bluuebunny/crossref_metadata_2025 huggingface dataset:
Hybrid Particle-In-Cell model with Adaptive Mesh Refinement
Authors: Aunai Nicolas , Smets Roch , Deegan Philip , Ciardi Andrea , Jeandet Alexis
Published: March 2022

Collisionless magentized plasmas a priori need to be evolved using Vlasov-Maxwell kinetic formalism.
However the tremendous number of spatial and temporal scales involved in phenomena of interest makes it prohibitive, from a computational standpoint.
Fully kinetic particle in cell and single fluid MHD codes are commonly used at very small or very large scales.
The hybrid formalism, treating ions kinetically and electrons as a fluid, is in principle advantageous to fill the gap between these two extremities.
However, a correct treatment of critical regions such as reconnection X-lines require a good resolution of sub-ion dissipative scales, which
still constitute a major challenge if aiming at simulating meso/macro scale systems.
This work presents a new code, named PHARE, which successfully implements the adaptive mesh refinement mechanism in a hybrid particle-in-cell code.
Such a code is able to dynamically focus the resolution in critical regions while others not only have a coarser spatial resolution, but are also
evolved much less often thanks to a recursive time stepping procedure.
Adopting a patch based AMR mechanism, the code architecture is made so that the specific solver/physical model that is solved at a given refined level
is abstracted, thus giving the opportunity to handling multi-formalisms AMR patch hierarchies, where, for instance, coarsest levels are solved in MHD while
dynamicall created refined levels are solved within the Hybrid framework.
Thermal regime of the Grigoriev ice cap and the Sary-Tor glacier in the Inner Tien Shan, Kyrgyzstan. 
Authors: Van Tricht Lander , Huybrechts Philippe
Published: March 2022

The thermal regime of glaciers and ice caps represents the internal distribution of ice temperatures. Accurate knowledge of the thermal regime is crucial to understand the dynamics and response of ice masses to climate change, and to model their evolution. The ice temperature for example strongly controls the plasticity and the deformation rate of the ice with higher temperatures encouraging movement, and whether a glacier can slide over its base. Although the assumption is that most ice masses in the Inner Tien Shan are polythermal, this has not been examined in appropriate detail so far. In this research, we investigate the thermal regime of the Grigoriev ice cap and the Sary-Tor glacier, both located in the Inner Tien Shan in Kyrgyzstan. A 3D thermo-mechanical higher-order model is applied. Input data and boundary conditions are inferred from a surface energy mass balance model, a historical air temperature and precipitation series, ice thickness reconstructions, and digital elevation models. Calibration and validation of the englacial temperatures is performed using historical borehole measurements on the Grigoriev ice cap, radar measurements for the Sary-Tor glacier and temperature measurements on other glaciers in the area. The results of this study reveal a polythermal structure of the Sary-Tor glacier and a cold structure of the Grigoriev ice cap. The difference is related to the larger amount of snow (insulation) and superimposed ice (release of latent heat) for the Sary-Tor glacier resulting in higher surface temperatures, especially in the accumulation area, which are subsequently advected downstream. Further, ice velocities are much lower for the Grigoriev ice cap compared to the Sary-Tor glacier with consequent lower advection rates. Since the selected ice masses are representative examples of the (Inner) Tien Shan glaciers and ice caps, our findings can be generalised allowing this to improve the understanding of the dynamics and future evolution of the studied ice masses as well as other glaciers and ice caps in the region.
Pollen-based reconstruction reveals the impact of the onset of agriculture on plant functional trait composition
Authors: Veeken Annegreet , Schrodt Franziska , McGowan Suzanne , Santos Maria J.
Published: March 2022

In the past two decades, plant functional traits have become an important tool in ecology and biogeography for the study of consequences of changing plant composition on ecosystem functioning and the effect of environment factors on plant composition. Recently, considerable interest in the trait-based approach has arisen in palaeoecology as well. Applying the trait-based approach could offer a new way of interpreting pollen data, but the intricacies of using this method in palaeoecology are underexplored. Here we test the validity of the use of pollen records for plant functional composition reconstruction using modern pollen samples. Using a Bayesian approach for reconstructing plant trait composition from pollen records, we provide a robust method that can account for trait variability within pollen types. We apply this method to assess changes in plant functional composition over 10 000 years for 79 European sites with an agricultural history. We evaluate how agriculture and climate affect plant functional composition. We reveal selection of common traits across agricultural landscapes, with resource-acquisitive communities of low stature and seed mass dominating after the arrival of agriculture. Understanding these selection processes and trade-offs between traits will advance our understanding of the legacy of human impact on ecosystems functions.
Modelling sediment yield in an elementary catchment: reducing the complexity to the key processes
Authors: Armitage John , Venisse Nolwen , Franke Christine , Alary Claire , Delaporte Morgan
Published: March 2022

The transport of sediment within a catchment is a complex interaction between the physics of granular transport and the intrinsic local conditions of the sedimentary basin. In trying to understand the causal relationship between climate and sediment transport within a process-based numerical model, the system needs to be simplified. At one extreme at geological timescales there are simple diffusion or advection-based models of transport with only a handful of parameters. At the other extreme complex land surface models for weather forecasting rely on a multitude of user defined parameters. In geomorphology we are faced with the challenge of scale – at what spatial and temporal scale are events important – combined with the uncertainty of various processes and the associated parameters. If we wish to forecast future sustainability for land use over the next 20 to 100 years (including soil loss), the problems of scale and unknown parameters becomes acute. To enter this problem, we have explored the potential of the process-based CAESAR-Lisflood (C++ version) model to simulate the observed erosion of a small sub-catchment within the upper Canche River watershed in the Haut-De-France region. The Pommeroye catchment is of a scale of 0.5 km2, it is composed of 14 cultivated fields and has had continuous monitoring of sediment yield for two years. We focus on using CAESAR-Lisflood as a platform to explore (1) what spatial and temporal scale and (2) what processes are required to match the observed relation between rainfall and sediment yield. We find that a relatively simple model with a 30 cm transport-limited top-soil layer above a detachment-limited layer can match the magnitude of sediment yield. In our set-up the model has only three unconstrained parameters that we tune to give a better fit to the observations: an infiltration parameter that controls peak run-off and the recession curve, a Manning’s roughness within the water routing algorithm, and the erodibility for the detachment-limited law. However, this reduced complexity model cannot capture the ephemeral nature of the landscape, where only certain rainfall events lead to significant sediment yield. A key uncertainty is infiltration and groundwater flow. The transition from precipitation to run-off is calculated by a local recession curve assuming storage at each model cell. However, within the study catchment groundwater pathways cannot be ignored, and it is only when the soil is saturated or when rainfall exceeds the infiltration rate that significant sediment transport occurs. We would therefore suggest that future efforts should be focused on understanding the relationship between the water flux at surface and in the sub-surface to understand how precipitation is translated into sediment flux.
Validation of an RCM over Mainland Southeast Asia focusing on the needs of hydrological models
Authors: Abel Daniel , Paeth Heiko
Published: March 2022

This work is part of the CLIENT II project Drought-ADAPT, which overall objective is to provide climate services to local stakeholders in the Central Highlands of Vietnam. The focus of the project lies on various aspects of drought, its characteristics and causes under recent and future climate change, as the study area has been shown to be vulnerable in this regard.

An important component for this is the use of the regional climate model REMO, which simulates the historical period from 2000-2018 over Mainland Southeast Asia at 0.11° resolution. With this, the run differs from existing CORDEX-simulations which are available in a coarser resolution of 0.22°. For a proper validation with respect to spatio-temporal aspects of its climatology, a comparison of different gridded validation datasets of temperature, precipitation, and potential evapotranspiration is performed as these are important forcing variables for hydrological modeling. Finally, a simple form of bias adjustment is done to compensate systematic model errors and, thus, make the data available and usable for a hydrological model.
Net effect of ice-sheet-atmosphere interactions reduces simulated transient Miocene Antarctic ice sheet variability
Authors: Stap Lennert B. , Berends Constantijn J. , Scherrenberg Meike D.W. , van de Wal Roderik S.W. , Gasson Edward G.W.
Published: March 2022

Benthic δ18O levels vary strongly during the warmer-than-modern early- and mid-Miocene (23 to 14 Myr ago), suggesting a dynamic Antarctic ice sheet (AIS). So far, however, realistic simulations of the Miocene AIS have been limited to equilibrium states under different CO2 levels and orbital settings. Earlier transient simulations lacked ice-sheet-atmosphere interactions, and used a present-day rather than Miocene Antarctic bedrock topography. Here, we quantify the effect of ice-sheet-atmosphere interactions, running IMAU-ICE using climate forcing from Miocene simulations by the general circulation model GENESIS. Utilising a recently developed matrix interpolation method enables us to interpolate the climate forcing based on CO2 levels (between 280 and 840 ppm) as well as varying ice sheet configurations (between no ice and a large East Antarctic ice sheet). We furthermore implement recent reconstructions of Miocene Antarctic bedrock topography. We find that the positive albedo-temperature feedback, partly compensated by a negative feedback between ice volume and precipitation, increases hysteresis in the relation between CO2 and ice volume. Together, these ice-sheet-atmosphere interactions decrease the amplitude of Miocene AIS variability in idealised transient simulations. Forced by quasi-orbital 40-kyr forcing CO2 cycles, the ice volume variability reduces by 21% when ice-sheet-atmosphere interactions are included, compared to when forcing variability is only based on CO2 changes. Thereby, these interactions also diminish the contribution of AIS variability to benthic δ18O fluctuations. Evolving bedrock topography during the early- and mid-Miocene reduces ice volume variability by 10%, under equal 40-kyr cycles of atmosphere and ocean forcing. 
Increased variability in Greenland Ice Sheet runoff detected by CryoSat-2 satellite altimetry
Authors: Slater Thomas , Shepherd Andrew , McMillan Malcolm , Leeson Amber , Gilbert Lin , Muir Alan , Kuipers Munneke Peter , Noël Brice , Fettweis Xavier , van den Broeke Michiel , Briggs Kate
Published: March 2022

Runoff from the Greenland Ice Sheet has increased over recent decades affecting global sea level, regional ocean circulation, and coastal marine ecosystems. Runoff now accounts for most of Greenland’s contemporary mass imbalance, driving a decline in its net surface mass balance as the regional climate has warmed. Although automatic weather stations provide point measurements of surface mass balance components, and satellite observations have been used to monitor trends in the extent of surface melting, regional climate models have been the principal source of ice sheet wide estimates of runoff. To date however, the potential of satellite altimetry to directly monitor ice sheet surface mass balance has yet to be exploited. Here, we explore the feasibility of measuring ice sheet surface mass balance from space by using CryoSat-2 satellite altimetry to produce direct measurements of Greenland’s runoff variability, based on seasonal changes in the ice sheet’s surface elevation. Between 2011 and 2020, Greenland’s ablation zone thinned on average by 1.4 ± 0.4 m each summer and thickened by 0.9 ± 0.4 m each winter. By adjusting for the steady-state divergence of ice, we estimate that runoff was 357 ± 58 Gt/yr on average – in close agreement with regional climate model simulations (root mean square difference of 47 to 60 Gt/yr). As well as being 21 % higher between 2011 and 2020 than over the preceding three decades, runoff is now also 60 % more variable from year-to-year as a consequence of large-scale fluctuations in atmospheric circulation. In total, the ice sheet lost 3571 ± 182 Gt of ice through runoff over the 10-year survey period, with record-breaking losses of 527 ± 56 Gt/yr first in 2012 and then 496 ± 53 Gt/yr in 2019. Because this variability is not captured in global climate model simulations, our satellite record of runoff should help to refine them and improve confidence in their projections.
Synergistic effects of grass coverage and dam land sedimentation on runoff and sediment yields in slope-gully system on the Loess Plateau of China
Authors: Shi Peng , Bai Lulu , Li Zhanbin , Li Peng
Published: March 2022

Grass coverage and check dam construction are important measures for soil and water conservation in Loess Plateau. They have a significant effect on the reduction of runoff and sediment, but the synergistic effects of their regulation of hydrological processes are not well understood. To understand the synergistic effects of grass and check dam construction on water erosion process, physical models of 10 slope-gully systems were established including grass cover slopes (0% and 33%) and dam land settlement slope-gullies (0,1, 2, 3 and 4 m during settlement). The single grass coverage reduced runoff and sediment of 155.91 L and 15155.33 g, respectively. Sediment reduction increased with siltation depth: 4 m (18056.73 g) > 3 m (15990.79 g) > 2 m (14173.79 g) > 1 m (6027.13 g), and the runoff reduction followed as: 4 m (122.21 L) > 3 m (87.48 L) > 2 m (50.37 L) > 1 m (28.77 L). Grass coverage and sedimentation had synergistic effects on water erosion, and the synergistic effects of sediment reduction increased with sedimentation process: 4 m (19.83%) > 3 m (18.68%) > 2 m (17.39%) > 1 m (16.70%). The results indicated that grass coverage on the slope and dam land sedimentation had a synergistic effect on hydrological process, which should not be ignored in the evaluation of soil and water conservation measures regulation.
Dual-polarisation X-band radar estimates of precipitation assessed using a distributed hydrological model for mountainous catchments in Scotland
Authors: Wallbank John R. , Cole Steven J. , Moore Robert J. , Dufton David , Neely III Ryan R. , Bennett Lindsay
Published: March 2022

Observing, in a quantitative and robust way, the dynamic space-time pattern of precipitation in mountainous terrain presents a major challenge of great practical importance. The difficulties of this task are further exacerbated in mid to high latitudes where the typical melting layer for precipitation (i.e. the 0°C isotherm) is often close to the surface during winter months. One way to address this challenge is by improving observations made using networks of weather radars. Quantitative Precipitation Estimates (QPEs) derived from these instruments have many applications, for example as input to a hydrological model to simulate river flow for flood forecasting purposes. 

Here, a set of QPEs - obtained from an observation campaign using the National Centre for Atmospheric Science’s mobile X-band dual-polarisation Doppler weather radar (NXPol) in a mountainous area of Northern Scotland - are assessed with reference to observed river flows. Each form of QPE is used as an input to Grid-to-Grid (G2G), a distributed hydrological model used for flood forecasting across Great Britain, and the simulated river flows compared to observations. The location of the radar was specially chosen to infill an area of reduced coverage in the existing C-band radar network for the British Isles.

Assessments of radar QPE often only examine a final precipitation “best estimate” product and typically with reference to raingauges at specific locations. Here, we exploit the processing capabilities of NXPol and the hydrological modelling framework to investigate the benefits of ten separate processing methods that increase with complexity and make differing use of dual-polarisation variables. The role of the radar beam elevation and distance from the radar is investigated, and NXPol QPEs are compared to that provided by the radar network. Additionally, a preliminary investigation is carried out into the role of the drop-size distribution on the relationship between radar-reflectivity and rain-rate using disdrometer data.

The hydrological assessment reported on here has the benefit of integrating the precipitation over space and time which serves to complement and extend a previous meteorological assessment using raingauge data alone. The assessment proves to be insensitive to issues affecting both raingauges (e.g. representativity, wind-induced under-catch) and local artefacts in the space-time radar-rainfall field. It facilitates a direct assessment of whether potential benefits in the new QPEs are carried forward to an end-use such as flood forecasting, providing fresh insights for the development of new dual-polarisation radar QPE methods.
Quantifying the impact of winter warming on arctic-boreal ecosystems and greenhouse gas exchange
Authors: Pongracz Alexandra , Wårlind David , Miller Paul A. , Parmentier Frans-Jan W.
Published: March 2022

Future projections suggest that the Arctic will undergo extreme changes in the near future, with the largest changes occurring during the wintertime. Still, cold season processes and their impact on the annual carbon and water budgets are often understudied.

We aim to assess and quantify the impact of winter warming on the arctic carbon cycle by improving the representation of cold-season processes in the LPJ-GUESS DGVM. Firstly, we developed and implemented a new, dynamic snow scheme into the model to enhance the simulation of snow-soil-vegetation interaction. These updates improved the simulation of modelled soil temperature and permafrost extent compared to observations. In our latest study, we are assessing the physical controls on non-growing season methane emissions in the model, focusing on potential burst-like methane emissions during the zero curtain period. We set out to evaluate whether enabling non-growing season methane emissions may influence the annual methane budget.

So far, we found that changes in the cold season significantly affect arctic biogeochemistry. We also observed that wintertime changes affect vegetation dynamics and composition over the Arctic. Improving the model representation of wintertime processes enables to further investigate the future snow-soil-vegetation interaction. These simulations can be used to assess the impact of warming on the arctic carbon cycle and its global consequences.
The effect of nutrient management on organic matter in subsoils of temperate and tropical agroecosystems
Authors: Müller Claude , Six Johan , Hartmann Martin , Van de Broek Marijn
Published: March 2022

One of the aims of sustainable soil management in agriculture is to preserve soil organic matter (SOM) because it relates to important ecosystem services such as carbon storage and soil fertility. Soil organic carbon (SOC) storage can contribute to climate regulation, while soil fertility is essential to provide food to a steadily growing population. Most studies focus on the topsoil (i.e., 0 to 30 cm depth). Nevertheless, studying only the topsoil SOC is not sufficient to estimate the effect of management practices on the organic carbon (OC) storage capacity of soils. Indeed, an important quantity of OC is present in the subsoil.

In this project, soil samples were collected in two long-term agricultural field experiments in temperate (Switzerland) and tropical (Kenya) climates. The Kenyan trial (the SOM trial) was established in 2002 and maize has been cultivated in monoculture in every growing season (two per year). The different treatments include the application of organic residues with different carbon to nitrogen ratios, and manure, with and without mineral nitrogen. Samples have been collected down to 70 cm depth in increments of 5 cm. The Swiss trial (the DOK trial) was established in 1978. Different crops (wheat, potato, soy, grass, and maize) are grown in rotation. The treatments include different fertilizer and crop protection regimes representing conventional and organic agricultural practices. Samples have been collected down to 90 cm depth in increments of 5 cm.

In the DOK trial, mean SOC concentration decreased from ca. 1.8 % in the 0-5 cm to ca. 0.5 % in the 85-90 cm depth layer. Soils under organic and biodynamic treatments had a higher SOC content over the whole depth profile compared to soils under conventional practices, pointing out the potential effect of these practices to increase SOC stocks over time. In the SOM trial, the mean SOC concentration decreased from ca. 2.2 % in the 0-5 cm to ca. 1.2 % in the 65-70 cm depth layer. Organic inputs had a positive effect on the SOC content over the whole depth profile, while the addition of mineral N without organic input had a negative effect. As the information on the effect of nutrient management practices on subsoil SOC content is limited, specifically in the tropics, these data help to improve our knowledge about these effects, while providing guidelines to farmers and farm advisors on how to maximize the SOC content of soils. In addition, these data provide a valuable resource for the formulation and calibration of model simulations of SOC dynamics in agroecosystems.
The Structure of North Atlantic Kinetic Energy Spectra
Authors: Dewar William K. , Uchida Takaya , Jamet Quentin , Poje Andrew
Published: March 2022

An ensemble of North Atlantic simulations is analyzed, providing estimates of kinetic energy spectra.  A wavelet transform technique is used permitting comparisons to be made between spectra at different locations in this highly inhomogeneous environment.  We find a strong tendency towards anisotropy in the spectra, with meridional spectra typically stronger than zonal spectra.  This holds even in the gyre interior where conditions might be expected to be homogeneous.  The spectra show reasonable ranges consistent with a downscale enstrophy cascade, but also a persistent tendency to exhibit steeper slopes at smaller scales.  The only location where the presence of an upscale cascade is supported is the Gulf Stream extension.  This is amongst first attempts to quantify and compare spectra and their differences in the inhomogeneous setting of the North Atlantic.
Making use of climate information for protecting cultural heritage from extreme weather events in a warming world
Authors: Kotova Lola , Leissner Johanna , Winkler Matthias , Antretter Florian , Kilian Ralf , Mossgraber Jürgen , Reuter Jürgen , Hellmund Tobias , Dolgov Anton , Matheja Katharina Matheja , Rhode Michael Rohde , Pollmer Uta , Mikolajewicz Uwe
Published: March 2022

The intensity and frequency of extreme weather events in Europe are one of the most dangerous consequences of a warming climate. Some regions suffer more under heat waves and droughts, while others are experiencing extreme rainfalls. Thus, for example, a severe flood in July 2021 in several European countries caused widespread damages particularly in Belgium and Germany.

Which extreme weather events are to be expected in the future? How can the damage of irretrievable historical sites be avoided or, at least, limited or dealt with? All these questions are addressed in the three-year research project KERES, which is funded by the German Federal Ministry of Education and Research (BMBF) and is coordinated by the Fraunhofer ISC together with the Fraunhofer EU Office in Brussels.

As first step the regional relevance of future extreme weather events in Germany will be investigated.  This information will be further used to estimate the potential damages to buildings and outdoor facilities. The precautionary and responsive measures to manage potential or acute damage situations will be investigated as well. The designed methodologies will be tested for five case studies including World Heritage Sites (historical buildings and historical gardens)  in Germany.

The major tools of KERES include building component and indoor climate simulations and high-resolution urban climate models. The necessary input will be taken from the most recent ensemble of regional climate change projections of the EURO-CORDEX Initiative (www.euro-cordex.net).  As a result, an ontology-based information system will be designed for managing the expected damage situations.

We will present first results from the KERES project. The discussion will be focused on how to access and visualize the robustness of projected changes of extreme weather events in a way oriented to individual cultural heritage sites.
Probabilistic Tsunami Hazard Assessments in Eastern Sicily (Italy) including sea level rise caused by climate change and local subduction effects. 
Authors: Grezio Anita , Baglione Enrico , Selva Jacopo , Tonini Roberto , Anzidei Marco , Vecchio Antonio
Published: March 2022

The coasts of the Mediterranean Sea are densely populated and exposed to tsunami inundations as reported by historical evidence. Measures to mitigate the tsunami risk in this region are based on Probabilistic Tsunami Hazard Assessments (PTHA) computed considering present coastal morphologies. However, mean sea level projections for the 21st century indicated a general sea level rise which can be substantially modified if uplift or subsidence may occur locally due to other geological factors. In order to reduce the potential impact of tsunamis all factors (climatic or not) should be included in the tsunami hazard analysis. In this study we focus on the Eastern Sicily and we examine how the PTHA can significantly change when the general trend of sea level rise, based on AR-5 and AR-6 IPCC climate scenarios and rates of Vertical Land Movements, are included in the region. Moreover, we take into account associated epistemic uncertainties related to the future sea level rise under different conditions of low- and high-emission representative concentrations. 
Exploring the solar wind-planetary interaction at Mars: Implication for Magnetic Reconnection
Authors: Bowers Charles F. , DiBraccio Gina A. , Slavin James A. , Gruesbeck Jacob R. , Weber Tristan , Romanelli Norberto , Azari Abigail R. , Xu Shaosui
Published: March 2022

The Martian crustal magnetic anomalies create a varied, asymmetric obstacle for the draped interplanetary magnetic field (IMF) to interact with. One possible result of this interaction is magnetic reconnection, a process by which anti-parallel magnetic field lines connect and reconfigure, transferring energy into the surrounding environment and mixing previously separated plasma populations. Here, we present an analysis to determine the draped IMF conditions that favor reconnection with the underlying crustal anomalies at Mars. First, we plot a map of the crustal anomalies’ strength and orientation compiled from magnetic field data taken throughout the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Second, we create “shear maps” which calculate and plot the angle of shear between the transverse component of the anomalies and a chosen overlaid draping direction. Third, we define a “shear index” which quantifies the susceptibility of a particular region to undergo reconnection based on a given draped IMF orientation and the resulting shear map for that region. We then compare the shear index for a variety of draped field orientations within different regions of the Martian magnetosphere. Our results suggest eastward/westward (horizontal) draped fields present regions that are more likely for anti-parallel magnetic reconnection to occur with the crustal anomalies than northward/southward (vertical) draped fields, with one notable exception being the strongest crustal anomalies located in the southern hemisphere ~180° longitude. An east/west draped field roughly corresponds to a +/- By IMF direction on the dayside, implying the rate of magnetic reconnection on the dayside of Mars may be enhanced for IMF field lines pointing in the +/- YMSO direction compared to that of IMF field lines pointing in the +/- ZMSO direction, with MSO referring to the Mars Solar Orbital coordinate system. Understanding the interplay between Mars’s crustal magnetic fields and the IMF is crucial to answer outstanding science questions regarding nightside magnetospheric activity at Mars, namely how IMF orientation affects the twisting of the magnetotail, open magnetic topology observations on the nightside, and discrete aurora observations in the southern hemisphere.
Multifaceted Aerosol Effects on Precipitation
Authors: Stier Philip ,   GEWEX Aerosol Precipitation (GAP) initiative expert workshop team
Published: March 2022

A wide range of aerosol effects on precipitation have been proposed, from the scale of individual clouds to that of the globe.

This presentation, based on the findings of an expert workshop under the umbrella of the GEWEX Aerosol Precipitation initiative, reviews the evidence and scientific consensus behind these effects and the underlying set of physical mechanisms, categorised into i) radiative effects via modification of radiative fluxes and the energy balance and ii) microphysical effects via modification of cloud droplets and ice crystals.

There exists broad consensus and strong theoretical evidence that, because global mean precipitation is constrained by energetics and surface evaporation, aerosol radiative effects (aerosol-radiation interactions and aerosol-cloud interactions) act as drivers of precipitation changes. Likewise, aerosol radiative effects cause well-documented shifts of large-scale precipitation patterns, such as the Inter-Tropical Convergence Zone (ITCZ). The extent to which aerosol effects on precipitation are applicable at smaller scales and driven or buffered by compensating microphysical and dynamical mechanisms and budgetary constraints is less clear. Although there exists broad consensus and strong evidence that suitable aerosol perturbations increase cloud droplet numbers, reducing the efficiency of warm rain formation across cloud regimes, the overall aerosol effect on cloud microphysics and dynamics as well as the subsequent impact on local, regional and global precipitation is less constrained.

This presentation provides a review of the physical mechanisms of aerosol effects on precipitation backed up by evidence from recent cloud-resolving and global modelling simulations as well as from satellite observations.
How do leaf phenology and microclimate influence carbon storage dynamics along the vertical canopy gradient of mature trees?
Authors: Zahnd Cedric , Zehnder Lia , Kahmen Ansgar , Hoch Günter
Published: March 2022

Leaves in tree crowns experience different microclimates depending on their vertical positions, particularly in light availability. This leads to different rates of carbon assimilation. Additionally, leaf phenology potentially varies along the same gradient. Therefore, it can be assumed that the size and seasonal dynamics of the non-structural carbohydrate (NSC) pool are different in sunlit and shaded twigs of individual trees.

Here we test how microclimatic gradients and leaf phenology influence the NSC dynamics of young twigs along the vertical gradient of individual tree crowns. Throughout the year 2020, we measured the NSC concentration in twigs from the top and bottom crown parts of mature trees from 9 species in a temperate mixed forest at the Swiss Canopy Crane II facility near Basel, Switzerland. We recorded the timing of budbreak along the canopy depth of those trees and continuously measured the light environment with loggers in various canopy positions in three consecutive seasons (2019-2021).

The timing of budbreak showed barely any difference between top and bottom crown parts in broadleaved species. However, in the conifers Abies alba and Picea abies, buds opened ca. 7 days earlier in the bottom crowns than the top. Light availability throughout the growing season in the lower crown parts was around 30 % of that at the top. In most species, the NSC pools were strikingly similar in sunlit and shaded twigs, both quantitatively and in terms of their seasonal dynamics. Only the two ring-porous species Quercus petraea and Fraxinus excelsior showed differences: in both, the lower twigs reached their minimum starch levels after budbreak about a week later than the top twigs, and took longer for the subsequent refilling. However, even in species that showed slight differences in the seasonal NSC dynamics between upper and lower canopy, the end of season NSC concentrations in late autumn were identical between top and bottom twigs.

The very similar NSC dynamics and pool sizes between twigs from upper and lower crown parts, despite stark differences in light availability, are surprising. Further analyses of carbon assimilation and the ratio of carbon source to sink tissues along these vertical canopy gradients will allow to better interpret those results and to get an improved understanding of how carbon storage is controlled in mature trees.
Amazon fires drive widespread changes to diurnal cloud regimes and radiation
Authors: Herbert Ross , Stier Philip
Published: March 2022

The long-lived and widespread nature of smoke, coupled with its ability to perturb the atmosphere simultaneously via aerosol-cloud and aerosol-radiation interactions, has proven a challenge to observe and simulate; as such, the impact of smoke on regional and global scales remains uncertain.

In this study we use an 18-year climatology from multiple instruments onboard AQUA and TERRA satellites to identify and characterise the relationships between aerosol-optical-depth (AOD) and the large-scale properties of the clouds, precipitation, and top-of-atmosphere radiation over the Amazon rainforest during the biomass burning season.

Our analysis provides robust evidence that localised smoke production drives widespread modification to the cloud regime over the region: in the morning (TERRA) cloud liquid water path increases with AOD, whereas in the afternoon (AQUA) convective activity is initially enhanced then supressed when AOD exceeds 0.4. During both time periods there is an increasingly pronounced presence of high-altitude, optically thin, clouds.

The result is a sharp contrast in the cloud-field properties and vertical distribution between low-AOD days and high-AOD days and a pronounced top-of-atmosphere radiative effect of -50 Wm­-2 (for AOD = 1.4), which persists throughout the day.
Automatic inspection and analysis of digital waveform images by means of convolutional neural networks
Authors: Pignatelli Alessandro , D'Ajello Caracciolo Francesca , Console Rodolfo
Published: March 2022

Analyzing seismic data to get information about earthquakes has always been a major task for seismologists and, more in general, for geophysicists.
Recently, thanks to the technological development of observation systems, more and more data are available to perform such tasks. However, this data
“grow up” makes “human possibility” of data processing more complex in terms of required efforts and time demanding. That is why new technological
approaches such as artificial intelligence are becoming very popular and more and more exploited. In this work, we explore the possibility of interpreting seismic waveform segments by means of pre-trained deep learning. More specifically, we apply convolutional networks to seismological waveforms recorded at local or regional distances without any pre-elaboration or filtering. We show that such an approach can be very successful in determining if an earthquake is “included” in the seismic wave image and in estimating the distance between the earthquake epicenter and the recording station.
Dilatancy Toughening of Shear Cracks and Implications for Slow Rupture Propagation
Authors: Brantut Nicolas
Published: March 2022

Dilatancy associated with fault slip produces a transient pore pressure drop which increases frictional strength. This effect has been argued to be at least partially at the origin of slow slip events in subduction zones. Recent experimental results have demonstrated that dilatancy hardening has the potential to stabilise rupture in rocks, but laboratory results need to be upscaled to account for large scale variations in slip along faults. Here, we analyze the dilatant hardening in a steadily propagating rupture model that includes frictional weakening, slip-dependent fault dilation and fluid flow. A fracture mechanics approach is used to show that dilatancy hardening tends to increase the stress intensity factor required to propagate the rupture tip. With increasing rupture speed, an undrained (strengthened) region develops near the tip and extends beyond the frictionally weakened zone. Away from the undrained region, pore fluid diffusion gradually recharges the fault and strength returns to the drained, weakened value. For sufficiently large rupture dimensions, the dilation-induced strength increase near the tip is equivalent to an increase in toughness that is proportional to the square root of the rupture speed. In general, dilation has the effect of increasing the stress required for rupture growth by decreasing the stress drop along the crack. The competing effect of thermal pressurization has the potential to compensate for the dilatant strengthening effect, at the expense of an increased heating rate, which might lead to premature frictional melting. Using reasonable laboratory-derived parameters, we show that the dilatancy-toughening effect leads to rupture dynamics that is quantitatively consistent with the dynamics of observed slow slip events in subduction zones.
Rainfall onset no longer a starting signal for planting crops?
Authors: Agoungbome Sehouevi Mawuton David , van de Giesen Nick , ten Veldhuis Marie-Claire
Published: March 2022

Adjusting the farming practices in West Africa (WA) to changing climate conditions is of utmost importance when considering that a quarter of the population in Sub-Saharan Africa lacks access to sufficient food (FAO et al., 2019). Climate change-induced effects such as delays in the start of the rainy season or intermittent dry spells at the beginning of the season also known as false start have devastating consequences on crop response and compromise food security in the region (Laux et al., 2008). Failing to plant at the right moment has led farmers to experience water stresses and yield reduction/failure at the end of the season.

To address the issue, several definitions have been proposed in order to identify a safe planting date. However, some of the assumptions on which the definitions were built are no longer valid under the current climate conditions leading to frequent cases of crop failure. In this study, we evaluated the most commonly used definition called the local onset, which is defined as one or two consecutive rainy days followed by 30 days without dry spells of 7 days or more (Marteau et al., 2009). We used a set of stations from the TAHMO network (https://tahmo.org/) across the Semi-Arid Zone of  WA to compute the local onset date. This onset date is then compared to the optimal sowing date derived from computed yields based on local rainfall patterns measured by the TAHMO stations, using the crop model AquaCrop (https://www.fao.org/aquacrop/en/).

The results indicate that the local onset generally leads to planting early in the season while that period is risky and characterized by intermittent dry spells. On the contrary, delaying the planting until later in the season reduces largely the risk of harvest failure and higher yield can be achieved. These outcomes highlight the necessity to update the coupling between rainfall onset detection and planting date, which will contribute to improving food security.

 

References:

FAO, IFAD, UNICEF, WFP, WHO, 2019. The State of Food Security and Nutrition in the World 2019. Safeguarding against economic slowdowns and downturns. Food and Agriculture Organization of the United Nations, Rome, Italy.

Laux, P., Kunstmann, H., Bardossy, A., 2008. Predicting the regional onset of the rainy season in West Africa. Int. J. Climatol. 28, 329-342. doi:10.1002/joc.1542.

Marteau, R., Moron, V., Philippon, N., 2009. Spatial coherence of monsoon onset over western and central Sahel (1950-2000). J. Climate 22, 1313-1324. doi:10.1175/2008JCLI2383.1.
Testing the response of proximal gamma ray spectroscopy and cosmic ray neutron sensors to dry and wet conditions in an agricultural field (Spain)
Authors: Gaspar Leticia , Franz Trenton , Lizaga Ivan , Navas Ana
Published: March 2022

Gamma ray spectroscopy (GRS) and cosmic ray neutron sensors (CRNS) have become promising proximal soil moisture sensing techniques at intermediate scale in recent years. The high efficiency and relatively good spectral resolution provided by Sodium Iodide (NaI) detectors allow gamma-ray surveys for monitoring the spatial and temporal distribution of terrestrial radioelements like 40K, which is inversely proportional to the volumetric soil water content SWC (m3/m3). Cosmic ray neutron sensors detect and count the number of neutrons in the soil and the air just above the soil. Dryer soil has more fast-moving neutrons, while wetter soil has fewer because more hydrogen from water is available to absorb energy.

The objective of this study is to test the response of the proximal gamma ray spectroscopy and the cosmic ray neutron sensor in an agricultural field under dry and wet soil conditions to infer the information of soil water content in the first 30 cm. For the first time in Spain GRS and CRNS sensors have been assayed on a test site of aprox. 40 × 80 m2 (41º 43’ 37’’ N, 0º 48’ 46’’ W) at the experimental farm of the Estación Experimental de Aula Dei (EEAD-CSIC, Zaragoza, Spain). The experimental setup is equipped of a Cosmic Ray Neutron Sensor placed at 2 m above the ground located at the middle of the field, and a proximal gamma-ray equipment composed by sodium iodide scintillator detector (NaI). The CRNS provided continuous data every 15 min, while NaI detector supplied data at selected sites before and after a 16-liter rain episode. In this contribution, we present the preliminary results under dry and wet conditions of the distribution of 40K (cps, Bq m-2) and analyse the SWC after performing GRS and CRNS measurements. Our results were also compared with soil moisture estimated by volumetric field sensors showing high sensitivity to the different status of soil moisture, highlighting the promising of the use of these nuclear techniques for environmental and agricultural purposes.
An open-top chamber system for exposing Amazon understory vegetation to elevated atmospheric CO2
Authors: Pereira Iokanam , Takeshi Bruno , Guedes Alacimar , Souza Crisvaldo , Quesada Carlos , Lapola David
Published: March 2022

Tropical forests play a key role in the flux of terrestrial carbon (C). However, recent studies show tropical forest are losing over the years the ability to sink C from the atmosphere, one of the best explanations for that is the climate change caused by humanity in the last centuries and accelerating slightly every year. One of the ways to understand the changes in C fluxes in forest ecosystems in the short, medium, and long term are the Earth system models (ESMs). Nevertheless, simulations demonstrate that ESMs are not able to represent the decline in C sink by tropical forests in recent decades. Experiments that fertilize the atmosphere with carbon dioxide (eCO2) are essential to reduce uncertainties in future ESM projections about the possible effects of eCO2 on the carbon cycle. Open top chamber (OTC) allow the exposure of understory vegetation to eCO2 allowing the control and monitoring of the microenvironment in which they are inserted. Here, we describe the OTC system currently operating in the Amazon Free-Air CO2 Enrichment research program (AmazonFACE) in a mature forest in Central Amazonia, the analysis period is from 01/01/2020 to 12/31/2020. Each OTC is 2.40 m in diameter by 3.00 m in height, in which the concentration of CO2 ([CO2]) is monitored minute-by-minute using infrared gas analyzers, allowing the spatial and temporal control of [CO2]. The operation consists of keeping the [CO2] in the treatment OTCs (i.e., with eCO2) ≈ 200 µmol. mol–1 above the [CO2] of the control OTCs (i.e., without eCO2) in the daytime (between 6:00 am - 6:00 pm). The [CO2] measurements on the treatment and control OTCs show that the desired concentration was successfully delivered, +262.4 ± 25.5 µmol / mol (mean ± SD) of the desired setpoint, i.e., 31 % above setpoint target. The eCO2 in the treatment OTCs worked 91% of the analyzed operational time, the remaining time was wasted with engineering failures (3%) and problems with the supply of CO2 (6%). The system was able to maintain the [CO2] above the setpoint, showing that the system configuration is capable of exposing understory vegetation even in a highly complex environment. The results demonstrate that the in-situ OTC system presented can be reproduced in different types of ecosystems, allowing better knowledge about metabolic processes that occur between atmosphere-plant-soil.
Clouds increase uncertainty in surface melt projections over the Antarctic ice shelves
Authors: Kittel Christoph , Amory Charles , Hofer Stefan , Agosta Cécile , Jourdain Nicolas C. , Gilbert Ella , Le Toumelin Louis , Vignon Etienne , Gallée Hubert , Fettweis Xavier
Published: March 2022

Recent warm atmospheric conditions have damaged the ice shelves of the Antarctic Peninsula through surface melt and hydrofracturing, and could potentially initiate future collapse of other Antarctic ice shelves. However, model projections with similar greenhouse gas scenarios suggest large differences in cumulative 21st century surface melting. So far it remains unclear whether these differences are due to variations in warming rates in individual models, or whether local surface energy budget feedbacks could also play a notable role. Here we use the polar-oriented regional climate model MAR to study the physical mechanisms that will control future surface melt over the Antarctic ice shelves in high-emission scenarios RCP8.5 and SSP585. We show that clouds enhance future surface melt by increasing the atmospheric emissivity and longwave radiation towards the surface. Furthermore, we highlight that differences in meltwater production for the same climate warming rate depend on cloud properties and particularly cloud phase. Clouds containing a larger amount of liquid water lead to stronger melt, subsequently favouring the absorption of solar radiation due to the snow-melt-albedo feedback. Since liquid-containing clouds are projected to increase the melt spread associated with a given warming rate, they could be a major source of uncertainties related to the future Antarctic contribution to sea level rise.