean absolute error, root mean square error and the index of agreement for each grid cell. Results show that model performance for mean and maximum temperature, is better when increasing the spatial resolution from 36Km to 12Km but no significant change is found when the spatial resolution is further increased to 4Km, in general. In addition, model performance for minimum temperatures and precipitation does not change significantly when moving to higher spatial resolution grids (i.e., 12Km and 4Km) compared to the 36Km domain,

Acknowledgments LIFE CLIMATREE project “A novel approach for accounting & monitoring carbon sequestration of tree crops and their potential as carbon sink areas” (LIFE14 CCM/GR/000635).
ACROSS: An Observational Campaign to Improve Understanding of Photochemistry of Mixed Urban and Biogenic Air Masses
Authors: Cantrell Christopher , Michoud Vincent , Formenti Paola , Doussin Jean-Francois , Gratien Aline , Dusanter Sebastien ,   ACROSS team
Published: March 2020

In recent decades, significant progress has been made in understanding the causes and impacts of urban air pollution, generally leading to improved air quality through enhanced knowledge and regulatory action. While a significant number of people still die prematurely each year from air pollution, progress continues to be made. Scientific investigation has exposed the processes by which primary pollutants, such as oxides of nitrogen and volatile organic compounds, are processed in the atmosphere, leading to their oxidation and ultimate removal, while at the same time producing secondary species such as ozone and organic aerosols.

Research has uncovered the complex chemistry of natural organic compounds released from trees and other plants. Because of the chemical structures of these compounds, they react somewhat differently than organic substances typically found in urban environments. The ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) project focuses on scientific research to understand the detailed chemistry and physics of urban air mixed with biogenic emissions with the goals to increase detailed understanding of the chemical processes and to use this knowledge to improve the performance of air quality models. Enhanced knowledge and improved models will allow society to develop better strategies to improve air quality and save lives.

The central component of ACROSS is a comprehensive summertime field study with many instruments for the measurement of primary and secondary constituents. Measurements will be made from research aircraft, a tower located in a forest, tethered balloons and/or drones, and mobile platforms. Observations from the field study will be analyzed in a variety of ways involving statistical approaches and comparisons with different types of numerical models.

This presentation describes activities in preparation of the ACROSS measurement campaign and provides information for interested parties to become involved.
Open Hydrosystem Information Network: Greece’s new research infrastructure for water
Authors: Efstratiadis Andreas , Mamassis Nikos , Koukouvinos Antonis , Koutsoyiannis Demetris , Mazi Katerina , Koussis Antonis , Lykoudis Spyridon , Dimitriou Elias , Malamos Nikos , Christofides Antonis , Kalogeras Demetris
Published: March 2020

The Open Hydrosystem Information Network (OpenHi.net) is a state-of-the-art information infrastructure for the collection, management and free dissemination of hydrological and environmental information related to Greece’s surface water resources. It was launched two years ago as part of a the national research infrastructure “Hellenic Integrated Marine Inland water Observing, Forecasting and offshore Technology System” (HIMIOFoTS), which also comprises a marine-related component (https://www.himiofots.gr/). The OpenHi.net system receives and processes real-time data from automatic telemetric stations that are connected to a common web environment (https://openhi.net/). In particular, for each monitoring site it accommodates stage measurements, raw and automatically post-processed. Furthermore, in some specially selected sites time series related to water quality characteristics (pH, water temperature, salinity, DO, electrical conductivity) are provided. The web platform also offers automatically-processed information in terms of discharge data, statistics, and graphs, alerts for extreme events, as well as geographical data associated with surface water bodies. At the present time, the network comprises about 20 stations. However, their number is continuously increasing, due to the open access policy of the system (the platform is fully accessible to third-parties uploading their data). In the long run, it is envisioned that a national-scale hydrometric infrastructure will be established, covering all important rivers, lakes and reservoirs of the country.
Recent developments in modeling ice sheet deformation
Authors: McCormack Felicity , Warner Roland , Treverrow Adam , Seroussi Helene
Published: March 2020

Viscous deformation is the main process controlling ice flow in ice shelves and in slow-moving regions of polar ice sheets where ice is frozen to the bed. However, the role of deformation in flow in ice streams and fast-flowing regions is typically poorly represented in ice sheet models due to a major limitation in the current standard flow relation used in most large-scale ice sheet models – the Glen flow relation – which does not capture the steady-state flow of anisotropic ice that prevails in polar ice sheets. Here, we highlight recent advances in modeling deformation in the Ice Sheet System Model using the ESTAR (empirical, scalar, tertiary, anisotropic regime) flow relation – a new description of deformation that takes into account the impact of different types of stresses on the deformation rate. We contrast the influence of the ESTAR and Glen flow relations on the role of deformation in the dynamics of Thwaites Glacier, West Antarctica, using diagnostic simulations. We find key differences in: (1) the slow-flowing interior of the catchment where the unenhanced Glen flow relation simulates unphysical basal sliding; (2) over the floating Thwaites Glacier Tongue where the ESTAR flow relation outperforms the Glen flow relation in accounting for tertiary creep and the spatial differences in deformation rates inherent to ice anisotropy; and (3) in the grounded region within 80km of the grounding line where the ESTAR flow relation locally predicts up to three times more vertical shear deformation than the unenhanced Glen flow relation, from a combination of enhanced vertical shear flow and differences in the distribution of basal shear stresses. More broadly on grounded ice, the membrane stresses are found to play a key role in the patterns in basal shear stresses and the balance between basal shear stresses and gravitational forces simulated by each of the ESTAR and Glen flow relations. Our results have implications for the suitability of ice flow relations used to constrain uncertainty in reconstructions and projections of global sea levels, warranting further investigation into using the ESTAR flow relation in transient simulations of glacier and ice sheet dynamics. We conclude by discussing how geophysical data might be used to provide insight into the relationship between ice flow processes as captured by the ESTAR flow relation and ice fabric anisotropy.
Temperature and fluid activation of contact healing and fault lubrication in rate-and-state friction
Authors: Barbot Sylvain
Published: March 2020

The frictional behavior of rocks under shear offers tremendous complexity depending among others on rock type, temperature, fluid content, and sliding velocity. A large body of laboratory experiments documents these effects, but a unifying theoretical framework linking these observations is still missing. Here, I present a constitutive law based on multiple temperature and fluid activated healing processes and a fluid lubrication phase to capture fault behavior in the brittle field in all conditions relevant to the seismic cycle. Distinct healing processes are activated at different temperatures, pore fluid pressures, and depths based on their respective activation enthalpy. A fluid phase is rapidly formed at the high temperatures facilitated by shear heating, allowing strong weakening at high slip velocity. The model explains the intricate change of frictional behavior of carbonate rocks at various temperatures, including simultaneous velocity-strengthening and temperature-weakening at temperatures lower than 70ºC, transitioning to simultaneous velocity-weakening and temperature-hardening at higher temperatures. With different parameters, the model explains the frictional properties of quartz and granitic rocks in hydrothermal conditions with velocity-strengthening behavior in nominally dry conditions, transitioning to velocity-weakening between 100ºC and 350ºC in wet conditions. Inclusion of a lubrication phase formed between the solidus and the liquidus of the host rocks explains the strong weakening at high slip velocity in a variety of rocks. The unified constitutive framework allows modeling of faults in varying temperature and pore pressure conditions, including for example injection of pore fluids in natural faults or shear heating of the host rocks. 
Chameleonic noise in GPS position series: what is the true color of the GPS error spectra?
Authors: Santamaría-Gómez Alvaro , Ray Jim
Published: March 2020

Chameleonic: readily changing color or other attributes.

Chameleon: a lizard that changes skin color to match what surrounds it so that it cannot be seen.

The error spectrum of decadal long GPS position time series is typically represented by a combination of flicker (pink) noise at long periods and white noise at short periods. It is known that when fitting a linear trend to the series, part of the flicker noise at the longest observed period will be absorbed by the trend. Here, using real and synthetic GPS position series, we show how the error spectrum is even more altered by the position discontinuities that populate the series. The fitted position offsets at the discontinuity epochs absorb a significant portion of the power spectrum at periods longer than the separation between the discontinuity epochs. The resulting error spectrum is flattened at long periods and this implies that:

the estimated content of colored noise is biased low and can even apparently change its color towards whiter noise, i.e. the true noise color is not observable due to the discontinuities,

the red (random walk) noise , most probably present in the series in small quantity, becomes undetectable even if long series are used,

the pink (flicker) noise is not the best color noise to represent the error spectrum in long series containing discontinuities,

the colored noise content cannot be compared between series with different sets of discontinuities.

These findings need to be considered when comparing the noise levels between series from different solutions, networks or monuments. In particular, and contrary to a recently published recommendation, station operators should make every effort to avoid adding new discontinuities into their station time series if reliable velocity estimates are expected.
New craters on Mars: Air shock wave traces
Authors: Ivanov Boris , Barnes Gwen , Daubar Ingrid , Dundas Colin , McEwen Alfred , Melosh Jay
Published: March 2020

The idea of visualizing shock wave passage along a dusty (sooty) surface was first proposed and tested by Ernst Mach. High resolution HiRISE images of new impact craters on dusty areas of Mars gave in many cases revealed dark “fresh” halos around craters. In ~7% of cases they have low albedo/color contrasting curved strips near craters referred to as “parabolas” and “scimitars”. We analyze these albedo details as the possible surface footprints of atmospheric shock waves generated during atmospheric passage and shocks from impact cratering by small meteoroids and their fragments. In this approach “parabolas” are the trace of two colliding air shocks propagated from a pair of neighboring craters formed after a meteoroid fragmented during the atmosphere passage. The mechanism of the “scimitar’s” formation is more enigmatic and tentatively could be related to the interaction of the ballistic cone wave and a spherical wave from the point of impact. The study of images is accompanied by numerical modeling of impact of small projectiles at the atmosphere/rock boundary. This modeling constrains the minimum efficiency of an impact to generate the air shock wave in the rarified Martian atmosphere below of 0.1% of the kinetic energy for non-volatile targets. Targets with near surface volatiles could amplificated the air blast (if volatiles are presented in the shocked zone). The study is intended to estimate the air-shock wave parameters along the visible surface traces around impact craters. By constraining shock wave parameters opens new possibilities for investigating the mechanical properties of the Martian surface.
The work is supported by RAS program 12 “Universe Origin and Evolution from Earth-based Observations and Space Missions” (BAI), and a grant from the NASA Mars Data Analysis Program, number 80NSSC18K1368.
Influence of floe-floe interactions on wave damping in marginal ice zones
Authors: Marchenko Aleksey
Published: March 2020

Numerous observations show that in spite of relative motions of floes caused by wave propagation in marginal ice zone (MIZ) direct contacts between them don’t occur. Nevertheless, relative motions of floes may influence formation of oscillating water currents between them which take and dissipate the energy of incoming waves. Full-scale and laboratory experiments were performed to investigate characteristics of water currents between interacting floes. The experiments included the investigation of vertical and horizontal oscillating motions of floes in ice environment. During the experiments we recorded floe accelerations, water pressure and water velocity. Main goal of the experiments was to estimate effective viscosity of water in gapes between interacting floes, describe floe-floe forces caused by the floe accelerations, and estimate the influence of slush formation on the effective viscosity of water. The floe motion was initiated by mechanical pooling, towing with a rope and by original pendulum rig. The experiments were performed in the Van-Mijen Fjord of Spitsbergen in winter seasons of 2018 and 2019, and in the wave flume at UNIS. A lubrication theory was used to describe the dependence of water pressure between interacting floes from their relative speed and the distance between approaching surfaces. Comparison of numerical simulations with experimental records showed that the action of water pressure and the formation of flow jets can prevent direct collision of approaching floes. Obtained analytical formulas are used for the formulation of rheological equations describing the behavior of broken ice in MIZ.                  
Assessing within-lake nutrient cycling through multi-decadal Bayesian mechanistic modeling
Authors: Obenour Daniel , Del Giudice Dario , Aupperle Matthew , Sankarasubramanian Arumugam
Published: March 2020

Nutrient recycling from bottom sediments can provide substantial internal loading to eutrophic lakes and reservoirs, potentially exceeding external watershed loads. However, measurements of sediment nutrient fluxes are rare for most waterbodies in the United States, causing many modeling studies to parameterize these fluxes in simplistic ways or else make assumptions about complex sediment diagenetic rates. Here we propose an alternative approach to understanding internal cycling, using a mass-balance model combined with Bayesian inference to rigorously update prior information on nutrient flux parameters. The approach is applied to Jordan Lake, a major water supply reservoir in North Carolina (USA) that has been highly eutrophic since impoundment in the early 1980s, with chlorophyll a concentrations occasionally exceeding 100 µg/L. We simulate monthly nitrogen and phosphorus dynamics in the water column and sediment layer of four longitudinal reservoir segments, forced by watershed flows, nutrient loads, and meteorology. The model is calibrated within the Bayesian framework and validated using a multi-decadal record of surface nutrient concentration data. We compare multiple versions of the model to assess the importance of prior knowledge from previous literature, the multi-decadal calibration period, and the mechanistic formulation for obtaining accurate and robust predictive performance. Overall, the model explains from 40-60% of the variability in observed nutrient concentrations. Model results indicate that a large fraction (>40%) of phosphorus is lost in the upstream reaches of the reservoir, likely due to rapid settling and burial of particulate material. Within the main body of the reservoir, phosphorus recycling rates were found to be higher than expected a priori, particularly in the summer season. Results show how nutrients stored in lacustrine sediment have been an important source of internal loading to the reservoir for multiple decades, and will dampen the effects of external watershed loading reductions, at least in the near term. To better understand potential time scales for reservoir recovery, we perform future simulations over a multi-decadal period and characterize forecast uncertainties.
The Granite of Pena, the Building Stone of the Most Important Buildings of the Twentieth Century in Vila Real (Northern Portugal)
Authors: Freire-Lista David Martín , Sousa Luis , Lourenço Martinho
Published: March 2020

Heritage stones have been used in different civilizations; they have a great social and economic relevance that attracts cultural tourism. In addition, they have an impact on human culture, geoheritage, geoarchaeology and architecture.

Industrialisation, the development of means of transport and new materials have led to the abandonment of historical quarries necessary for the conservation of monuments. Global Heritage Stone nomination aims at the inventorying of building stones that can be used for restoration and revitalisation of villages with quarrying tradition and focuses on the sustainable conservation of cultural heritage.

The geology of Northern Portugal is broadly composed of metamorphic rocks and granites with vestiges of historical stonework, since they have been profusely used for construction. Heritage stones have created a rich cultural heritage which has been preserved up to this date.

Documentary search, cartography and petrographic characterisation are necessary to locate the historical quarries of the stones with which monuments have been built. The use of analytical techniques, such as petrography, accelerated artificial ageing, ultrasound pulse velocity measurements and spectrophotometry will guarantee the quality, durability and colour of restoration stones.

The period of most intense development of traditional stonework in the Trás-os-Montes area occurred in the 18th century. An important historical quarry of granite with medium crystal-size was discovered in Picarreira mountain, near Pena village, in the municipality of Vila Real, Portugal (41.295378, -7.816378).

There are numerous door lintels that retain the construction date carved on them, as well as houses with carved ashlars, granite pinnacles, granaries and roadside granite crosses in Pena and its surroundings. The lintels and jambs of the doors and windows of the seminary, and the court and post office buildings, all of them in Vila Real, were built with Pena granite. The petrographic and petrophysical properties of this granite have been characterised in addition to its decay in the aforementioned buildings of Vila Real.

Given the ongoing transformation of the industry, it is important that urban planners and policy makers of cultural heritage work in tandem with contemporary needs of the cities. Furthermore, planning-led heritage conservation, careful attention and common criteria for the restoration and rehabilitation of each heritage stone are needed.

Acknowledgements: The Fundação para a Ciência e a Tecnologia (FCT) of Portugal supported the first author with the Stimulus of Scientific Employment, Individual Support 2017. CEECIND/03568/2017.
The Origin of Aeolian Dunes – PIV measurements of flow structure over early stage protodunes in a refractive-index-matching flume
Authors: Bristow Nathaniel , Best James , Christensen Kenneth , Baddock Matthew , Wiggs Giles , Delorme Pauline , Nield Joanna
Published: March 2020

Understanding the initiation of aeolian dunes poses significant challenges due to the strong couplings between turbulent fluid flow, sediment transport, and bedform morphology. While much is known concerning the dynamics of more mature bedforms, open questions remain as to how protodunes are formed, as well as the mechanisms by which they continue to evolve. The structure of the turbulent flow field drives the mobilization or deposition of sediment, thus controlling the initial formation of sand patches, yet is also strongly influenced itself by local conditions such as surface roughness and moisture. Furthermore, an additional feedback on the flow and transport is exerted by the sand patches themselves once they begin to form.

As protodunes begin to develop from this initial deposition, their morphologies possess unique characteristics involving a reverse asymmetry of the stoss and lee sides, wherein the crest begins upstream, close to the toe, and gradually shifts downstream toward the "regular" asymmetric profile exhibited by more mature dunes. However, these early stages of development also involve very gentle slopes and low profiles which make field measurements of the associated flow particularly challenging.

The current research effort involves a combination of field measurements, documenting the initiation and morphological development of sand patches and protodunes, in concert with detailed measurements of the flow-form interactions in a laboratory flume. The work presented herein focuses primarily on experiments conducted in a unique flow facility wherein high-resolution measurements of the turbulent flow field associated with the early stages of protodune development are obtained utilizing particle-image velocimetry (PIV) in a refractive-index-matched (RIM) environment. The RIM technique facilitates flow measurements extremely close to model surfaces as well as unimpeded optical access which are critical to understanding the flow-form coupling. A series idealized, fixed-bed models are fabricated to mimic the key morphological characteristics of early protodune development observed in the field, and the flow measurements associated with them are analyzed to reveal the mechanisms controlling the bedform dynamics.
Combining Sentinel-1A/B InSAR and high-resolution topography in the study of coastal megacities
Authors: Tiampo Kristy , Willis Michael , Nerem R. Steven , Eduard Heijkoop , Joel Johnson
Published: March 2020

Today, the joint phenomena of rapid urbanization and population growth has resulted in an increase in the number of cities of over 10 million inhabitants, or megacities, worldwide.  While western megacities such as Los Angeles have been relatively stable in recent years, the developing world saw an increase from two to thirteen between 1975 and 2000 (http://www.igbp.net). In 2011, sixteen of the 23 global cities that fell into that category were coastal (UN-DESA 2012). Their growth is often coupled with unplanned urbanization and sprawl, with important effects on coastlines, demographics and ecosystems (Angel et al. 2011; Allison et al., 2016).  The associated risk is exacerbated by anthropogenic coastal subsidence processes and sea-level rise due to climate change, potentially increasing inundation, flooding, storm surges and infrastructure damage. Ground deformation phenomena, either uplift and/or subsidence, can arise from volcanic and tectonic processes, hydrocarbon exploitation, groundwater pumping and shallow compaction of sediments, particularly along coastal deltas. A better understanding of the processes affecting coastal megacities can be achieved through the combination of satellite and ground-based measurements.  Here we combine both high-resolution topography, in the form of optical digital surface models (DSMs), and differential interferometric synthetic aperture radar (DInSAR), to better characterize the effects of local and regional subsidence, coastal erosion, sea-level rise and urbanization in several megacities from around the developing world.   DInSAR time series from Sentinel-1A/B images, coregistered to high-resolution DSMs, are used to constrain local and regional ground deformation, while those same DSMs can be used to better model inundation due to sea level rise.  Here we present results for a number of cities, including but not limited to Mumbai, Lagos and Dhaka.