bluuebunny/crossref_metadata_2025 huggingface dataset:
Glider observations of sediment resuspension during storm conditions
Authors: Gentil Mathieu , Bourrin François , Durrieu de Madron Xavier , Estournel Claude
Published: March 2021

Sediment resuspension and transport on continental shelves are primarily driven by episodic energetic events, such as storm. Unfortunately, resuspension processes remain poorly quantified using traditional sampling techniques due to the intermittency and the intensity of these events. The recent integration of Acoustic Doppler Current Profilers (ADCPs) onto underwater gliders changes the way current and sediment dynamics in the coastal zone can be monitored. Their endurance and ability to measure in all weather conditions increase the probability of capturing sporadic meteorological events. We used a Slocum glider equipped with a CTD (Conductivity, Temperature, Depth), an optical payload and a RDI 600 kHz phased array ADCP to examine storm-induced sediment resuspension in the Gulf of Lion’s shelf (NW Mediterranean). Observations show that early in the storm, when the waves are highest, resuspension is limited by stratification. During the storm, erosion of the pycnocline through thickening of the bottom and surface mixed layers lead to resuspension in the full water column. Coincident optical and acoustic backscatter measurements indicate that the resuspended particulate assemblage is homogeneous and composed of large particles. Glider-ADCP observations showed for the first time that waves may be the predominant forcing which drive the resuspension on the outer shelf (> 80 m) during the winter storm. While, in the Gulf of Lions, which is considered as a relatively low energy continental shelf, modeling studies consider that only current drive resuspension in the outer shelf. This study highlights the usefulness of glider-ADCP to describe episodic processes and to support validation and improvement of regional hydrodynamic models.
Moisture recycling in five different regions with Mediterranean climates around the world
Authors: Theeuwen Jolanda , Tuinenburg Obbe , Staal Arie , Hamelers Bert , Dekker Stefan
Published: March 2021

Weather extremes are predicted to be more intense and recurrent in the future because of climate change. Previous studies show that Mediterranean regions around the world are especially vulnerable to extreme events that depend on the hydrological cycle, such as droughts and floods. Land use and land cover changes may enhance these events, as they influence the exchange of moisture and energy between the land surface and atmosphere. To better understand the role of extremes in a future climate, we need to improve our understanding of the impact of climate change on the terrestrial hydrological cycle. Atmospheric transport of moisture is an important element of this cycle as it determines the allocation of evaporated moisture. We are especially interested in the sink-source relations. So, how land contributes to the moisture recycling over land further away, and the origin of the precipitation over, the so-called precipitation-shed. Tuinenburg et al. (2020) recently published a dataset with high-resolution global atmospheric moisture connections from evaporation to precipitation, allowing novel detailed insight. We used this dataset to study temporal variability in atmospheric moisture connections for five different regions with Mediterranean climates. We investigated the dependency of different Mediterranean regions on local and remote moisture sources, and how this dependency varies throughout the year. Large differences in the spatial pattern of moisture recycling over land showed to exist between the Mediterranean regions on the Northern and Southern Hemisphere. Additionally, of all regions, the Mediterranean Basin shows the largest temporal variability. This information is essential to study how local changes in land use and land cover have and will further affect the hydrological cycle in local and remote regions. This helps us to understand how climate extremes could change in the future as a result of land use and land cover changes.  

 

Tuinenburg, O. A., Theeuwen, J. J. E., and Staal, A. Global evaporation to precipitation flows obtained with Lagrangian atmospheric moisture tracking, PANGAEA, https://doi.org/10.1594/PANGAEA.912710, 2020.
Late Cretaceous to Paleogene exhumation in Central Europe – localized inversion vs. large-scale domal uplift
Authors: von Eynatten Hilmar , Kley Jonas , Dunkl István
Published: March 2021

Large parts of Central Europe have experienced exhumation in Late Cretaceous to Paleogene time. Previous studies mainly focused on thrusted basement uplifts to unravel magnitude, processes and timing of exhumation. In this study we present a comprehensive thermochronological dataset from mostly Permo-Triassic strata exposed adjacent to and between the major basement uplifts in central Germany, comprising an area of at least some 250-300 km across. Results of apatite fission track and (U-Th)/He analyses from >100 new samples reveal that (i) km-scale exhumation affected the entire region, suggesting long-wavelength domal uplift, (ii) thrusting of basement blocks like the Harz Mountains and the Thuringian Forest focused in the Late Cretaceous (about 90-70 Ma) while superimposed domal uplift of central Germany appears slightly younger (about 75-55 Ma), and (iii) large parts of the domal uplift experienced removal of 3 to 4 km of Mesozoic strata. Using spatial extent, magnitude and timing as constraints we find that thrusting and crustal thickening alone can account for no more than half of the domal uplift. Most likely, dynamic topography caused by upwelling asthenosphere has contributed significantly to the observed pattern of exhumation in central Germany.
Co-Evaluation as a step in the Co-Generation of Climate Services.  An analysis of the CLARA experience
Authors: Delpiazzo Elisa
Published: March 2021

Due to the pervasive nature of climate change impacts, and their relevance for human welfare, climate services delivering advanced knowledge of climate change and variation are crucial. They aid informed decision-making at relevant spatial and timescale and to improve prevention, preparation, adaptation, and minimize residual damages. It is also imperative to evaluate the climate services with a view to quantify the economic value added of these services. Particularly crucial is to assess how the decision-making process of the service end users would unfold with and without the service to identify its differential impact on properly selected indicators of performance.

The co-generation (also called co-creation) in products and services was made popular by the business literature in the early 2000s and represents a conceptual shift from an emphasis on output to an emphasis on a mutually satisfying relational process between developers and users in service creation. It mainly consists of four stages, namely co-design, co-development, co-delivery, and co-evaluation. The stage of co-evaluation refers to the development and application of agreed upon criteria for the measurement of results. The criteria will touch upon both substantial and procedural issues. From a user perspective, it will be important to evaluate relevance, impact/benefits, utility, credibility, and costs (financial and human resources) in using climate services. These elements are important to assess the effectiveness and uptake of the service and possibly refine it towards these goals. From a developer perspective, important aspects to evaluate will include, for instance, the scientific quality of the service or its skill.

This presentation introduces the lessons learnt in the context of the H2020 project CLARA (Climate forecast enabled knowledge services) on how to effectively implement the interactions among researchers, end users and service developers to unveil the economic value added of climate services.
Can the assimilation of IASI water isotopologue observations improve the quality of meteorological analyses fields?
Authors: Khosrawi Farahnaz , Toride Kinya , Yoshimura Kei , Diekmann Christopher , Ertl Benjamin , Hase Frank , Schneider Matthias
Published: March 2021

The strong coupling between atmospheric circulation, moisture pathways and atmospheric diabatic heating is responsible for most climate feedback mechanisms and controls the evolution of severe weather events. However, diabatic heating rates obtained from current meteorological reanalyses show significant inconsistencies. Water isotopologue observations (e.g. H2O and HDO) assimilated into meteorological reanalyses can make an invaluable contribution since the isotopologue composition depends on the history of phase transition. Therefore, isotopologue observations can provide information that is closely linked to latent heating processes. Using the retrieval recipe of MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water), the free tropospheric water vapour isotopologue composition can be retrieved from IASI spectra measured for cloud free conditions.

Here, we theoretically assess with an Observation Simulation Experiment (OSSE) the potential of the MUSICA IASI isotopologue data for constraining uncertainties in analyses fields. For this purpose, we use the isotopes-incorporated General Spectral Model (IsoGSM) and mock MUSICA IASI isotopologue observations. We use the Local Transform Ensemble Kalman Filter (LETKF) data assimilation method and perform two different experiments. In a first experiment we assimilate temperature, humidity and wind profiles obtained from radiosonde and satellite data. In a second experiment we assimilate additionally the mocked IASI isotopologue data. When mocked isotopologue data are additionally assimilated, we find reduced ensemble spreads with respect to meteorological variables and rain rates. This indicates that IASI isotopologue observations can indeed reduce the uncertainties of latent heating rates and meteorological analysis fields and in consequence offer potential for improving weather forecasts.
Downstream evolution of grain size in extremely mobile post-earthquake debris flows, China
Authors: Harvey Erin L. , Hales Tristram C. , Hobley Daniel E. J. , Fan Xuanmei , Liu Jie , Xu Qiang , Huang Runqiu
Published: March 2021

Large, catchment transitioning debris flows are an important mechanism for transporting sediment from hillslopes into higher order channels. Extremely large flows can exceed volumes of 109 m3, however even flows with volumes of  ~103 m3 can lead to fatalities and extensive damage. Few processes transport a wider range of grain sizes than debris flows, which can transport grains from clays to 10 m boulders. While the structure of debris flows can often be inferred by their deposits, the range of grain sizes presents a challenge for their interpretation. Debris flow grain size distributions can be used to constrain debris flow runout due to their effect on excess pore pressure dissipation. Currently, there is limited data available for the entire grain size distribution of debris flow deposits in the field.

We constrained the entire grain size distribution for two extremely large (>1 km in length) post-earthquake debris flows in Sichuan Province, China. These debris flows were triggered in August 2019 after an extreme rainfall event occurred close to the epicentre of the 2008 Wenchuan earthquake. We sampled the debris flows in November 2019 at intervals of 200 m and 500 m, respectively. At each site, we used a combination of field and laboratory sieving to obtain the coarse and fine fraction for both the surface and subsurface. We dug 1 m x 1 m x 0.5 m pits, excavating each layer at 10 cm depth increments. We sieved these increments into five size fractions in the field, including < 1 cm. We sieved 1 kg of the <1 cm fraction in the laboratory to estimate the distribution of the finest grains. The coarse surface fraction was then independently constrained using photogrammetry. Preliminary results for one debris flow show that the distribution of fine grains (~<4 mm) is consistent both laterally and vertically across the runout. This suggests that the processes occurring vertically and laterally during deposition result in the consistent distribution of fines.
Detecting the spatio-temporal propagation of heatwaves
Authors: Böhnisch Andrea , Felsche Elizaveta , Ludwig Ralf
Published: March 2021

Heat waves are among the most hazardous climate extremes in Europe, commonly affecting large regions for a considerable amount of time. Especially in the recent past, heat waves account for substantial economic, social and ecologic impacts and loss. Projections suggest that their number, duration and intensity increase under changing climate conditions, stressing the importance of quantifying their characteristics. Yet, apart from the analysis of single historical events, little research is dedicated to the general propagation of heat waves in space and time.  
Heat waves are rare in their occurrence and limited observational data provide little means for robust analyses and the understanding of dynamical spatio-temporal patterns. Therefore, we seek to increase the number of analyzable events by using a large climate model ensemble. The use of several model members of comparable climate statistics allows to robustly assessing various spatial patterns of heat waves as well as their typical temporal evolutions.  
Here, we explore a data-driven approach to infer cause-and-effect relationships from, in this case, regional climate model ensemble data in order to analyze the spatio-temporal propagation of spatially distributed phenomena. Our aim is to investigate specifically the transitions and inter-dependencies among heat waves in Europe. The approach includes the identification of most frequent heat wave patterns by clustering and the derivation of directed links between core regions of these heat wave classes using causal discovery in a data set of high spatial resolution. 
We present the setup of our framework, including clustering results of heat waves and first results of our analysis.
Continent-wide bimonthly mapping of Antarctic surface meltwater using Google Earth Engine
Authors: Tuckett Peter , Ely Jeremy , Sole Andrew , Livingstone Stephen , Lea James
Published: March 2021

Surface meltwater is widespread around the margin of the Antarctic Ice Sheet during the austral summer. This meltwater, typically transported via surface streams and rivers and stored in supraglacial lakes, has the potential to influence ice-sheet mass balance through ice-dynamic and albedo feedbacks. To predict the impact that surface melt will have on mass balance over coming decades, it is important to understand spatial and temporal variability in surface meltwater extent. A variety of methods have been used to detect supraglacial lakes in Antarctica, yet a multi-annual, continent-wide study of Antarctic supraglacial meltwater has yet to be conducted. Cloud-based computational platforms, such as Google Earth Engine (GEE), enable large-scale temporal and spatial analysis of remote sensing datasets at minimal time expense. Here, we implement an automated method for meltwater detection in GEE to generate continent-wide, bimonthly repeat assessments of supraglacial lake extent between 2013 and 2020. We use a band-threshold based approach to delineate surface water from Landsat-8 imagery. Furthermore, our method incorporates a novel technique for quantifying meltwater extent that accounts for variability in optical image coverage and cloud cover, enabling an upper uncertainty bound to be attached to minimum mapped lake areas. We present results from continent-wide mapping, and highlight initial findings that indicate evolution of lakes in Antarctica over the past seven years. This work demonstrates how platforms such as GEE have revolutionized our ability to undertake large-scale projects from remote sensing datasets, allowing for greater temporal and spatial analysis of cryospheric processes than previously possible.
Remote sensing for assessment of groundwater resources, A case study of Stampriet Transboundary Aquifer
Authors: Kinoti Irene , Leblanc Marc , Olioso Albert , Lubczynski Maciek , Poulain Angelique
Published: March 2021

Distributed integrated hydrological models (IHMs) are the most effective tools for estimating groundwater recharge in arid and semi-arid areas characterized by thick unsaturated zone. It is also important to capture spatio-temporal aquifer dynamics by using real-time or near-real-time data, for sustainable water resources management. However, such data is often unavailable in developing countries where monitoring networks are scarce. In recent years, remote sensing has played an important role in providing spatio-temporal information for evaluation and management of water resources. Nevertheless, application of remote sensing in groundwater studies is still limited and has mainly focused on assessment of groundwater recharge and groundwater storage as well as to provide boundary conditions and driving forces for both standalone groundwater models and IHMs. This study entails application of remote sensing data in developing the distributed integrated hydrological model for Stampriet transboundary multi-layered aquifer system shared between Namibia, Botswana and South Africa. A numerical model has been set – up using MODFLOW 6 coupled with the Unsaturated Zone Flow (UZF) Package where Climate Hazards Infrared Precipitation with stations (CHIRPS) rainfall data and Global Land Evaporation Amsterdam Model (GLEAM) potential evapotranspiration data were implemented as the model driving forces. Other input data used include digital elevation model, and land-use/landcover and also soil datasets to define unsaturated zone parameters. The model has been calibrated with groundwater level measurements as the state variables in transient conditions at daily time step for a period of 16 years. The model-simulated unsaturated zone and groundwater storage was compared to GRACE-derived sub-surface storage anomaly, further also used to constrain the model. The calibrated model provides spatio-temporal water flux dynamics as well as water balances and hence an understanding of the groundwater-resource dynamics and replenishment. This information is shown useful for proper management of the transboundary water resource as well as for policy making.
Identifying 2000 small and large creep events on the San Andreas Fault.
Authors: Gittins Daniel , Hawthorne Jessica
Published: March 2021

The San Andreas fault has been observed to creep at the surface along the 175km section between San Juan Bautista and Cholame (Titus et al., 2011). This section is known as the creeping section and accumulates slip in two modes: during continuous background slip at a long term slip rate and in accelerated slip bursts known as creep events (Gladwin et al., 1994). But the size and importance of creep events remain unclear. Some researchers treat them as small, ~100-m-wide near-surface events (Gladwin et al., 1994), but others suggest that many creep events reach 4 km depth, connecting the surface to the seismogenic zone (Bilham et al., 2016). So, in this study, we systematically characterize the along-strike rupture extents of creep events along the San Andreas Fault, to determine if these are small, localized phenomena or large, segment-rupturing events.

We detect creep events and analyse their propagation using 18 USGS creepmeter records from the San Andreas Fault. Each creepmeter operated for at least 9 of the years between 1985 and 2020. To begin we systematically detect creep events using a cross-correlation approach. We identify periods that have significant slip and signals with high similarity to a template creep event. This automated detection allows us to produce a catalogue with 2000 creep events. The method detects at least 95% of the creep events identified by visual inspection.

Once we have found creep events at each creepmeter, we examine how creep events propagate. We compare creep event detections between pairs of creepmeters to determine how many creep events propagate from one creepmeter to the other. At the northern end of the creeping section, we observe that 18-28% of the creep events found at Harris Ranch are also found at Cienega Winery within 24hrs. This coincident timing implies that 18-28% of creep events in the north have an along-strike length of at least 4 km. Many creep events at the southern end of the creeping section appear to be even larger. For instance, a few events appear to be at least 31 km long; 10-38% of creep events at Slacks Canyon also observed at Work Ranch (31 km away) within 24hrs. These large along-strike rupture extents imply that creep events connect the slip and stress field over large regions of the San Andreas Fault. These events may play an important role in the slip dynamics of the creeping section.
Is the Bay of Bengal at a tipping point?
Authors: Löscher Carolin
Published: March 2021

The Bay of Bengal (BoB) has the long-stood enigma of an oxygen minimum zone, which maintains traces of oxygen without becoming fully anoxic. This may, besides biological feedback loos stabilizing the low oxygen concentrations in those waters, have to do with low primary production in the BoB’s surface waters and the lack of subsequent respiration of organic material in intermediate oxygen poor waters. Recently, a small but significant decrease of global marine primary production has been reported based on ocean color data, which was mostly ascribed to decreases in primary production in the northern Indian Ocean, particularly in the Bay of Bengal.

Available reports on primary production from the BoB are limited, and due their spatial and temporal variability difficult to interpret. Primary production in the BoB has historically been described to be driven by diatom and chlorophyte clades, however, this is not consistent with newer data, which instead show an abundance of smaller, visually difficult to detect cyanobacterial primary producers. By combining the available metagenomic and biogeochemical datasets with satellite-based ocean color observations, a pattern can be derived showing a shift in community composition of primary producers in the BoB over the last two decades. This shift is driven by a decrease in chlorophyte abundance, and a coinciding increase in cyanobacterial abundance, despite stable concentrations of total chlorophyll. Statistical analysis indicated a correlation of this community change in the BoB to decreasing nitrate concentrations, which may provide an explanation for both, the decrease of eukaryotic nitrate-dependent primary producers and the increase of small unicellular cyanobacteria related to Prochlorococcus, which have a comparably higher affinity to nitrate. A potential change in primary producer community composition and especially a decrease in primary production in the BoB may thus have a significant impact on the distribution of low oxygen waters in this basin and may possibly mitigate their further expansion, therefore arguing against the BoB being at a tipping point to develop full anoxia.
Comparing inferred surface energy fluxes with observation-based flux estimates over the ocean
Authors: Mayer Johannes , Mayer Michael , Haimberger Leopold
Published: March 2021

We combine atmospheric energy transports from ECMWF's latest reanalysis dataset ERA5 with observation-based TOA fluxes from CERES-EBAF to infer net surface energy fluxes (FSinf) for the period 1985-2018. We present an extensive comparison at scales ranging from global to local using 15 in-situ buoy measurements, parameterized surface fluxes from ERA5, and previous evaluations of FSinf using ERA-Interim. We also combine FSinf with various estimates of the ocean heat content tendency (OHCT) and observation-based oceanic heat transports from RAPID and moorings in Fram Strait and Barents Sea Opening to evaluate the oceanic energy budget in the North Atlantic Ocean basin.

Our results show that the indirectly estimated FSinf has a 1985-2018 ocean mean of 1.7 W m-2 (see J.Mayer et al. (2021); under review), which is in good agreement with the long-term mean OHCT derived from ocean reanalyses as well as independent surface flux estimates presented in recent literature (e.g., von Schuckmann et al. (2020); https://doi.org/10.5194/essd-12-2013-2020), suggesting an only small global ocean mean bias of FSinf. Moreover, our FSinf product is temporally more stable than parameterized surface fluxes from ERA5 and previous FSinf estimates using ERA-Interim, at least from 2000 onwards. The evaluation of the oceanic energy budget in the North Atlantic shows good agreement between FSinf and observation-based divergence of oceanic heat transports and OHCT such that its residual is on the order of <0.2 PW (~7 W m-2). Even on station-scale, FSinf agrees reasonably well with buoy-based surface flux measurements with a bias of 19.7 W m-2 over all 15 buoys  (compared to 21.7 W m-2 for parameterized surface fluxes), with largest biases in the Indian Ocean. This assessment demonstrates that our inferred surface flux estimate using ERA5 data outperforms parameterized fluxes from the model on all considered spatial scales (global-regional-local) in terms of bias and temporal stability and thus is well-suited for climate studies and model evaluations.

 
Revised Southern Ocean sea surface temperatures over the last 180 ka
Authors: Chandler David , Langebroek Petra
Published: March 2021

Proxy records and climate models suggest that the Last Interglacial (LIG, ~130 to 115 thousand years before present) was characterised by high-latitude air and sea surface temperatures (SSTs) slightly warmer than present, and by mean global sea level a few metres higher. Therefore, the LIG is widely used as an analogue for near-future oceanographic/climatic conditions. Of particular interest is the Antarctic Ice Sheet’s contribution to rapid sea level rise and to Southern Ocean surface freshening, in response to warming. In the Southern Ocean, existing LIG temperature reconstructions suffer from very high variance amongst a low number of individual records. Recent syntheses have focused on the LIG climatic optimum, but conditions during the penultimate glacial are also important for forcing transient climate or Antarctic Ice Sheet simulations. Here we use databases of modern core-top sediments to evaluate the strengths of SST proxies available in the Southern Ocean, and consider their likely sources of bias and variance. By selecting only those paleo-temperature reconstructions which we believe are reliable in this region, we then compile a Southern Ocean SST synthesis covering the penultimate glacial and the LIG. This longer temperature time series can be used as a basis for LIG ice sheet simulations or for climate model development.  
Joint inversion of magnetotelluric tippers and geomagnetic depth sounding transfer functions constrains electrical conductivity beneath islands
Authors: Chen Chaojian , Kruglyakov Mikhail , Rigaud Rafael , Kuvshinov Alexey
Published: March 2021

Geomagnetic field variations recorded at island geomagnetic observatories are one of the data sources that can be used to constrain the electrical conductivity beneath oceans. Hitherto, magnetotelluric (MT) tippers (period range from a few minutes to 3 hours) and geomagnetic depth sounding (GDS) transfer functions (TFs; period range from 6 hours to a few months) were inverted separately to reveal the electrical conductivity structure underneath island observatories.  In this study, we develop a quasi 1-D tool to simultaneously invert MT tippers and GDS TFs. To account for source complexity, we resort to GDS TFs that relates a set of spherical harmonics coefficients describing the source (of ionospheric or magnetospheric origin) to a locally measured vertical magnetic field component. Joint inversion of multiple data sets from different sources helps to improve vertical resolution and reduce uncertainties in the recovered conductivity models. The stochastic optimization method, known as Covariance Matrix Adaptation Evolution Strategy, is applied to solve the inverse problem. The term “quasi” is used here to stress the fact that during 1-D inversion the 3-D forward modeling operator is exploited to account for the ocean induction effect (OIE), which is known to strongly influence the island electromagnetic (EM) responses. To efficiently model MT tippers and GDS TFs, the Cartesian-to-Cartesian and spherical-to-Cartesian 3-D EM modeling engines, based on a nested integral equation approach, are adopted. We apply the developed tool to jointly invert MT tippers and GDS TFs estimated at Honolulu geomagnetic observatory, located at Oahu island (Hawaii) in Pacific Ocean, and discuss the recovered conductivity structure.
Comparison of northern hemispheric and southern hemispheric Mean Age derived from in situ tracer measurements during POLSTRACC and SouthTRAC
Authors: Wagenhäuser Thomas , Jesswein Markus , Keber Timo , Schuck Tanja , Engel Andreas
Published: March 2021

The mean age of air is a powerful diagnostic tool to investigate stratospheric transport processes. It can be derived from suitable trace gas measurements and from model calculations. In contrast to the Northern Hemisphere (NH), data coverage of in situ measurements of such trace gases in the Southern Hemisphere (SH) is sparse. Due to its tropospheric trend and its very long atmospheric lifetime, SF6 is such a suitable trace gas. SF6 mixing ratios were measured with an airborne in situ GC-ECD system during several HALO aircraft campaigns, including locations in the SH polar vortex.

Here we present the mean age derived from in situ SF6 measurements during the POLSTRACC campaign (Polar Stratosphere in a Changing Climate) in NH winter/spring 2015/2016 and during the SouthTRAC campaign (Transport and Composition of the Southern Hemisphere UTLS) in SH winter/spring 2019. Mean age values over 4 years were observed in both polar vortices. On average, higher mean age values were observed at lower levels of potential temperature during SouthTRAC 2019 than during POLSTRACC 2015/2016. The findings will be discussed in context of the Brewer-Dobson circulation.
Carbon dioxide emissions variability monitoring, based on four years of Eddy Covariance measurements in a typical Mediterranean city
Authors: Politakos Konstantinos , Stagakis Stavros , Chrysoulakis Nektarios
Published: March 2021

Urban areas around the globe are growing rapidly and as a consequence the anthropogenic effects on the environment are ever-increasing. Understanding the dynamics, procedures and mechanics behind urban greenhouse gas emissions is a challenge for the scientific community. This study investigates the variability of urban CO2 emissions in the city centre of Heraklion, a typical Mediterranean city in Greece, during a four-year period with gradual changes in the traffic regulations and changes in traffic patterns due to the recent restriction measures imposed to limit the spread of the COVID-19 pandemic. The CO2 flux (Fc) was measured using the Eddy Covariance (EC) method with a single tower-based system, permanently installed in the centre of the city. Fc was calculated at a 30-min time step and the time-series were quality-controlled and gap-filled using a moving look-up table (mLUT) technique. Fc time series were then aggregated to monthly and yearly emissions totals. Annual flux source area was estimated with the Flux Footprint Prediction (FFP) model, parameterized using measured atmospheric parameters and urban morphological parameters extracted from a Digital Surface Model. The source area was characterized by complex urban morphology and land use types. Specifically, at North of the tower a commercial zone is located, where significantly higher Fc patterns were detected, compared to South, where a residential area dominates. A gradual reduction to CO2 emissions has been observed since 2016, due to urban planning interventions related to pedestalization of extended areas in the city centre and traffic regulation. During the COVID-19 lockdown period in the Spring of 2020, the diurnal Fc patterns and the monthly aggregated Fc showed significant reductions in the order of 70 % compared to the previous years. Fc values returned to the previous years’ levels with the end of the lock-down in the summer 2020, as it was expected. Finally, during the second lock-down, started in Greece in November 2020, the CO2 emissions were higher compared to the first lock-down, reflecting a higher level of mobility in Heraklion centre.
Satellite based county- to provincial-level ammonia emissions estimates
Authors: Dammers Enrico , Shephard Mark , White Evan , Griffin Debora , Chow Evan , Fioletov Vitali , Kharol Shailesh , Cady-Pereira Karen , van der Graaf Shelley , Tokaya Janot , Schaap Martijn , McLinden Chris
Published: March 2021

While ammonia (NH3) at its current levels is known to be a hazard to environmental and human health, the atmospheric budget is still quite uncertain. This can largely be attributed to the short lifetime of ammonia in combination with an overall lack of (dense) in-situ measurement networks. The capability to observe ammonia distributions with satellites has opened new ways to study the atmospheric ammonia budget. Previous studies have demonstrated the capability of current ammonia satellite sensors to resolve emissions from point like sources, biomass burning, and constraining emission sources at a regional level with methods involving the use of air quality models.

In this study, we present the first spatially resolved ammonia emission estimates across the globe using a consistent methodology based solely on ammonia satellite observations from the Cross-track Infrared Sounder (CrIS) instrument and ECMWF ERA5 wind fields. The concept was evaluated for North Western Europe and demonstrated the ability to constrain annual emissions at county- to provincial-levels with most deviations within the bounds found in the error analysis. Furthermore, we show that for some regions the spatial patterns found in the satellite observations are consistent while others do not match the current inventories. Finally, the results indicate that the absolute emission levels tend to be underestimated for parts of the globe.
Future opportunities and risks in managing the Eastern Nile water-energy-food-environment nexus
Authors: Etichia Mikiyas , Gutierrez Jose , Basheer Mohammed , Martinez Eduardo , Panteli Mathaios , Harou Julien
Published: March 2021

The interlinkages between the water, energy, food, and environment systems of the Eastern Nile Basin are becoming stronger due to an increase in the demand for water, energy, and food and two of the largest multi-year storage dams in the world (i.e., High Aswan Dam and Grand Ethiopian Renaissance Dam (GERD)). Significant benefits can be attained if these resource systems are managed in an integrated manner, which would result in improved efficiencies and reduced trade-offs in resource use, and better and more sustainable solutions to future water-energy-food-environment nexus problems. The ongoing construction of the GERD, the largest hydropower plant in Africa, reveals opportunities and challenges in managing the resource nexus of the Eastern Nile Basin. This study integrates an Eastern Nile river system model with a power system model comprising the Eastern portion of the East African Power Pool (i.e., Ethiopia, Sudan, Egypt, Djibouti, and Libya) to investigate how GERD influences the integrated resources of the Eastern Nile Basin countries. The system is modelled using an open-source water resource system simulator (Pywr) and an open-source Python power system simulator. The two simulators are linked using an open-source agent-based model integration framework (Pynsim). Based on existing and plausible future states of the system, three scenarios are formulated and examined: (1) a baseline scenario representing the existing system before GERD, (2) GERD added to the system, including the initial filling and long-term operation phases of the dam, and (3) increased irrigation water abstractions in Ethiopia and Sudan with GERD. Results show that GERD operation reduces (i) electricity curtailments in Ethiopia and Sudan, (ii) irrigation water deficits in Sudan, (iii) Sudan’s greenhouse gas emissions, and (iv) hydropower generation and irrigated water consumption in Egypt. Increasing irrigation water abstraction in Ethiopia and Sudan reduces hydropower generation basin-wide and irrigation water consumption in Egypt. This study demonstrates the benefits of an integrated modelling approach for exploring water-energy-food-environment nexus inter-connections in the Eastern Nile multi-resource system.
Compositional simulation of hydrogen storage in a depleted gas field
Authors: Scafidi Jonathan , Schirrer Laurent , Vervoort Isabelle , Heinemann Niklas
Published: March 2021

UK natural gas demand is 2-4 times that of electricity and characterised by seasonal differences in demand of almost triple in the winter with larger spikes during extreme cold weather events. This makes any decarbonisation effort reliant on its ability to handle these large changes in demand. Conversion of the gas supply to hydrogen is the most promising solution. To facilitate this, large-scale underground storage will be required in the order of 150 TWh or 40 days’ worth of supply.

Subsurface gas storage in porous rocks requires a proportion of the gas to remain in the reservoir to maintain the pressure required for the minimum economic flow rate from the wells. This is called the cushion gas requirement. In the case of a hydrogen storage reservoir the use of a cheaper cushion gas, such as CO2 or N2, is the subject of much research.

We investigate the possibility of using natural gas within a partially depleted gas reservoir as cushion gas. We will present the results of a compositional simulation of seasonal hydrogen storage over a 20 year period in a closed reservoir. The study shows that natural gas has potential as a cushion gas, in this case achieving greater than 95% hydrogen recovery factors with minimal amounts of mixing in the reservoir. Use of natural gas as cushion gas also reduces the risk of water coning which can lead to loss of hydrogen.

Although these results are promising, the study highlights several key areas that need further investigation to improve the reliability of future simulations. These include defining relative permeability curves for hydrogen, refinement of how simulators handle viscosity equations, and a greater understanding of hydrogen well engineering. All of these factors will influence estimates of the hydrogen capacity of a porous rock reservoir.
Inter-decadal Change of Tibetan Plateau Vortices during the past four Decades and its Possible Mechanism
Authors: Lin Zhiqiang , Guo Weidong , Yao Xiuping , Du Jun , Ge Jun
Published: March 2021

The Tibetan Plateau vortices (TPVs) are mesoscale weather systems active at the near-surface of the Tibetan Plateau (TP), which are one of the major precipitation-producing systems over the TP and its surrounding areas. TPVs mainly occur in the warm season from May to September. In this paper, we investigate the inter-decadal change of TPVs in the warm seasons of 1979–2017 by analyzing five widely used reanalysis datasets. A significant change of the TPVs’ frequency appears around the mid-1990s, associated with less TPVs during 1979–1996 and more TPVs during 1997–2017. The abrupt change is caused by a transition of the Atlantic Multi-decadal Oscillation (AMO) from a cold phase to a warm phase in the mid-1990s. The shift of AMO leads to a silk-road pattern wave train and a spatially asymmetric change of tropospheric temperature. It modifies the intensity of the subtropical westerly jet and the TP heating, leading to the inter-decadal change of TPV activities.
Solar-related and terrestrial drivers modulating the northern polar vortex
Authors: Salminen Antti , Asikainen Timo , Maliniemi Ville , Mursula Kalevi
Published: March 2021

The wintertime stratosphere is dominated by the polar vortex, a strong westerly wind, which surrounds the cold polar region. In the northern hemisphere the polar vortex can vary a lot during the winter and these variations affect the surface weather, e.g., in Europe and North America. Earlier studies have shown that the northern polar vortex is modulated by different terrestrial drivers and two solar-related drivers: electromagnetic radiation and energetic particle precipitation. Solar radiation varies in concert with the sunspot cycle by affecting the upper atmosphere at lower latitudes. Energetic electron precipitation (EEP) is driven by the solar wind and affects the polar stratosphere and mesosphere by forming ozone depleting NOx and HOx compounds. However, it is unclear how the effects of these solar-related and other, terrestrial drivers compare to each other. In this study we examine the effects of two solar-related drivers (solar radiation and EEP) and three terrestrial drivers (Quasi-Biennial Oscillation (QBO), El-Nino Southern Oscillation (ENSO) and volcanic aerosols) on the northern polar vortex. We use a new composite dataset including ERA-40 and ERA-Interim reanalysis of atmospheric variables and the multilinear regression analysis to estimate atmospheric responses to these five drivers in years 1957 – 2017. We confirm the findings of earlier studies that westerly QBO wind, cold ENSO, volcanic aerosols and increased EEP are associated with a stronger polar vortex. Furthermore, we find that EEP produces the strongest and most significant effect on the northern polar vortex among the studied variables. Only in December the effect of QBO is comparable to the EEP effect. We also find that EEP effect is strong and significant in the easterly QBO phase, while in the westerly phase it does not stand out from the effects of other drivers.
GlacierMIP3 global glacier mass change equilibration experiments - rationale and experimental design
Authors: Zekollari Harry , Hock Regine , Marzeion Ben , Maussion Fabien , Schuster Lilian ,   GlacierMIP3 participants
Published: March 2021

Glaciers outside the ice sheets are major contributors to today’s sea-level rise and are projected to remain so in the coming century. With the goal to better assess the future sea-level contribution from glaciers and to quantify related uncertainties, the Glacier Model Intercomparison Project (GlacierMIP) has set out to develop a series of coordinated experiments to be run as a community-wide effort.

The first two phases of the GlacierMIP have focused on the evolution of glaciers throughout the 21st century (Hock et al., 2019; Marzeion et al., 2020). In the third phase of GlacierMIP (GlacierMIP3 – equilibration), a new set of experiments has been designed to investigate the equilibration of glaciers under constant climate conditions. These experiments will allow us to answer the following fundamental questions:

1. What would be the equilibrium volume and area of all glaciers outside the ice sheets if global mean temperatures were to stabilize at present-day levels?

2. What would be the equilibrium volume and area of all glaciers outside the ice sheets if global mean temperatures were to stabilize at different temperature levels (e.g. +1.5, +2, relative to pre-industrial)?

3. For each of these global mean temperature stabilization scenarios, how much time would the glaciers need to reach their new equilibrium?

In this contribution, we present the experimental design of GlacierMIP3 and open up the floor for ideas and discussions about possible processing of these experiments. We also invite interested individuals and groups to join us to discuss the possibility of their model to be included in the newest phase of GlacierMIP.

 

References

GlacierMIP1: Hock, R., Bliss, A., Marzeion, B., Giesen, R.H., Hirabayashi, Y., Huss, M., Radic, V., Slangen, A.B.A. (2019), GlacierMIP – A model intercomparison of global-scale glacier mass-balance models and projections, Journal of Glaciology 65(251), 453-467, doi: 10.1017/jog.2019.22

GlacierMIP2: Marzeion, B., Hock, R., Anderson, B., Bliss, A., Champollion, N., Fujita, K., Huss, M., Immerzeel, W., Kraaijenbrink, P., Malles, J-H., Maussion, F., Radic, V., Rounce, D.R., Sakai, A., Shannon, S., van de Wal, R., Zekollari, H. (2020), Partitioning the Uncertainty of Ensemble Projections of Global Glacier Mass Change, Earth’s Future 8(7), e2019EF001470, doi: 10.1029/2019EF001470
Quasi in-situ snow and sea ice interface microstructure measured by micro-computed tomography
Authors: Macfarlane Amy R. , Dadic Ruzica , Hämmerle Stefan , Wagner David N. , Schneebeli Martin
Published: March 2021

The sea ice / snow interface in the high Arctic can no longer be thought of as simply black and white, but more complex than previously estimated. Our understanding of this interface is crucial for remote sensing, snow, brine and ice mass distribution, thermal conductivity and therefore ice growth and ice melt. To better understand the snow microstructure, we installed a micro-computed tomograph (micro-CT) in a cold laboratory on board Polarstern and measured a full annual cycle of the Arctic snow cover during the MOSAiC expedition. We discovered two large uncertainties when looking at the boundary between sea ice and snow boundary during the year.

1) Large temperature gradients of 100 K m-1 (compared to Alps (20 K m-1) specific to the high Arctic cause extreme metamorphism within the snowpack. This transports ice grains from the salty first year sea ice (FYI), across the interface up into the snowpack, producing snow with brine pockets on FYI. 10-30% of snow grains on FYI are affected by vapour migration from the sea ice, and can  now be thought of as  a mix of ocean and atmospheric sourced particles, which can be distinguished by oxygen isotope analysis. Brine in the snow structure has large implications for remote sensing backscatter and possibly mass balance.

2) Multi-year ice (MYI) also has large uncertainties, because the interface has a hard impenetrable layer- because of the porous summer ice surface, known as the surface scattering layer (SSL) after refreezing. In summer, this SSL  is thought of as an ocean water snow layer, with a density of <500 kg m-3. After refreezing in autumn, this layer produces a dense, icy 2-10 cm deep layer at the snow/ice interface and occasionally occupies up to 50% of the snow profile on MYI in winter.. This layer, which has previously not been observed, may, depending on the state of metamorphism and hardness,influence snow water equivalent and snow depth measurements.

This study uses a combination of micro-Computed Tomography measurements to determine geometrical snow properties combined with oxygen isotope analysis to understand the ice origin (atmospheric or marine). We aim to better understand processes at the snow/ice interface on Arctic sea ice and as a result, the infiltration of brine into snow on FYI.