bluuebunny/crossref_metadata_2025 huggingface dataset:
Early Holocene history of the Zachariae Ice Stream, NE Greenland: Evidence from geochemistry, grain size and sedimentary parameters
Authors: Davies Joanna , Møller Mathiase Anders , Pearce Christof , Seidenkrantz Marit-Solveig
Published: March 2020

The Arctic region exhibits some of the most visible signs of climate change globally. Arctic sea ice extent and volume has been declining sharply in recent decades; observations indicate a mean annual decrease of 3.2% since 1980. However, no extensive network of sea ice observations extends back further than the mid-18th century and satellite data since the late 1970s; this limits perspectives of sea ice variability on longer time scales. Thus, to understand the processes governing sea-ice cover and variability, predict how sea ice and ocean conditions will respond to anthropogenic climate change and to understand if the shrinking of Arctic sea ice is a unique and irreversible process, longer records of sea ice variability and oceanic conditions are required.

A multi-proxy approach, involving grain size, geochemical, foraminifera and sedimentary analysis, was applied to a marine sediment core from North East Greenland to reconstruct changes in sea ice extent and palaeoceanographic conditions throughout the early Holocene (ca. 12,400-7,800 cal. yrs. BP). The study aimed to improve the understanding of the interaction between ocean circulation, sea ice and fluctuations of the Zachariae Isstrøm (ZI), one of the main glacier outlets of NE Greenland. Four distinct zones have been identified: Zone 1 (12,400-11,600 cal. yrs. BP) covering the transition from the Younger Dryas into the Holocene which evidences a gradually warming climate, resulting in a retreat of the ZI; Zone 2 (11,600 – 10,300 cal. yrs. BP) which encapsulates two distinct cooling events as a result of cooler surface waters, rapid release of freshwater and local feedback mechanisms. This coincides with sudden re-advances of the ZI followed by gradual retreats; 3) Zone 3 (10,300 – 8,600 cal. yrs. BP) shows warm and stable conditions, with warm surface waters that resulted in the retreat of the ZI; 4) Zone 4 (8,600 – 7,800 cal. yrs. BP) which shows a rapid return to cooler conditions, with cold surface waters and rapid freshwater outbursts resulting in the re-advance of the ZI, forced by decreasing solar insolation and cold surface waters. Our investigation thus indicated that changes in oceanic conditions at the NE Greenland shelf had a significant impact on the extent and melting rate of the ZI glacier.
A scheme for forecasting severe space weather
Authors: Nanan Balan
Published: March 2020

We have developed and tested a scheme for forecasting severe space weather (SvSW) that caused all known electric power outages and telecommunication system failures since 1957 and the Carrington event of 1859. The SvSW events of 04 August 1972 has puzzled the scientific community as it occurred during a moderate storm (DstMin = -124 nT) while all other SvSW events occurred during super storms (DstMin ≤ -250 nT). The solar wind velocity V and IMF Bz measured by ACE satellite at the L1 point since 1998 are used. For the earlier SvSW events such as the Carrington event of 1859, Quebec event of 1989, and the events in February 1958 and August 1972 we used the information from the literature. The coincidence of high ICME front (or shock) velocity ΔV (sudden increase in V over the background by over 275 km/s) and sufficiently large Bz southward at the time of the ΔV increase is associated with SvSW; and their product (ΔV×Bz) is found to exhibit a large negative spike at the speed increase. Such a product (ΔV×Bz) exceeding a threshold seems suitable for forecasting SvSW, with a maximum forecasting time of 35 minutes using ACE data. However, the coincidence of high V (not containing ΔV) and large Bz southward does not correspond to SvSW, indicating the importance of the impulsive action of high ΔV and large Bz southward coming through when they coincide. The need for the coincidence is verified using the CRCM.
A new source location and attribute recognition method based on correlation analysis of gravity and magnetic anomaly
Authors: Lu Baoliang , Ma Tao , Xiong Shengqing , Wang Wanyin
Published: March 2020

The traditional gravity and magnetic correspondence analysis tends to have high correlation outside the field source area. In order to overcome the disadvantage, we propose a new method for identify the source position and attribute, which is based on similarity and vertical derivative of potential field. In this method, we put forward a new gravity and magnetic correlation parameter (GMCP), which can effectively reduce the range of potential field source and indicate the field intensity information. The distribution of the non-zero areas of GMCP reflects the size of the source. GMCP discriminant parameter values of positive and negative reflect the source attribute. When GMCP is greater than zero, it is a positive correlation indicating that there are high-density and high-magnetization or low-density and low-magnetization homologous bodies in this region; When GMCP is less than zero, it is negative correlation indicating that there are high-density and low-magnetic or low-density and high-magnetic density homologous bodies in this region. GMCP goes to zero, which means no gravity-magnetic homologous geological body. Complex models test results with different noise level and actual data processing of South China Sea Basin show the correctness and validity of identification of the proposed methods.
Modelling of frozen soil thermal conductivity
Authors: He Hailong , He Dong , Kojima Yuki , Flerchinger Gerald , Dyck Miles
Published: March 2020

Frozen soil thermal conductivity (FSTC), which describes frozen soils’ ability to conduct heat under a unit temperature gradient, is a critical parameter of the partial differential heat conduction equation required for numerical studies of coupled heat and mass transport processes and engineering applications in cold and arid regions. FSTC is complicated because it is affected by factors such as temperature, unfrozen water and ice content, and soil texture. Although many FSTC models are available in literature, many of these models were developed using steady-state method that are subject to errors associated with phase change and water redistribution or not even tested with experiments. In addition, no studies have assessed their applicability and reliability. We conducted an extensive literature review and collated over 30 FSTC models. Their performance was evaluated with a large compiled dataset measured with transient method (e.g., heat pulse method), which is less likely to be affected by phase change and water redistribution at unfrozen or low subfreezing temperatures. In addition, a new FSTC model that is capable of accurately estimating FSTC at both unfrozen and frozen conditions is proposed.
Effects of Plants for Gravity Erosion on the Loess Gully Sidewall under Intense Rainfalls
Authors: Zhao Xingyang , Xu Xiangzhou
Published: March 2020

To study the mechanism of vegetation on gravity erosion may provide the theoretical basis for the design of soil and water conservation on the Loess Plateau, China. This study explores the effects of vegetation on the gravity erosion using the models of loess gully sidewall with the slope degree of 70 ° and height of 1.5 m under series of rainfall simulations, in which vegetational and bare lands were used, respectively. The experimental results are shown as follows: (1) The influence of the vegetation on the total amount of gravity erosion may be ignored. The average amount of gravity erosion for each event of rainfall on the vegetational sidewall was only decreased by 12% compared with that on the bare sidewall. (2) The plant had a positive effect on the mass failures after rainfalls. The ratio of the failure mass volume after rainfall to the total on the planted slope was almost 12%, while the ratio on the bare slope was only 1%. (3) The vegetation on the gully sidewall had different influences on the varied types of gravity erosion. Compared with those on the bare land, the average amounts of the avalanche and mudslide on the vegetational slope was decreased by 72% and 69%, respectively. In the meantime, the average amount of landslide in the vegetational slope was increased by 220% compared with that in bare slope. (4) The effects of vegetation on gravity erosion were caused by several factors. The plant roots may reinforce the soil and reduce the amount of gravity erosion, but the self-gravity of the plant and increase of the permeability on the planted slope might increase the gravity erosion. In addition, the soil permeability was increased by the plant roots, which could intensify the landslides. As a result, the plant practice was preferable for the sidewall vulnerable to mudslide. The results may be referred to analyze the mechanism of gravity erosion and design the control of mass failure.
Fore-arc building and destruction: a critical interplay between fluid flow, megathrust strength and tectonic underplating
Authors: Menant Armel , Angiboust Samuel , Gerya Taras , Lacassin Robin , Simoes Martine , Grandin Raphael
Published: March 2020

Subduction zones are the loci of huge mass transfers, including accretion and erosion processes responsible for the long-term formation (and destruction) of fore-arc margins. Study of now-exhumed deep portions of the fore-arc crust revealed km-scale tectonic units of marine sediments and oceanic crust, which have been underplated (i.e. basally accreted) to the overriding plate. However, geophysical observations of this deep process in active subduction zones are unclear and the dynamics of tectonic underplating, as well as its existence, along most of active margins remain controversial. We attempt to shed light on this critical process from the plate interface where tectonic slicing is triggered, to the surface where topographic variations are expected in response to such a mass transfer.

Using high-resolution visco-elasto-plastic thermo-mechanical models, we present with unprecedented details the dynamics of formation, preservation and destruction of underplated crustal nappes at 10-40-km depth in subductions zones. Our results show that subduction segments exhibiting an increasing frictional behaviour control deep accretionary dynamics and that the long-term frictional zonation of the plate interface is stable due to a positive feedback between fluid distribution and effective stress. As a result, discrete underplating events follow one after another for tens of Myr, leading to the formation of a thick duplex structure supporting a coastal topographic high. The rise of this high topography is cadenced by Myr-scale uplift-then-subsidence cycles, characterising each underplating event and the subsequent period of wedge re-equilibration. This periodical evolution is significantly modified by changing the rheological properties of the material entering the subduction zone, suggesting that tectonic underplating is likely a transient process active along most of active margins, depending on severe variations of the hydro-mechanical properties of the plate interface at Myr timescale.
Analysis of a gigantic jet in southern China: morphology, meteorology, storm evolution, lightning and narrow bipolar events
Authors: Yang Jing
Published: March 2020

At about 22:43:30 BJT (Beijing Time = UTC + 8) on 13 August 2016, two amateur astronomers in Shikengkong, Guangdong province, and Jiahe County, Hunan province, respectively, fortunately captured a gigantic jet (GJ) event simultaneously and the GJ exact location could be triangulated. The parent thunderstorm was in a very humid environment [Precipitable Water (PWAT) in excess of 60 mm], featuring high convective available potential energy (CAPE) and weak 0-6 km vertical wind shear. The GJ occurred in the region with the coldest cloud top brightness temperature of −64 °C, suggesting the GJ was associated with strong vertical development of the thunderstorm. Vertical cross sections of radar reflectivity also show that the GJ occurred near the thunderstorm strong convection region as indicated by the results that a region of 25 dBZ (and 35 dBZ) in excess of the local tropopause (overshooting top in the parent thunderstorm) during a time window containing the GJ. The negative cloud-to-ground flashes dominated during the thunderstorm evolution. Three positive narrow bipolar events (NBEs) were detected within 30s before and after the GJ. It indicates that the NBEs were distributed between 11 and 13 km and occurred in the upper and middle layers of thunderstorm with radar reflectivity of 30-35 dBZ.
Seasonal and Diurnal Variations of Carbon Dioxide and Energy Fluxes over Three Land Cover Types of Nepal
Authors: Joshi Bharat Badayar , Ma Yaoming , Ma Weiqiang , Wang Binbin
Published: March 2020

This study examines the seasonal and diurnal variations of carbon dioxide and energy fluxes over three land cover types of Nepal by using the eddy covariance method from March to November 2016. The surface energy balance closures were moderate with the values of about 56%, 61%, and 64% closure at Kirtipur, Simara, and Tarahara sites respectively. The monthly average values of net radiation flux and latent heat flux peaked in August at Kirtipur and Tarahara sites whereas in June at Simara site respectively. The maximum monthly average measured sensible heat flux was 37 W m-2, 43.6 W m-2, and 36.3 W m-2 in April for all the sites whereas soil heat flux was 5.1 W m-2 and 2.9 W m-2 in April for Kirtipur and Simara sites and 6.2 W m-2 in June for Tarahara site. The magnitude of diurnal peak of net ecosystem CO2 exchange (NEE) reached up to 11.04 µmol m-2 s-1 at Kirtipur, 15.04 µmol m-2 s-1 at Simara, and 10.44 µmol m-2 s-1 at Tarahara sites respectively. Among the three study sites, the ecosystem at the Kirtipur site was a good carbon source; the ecosystems at Simara and Tarahara sites were low and good carbon sink in the growing season. In addition, all three different land cover ecosystems were carbon sources when accounted for the measurement period.    
Listening to the Oceans - Effective Techniques for Acoustic Imaging of Oceanic Structure
Authors: Ehmen Tobias , Sheen Katy , Watson Andrew , Brearley Alexander , Palmer Matthew , Roper Daniel
Published: March 2020

Sub-mesoscale variability in the ocean is poorly understood. The challenge is to observe oceanic thermohaline structures on sufficiently fine space and time scales. One promising approach is seismic oceanography, which applies acoustic reflection techniques to image temperature and salinity gradients within the water column. Here, we present three acoustic oceanographic datasets showing different survey methods and assess their advantages and disadvantages.

Firstly, seismic images from a 2D seismic survey in the Sub-Antarctic southwest Atlantic Ocean are shown. The study site is located northeast of Drake Passage, through which Pacific and Antarctic waters flow to merge with those from the Atlantic, making it a key confluence region. The data show detailed images of sub-mesoscale structures in the upper ocean. Future work will make use of coincident XBT measurements to invert the acoustic data and create detailed 2D maps of temperature distribution.

The second dataset contains samples from a 3D seismic survey in the narrowest part of the Mozambique Channel, which is affected by eddies and changes in transport direction and volume. It acts as a pacemaker for the Agulhas Current system, which plays an important role in global heat transport. The dataset, courtesy of Schlumberger Ltd, combines a high signal to noise ratio with a dense data grid, where locations are sampled several times over several days. These data were used to create time lapse images of the area, providing an invaluable insight into the variabilities in the Mozambique Channel.

Despite a lot of advantages, seismic surveys are generally expensive and lack mobility and versatility. Therefore, another acoustic dataset using a hull-mounted EK80 scientific echo sounder, as part of the ICEBERGS project, is presented as a cheaper and more readily available alternative. Images from the West Antarctic Peninsula show thermohaline structures recorded along the actively de-glaciating margin, contributing to the understanding of underlying physical processes that modulate the flux of oceanic heat to the Antarctic cryosphere, and how and where glacial meltwater is discharged, transported and modified. Furthermore, recording and processing difficulties are discussed.

Lastly, acoustic forward modelling work is discussed, which will wrap up the analysis of the methods presented earlier. Based on the three datasets, the use of different acoustic sources will be forward modelled. Through this ideal sources of different sizes and configurations for seismic oceanography can be analysed. Is it feasible to use acoustic sources small enough to be attached to autonomous vehicles, in order to overcome the current difficulties in extracting temporal variability of oceanic fine structure?
Estimating regional to global fresh-brackish-salt groundwater occurrence to support future projections
Authors: Bierkens Marc F.P. , King Jude A. , van Engelen Joeri , Verkaik Jarno , Zamrsky Daniel , Oude Essink Gu
Published: March 2020

Coastal areas, including deltas, are hotspots for population growth and economic development. The rising demand for fresh water that results from these developments has resulted in increased rates of groundwater pumping and an associated enhanced risk of groundwater salinization. Future sea-level rise, climate change and surface sealing due to urbanisation are likely to further increase salinization risk in the near future. In order to correctly project the future fate of fresh groundwater resources in coastal areas under climate and socio-economic change, a correct estimate of the current fresh-brackish-salt groundwater occurrence is imperative. The reason for this is that future salinity projections are very sensitive to initial conditions, due to the large inertia of variable-density groundwater systems. Here, we make a case that estimating the current fresh-brackish-salt groundwater distribution by itself is a major challenge. The presence of conductivity contrasts in coastal areas, the past occurrence of sea-level transgressions and the aforementioned system inertia makes that traditional estimation methods such as interpolations between in-situ salinity observations or equilibrium (steady-state) modelling approaches are incapable of producing sufficiently realistic fresh-brackish-salt groundwater distributions. Using examples from the Rhine-Meuse delta, the Nile delta and the global coast, we show that advancements in airborne geophysics and high-resolution paleo-groundwater modelling may be key to providing distributions that are both realistic and accurate.
Permafrost Dynamics and Indigenous Land Use: Tracing Past and Current Landscape Conditions and Effects of Environmental Change in Sakha/Yakutia, Russia
Authors: Ulrich Mathias , Habeck J. Otto
Published: March 2020

Arctic and Subarctic regions are currently experiencing a more rapid warming than other parts of the Earth. This trend is of particular salience for the Republic of Sakha/Yakutia (East Siberia, Russia) – a vast region where both permafrost research and social science research on animal husbandry have been conducted intensively but thus far separately. Here we are presenting a new project that will combine these disconnected strands and utilize an interdisciplinary approach for examining landscape and land use development under climatic change. Such an approach is topical because effects of past and imminent permafrost degradation on indigenous livelihoods have hitherto been described in rather simplistic terms. The project is designed as a comparative study of two regions in Central and Northeast Sakha/Yakutia. Both areas are susceptible to permafrost degradation, but under divergent zonal and socio-economic conditions (taiga vs. tundra; cattle and horse vs. reindeer husbandry).

A key element of landscape dynamics in both regions is thermokarst, i.e. the thawing of ice-rich deposits leading to soil subsidence and lake formation. Thaw lakes mark an early phase of thermokarst formation; they can serve as indicators for changes in climate, permafrost and vegetation. On the one hand, thermokarst processes have taken place in earlier millennia, notably in the Pleistocene/Holocene transition and during the mid-Holocene climate optimum; in the long run, this has led to the formation of grass-rich depressions (known as alas), creating the preconditions for cattle farming in Central Sakha/Yakutia which emerged at least 500 years ago. On the other hand, thermokarst processes occur at present in connection with global warming; the effects of the latter are likely to produce unprecedented rapid change, with very grave consequences for local land users.

In the analysis of landscape development and land use, we distinguish between two periods: before and after the start of pastoralism and farming. We test the hypothesis that landscape and land-use changes occurred at different scales and speeds in the two zonal settings (Central vs Northeastern Sakha/Yakutia). Furthermore, we postulate that existing forms of land use are going to influence landscape development in different ways: They (i) correlate with, (ii) exacerbate or (iii) neutralize the effects of climate change (owing to different feedback mechanisms). Finally, taking into account the most important demographic, economic and socio-cultural influences, the project will contribute to formulating parameters for modelling the future risks that permafrost degradation exerts on rural communities.
Spatial dependence of floods and droughts: learning from differences in regional and seasonal patterns
Authors: Brunner Manuela Irene , Gilleland Eric , Swain Daniel , Wood Andy , Clark Martyn
Published: March 2020

Regional flood and drought events often have more severe impacts than localized events in terms of damages and costs, the number of affected people, and habitat changes. Understanding which regions may be jointly affected by such extreme events can help us to derive reliable regional risk estimates, plan and manage resource flows, and develop suitable adaptation measures. However, the spatial dimension of droughts and floods is often neglected when deriving hazard estimates and we know little about the processes governing their spatial dependencies. Therefore, we investigate how and why spatial dependencies in droughts and floods vary seasonally and regionally over the United States. We aim to gain new insight into processes governing spatial dependencies of droughts and floods by contrasting their regional and seasonal patterns.

To map regions with a similar seasonal flood and drought behavior, respectively, we introduce a measure of connectedness, which quantifies the number of catchments with which a specific catchment co-experiences flood or drought events. We then summarize the spatial dependencies by identifying regions with a similar flood behavior and regions with a similar drought behavior. To do so, we use a hierarchical clustering procedure on the F-madogram, which is a measure of spatial dependence for extremes. We look at regional and seasonal differences in spatial dependence both for floods and droughts and subsequently compare the two phenomena.

We find that spatial dependence is over all seasons stronger for droughts than for floods. Both types of extremes, however, show regional and seasonal differences in spatial connectedness. Droughts show the strongest spatial dependence in fall. In contrast, the Rocky Mountains show the highest spatial dependence of droughts in winter because of snow accumulation. Very low spatial dependence is found in spring. The seasonal, spatial dependence patterns of floods are opposed to the one of droughts. Spatial flood dependence is highest in spring, especially in mountainous areas, high in winter at the Pacific coast and the Appalachian Mountains, and high in summer in the Rocky Mountains. In contrast, spatial connectedness is very weak in fall.
We conclude that spatial dependence patterns are stronger for droughts than floods because of the slower processes and longer durations associated with the phenomenon.   Furthermore, we conclude that both meteorological and land surface processes such as snowmelt and the availability of soil moisture shape the spatial dependence patterns of each extreme.

 
Characteristics of the dynamical tropopause derived from satellite observations
Authors: Shou Yixuan , Lu Feng , Shou Shaowen
Published: March 2020

                                                                                                                             Abstract

As the products of the complicated interactions and the kinematic, chemical and radiative balances between upper troposphere and lower stratosphere, dynamical tropopause is recognized as a key boundary of atmosphere closely related to weather and climate change. In this study, a high-spatio-temporal-resolution dynamical tropopause pressure estimation scheme based on the measurements from the Advanced Geostationary Radiation Imager boarded on the new generation geostationary satellite of China, FengYun-4A, is proposed. The implemented retrieval model is quantitative validated against ERA-Interim reanalysis dataset showing a high accuracy with the correlation coefficient of 0.9603 and root-mean-square-error of 42.96 hPa. The method is applied to a 1-year period starting in January 2018 over the east hemisphere. The geographic distributions and the seasonal cycle show that the dynamical tropopause height is varied with the latitudes and seasons which has the mean pressure of about 50 hPa over low latitudes and about 300 hPa over the high latitudes where the tropopause height reaches the minimum during March-May. Generally, the folds preferentially occur in the subtropics around 20-40º latitude where the upper fronts located. They are found to have potential connection with the rain band splitting during the Mei-Yu season in East Asia.

Keywords：Dynamic tropopause, FengYun-4 geostationary satellite, WV channels
Parameterization of Coastal Wetlands and Their Role in Back Bay Hydrodynamics
Authors: Cialone Mary , Slusarczyk Gregory
Published: March 2020

This paper will provide an evaluation of the role of coastal wetlands in flood risk mediation by performing hydrodynamic modeling of storm surge in back bays that include various configurations of wetland features. Wetland parameters varied in the research study include the elevation, shape, volume, and vegetation type (represented by the Manning’s friction coefficient) to identify the role of wetlands in reducing back bay flooding.   This information can be used to determine best future management practices for dredged material placement that will serve to maintain and restore wetlands in light of environmental pressures such as climate change, subsidence, storm-induced erosion, boat wakes, and other factors influencing coastal wetland dynamics.

Following Hurricane Sandy in 2012, the United States (U.S.) Congress authorized the large scale North Atlantic Coast Comprehensive Study (NACCS) to address the present and future flood risk to this region. Part of that study was an in-depth numerical modeling and statistical analysis using the ADvanced CIRCulation (ADCIRC) and STeady-state spectral WAVE (STWAVE) models and the Joint Probability with Optimal Sampling (JPM-OS) statistical technique. Following the NACCS, the New Jersey back bays were identified as a high-risk area requiring further in-depth analysis of the effectiveness of surge barriers and coastal wetlands to reduce water levels in the back bays during storms. This paper will discuss the analysis of a set of coastal wetland configurations in the New Jersey back bay region simulated with a set of 10 synthetic storm suite selected from the NACCS study.   Analysis of maximum surge envelopes, water level time series, and characteristics of tropical storm forcing conditions were used to evaluate and compare the effectiveness of the wetland configurations.
Slab deformation in the Bengal basin due to uplift of the Shillong Plateau and the Indo-Burmese Ranges since the Pliocene, constrained by a Dynamic Topo-Tomographic technique
Authors: Rakshit Raghupratim , Wasson Robert James , Bezbaruah Devojit
Published: March 2020

Earth’s topography is mainly controlled by the structures associated with density differences of the lithosphere and the crust. This is related to isostatic topographic processes which work in association with mantle-induced deformation that together leads to dynamic topography. In this study, the dynamic topographic model of Rubey et al. (2017) has been used. The model links sedimentary basin evolution with plate tectonics and mantle convection to deliver a quantitative framework to understand the combined roles of mantle convection and subduction processes in time and space. Dynamic topography is different from surface topographic variations and this difference can be used to explain past deformation. In the Bengal basin, sedimentation began in a deep basin and shelf region that endured continuous subsidence, and then became involved with crustal adjustments due to collision and uplift of the Himalayas and later on the Indo-Burmese Ranges (IBR). In this study, the dynamic topographic changes have been used to understand the past deformational history and plate dynamics beneath the Bengal Basin and IBR. The model has been run in a cloud-computing environment using the global mantle convection code TERRA along with the plate reconstruction Gplates software to reproduce dynamic topographic variations. In such conditions the shelf zones are the dynamic topographic representation. The results for Bengal basin region, 22.5° to 24.5°N latitude and 91.5° to 93.5° E longitude for the past 20Ma, showed that high sedimentation in the subducting basinal setting caused rising dynamic topography from 20 to 5 Ma continuously. A negative trend (i.e. subsidence) is seen for the past 5Ma. Moreover, when total change in subsidence in the last 5Ma is considered, it has been observed that the northern front of the Bengal Basin steeply plunged towards the north at a time when the Shillong Plateau was uplifted. While there has been overall subsidence of the region both the Shillong Plateau and IBR rose. Present day seismic tomographic study indicates the presence of denser magmatic mass beneath Shillong Plateau which might also be linked with Indian oceanic plate subduction. The Dynamic Topo-Tomographic Model suggests that slab bending associated with subduction caused detachment of the denser material zones and change in the slab setting above which the thick sedimentary column is stacked. The rise of the rigid Shillong Plateau caused a deformational front in the sedimentary zone, south of the Plateau, resulting in a steep plunging dynamic topography. 
A problem-based learning approach to increase the awareness of students towards natural risks and hazards: a case analysis
Authors: Occhipinti Susanna
Published: March 2020

The teaching learning of Earth science, particularly the Italian schools, where the research has been developed in the last ten years, has highlighted a widespread lack of knowledge among students, which corresponds to a lack of sensitivity in the common thought towards geological and environmental issues, to its territory, moreover often characterized by widespread disruption phenomena and natural hazards.

 As a consequence, too often the culture of geosciences is understood as a culture of emergencies and not of prevention. It is a priority to promote a widespread culture of natural hazards, the knowledge of natural phenomena, the danger inherent in the geological evolution of the territory, the responsible use of the environment, the perception of phenomenon as part of the dynamics of the Earth. This research presents a path,  defined with disciplinary objectives and specific skills to be developed and monitored, with the aim  to contribute in spreading a greater awareness of the dangers derived from natural phenomena. The training of students must pass through more effective methodological and educational approaches, active teaching, inquiry and investigation, promoting competences and skills. Since it is experienced that the usual transmissive approach of this content is not proving effective, a PBL approach was experimented. The different steps are to raise awareness of the  territory in which one lives, through a geological and historical analysis of the context, the understanding of the natural and inevitable evolution of the territory, the speed and frequency with can occur, the surface that can be affected by different natural phenomena and the transformations into risks factors. Finally, awareness that their knowledge is the basis for preventing and vulnerable contexts is needed.

The research has highlighted the need of new and more effectives educational tools and paths, that has product a widespread awareness towards the need of a repertory of practical activities. These applied, investigative and hands-on activities have shown growth of skills and competences in the involved students. The double result of a greater awareness of environmental dynamics and risks and of greater skills, technical, such as knowing how recognize relationships, and of citizenship, seem to have been achieved.

The  experience has also discoved new needs: the development of a unique and more consistent  epistemology of the discipline,  that is capable of giving links and coherence to phenomena, materials and processes, closely interconnected, but too often not recognized as a disciplinary unicum.
Uncertainties propagation in a hydrological empirical model
Authors: Santos Leonardo , Silva Emerson , Freitas Cíntia , Bacelar Roberta
Published: March 2020

Empirical models have been applied in several works in the literature on hydrological modeling. However, there is still an open question about uncertainties propagation in those models. In this paper, we developed an empirical hydrological model under a Machine Learning approach. Using the Keras interface and TensorFlow library, we trained and tested a Multilayer Perceptron. Our case study was conducted with data from the city of Nova Friburgo, in the mountainous region of Rio de Janeiro, Brazil. Precipitation and river level data were obtained from 5 hydrological stations (in situ), with a resolution of 15 minutes for 2 years. To quantify the propagation of uncertainties, we applied a stochastic perturbation to the input data, following an a priori defined probability distribution, and compared the statistical moments of this distribution with the statistical moments of the output distribution. Based on the proposed accuracy and precision indices, it is possible to conclude, from our case study, that the accuracy is higher but the precision is lower for uniformly distributed stochastic perturbation when compared to an equivalent triangular distribution case.
Evaluating anthropogenic CO2 emissions of China estimated from atmospheric inversions of “proxy” species against ground CO2 measurements
Authors: He Wei , Jiang Fei , Feng Shuzhuang , Nguyen Ngoc Tu , Wang Hengmao , Ju Weimin
Published: March 2020

Accurate estimation of anthropogenic CO2 emissions (ACE) is of great importance for climate change mitigation, however, it is quite challenging.  Co-emitted gases, e.g. CO and NOx, have been reported to be useful for tracking ACE. Here we estimated ACE of China based on “proxy” species (i.e. CO and NOx) inversions with emission ratios of CO2 and the “proxy” species and evaluated the estimates using ground CO2 measurements of three tower stations in population-dense areas based on the Stochastic Time-Inverted Lagrangian Transport (STILT) modeling driven by the Global Data Assimilation System (GDAS) meteorology. An ensemble of ACE of China were estimated from different combinations of anthropogenic CO or NOx flux estimates and emission ratios, where the CO or NOx fluxes were estimated from in-situ measured concentration data or satellite column concentration data, and the emission ratios were derived from two emission inventory datasets, i.e. multi-resolution emission inventory for China (MEIC) and Peking University global emission inventories (PKU-FUEL). We found all CO2 simulations with “proxy” based ACE estimates (either using in-situ or satellite data) in one year clearly fitted better to observations than those with inventory datasets did, especially during winter and early spring. Meanwhile, large mismatches between simulations and observations were found for some periods, which indicated the use of CO or NOx to track ACE may be not suitable for a whole year. Our preliminary result demonstrates the potential to use atmospheric “proxy” species to track anthropogenic CO2 emissions in China.

 
Large-scale particle acceleration during magnetic reconnection in solar flares
Authors: Li Xiaocan , Guo Fan
Published: March 2020

Magnetic reconnection is a primary driver of magnetic energy release and particle acceleration processes in space and astrophysical plasmas. Solar flares are a great example where observations have suggested that a large fraction of magnetic energy is converted into nonthermal particles and radiation. One of the major unsolved problems in reconnection studies is nonthermal particle acceleration. In the past decade or two, 2D kinetic simulations have been widely used and have identified several acceleration mechanisms in reconnection. Recent 3D simulations have shown that the reconnection layer naturally generates magnetic turbulence. Here we report our recent progresses in building a macroscopic model that includes these physics for explaining particle acceleration during solar flares. We show that, for sufficient large systems, high-energy particle acceleration processes can be well described as flow compression and shear. By means of 3D kinetic simulations, we found that the self-generated turbulence is essential for the formation of power-law electron energy spectrum in non-relativistic reconnection. Based on these results, we then proceed to solve an energetic particle transport equation in a compressible reconnection layer provided by high-Lundquist-number MHD simulations. Due to the compression effect, particles are accelerated to high energies and develop power-law energy distributions. The power-law index and maximum energy are both comparable to solar flare observations. This study clarifies the nature of particle acceleration in large-scale reconnection sites and initializes a framework for studying large-scale particle acceleration during solar flares.
Transforming understanding of paleomagnetic recording: Insights from experimental observations of laboratory aged thermal remanences
Authors: Tauxe Lisa , Santos Christeanne , Zhao Xiang , Roberts Andrew
Published: March 2020

Néel theory (doi: 10.1080/0001873550010120 ) predicts that natural remanent magnetizations (NRMs) of thermal origin will be nearly linearly related to the magnetic field in which they are acquired for field strenghts as low as the Earth's. This makes it in principle possible to estimate the strength of ancient magnetic fields. In practice, however, recovering the ancient field strength is complicated. The simple theory only pertains to uniformly magnetized (single domain, SD particles). While SD theory predicts that a magnetization acquired at a temperature T should be demagnetized by zero-field reheating to T, yet failure of this “reciprocity” requirement has long been observed and the causes and consequences for grains with no domain walls are unknown. Recent experiments (Shaar and Tauxe, doi: 10.1073/pnas.1507986112 and Santos and Tauxe, doi:10.1029/2018GC007946) have demonstrated that, in contrast to the stability of SD remanences over time, the remanence in many paleomagnetic samples typically used in paleointensity experiments are unstable, exhibiting an "aging" effect in which the unblocking temperature spectrum changes over only a few years.  This behavior is completely unexpected from theory. Solving these mysteries is key to cracking the problem of paleointensity estimation. In this presentation we will demonstrate that it is a shift in unblocking temperatures observed over even relatively short time intervals (two years) in certain samples that leads to the failure of reciprocity which in turn limits the ability to acquire accurate and precise estimates of the ancient magnetic field. From rock magnetic experiments (xFORCs) it seems likely that magnetic grains larger than the highly stable single vortex state are the source of the non-ideal behavior. This non-ideal behavior which leads to differences between known and estimated fields that can be rather large (up to 10 μT) for individual specimens, does appear to lead to a bias in field estimates.  It is unclear how this behavior can be compensated for using the most common paleointensity estimation methods.   
Impact of air transport and secondary formation on haze pollution in the Yangtze River Delta: In situ online observations in Shanghai and Nanjing
Authors: Sun Peng
Published: March 2020

Despite frequent haze pollution in China in recent years, our knowledge of regional pollution episodes associated with air transport and synoptic weather systems is limited. In this study, we conducted two intensive campaigns simultaneously to measure the highly time-resolved chemical composition of fine particles (PM2.5) in suburban Shanghai and Nanjing during the winter of 2017 and the summer of 2018. The average PM2.5 mass concentrations were 53.9 (65.7) µg m-3 and 32.8 (37.3) µg m-3 in Shanghai (Nanjing) in winter and summer, respectively. In winter, extreme haze episodes were observed synchronously with enhanced contributions of nitrate at both sites and of low-volatile oxidized organic aerosol (LV-OOA) in Shanghai. Long-range transport from Northern China was demonstrated to play an important role in the episodes, which occurred simultaneously at both sites. Influenced by the cold fronts, Nanjing had a relatively longer pollution duration, whereas Shanghai exhibited faster PM increases. In summer, air masses passing though the city-clusters of the YRD were responsible for the pollution episodes. Low wind speeds, which favored the accumulation of primary aerosols, and strong photochemical activity indicated by high ozone level, which promoted the formation of secondary aerosols, resulted in elevated contributions of nitrate, Hydrocarbon-like organic aerosol (HOA) and semi-volatile oxidized organic aerosol (SV-OOA) to PM in Shanghai. In addition, a pollution episode dominated by increases of nitrate and organic aerosols was observed in Nanjing two days later despite the clean situation in Shanghai. Our results highlight the importance of regional or sub-regional emission control to mitigate haze pollution in city clusters, such as the YRD in Eastern China.
The architecture of an intrusion in magmatic mush
Authors: Carrara Alexandre , Burgisser Alain , Bergantz George
Published: March 2020

Magmatic reservoirs located in the upper crust have been shown to result from the repeated intrusions of new magmas, and spend most of their dwelling time as cristal-rich mush. Despite advances in our understanding of the physical processes that may occur in a magma reservoir, the architecture of the intrusion into a mush remains poorly constrained. The geometry of such intrusions, however, may greatly affect the thermal and compositional evolution of the magmatic reservoir. We performed numerical simulations coupling computational fluid dynamics with the discrete element method to identify the geometry and emplacement dynamics of an intrusion in a mush, and the relevant physical parameters controlling it. Our results show that the intrusion geometry is to first-order controlled by the density contrast between the melt phases of the intruded and resident materials rather than the bulk density contrast as usually considered. When the melt phase of the intruded materials is denser than that of the host, the intrusion ponds at the base of the mush and is emplaced as a horizontal layer. However, when the intruded melt is lighter, the intrusion rises through the mush forming a Rayleigh–Taylor instability. In the absence of density contrast between the two melts, the intrusion fluidizes the host crystal network and slowly ascends through the mush. The presence of a viscosity contrast between the intruded and resident materials as well as the intrusion injection velocity were found to have less of an influence on the final geometry and intrusion dynamics in mush. In addition, we analyzed the eruptive sequence of well documented eruptions involving an intrusion as a trigger, and found good agreement with our modeling results. This study sheds light on the importance of explicitly considering granular mechanisms and the relative motion between the crystals and the melt phase when studying the physical processes of magmas and mush.
A closer look at the relationship between slab (un)bending and double seismic zone seismicity
Authors: Sippl Christian , John Timm , Schmalholz Stefan
Published: March 2020

The origin of double seismic zones (DSZs), parallel planes of intraslab seismicity observed in many subduction zones around the globe, is still highly debated. While most researchers assume that fluid release from prograde metamorphic reactions in the slab is an important control on DSZ occurrence, the role of slab unbending is currently unclear.
Slab bending at the outer rise is instrumental in hydrating the downgoing oceanic plate through bend faulting, and is evident from earthquake focal mechanisms (prevalence of shallow normal faulting events). Observations from NE Japan show that focal mechanisms of DSZ earthquakes are downdip compressive in the upper and downdip extensive in the lower plane of the DSZ, which strongly hints at slab unbending. This coincidence of slab unbending and DSZ seismicity in NE Japan has given rise to several models in which unbending forces are a prerequisite for DSZ occurrence.

To globally test a potential correlation of slab unbending with DSZ seismicity, we derived downdip slab surface curvatures on trench-perpendicular profiles every 50 km along all major oceanic slabs using the slab2 grids of slab surface depth. We here make a steady-state assumption, i.e. we assume that the slab geometry is relatively constant with time, so that the downdip gradient of slab curvature corresponds to slab (un)bending. We compiled the loci and depth extent of all DSZ observations avalable in literature, and compare these to the slab bending or unbending estimates.

Preliminary results indicate that while there is a clear correspondence between the depth of slab unbending to DSZ seismicity in the Japan-Kurile slab, most other slabs do not show this correlation. Moreover, some DSZs deviate from the above-mentioned focal mechanism pattern and exhibit downdip extension in both planes (e.g. Northern Chile, New Zealand). It appears that the global variability of slab geometries in the depth range 50-200 km is larger than anticipated, and DSZ seismicity is not limited to slabs where unbending is prevalent at these depths. The Northern Chile case is especially interesting because focal mechanisms there not only do not fit the pattern observed in NE Japan, but also can not be explained with the current slab geometry alone. This could indicate a direct influence of ongoing metamorphic reactions on focal mechanisms (e.g. via volume reduction and densification), or it may be a hint that our steady-state assumption is invalid for the Nazca slab here (i.e. that it is in the process of changing its geometry).