bluuebunny/crossref_metadata_2025 huggingface dataset:
Geophysical monitoring of temperature variation and water movement in a frost weathering cave
Authors: Moser Clemens , Oberender Pauline , Funk Barbara , Flores-Orozco Adrian
Published: March 2021

One third of the caves in the north-eastern part of the Eastern Alps are assumed to be created by frost weathering. The geomorphological process of frost weathering is linked to temperature variations around the freezing point and a sufficient amount of water in the inner of a rock. Fractured areas are highly sensitive to frost weathering and are characterised by high variations of temperature and water content. Geophysical electrical methods are widely used to monitor variations of temperature and water content with time, considering the sensitivity of the electrical resistivity to both properties. In this study, we present imaging results for electrical monitoring conducted in February 2020 in the ceiling of the Untere Traisenbacherhöhle, a frost weathering cave, which is located in the foothills of the Eastern Calcareous Alps. In total, 77 imaging measurements were conducted during the monitoring period of approximately 60 hours with an electrode separation of about 10 cm to gain data with high temporal and high spatial resolution during and after a raining event. Simultaneously, temperature was measured at one point in different rock depths. Geophysical data was pre-processed by a four-step filtering procedure to identify and remove spatial and temporal outliers. Then the data was inverted with the open-source library Pybert. Inversion results reveal that during the entire monitoring the resistivity varies up to ±30% compared with the values at the start of the monitoring. To investigate in more detail the temporal changes, we extracted pixel values in 16 areas. These pixels show a strong negative linear correlation with the temperature (correlation coefficients up to 99%), which ranges between 2 °C and 8 °C. However, in some areas a simple linear model seems to not represent the relationship of both parameters in the low temperature range adequately. Based on such correlation, the resistivity data was temperature-corrected to investigate water content changes affecting the resistivity of the ceiling of the cave. Such analysis permitted to delineate clear anomalies related to water seeping into the rock as well as drying processes at the inner parts of the rock wall. Further, geophysical measurements were conducted by means of the low-induction number electromagnetic method in June 2020 to evaluate the applicability of this to map the entire rock wall of the cave. Electrical resistivity (ERT) data differs strongly from the low-induction number electromagnetic (EMI) mapping, likely because of a contamination of the EMI data due to the presence of the metallic electrodes used for the ERT monitoring and due to different weather conditions. Our study reveals the possibility to quantify water content changes in caves in an imaging framework. Further, this information can be used to delineate fractured zones in carbonate rocks, which are supposed to be more sensitive to frost weathering.
Nitrogen inputs from smallholder farming in a tropical montane catchment - current state and outlook
Authors: Kasebele Miriam , Jacobs Suzanne , Rufino Mariana , Breuer Lutz
Published: March 2021

Rising human populations increase the demand for food and lead to the intensification of agriculture and nitrogen fertilization to sustain productivity. In the tropical montane Mau Forest Complex in Kenya, the annual export of nitrogen from a catchment dominated by smallholder agriculture were reported to almost double those from the native forest. Despite the assumption that this excess nitrogen originates from fertilizer application, there are no studies that provide empirical information on the amount and spatial distribution of nitrogen inputs from smallholder agriculture into these catchments. Given the fact that the Mau Forest complex lost 25% of its forest cover to agriculture and other encroachment activities, such information is essential to better quantify the effect of smallholder farming practices on the nitrogen cycle and its contribution to catchment nitrogen export.

This study aimed at quantifying spatial distribution of fertilizer inputs in a smallholder catchment in the Mau Forest Complex using a household survey (n=185).

Results show that almost all farmers (99.4%) use inorganic fertilizers with an average nitrogen (N) application rate of 41±7.8 kg N ha-1 yr-1 diammonium phosphate (DAP). Among the DAP users, 16% apply in addition 79±3.9 kg N ha-1 yr-1 as NPK fertilizer, and 11% add 29±5.3 kg N ha-1 yr-1 as calcium ammonium nitrate (CAN). Overall, the average nitrogen input from inorganic fertilizers is 64±13.7 kg N ha-1 yr-1. Only 6% of the cropland is fertilized using manure and other farmland residues with 79% of farmers anticipating to increase their inorganic fertilizer application rates in the future.

In conclusion, a future increase in nitrogen application rates on farmland in combination with continued conversion of natural forest to agricultural land raises a concern on whether nitrogen export will increase further, posing a threat to drinking water quality and the health of aquatic ecosystems downstream. To balance the trade-off between food production and the catchment nitrogen balance, there is a need to train farmers on appropriate methods, timing and optimal amounts of fertilizer application to prevent unnecessary losses.
Assessing the impact of exceptional inter-annual climatic variability on rates of net ecosystem carbon dioxide exchange at Clara bog.
Authors: Saunders Matthew , Ingle Ruchita , Regan Shane
Published: March 2021

Peatland ecosystems are integral to the mitigation of climate change as they represent significant terrestrial carbon sinks. In Ireland, peatlands cover ~20% of the land area but hold up to 75% of the soil organic carbon stock however many of these ecosystems (~85% of the total area) have been degraded due to anthropogenic activities such as agriculture, forestry and extraction for horticulture or energy. Furthermore, the carbon stocks that remain in these systems are vulnerable to inter-annual variation in climate, such as changes in precipitation and temperature, which can alter the hydrological status of these systems leading to changes in key biogeochemical processes and carbon and greenhouse gas exchange.  During 2018 exceptional drought and heatwave conditions were reported across Northwestern Europe, where reductions in precipitation coupled with elevated temperatures were observed. Exceptional inter-annual climatic variability was also observed at Clara bog, a near natural raised bog in the Irish midlands when data from 2018 and 2019 were compared. Precipitation in 2018 was ~300 mm lower than 2019 while the average mean annual temperature was 0.5°C higher. The reduction in precipitation, particularly during the growing season in 2018, consistently lowered the water table where ~150 consecutive days where the water table was >5cm below the surface of the bog were observed at the central ecotope location. The differing hydrological conditions between years resulted in the study area, as determined by the flux footprint of the eddy covariance tower, acting as a net source of carbon of 53.5 g C m-2 in 2018 and a net sink of 125.2 g C m-2 in 2019. The differences in the carbon dynamics between years were primarily driven by enhanced ecosystem respiration (Reco) and lower rates of Gross Primary Productivity (GPP) in the drier year, where the maximum monthly ratio of GPP:Reco during the growing season was 0.96 g C m-2 month in 2018 and 1.14 g C m-2 month in 2019. This study highlights both the vulnerability and resilience of these ecosystems to exceptional inter-annual climatic variability and emphasises the need for long-term monitoring networks to enhance our understanding of the impacts of these events when they occur.
Assessing magnitudes and directions of CO2 fluxes within a karst landscape
Authors: Thompson Taryn , Stewart Ryan , McLaughlin Daniel , Schreiber Madeline
Published: March 2021

Gas diffusion is a primary driver of carbon dioxide (CO2) movement through unsaturated soils. In typical soils, high soil concentrations of CO2 caused by autotrophic and heterotrophic respiration cause the gas to primarily diffuse upward. However, karst landscapes can have subsurface CO2 sinks, both due to CaCO3 weathering and losses via underlying caves and fracture networks. In this study our objective was to quantify the magnitude and direction of CO2 fluxes in a pastured karst system located in Southwest Virginia (James Cave). Our hypotheses were: 1) the zero-flux plane, or location of maximum CO2 concentration within the soil profile, is located at deeper depths, ≥60 cm depth during warmer months of the year and located at shallower depths, ≤60 cm, during the colder months of the year, 2) the zero-flux plane will exist ˂60 cm depth at the sinkhole location more often than at the upslope locations, and 3) CO2 fluxes will be primarily upward during the growing season and primarily downward during the colder months of the year. We installed paired CO2 and soil moisture sensors at 20 cm, 40 cm, and 60 cm depths, with profiles installed in the shoulder, midslope, and bottom (i.e., sinkhole) of a hillslope adjacent to the cave entrance. The sensors recorded hourly data between 7 February 2017 and 13 September 2019. The depth of the zero-flux plane was identified by the depth of maximum CO2 concentration for each profile, while the measured concentration gradient from 20 to 60 cm was used to estimate CO2 flux with Fick’s Law. Our findings support our hypotheses that the relative location of the zero-flux plane was located more often at deeper depths during warmer months of the year and located at shallower depths, i.e. ˂60 cm, during colder months of the year. The zero-flux plane was more frequently shallow (i.e., ˂60 cm) at the sinkhole location compared to the upslope profiles. The CO2 fluxes reflected upward movement during the growing season and downward movement during the colder months of the year. We speculate that these processes reflect the influence of the underlying cave system, which may serve as a CO2 sink during colder months, when the cave becomes vented via natural convection. Altogether, these findings suggest that downward diffusion may be an important yet oft-overlooked component of carbon fluxes in karst landscapes.
Simulation of the initial phase of Holuhraun eruption using the ICON-ART model to investigate aerosol- cloud interaction 
Authors: Zarei Fatemeh , Hoose Corinna , Vogel Heike
Published: March 2021

Clouds play a key role in the atmosphere by completing the hydrological cycle and transferring water from the atmosphere to the earth's surface on the one hand, and affecting terrestrial radiation and solar radiation on the other hand. Although cloud properties are primarily affected by atmospheric dynamics, cloud microphysical features, which themselves are influenced by the number and chemical composition of aerosols that act as cloud condensation nuclei (CCN) and ice nuclei (IN) within cloud droplets, also affect cloud formation.

 

The extent and quality of aerosols impact on cloud formation is one of the important open question of climate science. Volcanoes, which are a rich source of various chemical compounds, can help to improve the understanding of the effects of aerosols on clouds by providing a natural laboratory with locally high aerosol conditions adjacent to an unperturbed environment.

 

In the present study, the impacts of changing the aerosol number concentration on clouds are investigated using the ICON-ART model. For this purpose, the Holuhraun volcano, which erupted on the island of Iceland in 2014, was simulated. It emitted small amounts of volcanic ash, and large emissions of gases primarily sulfur dioxide (SO2), which formed sulfate particles serving as CCN. Three simulations representing low, control, and high emission conditions were conducted. For the control simulation, the source strength of SO2 was based on the estimate by Malavelle et al. (2017). This rate, then, was reduced to one-fifth for the low emission experiment and increased by a factor of 5 for the high emission experiment.

First results indicate that increasing the source strength of SO2 is associated with an enhancement of sulfate aerosol number concentration and thus an increase of the number of cloud droplets, but with strongly nonlinear effects. For clouds within the volcanic plume, droplet concentrations are already high in the low emission scenario and do not increase significantly with higher emission strengths, partly due to model limitations. In addition, the effect of aerosols on the formation of cloud droplets is strongly dependent on environmental factors such as updraft velocity and supersaturation.

Keywords: Aerosol, Cloud, ICON-ART Model, Holuhraun eruption
Glacial-isostatic adjustment in the Southern Patagonia Icefield based upon permanent GNSS stations
Authors: Lenzano María Gabriela , Rivera Andres , Durand Marcelo , Hernandez Jorge , Vasquez Rodrigo , Lenzano Luis , Rada Camilo
Published: March 2021

The Southern Patagonia Icefield (SPI) is the largest continuous ice mass in Southern Hemisphere outside Antarctica. It has been shrinking since the little Ice Age (LIA) period with increasing rates in recent years. In response to this deglaciation process an uplift crustal deformation has been expected. In order to test this hypothesis, a number of GNSS stations installed at both side of the international border between Chile and Argentina, have been repeatedly measured in recent decades yielding vertical velocities up to 41 mm/a.     The obtained horizontal velocities have also shown that GIA is only one of the main components been the tectonic deformations the other factors, including the western interseismic tectonic deformation field related to plate subduction (Richter et al., 2016).

We addressed this hypothesis by installing two permanent GNSS stations in nunataks located in the northern half of the SPI. The first one called ECRG was setup up within the accumulation area at 1417 m asl and was measuring with several interruptions due to power supply between 2015/10/24 and 2018/06/18, yielding a total of 371 days with data. The second station called ECGB was installed at 1610 m asl in 2015/10/08 and was continuously measuring also with interruptions until 2019/05/28, with a total of 542 measured days. The stations were equipped with a Trimble NetR9 receiver and a Trimble Zephyr (TRM41249.00) antennae without protective radomes. The collected data was processed with the Bernese v5.0 software and the data were linked to the International GNSS Service 2008 (IGS08) permanent stations.

The preliminary results indicate vertical velocities of 33.03 ±2.14 mm/a at ECRG and 36.55±2.58 mm/a at ECGB. The mean horizontal velocities reached 11.7 mm/a with an azimuth of 43º. These results are within the maximum values obtained in previous studies that measured nearby stations for short periods of time in several occasions. The high vertical velocities and their spatial distribution are a clear indication of the GIA response of this part of Southern Patagonia.

Reference

Richter, A., Ivins, E., Lange, H., Mendoza, L., Schröder, L., Hormaechea, J. L., … Dietrich, R. (2016). Crustal deformation across the Southern Patagonian Icefield observed by GNSS. Earth and Planetary Science Letters, 452, 206–215. https://doi.org/10.1016/j.epsl.2016.07.042
Late Pleistocene paleo-hydrological reconstruction based on a new lake-level curve of the Dead Sea
Authors: Mey Jürgen , Jara Juluis , Strecker Manfred R.
Published: March 2021

The Dead Sea depression features exceptionally well preserved lacustrine sedimentary sequences and fossil lake-level markers that attest to a much more extensive lake with a maximum highstand water level of more than 200 m above the modern Dead Sea. Lake-level reconstructions based on sedimentary sequences places this highstand phase within the interval of 15-29 ka. Regional paleoclimatic records, however, indicate arid conditions during this time. This apparent contradiction has been explained by spatially heterogeneous moisture delivery resulting from a southward shift of the Westerly wind system and a change in the path and intensity of winter storms. A newly established lake level-chronology based on 14C- and U/Th-dating of fossil stromatolites has provided contrasting results with respect to previous investigations. Accordingly, the paleolake-highstand was of much shorter duration and occurred at least 10 ka earlier than previously suggested. The new lake-level curve agrees with evidence of arid glacial and humid interglacial periods in the Levant.  In this study we compared these different lake-level reconstructions quantitatively, using a distributed hydrological balance model. This model computes evaporation based on an aerodynamic- /mass-transfer approach. Calibration and validation of this model is achieved by using ~30 years of pre-anthropogenic lake-level observations combined with interpolated climate surfaces based on weather-station records. In the paleo-hydrological reconstruction we account for parameter uncertainties using Monte-Carlo simulations. Our preliminary results show a pronounced sensitivity of the lake-level to precipitation, wind speed, and surface roughness.
Two-way nesting ocean models with different vertical coordinates
Authors: Chanut Jerome , Harle James , Graham Tim , Debreu Laurent
Published: March 2021

The NEMO platform possesses a versatile block-structured refinement capacity thanks to the AGRIF library. It is however restricted up to versions 4.0x, to the horizontal direction only. In the present work, we explain how we extended the nesting capabilities to the vertical direction, a feature which can appear, in some circumstances, as beneficial as refining the horizontal grid.

Doing so is not a new concept per se, except that we consider here the general case of child and parent grids with possibly different vertical coordinate systems, hence not logically defined from each other as in previous works. This enables connecting together for instance z (geopotential), s (terrain following) or eventually ALE (Arbitrary Lagrangian Eulerian) coordinate systems. In any cases, two-way exchanges are enabled, which is the other novel aspect tackled here.  

Considering the vertical nesting procedure itself, we describe the use of high order conservative and monotone polynomial reconstruction operators to remap from parent to child grids and vice versa. Test cases showing the feasibility of the approach are presented, with particular attention on the connection of s and z grids in the context of gravity flow modelling. This work can be considered as a preliminary step towards the application of the vertical nesting concept over major overflow regions in global realistic configurations. The numerical representation of these areas is indeed known to be particularly sensitive to the vertical coordinate formulation. More generally, this work illustrates the typical methodology from the development to the validation of a new feature in the NEMO model.
Time-evolving sea-surface warming patterns modulate the climate change response of precipitation in Mediterranean-like regions
Authors: Zappa Giuseppe , Ceppi Paulo , Shepherd Theodore
Published: March 2021

Regions with a Mediterranean-like climate, apart for California, are projected to receive less rainfall due to climate change, thus posing serious implications for future water availability for societal and agricultural needs. At a first order, it is often assumed that water availability is proportional to global mean warming. Yet, the mechanisms controlling the precipitation response in Mediterranean climates remain only partly understood, as shown by the substantial uncertainty that still characterises the climate model projections. Here, by analysing projections from the CMIP5 climate models, we show that the linear scaling with warming does not apply in three key Mediterranean-like regions, namely Chile, California and the Mediterranean proper. In particular, despite long-term warming, the models show that the projected precipitation reduction in Chile and the Mediterranean halts as soon as anthropogenic forcing is stabilised, while the precipitation increase in California accelerates. By examining the response to an abrupt quadrupling of CO2, we demonstrate that such non-linearity in the time-evolution of precipitation cannot be solely explained by the well-known rapid adjustment to radiative forcing, but it is instead due to distinct fast and slow patterns of atmospheric circulation change, that are themselves forced by the time-evolution in the spatial patterns of sea-surface temperature warming. In particular, while the fast warming is favourable to force a poleward shift of the mid-latitudes jets, hence drying the Mediterranean and Chile, the slow warming, including an el nino-like pattern in the tropical Pacific, inhibits such shifts and precipitation changes, while favouring the wetting of California. The results show that stabilising GHG concentrations will have an immediate benefit to the hydro-climate of these Mediterranean-like regions, while pointing to constraining uncertainty in the patterns of surface warming as an important step to increase confidence in the future projections. 
How does increasing CO2 influence the land-atmosphere exchange of carbon and water in response to soil and air dryness?
Authors: Zhan Chunhui , Orth René , Reichstein Markus , Migliavacca Mirco , Zaehle Sönke , Winkler Alexander
Published: March 2021

Variability in the photosynthetic uptake of CO2 by plants due to climate variability plays an essential role in modulating the growth rate of atmospheric CO2. In particular water stress induced by the compounding effect of vapor pressure deficit (VPD) and soil moisture anomalies has a large bearing on photosynthetic CO2 uptake, especially in semi-arid areas. The ongoing rise in atmospheric CO2 concentration can influence the water-use efficiency of plants, their carbon assimilation rate, and consequently the global cycles of carbon and water.  However, the extent to which physiological effects of increasing CO2 influence the coupling of VPD, soil moisture, and land-atmosphere CO2 fluxes is currently poorly understood.

In this study we use the terrestrial ecosystem model QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system, Thum et al. 2019, GMD) to study CO2-induced changes in the interaction of plant productivity and both soil moisture and VPD. With the sensitivity of stomatal conductance to atmospheric CO2 concentration implemented in the model, we investigate century-long simulations across different climate regimes and biomes. In semi-arid regions we find a positive relationship between anomalies of VPD and gross primary productivity (GPP) at both start and end of summer months, and a negative relationship in the dry period (usually from June to August in boreal summer). This suggests there is a transition in the limiting factor of GPP from energy (compound effect of temperature and radiation) to water and back in the course of one year. The negative correlation between VPD and GPP during the dry period weakens over time with rising CO2, while a stronger positive correlation between soil moisture and GPP becomes apparent. After quantifying and understanding the CO2 effects in these model simulations, we apply our analysis framework to observational data from the FLUXNET site collection to analyze whether we can confirm the model-based findings despite shorter records.
Simulating effects of the 774 AD solar proton event on atmospheric electricity
Authors: Misios Stergios , F. Knudsen Mads , Karoff Christoffer
Published: March 2021

High energy cosmic rays of galactic and solar origin, natural radioactivity, lighting in thunderstorms and electrified shower clouds, produce ion clusters and charge the whole atmosphere causing a ubiquitous potential difference between the ionosphere and the surface. This Global Electric Circuit (GEC) allows the flow of charges to the surface in the fair-weather regions of the globe. Here, we simulate the effect of highly energetic particle radiation, in particular the 774 AD solar proton event, on the GEC with the aid of the global circulation model EMAC/MESSy. The simulations assume pre-industrial atmospheric conditions and the coupling of aerosol and atmospheric electricity schemes allows for ion-ion and ion-aerosol capture reactions. We discuss effects in fair weather current and atmospheric conductivity at different latitudinal bands.
Geophysical measurements in an abandoned old railway tunnel located in a karst area
Authors: Rizzo Enzo , Capozzoli Luigi , De Martino Gregory , Fornasari Giacomo , Giampaolo Valeria
Published: March 2021

Carbonate aquifers in karst systems are very important water reservoir and are recognized as the most difficult to characterize. The purpose of this article is to present a project aimed to understand the circulation of fluids in carbonate reservoirs through innovative hydrogeophysical methodologies both in the laboratory and in the field. The test site is located in the Castel di Lepre karst system, which is disposed in the Mezo-Cenozoic carbonate substratum of the Monti della Maddalena ridge (Southern Appenines). In the karst area are located several caves, but the presence of an artificial tunnel (disused railway tunnel) could give the opportunity to characterize the whole area and the fluid circulation by multisensors geophysical sensors installed inside the karst aquifer. This natural laboratory permits to define an Applied Geophysics strategy developing several main topics from an engineering to hydrogeological point of view. Firstly, the geophysical investigations conducted, without altering the structure and in a fast manner, obtains important information concerning the construction of the tunnel, and the interaction between the infrastructure and surrounding rock, in that area that we define infrastructural critical zone. The study conducted aims to highlight the potential and any limitations of the use of geophysical techniques applied to infrastructures, emphasizing the emerging role of urban geophysics for the importance and topicality of its contents as well as the important innovations that the use of these techniques they can contribute to the hazardous processes. Secondly, the geophysical methods are used as a tool to characterize the fluid circulation by hydrogeophysal sensors installed inside the karst aquifer. The hydrogeophysics arose as an interdisciplinary field that focuses on the improved understanding of hydrological processes through geophysical observation. These approaches aimed at mitigating the detrimental effects of environmental problems.
Modifications of Atlantic inflow along the Fram Strait Branch to the Arctic Ocean and its variability north of Svalbard from ship-borne and moored observations in the last two decades.
Authors: Beszczynska-Möller Agnieszka , Walczowski Waldemar , Grynczel Agata
Published: March 2021

Understanding variable properties and dynamics of the Atlantic water (AW) inflow into the Arctic Ocean, and their impacts on ocean heat content, ocean-atmosphere-sea ice exchanges, changing sea ice cover and propagation of anomalies are key prerequisites to elucidate drivers and mechanisms behind the new, warmer regime of the Arctic Ocean. As the AW progress northwards, its properties are modified by ocean-atmosphere interactions, mixing and lateral exchanges. Warm anomalies reaching the Arctic Ocean can result from smaller heat loss during the AW northward passage through Fram Strait, and/or from an increased oceanic advection. Vertical structure of the Atlantic water layer implies the depth of winter convection and access to oceanic heat carried northward by the inflow.

During the last two decades warming of the Atlantic inflow has been reported to progress into the Arctic Ocean, however with strong interannual variations and quasi-periodic pulses of water with extraordinary high temperature. Here we present results from 20 years of annual hydrographic surveys, covering the Atlantic water inflow in the eastern Norwegian and Greenland seas, Fram Strait up to the southern Nansen Basin. Interannual changes in the AW properties and transport are analyzed with a focus on the en route modifications of AW inflow in the Fram Strait Branch and changes in the integrated ocean heat content.

After leaving Fram Strait, the part of AW continues eastward and enters the Arctic Ocean boundary current along different pathways north of Svalbard. The strongest ocean-atmosphere-sea ice interactions and lateral oceanic exchanges in this region lead to substantial local modification of the Atlantic inflow before it continues farther eastward around the rim of the Arctic Ocean. Observations from year-round moorings deployed since 2013 north of Svalbard are used to describe changes in the Atlantic water properties, vertical structure, and dynamics on monthly to seasonal and interannual time scales and their links to the upstream conditions and local and regional atmospheric forcing. Vertical heat fluxes from the Atlantic layer are derived to evaluate the ocean-air and ocean-sea ice exchanges in the only region of the Arctic Ocean where Atlantic-origin water has still contact with sea ice cover.
The role of updrafts in the scaling of extreme precipitation in mid-latitudes
Authors: Bentvelsen Falco , Lenderink Geert , Siebesma Pier
Published: March 2021

We investigate the hypothesis that invigoration of convective updrafts under warming conditions contributes to the stronger than Clausius-Clapeyron (CC) scaling. Focus is on a mid-latitude case of extreme precipitation, based on idealised forcing conditions derived for the Netherlands, with strong surface forcing as well as strong forcing from large-scale rising motion associated with the passage of a synoptic scale low pressure or frontal system. Various Large Eddy Simulations (LES) of this composite case have been performed on a 192x192 km domain. By systematically perturbing the atmospheric temperature profile, a large response of cloud dynamics to warming with larger and more vigorous cloud structures in the warmer runs has been found.*

Here, we study these cloud dynamics further by investigating the vertical wind velocity in the cloud (cores). Updrafts play a key role in rain formation by transporting moisture upward in the clouds. We will demonstrate how the distributions of these vertical velocities near the surface and at different levels in the clouds respond to warming in this mid-latitude setting and how they relate to cloud properties as cell size and buoyancy.

 

*Lochbihler, K., Lenderink, G., and Siebesma, A. P. (2019). Response of extreme precipitating cellstructures to atmospheric warming. Journal of Geophysical Research: Atmospheres
Characterising fracture patterns at growing lava domes
Authors: Myers Amy , Harnett Claire , Heap Michael , Holohan Eoghan , Walter Thomas
Published: March 2021

Volcanic domes form when lava is too viscous to flow away from an active volcanic vent; instead, the lava accumulates into a mound consisting of a hotter, ductile core and a colder, brittle outer layer. An existing lava dome grows when new material is injected into the core of the dome, causing the  outer layer to stretch and develop tensile fractures. With continued dome growth, these weaknesses can propagate to form an extensive fracture network and the dome may fail. Collapse events often generate rock falls and debris avalanches, lahars, and high-speed pyroclastic flows, endangering populations residing at the base of a volcano. Since such fractures represent potential failure planes, in this project we aim to understand the role they have in destabilising lava domes.

This project will build on the work published by Harnett et al. (2018), which demonstrates the suitability of a discrete element modelling approach to simulate dome emplacement and evolution. Specifically, this project is designed to:

1. Use high-resolution photogrammetry to characterise the possible fracture states of a dome;

2. Establish up-scaled rock-mass properties by performing geomechanical experiments on both fractured and non-fractured samples of dome rock from prior collapses;

3. Develop a numerical model to investigate how the presence and properties of fracture networks influence dome stability.

The model, developed using PFC, will be used to identify critical fracture states that can signify a dome collapse is likely to occur. Under the current model, parallel bonds simulate the fluid magma core and flat joints simulate the solid talus material. This project will build on this original model by incorporating discrete fracture networks into the smooth-joint model to implement dome fracturing. The new model will look to investigate the effect  of a fracture network on a static dome that, when in its unfractured state, is stable under gravity. Additionally, the model will be designed such that inputs can include experimentally derived rock-mass properties. It is hoped that, by incorporating observational and experimental data into a more  complex model, the dynamic evolution of fractures in a growing lava dome can be investigated and the ongoing likelihood of a dome collapse event can be assessed.

 

Harnett, C. E. et al., 2018. J. Volcanol. Geoth. Res., 359: 68-77.
Theoretical modelling of ice shelf vibrations forced by ocean surface waves
Authors: Bennetts Luke , Meylan Mike , Kalyanaraman Balaje , Lamichhane Bishnu
Published: March 2021

Seismic measurements show that ice shelves vibrate in response to ocean surface waves over a wide frequency range, from long swell to tsunami waves. The phenomenon of wave-induced ice-shelf vibrations has been linked to calving of large icebergs, rift propagation, icequake activity, and triggering of catastrophic disintegrations. I will present some recent advances in theoretical modelling of wave-induced ice-shelf vibrations, including coupling of the ice shelf/sub-shelf cavity to the open ocean, studying the influence of ice-shelf thickening and seabed shoaling towards the grounding line, simulating transient vibrations in response to incident wave packets, and incorporation of real ice-shelf and seabed geometries via the BEDMAP2 dataset. I will introduce the open-source software iceFEM, which contains many of the latest advances. 
Retrieval of ice nucleating particle concentrations from spaceborne lidar measurements
Authors: Alexandri Fani , Seelig Torsten , Braeuer Peter , Tesche Matthias
Published: March 2021

Aerosol particles affect the climate directly through interaction with radiation. They also can cause a radiative forcing due to aerosol-cloud interactions (ACI), by acting as cloud condensation nuclei (CCN) in the formation of warm clouds or as ice nucleating particles (INP) during the phase change in mixed-phase clouds. Spaceborne remote sensing is a promising approach for quantifying ACI at a global scale and a useful technique for assessing and improving the performance of climate models. A more than 14-year data set of height-resolved measurements of aerosol optical properties from the Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite (Winker at al., 2009) is utilized for estimating the vertical distributions of cloud-relevant particle concentrations. More specifically in this satellite-based study, conversion factors are applied to extinction coefficient observations to obtain vertical profiles of dry particle number and surface area concentration (Mamouri and Ansmann, 2015; 2016; Marinou et al., 2019). The last two are then used as input in measurement-based INP parameterizations in order to retrieve the INP active fractions for different aerosol types. Second part of this methodology is to combine images of geostationary sensors which provide continuously the history of cloud development with polar-orbiting observations on aerosol and cloud parameters that will allow the quantification of ACI. The spaceborne-based findings are crucial for identifying the effects of changes in aerosol concentration on the glaciation of warm and cold clouds.
Climate Oscillations from Mountain Uplift and Erosion are Damped by Bioactivity
Authors: Höning Dennis
Published: March 2021

Earth’s long-term carbonate-silicate cycle is continuously perturbed by processes of mountain building and erosion. Mountain uplift near convergent plate boundaries causes steep slopes, which in turn imply high rates of continental erosion. Erosion rates ultimately affect the weatherability and thereby the regulation of Earth’s climate. Using a simple 1D-model that includes the outlines processes, I investigate the resulting climate oscillations over timescales from thousands to millions of years. With a simple model of the long-term carbon cycle that includes biological enhancement of weathering and marine biogenic calcite precipitation, I study the role of Earth’s biosphere in damping these oscillations [1]. I show that both mechanisms play a role: Biological enhancement of weathering damps oscillations mainly on timescales > 1 Ma and marine calcification mainly on shorter timescales. Altogether, the results indicate that Earth’s biosphere contributes to a stable climate over a wide range of timescales.

In the context of anthropogenic emissions, a dramatic elevation in the atmospheric CO2 and related temperature is known to damage Earth’s biosphere [2] and may even trigger runaway processes [3]. The results presented here indicate that a damaged biosphere may furthermore cause the Earth system to react more sensitive to oscillations from geological forcing and may also affect climate recovery.

References:

[1] Höning 2020, Geochem. Geophys. Geosyst. 21(9), e2020GC009105
[2] Sully et al. 2019, Nat. Comm. 10, 1264
[3] Lenton 2013, Annu. Rev. Environ. Resour. 38, 1-29
Effects of ionisation on cloud behaviour in planetary atmospheres
Authors: Airey Martin , Harrison Giles , Aplin Karen , Pfrang Christian
Published: March 2021

Cosmic rays cause ionisation in all planetary atmospheres. As they collide with particles in the atmosphere, secondary charged particles are produced that lead to the formation of cluster ions. The incident cosmic ray flux and atmospheric density of the atmosphere in question determine a profile of ion production rate. From the top of the atmosphere to the planetary surface, this rate increases with atmospheric density to a point where the flux becomes attenuated such that the rate then decreases, resulting in a peak ion production rate at some height known as the Pfotzer-Regener maximum. When these ions interact with aerosols and cloud particles, a net charge results on those particles and this is known to affect their microphysical attributes and behaviour. For example, charging may enable the activation of droplets at lower saturation ratios and also enhance collision efficiency and droplet growth. This becomes important when clouds occur at a height where ionisation is sufficient to have a substantive charging effect on the cloud particles. This has very little direct effect on Earth as peak ion production occurs high above the clouds at 15-20 km; however, on Venus for example the Pfotzer-Regener maximum occurs at ~63 km, coinciding with the main sulphuric acid cloud deck. In situations such as this, the direct result of cloud charging due to cosmic ray induced ionisation may strongly influence cloud processes, their occurrence, and behaviour.

This work uses laboratory experiments to explore the effects of charging on cloud droplets. Individual droplets are levitated in a vertical acoustic standing wave and then monitored using a CCD camera with a high magnification objective lens to determine the droplet lifetime and evaporation rate. Experiments were conducted using both the droplets’ naturally occurring charge as well as some where the region around the drop was initially flooded with ions from an external corona source. The polarity and charge magnitude of the droplets was determined by applying a 10 kV/m electric field horizontally across the drop and observing its deflection towards one of the electrodes. Theory predicts that the more highly charged a droplet is, the more resistant to evaporation it becomes. Experimental data collected during this study agrees with this, with more highly charged droplets observed to have slower evaporation rates. However, highly charged drops were also observed to periodically become unstable during evaporation and undergo Rayleigh explosions. This occurs when the droplet evaporates until its diameter becomes such that its fissility reaches the threshold at which the instability occurs. Each instability of a highly charged drop removes mass, reducing the overall droplet lifetime regardless of the slower evaporation rate. Therefore, where enhanced ionisation occurs in the presence of clouds the end result may be to reduce droplet stability.
APAR: The Next Generation of Airborne Polarimetric Doppler Weather Radar
Authors: Grubišić Vanda , Kim Kyu , Lee Wen-Chau
Published: March 2021

A novel, airborne phased array radar (APAR) is currently under design at the NCAR Earth Observing Laboratory. This novel airborne radar is to be carried by the NSF/NCAR C-130 aircraft. The APAR system will consist of four removable C-band active electronically scanned arrays (AESA), strategically placed on the fuselage of the aircraft. Conceptually, the radar system is divided into the front-end, the backend, and the aircraft-specific section. The front-end primarily consists of AESAs, the backend of the signal processor, and the aircraft specific section includes a power system and a GPS antenna.

APAR, with dual-Doppler and dual polarization capabilities at a lesser attenuating C-band wavelength, is designed to enable further advancement in understanding of in-cloud microphysical and dynamical processes within a variety of precipitation systems. Such unprecedented observations, in conjunction with the advanced radar data assimilation systems, is anticipated to significantly improve understanding and predictability of hazardous weather events.

At present, and with funding from both the National Science Foundation and the National Oceanic and Atmospheric Administration, NCAR is engaged in the risk reduction and APAR preliminary design activities. In this talk, we will provide an update on the status of these activities for various system components as well as the system-level design. For the final design and development of APAR, NCAR plans to apply for the NSF Mid-scale Research Infrastructure funds in 2021. It is anticipated that the APAR final design and development will be a five-year effort.
Probabilistic climate projections with Minimal CMIP Emulator (MCE)
Authors: Tsutsui Junichi
Published: March 2021

One of the key applications of simple climate models is probabilistic climate projections to assess a variety of emission scenarios in terms of their compatibility with global warming mitigation goals. The second phase of the Reduced Complexity Model Intercomparison Project (RCMIP) compares nine participating models for their probabilistic projection methods through scenario experiments, focusing on consistency with given constraints for climate indicators including radiative forcing, carbon budget, warming trends, and climate sensitivity. The MCE is one of the nine models, recently developed by the author, and has produced results that well match the ranges of the constraints. The model is based on impulse response functions and parameterized physics of effective radiative forcing and carbon uptake over ocean and land. Perturbed model parameters are generated from statistical models and constrained with a Metropolis-Hastings independence sampler. A parameter subset associated with CO2-induced warming is assured to have a covariance structure as diagnosed from complex climate models of the Coupled Model Intercomparison Project (CMIP). The model's simplicity and the successful results imply that a method with less complicated structures and fewer control parameters has an advantage when building reasonable perturbed ensembles in a transparent way despite less capacity to emulate detailed Earth system components. Experimental results for future scenarios show that the climate sensitivity of CMIP models is overestimated overall, suggesting that probabilistic climate projections need to be constrained with observed warming trends.
A multi-observer approach to promote the conservation of north Adriatic marine biogenic habitats
Authors: Sigovini Marco , Tosi Luigi , Bergamasco Andrea , Donnici Sandra , Sabino Andrea , Bergamasco Alessandro
Published: March 2021

Environments along the ocean-land continuum strictly interlink to each other both in horizontal and in vertical. Most of the acting processes require investigation through a multi looking observation approach, integrating coastal oceanography, hydrogeology and marine ecology. This can be achieved by simultaneously looking from different perspectives at the same environmental context and processes.
The present study focuses on the northern Adriatic Sea, where a number of peculiar, diverse and valuable coastal and marine ecosystems are localized, characterized by high biodiversity and productivity, such as the Lagoon of Venice and the underwater biogenic-geogenic rocky outcrops named tegnùe. Their structural complexity and habitat heterogeneity is increased by the role of habitat forming species, bioconstructors and biodemolitors. To understand the ecological and morphogenetic role of these organisms, selected biogenic formations and habitats, such as the fan mussel Pinna nobilis colonies on both the Lagoon of Venice and the rocky outcrops, were investigated. Innovative approaches are here presented to map and characterize these biogenic habitats at different hierarchical levels, in order to promote their conservation.
Vegetation composition in Sanjiangyuan region compared with Hengduan Mountains (eastern Tibetan Plateau) since the Last Glacial Maximum revealed by plant metabarcoding of sedimentary ancient DNA
Authors: Shen Wei , Liu Sisi , Stoof-Leichsenring Kathleen R. , Courtin Jeremy , Mischke Steffen , Herzschuh Ulrike
Published: March 2021

The eastern Tibetan Plateau, particularly the Hengduan Mountains and Sanjiangyuan region, is a biodiversity hotspot also known for its sensitivity to climate change. How these vegetation communities assembled since the Last Glacial Maximum is still unclear. Here we present new results from plant metabarcoding of sediments from Lake Ximencuo (Nianbaoyeze Mountains, Sanjiangyuan region) covering the last 18 ka and compare them with records from Lake Naleng (Hengduan Mountains).  We investigate temporal changes of within-site and between-site alpha and beta diversities. Both sites show the highest richness between 14 and 10 ka when alpine meadows covered the areas while richness was rather low in forested periods during the early Holocene. Ordination results support that the vegetation composition was relatively low between-site beta-diversities indicate that the vegetation composition was relatively similar in the two study areas before the Holocene, particularly during the early late-glacial when alpine steppes dominated. The maximal between-site beta-diversity occurred between 10 and 8 ka when environmental filtering was most relevant, as suggested by the dominating turnover component. The nestedness component of beta-diversity reached a maximum during the middle Holocene indicating that between-site differences during this period possibly originated from e.g., dispersal limitation.