bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous detection of gaseous sulfuric acid and OH radicals using chemical ionization mass spectrometry
Authors: Zheng Jun , Lyu Tianchi , Ma Yan
Published: March 2024

Hydroxyl radical (OH) is the dominant oxidation agent in the atmosphere due to its high reactivity. OH plays a decisive role in the degradation of primary air pollutants and the formation of secondary air pollutants (e.g., SOA and O3). For the same reason, OH atmospheric abundance is extremely low, and its atmospheric measurement usually presents a challenging job. In this work, we have developed a new method to detect OH radicals using chemical ionization mass spectrometry (CIMS). The working principle of the new method is that OH was first completely converted into gaseous sulfuric acid (SA) and was then detected by a nitrate-CIMS. Potential interference from ambient SA and other reactive intermediates, such as Criegee Intermediates (CIs), was also dealt with by introducing free radical scavengers. A high-resolution time-of-flight mass spectrometer was also used to explore potential isotopic interferences. The new instrument was calibrated with artificially generated SA standards, quantified with the N2O-actinnometry. A field test was conducted in the Summer of 2023. The results demonstrated that OH concentration ranged from a few 106 molecules cm-3 up to ~2×107 molecules cm-3, basically in line with OH level reported in other areas of China. The ambient SA level was significantly lower than OH, likely due to the high condensation loss near the ground surface. These observation results were further verified by a master chemical mechanism (MCM) box model simulation.
Origins of the high-amplitude magnetic anomaly zone in the northern South China Sea continental margin
Authors: Doo Wen-Bin , Huang Yin-Sheng , Wang Hsueh-Fen
Published: March 2024

Similar to the feature in the U.S. East Coast, an obvious roughly NE-SW trending high-amplitude magnetic belt (NSCSMA) appears in the northern South China Sea (SCS) continental margin, which extends from southwest Taiwan to the area about 114.5°E and 20°N. The likely cause of this magnetic high is important and interesting but still controversial. This study uses wavelet spectrum analysis, 2-D magnetic modeling, and compact inversion to constrain its causative sources. Our analysis results show the evidence indicating that the geometry and depth of the causative magnetic sources were varied along the strike of the NSCSMA (~15 km in the east and ~25 km in the west). Based on our findings and previous studies, we proposed that the major causative source of the NSCSMA could be the serpentinized upper mantle material.
Seasonal and interannual variations in carbon fluxes over a rain-fed spring maize cropland in the Loess Plateau, China
Authors: Zheng Han , Guan Yijing
Published: March 2024

Under the background of climate change and water resource shortage, it is of great significance to study the dynamics of carbon exchange and its environmental responses for the agroecosystems in coping with increasingly severe drought in water-limited areas. As the largest arid and semi-arid area in China, the Loess Plateau is widely distributed as rain-fed farmlands, which are highly affected by hydrological condition. In this study, the seasonal and interannual variations in carbon fluxes for a rain-fed spring maize field located in the Loess Plateau was analyze based on eddy covariance method during 2019-2020. Precipitation varied substantially in both annual amounts and seasonal distribution during the study period, with 2019 as a drought year and 2020 as a hydrologically normal year. Carbon fluxes showed unimodal seasonal trends, with peaks observed during the growing season. The annual net ecosystem exchange (NEE) were -309.49 and -423.19  g C m-2 in 2019 and 2020, respectively. It indicates that the corn cropland studied here is a carbon sink, and stronger net carbon uptake occurred for the hydrologically normal year compared with the drought year. The gross primary productivity (GPP) was a stronger driver of NEE than ecosystem respiration (Re), and both ecosystem maximum photosynthetic capacity (Amax) and ecosystem respiration rate at 10 °C (Q10) were closely related with vapour pressure deficit (VPD). The light response of NEE was strongly affected by environmental factors, especially soil water content (SWC) and VPD. Based on the light response analysis of NEE, the structural equation models (SEMs) were constructed to investigate the dominant controlling factors for the seasonal variations in NEE, GPP and Re among contrasting hydrological years. Results revealed that the variations in NEE, GPP and Re during growing season were primarily controlled by direct effects of LAI in normal year, while the effects of LAI on carbon fluxes were much smaller or nonsignificant in the normal year. The SWC variation could only produce significant direct effects on Re in normal year, but could strongly indirectly affect GPP and Re variations in the drought year. Overall, NEE variations were mainly affected by LAI, VPD and photosynthetically active radiation (PAR) in the normal year, and were susceptible to variations in air temperature and PAR in the drought year. This study will provide insights into the effects of drought on carbon exchange and its environmental responses for the agroecosystems in the water-limited region.
Minimizing visual impacts of renewable energy technologies and its implications for potential, costs, and energy transformation pathways: A nationwide study on Germany
Authors: Tsani Tsamara , Weinand Jann Michael , Pelser Tristan , Hoffmann Maximilian , Ioannidis Romanos , Maier Rachel , Risch Stanley , Kullmann Felix , McKenna Russell , Stolten Detlef
Published: March 2024

The energy transition necessitates the massive deployment of large-scale wind turbines and solar photovoltaics (PV). However, numerous countries, including Germany, have experienced setbacks in the form of project cancellations and delays that impede the installation of these technologies, which are driven by various non-technical factors. Local opposition, prompted by concerns over the visual impact of renewable energy technologies on the surrounding landscape, is one of these. Past studies have sought to tackle this problem by incorporating the visibility of wind turbines into planning considerations and potential analyses. However, these analyses have been limited to small regions and do not account for the visibility of other renewable technologies, such as solar PV.This study employs a nationwide, integrated, reverse-viewshed analysis, potential analysis, and techno-economic analysis. Furthermore, we evaluate the effects of designing renewable energy systems that are not visible in scenic or densely-populated areas on the remaining energy potential, energy system costs, and technological choices necessary to achieving net zero emissions by 2045. Installations visible from areas with different scenicness ratings (1–9) and population density thresholds are used to define scenarios to account for the sensitivity of visual impacts on different degrees of landscape scenicness and viewed by different population segments.Our research reveals that wind turbines with the highest levelized cost of electricity (LCOE) in Germany coincide with those that are visible from the most scenic landscapes (scenicness level 9). Therefore, minimizing the visual impact of wind turbines by placing them out of sight from the most scenic landscape areas could align with cost-effectiveness objectives. However, if the visibility restrictions become too strict (e.g., that they not be visible from scenicness levels ≥ 5 or population densities ≥ 300 people/km2), there will not be enough wind power potential (e.g., the remaining 6.8 TWh/year or 2.4 TWh/year) to cost-effectively achieve German climate targets. Instead, PV systems, with a lower visual impact, would be more favorable and selected in the optimization to meet energy demands.
Improving Distributional Regression Forests for Post-processing Extreme Wind Gust Forecasts 
Authors: François Bastien , Kivril Harun , Schmeits Maurice , Whan Kirien
Published: March 2024

Extreme events, such as wind gusts or extreme precipitation, can generate huge impacts on our society. Accurate predictions of such events are thus vital for taking preventive measures. In spite of continued scientific progress in weather forecasting, ensemble forecasts exhibit biases and under-dispersion and have to be calibrated using observations before being used, e.g., in hydrological or renewable energy applications. Several post-processing techniques have therefore been developed and applied over the last decades in order to improve forecast quality. Many existing post-processing methods are parametric, i.e. they assume that the predictive distribution belongs to a class of known probability distributions. Parameters of the assumed distribution are then modeled as functions of predictors obtained from numerical weather prediction models, for example using nonhomogeneous regression or more advanced tree-based methods. One of the main limitations of such methods is that a suitable family of probability distributions has to be selected to describe the distribution of the target variable. This implies that intermediate and high values are modeled with the same parametric distribution, which can lead to suboptimal results for extremes. We propose to adapt an existing distributional tree-based technique (Distributional Regression Forests) used for ensemble post-processing to overcome this limitation by allowing the method to choose different statistical distributions to model intermediate and extreme values. The proposed method is applied to forecasts of 6-hourly maximum wind gusts from 2018 to 2022 over the Netherlands using the ECMWF-IFS ensemble data. Results are compared against several state-of-the-art parametric and non-parametric post-processing methods. In comparison with these alternatives, the proposed algorithm reasonably corrects intermediate values and presents the largest skill improvements for wind gust extremes depending on lead times, stations and thresholds. However, it remains difficult to beat the raw forecasts of extremes. Therefore, it encourages further research on adding more flexibility to parametric methods for the post-processing of extreme weather forecasts.
PM2.5 source allocation in 708 European cities: a modelling study
Authors: Zauli Sajani Stefano , Thunis Philippe , Pisoni Enrico , Bessagnet Bertrand , Monforti-Ferrario Fabio , De Meij Alexander , Pekar Ferenc , Vignati Elisabetta
Published: March 2024

Ambient fine particulate matter (PM2.5) represents the world's greatest environmental health risk factor and most EU citizens are still exposed to PM2.5 levels above WHO guidelines. Shaping effective urban air quality plans requires the knowledge of pollutants’ origin in terms of different spatial scales, emission sectors and precursors involved in their formation.Here we present a comprehensive PM2.5 source allocation assessment carried out with the SHERPA model in 708 urban areas in Europe. Urban sources show a significant impact on local PM2.5 levels (an average of 22% of local concentrations). With regard to emission sectors, the residential sector’s contribution is greater than 50% in most cities in Northern Italy and Eastern Europe while the average contribution across all cities is 27%. The average contribution from industry, agriculture and road transport is 18%, 17% and 14%, respectively. High contributions from shipping and natural sources (>50%) are found in some Mediterranean cities exposed to southerly winds.  Urban areas can be clustered in three main categories: a) where emissions from the residential sector and primary PM2.5 precursors dominate (northern Italy and Eastern Europe); b) where shipping and natural emissions are the main source and dust and SOx are the main precursors (Southern Europe); and c) where secondary PM2.5 (>70%) dominates with comparable contribution from agriculture, industry, and transport and NOx and NH3 are the precursors (Central Europe and UK).Secondary pollution accounts for more than half of PM2.5 concentrations in almost all cities with large areas of Germany and Netherlands showing secondary contribution higher than 70%. In these areas NOx and NH3 as precursors and the agriculture and industry sectors are the most important sources of PM2.5.This source allocation assessment of PM2.5 emissions in all medium to large urban areas in Europe highlights how crucial it is to reduce the emissions of the residential sector in most EU cities.    
A new method for modelling key hydrological processes in paddy-dominated watershed based on water balance and remote sensing
Authors: Gao Xiang , Wang Housheng , Ren Rui
Published: March 2024

This study addresses the need for accurate runoff data for sustainable water resource management in paddy fields, focusing on China, where agriculture consumes more than 62% of freshwater, and paddy rice is the most water-intensive crop. Given the risk of nitrogen and phosphorus loss through runoff, accurate models are crucial for enabling improved irrigation management and assessing agricultural non-point source pollution.Modern hydrological models range from semi-empirical models, which are deficient in describing the growth phase of paddy, to process-based models that span either single large-scale paddy fields or the entire watershed. However, variations in historical models—and specifically, models such as SWAT-Paddy—indicate significant uncertainties due to the uniform application of irrigation date, amount and drainage outlet height.This study introduces a novel method that synthesizes the spatial distribution patterns of drainage outlet height and irrigation information (date and amount), while integrating different irrigation and drainage management protocols across various phenological periods. This method uses Google Earth Engine to build a continuous spatiotemporal resolution evapotranspiration model based on multiple-source remote sensing satellites. It also leverages the water balance equation to automatically identify spatiotemporal patterns of runoff at the field scale.We anticipate that this inclusive, accurate, and automated method will not only facilitate accurate quantification and assessment of paddy runoff but also provide critical data for studying agricultural non-point source pollution. These findings contribute to the existing body of knowledge on paddy water cycle dynamics and highlight the potential of remote sensing technology in addressing data scarcity challenges.
A stochastic model of catchment baseflow dynamics
Authors: Di Dato Mariaines , Bellin Alberto , Cvetkovic Vladimir , Dagan Gedeon , Dietrich Peter , Fiori Aldo , Teutsch Georg , Zech Alraune , Attinger Sabine
Published: March 2024

Groundwater discharge profoundly influences river flow, especially during dry spells, potentially exacerbating drought conditions, an issue compounded by escalating climate change-induced hydrological extremes. Amidst this, understanding aquifer systems' efficacy in mitigating (sub-)seasonal fluctuations and their ecological impacts gains significance even in moderate climates.This work introduces a stochastic modeling approach for groundwater-fed baseflow, as an alternative to the traditional hydraulic theory by accounting for spatial heterogeneity of subsurface storage properties and associated uncertainties. Leveraging on readily available rainfall-generated recharge and river discharge series, stochastic tools determine baseflow characteristics. The model’s foundation lies on representing groundwater recharge and subsurface storage as stochastic variables.With the subsurface storage represented as multiple linear reservoirs with stochastic storage parameters, the proposed model reveals the baseflow dynamics and the interplay between heterogeneous reservoir timescales and recharge variability, elucidating temporal variance of baseflow at the catchment scale. Furthermore, the study investigates equivalent parameters for an upscaled unique reservoir to model catchment behavior. Utilizing established stochastic analysis tools in subsurface hydrology, this research advances our understanding of heterogeneous hydrological catchments. In addition, the investigation analyzes the temporal statistical moments of baseline discharge dependent on input recharge and sub-catchments' response times. This detailed analysis unveils the system's attenuation effect as a metric for catchment resilience during prolonged droughts, significantly influenced by underlying hydrogeological properties. As a practical consequence, quantifying the dependency of the attenuation factor on both temporal and hydrogeological variability can help in identifying particularly sensitive watersheds, crucial for tailored adaptation strategies.
Conformal mapping for the magnetosheath modeling problems
Authors: Narita Yasuhito , Schmid Daniel , Holzkamp Henry
Published: March 2024

Determining the plasma flow and magnetic field in the terrestrial and planetary magnetosheath region is a challenge both in theoretical and observational studies in space plasma physics. We are motivated by the discovery of the Kobel-Flückiger exact solution for the Laplace equation to the scalar shielding potential for the parabolic geometry of the magnetosheath, and develop a novel algorithm of the conformal mapping to exactly transform the Kobel-Flückiger scalar potential onto a user-specified, arbitrary geometry of the magnetosheath. The algorithm starts with the outer and innter boundary models (e.g., bow shock and magnetopause locations in the case of planetary magnetospheres). The shell variable v is constructed by smoothly interpolating between the two boundaries, and the connector variable u (connecting between the two boundaries in an orthogonal fashion to the shell variable) is determined by evaluating the gradient of the shell variable along the shell segment under the Cauchy-Riemann relations. The conformal mapping method is computationally by far inexpensive, and retains the exactness character of the steady-state magnetosheath solution. The method has a wide range of applications such as validating the numerical simulations, planning the space (planetary and heliospheric) missions, and even estimating the solar wind condition from the magnetosheath data.
The alignment of  STEREO-A and Earth: A unique opportunity to investigate Solar Energetic Particle events.
Authors: Heber Bernd , Banys Daniela , Berdermann Jens , Dröge Henrik , Hörlöck Malte , Kollhoff Alexander , Kühl Patrick , Malandraki Olga , Martens Janna , Posner Arik , Sierks Holger
Published: March 2024

A major impact on human and robotic space exploration activities is the sudden and prompt occurrence of solar energetic ion events. In 2023 and 2024,  {STEREO} is approaching the Earth from a behind position, soon passing Earth inside its orbit and thereafter moving ahead of Earth.  {STEREO} thus offers several unique opportunities during this passage. In the period from June 1 to November 1, 2023, 5 {SEP} events have been measured that cause proton fluxes of above 25~MeV to rise above 0.1 /(cm$^2$\; s\; sr\; MeV). Taking into account systematic and statistical uncertainties of the particle measurements we find a good agreement between both spacecraft.The SOHO/EPHIN and STEREO/SEPTproject is supported under Grant 50~OC~2102 by the German Bundesministerium für Wirtschaft through the Deutsches Zentrum für Luft- und Raumfahrt (DLR). This study has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101004159 (SERPENTINE).
Research on the Importance of Feature Parameters in Seismic Sequence Type Determination Based on Decision Tree
Authors: Zhao Xiaoyan , Su Youjin , Meng Lingyuan
Published: March 2024

Based on the catalog of 225 earthquakes with magnitudes 5 or above, the catalog of earthquake sequences, and the focal mechanism of the historical earthquakes in Sichuan-Yunnan region from 1966 to 2021, and referring to the previous research and practice on the estimation of the tendency of the aftershock activity, 10 sample datasets for the judging features of the earthquake sequence types have been constructed. According to the earthquake sequences types—swarm type, mainshock-aftershock type, as well isolated type—three labels have been made. After processing the imbalanced state and the missing state of the feature parameters, a decision tree model was used to study and analyze the importance of feature parameters. The results showed that there were differences in the importance categories of the feature parameters in different periods. As the sequence data increased, sequence type judgment relied more on dynamic sequence data; the parameters related to the main shocks’ focal mechanism and the main shocks’ parameters have a high contribution rate to the sequence classification, while the contribution rate of sequence parameters is extremely low. In overall, the results provided by the model are consistent with the actual empirical prediction methods. The above results can provide some ideas for the preliminary screening, exclusion, and selection of the complex and numerous feature parameters.
-km resolution inversion of NOx emissions based on satellite constrained by geodata
Authors: Kong Hao , Lin Jintai , Zhang Yuhang , Wang Sijie , Xu Chenghao
Published: March 2024

High-resolution spaceborne emission inversions play a crucial role in independent emission monitoring, small-scale pollution modelling, and exposure estimation. However, spaceborne emission inversion at 1-km resolution is still a challenge due to the insufficiency of satellite observations, along with limitations such as computational costs and meteorological data. The spatial resolutions of existing satellite-based NO2 observations (e.g. TROPOMI: nadir pixel of ~3.5×5.5 km2) fall short in capturing spatial features at 1-km resolution. Here we develop an innovative technique to integrate high-resolution geodata in emission inversions. This technique introduces constraints based on geodata associated with emissions to inversions independent of predefined downscaling schemes. Our inversions show advanced results of NOx emissions with detailed spatial patterns at small scale, especially for sources relevant to traffic and marine shipping which are of large uncertainties in current inventories.
Effect of National Clean Air Programme on radiative forcing over India
Authors: Nayak Diljit Kumar , Habib Gazala , Kota Sri Harsha
Published: March 2024

Alarmingly high particulate matter (PM) levels are frequently blamed for India's poor air quality. As a result, the government has developed a few measures to regulate PM in the nation. For instance, the National Clean Air Plan (NCAP) was introduced in 2019 with the goal of bringing down PM concentrations in non-attainment cities (NAC) by 40% by 2026. This study endeavors to evaluate the accuracy of emission inventories in replicating the satellite observed AOD for the Indian region, and to identify the most suitable emission inventory among the available options for the common baseline year of 2015. Four databases (three global and one regional) that furnish emission estimates for air pollutants in India, which include EDGARv5, REASv3.2, ECLIPSE V6b and SMOGv1 were analysed.Simulations were conducted for different seasons using WRF-Chem V3.8.1. The key finding of the study is that SMOG emerged as the best performing emission inventory among all databases across all seasons, with an average Root Mean Square Error (RMSE) of 0.41 for the entire year. The simulations were performed with emissions projected for the years 2019 and 2026 from the best emission inventory obtained and fixing the Land use Land Cover (LULC) and meteorology. A decrease of 52.15 W/m2 in surface radiative forcing was observed across the Eastern India for the simulation period. This study provides valuable insights to India's regulatory bodies, highlighting the need to prioritize on source specific emission reduction to effectively combat the alarming increase in radiative imbalance which drives the climate change.
Runoff coefficient modelling using Long Short-Term Memory (LSTM) in the Rur catchment, Germany
Authors: Rahi Arash , Rahmati Mehdi , Dari Jacopo , Morbidelli Renato
Published: March 2024

This research examines the effectiveness of Long Short-Term Memory (LSTM) models in predicting runoff coefficient (Rc) within the Rur basin at the Stah outlet (Germany) during the period from 1961 to 2021; monthly data of temperature (T), precipitation (P), soil water storage (SWS), and total evaporation (ETA) are used as an input. Because of the complexity in predicting undecomposed Rc time series due to noise, a novel approach incorporating discrete wavelet transform (DWT) to decompose the original Rc at five levels is proposed.The investigation identifies overfitting challenges at level-1, gradually mitigated in subsequent decomposition levels, particularly in level-2, while other levels remain tuned. Reconstructing Rc using modelled decomposition coefficients yielded Nash-Sutcliffe efficacy (NSE) values of 0.88, 0.79, and 0.74 for the training, validation, and test sets, respectively. Comparative analysis highlights that modelling undecomposed Rc with LSTM yields to a minor accuracy, emphasizing the pivotal role of decomposition techniques in tandem with LSTM for enhanced model performances.This study provides novel insights to address challenges related to noise effects and temporal dependencies in Rc modelling; through a comprehensive analysis of the interplay between atmospheric conditions and observed data, the research contributes in advancing predictive modelling in hydrology.
Seasonal variation in organic carbon and its bioavailability (Falljökull glacier, Iceland)
Authors: Wild Ann-Kathrin , Fasching Christina , Chifflard Peter
Published: March 2024

Predictions regarding the export of organic carbon (OC) linked to glacier runoff remain constrained. Conventional mass balance approaches, which calculate annual OC export based on singular sampling points, overlook potential diurnal and seasonal variations in OC dynamics. In our study, we address this gap by employing high temporal resolution to systematically explore the concentration and composition of glacier-derived OC. Moreover, we examine the bioavailability of OC in glacial discharge directly at the terminus. This comprehensive investigation aims to enable accurate predictions of future OC release resulting from glacier retreat. Our chosen study site is the temperate Icelandic glacier Falljökull, part of the Öræfajökull and Vatnajökull ice cap, selected for its year-round accessibility.Our findings reveal an average concentration of dissolved organic carbon (DOC) from the glacier of 0.14 mg L-1 based on 72 streamwater samples from the glacier terminus. Seasonal variations are evident with higher concentrations measured in winter (0.19 mg L-1) compared to summer (0.10 mg L-1). While the DOC concentration was relatively low during rain and glacial melt (0.12 mg L-1), snowmelt doubled the DOC concentration (0.20 mg L-1) indicating deposition as a source of glacial DOC. Furthermore, DOC concentration in glacial melt varied on a diurnal basis with peak values during early afternoon at highest discharges. The different weather events are reflected in the glacier discharge which could be shown by comparing the isotopic signature of ice, snow, and precipitation to the isotopic signature of the discharge water during designated events.Absorbance and fluorescence measurements pointed to a predominantly protein-like, labile composition of DOC in glacial runoff. However, using incubation experiments with glacial meltwater we often found DOC values to increase pointing to the production of OC. Preliminary results highlight the seasonal and diurnal variability of glacial OC concentration and composition and the need to further study glacial OC bioavailability.
Confronting Earth System Model Trends with Observations: The Good, the Bad, and the Ugly
Authors: Douville Hervé
Published: March 2024

Despite the early warnings of the scientific community in general and of the IPCC in particular, we have entered decades in which climate models are no longer black boxes as the consequences of past emissions of greenhouse gases are emerging rapidly in multiple climate records. This unprecedented situation is likely to change our methods and our view of the respective roles of models and observations in understanding recent and predicting future climate change, regardless of the considered emission scenario. Among the key questions raised are the role of observations in model tuning versus projection constraining and the design of future model intercomparison projects. These questions will be illustrated by several recent studies aimed at constraining CMIP6 projections and, hopefully, with a fresh although critical look on the forthcoming CMIP7 project.
Modeling drought effects on rainfed crop yields using probabilistic and machine learning approaches
Authors: Sohoulande Clement , Khedun Prakash
Published: March 2024

Drought is a major hazard with significant impacts on agriculture, water resource availability, and terrestrial ecosystems. Under climate change drought events are expected to increase in frequency, severity, duration, and propagation with consequent impacts on crop yields. Given these circumstances, a thorough understanding of drought is needed to increase societal preparedness to drought effects on food production particularly in regions where agriculture is dominantly rainfed. Unfortunately, drought events remain very unpredictable suggesting the need to enhance the understanding of drought effects on rainfed crops. Hence, this study aims to examine the relationships between drought characteristics and rainfed crop yields. Particularly, the study uses probabilistic and machine learning (i.e., random forest) approaches to investigate the influence of standardized precipitation and evapotranspiration index (SPEI) severity and duration on the yield of corn, cotton, peanuts, and soybeans in the southeast region of the United State (US). County wise analyses were conducted for three contiguous southeastern States including North Carolina, South Carolina, and Georgia. Preliminary results outlined different performances depending on the approach, the counties, and the crops. Highly performing approaches could be considered for modeling drought effect on crops at county, State, or regional levels.
Oceanic gateways to Antarctic grounding lines - Impact of critical access depths on sub-shelf melt
Authors: Nicola Lena , Reese Ronja , Kreuzer Moritz , Albrecht Torsten , Winkelmann Ricarda
Published: March 2024

Melting underneath the floating ice shelves surrounding the Antarctic continent is a key process for the stability of the Antarctic Ice Sheet and therefore its current and future mass loss. Troughs and sills on the continental shelf play a crucial role in modulating sub-shelf melt rates, as they can allow or block the access of relatively warm, modified Circumpolar Deep Water to ice-shelf cavities.In our study (Nicola et al., subm.), we identify potential oceanic gateways that could allow the access of warm water masses to Antarctic grounding lines based on critical access depths inferred from high-resolution bathymetry data. We analyse the properties of water masses that are currently present in front of the ice shelf and that might intrude into the respective ice-shelf cavities in the future. We use the ice-shelf cavity model PICO to estimate an upper limit of melt rate changes in case all warm water masses up to a certain depth level gain access to the cavities. The identification of oceanic gateways is thus valuable for assessing the potential of ice-shelf cavities to switch from a 'cold' to a 'warm' state, which could result in widespread ice loss from Antarctica.
WACCM-X simulations with NAVGEM-HA meteorological analyses and SABER observations of mesosphere and lower thermosphere temperature 
Authors: Liu Guiping , Klenzing Jeffrey , McDonald Sarah , Sassi Fabrizio , Rowland Douglas
Published: March 2024

Realistic modeling of the dynamics and variability in the mesosphere and lower thermosphere (MLT) is significant to understand the coupling of the whole atmosphere system. Here we present the simulations of the MLT temperatures at ~100 km altitude for one year during 2014 by Whole Atmosphere Community Climate Model with thermosphere-ionosphere extension (WACCM-X) constrained below ~90 km using meteorological analysis products of the high-altitude version of Navy Global Environmental Model (NAVGEM-HA). The model results are sampled at the same times and locations as the satellite observations from Thermosphere Ionosphere and Mesosphere Electric Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER). Comparisons of the daily mean temperatures show that the observed and modeled values are correlated (correlation coefficient equals to ~0.5-0.7) at latitudes away from the equator. Both the observations and simulations reveal an annual variation at mid-latitudes with the temperature maximum in summer and minimum in winter, and at lower latitudes the semiannual variation becomes stronger having the temperature maximums at equinoxes and minimums during solstices. However, the temperatures observed are on average ~5-10 K (3-5%) smaller than the model and the observations show a larger variability across all latitudes between 50oS-50oN. The WACCM-X simulations with constrains by NAVGEM-HA meteorological analyses are overall consistent with the SABER observations though some differences are noticed. Whole atmosphere models with high altitude observation constrains would be useful to improve the numerical simulations of the MLT variability and the atmosphere and ionosphere coupling.
Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya
Authors: Tiwari Jyoti , Bhakuni Surendra S. , Goswami Pradeep , Tiwari Anil
Published: March 2024

Understanding the geodynamics and seismotectonic characteristics of a region requires an integrated approach involving the analysis of structures, active deformations, seismicity, and tectonic stress conditions. Analysing the links between ongoing seismic activities and the development of the landscape provides a deeper understanding of the dynamic interplay between tectonic forces and geological formations. This study focuses on the Kullu-Larji-Rampur (KLR) window in the NW Himalaya, situated just south of the Main Central Thrust (MCT), where seismicity is notably frequent. The primary objective is to comprehensively analyse parameters in this region, located in Himachal Pradesh, India. Extensive fieldwork involved scaling and mapping active deformation and geomorphological features along major transverse routes of the Sutlej and its tributaries in Himachal Pradesh. Structural data collected encompass measurements of foliation/schistosity, lineations, bedding planes, fold hinge lines, limb of folds, axial planes, shear zones/planes, kinematic indicators, and more. Results from structural data, remote sensing data and field investigations indicate active footwall duplexing or faults along bounding surfaces of tectonic horses, including younger thrust splays within the footwall block of the Jutogh Thrust (JT) or within the KLR window. Additionally, the study assesses localized stress behaviour and seismicity parameters (b-value and source mechanisms) in this seismically active region using background seismicity. Notably, significant depth variations and anomalies in stress conditions are observed, interpreted as a brittle-semi-brittle and stress transition zone. The south-eastern section of the KLR window is identified as a high-stress accumulation zone. We have established a correlation between present-day seismicity and the evolving landscape of the region. The study concludes that continuous interseismic and co-seismic deformation, along with the active footwall duplex in the Lesser Himalayan Sequence (LHS), play pivotal roles in shaping the growth of the KLR window and driving active in-sequence thrusting along the younger splays of the Jutogh Thrust.
Gaming the Water Cycle: a student-led activity to explore climate change.
Authors: Blue Kendall
Published: March 2024

The water cycle plays an important part in climate change. This activity games the construction of the water cycle by students taking the role of a water molecule as it moves between reservoirs. The processes involved will be described and explained, however, students will have to work collaboratively in order to complete the water cycle in its entirety.The factors that power the movement (gravity and state changes) will be determined and linked to changes in the amount of water found in each reservoir. Although gravity can’t be changed, the heat budget can, and this will affect the change in state of water, leading to unbalancing the water cycle.Thought experiments and discussion on possible effects of climate change, especially through global warming, will allow students to understand its effects on the water cycle and the subsequent effects on the climate, in particular:Positive feedback of decreasing albedo and increased water vapour in the atmosphere.
Increase in liquid water resulting in sea level rise and flood risk.
After using the Water Cycle Game, students will have a better understanding of the complexities in the water cycle, its effect on the climate, and have an appreciation of how climate change can have a local and global effect in a highly likely future.
Fine-scale seafloor bedform morphology along a slope-confined submarine canyon in the Northern South China Sea
Authors: Sun Yue , Wang Dawei , Canals Miquel , Alves Tiago M , Zeng Fanchang
Published: March 2024

Bedforms are widely distributed within deep-water submarine canyons, which are usually documented by vessel-mounted sensors. Yet, fine-scale geomorphology and shallow structures of bedforms in deep-water submarine canyons remain poorly documented, and understood, because of the insufficient resolution of vessel-based data. This study utilizes high-resolution autonomous underwater vehicle (AUV) dataset combined with intermediate seismic reflection profile and sediment cores to analyze bedform sets along a slope-confined submarine canyon (canyon C14) from the northern South China Sea. A train of crescent-shaped to inverted U-shaped axial steps in plan view are aligned downstream along the canyon thalweg from upper course to lower course. Based on comprehensive analysis of morphologic features, subsurface structures, flow estimates, and potential origins, these steps are likely to be cyclic steps created by supercritical turbidity currents. Sediment cores mainly comprised by silt with minor sand contents further suggesting the shallow canyon sediments probably deposited by diluted turbidity currents. Axial steps (S1-S4) with lower asymmetry and wavelengths in the upper course show an erosional truncation and horizontal to sub-horizontal reflectors draping on the lee side and stoss side, respectively, illustrating the erosional-depositional cyclic steps formed by more confined flow with higher erosion capability due to the narrow canyon (average width of 3.5 km) and steep slope gradient (average of 2.36°). Leaving transition segment, the less confined flow passing through lower course can be subject to wider canyon (average width of 5.5 km) and gently slope gradient (average of 1.2°) that increases the asymmetry and wavelengths of axial steps (S5-S7) and leave backset bed deposits on the stoss sides, probably pointing to the depositional cyclic steps with higher aggradation. Sediment filling, almost padding each cyclic step-associated scour, indicate that the previous-formed bedforms can be reworked by subsequent gravity flows deposits which mainly consist of slope failures-associated mass-transport deposits and turbidity currents deposits. Near the lower end of the canyon, reduction in flow velocity caused by further decrease of slope gradient (average of 1.05°) as the key factor leading to the shift from cyclic steps to furrows, but always under supercritical flow conditions. In this context, a sector of axial channel probably promotes the re-convergence of turbidity currents, resulting in the erosion of fine-grained cohesive deposits on the canyon floor, to form linear furrows within the axial channel. This work provides a good opportunity to investigate the fine-scale morphological features and shallow structures of bedforms in deep-water submarine canyon, and understand their evolution under the influence of canyon topography.
High-cadence VLBI in Australia for an improved TRF in the southern hemisphere
Authors: McCallum Lucia
Published: March 2024

The accuracy and robustness of the International Terrestrial Reference Frame lies in the combination of the four space-geodetic techniques. Network imbalances, partly caused by geography and land coverage strongly favour the northern hemisphere in the number of observations and, to a less clear extent, in accuracies. This is evident in large tie discrepancies, for example in Katherine and Yarragadee in Australia, where results from the various techniques differ to a significant degree.In this contribution we investigate the hypothesis that those discrepancies stem from deficiencies in the global combination of the various techniques, rather than from the individual observations. Specifically, we show that a regionally processed VLBI dataset is superior in its local station coordinate repeatabilities than when processed as part of the global network.The Australian AuScope VLBI network has been operating for over 10 years, delivering higher cadence and partly more precise observations than the regular global IVS observations. It is our aim here to investigate whether a local comparison between VLBI and GNSS data in Australia can shed light into the mystery of significant tie discrepancies that are currently present in the ITRF for this region.
Intensified Structural Overshoot Aggravates Drought Impacts on Dryland Ecosystems
Authors: Liu Liu , Zhang Yixuan , Cheng Yongming , An Qiang , Kang Shaozhong
Published: March 2024

A favorable environment can induce vegetation overgrowth to exceed the ecosystem carrying capacity, exacerbating water resource depletion and increasing the risk of lagged effects on vegetation degradation. This phenomenon is defined as structural overshoot, which can lead to large-scale forest mortality and grassland deterioration. However, the current understanding of structural overshoot remains incomplete due to the complex time-varying interactions between vegetation and climate. Here, we used a dynamic learning algorithm to decompose the contributions of vegetation and climate to drought occurrence, trace the connection between antecedent and concurrent vegetation dynamics, thus effectively capturing structural overshoot. This study focused on the climate-sensitive hotspot in Northwest China drylands, where significant vegetation greening induced by a warming and wetting climate was detected during 1982–2015, leading to soil moisture deficit and aggravating vegetation degradation risks during droughts. We found that during this period, structural overshoot induced approximately 34.6% of the drought events, and lagged effects accounted for 16.7% of the vegetation degradation for these overshoot drought events. The occurrence of overshoot droughts exhibited an increasing trend over time, which was primarily driven by vegetation overgrowth followed by precipitation variation. Although the severity of overshoot and non-overshoot droughts were generally comparable in spatial distribution, the impact of overshoot droughts is still becoming increasingly obvious. Our results indicate that the expected intensified overshoot droughts cannot be ignored and emphasize the necessity of sustainable agroecosystem management strategies.
Ancient DNAs: Influence of Sedimentary Deposition on Bacterial Communities in Arctic Holocene Sediments
Authors: Dukki Han , Seung-Il Nam
Published: March 2024

Community assembly principles driving microbial biogeography have been studied in many environments, but rarely in the Arctic deep biosphere. The sea-level rise during the Holocene (11–0 ky BP) and its resulting sedimentation and biogeochemical processes can control microbial life in the Arctic sediments. We investigated subsurface sediments from the Arctic Ocean using metabarcoding-based sequencing to characterize bacterial 16S rRNA gene composition, respectively. We found enriched cyanobacterial sequences in methanogenic sediments, suggesting past cyanobacterial blooms in the Arctic Mid-Holocene (7–8 ky BP). Bacterial assemblage profiles with a sedimentary history of Holocene sea-level rise in the Arctic Ocean enabled a better understanding of the ecological processes governing community assembly across Holocene sedimentary habitats. The Arctic subsurface sediments deposited during the Holocene harbour distinguishable bacterial communities reflecting geochemical and paleoclimate separations. These local bacterial communities were phylogenetically influenced by interactions between biotic (symbiosis–competition or immigration–emigration) and abiotic (habitat specificity) factors governing community assembly under paleoclimate conditions. We conclude that bacterial profiles integrated with geological records seem useful for tracking microbial habitat preference, which reflects climate-triggered changes from the paleodepositional environment (the so-called ‘ancient DNAs’).