bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerosol Optical Depth Measurements at high altitude and polar WMO Global Atmospheric Watch - PFR Network Stations
Authors: Kazadzis Stelios , Kouremeti Natalia , Groebner Julian
Published: March 2020

Multiwavelength aerosol optical depth (AOD) has been defined as an essential climate variable for the Global Climate Observing System (GCOS) and the Global Atmosphere Watch (GAW) Program of the World Meteorological Organization. It is the most important parameter related to aerosol radiative forcing studies. PMOD/WRC have developed the Precision Filter Radiometer (PFR) that has been used for long term AOD measurements under a GAW-PFR Network of sun-photometers started in 1995 at Davos Switzerland and from 1999 at other locations, worldwide.

Here we present:

An overview of the results of the long term GAW-PFR AOD series for four high altitude stations (Izana/Spain, Mauna Loa/USA, Mt. Walliguan/China and Jungfraujoch/Switzerland). Mean AODs at 500nm were from 0.015 up to 0.096 with small negative changes per year for all stations.

An overview of the results for polar stations (Ny Ålesund/Norway, Summit/Denmark, Marambio/Finland). Ny Ålesund mean AODs at 500nm were almost double compared with the other stations.
Resilience indicator for ecosystems subject to high risk of irreversible degradation: a probabilistic method based on Bayesian inference
Authors: Liu Yong , Wu Sifeng
Published: March 2020

Ecosystem degradation is usually abrupt and unexpected shifts in ecosystem states that cannot be easily reversed. Some ecosystems might be subject to high risks of irreversible degradation (RID) because of strong undesirable resilience. In this study, we propose a probabilistic method to quantify RID by measuring the probability of the recovering threshold being unattainable under real world scenarios. Bayesian inference was used for parameter estimations and the posteriors were used to calculate the threshold for recovery and thereby the probability of it being unattainable, i.e., RID. We applied this method to lake eutrophication as an example. Our case study supported our hypothesis that ecosystems could be subject to high RID, as shown by the lake having a RID of 72% at the whole lake level. Spatial heterogeneity of RID was significant and certain regions were more susceptible to irreversible degradation, whereas others had higher chances of recovery. This spatial heterogeneity provides opportunities for mitigation because targeting regions with lower RID is more effective. We also found that pulse disturbances and ecosystem-based solutions had positive influences on lowering the RID. Pulse disturbances had the most significant influence on regions with higher RID, while ecosystem-based solutions performed best for regions with moderate RID, reducing RID to almost 0. Our method provides a practical framework to identify sensitive regions for conservation as well as opportunities for mitigation, which is applicable to a wide range of ecosystems. Our findings highlighted the worst scenario of irreversible degradation by providing a quantitative measure of the risk, thus raising further requirements and challenges for sustainability.
Ice-shelf instability due to surface meltwater systems on the George VI Ice Shelf
Authors: Banwell Alison F. , Dell Rebecca , Dunmire Devon , MacAyeal Douglas , Stevens Laura A. , Willis Ian C.
Published: March 2020

 

The evolution of surface and shallow subsurface meltwater bodies across Antarctic ice shelves has important implicationsfor their (in)stability, as demonstrated by the 2002 rapid collapse of the Larsen B Ice Shelf. Ice-shelf break-up may be triggered by stress variations associated with meltwater movement, ponding and drainage, causing ice-shelf flexure and fracture. We have recently begun a four year, jointly-funded US-NSF / UK-NERC project that will provide important geophysical insights into the stability of the George VI Ice Shelf on the Antarctic Peninsula, where hundreds of surface lakes form each summer.

In November 2019, we deployed global positioning systems, pressure transducers, automatic weather stations, and in-ice thermistor strings to record ice-shelf flexure, surface water depths, and surface and subsurface melting, respectively, in and around several surface lakes. Next austral summer (November 2020), we also plan to record fracture seismicity with a passive seismometer deployment, and to conduct ground penetrating radar surveys to detect subsurface water. Instruments, which are all within ~30 km of BAS's Fossil Bluff Station, will remain on the ice shelf until January 2022, resulting in a 27-month observational record in total.

Here, we report results of satellite image analysis of surface and shallow subsurface meltwater bodies, together with preliminary field and modelling results associated with our project. Using NDWIice thresholds applied to Landsat 8, Sentinel-2 and WorldView optical imagery, we show how patterns of surface meltwater evolve within and between summer melt seasons. Using Sentinel-1 SAR imagery and a convolutional neural network technique, we detect and track bodies of shallow subsurface water and show how they relate to patterns of surface water. We also report on field reconnaissance surveys made to two dolines (drained lake basins) on the ice shelf, and present a simple model to describe the process of doline formation. Throughout the project, we will combine field and remotely sensed data to extend and validate our existing approach to modelling ice-shelf flexure and stress, and possible ‘Larsen-B style’ ice-shelf instability and break-up at less geographically confined ice shelves.
The Reiner Gamma Swirl and Magnetic Anomaly: Why We Should Go There
Authors: Deca Jan
Published: March 2020

All lunar swirls are known to be co-located with crustal magnetic anomalies (LMAs). Not all LMAs can be associated with albedo markings, making swirls, and their possible connection with the former, an intriguing puzzle yet to be solved.

Given favorable conditions, an LMA can deflect the solar wind enough to form a mini-magnetosphere that partially (and possibly only temporarily) shields the underlying lunar regolith. Recent modeling efforts have shown that the resulting energy flux pattern to the surface is consistent with the underlying albedo (swirl) patterns. In particular, coupling a fully kinetic particle-in-cell code with a downward-continued magnetic field model based on orbital-altitude observations, we are able to produce a pattern similar to Reiner Gamma’s alternating bright and dark bands, but only when integrating over the full lunar orbit. Although consistent with the solar-wind standoff hypothesis for the origin of swirls, the match is not perfect. A combination of reasons could be the cause.

Here we discuss some of the unexplained discrepancies between the flux profile and the surface brightness and why the Reiner Gamma swirl region should be a prime target for future low-orbiting spacecraft or even landers/rovers, and we consider the potential role of human exploration.
Hydrologic characterization of an alpine valley infill through integration of ERT, active seismic and active/passive surface wave interferometry (Unaweep Canyon, US)
Authors: Behm Michael , Flores-Orozco Adrian , Chwatal Werner , Soreghan Gerilyn S.
Published: March 2020

Unaweep Canyon (Western Colorado, US) is an enigmatic alpine landform and hypothesized to represent a partially exhumed paleo valley which was glacially over-deepened in the late Paleozoic. Processing and interpretation of recently acquired 2D seismic reflection and refraction data support the concept of glacial over-deepening and indicate maximum bedrock depths of about 550 meters. Additionally, pronounced reflectors are observed within the sedimentary infill. The seismic data have also been subjected to surface wave analysis revealing a significant increase of the Vp/Vs ratio below a shallow (50 – 150 m depth) intra-sedimentary reflector. A large Vp/Vs ratio can be caused by both saturation and poor consolidation of dry low-porosity materials (e.g. dry sands).

To investigate the potential occurrence of an aquifer associated with this interface, a high-density/long-offset electrical resistivity survey was conducted in fall 2019 along the seismic line. The maximum offset is 915 m at an electrode spacing of 5 meters, aiming at reaching depths of investigations between 150 and 200 meters. Inversion of the ERT data was initially conducted by means of smoothness-constrained algorithms. The imaging results revealed consistent structures with those resolved through seismic methods, at least within the required depth of investigation between 150 – 200 m. Furthermore, improvements in the resolution of the ERT imaging results was investigated after the inclusion of seismic interfaces as structural constraints in the inversion of the data. The comparison of the two approaches permitted to improve the interpretation of the ERT imaging results, which indicate low resistivities in the zone of high Vp/Vs ratios and thus strengthen the aquifer hypothesis. We present an integrated interpretation based on seismic structure, resistivity distribution, Vp and Vs velocities, and a distant well core. In a larger context, the results provide new insights on the subsurface hydrology in this arid part of the continental US as well as on the significance of multi-valued datasets for the interpretation and characterization of aquifers.   
From concentrations requirements to emission committments: prospects and challenges for the Global Stocktake
Authors: Bowman Kevin , Liu Junjie , Bloom Anthony , Saatchi Sassan , Xu Liang , Miyazaki Kazayuki , Lee Meemong , Menemenlis Dimitris , Carroll Dustin , Schimel David
Published: March 2020

The Paris Agreement was a watershed moment in providing a framework to address the mitigation of climate change.  The Global Stocktake is a bi-decadal process to assess progress in greenhouse gas emission reductions in light of climate feedbacks and response.   However, the relationship between emission commitments and concentration requirements is confounded by complex natural biogeochemical processes potentially modulated by climate feedbacks.  We investigate the prospects and challenges of mediating between emissions and concentrations through the NASA Carbon Monitoring System Flux (CMS-Flux) project, which is an inverse modeling and data assimilation system that ingests a suite of observations including the Orbital Carbon Observatory (OCO-2) and state-of-the-art biomass change maps across the carbon cycle to attribute atmospheric carbon variability to anthropogenic and biogeochemical processes. We decompose the spatial drivers of CO2 accumulation since the beginning of the decade into component fluxes and emissions in the context of the historic 2010 and 2015 El Ninos, which had a tremendous influence on the CO2 growth rate.  These processes reshuffle the primary contributors of CO2 growth at Stocktake time scales that must be reconciled with Nationally Determine Contributions and concentration targets.  Based on these findings, we investigate how systems such as CMS-Flux can harness the carbon constellation to fill a vital gap between policy needs and scientific assessment needed for the Stocktake.
Time-Varying Meteorological Drought Index for a Changing Climate
Authors: Vinnarasi Rajendran , Dhanya Chandrika Thulaseedharan
Published: March 2020

Drought is considered as one of the most complicated natural disasters, whose adverse effects span over different domains such as agriculture, ecosystem, and economy. One of the widely used meteorological drought index is Standardized Precipitation Index (SPI), which is based on the stationary assumption (i.e., the statistical parameters does not change over time). Nevertheless, numerous studies have reported that the precipitation series has undergone remarkable changes, which emphasizes the need for developing a drought index incorporating the dynamic behavior of the precipitation. Hence, in this study, a non-stationary SPI (NSPI) is developed to capture the temporal dynamics of the precipitation and to identify the meteorological drought-prone areas over India. Before modelling, the non-stationarity in the distribution parameters of precipitation series are detected. If non-stationary is observed in any of the parameters, then that particular parameter is modelled as non-stationary, otherwise it is modelled as stationary. The proposed index provides a probability-based description of drought status and its uncertainty bounds, which are computed using Bayesian Inference. Results reveals that the traditional SPI is biased by the lowest magnitude of precipitation leading to overestimation of drought where frequent severe dry events are clustered, which is overcome by NSPI. Additionally, NSPI captured the historical drought, capturing the temporal dynamics of precipitation series in India and is more reliable than SPI. The proposed NSPI is found to be a potential index for drought monitoring in a nonstationary climate.
An annually dated Interdecadal Pacific Oscillation reconstruction spanning the last two millennia
Authors: Vance Tessa , Kiem Anthony , Roberts Jason , Jong Lenneke , Plummer Chris , Curran Mark , Moy Andrew , van Ommen Tas
Published: March 2020

The Interdecadal Pacific Oscillation (IPO) is a nominally 15-30 year climate mode that has been identified through analysis of tropical and extratropical Pacific sea surface temperatures over the past 150 years. It is still unclear whether the IPO is a true oscillation or whether it is simply the low frequency response of the climate system to forcing (natural and potentially anthropogenic), principally ENSO. Regardless of this, the IPO as it is currently known has clear climate impacts, one example being hydroclimate variability in Australia. In positive phases of the IPO, drought risk is heightened due to a reduction in the likelihood of large, recharging La Nina-derived rainfall events. Conversely, in IPO negative phases, flood risk in Australia is greatly increased due to an increased likelihood of such rain events.

Previous work derived a 1000 year, accurately dated reconstruction of the IPO from multiple palaeoclimate archives from the Law Dome ice core in East Antarctica. This reconstruction provided a long-term reconstruction with which to assess the true risk of drought- and flood-prone epochs in Australia. Subsequently, an entirely independent reconstruction of the IPO was developed using SE Asian tree rings by Buckley et al. in 2019, also spanning most of the last millennium. The fidelity the two reconstructions display with respect to the instrumental IPO record and with each other suggests both are faithfully representing IPO variability. Here we present an IPO reconstruction that doubles the temporal span of existing reconstructions to cover the last 2000 years using newly analysed and dated material from the Law Dome ice core. This new, longer reconstruction identifies important features of Pacific decadal variability that have significant implications for understanding hydroclimate epochs across not only Australasia, but the Pacific region as a whole.
A Lagrangian perspective on cold pool collisions
Authors: Torri Giuseppe , Kuang Zhiming
Published: March 2020

Collisions represent one of the most important processes through which cold pools—essential boundary layer features of precipitating systems—help to organize convection. For example, by colliding with one another, expanding cold pools can trigger new convective cells, a process that has been argued to be important to explain the deepening of convection and the maintenance of mesoscale convective systems for many hours. In spite of their role, collisions are an understudied process, and many aspects remain to be fully clarified. In order to quantify the importance of collisions on the life cycle of cold pools, we will present some results based on a combination of numerical simulations in radiative-convective equilibrium and a Lagrangian cold pool tracking algorithm. First, we will discuss how the Lagrangian algorithm can be used to estimate that the median time of the first collision for the simulated cold pools is under 10 minutes. We will then show that cold pools are significantly deformed by collisions and lose their circular shape already at the very early stages of their life cycle. Finally, we will present results suggesting that cold pools appear to be clustered, and we will provide some estimates of the associated temporal and spatial scales.
Nitrous oxide production and sources in response to a simulated fall-freeze-thaw cycle
Authors: Lin Sisi , Ramirez Guillermo Hernandez
Published: March 2020

Thaw-induced N2O emissions have been shown to account for 30-90% of N2O emissions in agricultural fields. Due to the climate change, increased precipitatio is expected in fall and winter seasons for certain regions. As a result, this would in turn enhance the thaw-induced N2O emissions and aggravate climate change. A mesocosm study was conducted to investigate N2O production and sources from soils under elevated soil moisture contents in response to a simulated fall-freeze-thaw cycle. Treatments included two levels of N addition (urea versus control) and two different management histories [with (SW) and without (CT) manure additions]. Our results showed that at least 92% of the N2O emissions during the study were produced during the simulated thawing across all treatments. The thaw-induced N2O emissions increased with increasing soil water content. The fall-applied urea increased the soil-derived N2O emissions during thawing, indicating an excessive mineralization of soil organic N. Compared to the CT soils, the SW soils induced more soil-derived N2O emissions. This could be because the SW soil had more easily decomposable organic matter which was likely due to historical manure additions. Regarding to the daily primed N2O fluxes, different soil water contents impacted the dynamics of daily priming effect. At the high water content, the soils experienced a shift in daily primed N2O fluxes from positive to negative and eventually back to positive throughout the simulated thawing, while the soils at lower water contents underwent positive primed fluxes in general. The shift in daily primed fluxes was probably driven by the preference of soil microbes on the labile N substrates. When the microbes switched from easily to moderately decomposed substrates (e.g., from dissolved organic N to plant residuals), they started to uptake inorganic N from the soil due to a relatively high C:N ratio of plant residuals. Therefore, a net N immobilization and negative primed N2O production occur in the short term in the soils at the high water content.
Characterizing Groundwater Response Time to Droughts Across the United States
Authors: Ajami Hoori , Schreiner-McGraw Adam
Published: March 2020

The global importance of groundwater as a resilient water supply has increased in recent years as groundwater is the major water supply for over 2 billion people worldwide. Global population growth and expansion of irrigated agriculture have caused groundwater depletion particularly in semi-arid and arid regions, and efforts are underway to achieve groundwater sustainability in these areas. As groundwater flow is slow, and most aquifers have very long residence times, time horizons of 50-100 years are often suggested for setting up groundwater sustainability goals. However, aquifer response time to various stressors is site specific and depends on aquifer properties, climatic conditions, and frequency and intensity of droughts. Here, we utilize daily groundwater observations from unconfined aquifers across the conterminous United States to quantify groundwater recovery time to meteorological droughts during 1981-2017 period. We consider two metrics to quantify groundwater recovery time: 1) the “time-lag” between the end of the precipitation drought and the termination of groundwater storage loss, and 2) the “time of rise”, the time that it takes until the aquifer storage reaches the pre-drought conditions. Our results indicate that the average time lag of aquifer response time to drought is 15 months, and the time lag can increase up to 15 years for some aquifers. Analysis across 634 wells reveal that depth to water table is the primary factor that determines whether aquifer physical properties or precipitation characteristics control this time lag to droughts. In regions with shallow water tables, aquifer physical properties determine lag time while in aquifers with deep groundwater tables precipitation properties are more important. The average recovery time of a shallow water table aquifer is about 3 years, and the recovery time is longer during severe droughts. It is expected that with projected increases in intensity and frequency of droughts in the future, the buffering capacity of aquifers will decrease, increasing the need for developing groundwater sustainability plans that consider conjunctive water use.  
Impact of mass human migration during Chinese New Year on Beijing urban heat island
Authors: Dou Jingjing , Miao Shiguang
Published: March 2020

The Chinese New Year (CNY, also called Spring Festival), which officially lasts for 7 days, is the most important holiday in China. Chinese people in large cities usually return to their hometowns for family reunions before the CNY holiday and return afterward. Nearly half of Beijing’s population has been reported to leave the city for family reunions before the CNY holidays in the past several years. Hourly automatic weather station (AWS) data during CNY 2010-2015 were used to analyze the changes in the temporal and spatial distribution of the Beijing urban heat island intensity (UHII) and the impact of mass human migration on urban temperature. Soil moisture, 10-m wind speed, and cloud cover were considered and indicated nearly no change during the pre-CNY period (2 to 4 weeks before CNY) and CNY week, which means that UHII variation was mainly affected by the mass human migration. Daily UHII during CNY week was lower than during pre-CNY period. UHII for daily maximum temperature decreased by 55% during CNY week than the pre-CNY period (0.6 °C during pre-CNY period vs. 0.27 °C during CNY week) due to mass human migration, which was much larger than the reduction in UHII for the daily maximum temperature (5%, 4.34 °C during the pre-CNY period vs. 4.11 °C during the CNY week). The spatial distribution of the UHII difference between CNY week and the pre-CNY period is closely related to the locations of functional population zones. UHII for daily maximum temperature decreases most (80%, 0.40 °C during the pre-CNY period vs. 0.08 °C during the CNY period) between the Third and Fourth Ring Roads (RRs), an area which experiences high human activity and has the highest floating population percentage. This study can provide suggestions for optimizing the layout of urban space and land-use structures.
Orthomosaics of Historical Aerial Photographs and Horizontal Accuracy Analysis
Authors: Suh Ji Won , Ouimet William
Published: March 2020

Orthomosaics from aerial photographs play a pivotal role in understanding land-use/land cover in broad area and the advent of image processing technology allows us to produce orthoimagery. However, recent advanced technologies are seldom applied to produce historical orthophotos from early or mid 20C old aerial photos in broad extent since they have limited information (e.g. camera position, flying altitude, and yaw) which is critical information for orthomosaics. In this context, this study aims to orthomosaic and georectify historical aerial photographs and validate the horizontal accuracy of orthomosacicked outputs. In order to achieve this, firstly, we collected 117 aerial photographs of 1934 (scale 1:12,000) and 68 of 1951 (scale 1:20,000) from UConn air photo achieve focused on Woodstock town in Connecticut, USA. Secondly, we created GCPs (Ground Control Points) as referenced points where they have not changed over time by overlaying multiple datasets such as LiDAR DEM, hillshade map, recent orthoimagery. Thirdly, we align photos with Control Points (CPs), build a mesh, and build orthomosaics of 1934 and 1951, respectively, using Agisoft Photoscan 1.5. Lastly, calculating RMSE (Root Mean Square Error) and offsets comparing between set of GCPs and CPs from Lidar DEM and set of them digitized from orthomosaics. As a result, RMSE values of GCPs and CPs between 1934 and 1951 mostly show that output of this work is acceptable to use for standard mapping and GIS work or visualization based on ASPRS 1990 horizonal accuracy standard. In addition, we found several factors affect horizontal accuracy of orthomosaics; resolution of aerial photos, spatial distribution of GCPs and CPs, the number of CPs and GCPs, the percentage of lateral overlapping area along flight strips, and margin area. Overall, applying automated orthomosaicking image processing to historical aerial photographs has the potential to represent historical landscape and even detect its change in broad extent.
Improving numerical simulation of typhoon LEKIMA(2019) through assimilating ATMS radiance data
Authors: Zhang Lei , Chen Baode
Published: March 2020

Lacking of high-resolution observations over oceans is one of the major problems for the numerical simulation of the tropical cyclones (TC), especially for the tropical cyclone inner-core structure’s simulation. Satellite observations plays an important role in improving the forecast skills of numerical weather prediction (NWP) systems. Many studies have suggested that the assimilation of satellite radiance data can substantially improve the numerical weather forecast skills for global model. However, the performance of satellite radiance data assimilation in limited-area modeling systems is still controversial.

This study attempts to investigate the impact of assimilation of the Advanced Technology Microwave Sounder (ATMS) satellite radiances data and its role to improve the model initial condition and forecast of typhoon LEKIMA(2019) using a regional mesoscale model. In this study, detailed analysis of the data impact will be presented, also the results from different data assimilation methods and different data usage schemes will be discussed.
New insights into the latitudinal ventilation variations in the Japan Sea since the Last Glacial Maximum: A radiolarian assemblage perspective
Authors: Dong Zhi , Shi Xuefa , Zou Jianjun , Liu Yanguang , Dou Ruxi , Gorbarenko Sergey
Published: March 2020

The formation of intermediate and deep water plays a key role in regulating climate changes at a variety of time scales through the heat redistribution and carbon cycling. The Japan Sea has unique water-mass characteristics in the North Pacific with its own deep-water formation within the Sea itself called Japan Sea Proper Water (JSPW). Latitudinal ventilation changes in the Japan Sea were reconstructed using radiolarian assemblage from three sediment cores, extending from the southwestern, central to northwestern Japan Sea. Here, we present downcore faunal records spanning the last 25 ka as well as other existing ventilation records in the Japan Sea, and provide reliable evidence to evaluate the potential controlling mechanism that lead to onset and interruption of JSPW ventilation. Taking all together, we argue that radiolarian assemblage records have revealed a distinct basin-scale transition in deep-water conditions from anoxic to oxic during the deglaciation related to changing surface hydrography. However, it should be recognized that there is significant potential for bias in the timing of the ventilation changes among regions. Deep ventilation in the central Japan Sea has been in an interglacial mode during the Bølling/Allerød presumably related to northward volume transport of the Tsushima Warm Current. Moreover, the decrease of JSPW Assemblage at the B/A in southwestern Japan Sea was attributed to higher export productivity, facilitating suboxic deepwater condition through enhanced consumption of oxygen, which was probably caused by coastal upwelling. In contrast, the weakening ventilation of the northwestern Japan Sea during the B/A and YD periods was probably caused by the blocking effect of the sea ice. Note: This study was supported by the National Natural Science Foundation of China (Grant No. 41420104005, U1606401) and National Program on Global Change and Air-Sea Interaction (GASI-GEOGE-04).
Neotectonic constraint on models of strain localisation within Australian Stable Continental Region (SCR) crust
Authors: Clark Daniel
Published: March 2020

The mechanisms that lead to the localisation of stable continental region (SCR) seismicity, and strain more generally, remain poorly understood. Recent work has emphasised correlations between the historical record of earthquake epicentres and lateral changes in the thickness, composition and/or viscosity (thermal state) of the lithospheric mantle, as inferred from seismic velocity/attenuation constraints. Fluid flow and the distribution of heat production within the crust have also been cited as controls on the location of contemporary seismicity. The plate margin-centric hypothesis that the loading rate of crustal faults can been understood in terms of the strain rate of the underlying lithospheric mantle has been challenged in that a space-geodetic strain signal is yet to be measured in many SCRs. Alternatives involving the release of elastic energy from a pre-stressed lithosphere have been proposed.

The Australian SCR crust preserves a rich but largely unexplored record of seismogenic crustal deformation spanning a time period much greater than that provided by the historical record of seismicity. Variations in the distribution, cumulative displacement, and recurrence characteristics of neotectonic faults provide important constraint for models of strain localisation mechanisms within SCR crust, with global application. This paper presents two endmember case studies that illustrate the variation in deformation characteristics encountered within Australian SCR crust, and which demonstrate the range and nature of the constraint that might be imposed on models describing crustal deformation and seismic hazard.

The ~0.5 m high 2018 MW 5.3 Lake Muir earthquake scarp in southwest Western Australia is representative of a class of ruptures in the Precambrian SCR of Australia where the scarps are isolated from neighbouring scarps and there is little or no landscape evidence for recurrence of morphotectonic earthquakes, or of the construction of regional tectonic relief. In contrast, scarps in the Phanerozoic SCR of eastern Australia typically occur within a scarp-length of neighbouring scarps, and demonstrate extended histories of recurrence of morphotectonic events. For example, the ~75 km-long Lake George fault scarp is associated with a vertical displacement of ~250 m which accrued as the result of many morphotectonic earthquakes over the last ca. 4 Myr. The scarp links into neighbouring scarps, forming a belt-like arrangement that defines the topographic crest of the southeast Australian highlands. The limited data available indicates that recurrence is highly episodic, with periods of fault activity potentially coinciding with changes at the plate boundaries.
The Measurement of Nitrophenols by Integrated Spectrum and TD-IBBCEAS
Authors: Wang Meng , Chen Jun , Lou Shengrong , Venables Dean
Published: March 2020

Atmospheric Brown Carbon (BrC) is an important component of aerosol particles that Influences the climate through interactions with incoming solar and emitted terrestrial radiation. BrC can be generated from a variety of primary emissions (such as traffic, coal combustion, biomass burning) and secondary formation. Nitrophenols are classified as Brown Carbon due to their strong absorption in near-ultraviolet and visible regions.

A heated single path absorption spectroscopy system is been built to measure the cross section of nitrophenols. Due to its semi-volatility, the nitrophenols were introduced into the cell by N2. The cross section of nitrophenols is obtained by calculating the integrated absorption.

A Thermal Decomposition - Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy (TD-IBBCEAS) system was setup for atmospheric measurement. This instrument covered the spectral region from 320 to 440nm which could contain the interested absorption of nitrophenols. A thermal decomposition device was used to heating the sample.  The system was characterized based in laboratory experiment.
The extent of igneous rocks of the South China Sea based on the correlational analyses of gravity and magnetic data
Authors: Yang Min , Wang Wanyin , Ji Xiaolin , Ma Tao , Ma Jie , Xiong Shengqing
Published: March 2020

The South China Sea is the biggest conjugate marginal sea in the West Pacific Ocean, which is influenced by the Eurasian plate, the Pacific plate, and the Indo-Australian plate. There have developed continental tectonic margins with different characters after experiencing subduction, collision, strike-slip and so on since the Mesozoic and Cenozoic (Yao et al., 2004; Zhang et al., 2014). However, the igneous rock can be regarded as a recorder to reveal some information of evolution and deep geodynamics of the South China Sea, which helps us to improve understanding of the continental rifting, the seafloor spreading, the formation of deep water basins and the process of hydrocarbon accumulation(Zhang et al., 2016).
The igneous rocks are studied by multiple types of data that are magnetic data, seismic profiles, and drilling data in the previous studies. Hence, there are bunch of research results about the igneous rocks that contain the reason and time of formation, the distribution of space, the period of eruption in the north of the South China Sea because of the abundant datasets (Zou et al., 1993,1995; Zhou et al., Yan and Liu, 2005; Xu et al., 2013; Zhang et al., 2013; Zhang et al., 2014; Zhang et al., 2015; Zhang et al., 2016), in addition, the Pearl River Mouth Basin is the most famous one among all of the basins in the South China Sea. However, the researchs related to the south of the South China Sea where are the deep-sea are far less knowledgeable about the distribution of the igneous rocks than the north because of the limitation of datasets that are poor quality and less quantity (Yao et al., 2004; Li et al., 2010; Hui et al., 2016), which lead to the less researches with respect to the big area of the South China Sea.
The followings can be concluded from the previous studies. The northern and continental margin of the South China Sea are distributed by Cenozoic extrusive rocks with high susceptibility and low density and Yanshanian intrusive rocks with low susceptibility and density (Hao et al., 2009; Lu et al., 2011; Hui et al., 2016), the Central Sub-basin is covered by Cenozoic extrusive rocks (Yan and Liu, 2005; Hui et al., 2016), however, there are few distributions of the Yanshanian intrusive rocks in the Southern South China Sea (Zhang et al., 2015; Hui et al., 2016). In this study, a new method, the fusion of gravity and magnetic data, is applied to detect the distribution of the igneous rocks in order to provide more geophysical data in the South China Sea.
Discovery and geological significance of the Magma-hydrothermal micro-jets at the bottom of a lake: A case from the Chang 7 section of the Yanchang Formation of the Triassic in the Ordos Basin, China
Authors: You Jiyuan , Liu Yiqun , Zhou Dingwu
Published: March 2020

The "black chimney" type of hydrothermal vents in the modern deep sea have become a popular research topic in many disciplines. Due to the actual conditions, the research on palaeo-thermal vents in geological history is relatively low. Fortunately, the discovery of hydrothermal vents and bio-fossils from the Chang 7 source rocks of the Yanchang Formation of the Triassic in the Ordos Basin, China, provides the best evidence for deciphering hydrothermal activity during geological history. Here, we report a case study. Through ordinary sheet observation, scanning electron microscopy and electron probe observation, layered grained siliceous rocks, dolomites, and hydrothermal mineral combinations, such as pyrite + dolomite + gypsum and calcite + barite, are found. Their unique petrological characteristics, mineral composition, and structure confirm the existence of palaeo-thermal fluid vents. We further analysed the geochemical characteristics and in situ isotope characteristics. The study found that Cs, U, Th, Pb, Ba and other trace elements of the sample showed positive abnormalities, in which values of U/Th were high; in addition, the enrichment of major elements such as Sr, Mn, and the in situ sulphur isotopes of pyrite reached 7.89%-10.88%. This study of hydrothermal vents over geological history is expected to provide new insights on the life forms of various extreme microorganisms in hydrothermal environments and on their formation of high-quality source rocks.
Post-fire carbon emissions from degraded tropical peat swamp forests in Brunei
Authors: Lupascu Massimo , Akhtar Hasan , Smith Thomas E.L. , Sukri Rahayu S.
Published: March 2020

Tropical peat swamp forests hold about 15–19% of the global organic carbon (C) pool of which 77% is found in Southeast Asia. Nonetheless, these ecosystems have been drained, exploited for timber and land for agriculture, leading to frequent fires in the region. Fire alters the physico-chemical characteristics of peat as well as the hydrology, which may convert these ecosystems into a source of C for decades as C emissions to the atmosphere exceeds photosynthesis.

To understand the long-term impacts of fire on C cycling, we investigated C emissions in intact and degraded PSFs in Brunei Darussalam, which has experienced 7 fires over the last 40 years. We quantified the magnitude and patterns of C loss (CO2, CH4, and Dissolved Organic carbon) and soil-water quality characteristics along with continuous monitoring of soil temperature and water table level from June 2017 to January 2019. To investigate the age and sources of C contributing to ecosystem respiration (Reco) and CH4, we used natural tracers such as 14C.

We observed a major difference in the physico-chemical parameters, which in turn affected C dynamics, especially CH4. In burnt areas (7.8±2.2 mg CH4 m-2 hr-1) the CH4 emission was approximately twice compared to the intact peat swamp forest (4.0±2.0 mg CH4 m-2 hr-1) due to prolonged higher water table creating optimum methanogenesis conditions. On the contrary, Reco did not show a significant difference between burnt (432±83 mg CO2 m-2 hr-1) and intact areas (359±76 mg CO2 m-2 hr-1). Further, radiocarbon (14C) analysis showed an overall modern signature for both CO2 and CH4 fluxes implying a microbial preference for the more labile C fraction in solution.

With frequent fires and more flooding in the future, these degraded tropical peat swamp forests areas may remain a hot spot of C emissions as suggested by our findings.
Coupling poroelastic stress change and rate-state fault slip models to simulate fluid injection induced seismic and aseismic slip
Authors: Liu Yajing , Verdecchia Alessandro , Deng Kai , Harrington Rebecca
Published: March 2020

Fluid injection in unconventional hydrocarbon resource exploration can introduce poroelastic stress and pore pressure changes, which in some cases may lead to aseismic slip on pre-existing fractures or faults. All three processes have been proposed as candidates for inducing earthquakes up to 10s of kilometers from injection wells. In this study, we examine their relative roles in triggering fault slip under both wastewater disposal and hydraulic fracturing scenarios. We first present modeling results of poroelastic stress changes on a previously unmapped fault near Cushing, Oklahoma, due to injection at multiple wastewater disposal wells within ~ 10 km of distance, where over 100 small to moderate earthquakes were reported between 2015/09 to 2016/11 including a Mw5.0 event at the end of the sequence. Despite the much larger amplitude of pore pressure change, we find that earthquake hypocenters are well correlated with positive shear stress change, which dominates the regimes of positive Coulomb stress change encouraging failure. Depending on the relative location of the disposal well to the recipient fault and its sense of motion, fluid injection can introduce either positive or negative Coulomb stress changes, therefore promoting or inhibiting seismicity. Our results suggest that interaction between multiple injection wells needs to be considered in induced seismicity hazard assessment, particularly for areas of dense well distributions. Next, we plan to apply the model to simulate poroelastic stress changes due to multi-stage hydraulic fracturing wells near Dawson Creek, British Columbia, where a dense local broadband seismic array has been in operation since 2016. We will investigate the relative amplitudes, time scales, and spatial ranges of pore pressure versus solid matrix stress changes in influencing local seismicity.

Finally, we have developed a rate-state friction framework for calculating slip on a pre-existing fault under stress perturbations for both the disposal and hydraulic fracturing cases. Preliminary fault slip simulation results suggest that fault response (aseismic versus seismic) highly depends on 1) the relative timing in the intrinsic earthquake cycle (under tectonic loading) when the stress perturbation is introduced, 2) the amplitude of the perturbation relative to the background fault stress state, and 3) the duration of the perturbation relative to the “memory” timescale governed by the rate-state properties of the fault. Our modeling results suggest the design of injection parameters could be critical for preventing the onset of seismic slip.
Discrete Element Modeling on Deformation Pattern of Composite Strata Induced by Repeated Thrust Faulting: Case Study of Chushan Site, Central Taiwan
Authors: Hung Chien-Hui , Lin Cheng-Han , Lin Ming-Lang
Published: March 2020

In 1999, Chi-Chi earthquake hit Taiwan and caused severe damage to the infrastructures along the Chelungpu fault because of overburden deformation. Previous study excavated several trenches near the Chelungpu fault to study the fault characteristics and the fault deformation zone. The most important trench, Chushan site, records the Chi-Chi earthquake with 1.7m vertical offset and other four large paleoseismic events. This fault trench was now retained in the Chelungpu Fault Preservation Park, Taiwan that greatly contributes to observing the deformation pattern of overburden layer induced by repeated thrust faulting. For the north wall of the Chushan trench, the east-dipping basal thrust with a dip angle of 24° splits into two branches and the sedimentary layer, which consists of silt layer and gravel layer, is deformed into an asymmetric anticline fold. This observation indicates that the overburden layer in natural is the composite strata and the presence of gravel layer in the composite strata could be an indicator for the coseismic deformation.

In this study, three-dimensional DEM simulations are conducted to identify the deformation pattern of composite strata under repeated thrust faulting. The numerical model was constructed based on the Chushan trench. Silt layers are made by balls and the gravel layer is compose of balls and ellipsoid particles. Results show that a fault-propagation fold forms during the initial stage of the deformation, and an asymmetric anticline fold with one limb slightly overturned forms in the Chi-Chi earthquake. The rotation of ellipsoid particles in the numerical model indicates the evolution of folding, which conduces to understand the deformation progress in the full faulting process.
Evaluation of NCEP next Global Ensemble Forecast System (GEFS v12)
Authors: Fu Bing , Zhu Yuejian , Zhou Xiaqiong , Hou Dingchen
Published: March 2020

With the successful upgrade of its deterministic model GFS (v15) on June 12, 2019, NCEP has scheduled the implementation of its next Global Ensemble Forecast System (GEFS v12) in the summer of 2020. These two model upgrades on deterministic and ensemble forecast systems are substantially different from previous upgrades. A new dynamical core (FV3) is adopted for the first time in the NCEP operational models, replacing the previous spectral dynamical core. The previous 3-category Zhao-Carr microphysics scheme is also being replaced by a more advanced 6-category GFDL microphysics scheme. From an ensemble model perspective, the previous GEFS has already demonstrated great success in past decades for weather and week-2 prediction by providing reliable probabilistic forecasts. Recently, there has been a large demand for subseasonal prediction, and GEFS v12 forecasts will be extended to 35 days to cover this time range. To better represent large uncertainties associated with this time scale, SPPT (stochastic physics perturbed tendency) and SKEB (stochastic kinetic energy backscatter) stochastic schemes are taking the place of the original STTP (stochastic total tendency perturbation), and a prescribed SST generated from combination of NSST and bias corrected CFS forecasts is also applied to simulate the sub-seasonal variation of SST forcing.    

As a major system upgrade,  a 2.5-year retrospective run of GEFS v12 is carried out to evaluate the model performance. A 30-year reforecast will be provided to stakeholders and the public to calibrate the forecast. The improvement of predictability and prediction skill will be studied through various measurements across tropical to extratropical areas in terms of deterministic (ensemble mean) and probabilistic (ensemble distribution) forecasts. The characteristics of model systematic error will be identified from comparing the major changes of the two state-of-art ensemble systems. As GEFS serves the most crucial model guidance for 5-7 day hurricane forecasts in support of the NHC (National Hurricane Center) and other customers, model capability in predicting tropical cyclone track and intensity is also examined from the retrospective runs. The results show there are significant improvements for tropical cyclone track forecast in North Atlantic and the western North Pacific, in particular, the intensity forecast is improved remarkably in all the basins.