bluuebunny/crossref_metadata_2025 huggingface dataset:
Constraints on the formation and nature of the Hellenic Triassic rift-related lavas
Authors: Koutsovitis Petros , Magganas Andreas , Ntaflos Theodoros , Koukouzas Nikolaos , Rassios Anne Ewing
Published: March 2020

Triassic volcanism developed during the rifting stage of Gondwana, with subsequent formation and development of the Tethyan oceanic basin as the Pangaea (Apulia promontory) and Pelagonia continents spread apart. Volcanic rocks formed from this activity outcrop over all mainland Greece, comprising of trachybasalts and basaltic trachyandesites. Relatively immobile to the effects of alteration processes major and trace element abundances classify the volcanics into OIB and E-MORB lavas. They have been distinguished based upon their: i) LREE contents, ii) silica-saturation index, iii) Zr/Nb and Nb/Y ratio values; iv) Th, U, and Ta contents v) geotectonic discrimination diagrams. Their geochemistry indicates that most rocks were affected by moderate to extensive differentiation processes, mostly expressed by clinopyroxene fractionation. Some of the OIB and E-MORB volcanics are considered as being primitive undersaturated, displaying relatively low SiO2 and S.I. index values and also high Mg# and CaO/Al2O3 ratios.

Calculated average mantle potential temperatures are comparable (1410 ˚C OIB; 1370 ˚C E-MORB), with melt fractions estimated at 3-5% for primary OIB magmas and 6-8%for primary E-MORB magmas. An asthenospheric origin is inferred for the OIB lavas, with melting in the garnet stability field (75-95 km; 2.5-3.0 GPa), whereas E-MORB parent magmas were generated with shallower melting processes within the garnet/spinel (transitional) stability field (55-70 km; 1.8-2.2 GPa). Lithospheric attenuation and extension, followed by subsequent asthenospheric upwelling of the mantle was enhanced due to lithospheric thinning as rifting progressed. The rather high calculated partial melting degrees and the observed relatively thick lava formations account for fast-spreading rift settings, consistent with the opening of the Tethys during the Triassic. Temperature results indicate that the Hellenic Triassic rift-related magmas were generated from mantle at ambient temperature, precluding a mantle plume-based scenario or of thermal anomalies.
From Drought to Flood: The Life Cycle of Drought
Authors: Gibson Abraham , Verdon-Kidd Danielle , Hancock Greg , Willgoose Garry
Published: March 2020

Australia’s climate is widely recognised as oscillating between drought and flood, with these cycles potentially intensifying under climate change. To reduce the impacts of both, being better prepared for, and more resilient to climate extremes is required . To develop management strategies that address these issues, improved prediction and an understanding of both drought onset and termination is required. Here, a whole-catchment assessment of drought from onset through to propagation and then termination for a 585 km2 agricultural catchment in eastern Australia was conducted. Meteorological and hydrological measurements of drought were combined with vegetation and soil moisture data to assess how the catchment responded to drought and then recovered during drought termination. Thirteen meteorological drought periods persisting more than six months were identified during this period. During these, vegetation health, soil moisture and streamflow declined, however, all indicators recovered quickly when rainfall surplus returned. Drought onset was tightly coupled to the combined state of large-scale ocean-atmosphere climate drivers and termination was caused by synoptic-scale events. The combination of climatic factors, topography, soils and vegetation are believed to be what makes the study catchments more resilient to drought than others in eastern Australia. The study diversifies traditional approaches to assessing hydrological extremes at the catchment-scale by examining the drought to flood cycle using a range of globally available measures. This is a key step towards improved drought prediction and management.
Assessing numerical impacts on stratospheric dynamics and transport using the age of air and the leaky pipe theoretical model
Authors: Gupta Aman , Gerber Edwin , Lauritzen Peter
Published: March 2020

Accurate representation of tracer transport --- the movement of trace constituents by the atmospheric flow --- continues to be a challenge for climate models. Differences in the resolved circulation, biases due to physical parameterizations, and differences in the numerical representation of trace gases result in large variations in transport, even among state-of-the-art climate models. These differences result in disagreement among model projections of the evolution of stratospheric ozone throughout the 21st century particularly in the recovery of the Antarctic ozone hole. In addition to transport, the delicate momentum balance in the upper-troposphere and lower-stratosphere (UTLS) also presents a stiff challenge for model numerics, exposing the impacts of numerical dissipation, the resolution of waves, and the consequences of imperfect momentum conservation. Biases in this region impact the global circulation, e.g., influencing the extratropics jets and stratospheric polar vortices, and alter the transport and exchange of trace gases between and through the troposphere and stratosphere.

 

In this study, we compare 2 modern dynamical cores (dycores) that employ very different numerics: the cubed sphere finite volume (CSFV) core from GFDL and the spectral element (SE) core from NCAR-CAM5. We force these dycores using identical Held-Suarez diabatic forcing in the troposphere and Polvani-Kushner diabatic forcing in the stratosphere, varying the horizontal and vertical resolution. We observe significant differences in circulation, between the two models at high vertical resolution in the lower and middle tropical stratosphere. While the finite volume core is relatively insensitive to any changes in vertical resolution, the PS and SE dycores resolve considerably different tropical stratospheric dynamics at high vertical resolution (80 levels). These models develop QBO-like westerly winds in the tropics and induce a secondary meridional circulation in the tropical stratosphere, which sets of transport between the models. Using the theoretical leaky pipe transport model we analyze and separate out the transport differences due to differences is diabatic circulation and isentropic mixing and infer that this secondary circulation strikingly modulates stratospheric tracer transport (age of air) by altering the tropical-extratropical mixing, and impacts the extratropical circulation through the subtropical jets. Implications for comprehensive atmospheric modeling are discussed.
Retrieving the Reflection events from passive signals
Authors: Hariri Naghadeh Diako , Bean Chris
Published: March 2020

To create virtual shot gather from passive signals it is essential to cross-correlate all the signals with the reference trace. Since surface sources dominate the origin of seismic noise, the correlated sections are highly dominated by surface waves. If the target is surface wave inversion general cross-correlation will suit the target. But if the extraction of body waves from those signals is the main objective, coherent ground roll events mask the body waves making it difficult to extract them. To tackle this issue a frequency-spatial nonCoherent filter (FX-NCF) plus a post-correlation processing module are introduced. FX-NCF is a prediction filter and the filter operator is a function of frequency, station interval and the slope of the interested event. In the frequency domain, the filter is looking for the prediction of n-th trace coherence spectrum from the (n-1)-th signal’s coherence spectrum by minimizing the objective function. Hybrid norms used to minimize the error. The coherence spectrum of each trace is the coherency between the reference signal and the desired trace. Applying the FX-NCF on 2D real recorded passive signals shows its superiority over general cross-correlation, deconvolution interferometry, cross-coherence and multi-taper-method-coherence-estimation methods in highlighting surface and body waves also improving the signal-to-noise (S/N) ratio. To show the necessity of post correlation processing (before applying on real recorded signals) to highlight reflection events, hyperbolic Radon transform (HRT) as a suitable post-correlation module applied on correlated section due to applied FX-NCF on simulated passive signals from a simple 2D synthetic model. The result encouraged us to apply the same hybrid modules (FX-NCF plus HRT) on real recorded passive signals to reconstruct wanted reflection events.
The quantification of development processes of explosive cyclones over Northwestern Pacific and Atlantic in boreal winter
Authors: Kang Joonsuk , Son Seok-Woo
Published: March 2020

A method utilizing a prognostic potential vorticity (PV) inversion is designed and applied to quantify the processes that contribute to the explosive cyclone (EC) development over Northwestern Pacific and Atlantic in boreal winter. The ECs deepening in the two remarked regions are identified and tracked, by using the automated tracking method on ERA-Interim reanalysis data over the period of 1979–2017. The quantification process first involves time differentiation of linearized potential vorticity (PV), which results in a linear function of geopotential height tendency. It is then equated with the PV tendency equation that consists of mean and transient advection terms to represent dynamical processes that contribute to EC development. The quantification, finally, is performed through the inversion of PV tendency budgets, which yields corresponding geopotential height tendency. The results indicate that EC development is primarily caused by zonal advection of PV anomalies by mean flow (~65%) and diabatic production of PV (~40%), with some negative factors in both regions. The former contributes more for ECs deepening over Northwestern Atlantic (~71%) than Northwestern Pacific (~60%), whereas the latter contributes to a similar extent.
Evaluation of snow albedo feedback simulated by CMIP6 coupled climate models
Authors: hu jiangling , ji duoying
Published: March 2020

As the land surface warms, a subsequent reduction in snow and ice cover reveals a less reflective surface that absorbs more solar radiation, which further enhances the initial warming. This positive feedback climate mechanism is the snow albedo feedback (SAF), which will exacerbate climate warming and is the second largest contributor to Arctic amplification. Snow albedo feedback will increase the sensitivity of climate change in the northern hemisphere, which affects the accuracy of climate models in simulation research of climate change, and further affects the credibility of future climate prediction results.

Using the latest generation of climate models from CMIP6 (Coupled Model Intercomparison Project Version 6), we analyze seasonal cycle snow albedo feedback in Northern Hemisphere extratropics. We find that the strongest SAF strength is in spring (mean: -1.34 %K-1), second strongest is autumn (mean: -1.01 %K-1), the weakest is in summer (mean: -0.18 %K-1). Except summer, the SAF strength is approximately 0.15% K-1 larger than CMIP5 models in the other three seasons. The spread of spring SAF strength (range: -1.09 to -1.37% K-1) is larger than CMIP5 models. Oppositely, the spread of summer SAF strength (range: 0.20 to -0.56% K-1) is smaller than CMIP5 models. When compared with CMIP5 models, the spread of autumn and winter SAF strength have not changed much.
Statistical characteristics of the morphological parameters of Chinese cities and the application in WRF model
Authors: Zhang Ning
Published: March 2020

With ever-increasing urban populations, cities face a serious of climatic and environmental issues such as urban heat islands (UHIs), air pollution and extreme weather. Urban morphological parameters can improve the performance of WRF model in urban areas. A 3-D urban canopy parameters (UCPs) are calculated for the 62 major cities in China.Chinese cities could be divided into two types (single_peak and double_peak) based on the distribution of building height, and the two peaks are located at level 2 (about 5m) and level 6 (about 20m). The mean number of buildings in single_peak city is much larger than that of double_peak.The building height of double_peak cities is larger than that of single_peak cities, but the building plan area fraction, building surface area to plan area ratio and frontal area index are opposite. The WRF default setting underestimates the street width but overestimates the building width of Chinese cities. The UCPs improve the simulation of nocturnal 2-m surface air temperature and 10-m wind speed in the testing cases.
Detrital zircon U-Pb and Hf isotope studies of the Paleozoic successions in the Korean Peninsula: Implications for the provenances and tectonic evolution of the Phanerozoic orogenic belts
Authors: Jang Yirang , Kwon Sanghoon , Kim Sung Won
Published: March 2020

Paleozoic orogenic belts developed between the basement rocks in the southern Korean Peninsula records important information to reconstruct the tectonic evolution of East Asia. Here we present SHRIMP and LA–(MC)–ICP MS U-Pb ages and Hf isotopes of detrital zircon grains from the Paleozoic metasedimentary successions that are incorporated into the major Phanerozoic orogenic belts (Okcheon and Hongseong-Imjingang Belts) in South Korea, providing new insights into provenances and tectonic evolution during the Paleozoic period. Based on the internal structures of the zircons from all the samples, they are mostly derived from igneous source rocks, showing two distinct spectra patterns in their presence/absence of Neoproterozoic ages. Our results suggest that (1) the presence/absence of the Grenville-age (ca. 1.3–0.9 Ga) detrital zircons and Hf data from the Early Paleozoic Joseon Supergroup in the Okcheon Belt suggest their derivations from different peripheral clastic provenances at least after the Early Cambrian, (2) ages and Hf isotope signatures of dominant Early Neoproterozoic and Silurian-Devonian detrital zircon populations from the Middle Paleozoic metasedimentary rocks in the Hongseong-Imjingang Belt reflect magmatic history involving juvenile input and crustal reworking, and (3) zircons from the Late Paleozoic Pyeongan Supergroup in the Okcheon Belt display dominant Paleoproterozoic and Carboniferous-Permian ages with Hf patterns showing vertical mixing trends between juvenile and recycled crustal material. These results, integrated with U-Pb and Hf isotope data from other parts of the Korean Peninsula and the Chinese cratons, will eventually help to understand the spatial and temporal relations of basins and orogenic belts in the Korean Peninsula, and will further provide important clues about Paleozoic evolution of the Korean Peninsula in relation to the tectonic history of East Asia.
Joint probability of storm surge and wave along Hainan Island based on bi-variate copulas analysis
Authors: Cheng Meng , Fang Weihua
Published: March 2020

Tropical cyclones (TCs) often bring multiple hazards to offshore and onshore areas, including wind, rainfall, riverine flood, wave and storm surge. These hazards usually interact with each other and cause greater amplified hazard intensity. In the coastal areas, wave may damage coastal defense system like sea walls and dykes, and overtopping storm surge could hence become severe flooding due to the breach of the dykes. The probability distributions of wave and surge, as univariate respectively, have been studies and used in the design in various research. However, far less investigations on their joint probability distribution have been carried out in the past.

In this study, the dataset of hourly surge height, and significant wave height of 89 TC events impacting along Hainan Island during 1949~2013 was obtained, which are simulated numerically with ADCIRC and SWAN respectively. Following that, 4 types of probability distributions for univariate were used to fit the marginal distribution of storm surge and wave. Secondly, Frank, Clayton and Gumbel Copula were tried to construct the joint probability distribution of wave and surge, and the optimal Copula was determined by K-S test and AIC, BIC criteria. Based on the optimal Copula selected for each area of interest, the joint return period of wave and surge was estimated.

The results show that, 1) the annual maximum value of the storm surge height and significant wave height of Hainan Island has a relatively obvious geographical distribution regularity. 2) GEV and Gumbel are the most optimal distribution for storm surge height and significant wave height respectively. 3) Clayton Copula is the best model for fitting joint probability of storm surge and wave. The estimated joining probability distribution can help the determination of design standard, and typical TC disaster scenario development.
Hydrochemical characteristics and processes for salinity sources of the shallow groundwater along the coast of northern Jiangsu, China
Authors: Hou Guohua , Gao Maosheng , Dang Xianzhang
Published: March 2020

Abstract：In order to find out the hydrochemistry and salinization of shallow groundwater in coastal aquifers, 76 ground- and surface-water samples, contained phreatic upper water, phreatic water, confined water, river water and seawater were collected for major ion and isotope analysis(2H/18O, 14C). The results show that: (1) The phreatic upper groundwater changes along the general flowpath towards the coast from fresh(TDS <1 g/L), brackish (1–3 g/L) to saline (3–50 g/L). The phreatic water and first confined water are basically unchanged, but mainly saline water. (2) Shallow groundwater is mainly derived from atmospheric precipitation and undergoes significant evaporation processes. The phreatic upper groundwater is mainly derived from modern atmospheric precipitation recharge. The phreatic water and first confined water are mainly derived from precipitation replenishment during the warm period of the Holocene and some relict seawater. (3) The processes for salinity sources of the shallow groundwater are that oceanic evaporative salt formed during the transgression and retreat period since the late Pleistocene was dissolved by atmospheric precipitation and river water for many periods. The salt in phreatic upper water of the estuary area is also derived from modern seawater intrusion.

Key words: coastal zone; groundwater; hydrochemistry; hydrogen and oxygen stable isotope; salinization

_____________

 

Corresponding author. Qingdao Institute of Marine Geology, China Geologic Survey, Qingdao, 266071, PR China.

E-mail address: gms532@163.com.

This study was financially supported by the National Natural Science Foundation of China (41977173), China Geology Survey project(DD20189503) and National key research and development projects(2016YFC0402801)
Long-term change of tropical cyclones activity and its potential impacts on Vietnam
Authors: Ho Thi Ngoc Huyen , Wang S.-Y. Simon , Balaguru Karthik , Lim Kyo-Sun , Yoon Jin-Ho
Published: March 2020

Tropical cyclones (TCs) are the most dangerous climatic events in Vietnam. Recently, most of the studies have focused on TCs frequency and intensity, yet the rainfall events caused by them have not been got adequate attention. We show here the long-term change of TCs activity developed in both the South China Sea and the Philippines Sea and estimated its potential impacts during the period of 1977 – 2016. The trend analysis reveals that TCs have not shown obvious variability in numbers and destructiveness ability, whereas the TCs-induced rainfall events and its spatial distribution exhibit more complex patterns in different parts of Vietnam. For example, increasing rainfall amounts in the northern part is likely caused by TCs despite the fact that the TCs frequency did not exhibit much of significant changes. Evaluating rainfall caused by TCs activity is of great practical significance for Vietnam. Our findings suggest that in addition to the TCs frequency and intensity, TCs-induced rainfall events should be considered and included in future preparedness and response plans both on regional and national scale.
Rainfall Runoff Hydrograph Prediction Using Dynamic Wave Based Instantaneous Unit Hydrograph
Authors: Jeong Minyeob , Kim Jongho , Kim Dae-Hong
Published: March 2020

A method to predict runoff based on the instantaneous unit hydrograph and dynamic wave approximation is proposed. The method is capable of generating IUH of a watershed without the need of observed rainfall and runoff data, and only topography and surface roughness of a watershed are needed. IUHs were generated using a dynamic wave model and S-hydrograph method, and IUH generated was a function of both watershed and rainfall properties. The ordinate of IUH depends on the rainfall intensities, and the peak value of IUH was proportional to the rainfall intensity while the time to peak of the IUH was inversely proportional to the rainfall intensity.  Corresponding IUHs for different rainfall intensities were used to generate runoff hydrographs. Since the IUH is generated using a dynamic wave model, it can be a tool to physically simulate the rainfall-runoff processes. Also, nonlinear rainfall-runoff relationship can be taken into account by expressing IUH as a function of rainfall excess intensity. Several test results in ideal basins and in a real watershed show that the proposed method has a good capability in predicting runoff, while several limitations remain.

Keywords: rainfall-runoff, instantaneous unit hydrograph, dynamic wave model
Magnetic and thermal constraints on the spatial distribution of continental seismicity
Authors: Jiao Liguo , Lei Yu
Published: March 2020

Recent fast developments of satellite magnetic observations facilitate global Lithospheric Magnetic Field (LMF) modelling and their applications to subsurface tectonics. Here, the vertical component (Bz) of LMF at an altitude of 200km in Mainland China and surroundings is calculated from two global LMF models NGDC-720 and EMM2017. Next, Bz is used to invert the Curie Point Depth (CPD) by Equivalent Source Dipole (ESD) forward and Nonlinear Conjugate Gradient Method (NCGM) inversion scheme. Then, the surficial Heat Flux (HF) is derived by a simple one-dimensional steady heat conduction equation from the CPD distribution. At last, the continental seismicity is compared statistically to Bz, CPD and HF. Our essential conclusions are as follow: 1) Histograms and boxplots show that most (81.8%) earthquakes (EQs, Ms≥5.0) occurred in negative Bz areas, and more than a half (53.2%) number of EQs (corresponding to an energy percent of 94.6%) occurred inside areas with Bz between -5 and -3nT, in a period between 2004 and 2007, which is the same with the satellite data collection. When the time span is extended (most to 110 years), these phenomena maintain while weaken; 2) Most (88%) EQs occurred in areas with CPD between 10 and 30km, while only a few (7% and 5%) occurred in shallow (<10km) and deep (>30km) CPD areas, in a period between 2000 and 2010; 3) EQs seldom occurred inside cold areas (HF<50mW/m2), and are prone to occur in warm areas (HF>120mW/m2). EQs are also prone to occur along the boundaries of warm or cold areas. The mechanism of the correlations between EQs and Bz, CPD and HF maybe the lithospheric strength jumps caused by the temperature variations at boundaries between blocks with different CPDs.
Continental sediment sources, sinks, and the human factor in large tropical rivers: the case of South America
Authors: Latrubesse Edgardo
Published: March 2020

Knowledge of river basins sediment yield at a continental scale, and accumulation in sedimentary basins (sinks) provides useful information for quantitative models of landscape evolution, geochemical and sediment mass balance studies for estimating continental and regional net erosion intensities, to quantify the fluxes of sediments exported to the Ocean. It also provides a crucial understanding of a variety of environmental and engineering applications. Although several estimations exist on the sediment fluxes of large rivers,  the role of continental sedimentary basins and fluvial environments (large rivers and megafans) acting as major sedimentary sinks is still partially understood. The assessment is additionally complicated by the human activities that contribute to modifying the original rates of production, trapping, and transference of sediments at continental scales.

South America is an ideal place to discuss these aspects because it contains a) the longest mountain chain on the planet, the Andes; b) the longest and more extensive foreland systems, c) huge lowlands/plains, d) the largest rivers, e) the largest megafans, f) major intracratonic, sedimentary basins. Simultaneously, the rivers basins are being submitted to extreme environmental pressure by the construction of dams, land use/land cover changes (LULC),  mining, etc.

Here, quantitative results on continental sources and fluxes are presented, with a focus on the role of the biggest source areas and the largest trapping systems at a continental scale such as megarivers and megafans.  Particular attention is devoted to sediment budgets of large rivers that have been intensively modified by human activities in recent times (dams, deforestation, etc) or that are vulnerable to the potential construction of dams.  

 
Study of changes of thermal neutrons intensity of lithospheric origin for the diagnostics and forecast of earthquakes
Authors: Antonova Valentina , Kryukov Sergey , Lutsenko Vadim , Malimbaev Andrey
Published: March 2020

Studies of variations in the intensity of thermal (epithermal) neutrons at the high-mountain station of cosmic rays near the fracture of the earth's crust (3340 m above sea level, Northern Tien- Shan) showed the promising of using them for the diagnosis and forecast of earthquakes in seismically active regions. A method is proposed for distinguishing features of changes in the intensity of thermal neutrons of lithospheric origin against the background of variations caused by solar and atmospheric disturbance sources. However, a necessary condition for this is the synchronous registration of high-energy neutrons of galactic origin.

It is known that neutrons in the Earth’s atmosphere arise mainly as a result of the interaction of primary cosmic radiation with the nuclei of air atoms. Statistical analysis of neutron measurements during effective solar events (coronal mass ejections), changes of atmospheric pressure confirmed the genetic relationship of thermal neutrons near the Earth's surface with high-energy neutrons of galactic origin and the similarity of the spectral composition of their variations. The difference is observed only in the range (2·10-7÷2·10-6)Hz. Variations with the period of 29.5 days (synodic lunar month), due to the gravitational influence of the moon, are present throughout the 12-year period of research of thermal neutrons. The amplitude and its changes were determined by the method of complex demodulation. The periodicity of 29.5 days is absent in the spectrum of high-energy neutrons variations.

 Analysis of experimental data during of seismic activity showed the frequent breakdown of the correlation between the intensity of thermal and high-energy neutrons. The cause of this phenomenon is the additional thermal neutron flux of the lithospheric origin, which appears under these conditions. Simple statistical processing of measured parameters makes it possible to exclude variations of interplanetary and atmospheric origin in the intensity of thermal neutrons and to isolate changes caused by seismic processes.

 We used this method for analysis of thermal neutrons intensity during earthquakes with intensity ≥ 3b in the vicinity of Almaty which took place in 2007-2018. The catalog includes 30 events. The increase of thermal neutrons flux was observed for ~ 60% of events. However, before the earthquake the increase of thermal neutron flux is only observed for ~ 25-30% of events. The amplitude of the additional thermal neutron flux of the lithospheric origin is equal to 5-7% of the background level. Sometimes it reaches values of 10-12%.

The analysis of our catalog of earthquakes in the vicinity of Almaty also showed that 70% of these events occurred during the full moon or new moon (+/- 2 days).
Linking high-temperature metamorphism, charnockite formation, and fluid-rock interaction during the waning stage of Paleoproterozoic hot orogeny in the Yeongnam Massif, Korea
Authors: Lee Yuyoung , Cho Moonsup , Kim Taehoon
Published: March 2020

Incipient charnockites are orthopyroxene-bearing granitic gneisses that are commonly considered to be a product of infiltration of CO2-rich fluids during high temperature dehydration in the granulite terrane. Greenish patches of incipient charnockite are locally present and hosted by granitic gneiss in the Sancheong-Hadong anorthosite complex, southern Yeongnam Massif. Both lithologies are foliated and show a variety of field evidence for partial melting and melt crystallization. Granitic leucosomes and biotite or garnet-rich residua are ubiquitous along ductile shear bands and/or penetrative foliations in the gneiss. These melt-related features are consistent with mineral assemblages and reaction textures, characterized by biotite-breakdown melting. Based on phase equilibria modeling, P-T conditions of peak metamorphism are constrained at 3.5–8.5 kbar and 770–840 °C. Sensitive high-resolution ion microprobe U-Pb analyses of inherited cores and overgrowth rims of zircon from a charnockite yielded the weighted mean 207Pb/206Pb ages of 1880 ± 5 Ma and 1861 ± 4 Ma, which are interpreted as the times for magmatic crystallization and subsequent anatexis of granitic protolith, respectively. This timeline is consistent with that determined from the host granitic gneiss. In contrast, monazite grains from the charnockite and granitic gneiss yielded the weighted mean 207Pb/206Pb ages of 1842 ± 8 Ma and 1838 ± 18 Ma, respectively, suggesting that an influx of aqueous fluid took place ~20 m.y. after the crystallization of granitic melt. Both charnockitic and granitic gneisses underwent high-temperature metamorphism and partial melting at ~1.86 Ga, and were followed by fluid influx at ~1.84 Ga, apparently characterized by monazite recrystallization in association with the retrogression of orthopyroxene to ferromagnesian amphibole-rich aggregates in the former. Thus, the timing and conditions of high-temperature metamorphism, charnockite formation, and fluid flow suggest that the granulite-facies metamorphism and fluid-rock interaction is linked to the waning stage of Paleoproterozoic hot orogenesis in the Yeongnam Massif.
Thermal behaviour of ram-facing instruments during deep dives into a planetary atmosphere: The case of Daedalus/CWS
Authors: De Keyser Johan , Echim Marius , Ranvier Sylvain , Chambon Thomas , Ordoubadian Björn , Lemke Norbert
Published: March 2020

Spacecraft that aim to study the atmosphere of a planetary object through in situ sampling face the problem of strong atmospheric drag. In order not to compromise mission lifetime, the orbit can be designed so that repeated deep dives into the upper atmosphere are performed to sample atmospheric density, pressure, and composition down to relatively low altitudes. During such deep dives, ram-facing instruments, such as ion and neutral wind instruments, in particular are exposed to a severe heating flux.

The present contribution focuses on the particular case of the neutral Cross-Wind Sensor (CWS) under study for the Daedalus Earth Explorer 10 mission led by ESA, which will sample the Earth’s upper atmosphere during its perigee passes at an altitude currently planned to be in the 110 to 140 km range. Thermal simulations are presented that show the transient heat loads on the CWS instrument. It is shown that, with an appropriate materials choice, these heat loads can be dealt with in a satisfactory manner.
Ocean Surface Currents in the northern Nordic Seas from a combination of multi-mission satellite altimetry and numerical modeling
Authors: Müller Felix L. , Dettmering Denise , Wekerle Claudia , Schwatke Christian , Passaro Marcello , Bosch Wolfgang , Seitz Florian
Published: March 2020

Satellite altimetry is an important part of the Global Geodetic Observing System providing precise information on sea level on different spatial and temporal scales. Moreover, satellite altimetry-derived dynamic ocean topography heights enable the computation of ocean surface currents by applying the well-known geostrophic equations. However, in polar regions, altimetry observations are affected by seasonally changing sea-ice cover leading to a fragmentary data sampling.

In order to overcome this problem, an ocean model is used to fill in data gaps. The aim is to obtain a homogeneous ocean topography representation that enables consistent investigations of ocean surface current changes. For that purpose, the global Finite Element Sea-ice Ocean Model (FESOM) is used. It is based on an unstructured grid and provides daily water elevations with high spatial resolution.

The combination is done based on a Principal Component Analysis (PCA) after reducing both quantities by their constant and seasonal signals. In the main step, the most dominant spatial patterns of the modeled water heights as provided by the PCA are linked with the temporal variability of the estimated dynamic ocean topography elevations from altimetry. At the end, the seasonal signal as well as the absolute reference from altimetry is added back to the data set.

This contribution describes the combination process as well as the generated final product:  a daily, more than 17 years covering dataset of geostrophic ocean currents. The combination is done for the marine regions Greenland Sea, Barents Sea and the Fram Strait and includes sea surface height observations of the ESA altimeter satellites ERS-2 and Envisat. In order to evaluate the combination results, independent surface drifter observations, corrected for a-geostrophic velocity components, are used.
Comparison of the Photochemical Reflectance Index and Solar-induced Fluorescence for Estimating Gross Primary Productivity
Authors: Zhang Qian , Chen Jinghua
Published: March 2020

Photochemical reflectance index (PRI) as a proxy for light use efficiency (LUE) has the potential to improve the estimates of vegetation gross primary productivity (GPP) using LUE model. Solar-induced fluorescence (SIF) has increasingly been shown to be a promising approach for directly estimating GPP. However, a number of factors including the view-geometry and environmental variables, which may disassociate PRI and SIF products from photosynthesis, are important for the estimation of GPP, but rarely investigated. In this study, we observed multi-angle SIF and PRI in a maize field during the 2018 growing season, and compared the PRI-based LUE model and SIF-based linear model in estimating GPP. Our results showed that the averaged PRI and SIF using the multi-angle observations performed better than the single angle observed PRI and SIF in estimating LUE and, GPP respectively. We also found that the seasonal GPP dynamics were better captured by the SIF-based linear model (R2=0.50) than the PRI-based LUE model (R2=0.45), while the PRI-based LUE model performed better in estimating the diurnal variations of GPP (R2=0.71). Random forest analysis demonstrated that PAR and RH were of the most importance in the estimation of diurnal GPP variations using the SIF-based and the PRI-based models, respectively. The PRI-based LUE model performed better than the SIF-based model under most environmental conditions, while SIF should be a preference under clear days (Q>2). Thus, our study confirmed the importance of multi-angle observation of SIF and PRI in estimating GPP and LUE, and suggested that the environmental effects should be considered for accurately estimating GPP using SIF and PRI.
Seismogenic structures of the collision-subduction zone in the eastern Taiwan
Authors: Chen Wen-Shan , Wu Yih-Min , Yang Hsiao‑Chin , Yeh Po-Yi , Lai Yi-Xiu , Ke Ming-Chun , Ke Siao-Syun , Lin Yi-Kai
Published: March 2020

The Taiwan orogenic belt is relatively young and active with an ongoing arc-continent collision since the middle Miocene. In this study, we systematically investigate the use of seismic tomography, focal-mechanism and distribution of earthquakes to analysis the seismogenic patterns in the collision-subduction zone in the eastern Taiwan, which can be delineated five seismogenic zones of the Longitudinal Valley Fault Seismic Zone (LVFZ), the Central Range Fault Seismic Zone (CRFZ), the Backbone Range Seismic Zone (BRSZ), the Ludao-Lanyu Fault Seismic Zone (LLFZ), and the Wadati-Benioff Seismic Zone (WBSZ).

The LVFZ and CRFZ, formed along the collision zone between the Philippine Sea and the Eurasian Plates, earthquake focal mechanisms show P axes distributed in direction of 285-335°, reflecting the compressive stress field due to the collision. The LVSZ is the collisional boundary between the Philippine Sea and Eurasian plates. The LLFZ is a high-angle, east-dipping reverse fault separating the Luzon Volcanic Arc and the North Luzon Trough. The Eurasian plate (the South China Sea oceanic crust) subducts beneath the Philippine Sea plat in the southeastern Taiwan forming the WBSZ to a depth of 160 km.

The CRFZ, located along the eastern limb of Backbone Range, is formed by a zone of west-dipping reverse fault. In addition, the earthquakes on the BRSZ generated by normal and strike-slip faults at about 5-15 km depth which occur in response to left-lateral transtensional deformation by the collision. Earthquake focal mechanisms show P and T axes distributed in direction of 280-330° and 20-70°, respectively.
Rogue waves occurred in the World Ocean from 2011 to 2018 reported by mass media sources
Authors: Didenkulova Ekaterina
Published: March 2020

A catalogue of anomalously large waves (rogue or freak waves) occurred in the World Ocean during 2011-2018 reported in mass media sources and scientific literature has been compiled and analyzed. It includes 210 hazardous events caused damages or human losses. The majority of events is based on eyewitness accounts, and as a rule is not confirmed by direct measurements. All collected events divided into deep water cases, shallow water cases and occurrences on the coast (gentle beach or rocks). The following parameters have been determined: date, location, damage, description, reference, and weather conditions. The most dangerous areas in the World Ocean in terms of freak waves are highlighted.

This work was supported by the Russian Science Foundation (project No. 18-77-00063).
Identitification and tracking of storms via infrasound detections
Authors: Pásztor Marcell , Czanik Csenge , Bondár István
Published: March 2020

One of the various sources of infrasound signals are lightnings in storms. These moving sources can be detected and tracked at infrasound arrays. We correlate lightning data from Blitzortung with the infrasound detections from the Hungarian infrasound station at Piszkes-teto (PSZI) that has been collecting data since May, 2017. The objective of this study is to track storms and to test the station's capability to detect thunderstorm signals. We invetsigate what conditions affect these detections; in what directions, distances and accuracy can we track storms. We also look at how various noise conditions influence the detection capability of the array.
Ultrahigh resolution 3D imaging and characterisation of nanoscale pore structure in shales and its control on gas transport
Authors: Garum Mohamed , Glover Paul , Lorinczi Piroska , Hassanpour Ali
Published: March 2020

 

Cost-effective and environmentally sensitive shale gas production requires detailed knowledge of the petrophysical characteristics of the shale from which the gas is extracted. Parameters such as the kerogen fraction, pore size distributions, porosity, permeability, the frackability of the rock and the degree to which natural fracturing already occurs are required in order to be able to estimate potential gas reserves and how easily it can be extracted. Innovative imaging techniques, including Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and Nanoscale X-Ray Tomography (nano-CT), can be used to characterise the microstructural properties of shale. Here we report using FIB-SEM serial sectioning and nano-CT on approximately cubic samples of side length about 25 µm. The resolution of the FIB-SEM scanning is approximately 20 nm, while that of the nano-CT is about 50 nm, providing between 125 and 1953 million voxels per scan. These ultra-high resolution techniques have been shown to be effective methods for the analysis and imaging of shale microstructure. Each technique can provide data over a different and separate range of scales, and with different resolutions. Results analysed so far indicate that pores which seem to be unconnected when imaged on a micrometre scale by micro-CT scanning, are connected by thin pathways when imaged at these higher resolutions. This nano-scale connectivity is responsible for the small but non-zero permeability of gas shales to gas flow, which is typically measured in the range 5 nD – 200 nD. The volume, size, aspect ratios, surface area to volume ratio and orientations have all been calculated from the scanned data as a function of scale. These data indicate an extremely complex, heterogeneous, anisotropic and multimodal pore nanostructure and microstructure for the shales, with structure at all scales contributing to both gas storage and gas flow. Further work analysing the connectivity of the microscale and nanoscale pore spaces within the rock is underway. We believe that the combination of nano-CT with FIB-SEM on the same sample has the potential for providing an enhanced understanding of shale microstructure, which is necessary for modelling elastic behaviour, gas storage, gas desorption and gas flow in gas shales.

Keywords: Gas shale, FIB-SEM, nano-CT, porosity, permeability, Kerogen, pore volume, size distribution, pore aspect ratio and surface area to pore volume.
Table-top Cathodoluminescence Microscopy for Geology
Authors: Coenen Toon , Polman Albert
Published: March 2020

Cathodoluminescence (CL) microscopy is a well-known technique for imaging geological specimens, in which the light that is generated with an energetic electron beam is collected and analyzed with a CL detector. CL provides a unique imaging contrast that can be used for visualizing growth zonation, distinguishing cement and granular detrital material, detecting trace elements, and characterizing fractures and deformation features in a large range of rocks, to name a few examples. In its simplest form CL imaging is performed with a static electron beam in an optical microscopy system (optical CL) but for more advanced experiments CL imaging is performed in a scanning electron microscope (SEM). This enables high scan speeds, high spatial resolution (< 100 nm), and correlation with other SEM based techniques such as X-ray imaging (EDS), secondary electron (SE) and backscattered electron (BSE) imaging, and more.

Currently, SEM-based CL work is mostly performed on costly floor model SEMs that require large amounts of space, complex auxiliary support systems, and an experienced operator to run the machine. In contrast, compact, affordable, and user-friendly table-top SEMs have improved substantially in the last years but they typically lack (advanced) CL imaging capabilities. Here, we will present our progress in developing a table-top SEM based CL system that can be used for geological research amongst other applications.

In particular, we have integrated a CL collection and detection system in a Thermo Fisher Scientific/Phenom XL table-top microscope, which already is equipped with SE, BSE, and EDS imaging modalities. In this SEM, electron energies of 5 – 15 keV can be used which is appropriate for most CL imaging experiments. The CL is collected using a multimode fiber optic cable connected with a graded index lens to increase the numerical aperture of the collection. Subsequently, the light is send to a spectrometer where the CL emission spectrum can be measured for every excitation point on the sample; a technique known as hyperspectral CL  imaging. To synchronize electron beam scanning with data acquisition and for data analysis we have developed dedicated software control.

We assess the potential of table-top CL by imaging representative polished zircon and quartz samples for various beam and acquisition parameters. To benchmark the system performance we compare our experimental results with results obtained from a state-of-the-art floor model SEM (Thermo Fisher Scientific Quanta 650 SFEG) system equipped with a high-end Delmic SPARC CL system. In the future, these developments may lower the threshold for using CL imaging through cost reduction and workflow simplification, making it accessible to a larger range of users within the field of geology and beyond.
Newly Formed Energy Dispersion Signatures of Low-energy Proton, Oxygen and Helium Ions in the Inner Magnetosphere
Authors: Ren Jie , Zong Qiugang , Yue Chao , Zhou Xuzhi
Published: March 2020

Here we report the observations of the simultaneously formed energy dispersion structures of proton, oxygen and helium ions in the inner magnetospehre using Van Allen Probes data. The energy of the ourter edge of this sturcture is only several eV, and the energy of this structure is increasing with the decreasing L shell, which can be up to several keV especially for oxygen ions. The energy dispersion structure has a larger upper energy limit for the particle species with largher mass. But the upper velocity limits for different ion species are almost the same, which indicates that these different ions are accelerated by electric fields via the ExB drift. A statistical study with four years data shows that 1. This kind of structure is mainly distributed in the duskside and nighside; 2. The upper velocity for the oxygen ion exhibits a linear relation with both proton and helium ions; 3. The relationship between the occurrence rates and different parameters such as solar wind velocity, solar wind pressure, SYMH, Kp and AE index indicates that the formation of this structure is probably related to substorm activities.
Increasing Influence of Central Pacific El Niño on the Interdecadal Variation of Spring Rainfall in Northern Taiwan and Southern China Since 1980
Authors: Kao Pei-ken , Hong Chi-Cherng , Hung Chih-wen
Published: March 2020

Decadal variation of spring (February–April) rainfall in Northern Taiwan and Southern China was significantly related to the Pacific Decadal Oscillation (PDO) during the twentieth century. However, this interdecadal relationship subsequently weakened, and the sea surface temperature (SST) associated with the central Pacific El Niño (CPEN) has determined the interdecadal variation of spring rainfall in Northern Taiwan and Southern China since the 1980s. In this study, the effect of CPEN-SST on the interdecadal variation of spring rainfall in Northern Taiwan and Southern China was investigated. We found that a CPEN-associated positive SST anomaly in the eastern North Pacific forced an east–west overturning circulation anomaly in the subtropical North Pacific, the descending motion of which may have generated an anticyclonic circulation anomaly in the Philippine Sea. Simultaneously, the anticyclone associated southerly winds anomaly may enhance the southwesterly in northwest of the anticyclone, which in term enhance the trough extending from Japan to Northern Taiwan. The anticyclone and trough associated with the respective southwesterly and northeasterly anomalies created a convergence environment in Northern Taiwan. In turn, this convergence environment contributed substantially to an interdecadal rainfall enhancement in Northern Taiwan and Southern China. Our results suggest that the effect of CPEN-SST on the interdecadal variation of spring rainfall in Northern Taiwan and Southern China has increased since 1980, especially during the transition period from the termination of a warm PDO phase to a cold phase in the late 1990s