bluuebunny/crossref_metadata_2025 huggingface dataset:
The middle-to-late Eocene greenhouse climate, modelled using the CESM 1.0.5
Authors: Baatsen Michiel , von der Heydt Anna S. , Huber Matthew , Kliphuis Michael A. , Bijl Peter K. , Sluijs Appy , Dijkstra Henk A.
Published: March 2020

Abstract. While the early Eocene has been considered in many modelling studies, detailed simulations of the middle and late Eocene climate are currently scarce. To get a better understanding of both Antarctic glaciation at the Eocene-Oligocene transition (~34 Ma) and late middle Eocene warmth, it is vital to have an adequate reconstruction of the middle-to-late Eocene climate. Results of higher (CMIP5-like) resolution coupled climate simulations are represented here using the Community Earth System Model (CESM) version 1. Two middle-to-late Eocene cases are considered with the same general boundary conditions but a different radiative forcing, using a new detailed 38 Ma geography reconstruction. Under 4× pre-industrial concentrations (PIC) of both CO2 (i.e. 1120 ppm) and CH4 (~2700 ppb), equilibrium sea surface temperatures correspond well to the available late middle Eocene (42–38 Ma; ~Bartonian) proxies. Being generally cooler, the simulated climate under 2× PIC forcing is a good analog for that of the late Eocene (38–34 Ma; ~Priabonian). Terrestrial temperature proxies, although their geographical coverage is sparse, also indicate that the results presented here are realistic. The reconstructed 38 Ma climate has a reduced equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. The collective effects of geography, vegetation and ice accounts for a global mean 5–7 °C difference between pre-industrial and 38 Ma Eocene boundary conditions, with important contributions from cloud and water vapour feedbacks. These simulations effectively show that a realistic middle-to-late Eocene climate can be reconstructed without the need for greenhouse gas concentrations much higher than proxy estimates (i.e. ~500–1200 ppm CO2). Equilibrium climate sensitivity is reduced (0.62 °C/W m2; 3.2 °C warming between 38 Ma 2× PIC and 4× PIC) compared to that of the present-day climate (0.79 °C/W m2; 3.1 °C per CO2 doubling). Despite very limited sea ice and snow cover in both 38Ma cases, the model still shows a factor ~2 polar amplification in response to a further increase of atmospheric greenhouse gas concentrations. High latitudes in the modelled Eocene climate are mainly kept warm by an altered radiative balance in combination with global changes in geography and the absence of polar ice sheets compared to the pre-industrial reference.
Cassini observations of magnetic holes in the solar wind and Saturn magnetosheath
Authors: Karlsson Tomas , Hadid Lina , Morooka Michiko , Wahlund Jan-Erik
Published: March 2020

We present the first Cassini observations of magnetic holes on the near-Saturn solar wind and magnetosheath, based on data from the MAG magnetometer. We conclude that magnetic holes (defined as isolated decreases of at least 50% compared to the background magnetic field strength) are common in both regions. We present statistical properties of the magnetic holes, including scale size, depth of the magnetic field reduction, orientation, change in magnetic field direction over the holes, and solar cycle dependence. For magnetosheath magnetic holes, also high-time resolution density measurements from the LP Langmuir probe are available, allowing us to study the anti-correlation of density and magnetic field strength in the magnetic holes. We compare to recent results from MESSENGER observations from Mercury orbit, and finally discuss the possible importance of magnetic holes in solar wind-magnetosphere interaction at Saturn.
Methane emissions from lakes in the Alpine region: insights from two years of mobile eddy covariance flux measurements
Authors: Scholz Katharina , Carotenuto Federico , Gioli Beniamino , Miglietta Franco , Pighini Sylvie , Sommaruga Ruben , Tomelleri Enrico , Tonon Giustino , Zaldei Alessandro , Wohlfahrt Georg
Published: March 2020

Lakes are considered an important natural source of methane (CH4). However, direct measurements of lake-atmosphere gas exchange are still sparse especially in the Alpine region. To overcome this shortcoming, we designed a mobile eddy covariance (EC) station to measure CO2, CH4, and energy fluxes at various lakes in the Alps. EC measurements were compared to flux measurements using floating chambers and related to abiotic and biotic factors like temperature, lake morphometry, dissolved components and trophic status.

During the first year, measurements were conducted at 9 lakes at different elevations ranging from 200 to 1900 m.a.s.l. to capture the spatial variability. The following year, measurements were repeated more frequently at three contrasting lakes to capture the seasonal trends of the fluxes.

The results indicate that all lakes were supersaturated with CH4. However, there was a high variability in the magnitude of CH4 emissions between lakes with generally higher emissions from warmer lakes at low elevation. In particular, the lake at the lowest elevation, Lake Caldaro, had highest dissolved CH4 concentrations and emissions and showed a clear seasonal trend with emissions peaking during the hot summer months. In contrast, the lake at the highest elevation, Lake Zoccolo, showed low CH4 concentrations and emissions with highest concentrations in fall when the water level was low.
Severe Space Weather: Simulations of Scaled-Up Storms
Authors: Raeder Joachim , Tulegenov Beket , Cramer William Douglas , Germaschewswski Kai , Ferdousi Banafsheh , Maruyama Naomi , Fuller-Rowell Timothy
Published: March 2020

Extreme space weather events are extremely rare, but pose a significant threat to our infrastructure. The one known event of such kind was the Carrington storm of 1859, but it was not well documented; in particular the solar wind and IMF conditions that caused it remain guesses. On the other hand, the STEREO-A observations of July 23, 2012 showed solar wind and IMF parameters that are most likely comparable to those of the Carrington event, and remind us that such extreme events are very well possible even during times of a quiet sun. Here, we use OpenGGCM simulations of such events to assess the effects of such solar wind and IMF on the magnetosphere. Precious work has shown that during the much more benign Halloween storm the nose of the magnetopause was as close as 4.9 RE, with an accordingly large polar cap. We will present simulations of a sequence of scaled-up storms with increasingly larger driving and demonstrate the further expansion of the polar cap, intensity of plasma injections, and the eventual saturation. In addition, we will show how the ionosphere potential penetrates to lower latitudes and affects the ionosphere and thermosphere at mid latitudes when the solar wind drivers become extreme.
Historical ablation rates and their drivers in Greenland – assessing the potential of the Wegener expedition for modern glaciological research
Authors: Abermann Jakob , Schöner Wolfgang , Fausto Robert Schjøtt
Published: March 2020

Alfred Wegener contributed extraordinarily to early days of scientific explorations in Greenland. Involved in three expeditions, we present unique historical data that is stored at Graz University, where Wegener filled his last academic position until his tragic death in Greenland in 1930. In this contribution we reevaluate data from his last expedition 1929-1931 acquired at the Qaamarujuup Glacier in West Greenland (71°09'N; 51°11'W). Sub-weekly ablation measurements along with air temperature, humidity, pressure, wind and short-wave radiation data exist for two full ablation seasons both near sea level and in 950 m a.s.l.. The 20th Century reanalysis product of the nearest grid-point performs well reproducing air temperature variability. Coincidentally, this expedition was carried out during a very warm period that was in fact comparable to recent years. We compare vertical ablation gradients from the years 1929/1930 obtained at Qaamarujuup in West Greenland with recent observations from the closest PROMICE automated weather station and discuss differences in a centennial perspective. Furthermore, we present a time-series of glacier stages from the little ice age (LIA) maximum up to present and quantify area and volume changes since. The glacier margin was in close proximity (<50 m distance) to the ocean during the LIA maximum, 660 m and almost 3 km horizontal distance from the ocean in 1930 and in 2019, respectively. Such a drastic geometrical change manifests in differing drivers of the glacier boundary layer with the impact of the cooling ocean during summer decreasing with time as the glacier margin’s distance to the ocean increases. We discuss the potential in using historical glacio-meteorological measurements along with a detailed glacier history in order to extract geometrical feedbacks from the climate change signal.
Experimental analysis of segregation in granular flows
Authors: D'Agostino Silvia
Published: March 2020

Natural granular flows have a widely dispersed grain size distribution. The majority of the numerical models and laboratory investigations of granular flows are developed assuming a single grain size. However, the geophysical massive flows involve several classes of particles and the bulk solid evolves spatially in a non-uniform state [1]. Segregation causes a different spatial distribution of the particles and influences the kinematic of the bulk solid, like the concentration, the run-out, the velocity and the granular temperature. During the flow motion, the largest particles are found at the surface due to the imbalances in the contact forces, and the smallest at the bottom as they percolate due to gravity [2].

To investigate the physical processes responsible of the particles transfer, we conducted a series of laboratory experiments, using two different grain size classes to reproduce the binary mixture. The measured data are required to calibrate the mathematical model and to set the coefficients that describe the percolation and the kinetic sieving mechanism. The experiments to study the free surface flow started considering the dry condition. Two different type of classes of particles flow over a loose deposit in homogenous and steady conditions. We used spherical particles of non-expanded polystyrene with a density of 1035 kg/m3. The small beads are black with a mean diameter of 0.00075 m and the large beads are white with a mean diameter of 0.0014 m. At the end of the flume there is a weir with two openings. The material is manually inserted and flow in the flume, it is then recirculated by an auger and finally conveyed in a hopper, from where it falls down in the chute again. The system works for at least 30 minutes, after reaching the steady condition.

The measurements were taken through a high speed camera in a section lateral to the flume. The flow field was measured with an optical method, that gives the velocity, the concentration and the granular temperature for both the small and the large particles, from the sidewalls.

Analyzing the experimental data, as regards the longitudinal velocity, it is possible to observe that the velocities of the two classes are similar and the large particles flow a bit faster. In contrast, there is a strong segregation in the concentration rates. After the running time, segregation causes the separation of the two classes: the largest classes are in the upper part and the smallest fraction at the bottom.

 

References

1 Drahun J.A., Bridgwater J. The mechanisms of free surface segregation, Powder Technology, 36, 39-53, 1988.

2 Savage S., Lun K.K. Particle size segregation in inclined chute of dry cohesionless granular solids, Journal of Fluid Mechanics, 189, 311-335, 1988.

 
Shattering Stereotypes
Authors: Campbell Heather
Published: March 2020

 

Shattering Stereotypes is a projecting that tackles and raises awareness of gender stereotyping in schools and how it can affect subject choice at GCSE and beyond.

In the last few years research by the Institute of Physics (IOP) and many others has shown that the lack of girls taking physics at A-Level is part of a wider problem; gender stereotyping in schools. The report Closing Doors concluded that schools which had low numbers of girls doing physics also had a small number of boys doing subjects which were stereotypically seen as girl subjects. Following this the IOP ran the Opening Doors project which generated a best practice guide for schools looking to tackle gender stereotyping.

Shattering Stereotypes builds on the best practice outlined in Opening Doors. The project is being piloted by the South East Physics network (SEPnet) in schools across the South East of England. The huge lack of diversity in physics is a problem that SEPnet partners are passionate about and are piloting this project as they want to tackle this problem.

Shattering Stereotypes is a set of three workshops for Year 8 students which aim to raise awareness of what gender stereotypes are, in particular:

Gender Stereotypes in the context of a student’s everyday life.

Gender Stereotypes and a student’s possible career path.

The project also aims to empower students so they can identify and challenge situations where they are presented with these stereotypes.
Experimentally disentangling drought from heat stress effects in European beech trees
Authors: Hoch Günter , Häfeli Nikita , Kahmen Ansgar
Published: March 2020

Hot summer droughts are becoming increasingly frequent in temperate biomes world-wide. In summer 2018, several weeks of drought paired with constantly high temperatures led to significant forest decline and mortality in mature trees in central Europe. In many regions, European beech was one of the most drought-sensitive tree species in 2018 with many trees showing partial or complete crown dieback by the end of the year, preceded by early leaf browning in mid-summer. So far it is disputed, if these symptoms were solemnly driven by a direct drought effect from dried-out soils, or if they were additionally amplified by hot mid-day temperatures and high atmospheric vapor pressure deficits (VPD).

In a recent study we therefore aimed to disentangle the effects of soil drought, air temperature and VPD on beech seedlings in a full-factorial experiment. Two-year old beech saplings were exposed to either cooler (daily max. temperature 24°C) or warmer (daily max. temperature 35°C) temperatures in walk-in phytotrons. Within each temperature treatment, half of the saplings were grown at either high or low relative humidity resulting in the same low or high mid-day VPD in both temperature treatments (0.7 vs. 2 kPa).Finally, half of the saplings from each temperature-VPD treatment combination where exposed to drought by stopping irrigation in July, with only compensatory water addition among pots to ensure the same dry-out rate among treatments (i.e. no faster soil drying at high VPD). Across all temperature-VPD treatment combinations, drought led to very similar decreases of stomatal conductance, photosynthesis and pre-dawn leaf water potential. There was only a tendency for an approximately 1 week earlier decline of Fv/Fm (leaf fluorescence) under drought at high VPD conditions, pointing at slightly faster stress occurrence at the leaf-level at very low air humidity. Neither high temperatures, nor high VPD induced stress symptoms at the leaf or whole-tree level in well-irrigated saplings. Overall, air temperature and VPD had no significant effect on the saplings' survival time under drought, with saplings from all temperature-VPD combinations dying on average after about 100 days into drought. Therefore, at the same decreasing rate of soil water availability, we did not find additional negative effects of warm temperatures or high VPD on tree survival, indicating that European beech is per se quite robust against heat and high VPD stress.
Geocenter motion determination and analysis from SLR observations to Lageos1/2
Authors: Yu Hongjuan , Sośnica Krzysztof , Shen Yunzhong
Published: March 2020

Accurate quantification and analysis of geocenter motion are of great significance to the construction and maintenance of the international terrestrial reference frame and its geodetic and geophysical applications. Here, the time series of 13-year geocenter motion coordinates (from 2006 to 2019) is determined by using the network shift approach from Satellite Laser Ranging (SLR) observations to Lageos1 / 2. Then, the geocenter motion time series is analyzed by using singular spectrum analysis. The principal components of geocenter motion are determined with the w-correlation criterion and two principal components with large w-correlation are regarded as the periodic signals. The results show that the annual periodic terms are clearly detectable in all out of three coordinate components, whereas the semi-annual term is only detected in the X-component. Moreover, weak periodic oscillations of 3 to 4 months exist in the X- and Y-components. Besides weak periodic signals with periods of about 8 months and 1 month for the X- and Y-components, respectively, a significant periodic signal of about 2.8 years exists in the  Z-component. Compared to the geocenter motion signals derived by the Center for Space Research (CSR) and Wrocław University of Environmental and Life Sciences (WUELS), both amplitude and phase agree well, with a better consistency with those from CSR, especially for the X- and Y-components.
CDOM Absorption Properties of Natural Water Bodies Along Extreme Environmental Gradients
Authors: Stamnes Jakob J. , Nima Ciren , Hamre Børge , Frette Øyvind , Chen Yi-Chun , Sørensen Kai , Norli Marit , Lu Daren , Xing Qiangguo , Muyiimbwa Dennis , Ssenyyonga Taddeo , Stamnes Knut , Erga Svein Rune
Published: March 2020

We present absorption properties of colored dissolved organic matter (CDOM) sampled in six different water bodies along extreme altitudinal, latitudinal, and trophic state gradients. Three sites are in Norway: the mesotrophic Lysefjord (LF), Samnangerfjord (SF), and Røst Coastal Water (RCW); two sites are in China: the oligotrophic Lake Namtso (LN) and the eutrophic Bohai Sea (BS); and one site is in Uganda: the eutrophic Lake Victoria (LV).

 

The site locations ranged from equatorial to subarctic regions, and they included water types from oligotrophic to eutrophic and altitudes from 0 m to 4700 m. The mean CDOM absorption coefficients at 440 nm [aCDOM(440)] and 320 nm [aCDOM(320)] varied in the ranges 0.063–0.35 m-1 and 0.34–2.28 m-1, respectively, with highest values in LV, Uganda and the lowest in the high-altitude LN, Tibet.

 

The mean spectral slopes S280-500 and S350-500 were found to vary in the ranges of 0.017–0.032 nm-1 and 0.013–0.015 nm-1, respectively. The highest mean value for S280-500 as well as the lowest mean value for S350-500 were found in LN. Scatter plots of S280-500 versus aCDOM(440) and aCDOM(320) values ranges revealed a close connection between RCW, LF, and SF on one side, and BS and LV on the other side.

 

CDOM seems to originate from terrestrial sources in LF, SF, BS, and LV, while RCW is characterized by autochthonous-oceanic CDOM, and LN by autochthonous CDOM. Photobleaching of CDOM is prominent in LN, demonstrated by absorption towards lower wavelengths in the UV spectrum. We conclude that high altitudes, implying high levels of UV radiation and oligotrophic water conditions are most important for making a significant change in CDOM absorption properties.

Considering all study sites, we find a strong negative linear relationship between the base-10 logarithm of aCDOM(440) and the spectral slope S280-500, and also between the base-10 logarithm of aCDOM(320) and the spectral slope S280-500.
Secondary circulation in shallow ocean straits: Observations and numerical modeling of the Danish Straits
Authors: Haid Verena , Stanev Emil , Pein Johannes , Staneva Joanna , Chen Wei
Published: March 2020

We study the secondary circulation in the Danish Straits using the unstructured-grid hydrodynamic model SCHISM covering the North Sea and Baltic Sea. The resolution in the straits is up to ~100 m. Since the large-scale atmospheric variability controls the transport in these straits, we focus on the processes with subtidal time scales. We compare the in- and outflows in the straits to flood and ebb flows in estuaries and analyze similarities and differences. Very prominently, the outflow and inflow phases of the Danish Straits feature substantial differences to the tidal straining in estuaries. With a resolution of ~100 m, new transport and mixing pathways, previously unresolved, appear fundamental to the strait dynamics. The variability of the strait bathymetry leads to a strongly differing appearance of secondary circulation. Helical cells, often with a horizontal extension of ~1 km, develop in the deep parts of the channels. A comparison between the high-resolution simulation and a simulation with a coarser grid of ~500 m in the straits suggests that the coarser resolution overestimates the stratification and misrepresents the transport balance. Axial velocities and transport through the Sound are underestimated by ~12%. These differences are explained by the underdeveloped secondary circulation in the coarse-resolution simulation and the associated changes in mixing along the straits. In conclusion, the use of ultrafine resolution grids is essential to adequately resolve secondary flow patterns and two-layer exchange.
Kinematic constraining of the multi-fault rupture dynamics of the Norcia, Mw 6.5, 30 October 2016, Central Italy earthquake
Authors: Tinti Elisa , Casarotti Emanuele , Gabriel Alice-Agnes , Taufiqurrahman Taufiqurrahman , Ulrich Thomas , Li Duo
Published: March 2020

The 2016 Central Italy sequence showed a remarkable complexity involving multiple faults. Highly heterogeneous slip distributions were inferred from kinematic finite source inversions. The coverage and quality of the geodetic and seismic data allow resolving high-resolution details of rupture kinematics of the largest event of the sequence, the Mw 6.5 30 October 2016 Norcia earthquake. Composite fault rupture models suggest that two fault planes may have slipped simultaneously. Nevertheless, kinematic modeling cannot assess the mechanic viability of such multiple fault plane models.

Using SeisSol, a software package for simulating wave propagation and dynamic rupture based on the arbitrary high-order accurate derivative discontinuous Galerkin method, we therefore try to generate spontaneous dynamic ruptures models compatible with the two fault planes constrained by kinematic inversions. To this end, we adopt a simple slip-weakening friction law with spatially variable dynamic friction and initial strength parameters along multiple faults, compatible with the slip distributions found in the literature. Although we do not to aim to explore the full parameter space, our approach allows testing the feasibility of kinematic models in conjunction with successfully generating spontaneous dynamic rupture scenarios matching seismic and geodetic observations with geological constraints. Such linking enhances and validates the physical implications of kinematic earthquake source inversion.
Ionisation effects on precipitation
Authors: Harrison R.Giles , Nicoll Keri , Ambaum Maarten , Marlton Graeme , Aplin Karen , Lockwood Michael
Published: March 2020

Cloud processes leading to rainfall generation are suspected to be influenced by droplet charge. Droplet charging is abundant, and even in layer clouds, charging of droplets readily occurs at the horizontal cloud-air boundary. Droplet charging in such circumstances is proportional to the vertical current driven through the cloud by the global electric circuit. Small global circuit variations from natural influences, such as solar modulation of cosmic rays can be used to investigate this, but an alternative is presented by artificial introduction of ionisation. The atmospheric nuclear weapons test period, which reached its peak 1962-1964, caused exceptional anthropogenic disturbance to the global circuit, through the increased ionisation from steady sedimentation of stratospheric radioactive debris.

Measurements of the vertical current Jz made at Kew Observatory near London (51°28′N, 0°19′W) were several times greater than normal during 1962-1964, as a result of the widespread extra ionisation in the lower atmosphere. At Lerwick, Shetland (60°09′N, 1°08′W) where deposition of radioactive material occurred, the atmospheric electrical parameters were strongly affected by the enhanced ionisation. To investigate tropospheric ionisation effects on local cloud processes, rainfall days at Lerwick in 1962-64 have been analysed by considering reduced and enhanced ionisation periods. During the enhanced ionisation, the Lerwick rainfall distribution shifted towards heavier rainfall and is significantly different from the rainfall distribution for reduced ionisation days; the Lerwick cloud was also significantly optically thicker during the enhanced ionisation. This contrasts with other years of the Kew record, when Jz was relatively undisturbed. Whilst the ionisation conditions of 1962-64 were exceptional, controlled methods of enhancing tropospheric ionisation by non-radioactive means - such as corona emission - may nevertheless be promising for local rainfall modification, or even geoengineering of cloud properties.
Convection is key to better polar low forecasts
Authors: Hallerstig Matilda , Magnusson Linus , Kolstad Erik
Published: March 2020

ECMWF HRES and Arome Arctic are the operational Numerical Weather Prediction models that forecasters in northern Norway use to predict Polar lows in the Nordic and Barents Seas. These type of lows are small, but intense mesoscale cyclones with strong, gusty winds and heavy snow showers. They cause hazards like icing, turbulence, high waves and avalanches that threaten offshore activity and coastal societies in the area. Due to their small size and rapid development, medium range global models with coarser resolutions such as ECMWF have not been able to represent them properly. This was only possible with short range high resolution regional models like Arome. When ECMWF introduced their new HRES deterministic model with 9 km grid spacing, the potential for more precise polar low forecasts increased. Here we use case studies and sensitivity tests to examine the ability of ECMWF HRES to represent polar lows. We also evaluate what added value the Arome Arctic model with 2.5 km grid spacing gives. For verification, we use coastal meteorological stations and scatterometer winds. We found that convection has a greater impact on model performance than horizontal resolution. We also see that Arome Arctic produces higher wind speeds than ECMWF HRES. To improve performance during polar lows for models with a horizontal grid spacing less than 10 km, it is therefore more important to improve the understanding and formulation of convective processes rather than simply increasing horizontal resolution.
Confinement of air in the Asian monsoon anticyclone and pathways of convective air to the stratosphere during summer season
Authors: Legras Bernard , Bucci Silvia , Chandra Sivan , Kottayil Ajil
Published: March 2020

We study the confinement of the air inside the Asian monsoon anticyclone during summer using both kinematic and diabatic Lagrangian trajectories with ERA5 and ERA-Interim reanalysis, and observed clouds. The improved consistency of ERA5 is demonstrated. It is shown that the escape time from the anticyclone estimated to be 13 days is of the same order as the circulation time which implies weak confinement. Parcels found inside the anticyclone have been mostly detrained by convection above θ =364 K, by about 2.6%  of the high clouds over Asia, with a prevalence of continental sources which are located beneath. The Tibetan plateau is found to be the most efficient provider with 10% of its high clouds but this is entirely due to the higher level of cloud tops in this region, and not to any preferred path above.  Actually,  most parcels escape the plateau to rise. The mean trapping is shown to be described by a 1D model that combines a simple mean ascent and a constant erosion loss, without any need of a “chimney effect”. The vertical dilution is exponential with a e-folding scale of 15 K in potential temperature from 370 K onward. The mean age of parcels with respect to convection exhibits a minimum at the centre of the Asian monsoon anticyclone due to the permanent renewal by fresh convective air and largest values on the periphery as air spirals out.

The variability of the the confinement is strongly linked with the oscillations of the anticyclone between its Tibetan mode and its Iranian mode, and to break and active periods of monsoon rain. We show that this variability modulates also the moisture in the lower stratosphere with wet events following active convection and dry events following the breaks.
The information content of skylight polarisation in MAX-DOAS trace gas and aerosol profiling applications
Authors: Tirpitz Jan-Lukas , Frieß Udo , Platt Ulrich
Published: March 2020

Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a well-established ground-based measurement technique for the detection of atmospheric aerosol and trace gases: ultra-violet and visible radiation spectra of skylight are analyzed to obtain information on different atmospheric parameters. An appropriate set of spectra recorded under different viewing geometries ("Multi-Axis") allows retrieval of aerosol and trace gas vertical distributions by applying numerical inversion methods. Currently one of the method’s major limitations is the limited information content in the measurements that reduces the sensitivity particularly at higher altitudes.

It is well known but not yet used in MAX-DOAS profile retrievals that measuring skylight of different polarisation directions provides additional information: the degree of polarisation for instance strongly depends on the atmospheric aerosol content and the aerosol properties and – since the light path (?) differs for light of different polarisation -  the set of geometries available for the inversion is extended. We present a novel polarization-sensitive MAX-DOAS instrument and a corresponding inversion algorithm, capable of using polarization information. Further, in contrast to existing MAX-DOAS algorithms consisting of separate aerosol and trace gas retrieval modules, our novel inversion scheme simultaneously retrieves aerosol and trace gas profiles of several species in a single step. The improvement over “unpolarised” MAX-DOAS approaches will be discussed, based on both, synthetic data and real measurements.
New unconstrained global ocean tide solutions for satellite gravimetry including minor tides
Authors: Sulzbach Roman , Dobslaw Henryk , Thomas Maik
Published: March 2020

The quality of global ocean tide models has increased drastically over the last decades due to the availability of dense open-ocean observations from satellite altimetry. In regions of poor altimetry coverage (e.g., polar seas and coastal areas) and for minor tides with a small signal-to-noise ratio, however, reliable estimates from unconstrained global numerical models are still (and will remain) critically important. We will present in this contribution recent results from the purely-hydrodynamic, barotropic tidal model TiME (Weis et al., 2008) that benefit from a newly introduced rotated grid avoiding the singularity at the North Pole; a revised scheme for dynamic feedbacks of self-attraction and loading; and revised bathymetry data-sets that also include water column height modifications in cavities underneath the Antarctic ice-shelves.

By focussing exemplarily on the M2 tide, we will demonstrate the individual impact of all those changes on the simulated water height variations. It will be shown that the effects of ice-shelf cavities extend well beyond the Southern Ocean and affect even amphidromic systems in the Northern Hemisphere. We will also emphasize the ability of unconstrained numerical models as TiME to explicitly simulate minor tidal lines, thereby allowing to thoroughly test (and subsequently improve) admittance-based methods currently employed for the processing of satellite gravimetry data from the GRACE and GRACE-FO missions.
Management and dissemination of global high-resolution agro-hydrological model simulation data from the Virtual Water Values project
Authors: Kurtz Wolfgang , Hachinger Stephan , Frank Anton , Mauser Wolfram , Weismüller Jens , Werner Christine
Published: March 2020

The ViWA (Virtual Water Values) project aims to provide a global-scale assessment of the current usage of water resources, of the efficiency of water use and of agricultural yields as well as the flow and trade of ‘virtual’ water across country boundaries. This is achieved by establishing a global management and monitoring system which combines high-resolution (1 km2) agro-hydrological model simulations with information from high-resolution remote-sensing data from Copernicus satellites. The monitoring system is used to judge the progress in achieving water-related UN sustainable development goals on the local and global scale. Specific goals of the project are, for example, to:

evaluate possible inefficiencies of the current water use in agriculture, industry and water management and its economic consequences.

assess the vulnerability of agriculture and ecosystems to climate variability with a special emphasis on water availability.

identify regional hot-spots of unsustainable water use and to analyze possible institutional obstacles for a sustainable and efficient water use.

identify trade-offs between the commercial water use and protection of ecosystem services.

A cornerstone for reaching these project goals are high-resolution global ensemble simulations with an agro-hydrological model for a variety of crop types and management practices. These simulations provide the relevant information on agricultural yields and water demands at different scales. In this context, a considerable amount of data is generated and subsets of these data might also be of direct relevance for different external interest groups.

In this presentation, we describe our approach for managing the simulation data, with a special focus on possible strategies for data provisioning to interested stakeholders, scientists, practitioners and the general public. We will give an overview on the corresponding simulation and data storage workflows on the utilized HPC-systems and we will discuss methods for providing the data to the different interest groups. Among other aspects, we address findability (in the sense of the FAIR principles) of simulation results for the scienctific community in indexed search portals through a proper metadata annotation. We also discuss a prototypical interactive web portal for visualizing, subsetting and downloading of selected parts of the data set.
Detection and characterization of fluid-driven earthquake clusters
Authors: Hainzl Sebastian , Fischer Tomas
Published: March 2020

Natural earthquake clusters are often related to a mainshock, which triggers the sequence by its induced stress changes. These clusters are called mainshock-aftershock sequences and statistically well explained by earthquake-earthquake interactions according to the Epidemic Type Aftershock Sequence (ETAS) model. Additionally, aseismic processes such as slow slip, dike propagation or fluid flow might also play a role in the initiation and driving of the earthquake sequence. Earthquake swarms, which lacks a dominant earthquake, are often believed to indicate such transient aseismic forcing signals. However, swarm-type clusters can also occur by chance in ETAS-simulations and thus not necessarily related to aseismic drivers. Thus, more sophisticated quantification of the space-time-magnitude characteristics of earthquake sequences are required for discrimination. Migration patterns are one of those properties which can be indicative for aseismic triggering. We suggest simple measures to identify and quantify migration patterns and test those for synthetic data, data from fluid injection experiments, and natural swarm activity related to fluid flow in NW Bohemia and Long Valley caldera. We analyze their potential to discriminate from ETAS-type clusters and compare it with those of time-magnitude characteristics of the activity such as seismic moment ratios and skewness. Our results are finally used to discriminate earthquake clusters in California and elsewhere.
Deposition of Organic Compounds on Alpine Snow
Authors: Francis Grant , Materić Dušan , Ludewig Elke , Röckmann Thomas , Holzinger Rupert
Published: March 2020

Currently, little is understood about the deposition and re-volatilisation of organic matter (OM) in snow. Understanding this balance for individual organic compounds has the potential to provide important information about present and past atmospheric conditions. This research investigates in detail the deposition and re-volatilisation rates for speciﬁc atmospheric OM that are present in alpine snow. Captured in the blank canvas of snow, any dissolved organic matter (DOM) in surface snow will reﬂect the relative abundances in the atmosphere once their deposition and revolatilisation rates are known. Likewise, DOM eﬀectively preserved in glacial ice will also express relative atmospheric composition of past climates. A recent pilot study by D. Materić et al.[1] investigates the post-precipitation change of OM in snow near the Sonnblick Observatory in the Austrian Alps. Using proton transfer reaction mass spectrometry, surface snow samples taken over several days were analyzed, and any organics found were grouped by their similar dynamics. This research expands on this study by analyzing snow samples over a larger spatial domain around Sonnblick during the course of ﬁve days in conjunction with long-term snow sampling currently underway at the observatory. Together, analysis of these samples will reveal changes in OM in surface snow over the course of the entire melt season. This research also considers both ﬁltered and unﬁltered snow samples to diﬀerentiate and identify OM of diﬀerent sizes that are present within each sample. Long-term measurements of post-precipitation OM in surface snow will provide more coherent trends for deposition and re-volatilisation rates of organics, which can be used to tie future measurements of DOM in surface snow to atmospheric OM.
Effects of long-term field experiments on early stage litter decomposition in Austria and Sweden
Authors: Gmach Maria Regina , Bolinder Martin A. , Menichetti Lorenzo , Kätterer Thomas , Sandén Taru
Published: March 2020

Soil organic matter decomposition affects the local and global C cycles. Decomposition is mainly affected by soil type and climatic conditions, for a given quality of organic material. This study tested the effect of land use and management, litter type, and climate on the early stage decomposition rate in long-term field experiments (LTEs) in Austria and Sweden. Standardized litter (Rooibos and Green tea) were used according to the Tea Bag Index (TBI) protocol (Keuskamp et al. 2013) for comparison of litter decomposition rate (k) and stabilization factor (S) in 11 sites in Austria (2015 and 2016) and 9 sites in Sweden (2016). The tea bags were buried at 8 cm depth and collected after ~90 days. Austrian LTEs focused on mineral nitrogen fertilization, mineral potassium fertilization, organic fertilization, tillage systems, and crop residues management. The LTEs evaluated in Sweden focused mainly on annual and perennial crops, mineral fertilization, and tillage systems. The impact of environmental parameters (air temperature and precipitation) was modeled to normalize the variance due to climatic effects at each site. The preliminary results show that in Austria TBI decomposition differed more between sites than between treatments at the same LTE. Minimum tillage treatment had significantly higher decomposition rates compared to reduced and conventional tillage. In Sweden, decomposition rate differed more between treatments than between sites. Fertilized plots showed higher stabilization than unfertilized, and maximum N fertilization had the highest k, while unfertilized had the lowest k. The effect of different tillage systems on k and S were variable across sites and treatments, although ploughing tended to result in the lowest k. The northernmost site resulted in the highest k value. Results indicated higher stabilization in perennial forage crops compared to annual crops. We also considered time-series decomposition for some sites with measurements at different time points by the TBI approach (retrieving tea bags after 15, 30, 60, and 90 days), and the use of Random Forest regressions to evaluate the importance of pedo-climatic variables on early stage decomposition.
Simulating bio-optical properties in the Mediterranean Sea.
Authors: Lazzari Paolo , Alvarez Eva , Terzic Elena , Salon Stefano , Organelli Emanuele , D'Ortenzio Fabrizio , Vellucci Vincenzo
Published: March 2020

We present the results of a series of simulations performed by a multi-spectral bio-optical model developed in the framework of the BIOPTIMOD Service Evolution project for the Copernicus Marine Environment Monitoring System (CMEMS-SE). In this research, we integrate the CMEMS Mediterranean Sea biogeochemical model MedBFM (multi-stoichiometric, phytoplankton functional types -PFT- based) with a bio-optical model able to resolve light propagation along the water column with 25 nm resolution in the visible range. Recent optical data streams provided by novel observations platforms, such as the Biogeochemical Argo floats (BGC-Argo) and the multi-spectral satellite sensors (ESA-CCI and Sentinel-OLCI), are used for the model validation. Our approach aims to improve the quality and reduce the uncertainty of paramount CMEMS biogeochemical products such as phytoplankton biomass and primary production.  

We present: 1) the optical dataset gathered from BGC-Argo floats and satellite sensors; 2) the multi-spectral upgrade of the bio-optical model including specific PFT optical properties  and CDOM formulation; 3) the assessment of the new bio-optical model within the CMEMS quality framework with particular reference to Remote Sensing Reflectance (Rrs) data and to light attenuation as inferred from BGC-Argo floats.

In particular, the analysis of Rrs spatial and temporal variability allows to evaluate the skill of different parameterizations for PFT (e.g. photochemical efficiency) and CDOM dynamics (e.g. photobleaching rate), using an ensemble of multi-annual 3D simulations.

The role of the CDOM deep inventory and river discharge in modulating light attenuation is also evaluated. Results indicates that the novel bio-optical model allows to reconstruct the West-East DCM gradient as a self-emergent property.

Major impacts of the project, potentially strategic for CMEMS users, involve: the improvement of CMEMS biogeochemical products quality, the development of new optics-related biogeochemical products for CMEMS, and the strengthening of the scientific and technological links with the new generation of marine bio-optical sensors, which may also support a stronger collaboration between modelling, remote sensing and experimental communities.
Datalogger development for tipping-bucket throughfall measurement with open-source tools
Authors: Kalicz Péter , Csáki Péter , Zagyvai-Kiss Katalin Anita , Gribovszki Zoltán
Published: March 2020

Manual throughfall gauges can not apply to explore the temporal properties of precipitation redistribution.  To follow the interception temporarily it is necessary to use automatic gauges. Commercial rainfall data-loggers are suitable but in a spatially heterogeneous environment, like agroforestry systems, need a large number to represent the spatial differences. To reduce the cost, we started to develop a microcontroller-based data logger.

As a test case, we develop new auxiliary equipment for an already working custom trough in our riparian alder plot. It is a large surface trough with a big container where water level change is sensed. This gauge works with a commercial data logger which will be used for validation purposes. The planned addition is a tipping bucket, which provides a digital signal directly. The simple task is to log the timestamp of the tips. After many iterations, an ARM
Cortex-M0+ based architecture was selected, which integrates all the necessary components of a simple data logger.  The development is fully open-source shared through git (https://github.com/kaliczp/hvlog). The presentation shares the experiences accumulated during the continuous development.

This research has been supported by the EFOP-3.6.2-16-2017-00018 in University of Sopron project and the corresponding author's work has been also supported by the János Bolyai Scholarship of the Hungarian Academy of Sciences and ÚNKP-19-4-I-4-SOE-4 New National Excellence
Program of the Ministry for Innovation and Technology.
Strain localization in abyssal peridotites from a magma-starved mid-ocean ridge: a microstructural study
Authors: Bickert Manon , Cannat Mathilde , Tommasi Andréa , Jammes Suzon , Lavier Luc
Published: March 2020

Detachment faults are large offset normal faults that exhume mantle-derived rocks on the seafloor at slow spreading ridges. They are assumed to root at the base of the brittle lithosphere. Magma, if present, can help localize strain at the base of the axial brittle lithosphere by its own presence or crystallization of weaker phases such as plagioclase. This is the case of the Mid-Atlantic Ridge, where ductile shear zones are preferentially formed in and next to magmatic veins (Boschi et al., 2006; Cannat, 1991; Cannat & Casey, 1995; Ceuleneer & Cannat, 1997; Dick et al., 2002; Hansen et al., 2013; Picazo et al., 2012, Schroeder & John, 2004).

Here we focus of a nearly amagmatic case, the eastern part of the Southwest Indian Ridge (SWIR). Partially serpentinized peridotites recovered from dredging on and off axis record variable degrees of a heterogeneous high stress deformation. Orthopyroxene is primarily brittle (kinks, fractures), while olivine displays a wide range of plastic to semi-brittle deformation, ranging from weak to strong with development of extensively recrystallized anastomosing microshear zones. These microshear zones, which are a few mm to cm wide, represent the highest strain localization recorded in these samples. No further evidence of high strain localization, such as high temperature mylonites, has been recovered in this area. The fine-grained microshear zones are preferentially located along orthopyroxene grains or around kinked olivines. Both represent stronger grains (rheological contrast at the grains scale) that produce stress concentrations. Rock-scale thermo-mechanical models using orthopyroxene and olivine flow laws reproduce the observations: ductile shear zones in olivine also initiate preferentially next to brittle orthopyroxene.

We propose that this deformation is linked to the rooting of the detachment faults at depth, where an anastomozed network of microshear zones localizes strain at the base of the lithosphere, allowing the exhumation of variably deformed rocks.