bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainty attribution in global hydrological models
Authors: Reinecke Robert , Pianosi Francesca , Wagener Thorsten
Published: March 2021

Global hydrologic models have become an important research tool in assessing global water resources and hydrologic hazards in a changing environment, and for improving our understanding of how the water cycle is affected by climatic changes worldwide. These complex models have been developed over more than 20 years by multiple research groups, and valuable efforts like ISIMIP (Inter-Sectoral Impact Model Intercomparison Project) contribute to our growing understanding of model uncertainties and differences. However, due to their complexity and vast data outputs, they remain a Blackbox to certain extents. Especially for processes that are poorly constrained by available observations – like groundwater recharge – model results vary largely, and it is unclear what processes dominate where and when. With the inclusion of even more sophisticated implementations e.g., coupled global gradient-based groundwater simulations, it is getting more and more challenging to understand and attribute these models' results. 

In this talk, we argue that we need to intensify the efforts in investigating uncertainties within these models, including where they originate and how they propagate. We need to carefully and extensively examine where different processes drive the model results by applying state of the art sensitivity analysis methods. To this end, we discuss development needs and describe pathways to foster the application of sensitivity analysis methods to global hydrological models.     
Earth's ice imbalance
Authors: Slater Thomas , Lawrence Isobel , Otosaka Inès , Shepherd Andrew , Gourmelen Noel , Jakob Livia , Tepes Paul , Gilbert Lin , Nienow Peter
Published: March 2021

Satellite observations are the best method for tracking ice loss, because the cryosphere is vast and remote. Using these, and some numerical models, we show that Earth lost 28 trillion tonnes of ice between 1994 and 2017. Arctic sea ice (7.6 trillion tonnes), Antarctic ice shelves (6.5 trillion tonnes), mountain glaciers (6.1 trillion tonnes), the Greenland ice sheet (3.8 trillion tonnes), the Antarctic ice sheet (2.5 trillion tonnes), and Southern Ocean sea ice (0.9 trillion tonnes) have all decreased in mass. Just over half (58 %) of the ice loss was from the northern hemisphere, and the remainder (42 %) was from the southern hemisphere. The rate of ice loss has risen by 57 % since the 1990s – from 0.8 to 1.2 trillion tonnes per year – owing to increased losses from mountain glaciers, Antarctica, Greenland, and from Antarctic ice shelves. During the same period, the loss of grounded ice from the Antarctic and Greenland ice sheets and mountain glaciers raised the global sea level by 34.6 ± 3.1 mm. The majority of all ice losses were driven by atmospheric melting (68 % from Arctic sea ice, mountain glaciers ice shelf calving and ice sheet surface mass balance), with the remaining losses (32 % from ice sheet discharge and ice shelf thinning) being driven by oceanic melting. Altogether, these elements of the cryosphere have taken up 3.2 % of the global energy imbalance.
Educational methods in Geoparks: Techno-Scientific voice-over as a key tool for accessibility
Authors: Martínez Martín Jesús Enrique
Published: March 2021

Earth Science education is at a turning point framed in a social and cultural way. The idea of sustainability and, consequently, accessibility to the educational system has shown important advances since the publication of the Sustainable Development Goals of the 2030 Agenda. The UNESCO Global Geoparks are internationally recognized as educational engines in pursuit of sustainability and instruction in geosciences, and they are making use of alternative teaching methods to get their message worldwide. Focused on geotourism and development, they try to continuously update themselves in order to offer quality education and accessibility for everyone. Information and communication technologies (ICT’s) keep also evolving and they are used as an interesting support within cognitive development and education at all levels. Voice-over is a classical tool used since the beginning of the recording era (radio, film, television, media ...) to communicate a specific message and transmit it adequately and coherently to the receiver.  It is mainly based on the correct use of the human voice to generate sensations and create, in an artistic way, an emotional atmosphere that keeps the viewer attentive to what you want to convey. The nuances, tones and melodic curves mean that no voice is the same as another and the information is disseminated in very different ways depending on that. In recent years, it has been possible to observe a great increase in the use of voice-over and an exemplary care in the selective tone of the messages that has been reflected in sectors such as advertising, general media or scientific documentaries. The promotion of its use in Geoparks as educational support in audiovisuals, presentations or even in geological routes, tailor-made for different collectives, is a key factor to take into account to facilitate the understanding of the information, increase the degree of accessibility and contribute, thus, to the Sustainable Development Goals.
The SWAG solution for probabilistic predictions with a single neural network
Authors: Haddad Yann , Defferrard Michaël , Ghiggi Gionata
Published: March 2021

Ensemble predictions are essential to characterize the forecast uncertainty and the likelihood of an event to occur. Stochasticity in predictions comes from data and model uncertainty. In deep learning (DL), data uncertainty can be approached by training an ensemble of DL models on data subsets or by performing data augmentations (e.g., random or singular value decomposition (SVD) perturbations). Model uncertainty is typically addressed by training a DL model multiple times from different weight initializations (DeepEnsemble) or by training sub-networks by dropping weights (Dropout). Dropout is cheap but less effective, while DeepEnsemble is computationally expensive.

We propose instead to tackle model uncertainty with SWAG (Maddox et al., 2019), a method to learn stochastic weights—the sampling of which allows to draw hundreds of forecast realizations at a fraction of the cost required by DeepEnsemble. In the context of data-driven weather forecasting, we demonstrate that the SWAG ensemble has i) better deterministic skills than a single DL model trained in the usual way, and ii) approaches deterministic and probabilistic skills of DeepEnsemble at a fraction of the cost. Finally, multiSWAG (SWAG applied on top of DeepEnsemble models) provides a trade-off between computational cost, model diversity, and performance.

We believe that the method we present will become a common tool to generate large ensembles at a fraction of the current cost. Additionally, the possibility of sampling DL models allows the design of data-driven/emulated stochastic model components and sub-grid parameterizations.

Reference

Maddox W.J, Garipov T., Izmailov P., Vetrov D., Wilson A. G., 2019: A Simple Baseline for Bayesian Uncertainty in Deep Learning. arXiv:1902.02476
Plastic pollution research in Indonesia: State of science and future research directions.
Authors: Vriend Paul , Hidayat Hidayat , Cordova Reza , Purba Noir. P. , Lohr Ansje , Ningsih Nining , Agustina Kirana , Husrin Semeidi , Suryono Devi D. , Hantoro Inneke , Widianarko Budi , van Leeuwen Judith , Vermeulen Bart , van Emmerik Tim
Published: March 2021

Observational and modeling studies have suggested that Indonesia among the top plastic polluting countries globally. Data on the presence of plastic pollution are crucial to designing effective plastic reduction and mitigation strategies. Research quantifying plastic pollution in Indonesia has increased in recent years. However, most plastic research to date has been done with different goals, methods, and data formats. In this study, we present a meta-analysis of 85 studies published on plastic pollution in Indonesia to uncover gaps and biases in current research, and to use these insights to suggest ways to improve future research to fill these gaps. Research gaps and biases identified include a clear preference for marine research, and a bias towards certain environmental compartments within the marine, riverine, and terrestrial ecosystems, which are compartments that are easier to quantify such as riverbanks and beaches. Moreover, we identify polypropylene (PP) and polyethylene variants (HDPE, LDPE, PE) to be among the most frequently found polymers in both macro- and microplastic pollution, though polymer identification is lacking in most studies. Plastic research is mostly done on Java (57%). We recommend a shift in ecosystem focus of research towards the riverine and terrestrial environments, and a shift of focus of environmental compartments analyzed within these ecosystems. Moreover, we recommend an increase in spatial coverage across Indonesia of research, a larger focus on polymer characterization, and lastly, the harmonization of methods used to quantify plastic. With these changes, we envision future research that can aid with the design of effective reduction and mitigation strategies.
Antimony-Gold mineralization in Rates (Northern Portugal)
Authors: Lima Alexandre , Frutuoso Rui , Leal Sara , Vieira André , Ribeiro Maria
Published: March 2021

In the Dúrico-Beirão mining district several paragenetic associations have been described in gold mineralizations, including Sb-Au. The objective of this research was the study of the Sb-Au mineralization in the Rates area, from field reconnaissance of the mineralized structures by soil sampling to the petrographic and mineralogical study of the parageneses associated with this gold mineralization, mined by the Romans.

The portable XRF was used to measure Sb and As in farms and forest soils. The observed Au-Sb-As anomalies in the Rates area must be linked to Lagoa Negra mine by the same north-western trend fault. Historical mining works have been identified both in Lagoa Negra and in Rates, where rock-chip sampling returned results up to 30 g/t Au from the Rates prospect.

Some rock samples from Rates were studied by geochemical and petrographic analyses and were analysed in detail by scanning electron microscopy. The results indicate that the paragenetic association in Rates is Sb-Au, with stibnite as primary Sb sulfide mineral, valentinite as alteration mineral, and gold in native and granular form.

Acknowledgment

The work was financial supported within the compass of the ERA-MIN/0005/2018—AUREOLE project, FEDER through operation POCI-01-0145-FEDER-007690 funded by the Programa Operacional Competitividade Internacionalização—COMPETE2020 and by National Funds through FCT within the ICT (reference UIDB/04683/2020).
Seasonal variations in the origin of river sediments (Baker River, Chile): A pre-requisite for climate and hydrological reconstructions
Authors: Amann Benjamin , Bertrand Sebastien , Alvarez Garreton Camila , Reid Brian
Published: March 2021

 

Fjord sediments are increasingly recognized as high-resolution recorders of past climate and hydrological variability. Using them as such, however, requires a comprehensive understanding of the variables that affect their properties and accumulation rates. Here, we conduct a spatial and temporal study of sediment samples collected at the head of Martínez Channel (Chilean Patagonia, 48°S), to understand how the fjord’s sediments register changes in the hydrodynamics of Baker River, Chile's largest river in terms of mean annual discharge. We apply end-member modeling to particle-size distributions of: (i) river suspended sediments, (ii) surface sediments collected along a proximal-distal transect at the fjord head, and (iii) fjord sediments collected in a sequential sediment trap at 15-day resolution during two consecutive years. Results show that the river suspended sediments and fjord sediments are consistently composed of two grain-size subpopulations. The finest end member (EM1; mode 4.03 μm) reflects the meltwater contribution, which dominates in all but the winter season. The coarser end member (EM2; mode 18.7 μm) dominates in winter, when the meltwater contribution is reduced, and is associated to rainfall events. We propose that log(EM1/EM2) can be used to reconstruct temperature in the lower Baker River watershed (r = 0.81, p < 0.001). We also show that the fluxes of EM1 and EM2 provide quantitative estimates of baseflow (r = 0.82, p < 0.001) and quickflow (r = 0.90, p < 0.001), respectively. These results support the use of fjord sediments for quantitative reconstructions of climate and hydrological changes in glacierized watersheds.
An ensemble-based eddy and spectral analysis, with application to the Gulf Stream
Authors: Dewar William K. , Jamet Quentin , Uchida Takaya , Poje Andrew
Published: March 2021

The `eddying' ocean, recognized for several decades, has been the focus of much observational and theoretical research.  We here describe a generalization for the analysis of eddy energy, based in the use of ensembles, that  addresses two key related issues: the definition of an `eddy' and the general computation of energy spectra. An ensemble identifies eddies as the unpredictable component of the flow, and permits the scale decomposition of their energy in inhomogeneous and non-stationary settings. It also avoids the `tapering' or `windowing' of the data required by traditional approaches. We apply the analysis to a mesoscale resolving  (1/12 degree) ensemble of the separated North Atlantic Gulf Stream. Our results show that the eddies are consistent with the theoretical predictions of quasi-geostrophy both at the surface and ocean interior. 
Lag-correlated rising tones of electron cyclotron harmonic and whistler-mode upper-band chorus waves
Authors: Gao Zhonglei
Published: March 2021

Electron cyclotron harmonic (ECH) and whistler-mode chorus waves can contribute significantly to the magnetospheric dynamics. In the frequency-time spectrogram, ECH usually appears as a series of harmonic structureless bands, while chorus often exhibits successive discrete elements. Here, we present surprising observations by Van Allen Probes of lag-correlated rising tones of ECH and upper-band chorus waves. The time lags of ECH elements with respect to chorus elements range from 0.05 to 0.28 s, negatively correlated with the chorus peak amplitudes. The ECH elements seemingly emerge only when the chorus elements are sufficiently intense (peak amplitude >3 mV/m), and their peak amplitudes are positively correlated. Our data and modeling suggest that upper-band chorus may promote the generation of ECH through rapidly precipitating the ~keV electrons near the loss cone. This phenomenon implies that ECH and chorus may not grow independently but competitively or collaboratively gain energy from hot electrons.
Fire and first olive cultivation: a new high-resolution macro-charcoal record from the Sea of Galilee, Israel
Authors: Miebach Andrea , Resag Tim R. , Netzel Timon , Power Mitchell J.
Published: March 2021

Throughout the Mediterranean biome, fire has been a dominant natural agent of change and a primary tool for anthropogenic landscape modifications. This research explores linkages among fire, vegetation, and human agricultural practices in the Eastern Mediterranean region, a region with limited evidence of the role these processes have in shaping the landscape.

Olive horticulture is among the oldest and most widespread agricultural forms in the Mediterranean Basin. The first major olive cultivation can be traced back in time with pollen evidence. In the Sea of Galilee, the earliest palynological evidence for olive horticulture suggest cultivation began approximately 7000 cal yr BP.

Here, we present a new high-resolution macro-charcoal dataset from the Sea of Galilee prior and during the first olive cultivation. Charcoal morphotypes were identified and are used to characterize fuel types. We also compare our data with a new multi-proxy dataset from the same record indicating the timing and impact of olive cultivation and related vegetation and climate changes.

The following questions are discussed: What was the natural fire regime (pre-large scale agriculture) around the Sea of Galilee basin? What role did fire play as a potential tool for clearing and fertilizing landscapes as the first olive orchards developed? How did fire regimes change once olive orchards were planted? Finally, can charcoal morphotypes provide novel insights into understanding paleofire regimes?

This study allows a new perspective into natural fire regimes in the Levant and an increased understanding of the role of fire during early horticulture practice. Moreover, it can serve as a basis for future fire management plans.
Indices of geomagnetic activity derived from space-born magnetic data from the Swarm mission
Authors: Papadimitriou Constantinos , Balasis Georgios , Boutsi Adamantia Zoe , Daglis Ioannis A. , Giannakis Omiros , de Michelis Paola , Consolini Giuseppe , Gjerloev Jesper W. , Trenchi Lorenzo
Published: March 2021

Ground based indices, such as the Dst and AE, have been used for decades to describe the interplay of the terrestrial magnetosphere with the solar wind and provide quantifiable indications of the state of geomagnetic activity in general. These indices have been traditionally derived from ground based observations from magnetometer stations all around the Earth. In the last 7 years though, the highly successful satellite mission Swarm has provided the scientific community with an abundance of high quality magnetic measurements at Low Earth Orbit, which can be used to produce the space-based counterparts of these indices, such the Swarm-Dst and Swarm-AE Indices. In this work, we present the first results from this endeavour, with comparisons against traditionally used parameters, and postulate on the possible usefulness of these Swarm based products for space weather monitoring and forecasting.
From Structures to Mountain Belt Dynamics – a global and multidisciplinary perspective 
Authors: von Hagke Christoph
Published: March 2021

Understanding the formation of mountain belts requires integrating quantitative insights on multiple scales. While this has long been known, it is now possible to enlarge the scales of observation by exploiting global data sets, making use of data sets covering large regions, or including automated data analysis. At the same time the lower limit of observation is pushed farther, and by now structures can be routinely analyzed at the micro- or even nano-scale over large areas making use of digital imaging techniques.

In this talk I will present results from a variety of geological settings illustrating the use of large data sets for better understanding of mountain belt dynamics. To this end, I will integrate micro-structural work, numerical and analog models, and regional studies of fault geometries and their time evolution constrained by digital field techniques and low-temperature thermochronometry. A particular focus will be laid on the role of mechanical heterogeneity and strain localization through time. It is shown that in some regions geodynamic processes are responsible for local fault geometries, while in others much more local factors such as rheological contrasts of individual layers or even the changes of rheology through time plays a major role. Multiscale studies exploiting digital techniques and including the dimension of time provide an exciting avenue for state of the art and future geological studies.
Components of apparent soil thermal conductivity measured by the heat pulse method
Authors: Lu Sen
Published: March 2021

Knowledge on the components of apparent soil thermal conductivity (λ) across various water contents (θ) and temperatures is important to accurately understand soil heat transfer mechanisms. In this study, soil thermal conductivity was measured for sandy loam and silty clay soils at various temperatures and air pressures using a transient method. Four components of λ, namely, heat conduction, latent heat transfer by water vapor diffusion, sensible heat transfer by liquid water, and sensible heat transfer by water vapor diffusion were quantified. Results showed that in uniform soils, the magnitudes of sensible heat transfers by liquid water and water vapor were negligible during these transient measurements. The contribution of latent heat transfer through vapor diffusion to total heat transfer increased as temperature increased, and the peak value occurred at an intermediate water content. The water content at which the maximum vapor diffusion occurred varied with soil texture. In addition to the four calculated components, a significant residual contribution to λ caused by an unidentified vapor transfer mechanism was observed between 3.5°C and 81°C. For example, calculations indicated that approximately 66% of the sandy loam λ at θ=0.11 m3 m−3 was caused by an unidentified vapor transfer mechanism at 81°C. This extra contribution by vapor transfer could be explained either as enhanced vapor diffusion or by an advection mechanism. Further investigation is needed to clarify whether enhanced diffusion or advection is occurring in unsaturated soils. 
Atlantic Water properties, transport, and water mass transformation north of Svalbard from one-year-long mooring observations
Authors: Koenig Zoé , Kalhagen Kjersti , Kolås Eivind , Fer Ilker , Nilsen Frank , Cottier Finlo
Published: March 2021

North of Svalbard is a key region for the Arctic Ocean heat and salt budget as it is the gateway for one of the main branches of Atlantic Water to the Arctic Ocean. As the Atlantic Water layer advances into the Arctic, its core deepens from about 250 m depth around the Yermak Plateau to 350 m in the Laptev Sea, and gets colder and less saline due to mixing with surrounding waters. The complex topography in the region facilitates vertical and horizontal exchanges between the water masses and, together with strong shear and tidal forcing driving increased mixing rates, impacts the heat and salt content of the Atlantic Water layer that will circulate around the Arctic Ocean.

In September 2018, 6 moorings organized in 2 arrays were deployed across the Atlantic Water Boundary current for more than one year (until November 2019), within the framework of the Nansen Legacy project to investigate the seasonal variations of this current and the transformation of the Atlantic Water North of Svalbard. The Atlantic Water inflow exhibits a large seasonal signal, with maxima in core temperature and along-isobath velocities in fall and minima in spring. Volume transport of the Atlantic Water inflow varies from 0.7 Sv in spring to 3 Sv in fall. An empirical orthogonal function analysis of the daily cross-isobath temperature sections reveals that the first mode of variation (explained variance ~80%) is the seasonal cycle with an on/off mode in the temperature core. The second mode (explained variance ~ 15%) corresponds to a short time scale (less than 2 weeks) variability in the onshore/offshore displacement of the temperature core. On the shelf, a counter-current flowing westward is observed in spring, which transports colder (~ 1°C) and fresher (~ 34.85 g kg-1) water than Atlantic Water (θ > 2°C and SA > 34.9 g kg-1). The processes driving the dynamic of the counter-current are under investigation. At greater depth (~1000 m) on the offshore part of the slope, a bottom-intensified current is noticed that seems to covary with the wind stress curl. Heat loss of the Atlantic Water between the two mooring arrays is maximum in winter reaching 250 W m-2 when the current is the largest and the net radiative flux from the atmosphere to the ocean is the smallest (only 50 W m-2 compared to about 400 W m-2 in summer).
Earth Orientation Parameters determination by GNSS & VLBI Combination at Normal Equation Level
Authors: Richard Jean-Yves , Bizouard Christian , Lambert Sebastien , Becker Olivier
Published: March 2021

The Earth orientation parameters (EOP), the regular products of IERS Earth Orientation Centre, are computed at daily bases by combination of EOP solutions using different astro-geodetic techniques. At SYRTE we have developed a strategy of combination of the Global Navigation Satellite Systems (GNSS) and Very Long Baseline Interferometry (VLBI) techniques at normal equation level using Dynamo software maintained by CNES (France). This approach allows to produce the EOP at the daily bases, which contains polar coordinates (x,y) and their rates (xr,yr), universal time UT1 and its rate LOD, and corrections from IAU2000A/2006 precession-nutation model (dX,dY), and in the same run station coordinates constituting the terrestrial frame (TRF). The recorded EOP solutions obtained from GNSS and VLBI combination at weekly bases is recently maintained by SYRTE.

The strategy applied to consistently combine the IGS and IVS solutions provided in Sinex format over the time period 2000-2021 are presented and the resulting EOP, station positions (TRF) are analysed and evaluated, differences w.r.t. the individual solutions and the IERS time-series investigated.
Evaluating the differenced Normalized Burn Ratio for assessing fire severity using Sentinel-2 imagery in Northeast Siberian larch forests
Authors: Combee Alisha , Delcourt Clément J.F , Izbicki Brian , Mack Michelle C. , Maximov Trofim C. , Petrov Roman E. , Rogers Brendan M. , Scholten Rebecca C. , Shestakova Tatiana A. , van Wees Dave , Veraverbeke Sander
Published: March 2021

Fire severity is a key fire regime characteristic with high ecological and carbon cycle relevance. Broadly defined, fire severity is a measure of the immediate impacts of a fire on the landscape, including the destruction and combustion of live vegetation and dead organic matter. Prior studies on boreal forest fires have mainly focused on mapping severity in North America’s boreal forests. However, the dominant tree species and their impacts on fire regimes are strikingly different between boreal North America and Siberia. Here we used Sentinel-2 satellite imagery to test the potential for using the most common spectral index for assessing fire severity, the differenced Normalized Burn Ratio (dNBR), over two fire scars and 41 field plots in Northeast Siberia. These field plots, sampled in the summer of 2019, corresponded to three different forest types: dense larch-dominated (Larix cajanderii) forest, open larch-dominated forest and open forest with a mixture of larch and pine (Pinus sylvestris). For this evaluation, the dNBR was compared to field measurements of the Geo Composite Burn Index (GeoCBI) and burn depth. The dNBR performed better when the field data were grouped by forest type (e.g. GeoCBI- dNBR R2 = 0.38 (p < 0.01) for all plots and 0.49 (p < 0.001) for open larch forest). The GeoCBI provides a holistic field assessment of fire severity, yet it is dominated by the effect of fire on vegetation. Nevertheless, the GeoCBI correlated reasonably well with the depth of burning in the organic soil (R2 = 0.11, p < 0.05 for all plots). This relationship also varied among forest types, and was the highest for the dense larch forests (burn depth- GeoCBI R2 = 0.27, p < 0.05). The dNBR showed some potential as a predictor for burn depth, especially in the dense larch forests (burn depth- dNBR R2 = 0.31, p < 0.05). This is line with previous studies in boreal North America. More research is needed to refine spaceborne fire severity assessments in the larch forests of Northeast Siberia, including assessments of additional fire scars and integration of dNBR with other geospatial proxies of fire severity.

 
Influence of the CME orientation on the ICME propagation
Authors: Martinić Karmen , Dumbović Mateja , Vršnak Bojan
Published: March 2021

Beyond certain distance the ICME propagation becomes mostly governed by the interaction of the ICME and the ambient solar wind. Configuration of the interplanetary magnetic field and features of the related ambient solar wind in the ecliptic and meridional plane are different. Therefore, one can expect that the inclination of the CME flux rope axis i.e. tilt, influences the propagation of the ICME itself. In order to study the relation between the tilt parameter and the ICME propagation we investigated isolated Earth-impacting CME-ICME evets in the time period from 2006. to 2014. We determined the CME tilt in the “near-Sun” environment from the 3D reconstruction of the CME, obtained by the Graduated Cylindrical Shell model using coronagraphic images provided by the STEREO and SOHO missions. We determined the tilt of the ICME in the “near-Earth” environment using in-situ data. We constrained our study to CME-ICME events that show no evidence of rotation while propagating, i.e. have a similar tilt in the “near-Sun” and “near-Earth” environment. We present preliminary results of our study and discuss their implications for space-weather forecasting using the drag-based(ensemble) [DB(E)M] model of heliospheric propagation.
Directional and frequency spread of surface ocean waves from CFOSAT/SWIM satelllite measurements
Authors: Hauser Danièle , Le Merle Eva , Aouf Lotfi , Peureux Charles
Published: March 2021

The CFOSAT (China France Oceanography Satellite) mission launched in 2018 now routinely provides at the global scale, directional spectra of ocean waves. The principle is based on the analysis of the normalized radar cross-section measured by the instrument SWIM (Surface Waves Investigation and Monitoring), a near-nadir pointing Ku-Band real-aperture scanning radar. From the ocean wave spectra derived from SWIM, the principal parameters of ocean wave spectra as significant wave height, peak wavelength, and peak direction are now available to better characterize the sea-state. However, it is known that these principal parameters are not sufficient not fully characterize the distribution of wave energy and understand or validate the physical processes impacting its evolution during growth order decay. Here we show that the parameters characterizing the shape of the wave spectra (e.g directional and frequency spread) can be estimated at the global scale from the SWIM measurements. We also show that they can provide consistent values of the Benjamin-Feir index, an index proposed to estimate the probability of extreme waves. Similarities of differences with the shape parameters of the MFWAM numerical wave model are also discussed.
Interactive effects of land use and soil erosion on soil organic carbon in the dry-hot valley region of southern China
Authors: Li Yawen , Duan Xingwu , Li Ya , Li Yuxiang , Zhang Lanlan
Published: March 2021

Changes in land use can result in soil erosion and the loss of soil organic carbon (SOC). However, the individual contribution of different land use types on SOC variability as well as the combined impacts of land use and soil erosion are still unclear. The aims of the present study were to: (1) evaluate soil erosion and SOC contents under different land use types, (2) identify the influences of soil depth and land use on SOC content, and (3) determine the contribution of land use and soil erosion on SOC variability. We assessed the SOC and total soil nitrogen (TSN) contents under three types of land use in the dry-hot valley in southern China. Caesium-137 (137Cs) and excess lead-210 (210Pbex) contents were also measured to determine soil-erosion rates. Land use was found to significantly affect soil erosion, and erosion rates were higher in orchard land (OL) relative to farmland (FL), which is in contrast with previous study results. SOC and TSN contents varied significantly between the three land use types, with highest values in forest land (FRL) and lowest values in OL. SOC was found to decrease with decreasing soil depth; the highest rate of reduction occurred in the reference site (RS), followed by FRL and FL. The interaction between soil erosion and land use significantly impacted SOC in the soil surface layer (0–12 cm); the direct impact of soil erosion accounted for 1.5% of the SOC variability, and the direct or indirect effects of land use accounted for the remainder of the variability. SOC content in deep soil was mainly affected by factors related to land uses (89.0%). This quantitative study furthers our understanding on the interactive mechanisms of land use and soil erosion on changes in soil organic carbon.
Consistent comparison of full-Stokes and higher-order approximation in the central North East Greenland Ice Stream
Authors: Rückamp Martin , Kleiner Thomas , Humbert Angelika
Published: March 2021

Modelling ice sheet flow is at best modelled using the full-Stokes (FS) equations. However, it rarely sees application even in recent years due to its high computational demand and problems in numerical convergence due to the thin aspect ratio of ice sheets. For this reason, the modelling community has relied on simplified mathematical models, such as the three-dimensional Higher-Order (HO) approximation which neglects horizontal gradients of vertical velocities and bridging effects. Here, we conduct an analysis of the difference in stresses and velocity fields solving the FS system of equation and using two different types of HO approximations equivalent to LMLa (known as Blatter-Pattyn type) and LTSML according to Hindmarsh (2004). Our intention was to avoid any bias from a difference in discretization or implementation, therefore we implemented it in a single ice sheet model to avoid effects arising from discretization and implementation. We selected a subset of the North East Greenland Ice Stream (NEGIS) as investigation area. As differences between FS and HO emerge in regions with steep bedrock gradients or high aspect ratios, we step-wise increase spatial resolution from 12.8 km down to 0.1 km. Our analysis reveals that surface velocity differences between the FS and HO solution emerge below 1km horizontal resolution and increase with resolution. Compared to the absolute ice flow velocity, the relative error between FS and HO remains small. We present an in-depth analysis, that reveals that different factors are affected by the approximation, such as basal drag and rheology

References:
Hindmarsh, R. C. A.: A numerical comparison of approximations to the Stokes equations used in ice sheet and glacier modeling, Journal of Geophysical Research: Earth Surface, 109, https://doi.org/10.1029/2003JF000065, 2004
Variability of river plume in the Gulf of Tonkin
Authors: Nguyen Duy Tung , Ayoub Nadia , Marsaleix Patrick , Toublanc Florence , De Mey-Fremaux Pierre , Ngo Duc Thanh
Published: March 2021

The quality of estuarine, coastal and marine environment in the Gulf of Tonkin, in the South China Sea, is an essential issue to the ecosystems’ health and to the living conditions and economy of the Viet Nam population. The stakes are particularly high since the demographic density in the Red River delta is one of the highest in the world. Understanding the physical processes that drive the ocean circulation and its response to anthropic pressure there is therefore of primarily importance for enlightened resource management, as well as for designing adequate monitoring and forecasting systems.

As a first step toward a better understanding of the physical coastal and marine environment, we present here a study on the Red river plume variability in the Gulf of Tonkin over the period 2011-2016. The study is based on a numerical simulation, under realistic conditions, using the SYMPHONIE coastal model developed at LEGOS (Marsaleix et al., 2008). Compared with various data sources, the model results show good performances. The river plume is then identified and examined at different time scales. In general, the surface coverage of the river plume is strongly correlated with the runoff but with a 1-month lag. However, in some years, a higher peak in runoff does not create a higher peak of the plume area, suggesting that other forcings need to be taken into account to explain the variability of the river plume.

Using K-mean clustering, the main patterns of the plume are identified. The result shows that the plume has a large variability at both seasonal and interannual scales. Each pattern shows the plume under different forcing conditions.  Most of the time, the plume is narrow and sticks along the coast due to the downcoast current and northeasterly wind. In the summer, due to monsoon, the wind direction changes to southwesterly and helps the plume to spread offshore. The plume reaches its highest coverage in September after the peak of runoff; then its coverage decreases again when the monsoon reverses.

We also analyze events of offshore export of freshwater at daily time scales and show that they can be associated with recurrent coastal eddies during the summer monsoon. We investigate the respective role of wind and runoff in the eddies formation. Comparison with a run without river allows to identify the main impacts of the plume on the ocean states, for example in the current and sea surface elevation.
Simulation of aerosol and its radiative effects from 1990 to 2017 by the CCM EMAC as contribution to SSIRC-ISAMIP and StratoClim
Authors: Brühl Christoph , Schallock Jennifer , Lelieveld Jos , Weigel Ralf , Appel Oliver , Schlager Hans
Published: March 2021

The chemistry climate model EMAC with interactive stratospheric and tropospheric aerosol is used for transient simulation of aerosol radiative forcing including effects of about 500 explosive volcanic eruptions and desert dust. We demonstrate that volcanic SO2 injections are needed to explain the StratoClim aircraft observations in August 2017 of SO2 and aerosol properties in the UTLS. This presentation includes studies to ISAMIP concerning aerosol optical depth at different wavelengths and contribution of different aerosol types, involving also multi-instrument satellite observations. We demonstrate that sulfate accumulation from consecutive smaller tropical and subtropical eruptions matters for radiative forcing, as for example in 2016.
Real-time flight simulation with highly resolved wind fields from a LES model
Authors: Liu Xinying , Anet Julien Gérard , Manfriani Leonardo , Fu Yongling
Published: March 2021

An overproportioned number of accidents involving general aviation occur in complex terrain. According to the statistics included in the accident investigation reports published by the Swiss Transportation Safety Investigation Board, in some cases, pilots overestimated the energy reserves of their aircraft leading to a loss of control. In order to increase flight safety for private pilots in mountainous regions, on behalf of the Swiss Federal Office of Civil Aviation, the Centre for Aviation (ZAV) at the Zurich University of Applied Sciences  develops an energy management system for general aviation, which displays the remaining airplane’s energy reserves taking into account meteorological information. The research project comprises two phases: i) concept and feasibility study and ii) prototype development. The project is currently running in phase one. In this phase, the first implementation of the energy management system was completed. The system was evaluated in the ZAV’s Research and Didactics Simulator (ReDSim). In order to generate highly resolved wind fields in the ReDsim, a well-established large-eddy simulation model, the Parallelized Large-Eddy Simulation (PALM) framework, was used in the concept study, focusing on a small mountainous region in Switzerland, not far from Samedan. For a more realistic representation of specific meteorological situations, PALM was driven with boundary conditions extracted from the COSMO-1 reanalysis of MeteoSwiss. The environment model in the ReDSim was modified to include a new subsystem simulating atmospheric disturbance. The essential variables (wind components, temperature and pressure) were extractred from the PALM output and fed into the subsystem after interpolation to obtain the values at any instant and any aircraft position. Within the subsystem, it is also possible to generate statistical atmospheric turbulence based on the Dryden turbulence model which refers to the military specification MIL-F-8785. This work focuses on the presentation of the PALM model setup and discusses the COSMO-1 forced PALM simulation results, including a statistical comparison of the simulation results with meteorological data from different meteorological reference stations.
On the role of vertical and horizontal model resolution for the simulation of stratospheric transport
Authors: Garny Hella , Dietmüller Simone , Eichinger Roland , Gupta Aman , Linz Marianna
Published: March 2021

The stratospheric transport circulation, or Brewer-Dobson Circulation (BDC), is often conceptually seperated into advection along the residual circulation and two-way mixing. In particular the latter part has recently been found to exert a strong influence on inter-model differences of mean age of Air (AoA), a common measure of the BDC. However, the precise reason for model differences in two-way mixing remains unknown, as many model
components in multi-model projects differ. One component that likely plays an important role is model resolution, both vertically and horizontally. To analyse this aspect, we carried out a set of simulations with identical and constant year 2000 climate forcing varying the spectral horizontal
resolution (T31,T42,T63,T85) and the number of vertical levels (L31,L47,L90). We find that increasing the vertical resolution leads to an increase in mean AoA. Most of this change can be attributed to aging by mixing. The mixing efficiency, defined as the ratio of isentropic mixing strength and the diabatic circulation, shows the same dependency on vertical resolution. While horizontal resolution changes do not systematically change mean AoA, we do
find a systematic decrease in the mixing efficiency with increasing horizontal resolution. Non-systematic changes in the residual circulation partly compensate the mixing efficiency changes, leading to the non-systematic mean AoA changes. The mixing efficiency changes with vertical and horizontal resolution are consistent with expectations on the effects of numerical dispersion on mean AoA. To further investigate the most relevant regions of mixing differences, we analyse height-resolved mixing efficiency differences. Overall, this work will help to shed light on the underlying reasons for the large biases of climate models in simulating stratospheric transport.
δ13C/Δ14C compositions of atmospheric CO2 and its applications in the quantifications of biosphere sink and anthropogenic source
Authors: Wang Yixin
Published: March 2021

Abstract

Constant increasing of atmospheric carbon dioxide (CO2) concentration has raised many concerns over the past 60 years due to its climate regulating effect. The ubiquitous increasing trends have been observed across the globe and it is believed to be a consequence of anthropogenic combustions of fossil fuels and land use change. For the anthropogenically emitted CO2, roughly 15% is fixed by the biosphere. Precise quantification of these two important carbon fluxes would provide us a better understanding of global carbon cycle as well as predicting future climate change. In this study, we used the CO2 and the δ13C/Δ14C  values measured at three different locations: Mauna Loa, Niwot Ridge and the South Pole, to explore the relative contributions of biosphere carbon sink, and the anthropogenic carbon sources to the atmosphere. Δ14C signatures showed that anthropogenically combusted fossil fuels are the primary source for the increasing atmospheric CO2 concentrations, and about a 3‰ decrease in atmospheric Δ14C equals to approximate 1.1 ppm of fossil fuel CO2 added to the atmosphere. The CO2-enhanced carbon storage (CO2-ECS) by the global biosphere was also calculated and we concluded that the biosphere is absorbing about an addition of at least 0.6 Pg CO2 yr-1 due to the CO2 enrichment.
Model of Daytime Oxygen Emissions in the Mesopause Region and Above: New Results
Authors: Yankovsky Valentine , Vorobeva Ekaterina , Manuilova Rada , Mironova Irina
Published: March 2021

Atmospheric emissions of atomic and molecular oxygen have been observed since the middle of the 19th century. In the last decades, it has been shown that emissions of excited oxygen atom O(1D) and molecular oxygen in electronically-vibrationally excited states O2(b1Σ+g, v) and O2(a1Δg, v) are related by a unified photochemical mechanism in the mesosphere and lower thermosphere (MLT). The current study is performed in the framework of the state-of-the-art model of ozone and molecular oxygen photodissociation in the daytime MLT. In particular, the study includes a detailed description of the formation mechanism for excited oxygen components in the daytime MLT and presents the comparison of widely used photochemical models. The study also demonstrates new results such as i) new suggestions about possible products of collisional reactions of electronically-vibrationally excited oxygen molecules with atomic oxygen and ii) new estimates of O2(b1Σ+g, v = 0 – 10) radiative lifetimes which are necessary for solving inverse problems in the lower thermosphere. Moreover, special attention is given to the Barth’s mechanism in order to demonstrate that its contribution to O2(b1Σ+g, v) and O2(a1Δg, v) populations is neglectable in daytime conditions regardless of fitting coefficients. In addition, possible applications of the daytime oxygen emissions are presented, e.g., the altitude profiles O(3P), O3 and CO2 can be retrieved by solving inverse photochemical problems where emissions from electronically vibrationally excited states of O2 are used as proxies. The funding of V.Y., R.M. and I.M. was partly provided by the Russian Fund for Basic Research (grant RFBR No. 20-05-00450).
Impact of circulation on tropical cloud feedbacks in cloud resolving models 
Authors: Mackie Anna , Byrne Michael P.
Published: March 2021

Uncertainty in the response of clouds to warming remains a significant barrier to reducing the range in projected climate sensitivity. A key question is to what extent cloud feedbacks can be attributed to changes in circulation, such as the strengthening or weakening of ascent or changes in the areas of convecting vs subsiding air. Previous research has shown that, in general circulation models (GCMs), the ‘dynamic’ component of the cloud feedback – that which is due to changes in circulation rather than changes in the thermodynamic properties of clouds (Bony et al., 2006) – is generally small (Byrne and Schneider, 2018). An open question, however, is whether this extends to models at cloud resolving resolutions that explicitly simulate deep convection.  

Here, we utilize simulations from the Radiative-Convective Equilibrium Model Intercomparison Project (RCEMIP, Wing et al., 2018, 2020) to quantify the impact of circulation on tropical cloud feedbacks. RCE is a simple idealisation of the tropical atmosphere and we focus on simulations in a long channel configuration with uniform sea surface temperatures of 295, 300 and 305K. The dynamic component of the total cloud feedback is substantial for this suite of cloud resolving models (CRMs), and is driven by circulation changes and nonlinearity in the climatological relationship between clouds and circulation. The large spread in dynamic component across models is linked to the extent to which convection strengthens and narrows with warming. This strengthening/narrowing of convective regions is further linked to changes in clear-sky radiative cooling and mid-tropospheric static stability in subsiding regions. 

 