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Abstract

Methane clumped isotope signatures of abiogenesis may be diagnostic of the origin of methane on Earth and other planetary bodies. We performed synthesis of abiogenic methane in hydrothermal conditions between 130 and 300°C and determined δ13C, δD, Δ13CH3D, and Δ12CH2D2. The experiments were performed by heating water in the presence of Fe0 powder and CO. The reduction of water on metallic iron led to the formation of H2. CO was reacted with both H2 and H2O, generating both CH4 and CO2. Methane δ13C values are isotopically depleted by ∼25‰ relative to the CO starting material. This is consistent with carbon isotopic equilibrium between methane, carbon monoxide and carbon dioxide in our experiments. In contrast, D/H ratios are inconsistent with equilibrium isotopic fractionation, as illustrated by δD values of methane fractionated by ∼500‰ relative to starting H2O. This suggests that under our experimental conditions, hydrogen additions to carbon may be governed by kinetics. Δ13CH3D values track experimental temperature, with values between +1.5‰ and +5.0‰ for most samples. In contrast, Δ12CH2D2 values are displaced from equilibrium. We find exclusively negative Δ12CH2D2 values, showing deficits down to 40‰ relative to thermodynamic equilibrium. We interpret the data as evidence for distinct, kinetically induced D/H pools contributing to methane assembly, that is, a combinatorial effect. The cumulative D/H fractionations associated with CO hydrogenation explain the direction and magnitude of Δ12CH2D2 values during abiotic methane formation. We suggest that near equilibrium Δ13CH3D with negative Δ12CH2D2 signatures will help identify methane formed abiotically in nature.

Abstract

In this study we apply electron tomography to characterize 3D dislocation microstructures in two quartz mylonite specimens from the Moine and Main Central Thrusts, both of which accommodated displacements by dislocation creep in the presence of water. Both specimens show dislocation activity with dislocation densities of the order of 3–4 × 1012 m−2 and evidence of recovery from the presence of subgrain boundaries. 〈a〉 slip occurs predominantly on pyramidal and prismatic planes (〈a〉 basal glide is not active). [c] Glide is not significant. On the other hand, we observe a very high level of activation of 〈c + a〉 glide on the 101‾0 $\left\{10\overline{1}0\right\}$, 101‾1 $\left\{10\overline{1}1\right\}$, 112‾n $\left\{11\overline{2}n\right\}$ (n = 1,2) and even 213‾1 $\left\{21\overline{3}1\right\}$ planes. Approximately 60% of all dislocations show evidence of climb with a predominance of mixed climb, a deformation mechanism characterized by dislocations moving in a plane intermediate between the glide and the climb planes. This atypical mode of deformation demonstrates comparable glide and climb efficiency under natural deformation conditions. It promotes dislocation glide in planes not expected for the quartz structure, probably by inhibiting lattice friction. Our quantitative characterization of the microstructure enables us to assess the strain that dislocations can generate. We show that glide systems indicated by the observed dislocations are sufficient to accommodate any arbitrary 3D strain by themselves. Although historically dislocation glide has been regarded as being primarily responsible for producing strain, activation of climb can also directly contribute to the finite strain. On the basis of this characterization, we propose a numerical modeling approach for attempting to characterize the local stress state that gave rise to the observed microstructure.

Abstract

Sea ice cools Earth by reducing its absorbed solar energy. We combine radiative transfer modeling with satellite-derived surface albedo, sea ice, and cloud distributions to quantify the top-of-atmosphere sea ice radiative effect (SIRE). Averaged over 1980–2023, Arctic and Antarctic SIREs range from −0.64 to −0.86 W m−2 and −0.85 to −0.98 W m−2, respectively, with different cloud data sets and assumptions of climatological versus annually-varying clouds. SIRE trends, however, are relatively insensitive to these assumptions. Arctic SIRE has weakened quasi-linearly at a rate of 0.04–0.05 W m−2 decade−1, implying a 21%–27% reduction in the reflective power of Arctic sea ice since 1980. Antarctic sea ice exhibited a regime change in 2016, resulting in 2016–2023 Antarctic and global SIRE being 0.08–0.12 and 0.22–0.27 W m−2 weaker, respectively, relative to 1980–1988. Global sea ice has therefore lost 13%–15% of its planetary cooling effect since the early/mid 1980s, and the implied global sea ice albedo feedback is 0.24–0.38 W m−2 K−1.

Abstract

Updated summaries of the August 1972 and March 1989 space weather events have been constructed. The features of these two events are compared to the Carrington 1859 event and a few other major space weather events. It is concluded that solar active regions release energy in a variety of forms (X-rays, EUV photons, visible light, coronal mass ejection (CME) plasmas and fields) and they in turn can produce other energetic effects (solar energetic particles (SEPs), magnetic storms) in a variety of ways. It is clear that there is no strong one-to-one relationship between these various energy sinks. The energy is often distributed differently from one space weather event to the next. Concerning SEPs accelerated at interplanetary CME (ICME) shocks, it is concluded that the Fermi mechanism associated with quasi-parallel shocks is relatively weak and that the gradient drift mechanism (electric fields) at quasi-perpendicular shocks will produce harder spectra and higher fluxes. If the 4 August 1972 intrinsic magnetic cloud condition (southward interplanetary magnetic field instead of northward) and the interplanetary Sun to 1 au conditions were different, a 4 August 1972 magnetic storm and magnetospheric dawn-to-dusk electric fields substantially larger than the Carrington event would have occurred. Under these special interplanetary conditions, a Miyake et al. (2012), https://doi.org/10.1038/nature11123-like extreme SEP event may have been formed. The long duration complex 1989 storm was probably greater than the Carrington storm in the sense that the total ring current particle energy was larger.

Abstract

Electron density enhancements in the ionospheric D-region due to the precipitation of high-energy electrons (>30 keV) have been measured as increases in cosmic radio noise absorption (CNA) using ground-based riometers. CNA has been studied since the 1960s. However, there have been few studies of the spatiotemporal development of CNA at multi-point ground stations distributed in longitude at subauroral latitudes, where plasma particles with a wide energy range are intermingled. In this study, we analyzed the longitudinal development of CNA steep increases using simultaneous riometer observations at six stations at subauroral latitudes in Canada, Alaska, Russia, and Iceland over 3 years from 2017 to 2020. The results revealed that the occurrence rate of steep increases in CNA was highest at midnight at 22-08 magnetic local time (MLT), and lowest near dusk at 17–21 MLT. We also showed statistically that the CNA steep increases expanded eastward on the dawn side and westward on the dusk side. The CNA expansion velocity was slightly faster than the results of previous studies in the auroral zone. Correlation and superposed epoch analyses of CNA with solar wind and geomagnetic parameters revealed that CNA intensity was dependent on the Interplanetary Magnetic Field Bz, Interplanetary Electric Field Ey, SYM-H index, and SME index. These results indicate that the CNA at subauroral latitudes is closely related to solar wind and geomagnetic activities, and its propagation characteristics correspond to the dynamics of high energy electrons in the inner magnetosphere.

Abstract

Electromagnetic Ion Cyclotron (EMIC) wave scattering has been proved to be responsible for the fast loss of both radiation belt (RB) electrons and ring current (RC) protons. However, its role in the concurrent dropout of these two co-located populations remains to be quantified. In this work, we study the effect of EMIC wave scattering on both populations during the 27 February 2014 storm by employing the global physics-based RAM-SCB model. Throughout this storm event, MeV RB electrons and 100s keV RC protons experienced simultaneous dropout following the occurrence of intense EMIC waves. By implementing data-driven initial and boundary conditions, we perform simulations for both populations through the interplay with EMIC waves and compare them against Van Allen Probes observations. The results indicate that by including EMIC wave scattering loss, especially by the He-band EMIC waves, the model aligns closely with data for both populations. Additionally, we investigate the simulated pitch angle distributions (PADs) for both populations. Including EMIC wave scattering in our model predicts a 90° peaked PAD for electrons with stronger losses at lower pitch angles, while protons exhibit an isotropic PAD with enhanced losses at pitch angles above 40°. Furthermore, our model predicts considerable precipitation of both particle populations, predominantly confined to the afternoon to midnight sector (12 hr < MLT < 24 hr) during the storm's main phase, corresponding closely with the presence of EMIC waves.

Abstract

We comprehensively analyzed geomagnetic perturbations using ground magnetic records from over 400 stations spanning four solar cycles, from 1976 to 2023. We assess the perturbations in the three magnetic components separately. Our study covers low, middle, and high magnetic latitudes in the northern magnetic hemisphere, with the primary objective of quantifying extreme values and evaluating their variability on magnetic latitude, local time, and solar cycle phases “minimum, ascending, maximum, and declining.” Our findings reveal spatial patterns to be less discernible as perturbations intensify, with distinct responses at middle and high latitudes. The extreme values, defined as percentiles 0 and 100, were observed to be localized and randomly distributed in local time, especially in the east magnetic component. Additionally, we observed dusk-dawn asymmetries in the magnitude of perturbations related to the auroral electrojets, indicating complex interactions between the magnetosphere and ionosphere. Furthermore, the results reveal a preference for the most significant extreme values to occur in the declining phase of the solar cycle. These insights deepen our understanding of geomagnetic perturbations and their variability, contributing to space weather forecasting and mitigation strategies.

Abstract

Instrumental data set have revealed several summer precipitation patterns in eastern China, being summarized as “tripole,” “dipole” and “coast” modes. The former two have been found to persist at different time scales, leaving the latter unclear in geological records. Here we present 1300-year hydroclimate records in a tropical maar lake in the southern coast of China using archeal lipid GDGTs, which can reflect lower water redox conditions largely regulated by lake water depth. The down-core GDGTs reveal a relatively drier condition during the medieval climate anomaly compared to the Little Ice Age, in-phase with other records in southeast coast of China but opposite to the inland region, hence demonstrating a persistent “coast” mode in eastern China. The thermal state of equatorial Pacific is suggested to play an important role in shaping the “coast” mode by modulating the location and strength of the western Pacific subtropical high and tropical typhoons.

Abstract

We investigate similarities and differences between natural and simulated slow earthquakes using nonlinear dynamical system tools. We use spatio-temporal slip potency rate data derived from Global Navigation Satellite System (GNSS) position time series in the Cascadia subduction zone and numerical simulations intended to reproduce their pulse-like behavior and scaling laws. We provide metrics to evaluate the accuracy of simulations in mimicking slow earthquake dynamics. We investigate the influence of spatio-temporal coarsening as well as observational noise. Despite the use of many degrees of freedom, numerical simulations display a surprisingly low average dimension, akin to natural slow earthquakes. Instantaneous dynamical indices can reach large values (>10) instead, and differences persist between numerical simulations and natural observations. We propose to use the suggested metrics as an additional tool to narrow the divergence between slow earthquake observations and dynamical simulations.

Abstract

Paleomagnetic analyses have suggested that the lunar magnetic field underwent a significant change from 4.25 to 3.19 Ga, indicating the rapid transition of the lunar dynamo mechanism. We used the van der Pauw (vdP) method to measure the electrical resistivity of Fe-S-P alloys under conditions relevant to the lunar core and estimated the thermal conductivity of the Fe-S-P lunar core. These values were incorporated into thermal and dynamo models to investigate the evolution of the lunar core. Our model indicates that the inner core began to grow as early as 4.35 Ga, the solidification regime switched at 3.50 Ga, and the thermal dynamo ceased between 3.78 and 3.51 Ga. The cessation of the dynamo could be due to a low buoyancy flux and insufficient entropy dissipation. Thermal and compositional dynamos cannot sustain the ancient strength of the Moon's magnetic field, and require other energy sources.

Abstract

A comprehensive statistical study is conducted on O+ and H+ outflows obtained from the TEAMS/FAST data during the 23rd solar cycle (1996–2007). The study investigates interhemispheric asymmetry in ionospheric outflows during local summer, winter, and equinox seasons. Data are classified into two distinct periods: the pre-storm and geomagnetic storm phases. Numerous statistical asymmetries are identified. The findings indicate that the dayside cusp consistently demonstrates more outflow rates of O+ and H+ in the northern hemisphere than southern hemisphere during geomagnetic storms in all seasons as well as during the pre-storm period in the summer season with the exception of H+ during summer storms. Conversely, the nightside O+ and H+ outflow rates are higher in the southern hemisphere during pre-storm and storm periods in the summer season. Additionally, the dawnside and duskside outflow rates of O+ and H+ are predominantly stronger in the southern hemisphere.

Abstract

Passive microwave radiometers onboard satellites rely on the received upwelling radiation to retrieve precipitation, which is a mixed signal from the surface, atmosphere and precipitation hydrometeors. Liquid precipitation droplets increase the upwelling radiation from the surface at lower frequencies, while ice particles cause a decrease in upwelling radiation at higher frequencies. The task of the retrieval algorithm is to identify the precipitation phase and to isolate the signal of precipitation from that of the surface. This study develops a machine learning method to retrieve rainfall and snowfall rates based on observations from the Microwave Hydrometer Sounder and Microwave Temperature Sounder onboard FY-3E. Self-organized mapping (SOM) is selected to classify the precipitation and underlying surface types, and an artificial neural network (ANN) is subsequently used to relate the brightness temperature to the precipitation rate for the clusters derived from the SOM. The half-hour product of the Integrated Multi-Satellite Retrieval for Global Precipitation Measurement (IMERG) is used to train the ANN. To address the issue that number of heavy precipitation samples are not enough for training, the simulation of radiative transfer for TOVS is used as a supplement to heavy rain samples. The SOM-ANN algorithm outperforms the IMERG and Goddard profiling algorithm (GPROF) retrieval products in both rainfall and snowfall retrieval. Compared with the hourly observations at ∼4,400 stations during a 2-year period, the root mean square errors of SOM-ANN proposed here are 1.06 and 0.34 mm/hr for the rainfall and snowfall rates, which are better than those of IMERG (1.23 and 0.42 mm/hr) and GPROF (1.22 and 0.44 mm/hr).

Brief communication: Storm Daniel flood impact in Greece in 2023: mapping crop and livestock exposure from synthetic-aperture radar (SAR)
Kang He, Qing Yang, Xinyi Shen, Elias Dimitriou, Angeliki Mentzafou, Christina Papadaki, Maria Stoumboudi, and Emmanouil N. Anagnostou
Nat. Hazards Earth Syst. Sci., 24, 2375–2382, https://doi.org/10.5194/nhess-24-2375-2024, 2024
About 820 km2 of agricultural land was inundated in central Greece due to Storm Daniel. A detailed analysis revealed that the crop most affected by the flooding was cotton; the inundated area of more than 282 km2 comprised ~ 30 % of the total area planted with cotton in central Greece. In terms of livestock, we estimate that more than 14 000 ornithoids and 21 500 sheep and goats were affected. Consequences for agriculture and animal husbandry in Greece are expected to be severe.

Comparing components for seismic risk modelling using data from the 2019 Le Teil (France) earthquake
Konstantinos Trevlopoulos, Pierre Gehl, Caterina Negulescu, Helen Crowley, and Laurentiu Danciu
Nat. Hazards Earth Syst. Sci., 24, 2383–2401, https://doi.org/10.5194/nhess-24-2383-2024, 2024
The models used to estimate the probability of exceeding a level of earthquake damage are essential to the reduction of disasters. These models consist of components that may be tested individually; however testing these types of models as a whole is challenging. Here, we use observations of damage caused by the 2019 Le Teil earthquake and estimations from other models to test components of seismic risk models.

Using deep learning to integrate paleoclimate and global biogeochemistry over the Phanerozoic Eon
Dongyu Zheng, Andrew S. Merdith, Yves Goddéris, Yannick Donnadieu, Khushboo Gurung, and Benjamin J. W. Mills
Geosci. Model Dev., 17, 5413–5429, https://doi.org/10.5194/gmd-17-5413-2024, 2024
This study uses a deep learning method to upscale the time resolution of paleoclimate simulations to 1 million years. This improved resolution allows a climate-biogeochemical model to more accurately predict climate shifts. The method may be critical in developing new fully continuous methods that are able to be applied over a moving continental surface in deep time with high resolution at reasonable computational expense.

Global application of a regional frequency analysis to extreme sea levels
Thomas P. Collings, Niall D. Quinn, Ivan D. Haigh, Joshua Green, Izzy Probyn, Hamish Wilkinson, Sanne Muis, William V. Sweet, and Paul D. Bates
Nat. Hazards Earth Syst. Sci., 24, 2403–2423, https://doi.org/10.5194/nhess-24-2403-2024, 2024
Coastal areas are at risk of flooding from rising sea levels and extreme weather events. This study applies a new approach to estimating the likelihood of coastal flooding around the world. The method uses data from observations and computer models to create a detailed map of where these coastal floods might occur. The approach can predict flooding in areas for which there are few or no data available. The results can be used to help prepare for and prevent this type of flooding.

Dynamics and Impacts of Monsoon-Induced Geological Hazards: A 2022 Flood Study along the Swat River in Pakistan
Nazir Ahmed Bazai, Mehtab Alam, Peng Cui, Wang Hao, Adil Poshad Khan, Muhammad Waseem, Yao Shunyu, Muhammad Ramzan, Li Wanhong, and Tashfain Ahmed
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-95,2024
Preprint under review for NHESS (discussion: open, 0 comments)
This study examines the 2022 monsoon in the Swat River basin, Pakistan, where record rainfall exceeded averages by 7–8 %, causing catastrophic debris flows and floods. These events worsened challenges for low-income communities, resulting in extensive damage and financial instability. Field investigations, remote sensing, and simulations identified deforestation and steep topography as key factors. The study advocates for disaster mitigation, reforestation, and better land use planning.

Abstract

The growth of newly formed particles through new particle formation (NPF) contributes a significant fraction to the cloud condensation nuclei, yet the driving mechanisms remain unclear, especially for polluted environments. To investigate the potential species contributing for nanoparticle growth in environments with significant anthropogenic influences, we measured the hygroscopicity of newly formed particles at 20–40 nm at a rural observational site in the North China Plain during winter 2018. Our results demonstrate that these particles were not very hygroscopic, with the mean hygroscopicity parameter κ of 0.13 ± 0.09. Clear differences in the inferred κ of the growing material responsible for the growth were observed among different events, indicating that even at the same region, the compounds driving particle growth may not be identical. This may be synergistically influenced by the NPF precursors, oxidants and meteorological conditions, suggesting complex mechanisms might co-exist behind nanoparticle growth in polluted environments.

Abstract

Satellite-retrieved vegetation optical depth (VOD) has provided extensive insights into global plant function (such as, carbon stocks, water stress, crop yields) because of VOD's ability to monitor plant water stress and biomass at near daily temporal frequency under all-weather conditions. However, arguably, the greatest challenge with broadly applying VOD is its lack of validation partly because of VOD's simultaneous sensitivity to plant water status and biomass changes, as well as intensive methods required to measure these properties in-situ. Here, inspired by the recent Yao et al. (2024), https://doi.org/10.1029/2023GL107121 article, I argue that VOD estimated from global navigation satellite systems (GNSS) and land surface models with plant hydraulic schemes are two emerging methods that show promise for more widely validating satellite-based VOD. I encourage wider adoption of these approaches to validate and further advance satellite-based VOD research.

Abstract

Chorus waves are intense electromagnetic emissions critical in modulating electron dynamics. In this study, we perform two-dimensional particle-in-cell simulations to investigate self-consistent wave-particle interactions with oblique chorus waves. We first analyze the electron dynamics sampled from cyclotron and Landau resonances with waves, and then quantify the advection and diffusion coefficients through statistical studies. It is found that phase-trapped cyclotron resonant electrons satisfy the second-order resonance condition and gain energy from waves. While phase-bunched cyclotron resonant electrons cannot remain in resonance for long periods. They transfer energy to waves and are scattered to smaller pitch angles. Landau resonant electrons are primarily energized by waves. For both types of resonances, advection coefficients are greater than diffusion coefficients when the wave amplitude is large. Our study highlights the important role of advection in electron dynamics modulation resulting from nonlinear wave-particle interactions.