bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-stationarity of extreme ground snow load in the French Alps
Authors: Le Roux Erwan , Evin Guillaume , Eckert Nicolas , Blanchet Juliette , Morin Samuel
Published: March 2020

In a context of climate change, assessing trends in hazards related to extreme events is urgent. Specifically current methods to compute European standards for snow load actions on structures do not account for the non-stationarity due to climate change. We present the first analysis of extreme ground snow load trends for the whole French Alps. Our method is based on non-stationary generalized extreme value (GEV) distribution, time derivative of return level and likelihood ratio test. Thanks to Météo France reanalysis and snowpack models, we study moutain massif scale data available every 300m of altitude from 1958 to 2017. We detect an overall decreasing trend for annual maxima of ground snow load between 900m and 2700m, which is significant in the Northwest of the French Alps until 1800m. Despite decreasing return levels, in 2017 half of massifs at altitude 1800m still exceeds standard return levels. We underline the importance of snowpack modelling and limitations of approaches relying on ground snow load computed with snow depth annual maxima and an hypothesis on snow density.
High Rate Real Time GNSS monitoring of active volcanoes: 20 years of applications to Italian volcanoes
Authors: Mattia Mario , Bruno Valentina , Cannavò Flavio , Rossi Massimo , Pellegrino Daniele , Pulvirenti Mario , Pandolfo Francesco , Dolce Mario , De Martino Prospero
Published: March 2020

Since 2000 an intense development of remote stations, transmission device, data processing software and tools for time series analysis aimed to high rate GNSS surveillance and monitoring of active Italian volcanoes has been realized or implemented at INGV. Since the very first case study (the 2001 Mt.Etna’s eruption) to the 2019 paroxysms of Stromboli, many observations and a lot of specific experience has been achieved on Italian active volcanoes (Etna, Stromboli) to track rapidly developing deformation patterns associated to different volcanic processes, as dike intrusions or explosive activity. Moreover, we here describe the hardware and software improvements for High Rate GNSS monitoring network with a specific attention to the recently realized network in the densely populated area of the Campi Flegrei caldera.
Time series of near-bottom currents and particle fluxes from Ocean Bottom Moorings in the NE equatorial Pacific
Authors: Hollstein Martina , Vink Annemiek , Schmidt Katja , Lahajnar Niko , Lückge Andreas , Purkiani Kaveh
Published: March 2020

The globally increasing demand for metals and rare earth elements has raised the interest for potential mining of deep-sea mineral resources such as polymetallic nodules. One important field of polymetallic nodules is located within the Clarion-Clipperton Fracture Zone (CCZ) in the northeastern equatorial Pacific. To date, the International Seabed Authority (ISA) has granted 25 licenses for the exploration of polymetallic nodules in the CCZ. However, the impact of potential future mining activities on the deep-sea environment is only insufficiently known. To assess the environmental impacts of potential future mining activities, a nodule pre-prototype collector test is scheduled to occur in the German license area within the CCZ in autumn 2020, and will be accompanied by an extensive environmental monitoring program (joint effort between BGR and the European research project JPI-Oceans “MiningImpact2”). However, to assess the environmental impact of mining activities, for example due to the development of an operational sediment plume on the seafloor, prior knowledge on the bottom current regime and variability of particle flux and composition within the CCZ under natural conditions is a prerequisite. In order to analyze the bottom current regime and background particle fluxes, BGR deployed Ocean Bottom Moorings (OBM) equipped with current and turbidity meters (4 years between 2013 and 2019), and a sediment trap (2018-2019). Here, we present preliminary results and analyses of these oceanographic and sedimentological time-series data, and compare the results with other available information deriving from the region.
Crustal scattering and intrinsic attenuation of S-waves in southern Aegean derived using envelope inversion
Authors: Ranjan Pratul , Konstantinou Konstantinos I.
Published: March 2020

Southern Aegean is the major part of the Eurasian plate overriding the subduction of African plate in eastern Mediterranean region. In this study, shallow depth (< 40 km) events recorded by temporary and permanent seismic networks in southern Aegean are used to study the crustal scattering attenuation (Qs-1) and intrinsic attenuation (Qi-1) of S-waves. The 3 component S-waveforms are filtered in 1-2, 2-4, 4-8, and 8-16 Hz bands and envelopes are calculated by smoothing the root mean square of individual components. The envelopes are modeled using the approximate analytical solution of 3D isotropic radiative transfer equation. The fitting is performed using grid search approach to obtain Qs-1 and then linear inversion is used to calculate Qi-1 for each source station pair. The results obtained from each source-station pair are assigned to an ellipsoid region and robust mean technique is used to map the results in each 0.20o x 0.20o bin. The final results indicate consistently high Qs-1 in western Crete in all 4 frequency bands. Also, high Qs-1 is observed in western Peloponnese in 1-2 and 2-4 Hz frequency bands. High Qi-1 is observed along the volcanic arc in all 4 frequency bands. Our results compare well with the recent S-wave scattering study in the region. They are also consistent with the geodynamics of southern Aegean subduction zone. Our study provides useful insight about the attenuation in the southern Aegean crust which has implications for ground motion and seismic hazard.
Shedding new light on the radiative impacts of ozone-depleting substances
Authors: Chiodo Gabriel , Polvani Lorenzo M.
Published: March 2020

It is well established that ozone-depleting substances (ODS) have been the primary cause of stratospheric ozone depletion. It is also widely accepted that stratospheric ozone depletion has been the primary driver of summertime circulation trends in the Austral Hemisphere in the second half of the twentieth century. However, the climate impacts of ODS that are independent of ozone depletion have received little attention. It has long been known that, while much less abundant than carbon dioxide, ODS have a much higher global warming potential (GWP) ecent studies have indicated that ODS may have played a key-role in the observed weakening trends of the Walker circulation (Polvani and Bellomo, 2019), and in the warming of the Arctic and the associated sea ice loss (Polvani et al., 2020). that the climate efficacy of ODS may be much larger than previously thought, but .

Here, we seek to better understand the radiative effect of ODS in the global atmosphere. Instead of confining our attention on a single metric, e.g. globally averaged radiative forcing (RF) or GWP which are typically reported in the IPCC Assessment Reports, we seek to understand how ODS alter the temperature structure of the entire atmosphere. Focusing on the half-century 1950-2000, which saw the largest growth of ODS concentrations in the atmosphere, we start by performing careful computations of the RF of individual ODS, including the effects of rapid temperature adjustments. We then explore how the vertical and latitudinal distribution of ODS (which are not well mixed in the stratosphere) affects their RF, and what temperature responses are associated with those changes. These calculations are repeated individually for each of the other well-mixed GHG, as well as for other composition changes arising from ODS (ozone depletion). It is shown that ODS, in contrast to other GHG, warm the lower stratosphere, implying a different fingerprint from CO2. Furthermore, the RF of ODS exhibits the largest meridional gradient of any other well-mixed GHG. Implications for the climate efficacy of ODS, and more generally for climate sensitivity, will be discussed.

References

Polvani, L.M and K. Bellomo: The key role of ozone depleting substances in weakening the Walker circulation in the second half of the 20th century, J. Climate, 32, 1411-1418 (2019).

Polvani et al.,: Substantial twentieth-century Arctic warmng caused by ozone depleting substances, Nature Climate Change, in press (2019)
Upper Mantle deformation patterns beneath norteast India from Shear-wave splitting analysis
Authors: Kanaujia Jyotima , Surve Ganpat , Hazarika Nava
Published: March 2020

Telesesimic earthquake data recorded at eight seismograph stations across the northeast India are analysed for shear-wave splitting from core-refracted XKS phases (collectively PKS, SKS and SKKS). Shear-wave splitting parameters, derived from the analysis provide information about seismic anisotropy and deformation of the crust and upper mantle beneath each seismograph stations site. The results point towards the presence of complex and highly anisotropic crust and upper mantle beneath northeast India. Being surrounded by two seismically active plate boundaries, to the north by India-Eurasia collision plate boundary and to the east by Indo-Burman subduction plate boundary, the crust and upper mantle beneath the northeast India has been assumed to have complex deformation pattern. This present study provides an evidence for this assumption. According to station locations, we have one station BONG situated near the Main boundary thrust (at India-Eurasia collision zone), one station NAMS and eastern syntexis Himalaya, five station AZWL, SILS, DIPH and NKCR at Indo-Burman subduction plate boundary, one station SHLS and Shillong plateau bounded by Oldham Fault, Dauki Fault and Kopli fault, and one station AGAR at the boundary of Bengal basin. The direction of anisotropy is nearly E-W at BONG, NE-SW in the Indo-Burman subduction zone, nearly N-S on Shillong plateau and NW-SE at eastern syntexis of Himalaya. Source of anisotropy in the Himalaya collision boundary is result of lithospheric deformation due to finite strain induced by collision. In Shillong plateau and Indo-burman subduction boundary, source of anisotropy seems to be the asthenospheric flow-related strain which is also in harmony with the absolute plate motion (APM) of the Indian plate in a no net reference frame.
Machine learning to identify sandstone properties from thin sections
Authors: Emmel Benjamin , Roli Ole-Andre , Romdhane Anouar
Published: March 2020

Sand volume and porosity measurements on sandstones are routine work in geoscientific applications, providing useful input to flow simulation in porous media-based analyses (e.g., in CO2 storage and/or hydrocarbon migration studies). The classic way to gain knowledge about these parameters is point counting on thin sections. This time-consuming, repetitive, and subjective work is usually done by an experienced petrographer. Attempts to automate and digitize this process are therefore promising. An example using image analysis has been discussed in Roduit, 2007. However, one step further is combining image analysis with machine learning.

In this work, we evaluate the use of a neural network learning algorithm to classify selected sandstone properties from thin section images. Our database consists of ca. 3500 thin section images from different sandstone types with known properties. The images are grouped into 8 different sand volume and 8 different porosity classes. We split the dataset into a training (85 %) and validation dataset (15 %). In the processing stage, we normalize and scale all the images to a reference number of 128 pixels. For both classifications, we trained a convolutional neural network consisting of 5 convolutional layers and 4 max pool layers. The batches are normalized after each pooling layer and a dropout layer used to reduce overfitting before flattening. A final soft max layer is added so that the recovered output can be interpreted as probability distributions. We perform the training phase with a varying number of epochs ranging between 20 and 200. A training and validation accuracy > ca. 90 % is obtained after 25 epochs. For both cases, we observe that initially high model loss for the validation data reaches low values after 50 epochs.

To further test the approach, we analyse in a second stage a holdout dataset of sandstones from the Norwegian Continental Shelf. Preliminary results show that the derived sand volumes classification reproduce the point counting results well (80 % accuracy of predicting classes or neighbouring classes). More problematic is the reproducibility of porosities. Here, models using different epochs show variable results and the ≥100 epochs models systematically underestimates the measured rock porosities. We observe that only porosity classes well represented in the initial population of training images are reproduced with high accuracy. We finally discuss strategies to overcome such limitations.

 

Roduit, N., 2007. JMicroVision: un logiciel d'analyse d'images pétrographiques polyvalent. PhD Thesis University of Geneva,116 pp. 
The role of convection in the momentum budget of ICON-LEM hindcasts over the North Atlantic
Authors: Helfer Kevin , Nuijens Louise , Dixit Vishal , Siebesma Pier
Published: March 2020

Motivated by the uncertain role of convective momentum transport from low clouds in setting patterns of wind in the trades, we discuss the impact of shallow convection on boundary-layer winds and its role in the overall momentum budget in the trades from large-domain large-eddy simulations. To this end, we analyse ICON-LEM hindcast simulations over the (sub)tropical North Atlantic during the NARVAL1 and NARVAL2 flight campaigns.

We describe that the character of the momentum flux profile differs significantly in regimes of shallow and deep convection and thus its influence on cloud-layer and near-surface winds. In particular, we establish that the momentum transport tendency is of similar importance as other terms in the momentum budget, and though the shape of the profile is remarkably insensitive to the horizontal resolution of the simulation, the relative role of subgrid and resolved fluxes changes with resolution. Furthermore, we find that counter-gradient transport occurs even in the absence of organisation, namely in the lower cloud layer, where cloudy updrafts carry slow momentum air upwards, which locally accelerates winds and may play a role at maintaining the cloud-base wind maximum.
CME arrival prediction and its dependency on input data and model parameters
Authors: Amerstorfer Tanja , Hinterreiter Jürgen , Reiss Martin A. , Bauer Maike , Möstl Christian , Bailey Rachel L. , Weiss Andreas J. , Amerstorfer Ute V. , Davies Jackie A. , Harrison Richard
Published: March 2020

During the last years, we focused on developing a prediction tool that utilizes the wide-angle observations of STEREO's heliospheric imagers. The unsurpassable advantage of these imagers is the possibility to observe the evolution and propagation of a coronal mass ejection (CME) from close to the Sun up to 1 AU and beyond. We believe that using this advantage instead of relying on coronagraph observations that are limited to observe only 14% of the Sun-Earth line, it is possible to improve today's CME arrival time predictions.
The ELlipse Evolution model based on HI observations (ELEvoHI) assumes an elliptic frontal shape within the ecliptic plane and allows the CME to adjust to the ambient solar wind speed, i.e. it is drag-based. ELEvoHI is used as an ensemble simulation by varying the CME frontal shape within given boundary values. The results include a frequency distrubution of predicted arrival time and arrival speed and an estimation of the arrival probability. ELEvoHI can be operated using several kinds of inputs. In this study we investigate 15 well-defined single CMEs when STEREO was around L4/5 between the end of 2009 and the beginning of 2011. Three different sources of input propagation directions (and shapes) are used together with three different sources of ambient solar wind speed and two different ways of defining the most appropriate fit to the HI data. The combination of these different approaches and inputs leads to 18 different model set-ups used to predict each of the 15 events in our list leading to 270 ELEvoHI ensemble predictions and all in all to almost 60000 runs. To identify the most suitable and most accurate model set-up to run ELEvoHI, we compare the predictions to the actual in situ arrival of the CMEs.
This model is specified for using data from future space weather missions carrying HIs located at L5 or L1 and can also directly be used together with STEREO-A near real-time HI beacon data to provide real-time CME arrival predictions during the next 7 years when STEREO-A is observing the Sun-Earth space.
Determining regional scale carbon losses from tropical peatlands using ISBAS-InSAR
Authors: Ledger Martha , Sjögersten Sofie , Sowter Andrew , Large David , Evans Chris , Morrison Keith
Published: March 2020

80% of peatlands in Indonesia and Malaysia (15% of Earth's soil carbon) are now drained for production of pulp wood and palm oil. Associated increased peat decomposition and large-scale forest fires are now significant contributors to global greenhouse gas emissions. However, carbon losses from these processes and the impact of peatland drainage remain poorly quantified across SE Asia because of the challenging scale and inaccessibility of dense tropical peatland forests.

Space-based platforms offer the opportunity for regular and efficient pan-regional monitoring and overcome inaccessibility of tropical peatland environments. A development in satellite interferometric synthetic aperture radar (InSAR) in monitoring surface motion has the potential to solve this problem. A new ‘intermittent small baseline subset’ (ISBAS) modelling technique provides excellent coverage across almost all land surfaces irrespective of ground cover, enabling long-term measurement of peatland surface motion across whole catchments, regions and countries. Importantly, the ISBAS technique is able to determine surface deformation under tropical forest canopy using C-band InSAR, enabling continuous monitoring of surface motion ranging from 0.1–40cm/yr at spatial scales ≥90x90m.

This project aims to determine whether rate of subsidence of the peat surface measured by ISBAS-InSAR is a proxy for rate of carbon loss in tropical peatlands in SE Asia. ISBAS-InSAR time series and field measurements of subsidence will be used to monitor and characterise seasonal tropical peat surface oscillations over time and field radar experiments will investigate C-band radar signal attenuation with the peat surface at different moisture contents.
Changes in oxygen concentrations of intermediate water in the eastern tropical north Pacific over the last 140,000 years.
Authors: Hoogakker Babette , Day Christopher , Leng Melanie
Published: March 2020

Intermediate waters (500 - 2000 m) from the equatorial- to North Pacific are currently hypoxic (oxygen concentrations below 120 µmol/kg), while deeper waters are well oxygenated. For the last ice-age, some proxy records suggested that this trend was reversed, with well-oxygenated Pacific intermediate waters, and lower oxygenated deeper waters associated with an increased deep carbon reservoir. Recent work however suggests that there was an overall expansion of oxygen depleted water in the eastern tropical North Pacific during the last glacial period (Hoogakker et al., 2018). To further assess the natural variability in intermediate water dissolved oxygen concentrations over longer time-scales we extend the bottom water oxygen record of ODP Site 1242 (1360 m depth located in the eastern tropical north Pacific), to 140,000 years, using  the benthic foraminifera carbon isotope gradient approach of Hoogakker et al. (2015).  Our reconstructions suggest that oxygen concentrations varied with an approximate 40 kyr period; with lowest concentration during cool periods of the penultimate glacial, MIS 5b, 4 and 2.
Neonicotinoids in the Environment- Fate and Impact
Authors: Potts Jessica , Jones David , Pywell Richard , Macdonald Andy , Cross Paul
Published: March 2020

Over the last half century, society’s dependence on insect-assisted pollination of crops has risen by over 300% globally, while recent findings have estimated a 76% decline in flying insect biomass over the last 27 years. These losses in invertebrate numbers are thought to be due to a possible combination of various factors including parasites and diseases, agricultural intensification, climate change and possible chemical exposure including pesticides such as neonicotinoids.

Neonicotinoids are one of the most widely used insecticides on the global market. Their systemic mechanisms allow for ease of application and relatively successful outcomes in controlling biting and sucking invertebrates, however neonicotinoids have been strongly associated with recent declines in non-target organisms. Many neonicotinoids come directly in contact with the soil, either through application as a seed coating or soil drench, or through spray drift and drip from foliar applications. Relatively little research has focussed on the movement, fate and interactions of these chemicals in UK soils under general field management strategies, although evidence suggests that the addition of soil bio-amendments, such as fertilisers, can influence the mechanisms behind pesticide mobility.

My study aims to quantify the effects of Acetamiprid-based pesticide mixtures on below-ground soil functions, through the analysis of their movement and behaviour in soils of contrasting organic matter contents. A secondary aim is to assess the impact of neonicotinoids on select non-target organisms.

We used 14C labelled Acetamiprid to track the behaviour of the mixtures compared to the pure active ingredient. Previous research has only used the pure active ingredient, however this isn’t representative of true field scenarios. These spiked pesticides were added to soils of contrasting organic matter content collected from a long-term experiment at Woburn Experimental Farm, Rothamsted Research. We assessed the behaviour of these mixtures across a range of leaching, sorption and mineralisation experiments.

The mineralisation of all mixtures was found to be comparatively slow, with <23% of any given chemical/SOM combination being mineralised over the 60 day experimental period. The highest mineralisation rates were in samples with the highest SOM levels. The preliminary leaching data found that >80% of each chemical was recovered from the soil during the experiment. This, combined with low sorption and mineralisation rates, suggests that neonicotinoids are highly persistent within the environment.

Ongoing work is being conducted to investigate the knock-on impacts and biological implications of acetamiprid use under true field conditions.
Hands-on activities in climate education at school: three successful examples
Authors: Kalvane Gunta , Kalvans Andis
Published: March 2020

According to studies and surveys, Latvian society is sceptical of climate changes – it is characterised by short-term thinking. STEM teachers acknowledge that the climate issue is one of the most difficult and incomprehensible topics for students. Students' understanding of climate change issues is low because there is poor understanding of concept of the climate itself and physical processes shaping the climate system. Students do not see the consequences and responsibilities of their actions. In addition, there is little climate-related teaching materials available in Latvian language hampering incorporation climate issues in the regular school programs or informal educational activities.

In collaboration with youth NGO, Latvian 4H club, Faculty of Geography and Earth Sciences at University of Latvia have developed several teaching materials, easy-to-read instructions and video demonstration in Latvian for hands on climate education activities. Low-cost and easily available materials and reagents have used for all the activities. Some of the examples: what is the difference in air temperature in a jar with and without CO2 heated by incandescent light bulb or how the water pH changes when CO2 is bubbled (blown) through it with a straw?

In the “60 elements in your pocket” project, we have dismantled mobile phones and discussed what raw materials have used to build and what are the environmental consequences of extracting them and demonstrating actual mineral samples. We discuss with students what are our consumption habits, and how can everyone mitigate the effects of climate change?

We strongly believe that hands-on activities have to be a crucial part in any climate-related education program. Experiments and demonstrations need to be simple, understandable, and show the complexity of climate and economic system.
Open data in building resilience to recurrent natural hazards in remote mountainous communities of Nepal
Authors: Parajuli Binod Prasad , Shakya Puja , Khadka Prakash , Liu Wei , Pudasaini Uttam
Published: March 2020

The concept of using open data in development planning and resilience building to frequent environmental hazards has gained substantial momentum in recent years. It is helpful in better understanding local capacities and associated risks to develop appropriate risk reduction strategies. Currently, lack of accurate and sufficient data has contributed to increased environmental risks, preventing local planners the opportunity to consider these risks in advance. To fulfil this gap, this study presents an innovative approach of using openly available platforms to map locally available resources and associated risks in two remote communities of Nepal. The study also highlights the possibility of using the combined knowledge of technical persons and citizen scientists to collect geo-spatial data to support proper decision making. We harnessed the power of citizen scientists to collect geo-spatial data by training them on currently available tools and platforms. Also, we equipped these communities with the necessary instruments to collect location based data. Later, these data collected by citizen scientists were uploaded in the online platforms. The collected data are freely accessible to community members, government and humanitarian actors which could be used for development planning and risk reduction. Moreover, the information co-generated by local communities and scientists could be crucial for local government bodies to plan activities related to disaster risk reduction. Through the piloting in two communities of Nepal, we have found that using open data platforms for collecting and analysing location based data has a mutual benefit to researchers and communities. These data could be vital in understanding the local landscape of development, environmental risk and distribution of resources. Furthermore, it enables both researchers and local people to transfer the technical knowledge, collect location specific data and use them in better decision making.
Deciphering Optical Water Types of Wetlands using multispectral Earth observation datasets
Authors: Allaka Satyasri , Singh Manudeo , Sinha Rajiv
Published: March 2020

Wetlands are important and highly productive ecosystems in a variety of geomorphic settings ranging from inland to coastal environments. Wetlands are very dynamic in nature and are driven by the water and sediment fluxes carried by the streamlets throughout the year. Wetlands are under tremendous pressure all over the world due to various natural and anthropogenic factors, and therefore, require an immediate attention for their conservation. The available studies on wetland have given much less importance to the internal dynamics of the wetlands, which is primarily driven by hydrology and Land Use Land Cover (LULC) changes. Here, we propose to use the Optical Water Types (OWTs) concept to understand the hydrodynamics within the wetland.

The OWTs are the aquatic counterpart of terrestrial LULC classification and can be created by clustering of optically sensitive parameters like chlorophyll content, turbidity, suspended organic and inorganic matter using remote sensing reflectance, absorption, and scattering parameters. The Forel Ule (FU) color index, a visual color comparison scale of water bodies ranging from blue to cola brown (1-21), used a similar idea but is fairly limited in scope. The hyperspectral datasets have distinct absorption and reflection spectrum for various optically sensitive parameters, and therefore, they are particularly suited for this work. However, the availability of the high-resolution hyperspectral data is very limited and hence this research explores the possibility of deciphering the OWTs using multispectral datasets.

A possible approach to create OWTs is using the spectral indices of the multispectral datasets which are sensitive to the optical parameters instead of using the FU color index as a single parameter. In this work, various spectral indices which are independent and highly sensitivity to chlorophyll content, turbidity, suspended organic and inorganic matter are identified using the principal component analysis. The OWT clusters are created using the iso-cluster unsupervised classification similar to the LULC classification but the spectral indices are taken into account instead of directly using the spectral bands of satellite datasets. In this work, the Sentinel – 2A and 2B datasets are used to create independent OWT clusters of the Chilika (a Coastal wetland, along the east coast of India covering an area of 1,165 km2) and Kaabar Tal (an inland wetland in north Bihar plains, India covering an area of 51 km2) using the supervised classification method. The developed framework is very simple and robust in nature but the only disadvantage is that the clusters are variable in the temporal context. However, the temporal variations can be integrated with the spatial analysis to understand the wetland dynamics in the context of both space and time.
Dispersion Modelling at the London VAAC 10 Years after the Eyjafjallajökull Ash Cloud
Authors: Beckett Frances , Witham Claire , Leadbetter Susan , Crocker Ric , Webster Helen , Hort Matthew , Jones Andrew , Devenish Benjamin , Thomson David
Published: March 2020

It has been 10 years since the ash cloud from the eruption of Eyjafjallajökull caused chaos to air traffic across Europe. Although disruptive, the longevity of the event afforded the scientific community the opportunity to observe and extensively study the transport and dispersion of a volcanic ash cloud. Here we present the development of the NAME atmospheric dispersion model and modifications to its application in the London VAAC forecasting system since 2010, based on the lessons learned.

Our ability to represent both the vertical and horizontal transport of ash in the atmosphere and its removal have been improved through the introduction of new schemes to represent the sedimentation and wet deposition of volcanic ash, and updated schemes to represent deep atmospheric convection and parameterizations for plume spread due to unresolved mesoscale motions. A good simulation of the transport and dispersion of a volcanic ash cloud requires an accurate representation of the source and we have introduced more sophisticated approaches to representing the eruption source parameters, and their uncertainties, used to initialize NAME. Further, atmospheric dispersion models are driven by 3-dimensional meteorological data from Numerical Weather Prediction (NWP) models and the Met Office’s upper air wind field data is now more accurate than it was in 2010. These developments have resulted in a more robust modelling system at the London VAAC, ready to provide forecasts and guidance during the next volcanic ash event affecting their region.
Effects of surface waves on hyporheic exchange over a permeable gravel bed
Authors: Shih WuRong , Wu Fu-Chun
Published: March 2020

Hyporheic exchange represents the interactions between surface and subsurface flows occurring at various geophysical scales. Its importance to the riverine ecological health and the fate of contaminants has long been recognized. Traditionally, the behaviors of hyporheic exchange are explained by the emergence of geomorphological features, such as dune-shaped bedforms, that usually introduce significant pressure differences along the channel bed and, therefore, facilitate exchanges by pumping the flow inward and outward the bed. In addition to this advective mechanism, near-bed turbulence has also been identified as another driver of flow exchange through the turbulent diffusive processes. This study, on the other hand, highlights the decisive control of surface waves on the hyporheic exchange at depth-limited flow conditions, especially for those unbroken standing waves commonly encountered in river riffle areas. It is hypothesized that the presence of surface waves will reshape the distribution of near-bed hydrodynamic pressures, thus altering the properties of advective flows along the channel bed. The validity of this hypothesis is carefully examined through the laboratory experiments using Refractive-Index-Matched (RIM) liquid and solid materials and Particle Tracking Velocimetry (PTV) techniques. This experimental setting helps to simultaneously resolve the surface and subsurface flow patterns to a sufficient detail; the hydrodynamic pressure field can then be derived from the obtained flow velocity fields. Further analysis in a Double-Averaged Navier-Stokes framework indicates that, among different contributing factors, pressure gradient is found to be the most dominant driver of interface exchange. The variations of this driving mechanism, interestingly, can be further decomposed into two parts, namely, the surface wave associated (global-scale) and the bed grain associated (local-scale) components, respectively.
Measuring the variability of the shallow convective mass flux profiles in the tropical trade wind region
Authors: Klingebiel Marcus , Konow Heike , Stevens Bjorn
Published: March 2020

Mass flux is a key parameter to represent shallow convection in global circulation models. To estimate the shallow convective mass flux as accurately as possible, observations of this parameter are necessary. Prior studies from Ghate et al. (2011) and Lamer et al. (2015) used Doppler radar measurements over a few months to identify a typical shallow convective mass flux profile based on cloud fraction and vertical velocity. In this study, we extend their observations by using long term remote sensing measurements at the Barbados Cloud Observatory (13° 09’ N, 59° 25’ W) over a time period of 30 months and check a hypothesis by Grant (2001), who proposed that the cloud base mass flux is just proportional to the sub-cloud convective velocity scale. Therefore, we analyze Doppler radar and Doppler lidar measurements to identify the variation of the vertical velocity in the cloud and sub-cloud layer, respectively. Furthermore, we show that the in-cloud mass flux is mainly influenced by the cloud fraction and provide a linear equation, which can be used to roughly calculate the mass flux in the trade wind region based on the cloud fraction.

 

References:
Ghate,  V.  P.,  M.  A.  Miller,  and  L.  DiPretore,  2011:   Vertical  velocity structure of marine boundary layer trade wind cumulus clouds. Journal  of  Geophysical  Research: Atmospheres, 116  (D16), doi:10.1029/2010JD015344.

Grant,  A.  L.  M.,  2001:   Cloud-base  fluxes  in  the  cumulus-capped boundary layer. Quarterly Journal of the Royal Meteorological Society, 127 (572), 407–421, doi:10.1002/qj.49712757209.

Lamer, K., P. Kollias, and L. Nuijens, 2015:  Observations of the variability  of  shallow  trade  wind  cumulus  cloudiness  and  mass  flux. Journal of Geophysical Research: Atmospheres, 120  (12), 6161–6178, doi:10.1002/2014JD022950.
Pushing the limits of CMT inversion with large seismic networks: Challenges and results for small to moderate earthquakes in the Alps
Authors: Petersen Gesa , Cesca Simone , Heimann Sebastian , Niemz Peter , Dahm Torsten ,   AlpArray working group
Published: March 2020

The AlpArray seismic network (AASN) was operated from 2016 to 2019 by a European initiative aiming for new insights into the orogenesis of the Alps as well as into past and recent geodynamic and tectonic processes. The network included more than 620 temporary and permanent broadband stations with a spacing of 50 - 60 km. It was accompanied by the even denser Swath-D seismic network in the Eastern Alps (~150 stations with 15 km spacing). While the extensive network provides an excellent station coverage for seismicity studies, the large number of stations (up to 100) poses new challenges to MT inversions. Automated quality control and the choice of appropriate configurations becomes crucial for the inversion process. Weak to moderate magnitude events and the complex heterogeneous tectonic setting in the Alps force us to push the limits of full waveform moment tensor inversions.

We develop semi-automatic, adaptive approaches for a standardized quality assessment of large seismic networks and for the selection of appropriate waveform fitting targets and frequency ranges. The earthquake source optimization framework ‘Grond’ uses a Bayesian bootstrap-based probabilistic inversion scheme with flexible integration of different waveform attributes in time and frequency domain to provide full or deviatoric moment tensor solutions including uncertainties. The entire workflow from station quality control to moment tensor inversion can handle more than 100 stations simultaneously. The large number of stations allows to study the influence of azimuthal gaps. Further, we are able to compare the inversion results of various methods and configurations in time- and frequency domain using different frequency ranges and epicentral distances. We inverted approximately 100 full moment tensor solutions for events down to Mw 3.1 occurring within the operating time of the AASN. For this magnitude range a combination of frequency-domain spectra and time-domain waveform fitting of surface waves (Z, R and T component, 0.02-0.07 Hz) provides most stable results. In case of distorted absolute amplitudes a combination of frequency spectra and maximum cross-correlation fitting proved to be useful. We find that for smaller events (Mw < 3.0) surface waves are not observed and higher frequency body waves are strongly influenced by complex heterogeneities along the travel path. To extend the source analysis to even weaker events the standard MT inversion approach is combined with network similarity cluster analyses, enabling the association of weaker events to larger ones and therefore the reconstruction of the geometry of active faults.
Necessary conditions for algorithmic tuning of weather prediction models using OpenIFS as an example
Authors: Tuppi Lauri , Ollinaho Pirkka , Ekblom Madeleine , Shemyakin Vladimir , Järvinen Heikki
Published: March 2020

Algorithmic model tuning is a promising approach to yield the best possible performance of multiscale multi-phase atmospheric models once the model structure is fixed. We are curious about to what degree one can trust the algorithmic tuning process. We approach the problem by studying the convergence of this process in a semi-realistic case. Let us denote M(x0;θd) as the default model, where x0 and θd are the initial state and default model parameter vectors, respectively. A necessary condition for an algorithmic tuning process to converge in a fully-realistic case is that the default model is recovered if the tuning process is initialised with perturbed model parameters θ and the default model forecasts are used as pseudo-observations. In this paper we study the circumstances where this condition is valid by carrying out a large set of convergence tests using two different tuning methods and the OpenIFS model. These tests are interpreted as guidelines for algorithmic model tuning applications.

The results of this study can be used as recipe for maximising efficiency of algorithmic tuning. In the convergence tests, maximised efficiency was reached with using ensemble initial conditions, cost function that covers entire model domain, short forecast length and medium-sized ensembles.
Innovative physiological indicators for drought stress in banana
Authors: Vantyghem Mathilde , Merckx Roel , Hood-Nowotny Rebecca , Stevens Bert , Resch Christian , Roman Gruber , Dercon Gerd
Published: March 2020

Banana is a very important crop in East-Africa, serving as a staple for millions of smallholder farmers. Aside from pests and diseases, lack of water is the major constraint to production. Climate change is expected to aggravate these problems, creating a need for improved resilience and better management practices. A major obstacle to the development and evaluation of such practices is the difficulty to measure drought stress in the field. In this research, we investigate physiological parameters that can provide information on drought stress in banana under field conditions. We evaluate the use of stable carbon isotope ratios (δ13C) and leaf temperature as indicators for stress, the former ones not well-established for banana. Leaf temperature is known to increase under drought stress due to stomatal closure. The existing methods to measure leaf temperature are however expensive and their use is limited to small greenhouse set-ups. In this research, we employ an infrared thermometer (±1°C) for temperature measurement under field conditions. The experimental set-up consists of a banana field trial with a blocked design (irrigated and rainfed treatments) in the Kilimanjaro region, Tanzania. Leaf samples for isotope analysis were taken from mature plants (mother plants) and the main on-growing sucker (daughter plants) in August 2019, during the dry season. Leaf temperature was monitored throughout the day. Results show significantly higher δ13C ratios in rainfed plants, compared to irrigated ones, indicating more drought stress. Within both groups, mother plants have higher δ13C ratios than daughter plants. At dawn, leaf temperature was similar for all treatments. During the day, rainfed banana plant leaf temperature increased 7°C more than in their irrigated counterparts. Daughter plants remained cooler than mother plants in both treatments. Leaf temperature and δ13C showed a strong correlation. While carbon isotope signatures are a known proxy, our results suggest that leaf temperature is a an easily measurable indicator of drought stress as well. The infrared thermometer is cheap, convenient to use in the field and provides in-situ information. Leaf temperature has an enormous potential as a drought stress sensor in banana, as well as in other plants. Our research will further optimize both methods for drought stress evaluation. This will facilitate management comparisons in the future as well as variety screening, eventually contributing to more resilient banana production systems.
What is the magma storage depth under Osorno Volcano (Southern Volcanic Zone, Chile)?
Authors: Bechon Tonin , Vander Auwera Jacqueline , Namur Olivier , Fugmann Paul , Bolle Olivier , Lara Luis
Published: March 2020

The depth at which magma chamber processes take place below magmatic arcs and the parameters controlling them are highly debated. These questions are fundamental for our understanding of the global magma differentiation as well as the formation of the continental crust at convergent margins, but also for evaluating the risks associated with volcanic eruptions.

In the Central Southern Volcanic Zone (Central-SVZ) of the Chilean Andes, a thin continental crust (30-40 km) and the occurrence of a major fault zone (Linquiñe-Ofqui) likely favor rapid magma ascent. This segment of the arc is as a consequence one of the most active in Chile with several recent eruptions (e.g. Llaima 2009, Cordon Caulle 2011, Calbuco 2015, Villarrica 2015 & 2019). The Central-SVZ is characterized by dominant mafic lavas (basalts, basaltic andesites), few rhyodacitic lavas, a noticeable compositional (Daly) gap in the intermediate compositions (andesites). Noteworthy, amphibole is usually absent, except in a few volcanoes (e.g. Calbuco) or only occurs as microliths in enclaves, which suggests rather low water contents. These observations contrast sharply with the Northern-SVZ where andesitic lavas are dominant and hydrous phases common.

We focused our research on the eruptive products of Osorno volcano (41°S, CSVZ) located between two volcanoes (Calbuco and Cordon Caulle) which recently showed very explosive eruptions and partly overlies an older Pleistocene eroded volcanic edifice (La Picada). A large series of samples were collected in four units spanning 200 kyr. They define a differentiation trend ranging from tholeiitic basalts to calk-alkaline dacites with a Daly Gap between 58 wt. % and 63 wt. % SiO2. Plagioclase and olivine are dominant before the gap while plagioclase and clino- and orthopyroxene dominate afterwards.

The use of recent thermobarometric models revealed two main storage regions: (1) at the MOHO interface (1-1.2GPa) and (2), at the upper/lower crust interface with rather low pressures (likely ≤0.3 Gpa). While at (1) primary magmas differentiate, (2) is interpreted as the depth of major differentiation and volatile exsolution. Thermodynamic simulations (Gualda et al., 2012; Ghiorso & Gualda, 2015) support these (2) depth estimates and reproduce the main paragenesis by simple fractional crystallization at 0.1-0.2 GPa. Our results may explain the recent seismic unrest below Osorno (from 2015 to 2019) with earthquakes mostly taking place between 0.1-0.3 GPa (4-10km below the summit). We suggest that Osorno is an important target to perform a comprehensive petrological study aiming at characterizing the Central-SVZ magmatic arc and the magmatic storage depths.
Screening the coupled atmosphere-ocean system based on Covariant Lyapunov Vectors
Authors: Galfi Vera Melinda , de Cruz Lesley , Lucarini Valerio , Schubert Sebastian
Published: March 2020

We analyze linear perturbations of a coupled quasi-geostrophic atmosphere-ocean model based on Covariant Lyapunov Vectors (CLVs). CLVs reveal the local geometrical structure of the attractor, and point into the direction of linear perturbations applied to the trajectory. Thus they represent a link between the geometry of the attractor and basic dynamical properties of the system, and they are physically meaningful. We compute the CLVs based on the so-called Ginelli method using the tangent linear version of the quasi-geostrophic atmosphere-ocean model MAOOAM (Modular Arbitrary-Order Ocean-Atmosphere Model). Based on the CLVs, we can quantify the contribution of each model variable on each scale to the development of linear instabilities. We also study the changes in the structure of the attractor - and, consequently, in the basic dynamical properties of our system - as an effect of the ocean-atmopshere coupling strength and the model resolution.
Response and Sensitivity Using Markov Chains
Authors: Santos Gutiérrez Manuel , Lucarini Valerio
Published: March 2020

Dynamical systems are often subject to forcing or changes in their governing parameters and it is of interest to study

how this affects their statistical properties. A prominent real-life example of this class of problems is the investigation

of climate response to perturbations. In this respect, it is crucial to determine what the linear response of a system is

as a quantification of sensitivity. Alongside previous work, here we use the transfer operator formalism to study the

response and sensitivity of a dynamical system undergoing perturbations. By projecting the transfer operator onto a

suitable finite dimensional vector space, one is able to obtain matrix representations which determine finite Markov

processes. Further, using perturbation theory for Markov matrices, it is possible to determine the linear and nonlinear

response of the system given a prescribed forcing. Here, we suggest a methodology which puts the scope on the

evolution law of densities (the Liouville/Fokker-Planck equation), allowing to effectively calculate the sensitivity and

response of two representative dynamical systems.