bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing the validity of simple models for tropical cyclones in high resolution simulations
Authors: Charinti Giousef Alexandros
Published: March 2024

Existing theoretical models for tropical cyclones have been instrumental in understanding the mechanisms under which their intensification occurs. The potential intensity (PI) which was first introduced by Emanuel 1986, provides an upper bound for the intensity a tropical cyclone can achieve based on the environmental conditions. However, this model and others naturally assume idealized settings which do not necessarily occur in the real world. Using simulations from the high resolution cloud resolving model SAM in rotating radiative-convective equilibrium settings, we assess the validity of these idealizations in the simulations. We find that some idealizations, such as assuming convection on a moist adiabat in the eyewall, are only partially valid. In order to understand why these deviations from the theory occur, we look at different possible mechanisms missing in simple models, such as upper level processes and entrainment.
Local thermal non-equilibrium in heterogeneous porous media identified through 3D heat transport modelling
Authors: Gebhardt Hannah , Zech Alraune , Rau Gabriel , Bayer Peter
Published: March 2024

Modelling heat transport in porous aquifers is generally based on the assumption of an instantaneous local thermal equilibrium (LTE) between the solid and the fluid phase. Previous studies have revealed that this assumption can be violated, e.g. in the presence of fast or preferential flow causing delayed heat diffusion into the grain structure matrix, referred to as local thermal non-equilibrium (LTNE). However, conditions and scales at which LTNE effects should be taken into account in natural heterogeneous sediments are almost unexplored. We study the relation between macro-scale heterogeneity, thermal dispersion and LTNE through numerical simulations of heat transport in three-dimensional heterogeneous hydraulic conductivity fields. The advection-diffusion equation is solved using the Multiphysics Object-Oriented Simulation Environment (MOOSE), an open-source, parallel finite element framework. The spatial and temporal evolution of the heat plume generated by a line source under steady-state flow conditions is examined. For understanding the propagation of heat plumes, the role of delayed diffusion caused by LTNE effects needs to be distinguished from hydro-mechanical dispersion. Therefore, we estimate the thermal dispersion and the effective thermal retardation for each time step using a stochastic approach. LTNE effects are present, when the effective thermal retardation deviates from the predicted, apparent thermal retardation. Simulations show good agreement between the effective and the apparent thermal retardation for homogeneous hydraulic conductivity. With increasing heterogeneity, characterized by a higher variance of the log-conductivity, the effective retardation becomes lower than the apparent retardation at early times. Furthermore, we estimate the effective thermal retardation for a homogeneous flow field with added thermal dispersion based on the dispersion coefficients resulting from the heterogeneous simulations. We find that there is a significant difference in the evolution of effective retardation between the homogeneous and the heterogeneous case both of the same thermal dispersion, which we associate to LTNE effects. Our modelling approach thus allows to quantify LTNE induced by field-scale heterogeneity.
Towards CO2 emission estimation in urban areas using a dense sensor network and the high-resolution GRAMM/GRAL model
Authors: Sommani Anna , May Maximilian , Turner Alexander J. , Cohen Ronald C. , Vardag Sanam N.
Published: March 2024

Urban areas are responsible for about 70% of anthropogenic CO2 emissions and are therefore an important system in which to develop mitigation strategies to reduce emissions. To assess these strategies and monitor mitigation efforts, independent knowledge of urban CO2 sources is required. A measurement-based estimation of emissions can be obtained using CO2 measurements, along with prior information on emissions from inventories and a high-resolution transport model.Here we use the forward model system GRAMM/GRAL. This consists of two nested models, a prognostic mesoscale model (GRAMM), and a microscale computational fluid dynamics and Lagrangian dispersion model (GRAL). We run GRAL on a 15 km x 15 km grid over the city of Oakland, California, at a horizontal resolution of 10 m x 10 m. This resolution of 10 meters is sufficient to resolve street canyon effects. We utilize the Berkeley Atmospheric CO2 Observation Network (BEACO2N), a unique high-density network of CO2 monitoring stations consisting of mid-cost sensors. To optimize computational time, GRAMM/GRAL is run in a steady-state mode where we compute hourly steady-state wind and concentration fields, corresponding to different synoptic meteorological situations. To infer the temporal evolution of the simulated CO2 concentration over a whole year we then use a match-to-observation algorithm that for each hour chooses the hourly steady-state wind field which minimizes the difference between the simulated wind and the observed wind time series from an urban network of wind measuring stations (May et al. 2024).In our study, we assess the performance of the GRAMM/GRAL model in Oakland and compare the modelled and measured wind and concentration fields over a year. In general, we find a good agreement between modelled and observed wind fields. Comparing the time series of simulated CO2 concentration to the observed CO2 concentration from the BEACO2N network, we analyze the agreement and difference between the modelled and simulated CO2 concentration and propose possible improvements in the modelling framework. Finally, we propose an inversion set-up to infer emission estimates at high resolution given the observations and discuss remaining challenges and limitations.
The influence of glyphosate on soil CO2 respiration and microbial communities structure in histosol and fluvisol
Authors: Furtak Adam , Szafranek-Nakonieczna Anna , Górski Andrzej , Pytlak Anna
Published: March 2024

Carbon dioxide is the most important among all greenhouse gases and microbial respiration is one of the fundamental soil processes, that contribute to atmospheric CO2 pool. Many factors influence the respiration of soil microbiota. With regard to agricultural soils, the most discussed are the type of cultivation and fertilisation. Much less attention is paid to herbicides, which are widely used and comprise a frequent contaminant of the soil environment. The most commonly used herbicide worldwide is glyphosate (GFP). In 2018, annual  GFP consumption exceeded 8.25 x 108 kg and is still increasing. GFP is a foliar herbicide that is used in agriculture in the form of commercial formulations (GFC). Due to imprecise dosing, leaf washoff or with plant necromass, GFC reaches the soil environment where can potentially modulate activity and abundance of soil microorganisms. Possible modes of action include toxicity (e.g. due to inhibition of the shikimate pathway) or stimulation due to the fact that GFP is biodegradable and can potentially be a source of all major biogenic elements C, N and P. Due to the widespread use of GFC in agriculture, it may be an important driver of soil-related CO2 emissions, but knowledge in this area is still fragmentary.  In the current study, a wide range of GFP and GFC (0 – 10 000µg g-1) doses were used to determine its effect on microbial respiration in two agriculturally used soils (histosol and fluvisol). In parallel, the qualitative and quantitative composition of the soil microbial community was studied. Pure glyphosate (GFP) and a commercial formulation (GFC) containing adjuvants in addition to glyphosate were tested.For both soils, the exposure to GFP and GFC resulted in an increase in microbial respiration. However, this effect was greater for GFC, indicating the important role of adjuvants in shaping the environmental effect of the herbicides used. In accordance with the respiration results, a significant increase in the total bacteria count was found in both studied soils. Qualitatively, communities' structures were not significantly transformed, even under the influence of high doses of the tested preparations.
Ensuring the monitoring of ground heat storage with satellite data
Authors: Cuesta-Valero Francisco José , Peng Jian
Published: March 2024

Global ground heat storage is the second largest term of the Earth heat inventory only after the ocean, representing a 4-5% of the total heat storage within the climate system. Furthermore, determining the heat storage and heat flux in the land subsurface is necessary for closing the surface energy budget and quantifying the total energy exchange between the lower atmosphere and the shallow continental subsurface. Global long-term estimates of ground heat storage have been retrieved from geothermal data, with measurements from Eddy-covariance stations as a complement. Nevertheless, these two databases are biased towards northern extratropical latitudes, and there are not enough records to obtain a global average of ground heat storage after the year 2000. For this reason, ground heat storage for the period 2000-2020 consists in an extrapolation of the trend from the previous 30 years.We estimate ground heat storage from six remote sensing products provided by the Climate Change Initiative of the European Space Agency (ESA-CCI). The products consist in land surface temperatures derived from three single-sensor (ENVISAT, MODIS-Terra, and MODIS-Aqua) and three multi-sensor datasets (IRCDR, IRMGP, and SSMI-SSMIS), covering all land surface except Greenland and Antarctica. First, ground heat fluxes are derived from the satellite land surface temperatures using two different methods, and are then evaluated against in situ heat flux observations at Eddy-covariance stations from the FLUXNET, the Integrated Carbon Observation System (ICOS), and Ameriflux databases. The heat fluxes are accumulated to derive ground heat storage for each satellite product, and combined with the estimates from geothermal data to cover the period 1960-2020. This new estimate yields a heat storage of 20.9 ± 4.3 ZJ during the period 1960-2018, while previous estimates reached 24.0 ± 5.4 ZJ and 20.47 ± 0.19 ZJ for the same period. During the period without geothermal estimates, from 2000 to 2020, the new multi-satellite average reaches 10.5 ± 6.4 ZJ, a similar value to the one based on a linear extrapolation of geothermal values (10.18 ± 0.22 ZJ). Furthermore, satellite estimates provide spatial patterns of heat flux changes at the global scale with a high spatial (1 km) and temporal (monthly) resolutions, which will allow to perform analyses not possible with other, more coarse, datasets. Overall, these results reinforce the values obtained in previous analyses, while the methodology used here ensures the monitoring of global ground heat storage in the next decades.
Comparison of different observational constraint methods to reduce the uncertainty in the AMOC at the end of the 21st century
Authors: portmann valentin , Swingedouw Didier , Chavent Marie , Khattab Omar
Published: March 2024

For a given greenhouse gas emission scenario, climate models are showing very significant differences for the future climate, due to processes complex to simulate. Among them, the Atlantic Meridional Overturning Circulation (AMOC) fate has been shown to be very uncertain, explaining large amount of the differences in climate projections in the North Atlantic region. Indeed, under the ssp2-4.5 scenario, CMIP6 models show an AMOC maximum at 26°N that goes from 18.1 ± 4.1 Sv (1 Sv=106 m3/s, ensemble mean of 30 models one standard deviation) during the period 1850-1900, to 11.6 ± 3,9 Sv in the last decade of 2100, with AMOC ranging from 4.3 to 21.3 Sv depending on the model. There is thus a clear need to improve estimates of the AMOC in the future.In this respect, methods called emergent or observational constraint (OC) have been recently developed. They combine climate models and observations, by finding and using an emergent relationship between a given climate variable in the future and observable predictors, to refine the best guess and uncertainty estimation of this climate variable. This study proposes to apply them to the case of AMOC projections. Both the choice of the predictor, and of the OC method can be key. What are the best choices to reduce most the uncertainty of the AMOC at the end of the 21st century? To answer such a question, this study compares two possible cases: it uses either only one predictor, the past AMOC, or a set of predictors, the sea surface temperature and salinity from various regions in the world, which are known to impact on-going and future fate of the AMOC. Moreover, this study compares five different OC methods. The uncertainty is evaluated for each couple of predictors and OC choice, considering cross-validation and observational errors.The best estimates of future AMOC under ssp2-4.5 scenario, constrained by the observed AMOC over the period 2004-2021, is 11,6 ± 2,5 Sv, using the linear regression method. When constrained by a larger set of predictors, it is 7,9 ± 2,1 Sv, using also the linear regression found here as the best OC method, with a Ridge regularization that limits overfitting. Thus, the future AMOC, in 2091-2100 compared to 1850-1900, is weakening by 56% when constrained by various recent observations that count for AMOC dynamics, in place of 36% when estimated using ensemble mean or AMOC observation only, as done in last IPCC reports. This result might have therefore considerable impacts on future adaptation plans within the North Atlantic regions.
Sediment-laden basal ice units near the onset of a fast-flowing glacier in East Antarctica
Authors: Franke Steven , Wolovick Michael , Drews Reinhard , Jansen Daniela , Matsuoka Kenichi , Bons Paul
Published: March 2024

Understanding the material properties and physical conditions of basal ice is crucial for a comprehensive understanding of Antarctic ice-sheet dynamics. Yet, direct data are sparse and difficult to acquire, necessitating geophysical data for analysis. We employed high-resolution ultra-wideband radar to map high-backscatter zones near the glacier bed within East Antarctica's Jutulstraumen drainage basin. In addition, we used radar forward modelling to constrain their material composition. Our results reveal along-flow oriented sediment-laden basal ice units connected to the basal substrate, extending to several hundred meters thick. Three-dimensional thermomechanical modelling suggests these units initially form via basal freeze-on of subglacial water originating upstream. We suggest that basal freeze-on and the entrainment and transport of subglacial material play a significant role in an accurate representation of the material, physical, and rheological properties of the Antarctic ice sheet's basal ice, ultimately enhancing the accuracy and reliability of ice-sheet modelling.
Implications of Energetic Neutral Atoms observed with IBEX-Lo for the pressure balance in the heliosphere
Authors: Galli André , Wurz Peter , Schwadron Nathan S. , Möbius Eberhard , Fuselier Stephen A. , Sokół Justyna M. , Bzowski Maciej , Swaczyna Paweł , Dialynas Kostas , McComas David J.
Published: March 2024

Energetic Neutral Atoms (ENAs) from the heliosphere are a unique means to remotely image the boundary regions of our heliosphere. NASA's Interstellar Boundary Explorer (IBEX) has been very successful in measuring these ENAs since 2008 at energies from tens of eV to 6 keV.The ENA low energy range from tens of eV to solar wind energy (roughly 1 keV) has been sampled throughout an entire solar cycle with the IBEX-Lo ENA imager. This enables us to study the physical implications for the structure of the heliosphere and for the parent proton populations in the heliosheath and other plasma regions that give rise to the observed ENAs. Here, we will discuss in particular the implications of the measured ENA intensities for the plasma pressure balance at the heliospheric boundary.
Ground-truthing the performance of Orbitrap-iso for ice core nitrate stable isotope ratios by comparison to traditional Isotope Ratio Mass Spectrometer (IRMS) measurements
Authors: Saville Jack , Gautier Elsa , Savarino Joël , Lamothe Alexis
Published: March 2024

Innovative enhancements to the bioanalytical Orbitrap mass spectrometer now allow quantification of stable isotope ratios of soluble species. The novel technique, known as Orbitrap-iso, enables deeper-than-ever isotopic analysis of ice core oxyanions, including nitrate and sulfate.On paper, the Orbitrap-iso methodology presents a compelling alternative to the established Isotope Ratio Mass Spectrometry (IRMS) approach for quantification of isotope ratios of ice core oxyanions. Unlike IRMS, which necessitates the conversion of nitrate samples into gases (N2, O2) for analysis, Orbitrap-iso directly measures isotopologue ratios on intact ions in liquid solution. This streamlined process significantly simplifies sample preparation and enables additional quantification of enrichments in multiply-substituted (clumped) isotopologues in ice core oxyanions. These enrichments can offer valuable insights into the historical oxidative environment of Earth's atmosphere.Moreover, Orbitrap-iso boasts the capability to deliver simultaneous measurements of multiple isotopologue ratios from minuscule sample quantities, as low as nanomoles. This requirement represents a monumental reduction in sample size compared to IRMS, empowering the extraction of higher temporal resolution records from ice cores.Despite these notable advantages of the Orbitrap-iso method, questions linger regarding its accuracy, reproducibility, and precision relative to the long-established industry standard, IRMS. In an effort to validate the quality of Orbitrap-iso isotopologue ratio measurements, our study rigorously compares the analysis of identical ice core nitrate samples using both systems, aiming to establish a ground truth for the Orbitrap-iso methodology.
Differences in annual signals between IGS- and NGL-derived position time series: testing different strategies of alignment to the reference frame
Authors: Bogusz Janusz , Rebischung Paul , Klos Anna
Published: March 2024

Annual signals derived from GNSS position time series have become a very important source of information on a variety of geophysical phenomena occurring in the closer or farther vicinity of the antennas. In this research, we investigated the vertical position time series obtained from the International GNSS Service (IGS) third reprocessing (repro3) and PPP times series from the Nevada Geodetic Laboratory (NGL). We selected 1019 globally distributed stations with good quality data and time spans longer than 5 years. First, we pre-processed them for outliers and identified the epochs of offsets using manual inspection. Then, we inspected the differences between the annual signals contained in both sets of time series. We noticed from the map of annual signal differences that there is a worldwide annual common mode in the series of “IGS-NGL” station position differences, with a median amplitude of the order of 2 mm, and a maximum around August. We hypothesized that those differences could be explained by different strategies of alignment to the reference frame, and in particular by the alignment of the NGL series to the scale of the ITRF. To investigate this, we produced additional series by applying different types of constraints to the daily repro3 normal equations. Namely, we compared four sets of time series: “IGS” which are the official repro3 solutions, aligned by no-net-rotation nor translation (NNR+NNT) constraints to the IGSR3 reference frame via the well-distributed IGSR3 core network; “IGa” which are repro3 solutions aligned by no-net-rotation, translation nor scale (NNR+NNT+NNS) constraints to IGSR3 via the same core network; “IGb” which are repro3 solutions aligned by NNR+NNT+NNS constraints to IGSR3 via the same daily sets of reference stations as used by Jet Propulsion Laboratory (JPL) to align their orbit and clock products; and “IGc” which are repro3 solutions aligned by NNR+NNT+NNS constraints to the IGb14 reference frame via the same set of reference stations as used by JPL. A comparison of these four sets of time series with the NGL PPP time series reveals that c.a. half of the systematic differences in vertical annual signals between IGS and NGL comes from the alignment of the NGL solutions in scale to the reference frame, and another half comes from the use of different station networks for the alignment to the reference frame.
The PANACEA project: Probabilistic AssessmeNt of volCano-related multi-hazard and multi-risk at Mount EtnA
Authors: Cappello Annalisa ,   PANACEA team
Published: March 2024

Volcanic risks cannot be stopped or eliminated, but their effects can be minimized by applying new methods and providing data to support decision-making processes. Etna is one of the most active volcanoes in the world, producing both effusive and explosive eruptions, together with very intense seismic activity, which significantly influence the territory and society. The PANACEA project intends to address some issues that are still open in the modeling and integration of risks deriving from seismic and volcanic hazards, in order not to be caught unprepared and implement proactive risk reduction policies. In particular, the project has focused on the: (i) classification and statistical analysis of the historical eruptions of Etna; (ii) revision of the historical earthquake catalogue and the related database of macroseismic intensities; (iii) assessment of the long-term probability of vent opening based on historical eruptions and seismicity; (iv) extraction of the input parameters to run numerical simulations; (v) physics-based modeling of complex geophysical flows; (vi) probabilistic hazard mapping for single eruptive products, i.e. lava, tephra fallout and PDCs; (vii) probabilistic seismic hazard assessment; (viii) harmonization of the different hazards in a single long-term hazard map; (ix) analysis of the possible interactions at the hazard and the vulnerability levels, in order to quantitatively update hazard and risk estimations; (x) exposure and vulnerability assessment of elements at risk; (xi) multi-risk analysis by combining multi-hazards, exposure and vulnerability assessment. The results of PANACEA demonstrate that a better understanding of geophysical flow mechanisms, as well as improvements in knowledge in volcanic and seismic multi-hazard and multi-risk assessment, both in conceptual and technological terms, provide a powerful tool to develop effective and operational strategies, improving safety and reducing the impact of Etna's eruptive events.
Shear‐Wave Velocity Structure beneath Southeast Coastal Areas of China from the F-J Multimodal Ambient Noise Tomography
Authors: Li Haiyan , Chen Xiaofei , Cai Huiteng
Published: March 2024

The Southeast Coastal Areas of China (SCAC) is part of the Cathaysia block, the convergence area of the Eurasian, Pacific and India-Australian plates. The Cathaysia and the Yangtze blocks collided and merged into the South China block in the Neoproterozoic. These areas have experienced complex geological evolution and multiple periods of intense magmatic events since the Paleozoic, mainly manifested as a large number of Paleozoic and Mesozoic granitic rocks and Cenozoic mafic magmatism. Large-scale structural deformation caused by emplacements is very strong to the stratum reconstruction, forming a series of faults with different scales and directions. The development of large-scale fault systems has led to the potential risk of strong earthquake disasters in the region. In addition, the urban agglomeration with its dense population, is located in SCAC. Thus, seismic risk assessment and seismic research are very urgent and critical. The high-resolution crustal structure model is especially necessary for understanding the geological processes and seismic hazards in and around the areas. We collected ambient noise data from fixed and temporary seismic stations in the SCAC, and used the frequency-Bessel transform (F-J) method to extract Rayleigh wave dispersion curves and performed multimodal ambient noise dispersion curves inversion. We constructed a 3D high-resolution S-wave velocity model for this area. Specifically, we extracted reliable multimodal dispersion curves (up to the 8th higher-order in some sub-areas) with a broad frequency band range (0.03Hz-0.65Hz). Preliminary results show a widespread mid-crustal low-velocity zone, and we will further discuss the crustal structural anomalies and their related tectonic implications and evolution mechanisms.
Climatic and environmental impacts of the ~74 ka Youngest Toba Tuff volcanic eruption in Indonesia as evidenced from the sediment record of Lake Chala (Tanzania/Kenya)
Authors: Park Jinheum , Wolff Christian , Verschuren Dirk , Leng Melanie J. , Lacey Jack H. , Van Daele Maarten , Lane Christine S. , Martin-Jones Catherine , Vidal Céline M. , Oppenheimer Clive , Barker Philip A.
Published: March 2024

The ~74 ka Youngest Toba Tuff (YTT) eruption of Mount Toba in Indonesia is considered to be the largest volcanic eruption during the last 2.6 Ma. Its impact on global climate regimes and ecosystems, especially in tropical regions, is important due to possible consequences for the evolution and dispersal of early modern humans. In this study, we utilise the high-quality lake-sediment record from Lake Chala (Tanzania/Kenya), recovered by the ICDP DeepCHALLA project, to reconstruct the climatic and environmental impacts of the YTT in eastern equatorial Africa. Previous work identified a cryptotephra layer that was geochemically correlated to the YTT. In this study, focusing on the section of finely laminated sediments lying directly below and above the YTT layer, we compile high-resolution data from thin-section optical microscopy, geochemistry and fossil diatom assemblages in order to trace changes in climatic, local lake-system and wider environmental conditions immediately before and after the YTT event. Most proxy analyses were conducted at annual or higher temporal resolution, which is rare for late-Pleistocene palaeo-records. Our results reveal changes in regional hydroclimate following the YTT eruption, possibly coupled with volcanically induced changes in the El Niño–Southern Oscillation dynamics. Further, the precise location of the YTT layer within varved Lake Chala sediments provides new information on the season of the YTT eruption.
Utilising Heliospheric Images for Space Weather Prediction: A Data Assimilation Strategy
Authors: Amerstorfer Tanja , Davies Jackie A. , Barnes David , Bauer Maike , LeLouëdec Justin , Weiler Eva , Möstl Christian
Published: March 2024

The STEREO mission has paved the way for the forthcoming Vigil mission, set to launch around 2030. Based on the extensive data archives from STEREO's wide-angle cameras, the heliospheric imagers (HI), we aim to assess the suitability of these data for real-time space weather prediction.This study focuses on modeling the evolution of coronal mass ejections (CMEs) as they progress towards Earth, employing STEREO-A and STEREO-B observations from Vigil's future vantage point, the L5 point of the Sun-Earth system, with the drag-based ensemble model ELEvoHI.Our investigation aims to determine to what extent incorporating additional HI data (as it would be received in real-time) improves the forecasting accuracy and its impact on the prediction lead time.
Lightning Activity in China and Its Optical Characteristics Observed by Geostationary Satellite
Authors: Hui Wen , Zhang Wenjuan
Published: March 2024

Lightning now has designated as an Essential Climate Variable in the Global Climate Observing System to understand the climate change. Lightning detection from geostationary satellites enables continuous monitoring of lightning activity. The satellite-borne lightning imagers take advantage of optical imaging technology combined with multiple filtering methods to extract the weak signals of lightning from very strong background signals and eventually clustering to reconstruct the original lightning flashes. By using the observation data of Fengyun-4A Lightning Mapper Imager (LMI), the first geostationary satellite-borne lightning imager developed in China, the lightning activity and the optical characteristics of lightning flashes in China were analyzed. The lightning activity observed by LMI exhibits obvious regional, seasonal and diurnal variation properties. The flashes are mainly concentrated in the southeastern coastal region in China and the southwestern China. During the pre-monsoon period (March-May), LMI detected lightning outbreaks in southwestern China and its surrounding areas, while during the monsoon period (June-September), both eastern southwestern China and southeastern coastal region in China show a significant dense distribution of lightning flashes. The climatic characteristics of lightning activity and the simultaneous observations of Lightning Imaging Sensor (LIS) on the International Space Station (ISS) confirm the LMI observations. However, there is a difference between the absolute amounts of the LMI and LIS observations. The overall number of lightning flashes observed by LMI is relatively lower than that observed by LIS. In addition, the detection capability of LMI is higher at low latitudes compared to mid-latitudes, and is higher during daytime hours than that during nighttime hours. As for the flash properties, which mainly refer to the optical radiance, area, and duration of lightning flashes, there are also regional differences for these properties observed by LMI. The high values of flash properties are concentrated in southern China. The LMI observations are related to the radiometric response of its detector and the difference in spatial resolution within the large field of view of geostationary orbit observations.
Clumped isotopes as a tool to discern the sources and sinks of methane in a subglacial environment
Authors: Adnew Getachew Agmuas , Röckmann Thomas , Blunier Thomas , Jørgensen Christian Juncher , Sivan Malavika , Sapper Sarah Elise , Popa Maria Elena , van der Veel Carina , Christiansen Jesper Riis
Published: March 2024

 Recent observations have revealed that the subglacial meltwater from the western margin of the Greenland Ice Sheet (GrIS) is a net source of methane (1,2). In the future, the Arctic region might become an important methane source due to its vulnerability to anthropogenic warming, glacier retreat, and thawing permafrost.Mapping the sources of methane and understanding its controlling mechanisms in the subglacial environment of the GrIS are essential for predicting its potential as a climate amplifier and determining its significance in the global carbon cycle. Previous studies used the bulk isotopic composition of methane (δ13C(CH4) and δD(CH4)) to understand the source and underlying cycling processes of methane below the GrIS (1,2). However, the bulk isotopes have overlapping isotope signatures from microbial, thermogenic, and abiotic sources. In addition, methanotrophic oxidation can modify the isotopic composition, making it challenging to distinguish the source of methane under the GrIS. Using only the bulk isotopes of methane, it is not possible to distinguish aerobic from anaerobic oxidation processes.Clumped isotopes are measures of how the distribution of heavy isotopes over the various isotopologues deviates from the expected random or stochastic distribution. Measuring the clumped isotopes of methane provides additional constraints to investigate the turnover of methane in the environment. When the methane is at thermodynamic equilibrium, clumped isotopes provide the formation temperature and when the methane is out of thermodynamic equilibrium, the clumped signatures can be used to identify various kinetic gas formation/consumption and fractionation processes that are not possible to reconstruct from the bulk isotopic composition alone. In this study, we will present the first data on clumped isotope composition of subglacial methane. We will discuss how this new data is used to detail our understanding of the source and sink pathways of subglacial methane. Furthermore, we will show the potential of measuring the clumped isotopes of methane in discerning environmental conditions and types of methanotrophs (oxidation pathways). Christiansen et al. (2021). DOI: 10.1029/2021JG006308
Lamarche-Gagnon et al. (2019). DOI: 10.1038/s41586-018-0800-0
Climate warming and elevated CO2 alter peatland soil carbon sources and stability 
Authors: Nicholas Ofiti , Michael Schmidt , Samuel Abiven , Paul Hanson , Colleen Iversen , Rachel Wilson , Joel Kostka , Guido Wiesenberg , Avni Malhotra
Published: March 2024

Peatlands are an important global carbon (C) reservoir storing at least one-third of global soil organic carbon (SOC), but little is known about the stability of these vast C stocks under climate change. Here, we examine the impact of four years of warming (+0, +2.25, +4.5, +6.75, +9 °C) and two years of elevated atmospheric CO2 concentration (eCO2) on the molecular composition of SOC to infer SOC sources (microbe-, plant- and fire-derived) and stability in a boreal peatland. We show that while warming alone decreased plant- and microbe-derived SOC due to enhanced decomposition, warming combined with eCO2 increased plant-derived SOC compounds. Further, using biopolymers distinct to either leaf/needle (cutin) or root (suberin), we observed increasing root-derived inputs and declining leaf-derived C inputs into SOC under warming and eCO2. Unsurprisingly, SOC derived from historical pyrolysis (pyrogenic C) was unaffected by warming or eCO2. The decline in SOC compounds with warming and gains from new root-derived C under eCO2, suggest that warming and eCO2 may shift peatland C budget towards pools with faster turnover. Together, our results indicate that climate change may increase inputs and enhance decomposition of SOC potentially destabilising C storage in peatlands.
Reducing biases in low cloud cover over the tropical Atlantic in the Norwegian Earth System Model
Authors: Davy Richard , Singh Tarkeshwar , Suo Lingling , Counillon Francois
Published: March 2024

Biases in the representation of low cloud cover in climate models has been identified as one of the leading causes of uncertainty in equilibrium climate sensitivity. It is therfore crucial to reduce current climate model biases in low cloud cover in order to reduce uncertainty in projected climate change. We have conducted perturbed parameter simulations to assess the sensitivity of the simulated low cloud cover in the Norwegian Earth System Model to parameters within the CLUBB scheme. The CLUBB scheme unifies the atmospheric boundary layer turbulence scheme with the clouds schemes and so has the potential advantage of reducing inconsistencies between these components of the atmosphere. However, there are many parameters within the CLUBB scheme that are not well constrained and have unknown effects on simulated climate. We demonstrate that of the 12 parameters in the CLUBB scheme selected for perturbed-parameter experiments, there are just 2 which control the low cloud cover in the model. We used a combination of multi-linear regression models and offline data assimilation with parameter estimation to identify the optimum values for these two parameters to eliminate the bias in low cloud cover, and confirmed this through a second iteration of perturbed-parameter experiments.
Investigating the impact of diet on the stable isotope composition of human scalp hair and fingernails
Authors: Agrawal Gunjan , Sanyal Prasanta
Published: March 2024

Diet-related diseases such as nutritional stress, malnutrition and eating disorders resulting from an unhealthy diet contribute to various health issues, which in some cases may be life-threatening. An accurate diet reconstruction is thus crucial for individuals at risk due to dietary concerns. The principle of diet reconstruction is rooted in the proverb ‘you are what you eat’, and an individual’s diet is the sole source of nitrogen and carbon in their body. The stable isotope composition of nitrogen (δ15N) and carbon (δ13C) can serve as a tool to recognise dietary patterns and identify health conditions. However, the variations in the values of δ15N and δ13C isotopes can imply either dietary changes or disorders associated with diet, making it challenging to ascertain the precise cause of such variations. This study aimed to establish the relationship between the isotopic composition of human tissues, specifically scalp hair and fingernails, and diet. Samples of human tissues were collected from 100 healthy participants within a 15-day period, with 74 of them providing comprehensive diet records. The participants resided in a controlled environment, a remote residential campus with limited food options and restricted access to external food sources. This controlled setting ensured that the isotopic composition of the collected samples solely reflected the impact of diet, eliminating the influence of environmental factors and dietary disorders on the isotopic composition. All the dietary sources and sixty-six food items available to the participants were considered and analysed, respectively, to determine the percentage of animal protein in their diet. This was correlated with the δ15N and δ13C values of human tissues to quantify the proportion of animal protein in diet using linear equations. The variations in the δ15N and δ13C values of human tissues resulting from dietary changes were calculated and distinguished from those caused by dietary disorders. The study results demonstrated that the amount and type of food consumed impact the δ15N and δ13C values of human tissues. An increase in animal protein intake was associated with an increase in the dual isotopic composition. Notably, the nitrogen isotope values of human tissues differed by 0.9‰ between lacto-vegetarians and omnivores. The study further revealed that a 5% dietary change resulted in fluctuation of 0.4 - 0.5‰ in both δ15N and δ13C isotope ratios. This was compared to changes caused by dietary disorders in δ15N and δ13C values of human scalp hair. These findings help in determining whether the variations in δ15N and δ13C values of human tissues result from increased animal protein intake or serve as indicators of dietary disorders.
Impact of warm and moist intrusions on black carbon deposition and summer snow melt in the central Arctic
Authors: Angot Hélène , Réveillet Marion , Schmale Julia ,   MOSAiC team
Published: March 2024

Warm and moist intrusions (WAMIs) into the central Arctic, predominantly observed in winter and early spring, are becoming more frequent, significantly affecting the region’s near-surface energy budget. This study focuses on the deposition pulses of black carbon (BC) triggered by WAMIs and their subsequent impact on snow properties and melting during the summer, using a modeling approach and comprehensive datasets from the 2019–2020 Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition. Our findings reveal that WAMIs induce episodes of intense BC wet deposition in the central Arctic shoulder season (Nov–Apr) due to transported pollution and moisture. We demonstrate that WAMIs result in exceptionally high BC deposition (> 4 orders of magnitude compared to typical winter/spring conditions) across an area of nearly 1 million km2, approximately 20% of the central Arctic Ocean. Furthermore, we establish a direct connection between these winter/spring BC deposition pulses and subsequent summer increases in absorbed solar energy (> 4 W/m2) and snowpack melt rate (+15%). Despite their sporadic occurrence (only 8% of the time), WAMIs play a significant role in the central Arctic surface energy budget through the BC snow albedo effect.
Floe-scale ocean / sea ice energy transfers in the marginal ice zone
Authors: Gupta Mukund , Thompson Andrew , Klein Patrice
Published: March 2024

Marginal ice zones are regions where individual sea ice floes interact mechanically and thermodynamically with turbulent ocean currents at the (sub-)mesoscale. Fine scale exchanges of momentum, heat and salinity at the interface between the ocean and the sea ice floes have important effects on upper-ocean energetics, under-ice tracer mixing, and the ice-pack melt rates. The dynamics of these moving floes remain poorly constrained, notably due to the challenge of numerically resolving sub-mesoscale processes and modelling the discrete behavior of sea ice in traditional climate models. Here, we use oceanic Large Eddy Simulations (LES), two-way coupled to a Discrete Element Model (DEM) of disk-shaped sea ice floes, to quantify the kinetic energy transfers between ocean and sea ice during summer-like conditions, varying sea ice concentration and floe size distribution. The damping of oceanic currents by floes is found to be important for a sea ice concentration as low as 40%, when the sizes of floes are comparable to the characteristic eddy size. This damping is largely compensated by the generation of kinetic energy due to melt-induced baroclinic instability at the edge of sea ice floes, leading to a net energy sink of approximately 15%, relative to a simulation with no floes. At higher sea ice concentrations, the oceanic kinetic energy production weakens, while energy loss due to ice/ocean damping and floe-floe collisions both increase. These energy fluxes are mediated by the spatial aggregation of sea ice floes that occurs within the high-strain regions surrounding ocean mesoscale eddies. Eddy-driven aggregation can also reduce the melt rate of small floes as they become shielded from warm waters by neighboring larger floes. These results highlight the need for scale-aware, and specifically floe-scale parameterizations of sea ice and its coupling to ocean turbulence, within global climate models.
Modelling future water resources in interconnected water systems: are catchment scales relevant?
Authors: Coxon Gemma , Murgatroyd Anna , Pianosi Francesca , Salwey Saskia , Wendt Doris , Zheng Yanchen
Published: March 2024

Freshwater resources are increasingly under threat from climate change and increasing water demand. Catchment-scale hydrological models generate hydrological projections that underpin the management and sustainability of future water resources. Yet, water systems are increasingly interconnected across catchment boundaries through nationally strategic water supply schemes that aim to ensure a reliable supply of water in a changing climate.In this presentation, we draw on a range of studies from across Great Britain to discuss the challenges and complexities of hydrological modelling for future water resources management from catchment to national scales. We focus on interconnected water systems including catchments impacted by (1) inter-catchment groundwater flows and (2) water transfers via reservoirs, abstractions and wastewater treatment plants. For the human-impacted catchments, we identify where and when representing human interactions are important for robust streamflow projections. As water systems become more interconnected in space and time, we highlight the need to move beyond the catchment scale for future water resources management.
Continuous-time state-space time series models for delta-O-18 and delta-C-13
Authors: Hillebrand Eric , Bennedsen Mikkel , Larsen Kathrine , Koopman Siem Jan
Published: March 2024

Time series analysis of delta-O-18 and delta-C-13 measurements from benthic foraminifera for purposes of paleoclimatology is challenging. The time series reach back tens of millions of years, they are relatively sparse in the early record and relatively dense in the later, the time stamps of the observations are not evenly spaced, and there are instances of multiple different observations at the same time stamp (Westerhold et al., 2020, Science 369 p. 1383). The time series appear non-stationary over most of the historical record with clearly visible temporary trends of varying directions. In this paper, we propose a continuous-time state-space framework to analyze the time series prepared in Westerhold et al. (2020). State space models are uniquely suited for this purpose, since they can accommodate all the challenging features mentioned above. We specify univariate models and joint bivariate models for the two time series of delta-O-18 and delta-C-13. The models are estimated using maximum likelihood by way of the Kalman filter recursions. The suite of models we consider has an interpretation as an application of the Butterworth filter (Gomez 2001 [JBES 19 p. 365], Harvey & Trimbur 2003 [REStat 85 p. 244]). We propose model specifications that take the origin of the data from different studies into account and that allow for a partition of the total period into sub-periods following Westerhold et al. 2020, which we have been able to confirm with a statistical method (Larsen et al. 2024: Estimating Breakpoints between Climate States in Paleoclimate Data, abstract submitted to EGU General Assembly Session CL3.2.3). The models can be used, for example, to generate evenly time-stamped data by way of Kalman filtering. They can also be used, in future work, to analyze the relation to proxies for CO2 concentrations.
Navigating challenges: Revitalising the Direct Solution Method for 3D heterogeneous media in global seismology
Authors: Fuji Nobuaki
Published: March 2024

Born in 1994 (Geller and Ohminato 1994) and grounded in the optimally accurate operator theory (Geller and Takeuchi 1994), the Direct Solution Method (DSM) has long been a reliable force in seismic wavefield computation for spherically symmetric planets, particularly excelling in high-frequency efficiency. However, as the nowaday seismology seeks greater realism in 3D heterogeneous media, DSM has been facing substantial hurdles in its extension.This contribution first revisits the historical successes and failures of the DSM, spotlighting its efficiency in computing seismic wavefields in spherically symmetric planets. However, the shift towards more complex models exposes DSM's limitations due to its trial functions, prompting various attempts to adapt it to 3D heterogeneous media. Analysing these endeavours, we uncover pitfalls and missteps that have hindered the extension of DSM to 3D heterogeneous media. Out critical assessment identifies common challenges, offering insights into essential modifications needed to overcome them. This contribution acts as a guide, emphasising what to avoid and illuminating potential avenues to enhance the DSM's applicability in global seismology within 3D heterogeneous contexts.We try to elucidate the shortcomings of previous efforts, providing valuable lessons for future endeavours. By steering researchers away from ineffective approaches, we aim to catalyse innovation, paving the way for the continued relevance and effectiveness of DSM in global seismology. This comprehensive exploration serves as a roadmap, directing attention towards necessary adjustments and innovations to sustain DSM's utility amidst the dynamic landscape of seismic wavefield computation.