bluuebunny/crossref_metadata_2025 huggingface dataset:
Land Use Dynamics in the Khor Abu Habil alluvial fan,Sudan
Authors: Seifelislam-Schreiber Aicha , AbdelRahman Elfatih , Bogner Christina
Published: March 2021

Introduction African wetlands in arid and semi-arid regions provide a multitude of ecosystem services and have been described as the “heart of Sahelian life systems". The Khor Abu Habil alluvial wetlands (Khor is the name given to ephemeral rivers in Sudan) are situated in the semi-arid zone in the southern part of the Sudan. These ephemeral wetlands are fed by seasonal wadi streams and remain for several months. They provide a habitat for migratory water birds and play a fundamental role in supporting the human population (agriculture, grazing, fishing, hunting and construction).

Goals In this study we analyse the Land Use and Land Cover (LUL) dynamics related to wetlands and the agricultural activities.

Material and Methods Landsat images between 1982 and 2018 were used to run a LULC analysis in the Khor Abu Habil alluvial fan using random forests (RF) and change vector analysis (CVA). Due to the political and the COVID-19 pandemic situations in the study area,  the field work aiming at collecting ground reference points could not be completed. Therefore, we decided to identify training data on different types of LULC classes that were dominant in the study area for the last 30 years using CVA, in addition to the collected ground reference points. High resolution images (Quickbird, Geoeye, WorldView) and expert knowledge were used for the selection of training data. For Landsat images acquired before 2018, the present training data were used where CVA showed no change in LULC. After creating accurate training data, the classification of the different Landsat images was run in R using RF.

Results Different types of LULC classes were detected over the past 30 years: Wetlands, Vegetation, Agriculture, Arenosols, Cambisols, Clays.  Our results show that many of those classes were "transformed" into other classes over the past years. We observe that many of those changes are related to different anthropological activities such as the expansion of agriculture or construction of dams.

Conclusions Wadis or Khors are particular ecosystems that occur in semi-arid regions. In our study area, the economic activities show a relationship between LULC and different human communities. It is crucial to understand those activities and their effects on an ecosystem, especially if the ecosystem is aimed to be protected. Our research is part of the FAO-supported project RESSOURCE with the overall goal to localise and study wetlands of international importance in the sub-saharan Africa and to possibly declare them as Ramsar protected zones.
Large-scale spatial characterization of a karst aquifer by combination of periodic and non-periodic responses (Lez aquifer, France)
Authors: Fischer Pierre , Jourde Hervé
Published: March 2021

Spatial characterization of the hydraulic properties in the subsurface is an extensively studied problematic. Inverse problems allow to image those properties by interpreting the information from a dataset of field measurements with a chosen physical formulation of fluxes in a numerical distributed model. However, karst media characterization remains a complex task, due to the fact that the matrix and conduits entities generate a highly contrasted distribution of property values. Thus, one needs to employ an inversion method able to represent this contrast and also use data providing information on the localization of the conduits network and its connectivity.

We propose a large-scale 2-D application of characterization of the Lez aquifer in southern France, covering a surface of about 400 km². We take advantages of long-terms measurements within the framework of the MEDYCYSS observation site, part of the Karst observatory network (www.snokarst.org) initiated by the French institute INSU/CNRS. Drawdown signals measured in 14 wells incorporating a periodic response due to a daily pumping at the aquifers spring were thus considered for this study. The periodic responses can provide connectivity information between wells in the inversion process, while non-periodic responses will permit to better assess the large-scale property values of the whole hydrosystem. A Cellular Automata-based Deterministic Inversion (CADI) is used to generate a contrasted property field able to reproduce the measured signals in the 2-D distributed numerical model. This application is led with responses obtained at a high water-table level and also at a lower level in order to highlight the change in connectivity and flow paths mobilized at different depths.
Full year of continuous N2O flux measurements in a drained agricultural peatland in northern Finland
Authors: Gerin Stephanie , Laurila Tuomas , Kulmala Liisa , Tuovinen Juha-Pekka , Vekuri Henriikka , Lohila Annalea
Published: March 2021

Pristine boreal peatlands are often considered neutral or even small sinks for nitrous oxide (N2O). However, drained peatlands are a significant source of N2O. In these managed sites, oxygen becomes more available, increasing denitrification and therefore N2O release into the atmosphere. N2O emissions do not typically follow a strong seasonal pattern like carbon dioxide but instead, have high spatial and temporal variability. Short-term N2O peak emissions can be observed after various meteorological or soil management events throughout the year, for example after soil freezing or thawing, or fertilization. However, it is not well known how exactly those events trigger the N2O emission peaks. Therefore, N2O annual budget based on punctual chamber measurement can introduce large uncertainties. That is why it is important to measure N2O emissions with a continuous method to better understand the controlling factors and to estimate the annual budgets more accurately.

For the first time in the boreal region of Europe, N2O emissions were continuously observed during a full year in a drained agricultural peatland with the eddy covariance (EC) technique. The study site is a managed peatland in northern Finland, in Ruukki (Latitude: 64.684010; Longitude: 25.106473), with a peat depth between 10 and 90 cm. It is currently managed as a grass field, composed of a mixture of timothy and meadow fescue. We will show a first overview of the N2O fluxes measured since November 2019 with the EC technique. We will present how various meteorological and management events can explain some short-term variations. Then, we will compare the N2O annual budget estimated from the EC measurements to the IPCC emission factor and to different estimates achieved using several sets of non-continuous data points, representing manual chamber measurements with varying frequency.
Photovoltaics in Austria - open space and rooftop potential analysis on a high spatial resolution
Authors: Mikovits Christian , Schauppenlehner Thomas , Scherhaufer Patrick , Schmidt Johannes , Schmalzl Lilia , Hampl Nina , Sposato Robert
Published: March 2021

Austria aims to meet 100% of its electricity demand from domestic renewable sources by 2030 which means, that an additional 30 TWh per year are required. Solar energy will play a significant role to reach this goal, meaning the need for a substantial increase in photo-voltaic capacity. While some federal states and municipalities released a solar roof-top cadastre, there is lacking knowledge on the estimation of the potential of both, open space installations and roof-top modules, on a national level with a high spatial resolution. Results show significant differences between urban and rural areas, as well as between the Alpine regions and the Prealpine- and Easter Plain areas.

The work includes a framework to automatically process solar PV data and land-use data was developed and openly available for usage. The framework is able to fetch solar data automatically from a defined source, and join, manipulate and alter it with geodata applying various spatial methods.
Analysis of the eastern Adriatic sea-level extremes
Authors: Pervan Marija , Šepić Jadranka
Published: March 2021

The Adriatic Sea is known to be under a high flooding risk due to both storm surges and meteorological tsunamis, with the latter defined as short-period sea-level oscillations alike to tsunamis but generated by atmospheric processes. In June 2017, a tide-gauge station with a 1-min sampling resolution has been installed at Stari Grad (middle Adriatic Sea), the well-known meteotsunami hot-spot, which is, also, often hit by storm surges. 

Three years of corresponding sea-level measurements were analyzed, and 10 strongest episodes of each of the following extreme types were extracted from the residual series: (1) positive long-period (T > 210 min) extremes; (2) negative long-period (T > 210 min) extremes; (3) short-period (T < 210) extremes. Long-period extremes were defined as situations during which sea level surpasses (is lower than) 99.7 (i.e. 2) percentile of sea level height, and short-period extremes as situations during which variance of short-period sea-level oscillations is higher than 99.4 percentile of total variance[J1]  of short-period series. A strong seasonal signal was detected for all extremes, with most of the positive long-period extremes appearing during November to February, and most of the negative long-period extremes during January to February. As for the short-period extremes, these appear evenly throughout the year, but strongest events seem to appear during May to July.

All events were associated to characteristic atmospheric situations, using both local measurements of the atmospheric variables, and ERA5 Reanalysis dataset. It was shown that positive low-pass extremes commonly appear during presence of low pressure over the Adriatic associated with strong SE winds (“sirocco”), and negative low-pass extremes are associated to the high atmospheric pressure over the area associated with either strong NE winds (“bora”), or no winds at all. On the other hand, high-pass sea level extremes are noticed during two distinct types of atmospheric situations corresponding to both “bad” (low pressure, strong SE wind) and “nice” (high pressure, no wind) weather.

It is particularly interesting that short-period extremes, of which strongest are meteotsunamis, are occasionally coincident with positive long-period extremes contributing with up to 50 percent to total sea level height – thus implying existence of a double danger phenomena (meteotsunami + storm surge). 
Simple regional analyses are still possible once correlated errors are removed
Authors: Crowley John , Huang Jianliang
Published: March 2021

Correlated errors in the monthly spherical harmonic coefficient (SHC) solutions provided by the GRACE data centers are estimated and removed using the destriping method of Crowley and Huang (2020). Regional estimates for mass change are calculated across Canada using the simple basin average technique of Swenson and Wahr (2002) as well as a simple mascon approach developed by the Canadian Geodetic Survey. A comparison with mascon solutions from the GRACE data centers demonstrates excellent agreement and in some cases reveals larger amplitudes and added temporal structure. This approach does not require additional constraints/dependencies, smoothing, normalizations or scaling factors and can easily be applied to any regional geometry without the need to calculate a global solution. Solutions tend to agree well when data quality is good and diverge when errors are larger. This is expected and demonstrates the underlying uncertainties that remain. The similarity in solutions using such different methodologies provides confidence in the time series solutions. We conclude with a regional validation that uses water level changes in the Great Lakes of North America to demonstrate the effectiveness of the method. The Great Lakes are large enough that GRACE clearly detects changes in their water levels. At the same time, the lakes are close enough to each other that distinguishing signals between adjacent lakes remains a challenge for any method.

References:

Crowley, J.W., and J Huang, A least-squares method for estimating the correlated error of GRACE models, Geophysical Journal International, Volume 221, Issue 3, June 2020, Pages 1736–1749, https://doi.org/10.1093/gji/ggaa104.

Swenson, S., and J. Wahr, Methods for inferring regional surface-mass anomalies from Gravity Recovery and Climate Experiment (GRACE) measurements of time-variable gravity, J. Geophys. Res., 107(B9), 2193, doi:10.1029/2001JB000576, 2002.
SedCas_Volcano: Simulating decadal patterns of lahar hazard and sediment transfer following volcanic disturbance in the Belham River Valley, Montserrat 
Authors: Christie James , Bennett Georgina , Hirschberg Jacob , Barclay Jenni , Herd Richard
Published: March 2021

Explosive volcanic eruptions are among the most significant natural disturbances to landscapes on Earth. The widespread and rapid influx of pyroclastic sediment, together with subsequent changes to topography and vegetation cover, drives markedly heightened runoff responses to rainfall and increased downstream water and sediment fluxes; principally by way of hazardous lahars. The nature and probability of lahar occurrence under given rainfall conditions evolves as the landscape responds and subsequently recovers following the disturbance. The relationship between varying sediment supply, rainfall patterns, vegetation cover and lahar activity is complex, and impedes forecasting efforts made in the interest of hazard and land use management. Thus, developing an improved understanding of how these systems evolve in response to volcanic eruptions is of high importance.

Here we present SedCas_Volcano[MOU1] , a conceptual sediment cascade model, designed to simulate the first-order trends, such as magnitude-frequency distributions or seasonal patterns, in lahar activity and sediment transport. We use the Belham River Valley, Montserrat, as a case study. This small (~15km2) catchment has been repeatedly disturbed by five phases of volcanic activity at the Soufrière Hills Volcano since 1995. The multi-phase nature of this eruption, together with the varying nature and magnitude of disturbances throughout the eruption, has driven a complex disturbance-recovery cycle, which is further compounded by inter-annual climatic variations (e.g. ENSO). Lahars have occurred frequently in response to rainfall in the Belham River Valley, and their occurrence has evolved through the repeated disturbance-recovery cycle. This activity has resulted in significant net valley floor aggradation and widening, consequent burial and destruction of buildings and infrastructure, as well as coastal aggradation of up to ~250m. Within SedCas_Volcano, we account for evolving sediment supply, vegetation cover and rainfall, to simulate the lahar activity and channel change observed in the Belham River Valley since January 2001. Following this, we test the model under different hypothetical eruptive scenarios. [MOU2] Our goal is to assess the efficacy of such models for reproducing patterns of lahar activity and geomorphic change in river systems that are repeatedly disturbed by volcanic activity.
How much variability in upper tropospheric cloud-radiative heating can be attributed to ice microphysics?
Authors: Sullivan Sylvia , Voigt Aiko , Miltenberger Annette , Rolf Christian , Krämer Martina
Published: March 2021

While large-domain simulations without convective parameterization are now computationally feasible, microphysics, particularly that of the ice phase, remains a persistent problem for high-resolution models. In 2.5-km equivalent resolution simulations with the ICON model, we find that switching between one- and two-moment ice microphysics can alter cloud top cooling by a factor of ten and in-cloud heating by a factor of four above 350 hPa. A consistent ice crystal effective radius between microphysics and radiation increases the cloud-radiative heating another two-fold, while inclusion of aerosol-cloud interactions reduces it at lower levels between 400 and 500 hPa. We also generate 60-hour trajectories from ICON within ice clouds and use them to force a detailed ice microphysics box model, the Chemical Lagrangian Model of the Stratosphere (ClaMs-ice). We compare the ice mass and number tendencies, as well as the sedimentation fluxes, between ICON and CLaMS-ice. These offline simulations also allow us to quantify the strength of microphysical-radiative feedbacks and investigate the impact on heating of particular ice microphysical factors, including gravity wave parameterization, ice-nucleating particle concentrations, and the number concentration of solution droplets.
A Machine Learning Heat Flow Model of Antarctica
Authors: Lösing Mareen , Bernales Jorge , Ebbing Jörg
Published: March 2021

We established a new Geothermal Heat Flow (GHF) model for Antarctica by using a machine learning approach. GHF is substantially related to the geodynamic setting of the plates, and global geophysical and geological data sets can provide information for remote regions like Antarctica, where only sparse direct measurements exist. We applied a Gradient Boosted Regression Tree algorithm in order to build an optimal prediction model relating GHF to the observables.
Employed data sets are reviewed for their reliability and quality in polar regions and we emphasize the need for adding reasonable data to the algorithm. The validity of our approach is indicated by predictions for Australia, where an extensive database of GHF measurements exists. Our new estimated GHF map exhibits rather moderate values compared to previous models, ranging from 35 to 156 mWm-2, and shows visible connections to the conjugate margins in Australia, Africa, and India.
Such estimates on the geothermal structure of Antarctica are for example needed for studies on ice sheet modeling. The internal thermal structure and the mass balance of the modeled Antarctic ice sheet (AIS) are significantly affected by the prescribed GHF distribution.  Applying a wide range of possible GHF maps within estimated uncertainties to ice-sheet-shelf set-ups, the influence of GHF on the modeled AIS response to a variety of climate scenarios is quantified. 
Contrasting thermal responses of permafrost to winter warming events under different snow regimes in the subarctic
Authors: Pascual Descarrega Didac , Johansson Margareta
Published: March 2021

Winter warming events (WWE) in the Swedish subarctic are abrupt and short-lasting (hours-to-days) events of positive air temperature that occur during wintertime, sometimes accompanied by rainfall (rain on snow; ROS). These events cause changes in snow properties, which affect the below-ground thermal regime that, in turn, controls a suite of ecosystem processes ranging from microbial activity to permafrost and vegetation dynamics. For instance, winter melting can cause ground warming due to the shortening of the snow cover season, or ground cooling as the reduced snow depth and the formation of refrozen layers of high thermal conductivity at the base of the snowpack facilitate the release of soil heat. Apart from these interacting processes, the overall impacts of WWE on ground temperatures may also depend on the timing of the events and the preceding snowpack characteristics. The frequency and intensity of these events in the Arctic, including the Swedish subarctic, has increased remarkably during the recent decades, and is expected to increase even further during the 21st Century. In addition, snow depth (not necessarily snow duration) is projected to increase in many parts of the Arctic, including the Swedish subarctic. In 2005, a manipulation experiment was set up on a lowland permafrost mire in the Swedish subarctic, to simulate projected future increases in winter precipitation. In this study, we analyse this 15-year record of ground temperature, active layer thickness, and meteorological variables, to evaluate the short- (days to weeks) and long-term (up to 1 year) impacts of WWE on the thermal dynamics of lowland permafrost, and provide new insights into the influence of the timing of WWE and the underlying snowpack conditions on the thermal response of permafrost. On the short-term, the thermal responses to WWE are faster and stronger in areas with a shallow snowpack (5-10 cm), although these responses are more persistent in areas with a thicker snowpack (>25 cm), especially after ROS events. On the long term, permafrost in areas with a thicker snowpack exhibit a more durable warming response to WWE that results in thicker active layers at the end of the season. On the contrary, we do not observe a correlation between WWE and end of season active layer thickness in areas with a shallow snowpack. 
Emergence of transverse size in electric streamers
Authors: Lehtinen Nikolai
Published: March 2021

The accurate determination of parameters of electric streamer propagation in air, such as their velocity, transverse size (radius) and the maximum field at the tip, is extremely important, e.g., for the studies of further lightning development and acceleration of electrons at the tip, which may lead to generation of x-rays. Relations between these parameters produce a family of streamer-shaped solutions, while the radius remains undetermined. We hypothesize that all these solutions are, in fact, valid solutions of hydrodynamic equations, but the physical radius emerges when one solution is selected by the condition of being maximally unstable, i.e., having the highest velocity.

Direct verification of this hypothesis by hydrodynamic simulations is complicated by the fact that the streamer length is one of the background conditions which determine its parameters, and in a propagating streamer the length is constantly changing. To circumvent this, we simulate a `steady-state' streamer, such that its length is kept constant by synchronizing the motion of the electrode to which it is attached. We show that the predicted maximally-unstable selected solution does, in fact, emerge in the infinite time limit of the simulation. We note, however, that we were yet unable to test the first part of the hypothesis, i.e. to produce the non-selected solutions in the predicted family, as they are quickly replaced by the selected one.

We present the calculated streamer parameter dependence on external uniform field and streamer length for an isolated streamer and streamers propagating parallel to each other. In the latter case, the field of neighboring streamers makes the streamer propagation independent of its length when it exceeds the inter-streamer distance. We draw parallels of this situation to the selected solution for a viscous Saffman-Taylor finger of infinite length in a narrow channel [Luque et al, 2008, doi:10.1103/PhysRevE.78.016206].

The practical interest of this work lies in reducing the complexity of streamer propagation modeling, by avoiding detailed simulation of the streamer head, if we can calculate the parameters by a simpler algorithm.
A numerical method for subglacial cavitation posed as a variational inequality
Authors: Gonzalez de Diego Gonzalo , Farrell Patrick , Hewitt Ian
Published: March 2021

Subglacial cavitation is a phenomenon that occurs at the base of an ice sheet or a glacier where the ice detaches from the bedrock at high water pressures. The process is recognised as an essential mechanism in glacial sliding. A mathematical description of subglacial cavitation involves a free boundary equation and a Stokes equation with contact boundary conditions. These contact boundary conditions model the process of detachment from the bed at each instant in time. 

In this talk we show that the problem can be written as a variational inequality and present a novel approach to solving the equations with finite element methods that exploit the structure of the variational inequality. In particular, we present a formulation involving Lagrange multipliers, which allows us to solve the discrete contact conditions exactly. Thanks to this latter property, the Stokes equations can be solved together with the free boundary equations in a robust and stable manner. A similar method should also prove useful for improving grounding-line calculations.

With this numerical method, we compute a friction law (the relation between sliding velocity and shear stress) for ice flowing over a periodic bed.  We recover existing results for the case when the cavities are in a steady state for a given effective pressure. We extend these results to consider time-varying cavitation driven by changes in subglacial water pressure.
Atmospheric chemistry of oxygenated mercury-containing compounds
Authors: Taamalli Sonia , Louis Florent , Pitonak Michal , Cernusak Ivan , Dibble Theodore S
Published: March 2021

Mercury is transported globally through the atmosphere as atomic mercury, but mostly it is transferred from the atmosphere to ecosystems in the form of Hg(II) compounds. As a result, scientists are increasingly focused on oxidation-reduction chemistry of mercury in the atmosphere. At present, little is known about the interaction of mercury compounds with environmental surfaces, which commonly possess adsorbed water.

As a first step towards understanding these interactions, we have theoretically studied the reaction of BrHgO• + CO → BrHg• + CO2, which constitutes a potentially important mercury reduction reaction in the atmosphere. We characterized the potential energy surface with CCSD(T)/CBS energies (with corrections for relativistic effects) at MP2 geometries. Master Equation simulations were used to reveal the factors controlling the overall rate constant.

In a second step and for the first time, the monohydration of several oxygenated mercury-containing compounds (BrHgO, BrHgOH, BrHgOOH, BrHgNO2 and its isomers, and HgOH) with one water molecule has been theoretically studied using the ωB97X-D/aug‐cc‐pVTZ level of theory. The thermodynamic properties of the hydration reactions have been calculated using DFT geometries with energies with coupled-cluster calculations DK-CCSD(T) and the ANO‐RCC‐Large basis sets. Standard reaction enthalpy and standard Gibbs free reaction energy were computed. The temperature dependences of ΔrG°(T) were evaluated for all studied aggregates over the temperature range 200 - 400 K. For the first time, the monohydration processes have been studied to elucidate the role of hydrating water molecules. Atmospheric implications have been discussed.
ASIM TGFs with accompanying elves
Authors: Bjørge-Engeland Ingrid , Østgaard Nikolai , Mezentsev Andrey , Neubert Torsten , Skeie Chris Alexander , Marisaldi Martino , Ullaland Kjetil , Genov Georgi , Chanrion Olivier , Reglero Victor
Published: March 2021

The Atmospheric Space Interactions Monitor (ASIM) was launched in 2018, and has since then observed Terrestrial Gamma-ray Flashes (TGFs) and Transient Luminous Events (TLEs). ASIM consists of the Modular X- and Gamma-ray Sensor (MXGS) and the Modular Multispectral Imaging Array (MMIA). Using data from both MXGS and MMIA, we investigate observations of TGFs (detected by MXGS) with accompanying elves (detected by MMIA). We study the optical signatures of the elves detected by a photometer of MMIA operating in the 180-230 nm band. Lightning sferics associated with these events have been detected by WWLLN and GLD360. Several TGFs have associated lightning sferics outside the field of view of MMIA, but due to the expanding rings of the elves we can still observe optical signatures from accompanying elves. Using GLD360 data we also study properties of the lightning strokes.
Quantification of the Emission Changes in Europe During 2020 Due to the COVID-19 Mobility Restrictions
Authors: Guevara Marc , Jorba Oriol , Petetin Hervé , Denier Van Der Gon Hugo , Kuenen Jeroen , Super Ingrid , Peuch Vincent-Henri , Pérez García-Pando Carlos
Published: March 2021

To hinder the circulation of the COVID-19 virus, European governments implemented emergency measures going from light social distancing to strict lockdowns, depending on the country. As a consequence, many industries, businesses and transport networks were forced to either close down or drastically reduce their activity, which resulted in an unprecedented drop of anthropogenic emissions. This work presents the Copernicus Atmosphere Monitoring Service (CAMS) European regional emission reduction factors associated to the COVID-19 mobility restrictions (CAMS-REG_ERF-COVID19), an open source dataset of daily-, sector-, pollutant- and country-dependent emission reduction factors for Europe linked to the COVID-19 pandemic. The resulting dataset covers a total of six emission sectors, including: road transport, energy industry, manufacturing industry, residential and commercial combustion, aviation and shipping. The time period covered by the dataset includes the first and second waves of the disease ocurred during 2020, starting from 21 February, when the first European localised lockdown was implemented in the region of Lombardy (Italy), until 31 December, when COVID-19 transmission remained widespread and several countries had nationwide restrictions still in place. The CAMS-REG_ERF-COVID19 dataset is based on a wide range of information sources and approaches, including open access and measured activity data and meteorological data, as well as the use of machine learning techniques. We combined the computed emission reduction factors with the Copernicus CAMS European gridded emission inventory to spatially (0.1x0.05 degrees) and temporally (daily) quantify reductions in 2020 primary emissions from both criteria pollutants (NOx, SO2, NMVOC, NH3, CO, PM10 and PM2.5) and greenhouse gases (CO2 fossil fuel, CO2 biofuel and CH4), as well as to assess the contribution of each pollutant sector and country to the overall reductions. The resulting gridded and time-resolved emission reductions suggest an heterogeneous impact of the COVID-19 across pollutants, sectors and countries.
Borehole logging and temperature measurements with the MARUM-MeBo sea bed drilling technology: Recent developments and scientific applications
Authors: Freudenthal Tim , Riedel Michael , Villinger Heinrich
Published: March 2021

The MARUM-MeBo sea bed drilling technology is developed since 2004 at the MARUM Center for Marine Environmental Sciences at the University of Bremen (Freudenthal and Wefer, 2013). Presently two drill rigs are in operation for drilling and coring down to more than 70 m (MARUM-MeBo70) and 200 m (MARUM-MeBo200), respectively. The robotic drill rig with the required drill tools is deployed on the seabed, where the drill string for conducting coring is assembled during the drilling operation. In addition to wireline core barrels a temperature probe can be used for measuring formation bottom hole temperature at discrete drilling depths by pushing the probe about 15 cm into the base of the bore hole. The temperature is logged for about 10 – 15 minutes in order to allow for dissipation of the frictional heat generated during pushing and equilibration to formation temperature. When the temperature measurement is completed, the probe is recovered out of the drill string and the drilling operation can be continued.

The trip out of the drill string after reaching the target drill depth can be used for logging of the geophysical properties within the borehole and the adjacent formation. A memory logging tool is lowered into the drill string with the sensor part penetrating through the drill bit. When the drill string is tripped out the probe is raised together with the drill string inside the borehole and conducts the geophysical measurements. This method called “logging while tripping” is especially suitable for unconsolidated sediments and logging in unstable borehole conditions, since the drill string stabilizes the borehole above the sensor part during the logging operation. For the MeBo drill rigs we have spectrum gamma ray, magnetic susceptibility, dual induction and acoustic probes available. The latter is also equipped with a temperature sensor for measuring borehole temperature. 

In this presentation we show examples from MeBo drilling campaigns where core drilling, borehole logging and formation temperature measurements where combined. A focus of this presentation is the analysis of borehole temperature measurements during trip out. We investigate how geothermal flux and lithological changes (i.e. thermal conductivity) influence the bore hole temperature measurement by modeling the temperature evolution within the borehole during drilling and trip out.

  

References:

Freudenthal, T and Wefer, G (2013) Geoscientific Instrumentation, Methods and Data Systems, 2(2). 329-337. doi:10.5194/gi-2-329-2013
Investigation of Lake and Wetlands Influence on Streamflow in Mesoscale Precambrian Shield Watersheds Using IsoWATFLOOD, A Tracer-Aided Hydrologic Model 
Authors: Tafvizi Arghavan , James April , Stadnyk Tricia , Yao Huaxia , Ramcharan Charles
Published: March 2021

Hydrologists continue to be challenged in accurately predicting spatial variation in storage, runoff, and other hydrological processes in both natural and disturbed landscapes. Lakes and wetlands are important hydrologic stores in Precambrian shield watersheds. Identifying how they affect streamflow, independently and/or collectively is a challenge. Tracer-aided hydrologic modeling coupled with field-based stable isotope surveys offer a potentially powerful approach to investigation of mesoscale streamflow generation processes because the influence of evaporative enrichment generates a distinct signature of the surface water endmember, and continuous and distributed simulated streamflow can be tested against field observations under a range of flow conditions. The main objectives of this research are to investigate the influence of lakes and wetlands on streamflow generation by developing application of the tracer-aided hydrologic model isoWATFLOOD for the ~ 15275 km2 Sturgeon - Lake Nipissing - French River (SNF) basin located on the Precambrian Shield in Northeastern Ontario, Canada. Monthly surveys of δ18O and δ2H in river flow were collected between 2013 to 2019 (weekly to monthly) across eight sub-catchments, with supporting observations of volumes and stable isotopes in snowcores, snowmelt, precipitation and groundwater. Application of the hydrologic model isoWATFLOOD to the SNF Basin is developed for the first time, allowing for simulation of discharge and stable isotopes in streamflow and soil moisture across multiple sub-catchments. In model building, consideration of differences in quaternary geology, landcover, and sub catchment locations are considered.  Landcover ranges from the boreal forests to impervious urban areas, while dominated by temperate forest, with some coverage of agriculture/disturbed impacted systems; several major sub-catchments having hydropower regulations. Previous statistical analysis has highlighted the importance of wetlands, lakes, and quaternary geology as influential on differences in hydrologic and isotope response in SNF watershed, as a result, model building is considering different landcover types as lakes and wetlands. Six different Landover are considered for generating Group Response Units (GRUs). The model is calibrated using discharge and stable water isotope.  IsoWATFLOOD can represent variation in streamflow generation across the study area. Identifying the different impacts of lakes and wetlands on streamflow generation processes in study area by applying isoWATFLOOD for the SNF watershed will be the main achievement of this study.
Inherent dissipation of upwind-biased potential temperature advection and its feedback on model dynamics
Authors: Gaßmann Almut
Published: March 2021

Higher order upwind biased advection schemes are often used for potential temperature advection in dynamical cores of atmospheric models. The inherent diffusive and anti-diffusive fluxes are interpreted here as the effect of irreversible sub-gridscale dynamics. For those, total energy conservation and positive internal entropy production must be guaranteed. As a consequence of energy conservation, the pressure gradient term should be formulated in Exner pressure form. The presence of local antidiffusive fluxes in potential temperature advection schemes foils the validity of the second law of thermodynamics. Due to this failure, a spurious wind acceleration into the wrong direction is locally induced via the pressure gradient term. When correcting the advection scheme to be more entropically consistent, the spurious acceleration is avoided, but two side effects come to the fore: (i) the overall accuracy of the advection scheme decreases and (ii) the now purely diffusive fluxes become more discontinuous compared to the original ones, which leads to more sudden body forces in the momentum equation. Therefore the amplitudes of excited gravity waves from jets and fronts increase compared to the original formulation with inherent local antidiffusive fluxes.

The means used for supporting the argumentation line are theoretical arguments concerning total energy conservation and internal entropy production, pure advection tests, one-dimensional advection-dynamics interaction tests and evaluation of runs with a global atmospheric dry dynamical core.
An object method to characterize grainflow morphology
Authors: Zhang Pei
Published: March 2021

Grainflow, a fundamental agent moving sediment from the crest to the base of dune surfaces, leaves a temporary geomorphological signature on the slipfaces of aeolian dunes. The grainflow signature reflects the complex morphodynamical interaction between wind-driven sand transport and gravity-driven grainflow on an inclined surface. The purpose of this study is to present a method to objectively and efficiently delineate grainflow boundaries and characterize their morphology features by processing Digital Elevation Models (DEMs) obtained by terrestrial laser scanner in Matlab and ArcGIS. The method allows large numbers of grainflows to be quickly and objectively delineated and extracted from LiDAR data. As an aid tp subsequent analysis, the process avoids the subjective nature of manual measurement, thereby improving the commensurability of different grainflow regimes in both terrestrial and extraterrestrial environments. The results can be compared with the available grainflows morphology characteristics which are manually measured. The method is presented here in the context of analyzing grainflows and related processes on the slipfaces of dunes, but it is applicable over the broader scope of other forms of slope failure and geophysical flows, such as avalanches, snowslides, landslides, and debris flows.
Characterizing an anticyclone in Western Mediterranean Sea using altimetric data and an eddy tracker
Authors: Pujol Cécile , Alvera-Azcárate Aida , Troupin Charles , Barth Alexander , Romanelli Hugo
Published: March 2021

In April 2019, a large anticyclonic Eddy has formed in Western Mediterranean Sea between Sardinia and Balearic Islands. This anticyclone was observable with Sentinel-3 SST satellite data for 7 months and its diameter was estimated to 150 km. Although mesoscale anticyclones are quite common in this part of the Mediterranean Sea, such large and long-live eddies remain exceptional and repercussions for ocean-atmospheric exchanges and for biodiversity might be consequent. However, due to the increase of temperatures during summer, the satellite SST track of the eddy has been lost during a few weeks in August and September. Indeed, the SST signature of the eddy was not distinguishable from surrounding waters anymore. In order to track the eddy during its entire life and have a better understanding of its characteristics, sea level anomaly derived from altimetric data will be analysed in this study with the Py Eddy Tracker toolbox to investigate the variation of its position, its altimetry and its size. The distribution of other remarkable eddies in this zone and period will also be considered. Moreover, a high-resolution SST field will be reconstructed with DINEOF method so the comparison between eddy’s SST and altimetric characteristics will be assured.
Abrupt last glacial loess-dust deposition over Southeast England coupled with dynamics of the British-Irish Ice Sheet
Authors: Stevens Thomas , Sechi Daniele , Bradák Balázs , Orbe Ragna , Baykal Yunus , Cossu Giulia , Tziavaras Charilaos , Andreucci Stefano , Pascucci Vincenzo
Published: March 2021

Loess deposits are globally important dust archives but are often limited by imprecise chronological control. In particular, loess records adjacent to former ice sheets seldom have detailed, independent age models yet have the potential to elucidate the causes of past high latitude (>50° N in Northern Hemisphere) coarse dust emission close to former ice sheets, a relatively poorly known aspect of past dust dynamics. Loess deposits in southern Britain were formed in close proximity to western parts of the last glacial Eurasian ice sheets. However, currently their age and accumulation rate remain poorly known, limiting interpretation of the controls on last glacial coarse dust emission and deposition in the region.

Here we apply high sampling resolution quartz optically stimulated luminescence (OSL) to constrain the timing of dust accumulation and loess formation at the Pegwell Bay site in east Kent, SE England. The OSL ages and Bayesian (Bacon) age modelling results are the most detailed to date for western European loess, and show that loess began to accumulate around c. 25 ka, coinciding with Heinrich event 2 and the coupling of Fennoscandian and British-Irish ice sheets. There were two phases of greatly enhanced dust accumulation at the site, at 25-23.5 ka and 20-19 ka, separated by a lower accumulation rate period. Loess accumulation appears to have stopped or been dramatically reduced after 19-18 ka. We propose that the dynamics of the British-Irish and Fennoscandian Ice Sheets, associated glacial lake drainage, and linked reorganisations of atmospheric circulation, act to control loess accumulation at the site. In particular, we argue that both periods of enhanced dust accumulation were caused by advance-retreat phases of the North Sea ice lobe, and associated drainage of Dogger Lake. These events would have led to abrupt input of sediment-rich ice dammed lake and melt water from northern and eastern England and the North Sea into the exposed southern North Sea basin. This would have dramatically increased sediment availability for transport and deposition as loess in SE England. Easterly and north-easterly winds that could have transported this dust to SE England would have been enhanced by presence of an ice sheet anticyclone, enlarged during Fennoscandian and British-Irish ice sheet coalescence, as well as katabatic winds and easterly flow occurring on the northern side of Atlantic cyclones forced south of southern Britain by the extended western British-Irish ice sheet. As such, last glacial dust dynamics and loess accumulation in Britain is highly influenced by the interaction of the British-Irish and Fennoscandian ice sheets, Atlantic storm tracks, and the topography and drainage of the exposed North Sea basin.
Management effects on nitrate and ammonium leaching in temperate grasslands
Authors: Apostolakis Antonios , Klaus Valentin , Schöning Ingo , Michalzik Beate , Schrumpf Marion
Published: March 2021

Grassland management can influence nitrogen leaching by changing respective inputs (like fertilization) and outputs (e.g. harvest) from the ecosystem but also through changes in plant and microbial communities and their interactions with the soil. Yet the mechanisms of these processes and their importance for nitrate (NO3-) and ammonium (NH4+) are poorly researched. Although temperate grassland management can cause a high leaching risk, studies measuring annual soil nitrogen fluxes and covering a high number of sites are limited. Using a resin method, we measured annual leaching fluxes of NO3-N and NH4-N in 150 grassland sites in three German regions from spring 2018 to spring 2019 at a depth of 10 cm. We used Structural Equation Modeling to identify direct and indirect management effects on nitrogen leaching. Both fertilization and grazing intensities increased NO3-N leaching to almost the same extent. Fertilization intensity increased NO3-N leaching directly and indirectly i) by decreasing the negative effect of plant richness on NO3-N leaching and ii) by increasing the positive effect of legume cover on NO3-N leaching. Similarly, grazing intensity increased NO3-N directly and indirectly i) by increasing the positive effect of legume cover on NO3-N leaching and ii) by decreasing the negative effect of grass cover on NO3-N leaching. Microbial biomass (nitrogen) increased NO3-N leaching and it was not controlled by management. Fertilization strongly increased NH4-N leaching, both by a direct effect and indirectly by increasing the positive effect of plant nitrogen on NH4-N. Grazing intensity and plant richness had no direct effects on NH4-N leaching. We have shown that grassland management considerably influences inorganic nitrogen leaching in the annual basis, and that fertilization intensity is more important than grazing, especially for NH4-N leaching. Moreover, we found that plant diversity decreases NO3-N leaching, but this effect is controlled by fertilization leading to increased leaching risks. Thus, reducing the management intensity, both in meadows and pastures, can be used as a mitigation tool for inorganic nitrogen leaching.
An Eddy-Zonal Flow Feedback Model for Propagating Annular Modes and their Dynamics
Authors: Lubis Sandro , Hassanzadeh Pedram
Published: March 2021

There is strong evidence that a positive feedback between the zonal-mean wind anomalies and the eddies (i.e. a positive feedback of EOF1 onto itself) is important for maintaining the wind anomalies associated with the annular modes. However, a recent study by Lubis and Hassanzadeh, (2021, JAS) shows that under some circumstances, EOF1 and EOF2 can interact and exert feedbacks on each other at some lag times, affecting the time scale of the annular modes. Building upon the seminal work of Lorenz and Hartmann (2001, JAS), we introduced a reduced-order model for coupled EOF1 and EOF2 that accounts for potential cross-EOF eddy-zonal flow feedbacks. Using the analytical solution of this model, we derive conditions for the existence of the propagating regime based on the feedback strengths. Using this model, and idealized GCMs and stochastic prototypes, we show that cross-EOF feedbacks play an important role in controlling the persistence of the annular modes by setting the frequency of the oscillation. We find that stronger cross-EOF feedbacks lead to less persistent annular modes. The underlying dynamics of the cross-EOF feedbacks for propagating annular modes in both reanalysis and an idealized GCM are also investigated. Using a finite-amplitude wave activity (FAWA) framework, we show that the cross-EOF feedbacks result from the out-of-phase oscillations of EOF1 (north-south jet displacement) and EOF2 (jet pulsation) leading to an orchestrated combination of equatorward propagation of wave activity (a baroclinic process) and nonlinear wave breaking (a barotropic process), which altogether act to reduce the total eddy forcings. The results highlight the importance of considering the coupling of EOFs and cross-EOF feedbacks to fully understand the natural and forced variability of the zonal-mean large-scale circulation.

Reference: Lubis, S. W., & Hassanzadeh, P. (2021). An Eddy–Zonal Flow Feedback Model for Propagating Annular Modes, Journal of the Atmospheric Sciences, 78(1), 249-267.