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Atmospheric plasma etching (APE) has been used to texture Si surfaces due to anisotropic material removal capability. Controlling features and size of the light-trapping structure are keys to improving the reflection performance of silicon (Si) solar cells, which need to fully understand the interfacial etching behavior and the microscopic topography formation mechanism of the Si surface. In this study, microwave plasma with a temperature below 100 °C is employed to investigate the dependence of microstructure evolution on the O/F atom ratios in plasma. The results show that as the O/F atom ratios increase, the microstructure of the Si surface changes from square opening pits to spherical opening pits. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy analyses indicate that the exciting F atoms dominate the orientation-selective etching process, causing the formation of square opening pits. The CFx and C2 radicals induce the generation of the Si interface reactive layer, resulting in the occurrence of amorphous layers and termination of the non ⟨111⟩-crystal face in APE. The exciting O atoms preferentially occupy the active site of Si surfaces, causing the isotropic etching and then the formation of spherical opening pits. In addition, the richer O atoms will weaken the anisotropic etching ability of F atoms, resulting in the etched surface trends' flattening. The insight into anisotropic etching behavior and topography formation mechanism of the silicon surface textured by atmospheric plasma is valuable for developing a new texturing approach to silicon solar cells. [ABSTRACT FROM AUTHOR]

Very low‐frequency earthquakes (VLFs) are characterized by longer source duration and smaller stress drop than regular earthquakes of similar magnitude. Recent studies have shown their frequent correlation with low‐frequency earthquakes (LFEs) on shared faults. The underlying source processes governing the occurrence of VLFs and their interaction with LFEs remain elusive. Here, we employ a slip‐weakening model for slow earthquakes. By comparing the source parameters of simulations and observations, it is suggested that VLFs are slow self‐arresting earthquakes that self‐terminate within the nucleation patch. Additionally, we adopt a composite model to reproduce the records of the simultaneous occurrences of a VLF and an LFE in the Nankai area. Our results present the possibility that VLFs, LFEs, and regular earthquakes can be distinguished using a unified dynamic framework. Plain Language Summary: Earthquakes can be divided into two groups: regular earthquakes and slow earthquakes. Regular earthquakes are the results of quick shear slip on faults, while slow earthquakes are generated from slow transient movements along the faults and radiate anomalous small energy. The mechanism that drives their different source characteristics remains elusive. Here, we employ an independent and composite dynamic source model to elucidate the unique attributes of very low‐frequency earthquakes (LFEs), a type of slow earthquakes. By comparing the source parameters and waveforms of observations with simulations. The outcomes indicate that very LFEs potentially represent a seismic type that self‐terminate within the region where the rupture is initially triggered. Key Points: Very low‐frequency earthquakes (LFEs) are characterized by slow self‐arresting processesOur model can simultaneously reproduce both very low‐frequency and LFEThe slip‐weakening frictional model generates both fast and slow earthquakes [ABSTRACT FROM AUTHOR]

The formation of new mineral phases in confined environments, especially in porous media, is crucial for various geological processes like mineralization and diagenesis. The nucleation and precipitation of minerals are initiated at the microscale through fluid‐rock interaction, where dissolution of primary phases leads to supersaturated conditions and nucleation and growth of secondary ones. Previous research has focused primarily on either precipitation or nucleation, without fully exploring their combined impact. Our study introduces a computational framework that integrates classical nucleation theory with the micro‐continuum method. We validated our model by comparing with experiments, and discovered that different surface nucleation rate changes the mode of precipitation from a preferential to uniform precipitate textures. Furthermore, our study uncovered that the conventional deterministic precipitation method tends to underestimate the permeability of the porous matrix. In contrast, the new framework significantly improves model accuracy by incorporating preferential precipitation and heterogeneous nucleation. Plain Language Summary: The formation of minerals in confined environments, especially in porous media, is important for both natural processes and industrial applications. The resulting solid phases can greatly affect the porosity and permeability of the porous structure. Many previous studies have focused on either nucleation or precipitation, we still have a limited understanding of how both processes interact at different scales. In this study, we integrated the Darcy‐Brinkman‐Stokes method and classical nucleation theory to investigate the interplay between nucleation, precipitation, species transport, and their impact on permeability. Our findings show that adjusting the surface nucleation rates can change the mode of mineral precipitation from preferential to uniform. We also found that the traditional deterministic precipitation method underestimates permeability in certain scenario. Therefore, considering probabilistic nucleation is crucial when there is preferential precipitation and heterogeneous nucleation on the interfaces between the minerals and surrounding liquid under reactive flow conditions. Key Points: The proposed computational framework focuses on investigating the heterogeneity of nucleation and its effects on mineral precipitationThe new model is validated by comparing with experimental data, demonstrating an agreement in both nucleation morphology and rateThe new model integrates probabilistic nucleation, resulting in a notable enhancement in the accuracy of permeability predictions [ABSTRACT FROM AUTHOR]

Observations of marine stratus clouds in clean air off the Californian coast reveal a functional relationship between the number of cloud condensation nuclei (CCN) and supersaturation. Satellite‐derived liquid droplet density estimates the number density of CCN. Combining the estimated supersaturation using Köhler theory, global maps of supersaturation and the critical activation size of CCN are estimated. Here, we show that high supersaturation >0.5% persists over the oceans with a critical CCN size of 25–30 nm, which is smaller than the conventional wisdom of 60 nm. Independent support for such high supersaturation in the marine cloud is obtained from CCN measurements provided by the "Atmospheric Tomography Mission." Higher supersaturation implies smaller activation size for CCN making cloud formation more sensitive to changes in aerosol nucleation. Plain Language Summary: Clouds in Earth's atmosphere are of fundamental importance for the climate by regulating the reflection of sunlight into space and interacting with thermal radiation from Earth. Clouds form when moist air ascends and gets supersaturated with water vapor that condenses on aerosol particles of sufficient sizes, which then grow into cloud droplets. The aerosol number‐density and size spectrum influence the resulting cloud properties, and the supersaturation determines which aerosols can be activated into cloud drops. Here, we show that the supersaturation in marine liquid clouds is significantly higher than in the conventional view. As a consequence, much smaller aerosols can serve as cloud condensation nuclei. This can make cloud formation more sensitive to changes in aerosol properties than previously thought. Such a result should be of general interest and lead to a better understanding of aerosol‐cloud interactions, which presently constitute the largest uncertainty in our understanding of climate. Key Points: On average, supersaturation in marine clouds is significantly higher than the conventional view of 0.2%–0.3%Due to the higher supersaturation, much smaller aerosols get activated into cloud dropletsThe results are essential for better understanding aerosols‐cloud interactions [ABSTRACT FROM AUTHOR]

Solar radiation modification by a sustained deliberate source of SO2 into the stratosphere (strat-SRM) has been proposed as an option for climate intervention. Global interactive aerosol–chemistry–climate models are often used to investigate the potential cooling efficiencies and associated side effects of hypothesized strat-SRM scenarios. A recent model intercomparison study for composition–climate models with interactive stratospheric aerosol suggests that the modeled climate response to a particular assumed injection strategy depends on the type of aerosol microphysical scheme used (e.g., modal or sectional representation) alongside host model resolution and transport. Compared to short-duration volcanic SO2 emissions, the continuous SO2 injections in strat-SRM scenarios may pose a greater challenge to the numerical implementation of microphysical processes such as nucleation, condensation, and coagulation. This study explores how changing the time steps and sequencing of microphysical processes in the sectional aerosol–chemistry–climate model SOCOL-AERv2 (40 mass bins) affects model-predicted climate and ozone layer impacts considering strat-SRM by SO2 injections of 5 and 25 Tg(S) yr −1 at 20 km altitude between 30° S and 30° N. The model experiments consider the year 2040 to be the boundary conditions for ozone-depleting substances and greenhouse gases (GHGs). We focus on the length of the microphysical time step and the call sequence of nucleation and condensation, the two competing sink processes for gaseous H2SO4. Under stratospheric background conditions, we find no effect of the microphysical setup on the simulated aerosol properties. However, at the high sulfur loadings reached in the scenarios injecting 25 Tg(S) yr −1 of SO2 with a default microphysical time step of 6 min, changing the call sequence from the default "condensation first" to "nucleation first" leads to a massive increase in the number densities of particles in the nucleation mode (R<0.01 µm) and a small decrease in coarse-mode particles (R>1 µm). As expected, the influence of the call sequence becomes negligible when the microphysical time step is reduced to a few seconds, with the model solutions converging to a size distribution with a pronounced nucleation mode. While the main features and spatial patterns of climate forcing by SO 2 injections are not strongly affected by the microphysical configuration, the absolute numbers vary considerably. For the extreme injection with 25 Tg(S) yr −1 , the simulated net global radiative forcing ranges from - 2.3 to - 5.3 Wm-2 , depending on the microphysical configuration. Nucleation first shifts the size distribution towards radii better suited for solar scattering (0.3 µm

Constructing artificial interface layer is an effective approach to facilitate the utilization rate of zinc metal, but the practical application is still hindered by the inferior mechanical strength, low ionic conductivity, and poor stability. Herein, robust organic–inorganic layer (Nafion/BM@Zn) is coated on zinc metal through ultrasonic spraying method with boehmite and Nafion as the composite precursor. As demonstrated, the high cation selectivity and high hydrophilicity of Nafion, as well as the zincophilic property and layered structure of boehmite, synergistically contribute to the low nucleation barrier, uniform deposition, and fast transport kinetics of Zn2+ ions. As a result, the Nafion/BM@Zn anode exhibits superior reversibility with a high Coulombic efficiency of 99.9% for 9000 cycles in asymmetrical cells and durable cycling stability for 4200 h in symmetrical cells at 5 mA cm−2−1 mAh cm−2. Even in the seawater‐based electrolyte, the Nafion/BM@Zn anode still displays reversible deposition behavior for 820 h and high Coulombic efficiency of 99.91% for 2800 cycles at 5 mA cm−2−1 mAh cm−2. Furthermore, the corresponding Nafion/BM@Zn//NH4V4O10 cell presents high capacity of 258.4 mAh g−1 after 1500 cycles at 5 A g−1. This work provides a new design strategy for high‐efficiency interfacial layer of zinc metal anode. [ABSTRACT FROM AUTHOR]

Cloud condensation nuclei (CCN) is a key factor in the formation and evolution of clouds and thereby the climate. An investigation on particle number size distributions (PNSDs) and CCN properties above the mixing layer (ML) was carried out, using a specifically designed sampler attached to a tethered balloon system. Aerosol microphysical and CCN properties above the ML differed distinctly from that near the ground. During the campaign, the average total particle number concentration (Np) near the ground (6200 ± 1700 cm−3) was found roughly twice that above the ML (2800 ± 1200 cm−3). The hygroscopicity parameter (κ), derived from size-resolved CCN measurements, ranged from 0.22 to 0.37 above the ML with an average of 0.29 ± 0.04. While near the ground, where particle properties were more directly and readily affected by various emission sources, aging and deposition than those above the ML, a larger variability in κ (from 0.17 to 0.47) was observed, with an average of 0.25 ± 0.08. The analysis regarding one haze process and one fog process revealed that κ above the ML stayed relatively stable, in spite of the simultaneous large variability in the surface κ. This observational study implies that the accurate and detailed chemical composition of aerosol particles, though quite important to investigate aerosol hygroscopicity within the ML, might not be highly demanded for characterizing the variability of aerosol hygroscopicity above the ML. Copyright © 2024 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

[Display omitted] Ice mitigation has received increasing attention due to the severe safety and economic threats of icing hazards to modern industries. Slippery icephobic surface is a potential ice mitigation approach due to its ultra-low ice adhesion strength, great humidity resistance, and effective delay of ice nucleation. However, this approach currently has limited practical applications because of serious liquid depletion in the icing/de-icing process. A new strategy of phase change materials (PCM)-impregnation porous metallic structures (PIPMSs) was proposed to develop phase changeable icephobic surfaces in this study, and aimed to solve the rapid depletion via the phase changeable interfacial interactions. Evaluation of surface icephobicity and interfacial analysis proved that the phase changeable surfaces (PIPMSs) worked as an effective and durable icephobic platform by significantly delaying ice nucleation, providing long-term humid tolerance, low ice adhesion strength of as-prepared samples (less than 5 kPa), and signally improved maintaining capacity of impregnated PCMs (less than 10 % depletion) after 50 icing/de-icing cycles. To explore the interfacial responses, phase change models consisting of the unfrozen quasi-liquid layer and solid lubricant layer at the ice/PIPMSs interfaces were established, and the involved icephobic mechanisms of PIPMSs were studied based on the analysis of interfacial interactions. [ABSTRACT FROM AUTHOR]

The quantification of aerosol size distributions is crucial for understanding the climate and health impacts of aerosols, validating models, and identifying aerosol sources. This work provides one of the first continuous measurements of aerosol size distribution from 1.02 to 8671 nm near the shore of Lake Michigan. The data were collected during the Lake Michigan Ozone Study (LMOS 2017), a comprehensive air quality measurement campaign in May and June 2017. The time-resolved (2-min) size distribution are reported herein alongside meteorology, remotely sensed data, gravimetric filters, and gas-phase variables. Mean concentrations of key aerosol parameters include PM2.5 (6.4 μg m-3), number from 1 to 3 nm (1.80x104 cm-3) and number greater than 3 nm (8x103 cm-3). During the field campaign, approximately half of days showed daytime ultrafine burst events, characterized by particle growth from sub 10 nm to 25–100 nm. A specific investigation of ultrafine lake spray aerosol was conducted due to enhanced ultrafine particles in onshore flows coupled with sustained wave breaking conditions during the campaign. Upon closer examination, the relationships between the size distribution, wind direction, wind speed, and wave height did not qualitatively support ultrafine particle production from lake spray aerosol; statistical analysis of particle number and wind speed also failed to show a relationship. The alternative hypothesis of enhanced ultrafine particles in onshore flow originating mainly from new particle formation activity is supported by multiple lines of evidence. [ABSTRACT FROM AUTHOR]

Minerals form in natural systems from solutions with varying ratios of their lattice ions, yet non‐stoichiometric conditions have generally been overlooked in investigations of new formation (nucleation) of ionic crystals. Here, we investigated the influence of cation:anion ratio in the solution on the initial steps of nucleation by studying positively and negatively charged triple ion complexes and subsequent particle size evolution. Our model systems are carbonates and sulfates of calcium and barium, as it was recently shown that solution stoichiometry affects the timing and rate of their nucleation. Molecular dynamics (MD) simulations and dynamic light scattering (DLS) flow experiments show that nucleation correlates with the stability and lifetime of the initial complexes, which were significantly impacted by the cation:anion stoichiometry and ion type. Specifically, BaSO422- ${{\rm B}{\rm a}{\left({{\rm S}{\rm O}}_{4}\right)}_{2}^{2-}}$ was found to have higher association constants and its lifetime was twofold longer than Ba2SO42+ ${{{\rm B}{\rm a}}_{2}{{\rm S}{\rm O}}_{4}^{2+}}$. Similar trends were observed for BaCO3 ${{{\rm B}{\rm a}{\rm C}{\rm O}}_{3}}$ and CaSO4 ${{{\rm C}{\rm a}{\rm S}{\rm O}}_{4}}$. Contrastingly, for CaCO3 ${{{\rm C}{\rm a}{\rm C}{\rm O}}_{3}}$ , CaCO322- ${{\rm C}{\rm a}{\left({{\rm C}{\rm O}}_{3}\right)}_{2}^{2-}}$ was found to have lower association constants and its lifetime was shorter than Ca2CO32+ ${{{\rm C}{\rm a}}_{2}{{\rm C}{\rm O}}_{3}^{2+}}$. These trends in stability and lifetime follow the same asymmetrical behaviour as observed experimentally for particle formation using techniques like DLS. This suggests a causal relationship between the stability and lifetime of the initial charged complexes and the nucleation under non‐stoichiometric conditions. [ABSTRACT FROM AUTHOR]

Geometric complexities play an important role in the nucleation, propagation, and termination of strike-slip earthquake ruptures. The 2021 Mw7.4 Maduo earthquake rupture initiated at a large releasing stepover with a complex fault intersection. In the epicentral region, we conducted detailed mapping and classification of the surface ruptures and slip measurements associated with the earthquake, combining high-resolution uncrewed aerial vehicle (UAV) images and optical image correlation with field investigations. Our findings indicate that the coseismic ruptures present discontinuous patterns mixed with numerous lateral spreadings due to strong ground shaking. The discontinuous surface ruptures are uncharacteristic in slip to account for the large and clear displacements of offset landforms in the epicentral region. Within the releasing stepovers, the deformation zone revealed from the optical image correlation map indicates that a fault may cut diagonally across the pull-apart basin at depth. The left-lateral horizontal coseismic displacements from field measurements are typically ≤0.6 m, significantly lower than the 1–2.7 m measured from the optical image correlation map. Such a discrepancy indicates a significant proportion of off-fault deformation or the possibility that the rupture stopped at a shallow depth during its initiation phase instead of extending to the surface. The fault network and multi-fault junctions west and south of the epicenter suggest a possible complex path, which retarded the westward propagation at the initial phase of rupture growth. A hampered initiation might enhance the seismic ground motion and the complex ground deformation features at the surface, including widespread shaking-related fissures. [ABSTRACT FROM AUTHOR]

Airborne particles alter the radiative forcing of climate and have further consequences on air visibility, atmospheric chemistry, and human health. Recent studies reported the existence of highly viscous semisolid and even solid amorphous organic aerosol (OA) particles. Particle viscosity has an impact on the heterogeneous chemistry, gas-particle partitioning, and ice nucleation properties. Consequently, variations in particle viscosity must be considered when predicting the atmospheric impact of OA. Here, we use scanning electron microscopy (SEM) and scanning transmission X-ray microscopy (STXM) to estimate the viscosity of individual particles deposited on substrates based on their characteristic height-to-width ratios, which are affected by changes in morphology upon deposition. The height-to-width ratios obtained from SEM and STXM exhibit a strong correlation, demonstrating that both imaging approaches can be applied separately for viscosity assessment of the substrate-deposited particles. While these metrics are largely qualitative, this method enables rapid assessment of particle viscosity ranges, distinguishing between semisolid (>1010 Pa·s), viscous (104–108 Pa·s), and liquid (10°–101 Pa·s) particles within ensembles of ambient particles collected for microscopy studies. Copyright © 2024 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Constraining strain localization and the growth of shear fabrics within brittle fault zones at sub‐seismic slip rates is important for understanding fault strength and frictional stability. We conducted direct shear experiments on simulated sandstone‐derived fault gouges at an effective normal stress of 40 MPa, a pore pressure of 15 MPa, and a temperature of 100°C. Using a passive strain marker and X‐ray Computed Tomography, we analyzed the spatial distribution of deformation in gouges deformed in the strain‐hardening, subsequent strain‐softening, and then steady‐state regimes at displacement rates of 1, 30, and 1,000 µm/s. We developed a machine‐learning‐based automatic boundary detection method to recognize the shear fabrics and quantify displacement partitioning between each fabric element. Our results show fabrics oriented along R1 and Y (including boundary) shears are the two major fabric elements. At rates of 1 and 30 µm/s, the relative amount of displacement on R1 shears is displacement dependent, increasing to ∼20% of the total displacement up to the strain‐softening stage, then decreasing to ∼10%–18% at the steady state. This trend is absent at the high rate where ∼18% of the displacement occurs on R1 shears throughout all investigated stages. At all rates, the relative amount of displacement on Y shears increases linearly with displacement to a total of larger than 50% at the steady state. Our study provides constraints on the development of the active slip zone, which is an important factor controlling heating and weakening associated with small‐magnitude earthquakes with limited displacement (mm‐dm), such as induced seismicity. Plain Language Summary: In the past few decades, several studies have focused on the mechanical behavior of simulated fault zones to understand earthquake nucleation. However, minor attention has been paid to the microstructural characterization of fault‐zone gouges due to the difficulties in quantifying deformation. An understanding of brittle fault‐zone fabrics and their development provides crucial constraints on the mechanical strength and stability of faults. We conducted laboratory experiments on simulated sandstone‐derived fault gouges with a passive strain marker under the conditions relevant to earthquake nucleation to explore the development and evolution of shear zone fabrics and their relations to fault strength. We combined X‐ray Computed Tomography (XCT) and a custom‐designed machine‐learning‐based automatic boundary detection method to analyze the spatial distribution of gouge deformation and to quantify displacement partitioning between deformation features. The results show that our samples have similar evolution of the shear fabrics, partitioning of displacement, and mechanical response with increasing shear strain at all tested nucleation velocities. The evolution of the mechanical behavior from strain‐hardening, to softening, to steady‐state stages is related to the transformation of R1 to shear‐parallel shear bands. Up to 50% of the total displacement can be accommodated within shear‐parallel shear bands, facilitating strain weakening of the materials. Key Points: We performed 3‐D analyses on the evolution of shear zone fabrics within sandstone‐derived fault gouges utilizing the X‐ray CT techniqueOur samples show similar evolution of shear fabrics, slip partitioning, and mechanical response with shear strain at all tested velocitiesUp to 50% of the total imposed displacement can be accommodated within shear‐parallel shear bands during earthquake nucleation [ABSTRACT FROM AUTHOR]

In the solid state, the thermal properties of SCO materials give rise to a rich variety of behaviors, ranging from (i) simple continuous gradual spin transitions, corresponding to a Boltzmann population of two degenerate states to (ii) sharp first-order hysteretic[11] transitions, including (iii) incomplete transitions and (iv) two-step or multi-step spin transitions,[12] characterized by the presence of a macroscopic intermediate state in the course of the transition between the LS and the HS states. Ndiaye I et al i .[33] establish the existence of an isomorphism between the electro-elastic models developed for the spin transition and Ising-like models including competing interactions, which confirms the relevance of the spin models in describing the multi-step spin transitions. Indeed, due to the volume change accompanying the spin transition between the LS and the HS states, crystallography appears as a direct probe of the spin transition at several scales, giving information about the deformation of the molecular structure and its consequence on the expansion/contraction of the lattice along the spin transformation. Later on, new interesting initiatives emerge through the introduction of spin-phonon models and elastic models in which the spin states were coupled to the atomic displacements of the SCO lattice, renormalizing the ligand field to which an elastic contribution arising from the lattice is added. [Extracted from the article]

The direct interactions of atmospheric aerosols with radiation significantly impact the Earth's climate and weather and are important to represent accurately in simulations of the atmosphere. This work introduces two new contributions to enable more accurate representation of aerosol optics in atmosphere models: 1) 'TAMie,' a new Python-based Mie scattering code that can represent both homogeneous and coated particles and achieves comparable speed and accuracy to established Fortran Mie codes. 2) 'NeuralMie,' a neural network Mie code emulator trained on data from TAMie, that can directly compute the bulk optical properties of a diverse range of aerosol populations and is appropriate for use in atmosphere simulations where aerosol optical properties are parameterized. NeuralMie is highly flexible and can be used for a large range of particle types and wavelengths. It can represent core-shell scattering, and by directly estimating bulk optical properties, is more efficient than existing Mie code and Mie code emulators while incurring negligible error (0.08 % mean absolute percentage error). [ABSTRACT FROM AUTHOR]

Carbon disulfide (CS2) has recently gained attention as an important precursor for the atmospheric trace gas carbonyl sulfide (OCS), which delivers sulfur to the stratospheric sulfur layer and impacts the radiative budget of the Earth. CS2 is naturally produced in the ocean and emitted to the atmosphere. However, the magnitude of its marine emissions is only poorly constrained due to lacking understanding of its production and consumption processes. Here, we present incubation experiments with and without UV light treatment and provide evidence for a previously not considered UV‐light‐driven degradation process of CS2 in seawater, following first‐order kinetics. In addition to its already known photochemical production process, CS2 production is found in the dark, depending on the amount of dissolved organic sulfur present in seawater. We provide novel production and consumption rates of CS2 in seawater that pave the way toward mechanistically quantifying marine emissions of this important trace gas. Plain Language Summary: The gas carbon disulfide (CS2) impacts the climate system of our planet as a precursor for sulfate aerosols. CS2 is naturally produced in the ocean, but how much marine CS2 is emitted to the atmosphere is not well known. In our study, we have experimentally derived production and degradation rates of CS2 in seawater and found processes that have previously not been considered: CS2 is degraded by UV radiation in seawater, and is produced in the absence of light. This dark production increases with the amount of dissolved organic sulfur in the water. Our results help to understand the production and degradation of CS2 in seawater, which is needed to quantify its emissions to the atmosphere. Key Points: Carbon disulfide in seawater is degraded by UV light at time scales of daysCarbon disulfide is produced in seawater without UV light at rates comparable to photochemical productionCarbon disulfide dark production is limited by dissolved organic sulfur [ABSTRACT FROM AUTHOR]

This study introduces an innovative outdoor nephelometer system designed to monitor the dynamic hygroscopic behavior of aerosols in ambient air. Field measurements conducted in the Pearl River Delta region of China unveil significant roles of relative humidity (RH) swings on aerosol phase states. Highlighting the occurrence of aerosol crystallization in the afternoon followed by gradual deliquescence as RH increases, particularly when minimum afternoon RH drops below 35%, with no such behavior observed when it exceeds 40%. Emphasizing that aerosol phase states are shaped not only by RH and chemical composition but also by their RH history, illustrating that RH levels of 70% in the morning or evening may correspond to fully dissolved metastable or partially dissolved metastable states of ambient aerosols. These findings underscore the need to account for RH history when predicting aerosol phase states and have broader implications for comprehending aerosol behavior and its atmospheric impacts. Plain Language Summary: This research introduces a new device to study how tiny particles called atmospheric aerosols in the air behave when they encounter moisture. We tested it in a region of China and discovered that relative humidity fluctuations from morning to evening impact significantly on phase state of atmospheric aerosols. In the afternoon, some of the particles might become solid, like tiny crystals, and later turn into liquid gradually as humidity increases. This phenomenon occurs when the afternoon minimum relative humidity is low, below 35%, but does not take place when it exceeds 40%. Suggesting that relative humidity history matters for aerosol phase. For example, relative humidity of 70% in the morning or evening, particles may be in a liquid or semi‐liquid state. This study helps us understand phase changes of atmospheric particles and their effects on our environment. Key Points: Innovative outdoor nephelometer system was developed to monitor aerosol hygroscopic behavior in ambient airAerosol crystallization in the afternoon followed by gradual deliquescence observedRelative humidity history plays significant roles in determining aerosol phase state [ABSTRACT FROM AUTHOR]

Large earthquakes can trigger smaller seismic events, even at significant distances. The process of earthquake triggering offers valuable insights into the evolution of local stress states, deepening our understanding of the mechanisms of earthquake nucleation. However, our ability to detect these triggered events is limited by the quality and spatial density of local seismometers, posing significant challenges if the triggered event is hidden in the signal of a nearby larger earthquake. Distributed acoustic sensing (DAS) has the potential to enhance the monitoring capability of triggered earthquakes through its high spatial sampling and large spatial coverage. Here, we report on an uncatalogued magnitude (M) 5.1 event in northeast Turkey, which was likely dynamically and instantaneously triggered by the 2023 M7.8 earthquake in southeast Turkey, located 400 km away. This event was initially discovered on ∼1,100 km of active DAS recordings that are part of an 1,850‐km linear array. Subsequent validation using local seismometers confirmed the event's precise time, location, and magnitude. Interestingly, this dynamically triggered event exhibited precursory signals preceding its P arrivals on the nearby seismometers. It can be interpreted as the signal from other nearby, uncatalogued, smaller triggered events. Our results highlight the potential of high‐spatial‐density DAS in enhancing the local‐scale detection and the detailed analysis of earthquake triggering. Plain Language Summary: Large earthquakes can trigger smaller ones even far away. This helps us understand more about how earthquakes start and develop. However, finding these smaller earthquakes can be difficult as sometimes they are hidden in the chaos of a bigger, nearby earthquake. There is a novel technology called Distributed Acoustic Sensing (DAS) that might help. DAS can listen for earthquakes over large areas and gives a more detailed picture of what's happening underground. In this study, we discovered a moderate‐size earthquake with a magnitude of 5.1 in Northeast Turkey that was triggered by a large earthquake with a magnitude of 7.8 in Southeast Turkey, using a DAS system that stretched over a thousand kilometers. We then checked this finding with conventional seismometers to be sure. Interestingly, this triggered earthquake showed precursory signals before its main shaking started, which could be signs of other smaller earthquakes happening nearby. Our findings deepen our understanding of how earthquakes interact with each other and offer insights into how earthquakes start. Our results also suggest that DAS could help us find and understand these triggered earthquakes, providing us with invaluable information for future seismology studies. Key Points: We find an uncatalogued M5.1 earthquake in NE Turkey dynamically and instantaneously triggered by the 2023 Mw 7.8 SE Turkey earthquakeWe uncover this event on a thousand‐kilometer linear distributed acoustic sensing array, then confirm its precise time, location, and magnitude with seismometersPrecursory signals of the M5.1 event are observed and are most likely resulting from other nearby events rather than its nucleation phase [ABSTRACT FROM AUTHOR]

We used local P and S waves, and regional Lg waves to investigate the Mw 4.9 Offshore Jeju Island earthquake, whose records show evidence of a complex rupture. This earthquake provides a rare window to understand the seismogenesis of moderate‐sized earthquakes on the southern Korea–East China Sea continental shelf. We computed the relative source time functions (RSTFs) by aligning the signals on the origin time of the main and its empirical Green's function (EGF) events, allowing us to use them as differential times of the EGF pair. We determined subevent locations using direct‐wave RSTFs, and captured the rupture variability of the two large subevents using waveform inversion of stacked Lg‐wave RSTFs. The first subevent rupture started by two weak nucleation phases and propagated slowly and bilaterally. Then the second subevent ruptured westward. Our analysis demonstrates that the Lg‐wave train observed at regional distances is useful in investigating detailed slip history. Plain Language Summary: In‐depth studies of small‐to‐moderate‐sized earthquakes in offshore regions are often limited by sparse seismographic station coverage and a lack of close observations. Here, we demonstrate the effective use of local P and S waves and regional Lg waves to investigate the detailed rupture process of the 2021 Mw 4.9 Offshore Jeju Island, Korea earthquake. Lg wave is a guided S wave composed of a superposition of post‐critical reflections in the crust. Detailed seismological analyses using Lg waves revealed that earthquake rupture processes can be spatially complex even in areas with low seismic activity. Our analysis demonstrates that the Lg wave observed at distances greater than 150 km from the epicenter alleviates the limited local station coverage and can be a very useful signal to image the detailed slip history of the earthquake. Our analysis revealed the rupture complexity of the earthquake, expressed as a cascade of four sequential ruptures consisting of two small nucleation phases and two large subevents. Such detailed knowledge of earthquake rupture evolution is critical for understanding seismogenesis in this stable continental region setting. Key Points: We demonstrate an approach to capture the complex rupture process of an offshore moderate‐sized earthquake using limited observationsDirect P and S waves and Lg waves are used to image a spatiotemporal slip history of the Mw 4.9 Offshore Jeju Island, Korea earthquakeResults show a cascading rupture of four subevents on a fault, offering a deeper understanding of event mechanism in low‐seismicity regions [ABSTRACT FROM AUTHOR]

Cloud-top phase (CTP) impacts cloud albedo and pathways for ice particle nucleation, growth, and fallout within extratropical cyclones. This study uses airborne lidar, radar, and Rapid Refresh analysis data to characterize CTP within extratropical cyclones as a function of cloud-top temperature (CTT). During the 2020, 2022, and 2023 Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign deployments, the Earth Resources 2 (ER-2) aircraft flew 26 research flights over the northeast and midwest United States to sample the cloud tops of a variety of extratropical cyclones. A training dataset was developed to create probabilistic phase classifications based on Cloud Physics Lidar measurements of known ice and liquid clouds. These classifications were then used to quantify dominant CTP in the top 150 m of clouds sampled by the Cloud Physics Lidar in storms during IMPACTS. Case studies are presented illustrating examples of supercooled liquid water at cloud top at different CTT ranges (−3° < CTTs < −35°C) within extratropical cyclones. During IMPACTS, 19.2% of clouds had supercooled liquid water present at cloud top. Supercooled liquid was the dominant phase in extratropical cyclone cloud tops when CTTs were >−20°C. Liquid-bearing cloud tops were found at CTTs as cold as −37°C. Significance Statement: Identifying supercooled liquid cloud tops' frequency is crucial for understanding ice nucleation mechanisms at cloud top, cloud radiative effects, and aircraft icing. In this study, airborne lidar, radar, and model temperature data from 26 research flights during the NASA IMPACTS campaign are used to characterize extratropical cyclone cloud-top phase (CTP) as a function of cloud-top temperature (CTT). The results show that liquid was the dominant CTP present in extratropical cyclone cloud tops when CTTs were >−20°C with decreasing supercooled liquid cloud-top frequency at temperatures < −20°C. Nevertheless, liquid was present at CTTs as cold as −37°C. [ABSTRACT FROM AUTHOR]

The analysis of on-fault seismicity can enlighten the current stress state on the fault itself. Its definition is relevant to individuate fault patches that have not released all the accumulated stress even after the occurrence of a high magnitude earthquake. We use the b value to characterize the stress state on the fault of the Antakya 2023 main events, being b inversely proportional to the stress. The small magnitude seismicity occurring on the maximum slip fault-patches does not allow the b value estimation. This represents a strong indication that the maximum slip zone released most of the stress previously accumulated. Conversely, the lowest b values are located at the bends of the faults and close to the nucleation zone suggesting that, there, still exists not released stress implying that it could be reactivated in the future. [ABSTRACT FROM AUTHOR]

In situ mineralization is a promising strategy to mimic the physicochemical properties of biominerals and is widely applied in the field of bone repair. Given the high requirement for substance exchange in cranial bone regeneration, in situ mineralized organic–inorganic hybrid materials exhibit advantages. However, the integration of remarkable mineral content, mechanical properties, and osteogenic properties also remains a major challenge. Herein, enhanced in situ mineralization through combining the enzymatic and anion‐boosted mineralization is applied to promote the mineralization efficiency, mineral content, and mechanical properties. Based on the results of computational calculations and in vitro mineralization experiments, the mechanism of mineralization enhancement is investigated from the perspectives of nucleation sites and the saturation of in situ mineralization. Anionic polyaspartic acid (pAsp) can increase the saturation of in situ mineralization; enzymatic mineralization shows high efficiency, with minerals of low crystallinity. The changes in the properties of the minerals effectively enhance the biological properties of 3D‐printed scaffolds, as confirmed by cell proliferation/differentiation experiments in vitro and in cranial bone regeneration in vivo. This strategy provides a new thinking for the preparation of bionic mineralized scaffolds for cranial bone repair, and can greatly promote the efficiency of bone regeneration. [ABSTRACT FROM AUTHOR]

Precipitation of marine biogenic CaCO 3 minerals occurs at specialist sites, typically with elevated pH and dissolved inorganic carbon, and in the presence of biomolecules which control the nucleation, growth, and morphology of the calcium carbonate structure. Here we explore aragonite precipitation in vitro under conditions inferred to occur in tropical coral calcification media under present and future atmospheric CO 2 scenarios. We vary pH, Ω Ar and pCO 2 between experiments to explore how both HCO 3 − and CO 3 2− influence precipitation rate and we identify the effects of the three most common amino acids in coral skeletons (aspartic acid, glutamic acid and glycine) on precipitation rate and aragonite morphology. We find that fluid Ω Ar or [CO 3 2−] is the main control on precipitation rate at 25 °C, with no significant contribution from HCO 3 − or pH. All amino acids inhibit aragonite precipitation at 0.2–5 mM and the degree of inhibition is inversely correlated with Ω Ar and, in the case of aspartic acid, also inversely correlated with seawater temperature. Aspartic acid inhibits precipitation the most, of the tested amino acids (and generates changes in aragonite morphology) and glycine inhibits precipitation the least. Previous work shows that ocean acidification increases the amino acid content of coral skeletons and probably reduces calcification media Ω Ar , both of which can inhibit aragonite precipitation. This study and previous work shows aragonite precipitation rate is exponentially related to temperature from 10 to 30 °C and small anthropogenic increases in seawater temperature will likely offset the inhibition in precipitation rate predicted to occur due to increased skeletal aspartic acid and reduced calcification media Ω Ar under ocean acidification. [ABSTRACT FROM AUTHOR]

• A powerful Mw = 7.2 earthquake occurred on August 14, 2021 at 12:29 UT. • Variations of electron density obtained from CSES-01 satellite were considered. • Findings acknowledge the sequence of seismic anomalies observed in the LAI. A powerful Mw = 7.2 earthquake occurred in Haiti on August 14, 2021 at 12:29:08 UTC (18.434° N, 73.482° W, depth ∼10 km). In this study, in a period of three months from June 1 to August 31, 2021, the variations in electron density and temperature parameters obtained from CSES-01 satellite measurements in the Dobrovolsky's area the Haiti earthquake are considered. With the aim of investigating the proposed mechanisms for interactions between different layers of the Earth in the process of earthquakes (LAIC-Lithospheric Atmospheric Ionospheric Coupling), the behavior of 48 other precursors obtained from the data of other satellites in the same location and time period were analyzed. These precursors are 1) TEC obtained from GPS satellite data, 2) scalar and vector magnetic field data as well as electron density and temperature measured by the related sensors of three Swarm A, B and C satellites during day and night and 3) Variations in lithospheric and atmospheric parameters NO2 and SO2 obtained from OMI satellite measurements and also Ozone, carbon monoxide and surface temperature parameters obtained from AIRS data. By analyzing the above mentioned precursors, abnormal behaviors are observed around 30 and 50 days before the earthquake, and especially 1 to 15 days before the earthquake and by comparative study of the observed anomalies, possible LAIC mechanisms are discussed. The findings of this study can acknowledge the sequence of seismic anomalies observed in the lithosphere, then the atmosphere and finally the ionosphere. Therefore, this study once again emphasizes the necessity of performing multi-precursor analysis with the aim of justifying the LAIC mechanism and also observing seismically prone anomalies in the time period of about 10 days before powerful earthquakes. [ABSTRACT FROM AUTHOR]

The main nucleating vapor in the atmosphere is thought to be sulfuric acid (H2SO4), stabilized by ammonia (NH3). However, in marine and polar regions, NH3 is generally low, and H2SO4 is frequently found together with iodine oxoacids [HIOx, i.e., iodic acid (HIO3) and iodous acid (HIO2)]. In experiments performed with the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we investigated the interplay of H2SO4 and HIOx during atmospheric particle nucleation. We found that HIOx greatly enhances H2SO4(-NH3) nucleation through two different interactions. First, HIO3 strongly binds with H2SO4 in charged clusters so they drive particle nucleation synergistically. Second, HIO2 substitutes for NH3, forming strongly bound H2SO4-HIO2 acid-base pairs in molecular clusters. Global observations imply that HIOx is enhancing H2SO4(-NH3) nucleation rates 10- to 10,000-fold in marine and polar regions. [ABSTRACT FROM AUTHOR]

We investigated the liquid water path and global solar irradiance (Q) at ground level according to the ICON model; CLOUDNET measurements in Lindenberg, Munich, and Jülich; and BSRN observations in Lindenberg. This research is focused on stratiform non-precipitating clouds. The liquid water path (LWP) is underestimated, while Q is overestimated. The lower LWP is due to liquid water content underestimation practically in all atmosphere layers and a lower frequency of liquid cloud occurrence compared to observations. This is partly associated with the structure of the cloud nucleation scheme of the ICON model and with the default cloud condensation nuclei (CCN) number concentration. An increase in CCNs from 250 cm−3 (typical background value for the region of interest) to 1700 cm−3 (characteristic of polluted continental clouds) leads to an increase in the grid-scale liquid water path by 40% and a decrease in Q by 12% in overcast conditions. However, we also showed that the liquid water path is not a key factor of Q overestimation. The main factor is an inaccurate description of the cloud spatial structure, where the correct prediction of the ratio of direct to global irradiance as a spatial characteristic of clouds plays a more important role than the standard cloud fraction. [ABSTRACT FROM AUTHOR]

Our understanding of ocean-cloud interactions and their effect on climate lacks insight into a key pathway: do biogenic marine emissions form new particles in the open ocean atmosphere? Using measurements collected in ship-borne air-sea interface tanks deployed in the Southwestern Pacific Ocean, we identified new particle formation (NPF) during nighttime that was related to plankton community composition. We show that nitrate ions are the only species for which abundance could support NPF rates in our semicontrolled experiments. Nitrate ions also prevailed in the natural pristine marine atmosphere and were elevated under higher sub-10 nm particle concentrations. We hypothesize that these nucleation events were fueled by complex, short-term biogeochemical cycling involving the microbial loop. These findings suggest a new perspective with a previously unidentified role of nitrate of marine biogeochemical origin in aerosol nucleation. [ABSTRACT FROM AUTHOR]

We explicitly calculate the efficiency with which submicron-sized aerosol particles (APs) with a diameter smaller than 0.2 μ m collide with cloud droplets and raindrops in air due to individual and combined, simultaneous action of all ice nucleation and all collection mechanisms, including electrostatic forces caused by electric charges on the cloud drops and APs. Brownian diffusion is a predominant collection mechanism up to the critical diameter of APs, which depends on the value of the coefficient of electrostatic collection α. For larger APs, electroscavenging (ES) is the dominant collection mechanism. When ice nucleation is added to all collection processes, at some moments a larger value of α results in a lower mass of APs in rainwater, but only for α = 1 and α = 3. Ice nucleation lowers the relative AP precipitation mass (RAPM) compared with a numerical experiment when all collection processes are included for almost 7% at the end of integration for α = 7 , while for all other values of α RAPM increases. α affects the mass more than the number of APs in cloud water when ice nucleation and all collection processes act simultaneously. The greatest scavenging in the air occurs for the largest α. ES significantly affects the mass of APs in precipitation at the end of the integration period, while its influence on the number of APs is not that important. The influence of APs charge distribution and an image charge on RAPM and RAPN is significant. For the RAPN the influence of APs distribution compared to an image charge is more significant. The addition of image force to Coulomb force and APs bipolar charge distribution contributes to RAPM for 3.9% and RAPN for 1.6%. Copyright © 2023 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Mixed‐phase clouds (MPCs) have been identified as significant contributors to uncertainties in climate projections, attributable to model representation of processes controlling the formation and loss of supercooled water droplets and ice particles from the atmosphere. Arctic MPCs are commonly widespread and long‐lived, with sustained ice crystal formation processes that challenge current understanding. This study examines the ice‐nucleating particle (INP) reservoir dynamics governing immersion‐mode heterogeneous freezing in an observed case of Arctic MPCs using a simplified 1D aerosol‐cloud model. The model setup includes prescribed dynamical forcings and thermodynamic profiles, and represents INPs as multicomponent and polydisperse particle size distributions. Diagnostic and prognostic approaches to immersion freezing parameterization are compared, including time‐independent (singular) number‐ and surface area‐based descriptions and a time‐dependent description following classical nucleation theory (CNT). The choice of freezing parameterization defines the size of the INP reservoir. The CNT‐based description yields an orders of magnitude larger INP reservoir than the singular parameterizations, which is the dominant factor for sustained ice crystal formation. The efficiency of the freezing process and cloud cooling are of secondary importance. A diagnostic treatment neglecting INP loss is only accurate when the INP reservoir size is large and INP depletion weak. Since a larger INP reservoir sustains ice crystal formation substantially longer, and ice water path scales with ice crystal concentrations for the conditions considered, resolving the source of differences in INP reservoir dynamics due to model implementation is a high priority for advancing climate model physics. Plain Language Summary: Knowledge gaps regarding long‐lived Arctic mixed‐phase clouds, wherein supercooled droplets and ice crystals coexist, lead to significant uncertainties when assessing Earth's surface warming from increasing greenhouse gases. The longevity of such clouds, sustaining both liquid and ice crystal formation over many hours, is poorly represented across global climate models. Application of a simplified column model shows that the underlying freezing parameterization defines the number of ice‐nucleating particles (INPs) available for ice formation, termed INP reservoir in this work. A time‐dependent freezing description yields a substantially greater INP reservoir than time‐independent approaches, and therefore greater ice formation over 10 hr, whereas other factors are less important. Future work will extend to additional environmental conditions and modeling approaches. Key Points: A 1‐D model informed by a large‐eddy simulation allows detailed study of immersion ice‐nucleating particles (INPs)Stochastic immersion freezing yields a greater INP reservoir and more sustained ice formation than singular approachesThe efficiency of the freezing process and cloud cooling are of secondary importance for the sustenance of ice crystal formation [ABSTRACT FROM AUTHOR]

Enzymatically induced carbonate precipitation (EICP) in heterogeneous subsurface is of interest in various geoscience and environmental applications. Through fabricating microfluidic cells with different pore networks, the pore-scale formation of biological CaCO3 was investigated experimentally by transverse mixing using time lapse high-resolution camera. The precipitation pattern over time was processed to obtain the evolution of distribution of CaCO3 volume fraction. The impact of flow rate and pore-scale heterogeneity were quantitatively evaluated with reaction index including overall pore filling ratio, precipitation rate and precipitation efficiency. The results showed that low flow rates and strong heterogeneity in porous media are the two favorable conditions for precipitation process due to more nucleation sites. At grain scale, a statistic of three-dimensional morphologies of individual crystals was evaluated with specific surface area and degree of anisotropy. Localized precipitates in multiple pores were adopted as a representative of the whole porous media. The analysis showed that the complex pore structures are generated due to precipitates in pores, thus limiting transport of reactants and result in the permeability reduction. We furthermore confirmed different polymorphs of calcium carbonate, mainly containing vaterite and calcite. Pore-scale analysis of biological CaCO3 in porous media significantly contributes to the understanding of advection–diffusion-reaction coupling effect, and further revealing the role of pore network on biomineralization process. [ABSTRACT FROM AUTHOR]

Synergistic interaction between the helium (He) atom and vacancy (Vac) in chromium (Cr) coatings plays an important role in the evolution of radiation-induced microstructures and He bubbles. First-principle calculations were utilized to investigate the contributions of Vac–Vac He–He and Hen-Vacm interactions (n = 1 ~ 10, m = 0 ~ 3) to electronic structures and energetics in Cr superlattice. It is found that the vacancy formation energy was dramatically decreased by the He dispersing distribution. The mono-vac (Vac1) was preferred to be occupied by one He atom, while the vacancy clusters can be formed by the most stable bi-vac (Vac2) and tri-vac (Vac3). Two He atoms with the second nearest-neighbor (T0–T2) structure at equilibrium distances of 1.60 Å was the most stable configuration of the He–He pair. Moreover, when the Vac1 accommodated 10 He atoms, the improved vacancy volume and lattice distortion may induce to capture more He atoms in the Vac1, and the He bubble was produced. The present research results provide the physical essence of vacancy aggregation and a theoretical foundation of the vacancy trapping mechanism for He atoms in Cr, which is extremely important for the nucleation and growth mechanism of He bubbles in Cr. [ABSTRACT FROM AUTHOR]

The generation of strong earthquakes is a long‐debated problem in seismology, and its importance is increased by the possible implications for earthquake forecasting. It is hypothesized that the earthquake generation processes are anticipated by several phenomena occurring within a nucleation region. These phenomena, also defined as preparatory processes, load stress on the fault leading it to reach a critical state. In this paper, we investigate the seismicity preceding 19 moderate (Mw ≥ 3.5) earthquakes at The Geysers, Northern California, aiming to verify the existence of a preparatory phase before their occurrence. We apply an unsupervised K‐means clustering technique to analyze time series of physics‐related features extracted from catalog information and estimated for events occurred before the mainshocks. Specifically, we study the temporal evolution of the b‐value from the Gutenberg‐Richter (b), the magnitude of completeness (Mc), the fractal dimension (Dc), the inter‐event time (dt), and the moment rate (M˙0 ${\dot{M}}_{0}$). Our analysis shows that out of 19 moderate magnitude events considered, a common preparatory phase for 11 events is clearly identified, plus other five events for which we can guess a preparatory phase but with different characteristics from the previous ones. The latter result confirms that even within the same tectonic context different possible activation behaviors may exist. The duration of the preparatory process ranges between about 16 hr and 4 days. We observe that also for the retrieved preparatory process a decrease in b, Mc, and Dc, and an increase of M˙0 ${\dot{M}}_{0}$. Finally, we show a clear correlation between events with a preparation phase and the location of injection's wells, suggesting an important role of fluids in the preparatory process. Plain Language Summary: We investigate the preparatory phase of moderate magnitude‐induced earthquakes at The Geysers geothermal field in California by studying the spatiotemporal evolution and dynamic properties of small magnitude events and using an unsupervised machine learning approach. To this aim, we rely on features extracted from seismic catalog information that are used for a K‐means clustering analysis. Our results highlight changes in the seismicity characteristics before the moderate‐induced earthquakes. We find that most of the analyzed target earthquakes present a preparatory phase, and that most of the cases the latter presents common characteristics in their key features. We show that the seismicity clusters in space and time before moderate events also becoming more energetic. We estimate a duration for the detected preparatory phases that ranges from 16 hr to 4 days. Finally, we show that the presence of a preparatory phase is correlated to the proximity of injection's wells, suggesting a significant role of fluids in the earthquake's nucleation process. Key Points: Moderate‐induced earthquakes at The Geysers can be preceded by a preparatory phase detectable using K‐means clustering on catalog featuresThe detected preparatory phase has common characteristics presenting negative trends of b‐value, Mc, and Dc and a positive trend of M˙0 ${\dot{M}}_{0}$The earthquakes with a preparatory phase are located nearer to the injection's wells in the area than the events without it [ABSTRACT FROM AUTHOR]

Ice nucleation in mixed‐phase clouds has been identified as a critical factor in projections of future climate. Here we explore how this process influences climate sensitivity using the Community Earth System Model 2 (CESM2). We find that ice nucleation affects simulated cloud feedbacks over most regions and levels of the troposphere, not just extratropical low clouds. However, with present‐day global mean cloud phase adjusted to replicate satellite retrievals, similar total cloud feedback is attained whether ice nucleation is simulated as aerosol‐sensitive, insensitive, or absent. These model experiments all result in a strongly positive total cloud feedback, as in the default CESM2. A microphysics update from CESM1 to CESM2 had substantially weakened ice nucleation, due partly to a model issue. Our findings indicate that this update reduced global cloud phase bias, with CESM2's high climate sensitivity reflecting improved mixed‐phase cloud representation. Plain Language Summary: Simulations of Earth's climate have revealed that the extent of greenhouse gas warming depends on a microscopic process in cold clouds known as ice nucleation. Problematically, this process is poorly understood and crudely represented in projections of future climate. Here we assess why ice nucleation affects Earth's projected future temperature, and estimate the sensitivity to different simulated representations of this process. We find that ice nucleation influences warming through feedback mechanisms in clouds in all regions and heights of the troposphere that are at temperatures where either ice crystals or liquid droplets may exist. The primary link between ice nucleation and warming is revealed to be the role this process has in setting the global mean ratio of ice to liquid water within clouds. We also demonstrate that an issue that weakened ice nucleation in a widely used climate model reduced bias in this ratio. Our findings suggest that the reduced bias is responsible for this model's strong global warming projections, enhancing the possibility that such projections may be realistic. Key Points: Ice nucleation representation is only found to sizably affect total cloud feedback when allowed to promote biased global mean cloud phaseCommunity Earth System Model 2's strongly positive cloud feedback is consistent with realistic mixed‐phase cloud representation despite a known model issueSimulated relationships among ice nucleation, cloud phase, and feedback strength are partly set by mid‐level and tropical high clouds [ABSTRACT FROM AUTHOR]

Solar radiation management as a sustained deliberate source of SO2 into the stratosphere (strat-SRM) has been proposed as an option for climate intervention. Global interactive aerosol-chemistry-climate models are often used to investigate the potential cooling efficiencies and side effects of hypothesised strat-SRM scenarios. A recent strat-SRM model intercompar-ison study for composition-climate models with interactive stratospheric aerosol suggests that the modelled climate response 5 to a particular assumed injection strategy, depends on the type of aerosol microphysical scheme used (e.g., modal or sectional representation), alongside also host model resolution and transport. Compared to short-duration volcanic SO2 emission, the continuous SO2 injections in strat-SRM scenarios may pose a greater challenge to the numerical implementation of of microphysical processes such as nucleation, condensation, and coagulation. This study explores how changing the timesteps and sequencing of microphysical processes in the sectional aerosol-chemistry-climate model SOCOL-AERv2 (40 size bins) 10 affect model predicted climate and ozone layer impacts considering strat-SRM SO2 injections of of 5 and 25 Tg(S) yr-1 at 20 km altitude between 30°S and 30°N. The model experiments consider year 2040 boundary conditions for ozone depleting substances and green house gases. We focus on the length of the microphysical timestep and the call sequence of nucleation and condensation, the two competing sink processes for gaseous H2SO4. Under stratospheric background conditions, we find no effect of the microphysical setup on the simulated aerosol properties. However, at the high sulfur loadings reached in the 15 scenarios injecting 25 Mt/yr of sulfur with a default microphysical timesetp of 6 min, changing the call sequence from the default "condensation first" to "nucleation first" leads to a massive increase in the number densities of particles in the nucle-ation mode (R < 0.01 µm) and a small decrease in coarse mode particles (R > 1 µm). As expected, the influence of the call sequence becomes negligible when the microphysical timestep is reduced to a few seconds, with the model solutions converging to a size distribution with a pronounced nucleation mode. While the main features and spatial patterns of climate forcing 20 by SO2 injections are not strongly affected by the microphysical configuration, the absolute numbers vary considerably. For the extreme injection with 25 Tg(S) yr-1, the simulated net global radiative forcing ranges from -2.3 W m-2 to -5.3 W m-2, depending on the microphysical configuration. "Nucleation first" shifts the size distribution towards radii better suited for solar scattering (0.3 µm < R < 0.4 µm), enhancing the intervention efficiency. The size-distribution shift however generates more ultra-fine aerosol particles, increasing the surface area density, resulting in 10 DU less ozone (about 3% of total column) in 25 the northern midlatitudes and 20 DU less ozone (6%) over the polar caps, compared to the "condensation first" approach. Our results suggest that a reasonably short microphysical time step of 2 minutes or less must be applied to accurately capture the magnitude of the H2SO2 supersaturation resulting from SO2 injection scenarios or volcanic eruptions. Taken together these results underscore how structural aspects of model representation of aerosol microphysical processes become important under conditions of elevated stratospheric sulfur in determining atmospheric chemistry and climate impacts. [ABSTRACT FROM AUTHOR]

New-particle formation from condensable gases is a common atmospheric process that has significant but uncertain effects on aerosol particle number concentrations and aerosol–cloud–climate interactions. Assessing the formation rates of nanometer-sized particles from different vapors is an active field of research within atmospheric sciences, with new data being constantly produced by molecular modeling and experimental studies. Such data can be used in large-scale climate and air quality models through parameterizations or lookup tables. Molecular cluster dynamics modeling, ideally benchmarked against measurements when available for the given precursor vapors, provides a straightforward means to calculate high-resolution formation rate data over wide ranges of atmospheric conditions. Ideally, the incorporation of such data should be easy, efficient and flexible in the sense that same tools can be conveniently applied for different data sets in which the formation rate depends on different parameters. In this work, we present a tool to generate and interpolate lookup tables of formation rates for user-defined input parameters. The table generator primarily applies cluster dynamics modeling to calculate formation rates from an input quantum chemistry data set defined by the user, but the interpolator may also be used for tables generated by other models or data sources. The interpolation routine uses a multivariate interpolation algorithm, which is applicable to different numbers of independent parameters, and gives fast and accurate results with typical interpolation errors of up to a few percent. These routines facilitate the implementation and testing of different aerosol formation rate predictions in large-scale models, allowing the straightforward inclusion of new or updated data without the need to apply separate parameterizations or routines for different data sets that involve different chemical compounds or other parameters. [ABSTRACT FROM AUTHOR]

Following laboratory experiments and friction theory, slow slip events and seismicity rate accelerations observed before mainshocks are sometimes interpreted as evidence of a nucleation phase. However, such precursory observations still remain scarce and are associated with different time and length scales, raising doubts about their actual preparatory nature. We study the 2017 Valparaiso Mw = 6.9 earthquake, which was preceded by aseismic slip accompanied by an intense seismicity, suspected to reflect its nucleation phase. We complement previous observations, which have focused only on precursory activity, with a continuous investigation of seismic and aseismic processes from the foreshock sequence to the post‐mainshock phase. By building a high‐resolution earthquake catalog and searching for anomalous seismicity rate increases compared to aftershock triggering models, we highlight an over‐productive seismicity starting within the foreshock sequence and persisting several days after the mainshock. Using repeating earthquakes and high‐rate GPS observations, we highlight a transient aseismic perturbation starting 1‐day before the first foreshock and continuing after the mainshock. The estimated slip rate over time is lightly impacted by large magnitude earthquakes and does not accelerate toward the mainshock. Therefore, the unusual seismic and aseismic activity observed during the 2017 Valparaiso sequence might be interpreted as the result of a slow slip event starting before the mainshock and continuing beyond it. Rather than pointing to a possible nucleation phase of the 2017 Valparaiso mainshock, the identified slow slip event acts as an aseismic loading of nearby faults, increasing the seismic activity, and thus the likelihood of a large rupture. Plain Language Summary: Both laboratory experiments and friction theory show that earthquakes do not begin abruptly but are preceded by an accelerating slip associated with a seismicity increase. On the field, however, such precursory observations still remain scarce and are associated with different characteristic time and length scales, raising doubts that they actually reflect the same nucleation phenomena. We study the 2017 Valparaiso M = 6.9 earthquake, which was preceded by both a slow slip and an intense seismicity suspected to reflect such nucleation phase. We complement previous studies, that have focused only on precursory activity, with a continuous investigation of seismic and slow slip before and after the mainshock. Using refined earthquake detection tools, we highlight a seismicity excess starting before and persisting several days after the mainshock. Using repeating earthquakes and high‐resolution GPS, we show that the slow slip does not accelerate toward the mainshock, but continues after it. Therefore, rather than pointing to a possible accelerating nucleation phase of the Valparaiso mainshock, we suggest that the slow slip drives an enhanced seismic activity that is not mainshock‐directed. Within such slow‐slip driven seismicity, the probability of triggering a large earthquake (subsequently considered as the mainshock) is increased. Key Points: We use a high resolution seismic catalog and GPS to investigate seismic and aseismic process before and after the Valparaiso mainshockAn unusually high seismicity and a slow slip event is continuously observed from the foreshock sequence up to days after the mainshockRather than a nucleation phase of the mainshock, the slow slip event acts as an aseismic loading of nearby faults during the entire sequence [ABSTRACT FROM AUTHOR]

Earthquake dynamic rupture requires a nucleation process to provide sufficient energy to overcome the fracture energy. Large earthquakes may occur via a cascading rupture process, which includes many triggering processes that cascade from small to large sections of the fault system. During such a process, the nucleation of a large section of the fault plane may occur dynamically via the propagating rupture from a small section of the fault plane. A quasi-static view of seismic nucleation has been widely discussed in earthquake seismology; however, the dynamic nucleation process remains poorly known. Here, we investigate one aspect of the dynamic nucleation process by focusing on the rupture propagation velocity during the nucleation process. We simplify this process as self-similar crack propagation at a constant rupture velocity in a finite nucleation zone within a target region that possesses a uniform fracture energy. We numerically solve this elastodynamic problem in two dimensions for both the anti-plane and in-plane cases using the Boundary Integral Equation method. As the rupture velocity increases, the critical ratio of the fracture energy step to continue the rupture increases and the critical size of the dynamic nucleation zone decreases. The rapid increase in the ratio of the fracture energy step toward infinity could explain why earthquakes never propagate at slow rupture velocities. However, the effect on the size of the nucleation zone is rather limited, with the size of the dynamic nucleation zone decreasing to ~ 70% of the static nucleation zone size. However, such a small difference would result in a significant overall difference if such a dynamic nucleation process repeatedly occurred in the cascading rupture process of a large earthquake, which would be a difficult situation for earthquake early warning. [ABSTRACT FROM AUTHOR]

A new mathematical model of the global transport of multicomponent gas impurities and aerosols has been constructed. The model includes the formation of sulfate aerosols in the atmosphere in both hemispheres. Calculations of the nucleation rates and particle number concentrations are performed for the winter period in the troposphere using a unified model that takes into account chemical and kinetic transformation processes (photochemistry, nucleation, condensation/evaporation, and coagulation). Along with the binary nucleation of sulfuric acid and water vapors, the formation of particle nuclei with the participation of atmospheric ions is also considered. The results indicate a significant role of ion nucleation in aerosol formation in the Northern and Southern hemispheres in winter. The factors controlling the dynamics of ionic processes and their influence on the spatiotemporal distribution of aerosol particles in the atmosphere include not only the level of air ionization, but also temperature, relative humidity, and the content of sulfuric acid and water vapors in the air. [ABSTRACT FROM AUTHOR]

Stress accumulation and release reflected by acoustic emissions (AEs) during shearing of granular materials provide important information on failure mechanisms in seismic faults and landslides controlled by stick‐slip. Among many characteristics (amplitude, energy, counts, and frequency) of AE signals generated by stick‐slip, stress changes corresponding to various frequency AEs in different stages of the stick‐slip process are not clear, which limits our knowledge of the characteristics of precursory signals before stick‐slip failure. To better understand the physical mechanisms of granular stick‐slip, we monitored the mechanical and AE signals using high‐frequency (2 MHz) synchronous acquisition during constant‐speed shear of packs of uniform glass beads with different sizes at different normal stresses. The release rate of AE energy was found to accelerate with the dilatation of the sample volume, and the stress drop of stick‐slip was augmented with the increase of normal stress and particle size. Three characteristic events of single cycle stick‐slip were observed in this study: main slip, minor slip, and microslip. We analyzed the AE frequency spectra of these three event types. Both main slip and minor slip corresponded to stress drop and generated high‐frequency AEs (about several hundred kHz), while the AE frequencies generated by microslip were lower (about tens of kHz) and exhibited stress strengthening, which were not apparent in previous studies due to the low frequency of acquisition. We propose that the microslip is mainly due to sliding on grain contacts, while the main slip and minor slip resulted from breakage and reforming of force chains. Low‐frequency AEs from microslip may suggest a crucial precursor of seismic faults and landslides. Plain Language Summary: The occurrence of earthquakes of similar magnitude (quasi‐periodic earthquakes) in a fault zone every few decades is thought to be controlled by stick‐slip of fault gouges. The mechanical evolution of fault gouges prior to earthquake occurrence is extremely complex and difficult to predict. However, many studies have observed the presence of significant microslip prior to stick‐slip failure of seismic faults, which may provide precursor information for an impending earthquake. Laboratory study of stick‐slip nucleation and failure mechanisms in granular materials provides important understanding of the physical mechanisms of quasi‐periodic earthquakes. Our experimental results of high‐frequency acoustic emission (AE) and ring‐shear simultaneous acquisition showed that stick‐slip failure (corresponding to the occurrence of an earthquake) leads to a decrease in the shear resistance of a granular system, generating high‐frequency acoustic signals. Increments of microslip increased the shear resistance of the granular system, and were recorded as low‐frequency acoustic signals before failure occurred. We suggest that the stick‐slip nucleation and failure were controlled by grain friction and collision, respectively. The different AE frequencies of the two may shed light on the precursor monitoring of quasi‐periodic earthquakes. Key Points: Stick‐slip failure was associated with high‐frequency (∼105 Hz) acoustic emissions (AEs) and micro‐slip during stick‐slip nucleation was associated with low‐frequency (∼104 Hz) AEsHigh‐frequency AEs may be caused by particle collisions after force‐chain breakageLow‐frequency AEs may be caused by particle friction during force‐chain adjustment and may suggest important precursors of laboratory earthquakes [ABSTRACT FROM AUTHOR]

Gas-phase dimethylamine (DMA) has recently been identified as one of the most important vapors to initiate new particle formation (NPF), even in China's polluted atmosphere. Nevertheless, there remains a fundamental need for understanding the atmospheric life cycle of DMA, particularly in urban areas. Here we pioneered large-scale mobile observations of the DMA concentrations within cities and across two pan-region transects of north-to-south (∼700 km) and west-to-east (∼2000 km) in China. Unexpectedly, DMA concentrations (mean ± 1 σ) in South China with scattered croplands (0.018 ± 0.010 ppbv, 1 ppbv=10−9 L/L) were over three times higher than those in the north with contiguous croplands (0.005 ± 0.001 ppbv), suggesting that nonagricultural activities may be an important source of DMA. Particularly in non-rural regions, incidental pulsed industrial emissions led to some of the highest DMA concentration levels in the world (>2.3 ppbv). Besides, in highly urbanized areas of Shanghai, supported by direct source-emission measurements, the spatial pattern of DMA was generally correlated with population (R 2 = 0.31) due to associated residential emissions rather than vehicular emissions. Chemical transport simulations further show that in the most populated regions of Shanghai, residential DMA emissions can contribute for up to 78% of particle number concentrations. Shanghai is a case study for populous megacities, and the impacts of nonagricultural emissions on local DMA concentration and nucleation are likely similar for other major urban regions globally. [ABSTRACT FROM AUTHOR]

The article presents several scientific news. It discusses practical demonstration of backpropagation-free training of wave-based physical neural networks, addressing challenges associated with conventional algorithms. It mentions about controlling thermal transport with a voltage-controlled thermal switch and the use of genomics to pinpoint the source and transit path of poached pangolins in Africa.

Below-cloud scavenging is the process of aerosol removal from the atmosphere between cloud-base and the ground by precipitation (e.g. rain or snow), and affects aerosol number/mass concentrations, lifetime and distributions. An accurate representation of precipitation phases is important in treating below-cloud scavenging as the efficiency of aerosol scavenging differs significantly between liquid and solid precipitation. The impact of different representations of below-cloud scavenging on existing model biases (Makar et al, 2018), was examined through implementing a new aerosol below-cloud scavenging scheme (from Wang et al., 2014) and comparing with the GEM-MACH's existing scavenging scheme, based on Slinn (1984). Further, the current GEM-MACH employs a single-phase precipitation for below-cloud scavenging: total precipitation is treated as either liquid or solid depending on a fixed environment temperature threshold. Here, we consider co-existing liquid and solid precipitation phases as they are predicted by the GEM microphysics. GEM-MACH simulations are compared with - observed precipitation samples, with a focus on the particulate base cation NH4 +, acidic anions NO3 -, SO4 =, HSO3 - in precipitation, and ambient particulate sulfate, ammonium and nitrate. Overall, the precipitation-phase partitioning and Wang et al. (2014) scavenging scheme improve GEM-MACH performance relative to earlier approaches. Including multi-phase approach leads to a decrease in SO4 2- scavenging and impacts the below-cloud scavenging of SO2 into the aqueous phase over the domain. Sulphate biases improved from +46% to -5% relative to Alberta Precipitation Quality Monitoring Program wet sulphate observations. At Canadian Air and Precipitation Monitoring Network stations the biases became more negative, from -10% to -30% for the tests carried out here. These may be compared to previously published annual average biases of +200% for SO4 2- from earlier versions of GEM-MACH (Makar et al, 2018), indicating an overall improvement in model performance relative to the prior results. Improvements in model performance (via scores for correlation coefficient, normalized mean bias, and/or fractional number of model values within a factor of two of observations) could also be seen, between the base case and the two simulations based on multiphase partitioning for NO3 -, NH4 +, and SO4 2. Whether or not these improvements corresponded to increases or decreases of NO3 - and NH4 + wet deposition varied over the simulation region. The changes were episodic in nature - the most significant changes in wet deposition were likely at specific geographic locations and represent specific cloud precipitation events. The aerosol scavenging rates of the two schemes differ during liquid precipitation in the size range of 0.1-1 µm, mostly at high precipitation intensity. The two schemes aerosol scavenging diverges for aerosols smaller than 1 µm for solid precipitation at lower intensity (R=0.01 mm/h), while at higher precipitation intensities (R=10 mm/h), the two schemes show bigger differences for aerosols larger than 1 µm. The changes in wet scavenging resulted a higher formation rate and larger concentrations of atmospheric particle sulphate. [ABSTRACT FROM AUTHOR]

Sinking detritus particles in the ocean help to regulate global climate by transporting organic carbon into deep waters where it is sequestered from the atmosphere. The rate at which bacteria remineralise detritus influences how deep particles sink and the length-scale of carbon sequestration. Conventional marine biogeochemical models typically represent particles as smooth spheres where remineralisation causes surface area (SA) to progressively shrink over time. In contrast, we propose that particle SA increases during degradation as microbial ectoenzymes cause a roughening of surfaces in a process similar to acid etching on previously smooth glass or metal surfaces. This concept is investigated using a novel model, SAMURAI (Surface Area Modelling Using Rubik As Inspiration), in which the biomass of individual particles is represented as a 3D matrix of cubical sub-units that degrades by progressive removal of sub-units that have faces in contact with the external environment. The model rapidly generates microscale rugosity (roughness) that profoundly increases total SA, giving rise to biomass-specific remineralisation rates that are approximately double those of conventional models. Faster remineralisation means less carbon penetrates the ocean's interior, diminishing carbon sequestration in deep waters. Results indicate that both SA and microbial remineralisation are highly dynamic, as well as exhibiting large variability associated with particles of different porosities. Our work highlights the need for further studies, both observational and modelling, to investigate particle SA and related microbial dynamics in order to reliably represent the role of ocean biology in global biogeochemical models. [ABSTRACT FROM AUTHOR]

Photochemical hazes are expected to form and significantly contribute to the chemical and radiative balance of exoplanets with relatively moderate temperatures, possibly in the habitable zone of their host star. In the presence of humidity, haze particles might thus serve as cloud condensation nuclei and trigger the formation of water droplets. In the present work, we are interested in the chemical impact of such a close interaction between photochemical hazes and humidity on the organic content composing the hazes and on the capacity to generate organic molecules with high prebiotic potential. For this purpose, we explore experimentally the sweet spot by combining N-dominated super-Earth exoplanets in agreement with Titan's rich organic photochemistry and humid conditions expected for exoplanets in habitable zones. A logarithmic increase with time is observed for the relative abundance of oxygenated species, with O-containing molecules dominating after 1 month only. The rapidity of the process suggests that the humid evolution of N-rich organic haze provides an efficient source of molecules with high prebiotic potential. [ABSTRACT FROM AUTHOR]

Determining the dominant ice nucleation mode in cirrus is still an open research question that impacts the ability to assess the climate impact of these clouds in numerical models. Homogeneous nucleation is generally well understood. More uncertainty surrounds heterogeneous nucleation due to a weaker understanding of the complex physio-chemical properties (e.g., ice nucleation efficiency and atmospheric abundance) of ice nucleating particles (INPs). This hampers efforts to simulate their interactions with cirrus, which is crucial in order to assess the effect these clouds have on the climate system. introduced a new deterministic heterogeneous ice nucleation parameterization based on the differential activated fraction (AF), which describes the number of INPs that activate ice within a specified temperature or ice saturation ratio interval. They argued that this new approach with explicit INP budgeting, which removes INPs from the total population after they nucleate ice, could help to correct a potential overprediction of heterogeneous nucleation within cirrus when budgeting is not considered. We formulated a general circulation model (GCM)-compatible version of the differential AF parameterization for simulating only deposition nucleation within in situ cirrus and compared it to the method currently employed in the ECHAM6.3-HAM2.3 GCM that is based on cumulative AF. This default cumulative AF approach does not use explicit INP budgeting but instead implicitly budgets for INPs that nucleated ice using a differential ice crystal number concentration variable to calculate whether new ice formation should be added to the pre-existing concentration. In a series of box model simulations that were based on the cirrus sub-model from ECHAM, we found that the cumulative approach likely underpredicts heterogeneous nucleation in cirrus, as it does not account for interstitial INPs remaining from the previous GCM time step. However, as the cases that we simulated in the box model were rather extreme, we extended our analysis to compare the differential and cumulative AF approaches in two simulations in ECHAM-HAM. We find that choosing between these two approaches impacts ice nucleation competition within cirrus in our model. However, based on our 5-year simulations, the small and insignificant difference in the top-of-atmosphere radiative balance of 0.02±0.35 Wm-2 means that the overall climate impact is negligible. We argue that while our GCM-compatible differential AF parameterization is closer to first principles, the default approach based on cumulative AF is simpler due to the lack of additional tracers required. Finally, our new approach could be extended to assess the impact of explicit versus implicit INP budgeting on the ice crystal number concentration produced by immersion freezing of mineral dust particles, as this is also an important mechanism in cirrus. [ABSTRACT FROM AUTHOR]

New particle formation including atmospheric aerosol nucleation and subsequent growth, contributes to about half of cloud condensation nuclei and can grow to form haze under certain conditions, so its role in climate change and air quality is indispensable. However, various kinds of nucleation precursors create vast combinations of molecular clustering, hindering the understanding the detailed picture of nucleation mechanism. The recently appeared general neural network potential, ANI‐2x, covering most of elements composing nucleation clusters, looks promising to be embedded into the nucleation theoretical workflows to improve the nucleation simulation accuracy. Here we benchmarked ANI‐2x's performance on both low and high energy isomers based workflows through comparing it with semi‐empirical (PM7) and DFT (ωB97XD/6‐31++G(d,p)) methods. Results show that ANI‐2x is superior to PM7 in single point energy and geometry optimization calculations when compared against DFT. However, generally ANI‐2x's accuracy on high energy isomers is still far less than that on low energy isomers. Besides, force comparison indicates that PM7's accuracy is better than that of ANI‐2x. After all, accuracy of the workflow that focuses on low energy isomers can be benefitted from ANI‐2x while for high energy isomers based workflow, PM7 is still the better choice than ANI‐2x due to the more important role of force labels than that of energy labels in preparing machine learning dataset. However, due to the linear relation between the ANI‐2x force and DFT force, a scale factor of approximately 0.50 is expected to greatly improve the ANI‐2x force performance. [ABSTRACT FROM AUTHOR]

Recent in situ observations show that haze particles exist in a convection cloud chamber. The microphysics schemes previously used for large‐eddy simulations of the cloud chamber could not fully resolve haze particles and the associated processes, including their activation and deactivation. Specifically, cloud droplet activation was modeled based on Twomey‐type parameterizations, wherein cloud droplets were formed when a critical supersaturation for the available cloud condensation nuclei (CCN) was exceeded and haze particles were not explicitly resolved. Here, we develop and adapt haze‐capable bin and Lagrangian microphysics schemes to properly resolve the activation and deactivation processes. Results are compared with the Twomey‐type CCN‐based bin microphysics scheme in which haze particles are not fully resolved. We find that results from the haze‐capable bin microphysics scheme agree well with those from the Lagrangian microphysics scheme. However, both schemes significantly differ from those from a CCN‐based bin microphysics scheme unless CCN recycling is considered. Haze particles from the recycling of deactivated cloud droplets can strongly enhance cloud droplet number concentration due to a positive feedback in haze‐cloud interactions in the cloud chamber. Haze particle size distributions are more realistic when considering solute and curvature effects that enable representing the complete physics of the activation process. Our study suggests that haze particles and their interactions with cloud droplets may have a strong impact on cloud properties when supersaturation fluctuations are comparable to mean supersaturation, as is the case in the cloud chamber and likely is the case in the atmosphere, especially in polluted conditions. Plain Language Summary: In atmospheric models, cloud droplet formation is usually simulated to occur when a submicron dry aerosol particle encounters supersaturated conditions. In reality, dry aerosol particles composed of water‐soluble compounds form aqueous haze particles first before they activate to cloud droplets. However, haze particles and the associated interactions with cloud droplets are usually not fully resolved in atmospheric models. In this study, we develop two types of microphysics schemes to explore haze‐cloud interactions in a convection cloud chamber. Our results show that recycling of deactivated cloud droplets through either dry aerosol or haze particles can significantly enhance the cloud droplet number concentration in the cloud chamber. Our study indicates that it is important to properly resolve haze particles and haze‐cloud interactions for cloud chamber simulations, which is likely also true for atmospheric cloud simulations, especially under polluted conditions. Key Points: Bin and Lagrangian microphysics schemes with various levels of complexity are used to handle aerosol‐cloud interactions in a cloud chamberSimulations using haze‐capable bin and Lagrangian schemes capture the observed haze mode in the chamberActivation and deactivation rates are overestimated when using a CCN‐based bin scheme compared with haze‐capable schemes [ABSTRACT FROM AUTHOR]

• A droplet-freezing apparatus was developed to investigate ice nucleation activities of atmospheric particles. • Heterogeneous uptake of NO 2 led to significant decrease in ice nucleation activities of feldspar and ATD. • The impacts of NO 2 uptake on ice nucleation activities were more significant for feldspar than ATD. Mineral dust is an important type of ice nucleating particles in the troposphere; however, the effects of heterogeneous reactions on ice nucleation (IN) activities of mineral dust remain to be elucidated. A droplet-freezing apparatus (Guangzhou Institute of Geochemistry Ice Nucleation Apparatus, GIGINA) was developed in this work to measure IN activities of atmospheric particles in the immersion freezing mode, and its performance was validated by a series of experimental characterizations. This apparatus was then employed to measure IN activities of feldspar and Arizona Test Dust (ATD) particles before and after heterogeneous reaction with NO 2 (10±0.5 ppmv) at 40% relative humidity. The surface coverage of nitrate, θ (NO 3 −), increased to 3.1±0.2 for feldspar after reaction with NO 2 for 6 hr, and meanwhile the active site density per unit surface area (n s) at -20°C was reduced from 92±5 to <1.0 cm−2 by about two orders of magnitude; however, no changes in nitrate content or IN activities were observed for further increase in reaction time (up to 24 hr). Both nitrate content and IN activities changed continuously with reaction time (up to 24 hr) for ATD particles; after reaction with NO 2 for 24 hr, θ (NO 3 −) increased to 1.4±0.1 and n s at -20°C was reduced from 20±4 to 9.7±1.9 cm−2 by a factor of ∼2. Our work suggests that heterogeneous reaction with NO 2 , an abundant reactive nitrogen species in the troposphere, may significantly reduce IN activities of mineral dust in the immersion freezing mode. Graphical Abstract [Display omitted] [ABSTRACT FROM AUTHOR]

Previous experiments and modeling on earthquake nucleation reveal accelerating slip and development of a final patch of fixed or expanding length, but whether the nucleation phase is spatially large enough to be detected in real‐Earth conditions with durations long enough to be helpful is unknown. This study performed a suit of simulations of the nucleation process based on the rate‐and‐state friction law on homogeneous faults started from a "locked" state. Our results reveal the development of a weakening‐zone core (WZcore, defined as a region bounded by two outwardly moving shoulders of stress distribution during the early phase, and later bounded by two inwardly shifting edges between the stress‐releasing region and stress‐increasing exterior) where stress releases continuously, which expands first to a dimension less than the half fault length then shrinks to a final length before re‐expanding. The slip rate within the WZcore is above several times of the driving rate, and the high‐rate region expands constantly up to the instability. The WZcore is similar to a strain‐releasing zone in our new experiment. Under the assumption that much higher seismicity rate can be observed within the WZcore due to higher slip rate and stress‐releasing state as augmented driving force for small asperities, these nucleation features, as well as the slip rate levels in our model, are consistent with step‐like increases in seismicity preceding large subduction earthquakes. On the time scale, duration of the WZcore is weeks before large subduction earthquakes under high driving rate, but years on low‐rate continental faults. Plain Language Summary: As earthquake is understood to be generated on rock surfaces rubbing each other, the precursory behavior is thought to be related to the friction therein, which is now known to depend on both slip speed and its effective contact age. With this type of friction of the fault embedded in an elastic medium, we tried numerical simulations of earthquake preparation to find the features of this process. By observing the evolution of stress distribution, we find the development of a main stress‐releasing zone during the preparation process, which expands first with time then shrinks in its later stage. The main stress‐releasing zone is consistent with a strain‐releasing zone in our new experiment. Assuming that higher rates of seismicity can be observed within the main stress‐releasing zone due to higher slip rates and the stress‐releasing state as the intensified driving force for small asperities, the precursory feature described in the numerical model is consistent with the spatiotemporal migration of microearthquakes observed before large subduction earthquakes. The duration of the main stress‐releasing zone is weeks before large subduction earthquakes under high driving rate, but years for low‐rate continental faults. Key Points: A weakening‐zone core forms in the final stage of simulated earthquake nucleation which expands first and then shrinks to an unstable lengthSpatiotemporal evolution of micro‐seismicity observed before a few large subduction earthquakes is similar to simulated nucleation featuresComparison between aseismic slip rate and the driving rate may help indicate the final stages of mainshock nucleation [ABSTRACT FROM AUTHOR]