bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetostratigraphy of the Eocene Jianchuan Basin in southeast Tibet: A preliminary result
Authors: Luo Cairong , Wang Ping , Li Yongxiang , Li Shanying , Wei Xiaochun , Huang Yongjie
Published: March 2020

Early Cenozoic continental sediments deposited contemporaneously or soon after the onset of India-Asian collision provide an obvious target for gaining insight into the early stages of the growth of the Tibetan plateau. These continental sequences are generally found in an arcuate belt that extends from the central plateau into the western Yunnan province (e.g. Nangqian-yushu Basin, Gongjo Basin and Jianchuan Basin). With limited exposure and elusive datable horizons except for a few dikes cross-cutting stratigraphy and interbedded lava flows, there were few constraints on absolute time of these Cenozoic sediments, limiting further studies of the tectonic, topographic and environmental evolution in southeast Tibet. Here, we focus on the Jianchuan basin, the age of which was mapped from the Paleocene up to the Pliocene but recently reassigned to the Paleocene/Eocene as a whole. The Xinsong section with 1547 meters in thickness was measured at the meter scale to determine vertical changes through the depositional facies. The lower part of the section consists of 1027 m thick red-colored, massive siltstone with many fine sandstone interlayers, while the upper part of the section is composed by a series of basal-scoured, upward-fining and stacked sand bodies with the thickness of 520 m. A total of 981 standard paleomagnetic oriented samples were collected. Samples were subjected to stepwise thermal demagnetization that revealed either two or three component magnetizations with the high temperature component (HTC) unblocked at ∼660-680 °C. Our preliminary results show multiple polarity reversals that can be well correlated with the Geomagnetic Polarity Time Scale (GPTS) between ca. 50 and ca. 40 Ma. We interpret that these sediments were deposited in a restricted, narrow basin in the footwalls of thrust fault where the depositional environments were highly related to the compressional deformation. Our new result may be of great significance for understanding the kinematic and dynamic models of the deformation and evolution of the Tibetan plateau.
Advances on multiobservable thermochemical tomography for the physical state of the upper mantle
Authors: Fomin Ilya , Afonso Juan
Published: March 2020

Multiobservable thermochemical tomography (MTT) is a recent computational approach to obtain estimates of the physical state (e.g. temperature distribution, compositional structure and rock properties) for the upper mantle [1]. It allows to jointly invert multiple independent datasets (e.g. gravity, seismic, magnetotelluric) within a thermodynamically-constrained and fully probabilistic framework. Evaluation of the plausibility of different physical states of the mantle with Markov Chain Monte Carlo (MCMC) simulations requires the solution of complex forward problems (e.g. Stokes flow, Maxwell’s equations, etc.) millions of times, making MTT computationally demanding for large-scale inverse problems. Furthermore, the number of parameters in a global study can easily reach several millions, making it increasingly difficult to 1) locate the regions of high probability and 2) sample these regions appropriately.

In order to overcome these limitations, we have combined and implemented a number of techniques, such as reduced-order modelling and efficient parallelization of both the forward problems and the MCMC algorithms, which dramatically accelerate the solution of the forward problems. Our software, LitMod1D_4INV and LitMod3D_4INV, allow to compute a proposal in less than 1 second, even when solving multiple complex forward problems together. We develop a multi-level parallel MPI driver for a collection of advanced MCMC sampling strategies to locate and sample high-probability regions efficiently. The massive amounts of data generated by large-scale MTT inversions need to be managed efficiently. We output results to open-source freeware formats, such as HDF5, TileDB, designed for big data problems. We emphasize that our methods and approaches are not only useful for MTT, but for any demanding inverse problem.

In this contribution, we will present applications of our software to complex, large-scale MTT problems and discuss its benefits, limitations and future improvements.

[1] J.C. Afonso, N. Rawlinson, Y. Yang, D. L. Schutt, A. G. Jones, J. Fullea, W. L. Griffin, 3‐D multiobservable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle: III. Thermochemical tomography in the Western‐Central U.S., Journal of Geophysical Research, 121, doi:10.1002/2016JB013049, 2016
Comparison of INP Parameterizations for Dust Minerals in Climatological Simulations With a Global Model
Authors: Perlwitz Jan , Knopf Daniel , Miller Ron
Published: March 2020

The effect of aerosol particles on ice nucleation and, in turn, the formation of ice and mixed phase clouds is recognized as one of the largest sources of uncertainty in weather and climate prediction.  We utilize an improved sectional dust module in NASA GISS Earth System ModelE2.1, which distinguishes eight different mineral species and accretions between iron oxides and the other minerals.  Simulations over a period of 20 years have been carried out with this model, and the mineral fields and other model variables (temperature, relative humidity) are used to calculate the ice nucleating particle (INP) number concentration, applying time-independent and time-dependent INP parameterizations, such as active site parameterization and water activity based immersion freezing model (ABIFM).  We study how the dependence of the parameterizations on different model variables affects the mean INP number concentration.  The sensitivity of the INP number concentration to fundamental dust properties such as emitted mineral size distributions and mixing state between minerals is also investigated.  Results show that the sensitivity of the total INP number concentration to the emitted dust size distribution is rather small, but the sensitivity over the whole size range obscures offsetting differences in the magnitude and the sign of the sensitivity between smaller and larger particles.
Modelling of in-stream nutrient uptake beyond the river reach scale
Authors: Dehaspe Joni , Musolff Andreas
Published: March 2020

Nutrient excess in rivers leads to ecosystem harm and can induce detrimental algae growths in coastal areas. In Germany and Europe, the management of riverine systems is complicated by the lack of understanding of nutrient pathways and effectiveness of retention processes from application to export. In this work, we hypothesize that in-stream nitrate uptake effects are linked to the shape or ‘bending’ of the concentration discharge (C-Q) relationship. Therefore, the analysis of observational C-Q data may give insight into the dominant controls of the magnitude of in-stream nitrate uptake across different catchment. To explore the concentration discharge (C-Q) behavior in a range of hydrological and biogeochemical conditions, we developed a catchment wide parsimonious (7 parameter) network model framework (spatially explicit at 1x1km²). Here, land-to-stream nutrient transfer was modelled as a power law (C=aQb), resulting in different nutrient loading according to the contributing area of each grid cell in the network and in-stream load uptake follows Li = Lin*e-vf*w*L/Q, with vf the uptake rate, w and L the width and length of the river section. This approach acknowledges both, spatial variability between river sections (e.g. residence time distributions) as well as at-a-station temporal variability depending on Q. Ten existing stream networks in Germany were evaluated with this model framework in a ‘Monte Carlo approach’ for about 1000 predefined parameter combinations and 10 years of discharge data. First results show total nitrate uptakes ranging from almost 0 to 15% and high bending of C-Q curves correlated to high uptake rates. Furthermore, it was found that mean in-stream residence times, more than land-to-stream loading concentrations influence exported nutrient concentrations. The final result of our analysis will allow us to argue if the observed C-Q bending can be indeed related to instream uptake and not to other processes (e.g. denitrification along the subsurface flow path) and to derive the dominant processes shaping the uptake (such as light availability, instream travel time, nutrient stoichiometry, and impact of fine sediments).
Effects of GCM selection for regional climate modelling illustrated by the interactive tool GCMeval
Authors: Landgren Oskar A. , Parding Kajsa , Dobler Andreas , McSweeney Carol F. , Benestad Rasmus , Erlandsen Helene B. , Mezghani Abdelkader , Gregow Hilppa , Räty Olle , Viktor Elisabeth , El Zohbi Juliane , Bøssing Christensen Ole , Loukos Harilaos
Published: March 2020

With the increasing number of global climate models available, regional modellers have to make choices to select a manageable subset for downscaling. This limits the representation of both present day climate and future climate change compared to the full GCM ensemble.

We present the interactive web-based tool called “GCMeval”, available at https://gcmeval.met.no. This tool lets you assign weights to different regions, seasons, climate variables, and skill scores and presents a ranking with model performance for a historical period. We demonstrate how the tool can be used to, for example, remove models with the largest historical biases for the selected criteria, or to optimise the spread. The weighting can be used to illustrate the sensitivity of the results to model choice.

Based on the choice of regions and weights, the tool produces scatter plots of projected future temperature and precipitation and shows how the selected sub-ensemble compares to the full ensemble. The tool can also be used to evaluate ensemble selections "post-hoc", as demonstrated with examples from CORDEX.
Unsupervised classification of 30 years of near-fault seismological data: What can we learn about fault physics?
Authors: Poli Piero , majstorovic Josipa
Published: March 2020

The exponential growth of geophysical (seismological in particular) data we faced in the last years, made it hard to quantitatively label (e.g. systematical separation of earthquakes and noise) the daily and continuous stream of records. On the other hand, these data are likely to contain an enormous amount of information about the physical processes occurring inside our planet, including new and original signals that can shed light on new physics of the crustal rocks.

Of particular interest are data recorded near major faults,where one hope to detect and discover new signals possibly associated with precursory phase of significant and hazardous earthquakes.

 

 

With the above ideas in mind, we perform an unsupervised classification of 30 years of seismological data recorded at ~10km from the L’Aquila fault (in Italy), which hosted a magnitude 6 event (in 2009) and still poses a significant hazard for the region.

 

We based our classification on daily spectra of three component data and relative spectral features. We then utilize self-organizing map (SOM) to perform a crude clustering of the 30 years of data. The data reduction offered by SOM permits a rapid visualization of this large datasets (~11k spectra) and individuation of main spectral groups. In a further step, we test different clustering algorithms (including hierarchical ones) to isolate groups of records sharing similar features, in a non-subjective manner. We believe that from the quantitative analysis (e.g. temporal evolution) of the retrieved clusters, the signature of fault physical processes (e.g. preparation of the magnitude 6 earthquake, in our case) can be retrieved. The newly detected signals will then be analyzed to learn more about the causative processes, generating them.
Parameter uncertainty analysis for streamflow prediction in a cascade hydropower basin of southwest China
Authors: Liang Yanan , Cai Yanpeng
Published: March 2020

Semi-distributed model of SWAT based on physical-chemical spatial information has been an effective tool for simulating hydrological cycle in the basin whereas it can’t completely restore all natural processes. Therefore, uncertainty analysis is needed to be conducted in order to achieve the reliability of the model. Yalong River Basin (YLRB), which is listed as the top ten hydropower bases in China, contains abundant water resources with plentiful runoff. Here a case study in YLRB was conducted to explore the parameter uncertainties of the SWAT model to runoff simulations based on multiple optimization algorithms. The following results were obtained: 1) setting the same objective function of Nash–Sutcliffe Efficiency, three optimization methods including Sequential Uncertainty Fitting version 2 (SUFI-2), Generalized Likelihood Uncertainty Estimation (GLUE) and Particle Swarm Optimization (PSO) all performed satisfactory fitting results and produced similar parameter ranges in YLRB, while SUFI-2 achieved better uncertainty analysis, followed by PSO and the last GLUE; 2) five general sensitive parameters to model output were ALPHA_BF, CH_K2, SOL_K(1), GW_REVAP and ESCO based on above three algorithms; 3) from the contribution network analysis in economics, the positive correlation between ALPHA_BF and CH_K2 exhibited the highest weight among all parameter relationships; and 4) the much lower sensitivity of parameter CN2 to streamflow in YLRB revealed that most commonly modified parameter CN2 was less applicable to land with adequate surface water than dry land. This work will be conducive to further hydrological analysis based on a reliable fitting model for this hydropower watershed. Additionally, this work will provide references and insights for sensitive parameter modification and prediction uncertainty reduction of streamflow simulation furthermore contributing to an optimal water resource management.
A Guiding Principles for Choosing Numerical Precision in Atmospheric Model based on CESM
Authors: Lai Jiayi
Published: March 2020

The next generation of weather and climate models will have an unprecedented level of resolution and model complexity, while also increasing the requirements for calculation and memory speed. Reducing the accuracy of certain variables and using mixed precision methods in atmospheric models can greatly improve Computing and memory speed. However, in order to ensure the accuracy of the results, most models have over-designed numerical accuracy, which results in that occupied resources have being much larger than the required resources. Previous studies have shown that the necessary precision for an accurate weather model has clear scale dependence, with large spatial scales requiring higher precision than small scales. Even at large scales the necessary precision is far below that of double precision. However, it is difficult to find a guided method to assign different precisions to different variables, so that it can save unnecessary waste. This paper will take CESM1.2.1 as a research object to conduct a large number of tests to reduce accuracy, and propose a new discrimination method similar to the CFL criterion. This method can realize the correlation verification of a single variable, thereby determining which variables can use a lower level of precision without degrading the accuracy of the results.
Particle and aggregates size distribution of soil transported due to surface runoff and rill erosion
Authors: Kubínová Romana , Kavka Petr , Neumann Martin , Laburda Tomáš
Published: March 2020

In this contribution the grain size distributions of the soil sediment obtained from soil erosion experiments were analysed. All the tests were done on arable topsoil’s, separately the size distribution of the soil aggregates and individual soil particles were evaluated. Soil erosion was initiated under the controlled conditions in the laboratories. The rainfall was artificially generated with use of a nozzle type rainfall simulator. The sediment transported due to the surface runoff and rill erosion was collected from the discharge of the inclined soil erosion plots (slopes 20 – 34°, slope length 4 m).

The soil sediment was collected in four sampling times. The first and the second were collected in fifteen and thirty minutes from the beginning of the simulation, then followed fifteen minutes long pause without raining and then the simulation continued and soil samples were collected again in fifteen and thirty minutes from the beginning of the rain. After ten days long pause whole process were repeated at the same experimental plot contains rills from previous simulation. Experimental plots were vertically divided into two parts. On one part was an eel and on the second part were different types of rolled erosion control products (RECPs) – Enkamat 7010, Biomac-C, coir fibres K700 and K400, jute, Macmat 8.1 with soil, mulch, hay and nonwoven. The influence of RECPs to the grain size distribution was investigated.

Laser diffraction has been selected as a method to determine grain size distribution and device Mastersizer 3000 was used. By the comparison of the grain size distribution, of more than five hundreds samples, the different response to the soil erosion mechanism and the influence of external factors (experimental plot slope, sampling time from the surface runoff and presence of RECPs) on the grain size distribution and soil aggregates content in eroded sediment were investigated. It has been found that both the particle size and aggregates size distribution of the eroded sediment changes considerably in time.

This research is funded by the TH02030428 - „Design of technical measures for slopes stabilization and soil erosion prevention”.
Modelling mixed-phase clouds with large-eddy model UCLALES-SALSA
Authors: Ahola Jaakko , Korhonen Hannele , Tonttila Juha , Romakkaniemi Sami , Kokkola Harri , Raatikainen Tomi
Published: March 2020

We have extended the large-eddy model UCLALES-SALSA (Tonttila et al., 2017) to include formation of ice and mixed-phase clouds. The model has exceptionally detailed aerosol description for both aerosol number and chemical composition. We confirmed the accuracy of newly implemented ice microphysics with a comparison to a previous mixed-phase cloud model intercomparison study.

In a further simulation the model captured the typical layered structure of Arctic mixed-phase clouds: a liquid layer near cloud top and ice within and below the liquid layer. The simulation also demonstrated how larger droplets froze first. Moreover, the simulation showed realistic freezing rates of droplets within the vertical cloud structure. These characteristics were possible to capture with a heterogeneous ice nucleation scheme, where also ice nucleating particles (INP) are prognosed. Here, dust containing particles acted as INPs.

The prognostic simulation showed the importance of the self-adjustment of ice nucleation active particles. This is in good agreement with an observational study where resilient mixed-phase clouds are seen together with relatively high ice nuclei concentrations.

The implemented detailed sectional ice microphysics with prognostic aerosols is essentially important in reproducing the characteristics of mixed-phase clouds. The manuscript of this study is submitted for publication.
Can we observe a correlation between vertical Doppler velocity and upwelling solar radiance for shallow marine boundary clouds?
Authors: Ewald Florian , Groß Silke , Hagen Martin , Kölling Tobias , Mayer Bernhard
Published: March 2020

Clouds play an important role in the climate system since they have a profound influence on Earth’s radiation budget and the water cycle. Uncertainties in current climate models arise from a limited understanding of the coupling between cloud dynamics, cloud microphysics and, in turn, cloud radiative properties. Over decades, radiative properties of cloud tops were extensively studied using passive observations from multiple satellite missions. In recent years, our understanding of the inner workings of clouds has been greatly advanced by the deployment of cloud profiling microwave radars from low-earth orbit like CloudSat or the upcoming EarthCARE satellite mission. In order to exploit the future synergy between the cloud radar and the passive imager on EarthCARE, the scientific community is in dire need of collocated and spatially highly resolved measurements in advance of future spaceborne missions.  

In this context, the German research aircraft HALO is equipped with the high-power (30kW) cloud radar HAMP MIRA operating at 35 GHz and the hyperspectral imager specMACS (400 nm – 2500 nm). During the EUREC4A campaign, a number of flights were conducted over shallow marine boundary clouds in the vicinity of Barbados to collect simultaneous measurements with both instruments. For the first time, the spatial resolution of the Doppler velocity measurements from HALO now better match (<100 meter) the spatial resolution of the radiance imager, allowing for a more detailed separation of small up- und down-drafts.

In this presentation, we will give first impressions of these collocated, highly resolved radar-imager measurements of shallow marine boundary clouds during EUREC4A. On the basis of this data set we will try to answer the question if a correlation between the vertical Doppler velocity and the upwelling solar radiance for this kind of clouds can be observed. Such a relationship could prove valuable to assist synergistic retrievals (e.g. radar-lidar) in narrowing down the microphysical assumptions on which these retrievals rely upon. Furthermore, this data set could serve as a benchmark for cloud resolving modeling by constraining the relationship between cloud dynamics and radiation.
Characterization of the ocean mesoscale eddies in the Antarctic Circumpolar Current from in situ, model and remotely sensed data
Authors: Cotroneo Yuri , Patara Lavinia , Menna Milena , Falco Pierpaolo , Rieck Jan Klaus , Notarstefano Giulio , Fusco Giannetta , Budillon Giorgio , Poulain Pierre-marie
Published: March 2020

Mesoscale variability and associated eddy fluxes play crucial roles in the ocean dynamics, transport of water mass properties and ecology of the upper ocean. In the Southern Hemisphere, where the nearly zonal flow of the Antarctic Circumpolar Current (ACC) acts as a barrier to the direct poleward transport toward the Antarctica, the eddy flux across the ACC is the main mechanism that guarantees the heat budget and distributes physical and biogeochemical properties between subtropical and polar regions. We focused on a high dynamical region located between the South-West Indian Ridge and the South Pacific Ridge. In this area, the interaction between the ACC and the major bathymetric features produces relatively large values of eddy kinetic energy and eddy heat fluxes as well as a relevant forcing for the ACC path.

The aim of this study is to evaluate the actual efficiency of mesoscale eddies to exchange heat and other properties across the different ACC fronts and to describe the vertical properties of the eddies, their tracks and evolution. To this end, we used in-situ and satellite data in conjunction with a hindcast simulation from 1958 to 2018 performed with a 1/10° ocean biogeochemistry model.

Eddies are identified and tracked in both the model output and altimetry data while their thermohaline properties and vertical extension are described using model outputs and in situ data, which include available repeated XBT sections (i.e. New Zealand – Antarctica and Hobart – Antarctica) and Argo float profiles located inside these structures.

Thanks to the joint analysis of model and observational data, we are able to 1) assess the ability of the 1/10° ocean model of simulating the eddy field properties, and to 2) better interpret the spatial and temporal variability of the observed eddy characteristics in the larger and longer framework of the ocean simulation.
Validation for ESA’s Aeolus Mission using the in-situ instruments at Canadian Arctic and reanalysis data
Authors: Chou Chih-Chun , Kushner Paul , Mariani Zen , Rodriguez Peter , Fletcher Christopher
Published: March 2020

ESA’s Aeolus mission, launched in August 2018, is designed to capture tropospheric wind profiles on a global scale in near-real time. The Aeolus lidar system, Atmospheric LAser Doppler INstrument (ALADIN), uses two modes of lidar-driven active scattering, Mie and Rayleigh scattering channels, to retrieve horizontal line-of-sight (HLOS) winds under both clear and cloudy conditions. ESA Aeolus aims to improve numerical weather and climate prediction, and to advance understanding of atmospheric circulation and weather systems.

This presentation will describe the Canadian validation activities for ESA Aeolus level-2B product, coordinated by the University of Toronto’s Department of Physics and Environment and Climate Change Canada (ECCC). The main focus is the evaluation of Aeolus overpasses using the fifth major global reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF ERA5), and in-situ measurements at Environment and Climate Change Canada’s (ECCC) Iqaluit and Whitehorse supersites where several wind sensing instruments are co-located. It will compare the Aeolus HLOS winds with the profiles of wind vector from regular radiosonde launches, line-of-sight winds from Doppler Lidar and Ka-Band Radar. The accuracy of the Aeolus measurements is analyzed based on the type of scattering and natural variability of the wind on different levels.

The radiosonde measures the profiles of temperature, relative humidity, pressure, and winds twice a day with a vertical resolution of 15 m up to 30 km. On the other hand, the Mie scattered 1.5 micron Doppler Lidar retrieves LOS winds at every 3 m as well as aerosol backscatter and depolarization ratio every 5 minutes up to 3 km. Lastly, for every 10 minutes, the dual-polarization Doppler Ka-Band Radar measures the LOS wind speed and direction, cloud and fog backscatter, and depolarization ratio up to a range of 25 km with a vertical resolution of 10 m.

The wind profiles were directly compared to the profiles derived from other instruments or reanalysis. The vertical structure of the Aeolus winds, for example the wind shear, will also be compared and discussed. The validation results showed that Aeolus is providing some promising initial products and that the ERA5 reanalysis is the most consistent dataset with the Aeolus wind measurements from level-2B product.
Application of nonparametric trend analysis to concentration time series
Authors: Kohler Artur
Published: March 2020

Groundwater contamination resulted from chemical releases related to anthropogenic activity often proves to be a persistent feature of the affected groundwater regime.  The affected volume (i.e. where the concentration of hazardous substances exceeds a certain threshold) is a complex and dynamic entity commonly called “contaminant plume”.  The plume can be described as a spatially dependent concentration pattern with temporal behavior.  Persistent plumes are regularly monitored, concentration data gained by repeated sampling of monitoring points and laboratory analyses of the samples are used to assess the actual state of the plume.  The change of the concentrations at certain points of the plume facilitates the assessment of the temporal behavior of the plume.  Repeated sampling of the monitoring points provides concentration time series.

Concentration time series are evaluated for trends.  Methods include parametric (regression using least squares) and non-parametric methods.  Mann-Kendall statistic is a commonly used, well known non parametric method.

When using Mann-Kendall statistics consecutive concentration data are compared to each other, their cumulative relation defines Mann-Kendall statistic ‘S’.  However, when comparing concentration data laboratory uncertainties are usually neglected.  Allowing for laboratory uncertainties, rises the question of what concentrations are considered equal, less or more than other concentrations.  In addition aggravating concentration data will change the previous equal – more - less status of two concentrations, thus changing the Mann-Kendall statistics value, which sometimes results in differences in trend significance.
How will climate change affect the planktonic food web and the biogeochemistry of the Mediterranean Sea according to the RCP 8.5 scenario ?
Authors: Baklouti Melika , Pagès Rémi , Ayache Mohamed , Barrier Nicolas , Sevault Florence , Somot Samuel , Moutin Thierry
Published: March 2020

In recent studies, the Mediterranean region is once again identified as a region particularily sensitive to climate change, with recorded temperature and sea level rises during the last decades exceeding the mean variations recorded at global scale. Moreover, according to climate scenarios, there seems to be some consensus regarding the impact on climate change on some hydrodynamical features, as for example on stratification which should become stronger and more persistant. However, nothing or very few is known about the expected changes nor in the structure and the functionning of the planktonic food web, neither in the main biogeochemical cycles. This study is intended to progress on this issue, using a coupled (one way) physical-biogeochemical model: CNRM-RCSM4/NEMO-MED12/Eco3M-Med. A 110-year simulation over the period 1990-2100 has been run and from 2006, the simulation is forced by a RCP 8.5 regional scenario of the Med Sea (a control simulation has also been run simultaneously). After having verified the model's ability to describe the main characteristics of the marine planktonic food web and biogeochemistry through several comparisons with available data during the historical period, the model outputs have been analyzed. Preliminary results indicate a significant decrease in the annual primary production and the export of organic carbon at 200 and 1000 m in both the eastern and the western basins, associated with changes in the structure of the planktonic community.
Estimation of winter PM2.5 concentrations in East Asia associated with climate variability
Authors: Jeong Jaein , Park Rokjin , Yeh Sang-Wook , Roh Joon-Woo
Published: March 2020

Interannual variability in large circulations associated with climate connections, such as monsoon and El Niño, have a significant impact on winter PM2.5 concentrations in East Asia. In this study, we use the global 3D chemical transport model (GEOS-Chem) over the last 35 years to investigate the relationship between major climate variability and winter PM2.5 concentrations in East Asia. First, the model is evaluated by comparing the simulated and observed aerosol concentrations with the ground and satellite-based aerosol concentrations. The results indicate that this model well reproduces the variability and magnitude of aerosol concentrations observed in East Asia. Sensitivity simulations are then used with fixed anthropogenic emissions to investigate the effects of meteorological variability on changes in aerosol concentrations in East Asia. The variability of winter PM2.5 concentrations in northern East Asia was found to be closely correlated with ENSO and Siberian high position. To predict PM2.5 concentrations using key climate indices, we develop multiple linear regression models. As a result, the predicted winter PM2.5 concentrations using the key climate index are well reproduced in the simulated PM2.5 concentrations, especially in northern East Asia.
Lagrangian Analysis of the Dynamical and Thermodynamic Drivers of Greenland Melt Events during 1979-2017
Authors: Hermann Mauro , Papritz Lukas , Wernli Heini
Published: March 2020

Specific atmospheric circulation patterns can lead to strongly positive near-surface temperature anomalies over Greenland, fostering the occurrence of extensive surface melt events. In this study, we objectively identify 77 Greenland melt events in June-August 1979-2017, which also affect high-elevated regions of the Greenland ice sheet (GrIS), from ERA-Interim reanalysis data. Eight-day backward trajectories from the lowermost 500 m above the GrIS are used to investigate the air mass history and the synoptic, dynamical, and thermodynamic drivers of Greenland melt events. The key synoptic feature is a high-pressure system, in 65% of the events classified as atmospheric blocking, southeast of the GrIS. It is favorably located to induce rapid and long-range poleward transport of anomalously warm air masses (compared to climatology) from the lower troposphere to the GrIS. Due to orographic and dynamical lifting, latent heating from condensation of water vapor contributes additionally to the air mass’ warm anomaly - most important for melt events on top of the GrIS. Adiabatic warming by subsidence, however, is insignificant, in contrast to warm events in the central Arctic. Exemplarily, the warm anomaly of air masses arriving in the Summit area during the most extensive melt event in early July 2012 arose due to strong meridional transport, mainly from the western North Atlantic, and latent heat release during ascent to Greenland. The simultaneous occurrence of a North American record heat wave did not play any direct role for the Greenland melt event. Further, regionally varying short- and longwave radiative effects induced by the warm-moist air masses enhance melt all over the GrIS. The identified mechanisms that cause Greenland melt events imply that the understanding of the formation of high-pressure systems and their representation in climate models is crucial in determining future GrIS melt. More generally, we highlight the importance of atmospheric dynamics and air flow patterns for Greenland melt events as they eventually determine the temperature pattern and surface energy budget over the GrIS with consequences for global sea-level rise.
​Impact of changes in rivers inputs during the last decades on the biogeochemistry of the eastern Mediterranean basin
Authors: Pagès Rémi , Baklouti Melika , Barrier Nicloas , Richon Camille , Dutay Jean-Claude , Ayache Mohamed , Moutin Thierry
Published: March 2020

The Mediterranean Sea (MS) is a semi-enclosed sea characterized by a zonal west-east gradient of oligotrophy, where microbial growth is controlled by phosphate availability in most situations. External inputs of nutrients including Gibraltar inputs, river inputs and atmospheric deposition are therefore of major importance for the biogeochemistry of the MS. The latter has long been considered to be driven mainly by nutrient exchanges at Gibraltar. However, recent studies indicate that river inputs significantly affect nutrients concentrations in the Mediterranean Sea, although their resulting impact on its biogeochemistry remains poorly understood. In this study, our aim was to help fill this knowledge gap by addressing the large-scale and long-term impact of variations in river inputs on the biogeochemistry of the Mediterranean Sea over the last decades, using a coupled physical- biogeochemical 3D model (NEMO-MED12/Eco3M-Med). As a first result, it has been shown by the model that the strong diminution (60%) of phosphate (PO4) in river inputs into the Mediterranean Sea since the end of the 1980s induced a significant lowering of PO4 availability in the sub-surface layer of the Eastern Mediterranean Basin (EMB). One of the main consequences of PO4 diminution is the rise, never previously documented, of dissolved organic carbon (DOC) concentrations in the surface layer (by 20% on average over the EMB). Another main result concerns the gradual deepening of the top of the phosphacline during the period studied, thus generating a shift between the top of the nitracline and the top of the phosphacline in the EMB. This shift has already been observed in situ and documented in literature, but we propose here a new explanation for its occurrence in the EMB. The last main result is the evidence of the decline in abundance and the reduction of size of copepods calculated by the model over the years 1985–2010, that could partially explain the reduction in size of anchovy and sardine recently recorded in the MS. In this study, it is shown for the first time that the variations in river inputs that occurred in the last decades may have significantly altered the biogeochemical cycles of two key elements (P and C), in particular in the EMB.
The effect of dust absorption on Sahel precipitation
Authors: Balkanski Yves
Published: March 2020

Absorption of shortwave radiation by dust depends on its iron oxide content. Iron oxides amount to just a few percents of dust mineralogy. In the Sahel, the amount of iron oxide in soils is significantly greater than over the rest of North Africa. Recent measurements from the AER-D campaign have evidenced the presence of large dust particles over Northern African sources, which measurements showed absorb higher shortwave radiation than smaller ones.

I present two 100-years simulations of the earth system model IPSLCM6, one with a detailed description of dust and one without dust. Over the summer months (JJAS), dust absorption amounts to 25 W.m-2 over the region. The changes caused by this absorption to the water budget are analyzed. Dust absorption causes an increase of 16% of summer Western Sahel precipitation, whereas in the Eastern Sahel, summer precipitation is increased by 7%. The analysis is extended to evaporation, surface relative humidity, low-level clouds and total cloud liquid water path, all of which show a significant increase caused by absorbing dust.

The water budget over the Sahel is computed over an airshed that covers the region, 16W:36E and 10N:20N from the surface to 200mb, contrasting the water flux with and without aerosol absorption. Dust absorption causes a change in the mean circulation between 1000 and 800mb that induces an increased inflow of moist air at these levels at the western and southern Sahel boundaries during the summer monsoon.  Hence, it is important to understand the influence of aerosol absorption when studying the causes of variations in Sahel precipitation.
Contribution of vegetation to methane emission produced in the soil of an upland forest: a 13CH4-labelling approach
Authors: Plain Caroline , Epron Daniel
Published: March 2020

The role of vegetation on net methane fluxes from upland forest ecosystem has only recently been underlined and is still not fully understand and quantify. Indeed, influences of forest plants on the methane budget could be antagonist, being a net methane producer or emitter in some cases or enhancing the methane consumption in others. But the vegetation in upland forests decreases the net methane uptake by 0 to 63%, and in a few cases, increases the methane uptake up to twice. One of the mains source of methane emission related to the vegetation is the transport of methane from deep anoxic soil layers where the methane is produced to the atmosphere through plant stems.

In order to quantify if vegetation is a preferential way of methane emission in our field site, a 13CH4 labelling had been undertaken in soil (at 40 cm depth) and 13CH4 had been traced in upper soil layers (0, 5, 10, 25 cm depth), on the soil surface with soil chambers with or without herbaceous vegetation and in tree stem chambers for two days after the pulse labelling.

13CH4 was recovered in all compartments even though the forest ecosystem was mainly a methane sink during this period when methane uptake dominated.

In our study, the vegetation (tree stems and herbaceous vegetation) have a limited contribution on the recovery of 13CH4 at the forest scale, which is dominated by soil emissions.
Propagating uplift controls on formation of low-relief, high-elevation surfaces in the SE Tibetan Plateau
Authors: Yuan Xiaoping , Huppert Kimberly , Braun Jean , Guerit Laure
Published: March 2020

The SE Tibetan Plateau has extensive broad, low-relief, high-elevation surfaces perched above deep valleys, as well as in the headwaters of the three rivers (the Salween, the Mekong, and the Yangtze). However, understanding the presence of these low-relief surfaces is a long-standing challenge because their formation process remains highly debated. While alternate mechanisms have been proposed to explain the low-relief surface formation in this setting (e.g., drainage-area loss mechanism due to horizontal advection; Yang et al., 2015, Nature), a long-standing hypothesis for the formation of low-relief surfaces is by a step change in uplift and incision into a pre-existing, low-relief surface (Clark et al., 2006, JGR; Whipple et al., 2017, Geology).

The morphology of low-relief surfaces in the SE Tibetan Plateau is largely consistent with formation by a step change in uplift, but one problem with this model is that low-relief surfaces formed by a step change in uplift are relatively short-lived, since they are incised and steepened by erosion, which sweeps upstream at the response time of mountain ranges (in the order of several million years). Using a landscape evolution model that combines erosion, sediment transport and deposition processes (Yuan et al., 2019, JGR), we demonstrate that propagating uplift form large parallel rivers, with broad low-relief, high-elevation interfluves that persist for tens to hundreds of million years, consistent with various dated ages. These low-relief surfaces can be long-lived because the drainage areas in these interfluves are insufficient to keep up with rapid incision of the large parallel mainstem rivers. Our simulated features match various observations in the SE Tibetan Plateau: (i) low-relief surfaces are approximately co-planar in headwaters, and decrease in elevation smoothly from northwest to southeast across the plateau margin; (ii) χ-elevation plots of the mainstem rivers are convex; (iii) low-relief surfaces have low erosion rates; and (iv) erosion rates are high in the mainstem rivers at the propagating margin.
Drought monitoring incorporating precipitation and climate variables and its application for future drought projection
Authors: Won Jeongeun , Kim Sangdan
Published: March 2020

In drought monitoring, it is very important to select climate variables to interpret drought. Most drought monitoring interprets drought as deficit in precipitation, so drought indices focused on the moisture supply side of the atmosphere have been mainly used. However, droughts can be caused not only by lack of rainfall, but also by various climate variables such as increase in temperature. In this regard, interest in potential evapotranspiration(PET), which is an moisture demand side of the atmosphere, is increasing and a PET-based drought index has been developed. However, complex droughts caused by various climate variables cannot be interpreted as a drought index that only considers precipitation or PET. In this study, we suggest a drought monitoring method that can reflect various future climate variables, including precipitation. In other words, copula-based joint drought index(CJDI), which incorporate standardized precipitation index(SPI) based on precipitation and evaporative demand drought index(EDDI) based on PET, is developed. CJDI, which considers both precipitation and PET, which are key variables related to drought, is able to properly monitor the drought events in Korea. In addition, future Drought severity – duration - frequency curves are derived to project future droughts compared to various drought indices. It is shown that CJDI can be used as a more reasonable drought index to establish the adaptation policy for future droughts by presenting the pattern of future droughts more realistically.

Acknowledgment: This study was funded by the Korea Ministry of Environment (MOE) as Smart Urban Water Resources Management Program. (2019002950004)

Keywords: Climate change; Copula; Drought; CJDI; Drought severity-duration-frequency curve
Root water uptake and its pathways across the root: quantification at the cellular scale
Authors: Zarebanadkouki Mohsen , Trtik Pavel , Hayat Faisal , Carminati Andrea , Kaestner Anders
Published: March 2020

The pathways of water across root tissues and their relative contribution to plant water uptake remain debated. This is mainly due to technical challenges in measuring water flux non-invasively at the cellular scale under realistic conditions.  We developed a new method to quantify water fluxes inside roots growing in soils. The method combines spatiotemporal quantification of deuterated water distribution imaged by rapid neutron tomography with an inverse simulation of water transport across root tissues. Using this non-invasive technique, we estimated for the first time the in-situ radial water fluxes [m s-1] in apoplastic and cell-to-cell pathways. The water flux in the apoplast of twelve days-old lupins (Lupinus albus L. cv. Feodora) was seventeen times faster than in the cell-to-cell pathway. Hence, the overall contribution of the apoplast in water flow [m3 s-1] across the cortex is, despite its small volume of 5%, as large as 57±8 % (Mean ± SD for n=3) of the total water flow. This method is suitable to non-invasively measure the response of cellular scale root hydraulics and water fluxes to varying soil and climate conditions.
Recent Advances in the Identification of Onshore and Offshore Tsunami Deposits from the Eastern Mediterranean Coastline of Israel
Authors: Goodman Tchernov Beverly
Published: March 2020

The first physical field evidence for any dated tsunami event on the coast of Israel was discovered twenty years ago.  Since then, three campaigns of offshore core collections were completed with the aim of testing the validity of that interpretation, further completing the catalogue of known tsunami events, providing constraining data for models, determining associations with potential source tsunami-generating mechanisms, and assessing risk for purposes of emergency planning and coastal management.  Those follow-up coring campaigns provided many additional examples of anomalous sedimentary deposits that agreed with tsunami-derived interpretations and failed to fit criteria of other potential causes (e.g. floods, storms); reinforcing the theory that multiple tsunami events impacted that coastline and building a more complete record.  The interpretation of these offshore deposits has been improved by ongoing contributions from modern sedimentological studies following the set of recent megatsunamis.  Specifically, tsunami sediment characterization from modern tsunami studies has greatly improved the ability to recognize cryptic, anomalous deposits with higher confidence.  In addition, a small set of new land-based evidence has been identified, some of which match written historical records, and many that corroborate the offshore sedimentary record. In this presentation, a summary of these finds and the latest, most updated catalogue of events based on physical sedimentary deposits will be presented highlighting knowledge gained regarding variations in the efficacy of various proxies in the tsunami ‘tool box’ with relationship with this particular stretch of coastline.