bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical roughness controls sliding instability of laboratory earthquakes
Authors: Morad Doron , Sagy Amir , Tal Yuval , H. Hatzor Yossef
Published: March 2022

The frictional strength of discontinuities in the upper earth crust controls the stability and dynamics of slip in diverse catastrophic phenomena such as earthquakes and landslides. Natural rock surfaces are rough at various scales with significant variability that affects their frictional behavior. Seismological and geophysical observations of large thrust faults suggest that fault geometry affects earthquake characteristics, yet the exact effects are currently being debated. In this study we show, using laboratory direct shear experiments, that a specific surface geometry enhances sliding instability and that the transition from stable to unstable sliding is non-linearly controlled by the magnitude of the initial roughness. In order to isolate the effect of roughness, we generate six levels of surface roughness in split prisms of Diabase rocks, with four orders of RMS magnitude difference between the smoothest and the roughest samples. The experiments are performed under an imposed constant normal stress of 5 MPa and load point (shear piston) velocity of 0.01 mm/s. The sliding target is typically set to 10 - 13 mm as monitored from two horizontal LVDT’s that are attached to the shear box very close to the tested interface. We show that the amplitude of the stick-slip events diminishes towards the two roughness extremes. The roughest sample (RMS = 1300 µm) exhibits a gradual increase of shear stress to a peak value of ~13 MPa, followed by brittle fracture expressed by a large stress drop of 3 MPa and then by transition to a relatively stable sliding. For the midrange roughness (RMS = 7 µm), stick-slip oscillations are obtained with different levels of stress drops and sliding dynamics characteristics. The smooth sample (RMS = 0.85 µm) slide in a relatively stable manner while the smoothest surface (RMS = 0.7) exhibits local peak friction of 0.18, followed by stable sliding with moderate slip hardening. We further demonstrate, both experimentally and numerically, that stick-slip oscillations commonly referred to as laboratory earthquakes, are constrained to a very limited range of surfaces roughness within which a specific level, defined here as the critical roughness, triggers the highest amplitude of oscillations. We therefore suggest that the roughness amplitude strongly affects the frictional stability and slip dynamics of natural faults.
Linking surface Observables to sub-Volcanic plumbing-system:a multidisciplinary approach for Eruption forecasting at Campi Flegrei caldera (Italy).
Authors: Pappalardo Lucia , Caliro Stefano , Tramelli Anna , Trasatti Elisa ,   LOVE-CF team
Published: March 2022

The Campi Flegrei caldera (Italy) is one of the most dangerous volcanoes in Europe and is currently in a new phase (started in 2000 and still ongoing) of the unrest that has persisted intermittently for several decades (main crises occurred in 1950-52, 70-72 and 82-84). The current activity has prompted the Italian Civil Protection to move the Campi Flegrei volcano from the first (“base” or “green”) to the second (“warning” or “yellow”) level of alert since the end of 2012.

The geophysical and geochemical changes accompanying the unrest stimulated a number of scientific investigations that resulted in a remarkable production of articles over the last decade. However, large uncertainties still persist on the architecture of the caldera plumbing system as well as on the nature of the subsurface processes driving the current (and previous) unrest.

LOVE-CF is a 4-years project started in October 2020 and funded by INGV (Istituto Nazionale di Geofisica e Vulcanologia), with the aim of improving our ability to forecast the behaviour of the Campi Flegrei caldera, through a multi-disciplinary approach based on a combination of volcanological, petrological, geochemical, seismological and geodetic observations, as well as experiments and numerical models. 

We present the project objectives and methods, and show obtained preliminary results. Particularly our investigation includes: 

a) the integration of structural, volcanological and petrological data from representative past eruptions with results of decompression experiments and numerical models of conduit dynamics and dyke propagation;

b) innovative geochemical (new redox gas species and CH4isotopes), minero- petrological (alteration products) and seismic (fumarolic tremor) measurements at the crucial “Solfatara-Pisciarelli” hydrothermal site as well as geochemical characterization of submarine emissions in the area of “Secca delle Fumose” in the Gulf of Pozzuoli which has been poorly-explored so far;

c) novel multi-dimensional statistical analysis of seismic, geochemical and geophysical records collected (both on land and offshore) in the last decades and in the recent period of unrest, constrained by geological observations and advanced numerical modelling;

d) comprehensive analysis of surface deformations from historical data (since 35 BC) to modern techniques (both in-situ and remote sensing), and related modelling to disclose the active plumbing system and the relationship among the different sources of deformation throughout the decades and centuries.
First steps for a 3d flexible, unstructured finite element ocean model for flow under ice shelf cavities: an ISOMIP+ case study
Authors: Scott William , Kramer Stephan , Yeager Benjamin , Holland Paul , Nicholls Keith W. , Siegert Martin , Piggott Matthew
Published: March 2022

Accurate modelling of basal melting beneath ice shelves is key to reducing the uncertainty in forecasts of ice-shelf stability and, thus, the Antarctic contribution to sea level rise. However, the lack of flexibility inherent to traditional ocean models can pose problems.

Obtaining accurate melt estimates requires capturing the turbulent exchange of momentum, heat and salt at the ice-ocean interface, which may be modulated by the competing effects of stratification and basal slope. There are still significant uncertainties surrounding the trade-off between the simplicity of the melt parameterisation and the processes that need to be resolved by the numerical ocean model near the boundary.

Real ice-shelf cavity geometries are complicated. Bathymetric valleys are common and provide pathways for warm circumpolar deep water. The ice base is marked by channels, crevasses and terraces. These features will affect the boundary flow, with an added complication that melting plays a role in their formation. It is very difficult to model such flow regimes using a traditional ocean model not only because of the resolution constraints imposed by inflexible grids, but also due to the inbuilt assumptions of large aspect ratio processes and domains that may be violated when flow occurs past these features.

Ice flow models are very sensitive to how they are forced by melting at the grounding line, where the ice starts to float. The grounding line is precisely the region where ocean models are most questionable due to insufficient resolution imposed by limitations on the grid. Subglacial outflow into the cavity will likely break the inherent physical assumptions of hydrostatic, non-negligible vertical accelerations in large aspect ratio domains.

To model these effects requires the use of an ocean model that contains a flexible, unstructured mesh, is applicable at a range of length scales and, crucially, is still valid when the vertical-to-horizontal grid aspect ratio approaches order one. We are developing such a model for simulating flow under ice shelf cavities using the Firedrake finite element framework, primarily because it enables adjoint sensitivities to be calculated automatically. We present our 3d simulations of ISOMIP+ experiments alongside simulations using the MITgcm ocean model, a commonly used z-layer (constant vertical resolution) model. We have found that the ability to vary the mesh resolution flexibly in the horizontal and vertical, even in a relatively simple ISOMIP+ domain (i.e., no channels or crevasses) is very useful to investigate how melt rate depends on grid resolution, which ultimately must be the first aim of any study using a numerical model.
Future occurrence and magnitude of flood events in the Panaro River (Northern Italy): coupling bias-corrected hourly climate scenarios and semi-distributed rainfall-runoff modelling
Authors: Toth Elena , Neri Mattia , Reder Alfredo , Rianna Guido
Published: March 2022

The evaluation of the resilience of flood protection systems requires the assessment of the impact of climate change scenarios on future flood regimes. Due to the high computational effort and to the scarcity of hourly climate modelling chains, expected changes in future floods are often simulated by hydrological models on a daily basis, even for basins with short response times, where hourly simulations would be needed.

In this work, the expected occurrence and magnitude of future flood events is modelled through the coupling of bias-corrected local climate scenarios at hourly time scale and continuous rainfall-runoff modelling, in reference to the Panaro river (one of the OpenAir Laboratories in the OPERANDUM H2020 project), a tributary of the Po River in the Apennines.

The investigation exploits hourly precipitation and daily max/min temperature (used for interpolation at hourly scale) timeseries for a subset of climate modelling chains included in the EURO-CORDEX initiative through the dynamical downscaling of Global Climate Models under the RCP 8.5 concentration scenario. The comparison with observed spatial fields obtained from weather stations and from gridded E-OBS products allows to assess the biases affecting the climate raw data.

The Scaled Distribution Mapping (SDM) bias correction procedure (Switanek et al. 2017), that preserves raw climate model projected changes in the bias-corrected series, is then applied to adjust the raw model output towards observations.

A semi-distributed, continuously simulating rainfall-runoff model is parameterised on the basis of the observed meteorological and streamflow time-series, especially focusing on the reproduction of past flood events. The model is then run to reproduce the continuous hourly streamflow time-series in the Panaro river over past and future decades, providing in input i) observed meteorological forcing based on ground stations, ii) raw and bias-corrected climate scenarios over the control period, iii) bias-corrected climate scenarios for the future decades. Finally, the flood events are extracted from the continuous streamflow simulations and the changes in the flood signals expected over the future decades are analysed, in terms of both peaks and volumes.

 

References

Switanek, M. B., Troch, P. A., Castro, C. L., Leuprecht, A., Chang, H.-I., Mukherjee, R., and Demaria, E. M. C.: Scaled distribution mapping: a bias correction method that preserves raw climate model projected changes, Hydrol. Earth Syst. Sci., 21, 2649–2666, https://doi.org/10.5194/hess-21-2649-2017, 2017.
Insight into glacier evolution, proglacial lake dynamics, and paleoclimate from Lago Argentino, Patagonia
Authors: Van Wyk de Vries Maximillian , Ito Emi , Shapley Mark , Brignone Guido , Romero Matias , Wickert Andrew D.
Published: March 2022

Proglacial lakes provide valuable records of paleoclimate, volcanism, and glaciation. We present results from spatially extensive coring of Lago Argentino, a 1500 km2 proglacial lake on the eastern margin of the Southern Patagonian Icefield (SPI). We recovered forty-seven sediment cores from water depths up to 600 m. Detailed analysis of this sediment reveals annual laminations – known as varves – which we use to build a high-resolution age-depth model for each core.

In this presentation, we discuss the insight gained into varve formation mechanisms, paleoclimate, and glacier change in the Lago Argentino basin of the Southern Patagonian Icefield. Firstly, we show that varves form by three distinct mechanisms across Lago Argentino (~west to east): a seasonal cycle in glacial sediment influx, a seasonal cycle in lake mixing, and a seasonal cycle in fluvial sediment influx. Second, we examine the evidence for recent glacier fluctuations across Lago Argentino. We find evidence that glaciers were locally larger early in the last millennium than during the Little Ice Age. Finally, we examine the periodicity of sediment mass accumulation rate and find dominant decadal to centennial periodicities (35, 80, 150 and 200 years). We relate periodicities in sediment accumulation to periodicities in known climatic drivers, specifically the Southern Annular Mode. These results provide new insight into multiannual glacial change and sedimentation dynamics in a complex glacio-lacustrine system and highlight the value of proglacial lake records for understanding present-day glacier change.
The role of different land cover input data on local climate and its extremes
Authors: Tölle Merja , Churiulin Evgenii
Published: March 2022

The spatio-temporal heterogeneity in surface characteristics is considered to play a key role in terrestrial surface processes. Its characterization is essential for adaptation strategies. Here, we conducted regional climate simulations with COSMO-CLM (v5.0_clm16) with different land cover input data driven by ERA5 reanalysis over Germany at convection-permitting horizontal resolution of 3 km from 2000 to 2011. The difference between the land cover data of GLC2000, CCI_LC and ECOCLIMAP and the operational used GLOBCOVER2009 dataset on temperature and its extremes is investigated. The results reveal that the differences in turbulent fluxes and temperature are related to land cover classes. Even though the land cover class fractional differences are small among the land cover maps, some land cover types, such as croplands and urban areas, have greatly changed over the years. These distribution changes can be seen in the temperature differences. Simulations based on the CCI_LC retrieved in 2000 and 2015 revealed no accreditable difference in the climate variables as the land cover changes that occurred between these years are marginal, and thus, the influence is small over Germany. Increasing the land cover types as in ECOCLIMAP leads to higher temperature variability. The largest differences among the simulations occur in maximum temperature and from spring to autumn, which is the main vegetation period. The temperature differences seen among the simulations relate to changes in the leaf area index, plant coverage, roughness length, latent and sensible heat fluxes due to differences in land cover types. The vegetation fraction was the main parameter affecting the seasonal evolution of the latent heat fluxes based on linear regression analysis, followed by roughness length and leaf area index. If the same natural vegetation (e.g. forest) or pasture grid cells changed into urban types in another land cover map, daily maximum temperatures increased accordingly. Similarly, differences in climate extreme indices (e.g., SU or TR) are strongest for any land cover type change to urban areas. The uncertainties in regional temperature due to different land cover datasets were overall lower than the uncertainties associated with climate projections. Although the impact and their implications are different on different spatial and temporal scales as shown for urban area differences in the land cover maps. Thus, to realistically simulate land use/cover change effects on regional and local climate and draw conclusions for management strategies, numerical models would benefit from land surface characteristics, which are as accurate as possible in retrieval year, number of land cover classes, their distribution and fractions and have a high spatial resolution.
Global climatalogy of cyclone clustering
Authors: Weijenborg Chris , Spengler Thomas
Published: March 2022

Cyclone clustering, the succession of multiple extratropical cyclones during a short period of time, has a huge impact on European weather extremes. The idea that several cyclones follow a similar track already dates back to the concept of cyclone families of Bjerknes and Solberg. To investigate the dynamical causes of cyclone clustering, one needs to diagnose where cyclone clustering occurs and determine their characteristics. So far most diagnostics either focused on either local impact-based diagnostics or on a statistical analysis of storm recurrence. While the first cannot be applied globally, the latter is difficult to relate to individual events. We therefore present a new way to globally detect cyclone clustering that is closer to the original concept of Bjerknes and Solberg that extratropical cyclones follow similar tracks.

Using this new cyclone clustering diagnostic based on spatio-temporal distance between cyclone tracks, we analyse cyclone clustering globally in Era-Interim for the period 1979 until 2016. We complement this analysis with a baroclinicity diagnostic based on the slope of isentropic surfaces. With the isentropic slope and its tendencies, the relative role of diabatic and adiabatic effects associated with extra-tropical cyclones in maintaining baroclinicity are assessed. We find that cyclone clustering mainly occurs along the climatological storm tracks. In general, clustered cyclones are stronger than non-clustered cyclones. Moreover clustered cyclones are more often related to atmospheric rivers and stronger isentropic slope, indicating that diabatic effects might be an important mechanism in the formation of cyclone clustering. 
Early Permian deformational ages of Late Carboniferous basalt dykes in the İstanbul-Zonguldak Tectonic Unit: Implications for the Variscan orogeny in the Pontides
Authors: Şen Fatih
Published: March 2022

The İstanbul-Zonguldak Tectonic Unit (NW Turkey) is regarded as the unmetamorphosed continental fragment of Far East Avalonia in the Pontides. It is to the east of the Rhodope-Strandja Massif, which is a part of the metamorphosed section of Far East Avalonia, and is to the north and west of the Sakarya terrane. The Variscan orogeny in the Pontides defines as the collision of the Sakarya terrane with the İstanbul-Zonguldak Tectonic Unit during the early Carboniferous. But, the Late Carboniferous arc magmatism (c. 306-301 Ma) in the eastern sector of the İstanbul-Zonguldak Tectonic Unit rejects this view. Here, I present analytical data of basalt dykes in the western sector of the İstanbul-Zonguldak Tectonic Unit. Basalt dykes have porphyritic and holohyaline textures. Geochemically, they display calc-alkaline affinities and show depletion in Nb relative to Ce. They contain subduction components and are associated with the arc-related geodynamic setting. U–Pb dating on igneous zircons from two basalt dykes yielded Late Carboniferous ages of ca. 321.6 ± 1.6 and 311.4 ± 0.75 Ma (2σ), and their Pb-loss ages from the white spot in zircons calculated Early Permian ages of ca. 295.1 ± 1.1 to 285.0 ± 1.3 Ma and 295.5 ± 1.2 to 284.0 ± 1.4 Ma, respectively. In conjunction with the data from the literature, the Late Carboniferous arc magmatism (c. 321-311 Ma) in the western side of the İstanbul Zonguldak Tectonic Unit corresponds to the Late Carboniferous arc magmatism (c. 306-301 Ma) in the eastern side of the İstanbul Zonguldak Tectonic Unit, thus indicating that the Rheic Ocean continued to subduct under Far East Avalonia during the Carboniferous. As for the Pb-loss ages obtained from the Late Carboniferous arc basalt dykes, the earliest-latest Cisuralian ages (c. 295-285 Ma) correspond to regional deformation events at the Carboniferous-Permian boundary in the Rhodope-Strandja Massif (c. 298-296 Ma) and at the ending of the early Permian in the Sakarya terrane (c. 282-275 Ma), respectively. All in all, I suggest that the docking of Far East Avalonia, including the İstanbul-Zonguldak Tectonic Unit and Rhodope-Strandja Massif, with the Sakarya terrane formed during the early Permian instead of the early Carboniferous.
Bistability and hysteresis of the large-scale tropical circulation in idealized GCM simulations
Authors: Herbert Corentin
Published: March 2022

The potential impact of tipping points for climate dynamics is now widely recognized. Furthermore, paleoclimate records suggest that abrupt climate changes have indeed occurred in Earth’s past, potentially on timescales which do not exceed a decade. Several tipping elements, involving various components of the climate system, such as the ocean circulation, sea-ice, continental ice sheets, vegetation, and their couplings, have been suggested. Yet, it remains virtually unknown whether the large-scale atmospheric circulation, the component of the climate system with shortest response time, may undergo bifurcations that could trigger abrupt climate change.

    In this talk I will discuss the possibility of abrupt transitions of the large-scale circulation in the tropics. Specifically, I will consider potential reversals of the mean zonal winds, from the weak easterlies observed in current climate to a "superrotation" state with prevailing westerly winds. The superrotating state exhibits a strongly reduced Hadley circulation.
    I will discuss positive feedback mechanisms and their relevance for the Earth across a hierarchy of models of increasing complexity. A low-dimensional model based on Rossby wave resonance exhibits bistability, and provides a simple criterion for the region of parameter space where this regime exists. We then study the nature of the transition to superrotation in a dry dynamical core, forced in an idealized manner. The main result is that there exists a parameter regime where the dry primitive equations support two coexisting states, with and without an equatorial jet. We will discuss the role of parameters such as the meridional temperature gradient and the boundary layer friction on the existence of this bifurcation.
IMPLEMENTING A TERRESTRIAL NITROGEN AND PHOSPHORUS CYCLE IN THE UVIC ESCM: Validation and first results 
Authors: De Sisto Makcim , MacDougall Andrew
Published: March 2022

 

Nitrogen and phosphorus biogeochemical dynamics are crucial for the regulation of the terrestrial carbon cycle. In ESMs and EMICS the implementation of nutrient limitation has shown to improve the carbon feedbacks representation and hence, the response of land to atmospheric CO2 rising in simulation scenarios. We aimed to implement a nitrogen and phosphorus cycle in the UVic ESCM to improve projections of the future CO2 fertilization feedbacks. The nitrogen cycle is a modified version of the original N model developed in 2012, the basic structure was left in place with the most prominent changes being the enforcement of N mass conservation and the merger with a deep land-surface and wetland module that allowed the estimation of N2O and NO fluxes. The N cycle estimates fluxes from three organic (litter, soil organic matter and vegetation) and 2 inorganic (NH4+and NO3-) pools, it accounts inputs from biological nitrogen fixation and N deposition. The P cycle contains the same organic pools with one inorganic P pool, it estimates influx of P from rock weathering and losses from leaching and occlusion. Two historical simulations were carried for the different nutrient limitation setups of the model: CN and CNP, with a control run that consisted in an only C cycle simulation. The N cycle now conserves mass, the original and added fluxes (NO and N2O), along with the N and P pools are within the range of other studies and literature. The implementation of nutrient limitation resulted in a reduction of GPP from the CN (125 Pg yr-1) and CNP (111 Pg yr-1) simulations compared the C only control (148 Pg yr-1) by the year 2020; which implies that the model efficiently represents a nutrient limitation over the CO2fertilization effect. Furthermore, the tropical latitudes in the CNP simulation resulted in a reduction of 33% of the mean GPP and 41% of the vegetation biomass compared to the C only run; these results are in better agreement with observations and with the notion that P limitation have been shown to limit vegetation specially in tropical regions. In summary, the implementation of the nitrogen and phosphorus cycle have successfully enforced a nutrient limitation in the terrestrial system, which now have reduced the primary productivity and the capacity of land to uptake atmospheric carbon.
Quantification of methane emissions from anthropogenic sources: A case study in Canada
Authors: Vogt Judith , Perrine Gilles , Bourlon Evelise , Lavoie Martin , Risk Dave
Published: March 2022

Anthropogenic methane emissions are generated in several economic sectors, including agriculture, waste management, oil and gas production, and others. Canada is one of the world’s largest oil and gas producers, ranks in the top-25 for agricultural production, and is the world’s largest waste producer per capita. As a result, the methane emission potential is high in parts of Canada where all these activities co-occur. To quantify emissions from multiple co-located sectors, we conducted a case study in Grande Prairie, a small city in Canada’s west dominated by oil and gas production and agriculture. Our goal in this study was to produce a gridded dataset of emissions for the Grande Prairie region. In November 2021, we measured atmospheric mixing ratios of methane using a high-precision gas analyzer mounted in a truck, and estimated emission rates using an inverse Gaussian plume model. During our campaigns, we passed downwind of roughly 220 oil and gas sites and 20 farms with grazing cattle or bison present. We detected emissions at about one-quarter of the oil and gas sites and one-third of the farms, and we also observed emissions from waste management and power generation facilities. Methane emissions from oil and gas production sites were relatively low compared to others we have measured in Canada, but despite this we still found that oil and gas was the dominant methane-emitting sector in the Grande Prairie region. The results of this study feed into a long-term methane monitoring study, focused on multiple economic sectors, methane source types, and detection approaches.
Amplification across a seismic network - regional application to the Gulf of Corinth
Authors: Ktenidou Olga-Joan , Gkika Faidra , Pikoulis Erion-Vasilis
Published: March 2022

Modern engineering applications necessitate station metadata beyond a simple geological classification/characterisation. Recording stations should include detailed site metadata indicating the expected site response. However, this is not yet a general rule in Greece, due to their large number and distribution. In-situ-characterisation campaigns for the entire network would be unattainable across hundreds of stations in terms of time/budget. We resort to using the recorded data, namely the horizontal-to-vertical spectral ratio technique, to better understand site conditions. We compare with proxy-based estimations of scalar site metadata and show that the inherent variability of site response cannot be captured by such simplifications. We present results from one of the most seismically active regions in Greece, the Gulf of Corinth.  
Charting Australia’s changing hydrological extremes from the past to the present through to the future
Authors: Sharples Wendy , Bende-Michl Ulrike , Vogel Elisabeth , Holgate Chiara , Bahramian Katayoon , Khan Zaved , Carrara Elisabetta
Published: March 2022

In a changing climate, Australia’s ability to protect life and property against water related hazards such as floods, landslides, bushfires and droughts, will depend on high quality water resource information which is consistent across spatio-temporal scales. The Australian Bureau of Meteorology has recently released a new service: The Australian Water Outlook (awo.bom.gov.au) which provides nationally consistent water information including historical to near-real time hydrological monitoring, seasonal forecasts and long-term projections, offering a seamless perspective of Australian hydrology.

 

We exploit the seamless nature of this dataset to track the change in frequency, duration, magnitude and spatial extent of hydrological extreme events such as hydrological, agricultural and meteorological droughts, floods, and heavy rainfall events, using a range of different indicators, across different hydro-climate regions in Australia. Taking a multiple lines of evidence approach by using a combination of indicators which leverage water balance components of rainfall, soil moisture, evapotranspiration and runoff, we can reduce uncertainty in extreme event identification, and estimated magnitude and duration. Charting hydrological extreme events across regions and timescales will bolster Australia’s emergency management efforts in planning, preparedness and response as well as facilitate recovery. 
Ice microphysics retrievals using polarimetric and dual-wavelength radar data – a sensitivity study regarding the assumed ice particle model
Authors: Tetoni Eleni , Ewald Florian , Hagen Martin , Köcher Gregor , Zinner Tobias , Mayer Bernhard , Groß Silke
Published: March 2022

The importance of robust ice microphysics retrievals has been highlighted in the past by several studies. The accurate representation of ice microphysical processes can reduce the uncertainty in numerical weather models which have to deal with the complex nature – various habits, densities, sizes – of ice hydrometeors. To constrain microphysics information, we developed an ice microphysics retrieval algorithm combining measurements from two spatially separated radar instruments. The radar measurements comprise a novel combination of dual-wavelength and polarimetric perspective (i.e., differential radar reflectivity, ZDR) on ice hydrometeors. Exploiting the different scattering behavior (Rayleigh or Mie region) in different radar bands, the dual-wavelength dataset provides information about the ice hydrometeor size within clouds. In addition, ZDR from one of the radar instruments was also used to constrain the shape of ice particles. The measurements were performed with the C-band POLDIRAD (German Aerospace Center, Oberpfaffenhofen) and the Ka-band MIRA-35 (Ludwig-Maximilians-Universität, Munich) using coordinated range-height-indicator (RHI) scans to capture precipitation formation within the 23 km long cross-section between both instruments. To infer microphysical properties, T-matrix scattering simulations were performed in combination with necessary a-priori assumptions about the ice hydrometeors. Due to its versatility, we used the soft spheroid approximation to represent the prevalent ice particles. This approach along with a pre-defined relation between mass and particles dimension (mass-size relation) can help to constrain the prevalent ice particle density, a parameter which is known to be hardly constrained in numerical weather and climate models. In this work, we conducted several sensitivity studies to investigate which assumptions on mass-size relation, particle size distribution and shape (oblate or horizontally aligned prolate) can reproduce our radar observations for the soft spheroid ice model. We also investigated how these assumptions can influence the retrieved median size, the apparent shape and the ice water content of ice particles populations. Our hypotheses were tested for a stratiform precipitation case from a snowfall event over Munich in January 2019. 
Increasing compound concurrent hot day and night extremes in five big cities of Switzerland
Authors: Ashraf Vaghefi Saeid , Muccione Veruska , Neukom Raphael , Huggel Christian , Salzmann Nadine
Published: March 2022

The interaction of multiple hazards across various spatial and temporal scales typically causes compound climate and weather extreme events. Compound concurrent hot day and night extremes that combine daytime and nighttime heat are of greater concern for health than individual hot days or hot nights. Continuous day and nighttime heatwaves can exacerbate human discomfort and therefore increase the risks of heat-related morbidity and mortality. However, little is known about the evolution of such events in the observed and projected climate. Four compound event types, namely (a) preconditioned, (b) multivariate, (c) temporally compounding, and (d) spatially compounding events were introduced in the literature that facilitates the selection of the proper approaches in the study of compound extreme events. The impact of a single or the combination of multiple types could shape more severe extreme events. In our study, we considered the temporally compounding and multivariate types and used climate observations (1981-2020) and high-resolution bias-corrected climate model scenarios of Switzerland (CH2018). Our analyses show that the average frequency and intensity of compound consecutive hot days and nights increase in five big cities of Switzerland until 2100 under RCP4.5. We projected 1.83 ± 0.07 (days decade−1) for Basel, 1.57 ± 0.1 (days decade−1) for Bern, 2.34 ± 0.13 (days decade−1) for Geneva, 2.55 ± 0.17 (days decade−1) for Lugano, and 1.93 ± 0.12 (days decade−1) for Zürich. Moreover, we found an increase in the intensity of summertime (April-October) compound hot extremes days and night in Basel (0.28 ± 0.03 °C decade−1), Bern (0.23 ± 0.02°C decade−1), Geneva (0.37 ± 0.04 °C decade−1), Lugano (0.4 ±0.07°C decade−1), and Zürich (0.44 ± 0.05°C decade−1).
Can simple machine learning methods predict concentrations of OH better than state of the art chemical mechanisms?
Authors: Hickman Sebastian , Griffiths Paul , Weber James , Archibald Alex
Published: March 2022

Concentrations of the hydroxyl radical, OH, control the lifetime of methane, carbon monoxide and other atmospheric constituents.  The short lifetime of OH, coupled with the spatial and temporal variability in its sources and sinks, makes accurate simulation of its concentration particularly challenging. To date, machine learning (ML) methods have been infrequently applied to global studies of atmospheric chemistry.

We present an assessment of the use of ML methods for the challenging case of simulation of the hydroxyl radical at the global scale, and show that several approaches are indeed viable.  We use observational data from the recent NASA Atmospheric Tomography Mission to show that machine learning methods are comparable in skill to state of the art forward chemical models and are capable, if appropriately applied, of simulating OH to within observational uncertainty.  

We show that a simple ridge regression model is a better predictor of OH concentrations in the remote atmosphere than a state of the art chemical mechanism implemented in a forward box model. Our work shows that machine learning may be an accurate emulator of chemical concentrations in atmospheric chemistry, which would allow a significant speed up in climate model runtime due to the speed and efficiency of simple machine learning methods. Furthermore, we show that relatively few predictors are required to simulate OH concentrations, suggesting that the variability in OH can be quantitatively accounted for by few observables with the potential to simplify the numerical simulation of atmospheric levels of key species such as methane. 
Radial diffusion coefficients database in the framework of the SafeSpace project: A Machine Learning model and the application to radiation belt simulations
Authors: Daglis Ioannis A. , Katsavrias Christos , Aminalragia-Giamini Sigiava , Nasi Afroditi , Dahmen Nourallah , Brunet Antoine , Bourdarie Sebastien , Papadimitriou Constantinos
Published: March 2022

Radial diffusion has been established as one of the most important mechanisms contributing to the acceleration and loss of relativistic electrons in the outer radiation belt. Over the past few years efforts have been devoted to identify empirical relationships of radial diffusion coefficients (DLL) for radiation belt simulations, yet several studies have suggested that the difference between the various models can be orders of magnitude different at high levels of geomagnetic activity, as the observed DLL have been shown to be highly event-specific. In the framework of the SafeSpace project we have used 12 years (2010 – 2020) of multi-point magnetic and electric field measurements from THEMIS A, D and E satellites to create a database of calculated DLL. In this work we present the statistics on the evolution of DLL during the solar cycle 24 with respect to the various solar wind parameters, geomagnetic indices and universal coupling functions. Furthermore, we show the importance of the use of event-specific DLL through simulations of seed and relativistic electrons with the Salammbo code during the intense storm of St. Patricks 2015 and the high-speed stream driven storm of Christmas 2013. Finally, we present a new approach for a Machine Learning model driven solely by Solar wind parameters.

This work has received funding from the European Union's Horizon 2020 research and innovation programme “SafeSpace” under grant agreement No 870437.
Trends and Drivers of Bedload and Suspended Sediment Fluxes in Global Rivers
Authors: Cohen Sagy , Syvtski Jaia , Ashley Thomas , Lammers Roderick , Fekete Balazs , Li Hong-Yi
Published: March 2022

Bedload flux is notoriously challenging to measure and model. The dynamics of bedload, therefore, remains largely unknown in most fluvial systems worldwide. We present a global scale bedload flux model as part of the WBMsed modeling framework. Our results show that the model can very well predict the distribution of water discharge and suspended sediment and well predict bedload. We analyze the model’s bedload predictions sensitivity to river slope, particle size, discharge, river width, and suspended sediment. We found that the model is most responsive to spatial dynamics in river discharge and slope. We analyze the relationship between bedload and total sediment flux globally and in representative longitudinal river profiles (Amazon, Mississippi, and Lena Rivers). We show that while, as expected, the proportion of bedload is decreasing from headwater to the coasts, there is considerable variability between basins and along river corridors. The latter is largely responsive to changes in suspended sediment and river slope due to dams and reservoirs. We provide a new estimate of water and sediment fluxes to global oceans from 2,067 largest river outlets (draining 67% of the global continental mass). Estimated water discharge (30,579 km3/y) corresponds well to past estimates however sediment flux is considerably higher. Of the total 22 Gt/y estimated average sediment flux to global oceans, 19 Gt/y is transported as washload, 1 Gt/y as bedload, and 2 Gt/y as suspended bed material. The largest 25 rivers are predicted to transport over 55% of total sediment flux to global oceans.
New global constraints on transition-zone topography from normal-mode tomography 
Authors: van Tent Rûna , Deuss Arwen
Published: March 2022

Lateral variations in the depths of the transition-zone discontinuities are generally attributed to variations in temperature, causing local changes in the depth of the dominant phase transition. At moderate temperatures the dominant phase transitions are those of olivine, characterized by a positive Clapeyron slope (dP/dT) at 410 km depth and a negative Clapeyron slope at 660 km depth. An anticorrelation between topography on the 410 and 660-km discontinuities is therefore expected in the absence of variations in chemical composition, as an increase in temperature would lower the 410-km discontinuity and elevate the 660-km discontinuity. Simultaneously, this temperature increase would result in a decrease in seismic velocity and density of the mantle material. Comparing models of transition-zone topography, seismic velocity and density therefore gives valuable insight into the nature of transition-zone discontinuities. Existing global models of transition-zone topography have been created using SS and PP precursor measurements, which need to be corrected for mantle velocity structure using an independent velocity model before the discontinuity depths can be calculated. Here, we present new global models of transition-zone topography and whole-mantle S-wave velocity, P-wave velocity and density that have been simultaneously inferred from a different type of seismic data: Earth’s normal modes. Normal modes are whole-Earth oscillations induced by large earthquakes (Mw≥7.5). We use our models, which can be readily compared to one another, to analyze the nature of the transition-zone discontinuities. We also discuss the trade-offs between the different model parameters and the model uncertainties, the latter of which is additional information provided by the Hamiltonian Monte Carlo method used for our inversion. Finally, we compare our models to transition-zone topography obtained from SS precursor data.
Incorporating climate-induced hydro-meteorological extremes in global health security: A waterborne disease perspective
Authors: Darnault Christophe
Published: March 2022

Climate-induced hydro-meteorological extreme events such as the occurrence of heavy precipitations or lack thereof, intense continuous rainfall, flooding, and drought are increasing worldwide and will likely be escalating in the future. Understanding of climate-induced hydro-meteorological extremes is essential to characterize the fate, transport, and survival of pathogens in the environment and strengthen global health security. This study discusses the role of climate-induced hydrological and meteorological extreme events and tipping points on the environmental transmission of pathogenic microorganisms in terrestrial and aquatic systems, waterborne disease outbreaks, and biological threats to human health. Research on the effects of climate-induced hydro-meteorological extremes on the incidence of infectious diseases will allow the development of climate-driven early warning systems and risk forecasting to reduce infectious diseases threats to human populations.
How to break the lithosphere: a compressible pressure-velocity formulation for elasto-visco-plastic rheologies that includes shear and tensile failure with dilation
Authors: Berlie Nicolas , Kaus Boris , Popov Anton , Kiss Daniel , Riel Nicolas
Published: March 2022

One of the great challenges involved in modelling the lithosphere is its plastic behaviour, especially when dealing with compressible materials. Shear fractures are designated as mode 2 and 3 and can be described using a Linear Mohr Coulomb envelope  or a simplification of it like Drucker-Prager. Meanwhile, mode 1 fractures are created when the normal stresses become tensile  and require another yield function, such as the Griffith criterion or a tension cap function.

While the governing equations are well known and widely employed in engineering codes, they are usually expressed with a displacement formulation. Most geodynamic codes, on the other hand, use pressure and velocity as their primary variables. A numerically robust method that takes all plasticity modes into account in a staggered finite difference discretization remains an open task. Here we present a composite yield function implemented with pressure-velocity formulation, capable of producing produce shear and tensile failure.

We have implemented this in a new code that employed PETSc through the recently updated PETSc.jl Julia interface, while utilizing the automatic differentiation tools in julia. We found this workflow to significantly reduce the development time of complex nonlinear coupled codes.  

We will describe the implementation, propose regularization schemes and discuss benchmark cases and simple applications. We demonstrate Newton convergence for most cases and will discuss different methods to combine multiple plastic flow laws.
Parallel volcanic chains generated by plume-slab interaction
Authors: Mather Ben , Seton Maria , Williams Simon , Whittaker Joanne , Carey Rebecca , Arnould Maëlis , Coltice Nicolas , Rogers Angus , Ruttor Saskia , Nebel Oliver
Published: March 2022

Deep mantle plumes are buoyant upwellings rising from the Earth’s core-mantle boundary to its surface, and describing most hotspot chains. Mechanisms to explain dual chains of hotspot volcanoes for the Hawaiian-Emperor and Yellowstone chains fail to explain the geochemical similarity and large distances between contemporaneous volcanoes of the Tasmantid and Lord Howe chains in the SW Pacific. Using numerical models of mantle convection, we demonstrate how slab-plume interaction can lead to sustained plume branching over a period of >40 million years to produce parallel volcanic chains that track plate motion. We propose a three-part model: first, slabs stagnate in the upper mantle, explaining fast upper mantle P-wave velocity anomalies; second, deflection of a plume conduit by a stagnating slab splits it into two branches 650-900 km apart, aligning to the orientation of the trench axis; third, plume branches heat the stagnating slab causing partial melting and release of volatiles which percolate to the surface forming two contemporaneous volcanic chains with slab-influenced EM1 signatures. Our results highlight the critical role of long-lived subduction on the evolution and behaviour of intraplate volcanism.
The Influence of pH on Ice Nucleation by α-alumina 
Authors: Ren Yi , Soni Abhishek , Bertram Allan , Patey Gren
Published: March 2022

Heterogeneous ice nucleation refers to ice nucleation initiated by an ice nucleating particle (INP). Important INPs include mineral dust and biological particles. Cloud conditions, such as pH, significantly affect ice nucleation. Clouds are generally acidic but can have a range of pH values, depending on their compositions. Studies have shown that α -alumina is an efficient INP in both laboratory experiments and Molecular Dynamics (MD) simulations. The (0001) plane of α-alumina is covered by hydroxyl groups in aqueous solutions, therefore, the surface is expected to undergo dual protonation (acidic conditions) and deprotonation (basic conditions). We investigate the effect of pH on the ice-nucleating efficiency of the α-alumina (0001) plane in MD simulation. Multiple surface proton coverages are considered, and we relate the surface proton coverage to pH through pKa values reported in the literatures. Among all possible surface proton coverages, the mono-protonated surface, which dominates under neutral condition, appears to be most efficient in nucleating the basal plane ice. For dual-protonated and deprotonated surfaces, the ice bilayer above the surface becomes less ice-like, leading to less efficient ice nucleation. Our MD results suggest that the (0001) plane of α-alumina is most efficient in nucleating ice under neutral condition, and less efficient under acidic and basic conditions.  