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We propose an integrated dynamics‐physics coupling framework for weather and climate‐scale models. Each physical parameterization would be advanced on its natural time scale, revise the thermodynamics to include moist effects, and finally integrated into the relevant components of the dynamical core. We show results using a cloud microphysics scheme integrated within the dynamical core of the Geophysical Fluid Dynamics Laboratory System for High‐resolution prediction on Earth‐to‐Local Domains weather model to demonstrate the promise of this concept. We call it the in‐line microphysics as it is in‐lined within the dynamical core. Statistics gathered from 1 year of weather forecasts show significantly better prediction skills when the model is upgraded to use the in‐line microphysics. However, we do find that some biases are degraded with the in‐line microphysics. The in‐line microphysics also shows larger‐amplitude and higher‐frequency variations in cloud structures within a tropical cyclone than the traditionally‐coupled microphysics. Finally, we discuss the prospects for further development of this integrated dynamics‐physics coupling. Plain Language Summary: Resolved‐scale air flow ("dynamics") and sub‐grid parameterizations ("physics") are two essential components of a weather or climate model. They work together through dynamics‐physics coupling in weather and climate models. However, traditionally dynamics and physics are engineered in isolation and developed independently in models, and many parts of the physics run at a physically‐inappropriate time frequency, or with heat transfers that are inconsistent with the dynamics, leading to errors. This paper proposes an integrated dynamics‐physics coupling framework that can significantly improve weather prediction skills. A concrete example is the cloud and precipitation physics integrated within the dynamics in a global weather model developed at Geophysical Fluid Dynamics Laboratory. When a large number of 10‐day forecasts are run, the version with integrated cloud and precipitation physics shows significantly lower errors and higher skill, especially for large‐scale weather patterns, compared to a traditionally‐coupled physics scheme. The integrated physics also shows promise for improved simulation of high‐impact weather events such as hurricanes. The prospects for the integration of other physics processes are also discussed. Key Points: A new integrated dynamics‐physics coupling framework is designed to enhance dynamics‐physics interaction and thermodynamic consistencyIn‐line microphysics coupling shows significant improvements to weather prediction skills in Geophysical Fluid Dynamics Laboratory System for High‐resolution prediction on Earth‐to‐Local DomainsIntegrated physics shows promise for improved simulation of high‐impact weather events such as hurricane [ABSTRACT FROM AUTHOR]

The magnitude and distribution of the ocean's biological pump (the downward flux of organic carbon (OC) from the ocean surface) influences the pCO2 of the atmosphere and the O2 content of the deep sea, but has not been well quantified. We determine this flux in the ocean's five subtropical gyres using upper‐ocean oxygen mass balance and measurements of T, S, and pO2 by autonomous profiling floats. Our results suggest that the biological OC pump is not globally uniform among the subtropical gyres: values in the North Pacific and Atlantic indicate distinct autotrophy (1–2 mol C m−2 yr−1) while near zero values in the S. Indian Ocean suggest the possibility of net heterotrophy. There is a correlation between the surface water iron/nitrate ratio and the magnitude of the biological pump suggesting an important role for nitrogen fixation in controlling the global distribution. Plain Language Summary: The ocean's biological pump is the most important natural flux controlling ocean and atmosphere carbon concentrations on decadal to millennial time scales, with a value that is fortuitously about the same as the present anthropogenic flux of carbon to the atmosphere. Understanding this flux is key to determining the marine carbon cycle feedback to global warming, but presently even the sign of this flux is debated in some subtropical ocean regions. This paper demonstrates how it is possible to determine the global value of the biological pump by remote measurements on autonomous profiling floats. Our findings suggest that the ocean's biological pump is very different in the subtropical northern and southern hemispheres probably because of the geographic variability of the flux of iron to the surface ocean. Key Points: The geographic distribution of the downward flux of biological organic carbon from the upper ocean (the ocean's biological pump) is uncertain and difficult to determine from observationsT, S, and pO2 measurements from 21 profiling floats in the world's subtropical oceans are interpreted in terms of the net biological oxygen production in the upper oceanThe measured net biological oxygen flux is higher in the northern hemisphere subtropics than in the southern subtropics and correlated with surface‐water iron concentration [ABSTRACT FROM AUTHOR]

The subduction and export of Antarctic Intermediate Water (AAIW) is important for the heat, freshwater, carbon, and nutrient budgets of the world's oceans. Three types of AAIW are identified by applying an unsupervised machine learning approach to individual Argo profiles. The likely sources and pathways of these AAIWs are indicated by the locations and magnitudes of the salinity and oxygen extrema. The Southeast Pacific AAIW forms north of the Subantarctic Front (SAF) in the west corner of the Drake Passage and is exported north into the subtropical gyre. The South Pacific AAIW forms in the South Pacific along the SAF and is transported through the Drake Passage, thereby becoming a saliter and denser AAIW. The circumpolar AAIW, the coldest and freshest AAIW, has a circumpolar source and is injected into the ocean interior in the Brazil‐Malvinas confluence. The results clarify different types of AAIW have different origins. Plain Language Summary: The formation and export of Antarctic Intermediate Water (AAIW) strongly influence the global climate system by redistributing heat, freshwater, carbon, and nutrients from high latitudes to the tropics. Thanks to an increasing number of observations from autonomous instruments and Argo floats, our understanding of the sources and pathways of AAIW has deepened in recent decades. Even so, there is controversy about the formation of AAIW. Unlike previous studies using traditional property‐driven classification, we apply an unsupervised classification technique to automatically classify the Argo temperature and salinity profiles and identify three types of AAIWs from the regimes in the Southern Ocean. The classification results are consistent with previous studies. Moreover, we find that different types of AAIW form in different regions. This paper shows that the machine learning technique benefits us in dealing with a large data set and identifying AAIW classes that is hard to distinguish by the traditional property‐driven classification method. Key Points: An unsupervised learning approach, the profile classification model (PCM), is applied to classify Argo temperature and salinity profilesPCM identifies three types of Antarctic Intermediate Water (AAIW) in the Southern Ocean and reveals their locations and boundariesThe Polar Frontal Zone in the South Pacific sector is established as the source region for AAIW formation [ABSTRACT FROM AUTHOR]

The urban barrier effect is one possible physical mechanism by which the urbanization alters the spatial distribution of cloud‐to‐ground (CG) lightning activity in a city. There is a gap in the preceding research on an urban barrier effect to alter patterns of CG lightning in Beijing, and the urban morphology does not receive enough attention as an important influencing factor. By combining lightning location data, ground meteorological data, and urban morphology datasets, we identify a possible urban barrier effect from the perspective of CG lightning in Beijing during 2010–2017. Analysis of one typical thunderstorm on 13 July 2017 revealed that the barrier effect might result in a bifurcation of low‐level airflow and splitting of the convergence line. A more important finding was the modulation of the barrier effect by the scale and density of the built‐up area, and the numerical simulation experiments further confirmed this potential association. Plain Language Summary: Lightning is a common hazard associated with thunderstorms, which can result in $332 million of property damage annually in the United States and cause more than 1,000 casualties per year in China. Beijing, as one of the first‐tier cities in China, is undergoing a rapid urbanization in both city size and building density. Statistical results of cloud‐to‐ground lightning activity over 8 years showed that there were lots of lightning at the edge of the city, and most lightning seemed to be diverted around the city center. Due to a possible barrier effect, the path of a thunderstorm on 13 July 2017 was obviously altered by the city, also resulting in the change of near‐surface wind field. Except for synoptic forcing, wind speed, and urban heat island, this paper pointed out that the size of a city and its building density could influence whether the barrier effect occurred and how strong it was. Key Points: The strong synoptic forcing, strong wind speed, and weak urban heat island were in favor of the formation of a barrier effect in the built‐up area of BeijingWhen thunderstorms passed over city, the bifurcation of low‐level airflow and splitting of convergence line was a result of the urban barrier effectThe size of a city and its building density might influence the occurrence and strength of a barrier effect [ABSTRACT FROM AUTHOR]

Serpentinization and carbonation of mantle rocks (peridotite alteration) are fundamentally important processes for a spectrum of geoscience topics, including arc volcanism, earthquake processes, chemosynthetic biological communities, and carbon sequestration. Data from a hydrophone array deployed in the Multi‐Borehole Observatory (MBO) of the Oman Drilling Project demonstrates that free gas generated by peridotite alteration and/or microbial activity migrates through the formation in discrete bursts of activity. We detected several, minutes‐long, swarms of gas discharge into Hole BA1B of the MBO over the course of a 9 month observation interval. The episodic nature of the migration events indicates that free gas accumulates in the permeable flow network, is pressurized, and discharges rapidly into the borehole when a critical pressure, likely associated with a capillary barrier at a flow constriction, is reached. Our observations reveal a dynamic mode of fluid migration during serpentinization, and highlight the important role that free gas can play in modulating pore pressure, fluid flow, and alteration kinetics during peridotite weathering. Plain Language Summary: Serpentinization, the reaction between water and upper mantle rocks, is a widespread process on Earth that has important implications for a variety of topics, including the origin of life and carbon sequestration. We monitored the acoustic pressure inside a well established in a serpentinizing region for 9 months, and found that intense swarms of gas bubbles were discharged into the well in several discrete episodes. The nature of these episodes indicates that free gas accumulates in the formation and then rapidly migrates through fractures when the gas pressure is high enough. This is the first time this type of gas pressure and migration cycle has been recognized during serpentinization. An important consequence is that gas is expelled out of the peridotite during its alteration, maintaining the weathering reactions far from equilibrium, a process which may be added in existing kinetics models of serpentinization. Key Points: This paper presents hydrophone array data from a borehole in an actively serpentinizing terrain contain acoustic signals from bubble swarms discharging into the holeFree gas accumulates in the formation and migrates rapidly in discrete swarm episodes when a pressure threshold is reachedResults reveal a gas migration mechanism associated with peridotite alteration, a process which enhances the kinetics of peridotite weathering [ABSTRACT FROM AUTHOR]

Electromagnetic ion cyclotron (EMIC) waves could cause a simultaneous dropout of radiation belt electrons and ring current protons. However, their effects on the dropout of both plasma populations have not been quantified in previous studies. In this paper, we model the simultaneous dropout of MeV electrons and hundreds of keV protons observed by Van Allen Probes within ∼40 min on 27 February 2014. The wave and particle measurements during the period of most intense EMIC waves at L ∼ 5.2 are used to calculate the quasilinear diffusion coefficients and simulate the evolution of both energetic electrons and protons. Our model well captures the dropout of electrons with energies >1 MeV and pitch angles <75°, and the concurrent dropout of protons with energies >200 keV and pitch angles >40°. This is the first modeling work quantitatively reproducing the simultaneous dropout of both populations due to EMIC wave scattering. Plain Language Summary: Electromagnetic ion cyclotron (EMIC) waves are one of the plasma waves in the Earth's magnetosphere. Both radiation belt electrons and ring current protons can be scattered by EMIC waves into the atmosphere within a short timescale (∼hours). However, the role of EMIC waves in driving the simultaneous fast depletion of both populations has not been quantified. In this study, for the first time, we quantitatively modeled the temporal evolution of radiation belt electrons and ring current protons during a geomagnetic storm event based on the particle and wave observations by Van Allen Probes. The results suggest that EMIC wave scattering can efficiently cause the simultaneous depletion of both energetic electrons and protons on a timescale of ∼40 min. Key Points: Van Allen Probes observed a simultaneous dropout of radiation belt electrons and ring current protons within 40 min accompanied by electromagnetic ion cyclotron (EMIC) wavesThe simulation indicates that fast EMIC wave scattering causes the dropout of electrons with energies >1 MeV and pitch angles <75°Concurrent dropout of protons with energies >200 keV and pitch angles >40° is also reproduced by EMIC wave scattering [ABSTRACT FROM AUTHOR]

Two‐dimensional modeling of gravity and magnetic anomalies in terms of polygonal bodies is a popular approach to infer possible configurations of geological structures in the subsurface. Alternatively to the traditional trial‐and‐error manual fit of measured data, here we illustrate a probabilistic strategy to solve the inverse problem. First we derive a set of formulae for solving a 2.75‐dimensional forward model, where the polygonal bodies have a given finite lateral extent, and then we devise a Hamiltonian Monte Carlo algorithm to jointly invert gravity and magnetic data for the geometry and properties of the polygonal bodies. This probabilistic approach fully addresses the nonlinearity of the forward model and provides uncertainty estimation. The result of the inversion is a collection of models which represent the posterior distribution, analysis of which provides estimates of sought properties and may reveal different scenarios. Plain Language Summary: A probabilistic Monte Carlo method to infer the shape and properties of geological bodies in the subsurface from gravity and magnetic data is discussed in this paper. The geological bodies are represented as polygons with constant density and magnetic properties. The results of applying the proposed algorithm is a collection of models of the subsurface that can be statistically analyzed to infer structure and properties of the subsurface. Key Points: Contrary to the traditional manual approach, an objective procedure to jointly invert gravity and magnetic anomalies for 2.75D polygonsSampling using gradient information is an efficient nonlinear strategy to explore plausible solutions, where deterministic methods failInterrogation of the collection of posterior solutions provides statistical answers to complex questions including uncertainty estimation [ABSTRACT FROM AUTHOR]

The Puebla‐Morelos (Mexico) 2017 earthquake nucleated ∼250 km inland from the trench within the Cocos oceanic plate mantle. Here, we argue that the Puebla‐Morelos (Mexico) 2017 earthquake resulted from changes in effective stress due to the reaction brucite + antigorite = olivine + H2O leading to the reactivation of pre‐existing seafloor faults. Fluid release (∼185 kg of H2O per m3 of subducted hydrated harzburgite) and volume increase (ΔVrsolid+fluid = ∼0.8%) likely occur along subducted seafloor‐inherited faults. The amount of H2O released, and magnitude of volume change depends on the degree of faults hydration; only highly hydrated (>40% of hydration) faults will stabilize brucite and experience this reaction at depth. The brucite + antigorite dehydration reaction may be key for intermediate seismicity worldwide. Plain Language Summary: The Puebla‐Morelos (central Mexico) Mw7.1 earthquake occurred in an uncommon locality in Mexico compared to most of the catastrophic earthquakes that have occurred in this part of the world—it nucleated ∼250 km inland, almost below Mexico City. In this paper, we explore the role of mineralogical changes occurring in the Cocos tectonic plate, which is currently descending below the North America plate. Our model tracked the changes in the minerals within the rocks and show that the earthquake might have been triggered by the physical changes associated with the mineral reaction: brucite + antigorite = olivine + H2O. We suggest that this mineral reaction primarily occurred along faults in the subducting oceanic floor along which the mantle lithosphere was hydrated prior to subduction. The brucite + antigorite dehydration reaction may be key for intermediate seismicity worldwide. Key Points: The dehydration of antigorite + brucite has a positive total volume change and leads to fluid‐induced fault reactivationWe hypothesize that fluid‐induced fault reactivation triggered the Puebla‐Morelos 2017 earthquakeThe antigorite + brucite reaction only happens in highly hydrated regions of the upper lithospheric mantle [ABSTRACT FROM AUTHOR]

Prompted by field observation of an aufeis‐induced channel avulsion along the Hula Hula River in June 2021, we use measurements of channel migration zone width along 15 rivers flowing north across the Arctic coastal plain in Alaska, USA. We differentiated sites with aufeis that covered ≥1 km2 in early summer during the period 2017–2021 from sites without such aufeis formation. All but four of the 28 sites with aufeis have widths greater than the 95% confidence interval and 20 sites fall outside of the 95% prediction interval for channel width based on drainage area. Pairwise comparison indicates that the population of aufeis sites have significantly wider channel migration zones (p < 0.0001) than non‐aufeis sites after accounting for drainage area. Seasonal aufeis facilitates lateral channel migration and associated heterogeneity. Loss of aufeis under warming climate may reduce habitat diversity in these river corridors. Plain Language Summary: Aufeis forms in Arctic river corridors when groundwater springs continue to provide water to the surface after the river is covered by ice. The resulting shelves of ice can be up to 3 m thick and extend across the channel and floodplain. As this ice slowly melts in early summer, it can divert river flow from the active channel onto the floodplain, creating new channels. This paper examines the resulting width of the floodplain across which active channel migration occurs. Comparing sites with and without aufeis, we find that sites with aufeis are significantly wider. Loss of aufeis with warming climate will reduce the habitat diversity of Arctic rivers. Key Points: Aufeis that persists into summer on rivers of the Alaskan Arctic coastal plain can force channel avulsionSites with repeated aufeis in successive years have wider channel migration zonesLoss of aufeis as climate warms may result in narrower and less diverse river corridors [ABSTRACT FROM AUTHOR]

On 15 January 2022, Tonga's Hunga Tonga‐Hunga Ha'apai (HTHH) volcano violently erupted, generating a tsunami that killed three people. Acoustic‐gravity waves propagated by the eruption and tsunami caused global complex ionospheric disturbances. In this paper, we study the nature of these perturbations from Global Navigation Satellite System observables over the southwestern Pacific. After processing data from 818 ground stations, we detect supersonic acoustic waves, Lamb waves, and tsunamis, with filtered magnitudes between 1 and 7 Total Electron Content units. Phase arrivals appear superpositioned up to ∼1,000 km from HTHH and are distinct by ∼2,200 km. Within ∼2,200 km, signals have an initial low‐frequency pulse that transitions to higher frequencies. We note the presence of a faster perturbation generated 1 hr post‐eruption which crosses the tsunami disturbance ∼3,000 km from HTHH, potentially contributing to premature land arrivals. Lastly, the arrival of tsunami‐generated disturbances coincides with deep‐ocean observations. Plain Language Summary: The 15 January 2022 volcanic eruption of Hunga Tonga‐Hunga Ha'apai and subsequent tsunamis sent powerful energy waves into the ionosphere (a layer of Earth's atmosphere that is deformed by energy emitted from events like volcanic eruptions, tsunamis, earthquakes, tornadoes, hurricanes, and large man‐made explosions). These waves can provide valuable information about different phases of the event, such as the powerful explosion, sound wave, and tsunami. Using Global Positioning Systems data, we measure these ionospheric signals over the southwestern Pacific Ocean to examine which phases of the event contributed to each ionospheric disturbance. We successfully detect all three event phases in the ionosphere and determine the distance at which these signals separate from one another. Furthermore, we validate our data by comparing tsunami signals in the ionosphere against direct ocean‐based observations of tsunami activity. Of particular note is our observation of a faster ionospheric signal that forms an hour after the eruption and catches up to the tsunami's disturbance. Our work supports the hypothesis that others have proposed in which high‐energy waves from the eruption escalated tsunami speeds and wave heights. This, in turn, supports the observation of early tsunami arrivals that were reported along many Pacific coastlines. Key Points: We see distinct phase arrivals in the ionosphere for a supersonic wave, Lamb wave, and tsunami (the latter is validated by ocean sensors)Phase arrivals begin to separate at ∼1,000 km from Tonga and are fully separated by ∼2,200 kmWe highlight a faster disturbance that propagates 1 hr post‐eruption and meets the tsunami perturbation ∼3,000 km from the volcano [ABSTRACT FROM AUTHOR]

Like faults, landslides can slip slowly for decades or accelerate catastrophically. However, whereas experimentally derived friction laws provide mechanistically based explanations for similarly diverse behavior on faults, little monitoring exists over the temporal and spatial scales required to more clearly illuminate the mechanics of landslide friction. Here we show that displacement of an active slow landslide is accommodated primarily through mm‐scale stick‐slip events that recur on timescales of minutes to hours on asperities that are small (<100 m) relative to the landslide. The frequency of slip events tracks both landslide velocity and pore fluid pressure. The stick‐slip nature demonstrates by itself that slow slip is governed, at least in part, by velocity‐weakening frictional asperities. This observation, in combination with the sensitivity of slow slip to pore fluid pressure and the small relative scale of asperities, suggests similarities between slow slip in landslides and episodic slow slip along faults. Plain Language Summary: Some landslides creep steadily for years or decades. In others, the creep appears similar, then abruptly transitions to catastrophic failure. Distinguishing these two scenarios is crucial for landslide hazard mitigation. Given the obvious similarities between landslides and faults, some have proposed using models of fault friction to understand and predict landslide failure. In this paper, we show that motion of a slow landslide that has been active for decades occurs through mm‐scale stick‐slip events (analogous to very small earthquakes) that occur more frequently when pore water pressure is higher. These results suggest that slow slip in landslides and episodic slow slip events observed on some faults may be similar, and that a fault mechanics treatment of landslide failure is appropriate. Key Points: Displacement of an active slow landslide occurs via mm‐scale stick‐slip events that recur on timescales of minutes to hoursThe stick‐slip nature demonstrates by itself that slow landslide displacement is governed, at least in part, by velocity‐weakening frictionThe small scale of asperities and the sensitivity of stick‐slip to pore pressure suggests similarities to episodic slow fault slip [ABSTRACT FROM AUTHOR]

Deception Island is one of the most active and best‐documented volcanoes in Antarctica. Since its last eruption in 1970, several geophysical surveys have targeted reconstructing its magmatic systems. However, geophysics fails to reconstruct the pathways magma and fluids follow from depth to erupt at the surface. Here, novel data selection strategies and multi‐frequency absorption inversions have been framed in a Geographical Information System, using all available geological (vents and faults distribution), geochemical and geophysical knowledge of the volcano. The result is the detection of these eruptive pathways. The model offers the first image of the magma and associated fluids pathways feed the 1967, 1969, and 1970 eruptions. Results suggest that future ascending paths might lead to active research bases and zones of planned helicopter rescue. The connection between seismic absorption, temperature, and fluid content makes it a promising attribute for detecting and monitoring eruptions at active calderas. Plain Language Summary: Deception Island is the gateway for tourists to Antarctica and a laboratory to understand ice‐capped volcanoes and their eruptions. While the Island has been the target of many geophysical studies, no clear tomographic model shows how deep eruptive pathways of its last eruptions have reached the surface in the 1960s and 1970s. This is a recurrent topic in volcano geophysics: dikes and fluid migrations develop across structures considered too small to be detected by tomographic techniques. This paper demonstrates that seismic absorption has sufficient sensitivity to temperature and fluid content to detect these pathways. Once integrated within a Geographical Information System with all the information we have on the volcano, the models resolve the feeding systems of these eruptions, from a tectonically deformed deep magma chamber to shallow cold dyke intrusions and fluid migrations still feeding the volcano today. The correlation between seismic absorption, temperature, and fluid content offers a new tool for detecting and monitoring shallow volcanic hazards. Key Points: High absorption detects deep eruptive pathways from the caldera center to its rimAbsorption imaging reconstructs shallow pathways of hazardous materialsSeismic absorption is sensitive to thermal anomalies at depth [ABSTRACT FROM AUTHOR]

Wildfires are a significant source of PM2.5 that adversely affect local and regional air quality. However, tracking wildfire smoke and their impacts are difficult. This study explores how a ground‐based Doppler lidar network can improve monitoring of long‐range transported wildfire smoke. As a case study, this paper reviews the transported wildfire smoke and its impact on air quality across New York State (NYS) during two events: 18–21 and 25–27 July 2021. Observations of wildfire smoke and enhancement of PM2.5 across NYS during those events were consistent across ground‐based sensors, satellites, back trajectory analyses, and model forecasts. However, for some of the days, the model over/under‐forecasted smoke plumes. Overall, this study highlights the value of the NYS Mesonet Profiler Network to monitor wildfire smoke with high spatiotemporal resolution. Such a relatively dense network can be a valuable observational tool for evaluating PM2.5, and aiding satellite measurements and air quality forecasting models. Plain Language Summary: Anthropogenic emissions of PM2.5 have declined across New York State (NYS) and nationally over the last two decades. However, increasing frequency and intensity of wildfire activity threatens to reverse this long‐term PM2.5 trend. During July 2021, wildfire smoke from Southern Canada and Northwestern US significantly elevated PM2.5 (in exceedance of the US EPA standards) 5,000 km away in NYS. Yet, air quality forecasting models performed poorly in the presence of the wildfire smoke. Thus, it has become increasingly important to monitor transported wildfire smoke and understand its impact on surface air‐quality. The New York State Mesonet Profiler Network is one such tool that can be used to monitor long‐range transported wildfire smoke, track its vertical and spatial extent across NYS in real‐time, assess its impact on air quality and complement/augment air quality forecasting models and satellite observations. Key Points: A long‐range transported wildfire smoke event significantly enhanced PM2.5 across New York State in July 2021Multi‐platform observations are used to understand the details of the eventA lidar network can help to monitor smoke event, assess impacts on surface PM2.5, aid satellite measurements and improve forecasting models [ABSTRACT FROM AUTHOR]

The North American Monsoon (NAM) is a critical component of the hydrologic cycle in southwestern North America. However, our understanding of the long‐term evolution of this monsoon system is incomplete due to a paucity of long‐term paleoclimatic records from the core and periphery of the NAM domain. C. Routson et al. (2022, https://doi.org/10.1029/2022gl099772) leverage a new compilation of Holocene proxy records to generate a new composite index of NAM evolution over the Holocene. They identify a relationship between NAM strength and the latitudinal temperature gradient over the Holocene. The authors suggest that shifts in the strength of the westerlies altered NAM convection via ventilation, a process whereby the large‐scale circulation imports low moist entropy air into the monsoon domain. These results highlight the importance of paleoclimatic records, especially from past "warm" intervals, for generating new insights about the evolution of regional monsoons. Plain Language Summary: The North American Monsoon is a circulation that brings summer rain to regions of the US southwest and western Mexico. Despite the fact that this circulation provides a majority of the precipitation in many parts of the arid southwest, we do not fully understand the factors that govern long‐term changes in this monsoon. A new paper by C. Routson et al. (2022, https://doi.org/10.1029/2022gl099772) uses proxy indicators of past summer rainfall, stretching from Central America to Arizona, to reconstruct changes in the monsoon over the geologic epoch known as the Holocene, or the last 11,000 years of Earth history. The results of this study suggest that Holocene changes in the temperature difference between the equator to pole, known as the "latitudinal temperature gradient," exerted an important influence over monsoon strength in the southwest. This has implications for the future of the summer monsoon, especially as the high latitudes of the northern hemisphere are expected to warm in the future. Key Point: The strength North American Monsoon tracks changes in the position of the midlatitude westerlies over the Holocene [ABSTRACT FROM AUTHOR]

The relative importance of radiative feedbacks and emissions scenarios in controlling surface warming patterns is challenging to quantify across model generations. We analyze three variants of the Community Earth System Model (CESM) with differing equilibrium climate sensitivities under identical CMIP5 historical and high‐emissions scenarios. CESM1, our base model, exhibits Arctic‐amplified warming with the least warming in the Southern Hemisphere middle latitudes. A variant of CESM1 with enhanced extratropical shortwave cloud feedbacks shows slightly increased late‐21st century warming at all latitudes. In the next‐generation model, CESM2, global‐mean warming is also slightly greater, but the warming is zonally redistributed in a pattern mirroring cloud and surface albedo feedbacks. However, if the nominally equivalent CMIP6 scenario is applied to CESM2, the redistributed warming pattern is preserved, but global‐mean warming is significantly greater. These results demonstrate how model structural differences and scenario differences combine to produce differences in climate projections across model generations. Plain Language Summary: Earth System Models are used to project climate change through the 21st century. Such projections are constrained by a range of assumptions about emissions of greenhouse gases as well as other climate‐relevant human activities like deforestation and emissions of aerosols. These assumptions are carefully evaluated and represented in an emissions scenario. In a coordinated set of experiments, a given emissions scenario is applied to a number of different Earth System Models to test differences in climate projections that arise from physical (or "structural") differences among the models. However, over time, models are updated and improved, and emissions scenarios are updated as well. This continuous updating makes it difficult to track whether a new set of climate projections is different from its predecessor due to model changes or due to scenario changes. In this paper, we disentangle these two factors, clarifying the role of each. For the Earth System Model that we use, the emissions scenario largely controls the amount of global‐mean warming projected for the 21st century, but the model or structural differences matter greatly for the regional patterns of warming. Key Points: Higher equilibrium climate sensitivity, from more positive cloud feedbacks, only slightly increases 21st century transient warmingCloud and surface albedo feedbacks redistribute warming from the middle and high northern latitudes to lower latitudesThese warming pattern differences result from feedback differences, not CMIP5 to CMIP6 forcing scenario differences [ABSTRACT FROM AUTHOR]

Gamma‐ray glows associated with thunderclouds have been observed since the 1980s, however it remains unclear how, and at which thunderstorms gamma‐ray glows are generated in dense atmospheres. In this study, we report the first Compton camera imaging of a gamma‐ray glow from a winter thundercloud. On 14 January 2022, using two identical Bi4Ge3O12 scintillators in energy range of 0.05–5 MeV, we detected two gamma‐ray glows lasting ∼4 min in a mountain area 25 km from the Japan Sea and 410 m above sea level. The same events were also observed by the Compton camera, where the first glow we observed suggested statistically significant (4.0 and 5.9 σ level) signals of two enhanced concentrations in gamma‐ray photon images in a range of 0.15–1.5 MeV. These concentrations were most clearly observed in a time window of Δt = 50 s around the peak intensity of the gamma‐ray glow. Plain Language Summary: Observations of gamma rays from thunderclouds started in 1980s, leading to intensive studies in the last 40 years. However, the question of where and how such gamma rays are produced in thunderclouds remains unclear, as no gamma‐ray images have been obtained to date. This paper presents the first successful gamma‐ray imaging of a thundercloud in a winter of Japan. In particular, we installed a Compton camera of 10 × 10 cm2 in size, that is a compact but high sensitivity camera originally developed in the field of astronomy to observe gamma‐ray sky. At the peak of a gamma‐ray emission, we detected significant enhancements in the gamma‐ray photon image. The image provides the source position and beam pattern of the gamma‐ray emission, thus may be connected to highly electrified region and electron acceleration inside thunderclouds. Key Points: Gamma‐ray glows were observed in a mountainous area 25 km from the Japan Sea and 410 m above sea level on 14 January 2022, during winterOne of the glows suggested two enhanced concentrations in gamma‐ray images, which was taken for the first time with a Compton cameraThe first successful gamma‐ray imaging provides a new means of investigating radiation beam pattern of gamma‐ray glows in thunderclouds [ABSTRACT FROM AUTHOR]

The current paper investigates the shallow layers of the lunar regolith at the Chang'E‐4 landing site. Four layers between 0 and 10 m were identified using lunar penetrating radar. Based on these outputs, a revised stratigraphic model is suggested for the post‐Imbrian ejecta at the Von Kármán crater. The layers were previously unseen due to the smooth boundaries between them. The revised model was inferred using an advanced hyperbola‐fitting scheme. Applying conventional hyperbola‐fitting to non‐homogeneous media results in errors and inaccuracies that are often wrongly assumed to be negligible. We propose a novel hyperbola‐fitting scheme that is, not constrained to homogeneous media and can be applied subject to any arbitrary one‐dimensional permittivity distribution. Via this approach, we can estimate the permittivity profile of an investigated area and detect layered structures that were previously transparent to electromagnetic waves due to the gradational dielectric properties at their interfaces. Plain Language Summary: The landing site of Chang'E‐4 is at the Von Kármán (VK) crater at the South Pole‐Aitken (SPA) basin. The SPA basin is the oldest and biggest basin on the Moon created at the early stages of its evolution by an impact that is, believed to have penetrated the lunar crust and uplifted materials from the top mantle. Understanding the geology and stratigraphy of the SPA basin can help us understand cratering processes and shed light on the evolution of the Moon. To that extent, ground penetrating radar (GPR) has been added to the payload of Yutu‐2 to investigate the stratigraphy of the Chang'E‐4 landing site. One drawback of GPR is that conventional processing methods fail to detect layers with smooth boundaries between them. Consequently, GPR data might give the false impression that an area is relatively homogenous, while in fact it might consist of numerous gradational layers representing a much more complex geological history. In the current paper, a novel interpretation tool is described, capable of detecting smooth transitions between layers. The proposed methodology revealed a previously unseen layered structure for the first ∼10 m of the VK crater. Key Points: We suggest a novel hyperbola‐fitting technique that assumes an arbitrary permittivity distribution with respect to depthThe proposed method is used to map the lunar regolith at the Chang'E‐4 landing siteA layered structure is revealed at the first 10 meters. A new stratigraphic model is suggested for the Von Kármán crater [ABSTRACT FROM AUTHOR]

A quantitative analysis of any environment older than the instrumental record relies on proxies. Uncertainties associated with proxy reconstructions are often underestimated, which can lead to artificial conflict between different proxies, and between data and models. In this paper, using ordinary least squares linear regression as a common example, we describe a simple, robust and generalizable method for quantifying uncertainty in proxy reconstructions. We highlight the primary controls on the magnitude of uncertainty, and compare this simple estimate to equivalent estimates from Bayesian, nonparametric and fiducial statistical frameworks. We discuss when it may be possible to reduce uncertainties, and conclude that the unexplained variance in the calibration must always feature in the uncertainty in the reconstruction. This directs future research toward explaining as much of the variance in the calibration data as possible. We also advocate for a "data‐forward" approach, that clearly decouples the presentation of proxy data from plausible environmental inferences. Plain Language Summary: Earth's surface environments have varied significantly throughout geologic time. Accurate quantification of these ancient environmental changes relies on proxies—materials that are known to change composition or morphology with the ambient environment. These approaches have provided insight into important questions across the Earth sciences, from the context and consequences of biological evolution and volcanic eruptions, to threshold behavior and long‐term feedbacks within the modern climate system. Although the uncertainty associated with an estimate of an environmental change is of equal importance to the estimate itself, uncertainties are widely either underestimated or else rely on proxy‐specific statistical models. Fortunately, a very good, and broadly applicable, estimate of uncertainty is extremely simple to calculate. In this paper we show that statistical uncertainty in proxy reconstructions is mostly due to the magnitude of scatter around the calibration line. We furthermore attempt to give the reader an intuition for how large reported uncertainties in proxy reconstructions should be, how and when they can be reduced, and where future efforts to reduce uncertainty should be directed. Key Points: Statistical uncertainties in proxy reconstructions are dominated by unexplained variance in the calibrationProxy data should be presented as explicitly distinct from environmental interpretationsFuture efforts should prioritize collection of multiple explanatory variables for calibrations, and true replicate paleoanalyses [ABSTRACT FROM AUTHOR]

The present paper demonstrates the first observations by the Magnetospheric Multiscale (MMS) mission of the counter‐streaming energetic electrons and trapped energetic protons, localized in the magnetic field depressions between the mirror mode peaks, in the Earth's dusk sector high‐latitude magnetosphere. This region is characterized by high plasma beta, strong ion temperature anisotropy, and intermediate plasma density between magnetospheric and magnetosheath plasma. We show that these plasma conditions are unstable for the drift mirror instability. The counter‐streaming electron feature resembles those of the previously reported energetic electron microinjections, but without the energy‐time dispersion signature. This suggests that MMS is passing through one of the potential microinjection source regions. The energetic ion data in the present study is mainly used to estimate the scale size of the mirror mode structures. Plain Language Summary: Understanding the physical mechanisms that result in energetic electron acceleration and loss within the Van Allen radiation belts has been an active area of research for decades, and due to advances made possible by the Van Allen probe mission are now relatively well understood. However, the origin of the several 10–100s of keV seed population that can be accelerated to relativistic energies has remained more elusive. It is well known that magnetic reconnection and related secondary processes in the Earth's magnetotail during substorms can accelerate particles and inject them inward toward the radiation belts. In this paper we show the first observations of a possible source region of 10–100s of keV electrons and protons at the dayside of the Earth's high‐latitude magnetosphere. Four MMS spacecraft periodically encountered high fluxes of energetic electrons at wide energy range which were streaming both parallel and anti‐parallel to the magnetic field. Enhanced fluxes of counter‐streaming energetic electrons and trapped protons were observed between magnetic field peaks of the ULF waves identified as mirror mode peaks. The source region of these electrons and protons are likely the large diamagnetic cavities created by magnetic reconnection. Key Points: MMS detected dispersionless electron microinjections in ULF magnetic field wave depressions at the high‐latitude magnetosphereULF waves were consistent with mirror mode waves created by the drift mirror instability [ABSTRACT FROM AUTHOR]

The present paper is the investigation of the semi‐diurnal tide (SDT) and gravity waves (GW) through coupling effects on propagating Very low frequency (VLF) signal. One year of recorded VLF data is used. The first modulation of the VLF signal with SDTs and GWs is presented. The structures associated with SDT and GW are analyzed, and the daily and monthly variations are determined. Wavelet and spectrum analysis is applied to the data to determine the origin of the SDT. The corresponding period of the observed SDT is matched with solar SDT (SSDT). Seasonal variability of the SSDT in the lower ionosphere has been investigated using the VLF radio sounding for the first time. Developmental, evolution, and dissipation phases of GW with daytime and month are resolved. A plan to deploy 8 VLF stations to probe the shoreline and characterize the generation and development of SDT and GWs along the coastline is discussed. Plain Language Summary: The mesosphere and lower thermosphere (MLT) has a great impact on ionospheric dynamics and electrodynamics. Atmospheric tides are one of the main drivers of MLT energetic variabilities. Atmospheric tides can be divided into lunar tides mainly generated by gravitational forcing of the moon caused in the dense lower atmosphere or solar tides generated by the absorption of solar radiation by different chemical species. The main absorption of solar radiation that occurs by water vapor in the troposphere, ozone in the stratosphere, and nitrogen and oxygen in the mesosphere excites various tidal modes in the respective regions. The lunar signal is often small in comparison with the solar tide and may also be subject to fluctuations in amplitude and phase over periods of a few days. The induced modulation of tidal winds with upper atmospheric constituents can lead to a modification in ionospheric currents, electric fields, and electron densities. The behavior of the VLF radio signal is mostly governed by the ionospheric plasma influenced by SDT and GW. The observations presented in this paper show that VLF radio sounding can be employed to study the time evolution and development of SDT in the various region providing high spatial resolution. Key Points: Development of a new remote sensing technique to characterize the semidiurnal tide is proposedThe first observation of the modulated Very low frequency (VLF) signal with semi‐diurnal tide (SDT) and gravity waves (GW) is providedDaily and monthly characteristics of SDT and GW in the Persian Gulf is derived [ABSTRACT FROM AUTHOR]

We present initial results of low‐energy ion observations from BepiColombo's first Mercury flyby. Unprecedentedly high time resolution measurements of low energy ions at Mercury by BepiColombo Mio reveal rapid (a few seconds) and large (1–2 orders of magnitude) fluctuations of ion flux around the magnetopause and within the magnetosphere. Around the magnetic equator in the pre‐midnight magnetotail, Mio observed plasma sheet ions consistent with previous observations. In the midnight magnetotail near the closest approach, Mio observed the co‐existence of high‐energy (∼keV/q) and low‐energy (<∼300 eV/q) ion components. The low‐energy component is inferred to be cold with a temperature well below 100 eV and have a major contribution to the total density as opposed to previously reported cold tenuous ions. Future observations by Mio will provide insights into the sources, transport, and acceleration of the newly identified ion components. Plain Language Summary: BepiColombo, launched on 20 October 2018, is now en route to Mercury. Along its 7‐year journey to the Mercury orbit insertion, BepiColombo conducted, and will conduct, nine planetary flybys in total. This paper presents brand‐new observations of ions (positively charged particles) in Mercury's magnetosphere by BepiColombo Mio during its first encounter with Mercury. Thanks to high‐time resolution measurements by Mio, it is revealed that ions around Mercury change dramatically and rapidly just over a few seconds. Mio also observed an unexpectedly dense ion population with low energies, for which we do not have a definitive explanation yet. Future flyby and in‐orbit observations by BepiColombo will provide key information for unraveling the dynamics and sources of ions in Mercury's magnetosphere. Key Points: We present initial reports on low energy ion observations during BepiColombo's first Mercury flybyMio observed large fluctuations of ion flux with time scales down to a few seconds around the magnetopause and within the magnetosphereIon energy spectra obtained in the midnight magnetotail suggest the presence of an unexpectedly dense cold component [ABSTRACT FROM AUTHOR]

The existence of shocklets, a kind of solitary structure, has been demonstrated in the Earth's foreshock regions for decades. Their formation and evolution are believed to be controlled by ions. However, the detailed behavior of ions at them has not been well investigated observationally yet. Here, we investigate a shocklet observed by the Magnetospheric Multiscale mission in the Earth's foreshock. Analysis of ion observations reveals that the solar wind (SW) ions are bunched in gyrophase space when interacting with the whistler precursor of the shocklet, suggesting the occurrence of cyclotron resonance between them. A more detailed examination suggests that the cyclotron resonance induces a net energy flow from the whistler precursor to the SW ions. Thus, the observations presented here indicate that the cyclotron resonance between shocklet whistler precursors and the SW ions could provide a mechanism for shocklet dissipation and SW ion energization. Plain Language Summary: Shocklets, a kind of solitary structure, are thought to play a crucial role in the reformation processes of quasi‐parallel shocks. They are also suggested to be able to efficiently decelerate and heat the solar wind ions and electrons. Their formation and evolution are believed to be controlled by ion dynamics. However, the detailed behavior of ions at them has not been well investigated yet. In this paper, we study in detail a shocklet event observed by the Magnetospheric Multiscale mission in the Earth's foreshock. We especially focus on ion observations. Analysis of the data reveals that the solar wind ions are bunched in gyrophase space when interacting with the shocklet whistler precursor, indicating the occurrence of cyclotron resonance between them. Resulting from this interaction, the solar wind ions exchange energy with the whistler precursor. Viewed in the rest frame of the plasma, this energy flow is directed from the whistler precursor to the solar wind ions. Thus, the observations presented here indicate the cyclotron resonance between shocklet whistler precursors and the solar wind ions could provide a mechanism for shocklet dissipation and solar wind ion energization. Key Points: A shocklet observed by Magnetospheric Multiscale is examined in great detail to reveal the behavior of ions at shockletsGyrophase bunching indicative of cyclotron resonance is observed in the velocity distributions of the solar wind ionsCyclotron resonance could provide a mechanism for shocklet dissipation and solar wind ion energization [ABSTRACT FROM AUTHOR]

The structure of the lowermost mantle and the core‐mantle boundary (CMB) has profound implications for Earth's evolution and current‐day dynamics. Whilst tomographic studies of VS show good agreement in the lowermost mantle, consensus as to VP and especially CMB radius has not yet been reached. We perform a hierarchical Bayesian inversion for VP in the lowermost 300 km of the mantle and the radius of the CMB using differential travel time data. Concurrent with finding VP perturbations of 0.56% RMS amplitude that spatially agree with previous studies in areas of low posterior variance, we find 4.5 km RMS amplitude CMB radius perturbations with a broadly north‐south hemispherical character, with spherical harmonic power evenly distributed between degrees 1–3. These results suggest that CMB radial processes are set by a longer scale process than the VP perturbations. Plain Language Summary: The most important internal boundary of the Earth is the core‐mantle boundary (CMB), between the liquid iron outer core and the rocky mantle above it. The shape of this boundary has important implications for how the Earth has evolved through time, in particular due to being an indication about how heat flows out of the core and into the mantle. However, determining this shape has remained stubbornly difficult for the past 40 years. In this paper, we use a data set that is particularly targeted toward this region to image the CMB shape and the lowermost mantle using a robust statistical method. We find that the CMB boundary has large hills and valleys, but is relatively smooth compared to the complex structure of the lowermost mantle above it. Key Points: We derive a Bayesian inversion of lowermost mantle VP structure and core‐mantle boundary (CMB) topography with differential traveltime dataThe spectra of VP perturbations is wide, while CMB perturbations are mainly constrained to l = 1–3These results suggest the CMB is strongly deformed by dynamic topography, and do not require a low viscosity channel in the lowermost mantle [ABSTRACT FROM AUTHOR]

The Madden‐Julian oscillation (MJO) is the dominant source of sub‐seasonal variability in the tropics. It consists of an Eastward moving region of enhanced convection coupled to changes in zonal winds. It is not possible to predict the precise evolution of the MJO, so sub‐seasonal forecasts are generally probabilistic. We present a deep convolutional neural network (CNN) that produces skilful state‐dependent probabilistic MJO forecasts. Importantly, the CNN's forecast uncertainty varies depending on the instantaneous predictability of the MJO. The CNN accounts for intrinsic chaotic uncertainty by predicting the standard deviation about the mean, and model uncertainty using Monte‐Carlo dropout. Interpretation of the CNN mean forecasts highlights known MJO mechanisms, providing confidence in the model. Interpretation of forecast uncertainty indicates mechanisms governing MJO predictability. In particular, we find an initially stronger MJO signal is associated with more uncertainty, and that MJO predictability is affected by the state of the Walker Circulation. Plain Language Summary: The Madden‐Julian oscillation (MJO) is an important tropical climate phenomenon. It consists of enhanced convective thunderstorms and anomalous winds that propagate eastward along the Equator for a few weeks. The MJO is difficult to predict and exhibits great variability. This means that forecasts are often probabilistic. However, current models have difficulty in correctly predicting the uncertainty in the forecast based on the current conditions. In this paper, we propose a model using neural networks capable of making reliable probabilistic forecasts. We interpret the behavior of the algorithm to verify its consistency with the known physical mechanisms of the MJO and to highlight new physical conditions that affect MJO prediction uncertainty. Key Points: A deep convolutional neural network (CNN) is used to produce probabilistic forecasts of the Madden‐Julian oscillation (MJO)The forecasts provide well‐calibrated state‐dependent estimates of forecast uncertaintyThe CNN forecasts are used to probe sources of predictability for the MJO [ABSTRACT FROM AUTHOR]

A new radio component namely Saturn Anomalous Myriametric Radiation (SAM) is reported. A total of 193 SAM events have been identified by using all the Cassini Saturn orbital data. SAM emissions are L‐O mode radio emission and occasionally accompanied by a first harmonic in R‐X mode. SAM's intensities decrease with increasing distance from Saturn, suggesting a source near Saturn. SAM has a typical central frequency near 13 kHz, a bandwidth greater than 8 kHz and usually drifts in frequency over time. SAM's duration can extend to near 11 hr and even longer. These features distinguish SAM from the regular narrowband emissions observed in the nearby frequency range, hence the name anomalous. The high occurrence rate of SAM after low frequency extensions of Saturn Kilometric Radiation and the SAM cases observed during compressions of Saturn's magnetosphere suggest a special connection to solar wind dynamics and magnetospheric conditions at Saturn. Plain Language Summary: This paper reports a new type of radio emission at Saturn. We name this emission "Saturn Anomalous Myriametric Radiation" (SAM). Due to the different morphological behavior of SAM emissions in the spectrogram, compared to the regularly observed narrowband emissions, SAM emissions are identified as a new radio component. We search for SAM events by using all the available data acquired by the Cassini spacecraft. A total of 193 SAM events are found and we summarized its characteristics. The spatial distribution of SAM shows a high latitude preference in occurrence. The observed intensities of SAM increase as the spacecraft approaches Saturn, suggesting a source near Saturn. The typical central frequency of SAM is near 13 kHz and the duration of SAM can extend to near 11 hr and even longer. The majority of the 193 SAM emissions are observed after the enhancement of the dominant Saturn radio emission Saturn Kilometric Radiation (SKR), which is deemed to be closely connected to the solar wind dynamics at Saturn. Therefore, SAM emissions are also possibly related to the conditions that cause the enhancement of SKR. This newly identified SAM emission may be used to study the magnetospheric dynamics of Saturn in the future. Key Points: A new radio component namely the Saturn Anomalous Myriametric Radiation (SAM) is reportedThe characteristics of SAM are given including its spatial distribution, typical frequency, bandwidth and time durationSAM shows a possible connection to the compression of the magnetosphere [ABSTRACT FROM AUTHOR]

Under the context of global warming, we identified a significant increase in lightning activity in the last two decades over the Tibetan Plateau (TP), the highest plateau on earth, based on two data sets. The largest rise of lightning activity was found over the region with high lightning density represented by the eastern TP at a rate of 0.072 ± 0.069 fl km−2 yr−1 during 1996–2013 from Optical Transient Detector/Lightning Imaging Sensor. World Wide Lightning Location Network data also showed a remarkable increase in lightning strokes during 2010–2019 in the maximum lightning density region, while the change was insignificant in the low lightning density region. Further investigations revealed that most of the TP region experienced a significant increase in thunderstorm frequency, which was responsible for the increase in lightning activity, rather than an increase in thunderstorm intensity. Increased lightning activity implies a potential risk to human beings and the fragile ecosystem over the TP in a warmer climate. Plain Language Summary: Lightning is a natural source of nitrogen oxides and wildfires, and thus has important effects on atmospheric chemistry and ecosystem. Lightning is also a serious threat to human life and property. Using satellite‐based and ground‐based data, the trend of lightning activity over the Tibetan Plateau (TP) in the past two decades has been investigated in this paper. In the global warming context, TP experienced an increase in lightning activity. The lightning increase was significant in the high lightning density region, such as the central and eastern TP, and insignificant in the lower lightning density region, such as the western TP and the Brahmaputra Valley. The thunderstorm frequency also experienced an increase over most parts of the TP, which caused the rising trend in lightning activity. However, the thunderstorm intensity shows weak and insignificant changes. Since the TP is getting warmer much faster than that observed over the globe, the increased lightning activity over the TP may exert enhanced potential threat to human beings and impacts on the fragile ecosystem over the Plateau. Key Points: Lightning activity over the Tibetan Plateau increased significantly in the past two decades based on the Optical Transient Detector/Lightning Imaging Sensor and World Wide Lightning Location Network datasetsLightning activity in the high‐flash‐density region increased faster than that in the low‐flash‐density regionThe apparent rise in lightning activity is due to increase in thunderstorm rate rather than change in thunderstorm intensity [ABSTRACT FROM AUTHOR]

Field measurements of aeolian sediment transport during major storm events are challenging in coastal settings due to the common coincidence of high winds with elevated water levels that can cover beaches. This work demonstrates a new application of lidar to remotely measure properties of wind‐blown sand transport at high spatial resolution. A data set of spatially continuous saltation heights was remotely developed from rapid (7.1 Hz) lidar scanning along a two‐dimensional transect across a beach during wind speeds of between 3.1 and 15.8 m/s associated with the passing of Tropical Storm Isaias. Outputs from the lidar demonstrate the ability to remotely observe the threshold velocity for the initiation of motion for sand transport and show that the upper limit of the saltation layer rises with increasing wind speed. Plain Language Summary: Wind can be an important contributor to landscape changes in sandy desert and coastal environments. There are complex mechanisms by which wind moves sand that are not yet entirely understood. To answer questions about how, when, and why sand is transported by wind, experiments commonly use point‐based sensors that are unable to capture the full spatial and temporal complexity of sand movement very close to the ground. This paper shows that new laser sensors can be utilized to remotely measure properties of sand transport simultaneously at multiple points and with increased detail compared to prior approaches. High resolution, remote measurements from a tropical storm event are used to show how high wind‐blown sand is lifted off of the ground surface and how different wind speeds influence these sand transport patterns. Key Points: Wind‐driven sand transport can be measured using repeat terrestrial laser scanningRemote measurements are used to characterize time and space variable saltation heights during energetic wind forcingMaximum saltation heights respond to changes in wind speed on a coastal beach [ABSTRACT FROM AUTHOR]

The North American monsoon (NAM) is an important source of rainfall to much of Mexico and southwestern United States. Westerly winds (westerlies) can suppress monsoon circulation and impact monsoon timing, intensity, and extent. Recent Arctic warming is reducing the temperature gradient between the equator and the pole, which could weaken the westerlies; however, the implications of these changes on the NAM are uncertain. Here we present a new composite index of the Holocene NAM. We find monsoon strength reached a maximum circa 7,000 years ago and has weakened since then. Proxy observations of temperature, hydroclimate and upwelling, along with model simulations, show that the NAM was modulated by the westerlies over the Holocene. If the observed Holocene pattern holds for current warming, a weaker meridional temperature gradient and weaker westerlies could lead to a stronger future NAM. Plain Language Summary: The North American monsoon (NAM) is a main source of summertime rain in Mexico and southwestern North America. Here we explore how the NAM rainfall has changed over the past 11,000 years using information from natural archives of past climate (called "proxies") as well as climate models. We find that monsoon was strongest around 7,000 years ago and has weakened since then. This weakening of the monsoon appears to be caused by a strengthening of the mid‐latitude jet stream, which was influenced by changes in high‐latitude versus low‐latitude temperatures over that period. This paper explores the relationship between temperatures, the jet stream, and the NAM in data and models, which is relevant to future climate in the region. Key Points: A new multi‐proxy‐based estimate of the Holocene North American monsoon (NAM) is presentedProxy and modeled evidence show westerly winds were a dominant control on the Holocene NAMHigh‐latitude temperature drove changes in the Holocene westerly winds and thus the NAM [ABSTRACT FROM AUTHOR]

This paper investigates the impacts of extratropical Pacific on El Niño‐Southern Oscillation (ENSO) spring predictability barrier (SPB). Using an empirical dynamical model – Linear Inverse Model (LIM), we find that the dynamics of the northern and southern extratropical Pacific can significantly and equally weaken the Eastern Pacific (EP)‐ENSO SPB, while the North Pacific is more important for weakening the Central Pacific (CP)‐ENSO SPB. The evolution of the extratropical optimum initial structures illustrates the different roles of the northern and southern extratropical Pacific in crossing EP and CP ENSO SPBs and demonstrates the decisive role that the South Pacific initial condition plays in ENSO diversity. Additionally, the extratropical Pacific greatly influences the forecast skill of El Niño during SPB, while tropical dynamics may be more important for crossing the SPB of La Niña. Plain Language Summary: The spring predictability barrier (SPB) is a sudden reduction of the prediction skill of the El Niño‐Southern Oscillation (ENSO) in the boreal spring. Using a linear dynamical model, we find the correlation forecast skill of Central Pacific ENSO in boreal spring and summer is significantly enhanced by including the dynamics of northern extratropical Pacific, therefore weakening the SPB. For the Eastern Pacific ENSO, both the northern and southern extratropical dynamics are equally important for weakening the SPB. Our results also show that the initial state of southern extratropical Pacific may determine the type of ENSO. Additionally, including the extratropical dynamics helps to improve the forecast skill of El Niño events in boreal spring and summer while the extratropical dynamics may not be essential for the prediction of La Niña. Key Points: A linear dynamical model suggests that including the dynamics of extratropical Pacific can significantly weaken the ENSO SPBNorth Pacific plays a role both in the central and eastern Pacific, while South Pacific may be essential in determing ENSO diversityExtratropical Pacific greatly influences the forecast skill of El Niño during SPB, while the impact on La Niña is limited [ABSTRACT FROM AUTHOR]

The lightning channel morphology is closely related to developmental processes, which depends on the charge structure. There is currently a lack of understanding of how lightning channel morphology reveals developmental characteristics and charge structure. Based on the Lightning mapping array radiation source localization data of six lightning flashes, we studied the lightning channel morphology characterization method and obtained the spatial distribution of the fractal dimension (FD). We found that the fractal distribution had a consistent spatial and temporal correspondence with the channel development characteristics. Compared to regions with unidirectional extended channels, regions with more channel branches or direction change of channel development have a larger FD and a higher power density, where horizontal channel development is accelerated. These correspondence features reflect the inhomogeneous presence of pocket charge, which provides a new method to use lightning morphology information to reveal the characteristics of charge level distribution within thunderstorm clouds. Plain Language Summary: The charge distribution within the horizontal charge region may have a more significant effect on the extension of the lightning channel. At present, it is still difficult to directly observe the charge structure of thunderstorm clouds, especially the horizontal charge structure. Also, the morphological study of the channel is not perfect due to the limitations of observation and data acquisition. Therefore, there is currently a lack of understanding of how lightning channel morphology reveals developmental characteristics and charge structure. In the paper, the relationship between the lightning channel morphology, developmental characteristics, and charge structure was investigated for the first time based on Lightning mapping array localization data, and the spatial distribution of the lightning fractal dimension (FD) was obtained. It is found that, compared to regions with unidirectional extended channels, regions with more channel branches or direction change of channel development have a larger FD and a higher power density, where horizontal channel development is accelerated. These correspondence features reflect the inhomogeneous presence of pocket charge, which provides a new method to use lightning morphology information to reveal the characteristics of charge level distribution within thunderstorm clouds. Key Points: The spatial distribution of fractal dimension (FD) is obtained, and uesd to describe lightning channel morphologyThe channel morphology characterized by the FD is closely related to channel development velocity and radiation power densityThe channel morphology can be used to reflect the inhomogeneous state of charge level distribution [ABSTRACT FROM AUTHOR]

Aerosol optical effects can trigger complex changes in solar shortwave radiation (SW) in the atmosphere, resulting in significant impacts on the photochemistry and vertical structure of ozone. This paper provides observational evidence of aerosol absorbing and scattering effects on modifying the SW and ozone profiles in the low troposphere. Using field vertical measurements and observation‐based model simulations, we demonstrated that absorbing aerosols decreased SW, resulting in substantial inhibition of ozone production throughout the boundary layer (BL). A similar inhibition effect occurred within the lower BL under sufficient scattering aerosols. However, the scattering augmentation effect played an additional role in enhancing the photolysis rate and promoting ozone generation in the upper BL. Hence, the observational evidence as well as our model simulations disentangled the radiative effects of different types of aerosols on the vertical structures of ozone. Plain Language Summary: Atmospheric aerosols can modify incident solar radiation by scattering and absorption, resulting in significant impacts on the photolysis rate and photochemical products in the lower troposphere. Such influences could be physically understood, but can only be observed with a detailed vertical measurement system. In this study, through vertical observational data analysis and observational constrained numerical simulations, we found that absorbing aerosols can weaken the shortwave radiation (SW) and photolysis rate in the entire layer, resulting in less ozone formation. In contrast, scattering aerosols enhance the SW and photolysis rate above the aerosol layer and promote ozone formation. Overall, the radiative effects of aerosols lead to an ozone decrease in the low layer and an increase above the boundary layer. Key Points: Observational evidence of aerosols modifying ozone profiles through their direct radiative effectsAn observation‐based model disentangles the radiative effects of aerosols of different typesAerosol scattering augmentation effect promotes ozone formation in the upper boundary layer [ABSTRACT FROM AUTHOR]

The relationships among the abundance of magnetofossils, the ensuing magnetic properties, and the controlling paleoenvironmental factors in marine sediments remain broadly unexplored. Here, we identify magnetofossils in core XB1 from the northwestern South China Sea (SCS) since end of the Last Glacial. Using rock magnetic and electron microscopic data, we propose a model that links the anisotropy of magnetic susceptibility fabric and the abundance of magnetofossils. The magnetofossil concentration in sediments increases significantly during the 14.7–4.7 ka period, which in turns leads to inverse magnetic fabrics and near‐horizontal of the minimum magnetic susceptibility axes. Further, we show that the abundance of magnetofossils is linked to paleoenvironmental changes in the northwestern SCS. The production and preservation of magnetofossils during the 14.7–4.7 ka period are promoted by an intensified East Asian summer monsoon and sluggish deep‐water ventilation, while the paucity of magnetofossils after 4.7 ka is attributed to high oxygen content. Plain Language Summary: The anisotropy of magnetic susceptibility (AMS) is a useful magnetic property of rocks for a wide range of scientific questions. Typically, the sedimentary AMS fabric carried by coarser‐grained magnetic particles (i.e., multi‐domain, MD) exhibits an oblate shape with a horizontal maximum magnetic susceptibility axis. However, single‐domain (SD) magnetic particles (e.g., nano‐sized magnetofossil magnetites) complicate the AMS fabric, through their intrinsic inverse magnetic fabric with the minimum magnetic susceptibility axis aligned along the horizontal plane. For natural samples, quantification of the contributions of SD and MD particles to AMS is essential for accurate interpretation of the AMS. This paper puts forward a novel approach that links the AMS and the abundance of magnetofossils. By applying this new method to sediments from the South China Sea, we found that the inverse magnetic fabrics in the studied sediments are associated with high magnetofossils concentration, which can be affected by various factors including the East Asian monsoon, nutrient supply or deep‐water ventilation. Key Points: Values of the minimum susceptibility axis inclination are associated with the abundance of magnetofossilsThe magnetofossils can be quantified by the proportion of inverse component in sedimentsThe strong deep‐water ventilation hinders the production and preservation of magnetofossils in the South China Sea [ABSTRACT FROM AUTHOR]

Both the source of methane on Mars and the mechanism for transmission from the subsurface to the atmosphere are not fully understood. Previous seepage simulations have invoked relatively shallow subsurface sources to explain observed methane signatures on Mars. We propose that barometric‐pressure pumping through fracture networks could be an effective mechanism for methane transport from the deep subsurface on Mars. Using atmospheric pressure data gathered by Curiosity as input, we simulate methane gas transport from depths of 200 m to the surface. Even with such a deep source, our model reproduces the observed seasonality of methane, and the simulated surface methane fluxes fall within the range of previous estimates derived from atmospheric observations. Because 200 m is the likely minimum hospitable depth for living methanogenic microbes, our fracture network model indirectly reinvigorates the possibility of a microbial source of methane on Mars. Plain Language Summary: The existence of methane on Mars is a topic of significant interest because of its potential association with subsurface microbial life. Measurements of methane in the atmosphere of Mars indicate that its abundance fluctuates over time. Although the source of methane is unknown, it most likely comes from below the surface of Mars; however, the range of depths of potential methane sources is not well constrained. If methane is currently being produced by living microbes, it would have to be at depths of at least 200 m in order to support life. Nearly all prior modeling work in this area has considered relatively slow, inefficient methane transport mechanisms, which limits the methane sources to the shallow martian subsurface. In this paper, we describe and model a mechanism capable of transporting significant quantities of methane to the atmosphere from depths capable of supporting living methane‐producing microorganisms. We also find that the methane seepage pattern generated by our model is highly seasonal, and closely follows the pattern of atmospheric methane concentrations measured by the Curiosity rover. Key Points: Atmospheric pressure fluctuations on Mars can produce significant methane seepage from potentially habitable depths (up to 200 m)Modeled surface methane seepage patterns are highly seasonal and coincide with rover measurements of elevated concentrations at Gale craterMagnitude and timing of modeled surface flux is comparable to existing plume estimates, supporting a model of localized surface releases [ABSTRACT FROM AUTHOR]

The lack of evidence for large‐scale glacial landscapes on Mars has led to the belief that ancient glaciations had to be frozen to the ground. Here we propose that the fingerprints of Martian wet‐based glaciation should be the remnants of the ice sheet drainage system instead of landforms generally associated with terrestrial ice sheets. We use the terrestrial glacial hydrology framework to interrogate how the Martian surface gravity affects glacial hydrology, ice sliding, and glacial erosion. Taking as reference the ancient southern circumpolar ice sheet that deposited the Dorsa Argentea formation, we compare the theoretical behavior of identical ice sheets on Mars and Earth and show that, whereas on Earth glacial drainage is predominantly inefficient, enhancing ice sliding and erosion, on Mars the lower gravity favors the formation of efficient subglacial drainage. The apparent lack of large‐scale glacial fingerprints on Mars, such as drumlins or lineations, is to be expected. Plain Language Summary: Water accumulates under ice masses, including glaciers and ice sheets, lubricating the base of the ice and accelerating ice motion. On Earth, this glacial motion has produced scoured landscapes in northern Europe and North America. Mars lacks such large‐scale glacial erosion even in areas with other signs of widespread glaciation. This paper uses the existing framework describing the physical interactions of water and ice, and how they affect ice motion, to show that a lack of landforms recording glacial erosion is expected even if glaciation were widespread on Mars. Key Points: Glacial hydrology feedback dynamics can explain the lack of glacial sliding on the Martian geological recordSubglacial water drainage develops faster, and is more resilient under lower Martian gravityThe fingerprints of Martian wet‐based glaciation are predicted to be channels and eskers [ABSTRACT FROM AUTHOR]

Jamming is the transition from a fluid‐like state to a solid‐like state of a packing system. Recent studies have shown that jamming transition depends upon many factors: particle shape, friction/cohesion between particles, particle size dispersity, the stress of the packing, etc. This study aims to contribute to this growing area of research by exploring the jamming density of soil with strong dispersity. In analogous to Gibbs excess energy, we introduce excess volume‐potentials for each species. We then proposed a mathematical model to quantitatively compute the jamming density based on the second law of equilibrium in thermodynamics. This approach is validated using experimental results on glass beads and on silty sand. It is hoped that this study will provide to a deeper understanding of the link between jamming density, packing dispersity and the second law of thermodynamics. Plain Language Summary: Granular soil, in a form of dry particles, can display a phase transition from a solid‐like state to a fluid‐like state (e.g., under slope failure or avalanching). Recent studies have introduced an intriguing concept of granular temperature enabling the analogy of phase transition of granulates to the phase transition of ice to water using thermodynamics theory. This approach has shed a new light on the physics of granular media. In this paper, we attempt to analyze the phase transition of silty sand, a granular packing with two different particle sizes, using another branch of well‐established methodology in thermodynamics on chemical liquid mixtures. We introduce particle volume‐potential, in analogous to the molecule chemical‐potential, and developed a mathematical model, which is validated by experimentally measured results. It is hoped that this study will provide a deeper understanding of the link between the phase transition and the size dispersity of granular soil. Key Points: Dispersity of particle sizes significantly affect the jamming density of silty sand at phase transitionParticle size ratio is the primary factor that controls the particle volume‐potential of each species in a bi‐dispersed packingThe analogy of particle volume‐potential to molecule chemical‐potential enables the application of the principles in thermodynamics [ABSTRACT FROM AUTHOR]

This paper provides analyses to quantify the maturity of regolith within 24 m depth using a novel polarimetric attributes analysis of lunar penetrating radar (LPR) data. The results demonstrate that LPR signals were mainly from subsurface rock fragments of different sizes and were rarely from strata interfaces. The averages and ranges of maturities for the near‐surface (0–2 m), the fine‐grained regolith (2–12 m), and the coarse‐grained ejecta (12–24 m) are 68.98% (0%–99.82%), 82.61% (41.52%–96.56%), and 72.33% (5.91%–96.66%), respectively. Local regions with anomalously low maturities on the lunar surface may be due to the dense materials formed by local impacts or the rock fragments from distal impacts; a newly discovered sandwich structure with low maturity at a depth between 12 and 18 m is formed by the heterogeneous weathering in a paleo‐crater. Based on these new insights, we infer a heterogeneous weathering process of the regolith. Plain Language Summary: The entire lunar surface is considered to be covered by a layer of regolith. The study of regolith weathering degree almost focused on the near‐surface because the traditional techniques cannot detect the regolith at large depths. The Chang'E‐4 lunar penetrating radar (LPR) can detect the regolith structure within dozens of meters depth. However, previous publication of LPR results only use the macro layering model to interpret the regolith structure. This study innovatively extracts new properties from the LPR data acquired while the rover was turning and estimated the quantitative maturity of regolith within ∼24 m depth at lunar farside. We found that the LPR can mainly detect the subsurface rock fragments that survived weathering and rarely the interfaces of strata because the materials of different strata are mixed at interfaces and make it gradational. Our results also reveal the spatial difference of weathering in the regolith. We investigate the formations and material compositions of several interesting regions with unusual weathering degrees. Based on these new insights, we establish a model to illustrate the weathering process of the regolith at the CE‐4 landing site. Key Points: We quantify the maturity of the lunar regolith within 24 m depth by analyzing the lunar penetrating radar (LPR) data acquired during the rover turningsLPR signals were mainly from subsurface rock fragments of different sizes and were rarely from strata interfacesInferring the heterogeneous weathering process by comprehensively investigating the regions with anomalous maturities in the regolith [ABSTRACT FROM AUTHOR]

Evidence from Arrokoth and comets strongly suggests a very low density for this and similar small Kuiper belt objects. Plausible compositions imply high porosities, in excess of 70%, and low compaction crush strengths. If so, impact craters on Arrokoth (especially Sky, its largest) formed largely by compaction of pore space and material displacement. This is consistent with geological evidence from New Horizons imaging. High porosity reduces cratering efficiency in the gravity regime whereas compaction moves it toward crush strength scaling and increased efficiency. Compaction also guarantees that most impactor kinetic energy is taken up as waste heat near the impact point, with momentum transferred to the rest of the body by elastic waves only. Monte Carlo simulations of Sky‐forming conditions indicate that the momentum imparted likely separated Arrokoth's two lobes, but displacement was limited by dissipation at the neck between them. Unusual strength properties are not required to preserve Arrokoth's bilobate configuration. Plain Language Summary: It has become apparent over the last few years that small asteroids and comets are very underdense compared with the materials they are made of. This means that their total porosities are likely quite high, in excess of 70%, both as tiny voids within particles (so‐called microscopic porosity) and spaces between particles (macroscopic porosity). But none are likely as porous as the distant denizens of the Kuiper belt such as Arrokoth (visited by the New Horizons spacecraft in 2019). This paper concerns impact craters on Arrokoth and similar small bodies, and the rather unusual effects expected. Imagine a fluffy (fine powder) snowball striking a much larger fluffy snowball, only that the snow is not pure ice but a mixture of porous icy, rocky, and carbon‐rich particles. Even at high velocities (>100 s of m/s) craters should mostly form by compacting pore space and pushing material away from the impact point, not the traditional blasting of ejecta back into space. Similar to crush‐up of an automobile bumper, compaction helps to protect from the potentially catastrophic effects of large impacts, such as complete disruption of the target or breakup of bilobate bodies like Arrokoth, and should be incorporated in future collisional evolution studies. Key Points: Arrokoth is likely a low density, highly porous, contact binary planetesimalImpact craters on Arrokoth, and particularly its largest, likely formed as compaction craters, with modest or little ejectaHigh porosity acted to protect Arrokoth from catastrophic disruption, ejecta recoil, and lobe dislocation and rearrangement [ABSTRACT FROM AUTHOR]

RETRACTION: D. Qi, Y. Wu, L. Chen, W.‐J. Cai, Z. Ouyang, Y. Zhang, L. G. Anderson, R. A. Feely, Y. Zhuang, H. Lin, R. Lei, H. Bi. (2022). Rapid Acidification of the Arctic Chukchi Sea Waters Driven by Anthropogenic Forcing and Biological Carbon Recycling. Geophysical Research Letters, 49, e2021GL097246. https://doi.org/10.1029/2021GL097246. The above article, published online on 21 February 2022 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the journal Editor‐in‐Chief, Harihar Rajaram; American Geophysical Union; and John Wiley & Sons LLC. The retraction has been agreed as it was discovered that the 2019 pCO2 data collected on the 10th Chinese National Arctic Research Expedition and analyzed along with other data in this paper was used without proper permission. AGU Publications and Wiley evaluated all information submitted by the authors and scientific agencies and carefully considered Committee on Publication Ethics (COPE) guidelines before making this decision. The authors have revised their statistical analyses by excluding the 2019 Chinese National Arctic Research Expedition data and have stated they intend to submit the revised manuscript to the journal. D. Qi acknowledges that the data ownership is disputed, and therefore accepts the retraction. L. Chen and W.‐J. Cai disagree with the retraction. Z. Ouyang, Y. Zhang, L. G. Anderson, R. A. Feely, Y. Zhuang, H. Lin, R. Lei, and H. Bi did not respond to our notice of retraction. [ABSTRACT FROM AUTHOR]

The Galileo spacecraft passed close to Europa on 11 encounters, two of which (E12 and E26) came within 400 km of the surface. In E12 data, there are perturbations in field and plasma data consistent with effects of a nearby plume (Jia et al., 2018). Huybrighs et al. (2020, https://doi.org/10.1029/2020GL087806) report depletions of proton flux in one channel of the Galileo Energetic Particle Detector (EPD) as Galileo passed close to Europa on E26. They trace particle trajectories in the magnetic field provided by a magnetohydrodynamic simulation and conclude that the spacecraft probably also passed through or close to a vapor plume on E26. However, the absence of a related signature in the measured magnetic field led us to question this conclusion. Examination of the EPD data remote from Europa on the E26 flyby reveals that the putative plume signature in the EPD data is an artifact. Plain Language Summary: In recent years, there have been reports that plumes, or extraterrestrial geysers, rise hundreds of kilometers above the surfaces of Saturn's moon, Enceladus, and Jupiter's moon, Europa. A very recent paper examines data from a close pass by Europa (E26 flyby) made by the Galileo spacecraft on January 3, 2000. The paper identifies a localized decrease in the count rate of energetic protons lasting about 20 s very near closest approach to Europa's surface and attributes the decrease to an interaction with a plume rising above Europa's surface. In this "comment" we demonstrate that a localized decrease of proton count rates is recorded at the same point in almost each measurement cycle (every 280 s) even very far from Europa on this pass due to an anomaly in the Energetic Particle Detector (EPD) channel in question. Therefore, the use by the authors of the EPD data to establish the presence of a plume during this pass is erroneous. Our conclusion is that during E26 the Galileo EPD data has to date not shown evidence of a plume. Key Points: The energetic proton flux decrease previously interpreted as the signature of a plume on the Galileo E26 flyby is an artifactThere is yet no convincing evidence for a plume encounter on Galileo's E26 pass by Europa [ABSTRACT FROM AUTHOR]

In recent years, major progress has been made in measuring weakly absorbing atmospheric trace gases from high spectral resolution space observations. In this paper, we apply the so‐called whitening transformation on spectra of the Infrared Atmospheric Sounding Interferometer, and show that it allows removing most of the climatological background from spectra, leaving a residual that contains those spectral signatures that depart from normality. These can subsequently be attributed to changes in the abundance of trace species. This is illustrated for two diverging cases: (1) a biomass burning plume from the 2019/2020 Australian bushfires, leading to the unambiguous identification of nine reactive trace gases, including a first observation of glycolaldehyde; (2) spectra observed a decade apart, from which changes in eight long‐lived halogenated substances are identified; three of them never observed before by a nadir sounder. Plain Language Summary: In recent years, several techniques have been developed for the detection of gases present in very small quantities in the atmosphere, which has significantly improved our knowledge on atmospheric composition and chemistry. In this paper, we describe a powerful complementary technique that transforms atmospheric spectra to highlight and attribute the spectral signatures of different species. We apply it on spectra measured by the spaceborne Infrared Atmospheric Sounding Interferometer for two different cases: (1) a plume from the 2019/2020 Australian bushfires leading to the clear identification of nine rare gases including a first observation from space of glycolaldehyde; (2) spectra observed a decade apart, of which eight long‐lived halogenated substances were identified; three of them never observed before by a nadir sounder. The detection of these reactive and long‐lived trace gases is very promising for the monitoring of their temporal evolution and the attribution of their sources. Key Points: The whitening transformation allows analyzing anomalies in hyperspectral infrared spectraIn a biomass burning plume we identify nine compounds including a first observation of glycolaldehydeOn spectra observed a decade apart we identify atmospheric changes in eight long‐lived halocarbons [ABSTRACT FROM AUTHOR]

No observations show evidence of ionization in long air gap discharge during dark periods. However, for the first time, weak channel illuminations are observed during the so‐called dark periods in this paper. The length of these faint bright channels is almost constant during each dark period and is nearly equal to that of the remaining low‐density channels created by the previous discharge. The phenomenon, that is, the dark period is not really dark, is more likely to occur at the time when there is a greater change rate of the applied voltage. These findings are based on the high‐speed direct imaging and Schlieren photography together, in which the former is used to visualize the bright channels and the latter to detect the low‐density area. Plain Language Summary: Although a large amount of related experimental and theoretical researches on long positive sparks have been carried out, there are still some phenomena to be explained, such as the abrupt elongation of leader channel, and the intermittent propagation of upward positive leader. Together with the above phenomena, dark periods are often accompanied before the channel re‐illumination, during which no observations show evidence of ionization as no current and light are measured. However, for the first time, this paper shows the direct experimental evidence that channels in dark periods are not always dark in long positive sparks, but have weak illumination with a length equal to the low‐density channel left by previous discharges. It is thought that the capacitive current due to the varying applied voltage may make the left low‐density channels to emit weak light. New findings can inspire researchers to pay attention to the capacitive current in the dark period instead of directly ignoring them as before. This may help to explain the above‐mentioned mysterious phenomena to a certain extent. Key Points: More direct experimental evidence to show that discharge channels during dark periods are not always dark in long positive sparksThe length of faint bright channels in each dark period is almost constant and nearly the same as that of the remaining low‐density channelsCapacitive current due to the varying applied voltage may cause the channel illumination in dark periods [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a universal process where energy is transferred from magnetic fields to particles. However, it remains unclear whether this transfer of energy includes the direct energization of particles to high energies (i.e., >10s of keV). We compare the spectral indices of energetic (50–200 keV) electrons from six magnetotail electron diffusion region candidates encountered by MMS with those from "quiet‐time" plasma sheet crossings to test whether energetic electron enhancements result from direct energization at/near the reconnection site or simply focusing high‐energy populations that do not originate from the nearby X‐line and already exist in the plasma sheet along the newly reconnected field lines. The study suggests that active reconnection can be a source of localized electron energization. However, the EDR spectra are not outside the range of those from the quiet‐time plasma sheet, which surprisingly still often have very energetic (up to and beyond 200 keV) electrons present. Plain Language Summary: Magnetic reconnection is a fundamental process in plasma physics and is hypothesized to be an efficient process to accelerate particles up to very high energies by transferring energy held in the magnetic field to the particles. Similar to how a taught rubber band can snap, releasing its latent energy—so too do magnetic fields "snap" in reconnection; as the field lines relax to their normal state, they transfer their energy to particle. This paper addresses an outstanding question of whether magnetic reconnection in fact produces high energy electrons. While many computer simulations have predicted this, most in situ observations have focused on energization at much lower energies than we look at here. However, this paper compares a handful of events very near the region where reconnection is believed to occur to a "control group" of nonactive regions not near a reconnection site and finds that the events nearest the reconnection do tend to have more energetic electrons. This provides evidence that the energetic electrons are in fact coming from the reconnection site. Key Points: Six candidate EDRs identified by the MMS team are compared to a statistical database of quiet‐time plasmasheet crossingsThe spectral indices of energetic electrons near the EDRs are indeed harder than the plasmasheet crossings, suggesting local energizationEven the quiet‐time plasmasheet crossings include cases with surprisingly hard spectra, perhaps sourced by distant tail reconnection [ABSTRACT FROM AUTHOR]

Solar wind protons can interact directly with the hydrogen corona of Mars through charge exchange, resulting in energetic neutral atoms (ENAs) able to penetrate deep into the upper atmosphere of Mars. ENAs can undergo multiple charge changing interactions, leading to an observable beam of penetrating protons in the upper atmosphere. We seek to characterize the behavior of these protons in the presence of magnetic fields using data collected by the Mars Atmosphere and Volatile EvolutioN spacecraft. We find that backscattered penetrating proton flux is enhanced in regions where the magnetic field strength is greater than 200 nT. We also find a strong correlation at CO2 column densities less than 5.5 × 1014 cm−2 between magnetic field strength and the observed backscattered and downward flux. We do not see significant changes in penetrating proton flux with magnetic field strengths on the order of 10 nT. Plain Language Summary: Positively charged particles in the solar wind can directly interact with hydrogen in the Martian environment. These positively charged particles can charge exchange with hydrogen atoms, becoming fast, neutral atoms that are able to navigate their way deep into the upper atmosphere of Mars. These fast neutrals can undergo further charge‐changing reactions and become positively charged once more. This paper seeks to understand how these positive particles, or penetrating protons, behave in the presence of magnetic fields using data collected by the Mars Atmosphere and Volatile EvolutioN spacecraft. We find that strong magnetic fields enhance the number of backscattered penetrating protons we observe. At low atmospheric column densities, strong magnetic fields significantly deflect these protons back to higher altitudes. At high atmospheric column densities, magnetic fields do not appear to affect these penetrating protons to the same degree as collisions with other neutral molecules. We also find that small magnetic field strengths do not affect the penetrating proton flux we observe. Key Points: Backscattered penetrating proton flux is enhanced in magnetic field regions with strengths greater than 200 nTPenetrating protons are influenced by strong magnetic fields at column densities less than 5.5 × 1014 cm−2Penetrating proton fluxes are not greatly affected by magnetic field strengths on the order of 10 nT [ABSTRACT FROM AUTHOR]

This paper investigates the relationship between heterogeneous predictability and homogeneous predictability for El Niño‐Southern Oscillation (ENSO) prediction. Previous studies showed that a larger heterogeneous predictability than homogeneous predictability, referred as the signal‐to‐noise paradox, is caused by a higher persistence in the observations than in the model. By using the recharge oscillator model, it is found analytically and numerically that both ENSO growth rate and period contribute to this paradox. A larger ENSO growth rate in the observation can lead to a higher persistence and heterogeneous predictability. However, a larger ENSO growth rate associated with a shortened ENSO period can also lead to this paradox although the persistence of the observation is lower than forecast model. Finally, we apply it to explain the paradox after 1960 is caused by a larger ENSO growth rate and a shortened ENSO period. Plain Language Summary: El Niño‐Southern Oscillation (ENSO) is the most significant interannual signal on Earth and its influence is worldwide, thus its predictability and prediction draw much attention. One interesting feature is that the model makes better prediction for the observation than predicting itself, referred as signal‐to‐noise paradox, even in a simple ENSO model: recharge oscillator model (ROM). Previous studies have shown that the higher persistence of the observation than model may play a role in this paradox. Here, we find that a paradox can occur in ROM even when persistence of the observation is lower. By using the analytical and numerical solutions of the ROM, it is suggested that a larger ENSO growth rate and a shortened period can cause the paradox even when the persistence of the observation is lower. By using the second‐order regression model to do ENSO forecasts during 1910–2010, we suggest that a paradox occurs after 1960 is caused by a larger ENSO growth rate and a shortened ENSO period. Key Points: El Niño‐Southern Oscillation (ENSO) growth rate can explain the signal‐to‐noise paradox through the persistence‐skill rule in an ENSO modelA larger ENSO growth rate associated with a shorter period causes this paradox even when the persistence of "truth" is lower than modelThe higher heterogeneous than homogeneous predictability after 1960 is caused by a larger ENSO growth rate and a shorter period [ABSTRACT FROM AUTHOR]

High‐resolution imagery of the morphological character of modern active turbidite systems are critical for understanding the complexity of turbidity current processes occurring on the seafloor. Here, we describe a 30 cm‐resolution autonomous underwater vehicle repeat bathymetric dataset that allows to significantly increase the geomorphological detail of crescentic bedforms in turbidite systems. This repeat imagery shows the erosion produced by dense basal layers at the base of turbidity currents, the inception of plunge pools, and the controls that hydraulic jump troughs have on subsequent flow path of weaker turbidity currents. Transverse small‐scale scours located in cyclic step troughs suggest that weak flows follow local relief, therefore explaining the wide variability of turbidity current flow indicators observed in outcrops. This imagery demonstrates that turbidite systems are formed by the superimposition of erosion surfaces and depositional patterns recording contrasted flow behavior and provides new views on turbidity current behavior in natural environments. Plain Language Summary: Turbidity currents transport large amounts of sediment, macro‐nutrients and carbon to the deep‐sea. During their passage, they generate a wide variety of bedforms from which these flows can be reconstructed. However, the lack of detailed and very high‐resolution imagery of these bedforms prevents detailed understanding of the 3D behavior of turbidity currents. In this paper, we describe a 30 cm‐resolution autonomous underwater vehicle repeat bathymetric dataset that allows to map very‐fine scale features of turbidity current bedforms. This repeat imagery reveals the erosion produced by the base of turbidity currents and shows the formation of new small‐scale scours linked to the currents. The data also reveals the effect of large turbidity currents on the subsequent path of smaller ones. This high‐resolution imagery allows to bridge the gap between observations on the modern seafloor and those observed in outcrops. Key Points: 30 cm resolution AUV repeat imagery (2019–2020) of active turbidity current bedformsDetailed imaging of seafloor erosion from basal parts of turbidity currents and of plunge pool inceptionTrough of bedforms believed to control subsequent flow path of weaker turbidity currents [ABSTRACT FROM AUTHOR]

Resonant scattering by electromagnetic ion cyclotron (EMIC) waves is one of the most effective mechanisms of relativistic electron losses in Earth's inner magnetosphere. Low‐altitude spacecraft measurements, however, often show that the energy range of precipitating electrons is wider than theoretical predictions based on the cold plasma dispersion of EMIC waves. To explain this discrepancy, we examine the diffusion rates of EMIC waves by including hot plasma effects in their dispersion relation. Using the observed ion distribution functions, we investigate the hot plasma effects on the EMIC wave dispersion for a wide frequency range. We develop analytical equations for hot plasma effects on EMIC dispersion, and apply this model to diffusion rate evaluations. We show that hot ion effects tend to increase the minimum resonant energy for the frequency range around wave intensity maxima, but can decrease the minimum resonant energy for the higher‐frequency part of wave spectra. Plain Language Summary: Quantification of dynamics of relativistic electron fluxes in the Earth's radiation belts is one of the main problems of space plasma physics. Resonance of such relativistic electrons with electromagnetic ion cyclotron (EMIC) waves is considered to provide a very effective electron scattering into the Earth's atmosphere. Energies of electrons resonating with EMIC waves for typical wave characteristics and background plasma conditions rarely fall below 1 MeV, and most of the observed EMIC waves are believed to scatter and precipitate ultra‐relativistic electrons. Conjugate observations from near‐equatorial and low‐altitude spacecraft, however, often show near‐equatorial EMIC waves correlated with precipitation of sub‐MeV electrons below the minimum resonant energy. Such a decrease in resonant energy can be attributed to hot ion contribution to EMIC wave properties. This paper provides a generic hot plasma model which agrees well with the exact numerical solution and highlights the importance of hot plasma effects on the relativistic electron scattering by EMIC waves for a wide range of plasma parameters. Key Points: Hot plasma effects are analyzed and parameterized using analytical equations for observed electromagnetic ion cyclotron (EMIC) wavesHot plasma parametric model agrees very well with numerical results and can be implemented to evaluate diffusion coefficients more preciselyHot plasma effects may decrease the minimum resonant energy of electrons for high‐frequency EMIC waves [ABSTRACT FROM AUTHOR]

On 6–8 June 2015, the Ion and Electron Sensor on board Rosetta observed keV‐range water‐group pickup ions arriving from the solar direction. Based on magnetic field intensification and variations, the appearance of the ions was likely to have been caused by a coronal mass ejection. During the 3‐day period when Rosetta was 200 km from the comet, peak ion energy/charge (E/q) varied over a range from 50 eV to 1 keV in concert with neutral gas density variations caused by the rotation of the comet and its variable solar illumination. Thermal ion densities showed the same variations. The neutral density variations provided a unique opportunity to observe the repeated slowing of the solar wind by mass loading caused by charge exchange between energetic water‐group ions and thermal water‐group molecules. Such solar wind slowing was observed previously only by flyby missions that provided single events. Plain Language Summary: The Rosetta orbiter carried a number of instruments to measure the properties of the neutral and ionized gas surrounding the nucleus. Included in these were plasma instruments to measure the characteristics of the charged particles. The Ion and Electron Sensor was one of them. Also on board were the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, the Ion Composition Analyzer, and the Langmuir Probe. This paper discusses some of the results of measurements by these instruments and their relation to each other. It was found that the neutral gas emitted by the comet nucleus and the resulting positively charged ions interact in such a way to produce slowing down of the solar wind as a result of what is called "charge exchange", in which an electron is transferred from a neutral molecule to an ion. Key Points: Charge exchange of energetic water group pickup ions with coma water molecules is observed within the solar wind cavity of Comet 67P Churyumov‐GerasimenkoRotation of the comet produced variations in the neutral density at the spacecraft causing strong charge‐exchange deceleration of the incoming ions within the density peaksRecovery to the initial water‐group ion beam as minimum neutral densities, again appeared, was shown to result from pickup of thermal ions in the coma [ABSTRACT FROM AUTHOR]

The geometry of continental fault systems, and more specifically the spatial organization of faults, is a central topic to understand how earthquake ruptures start, propagate, and stop. By exploring the origin of unexpected high frequency emission during earthquakes, Chu et al. (2021), (https://doi.org/10.1029/2021GL095271) show that the most likely source for these emissions is the interaction between nearby misaligned faults. Thus, this result emphasizes the discrete nature of the strike‐slip fault segments at seismogenic crustal scale, adding to a set of evidence for spatially structured fault systems drawn from independent observations in geophysics and geology. This observation should bring some new constrains to earthquake rupture scenario by limiting the range of possible ruptures included in these models. Plain Language Summary: The geometry of faults at depth remains difficult to document, although it exerts a critical influence on the way earthquakes propagate along faults. In the case of continental strike‐slip faults, a long‐lasting discussion questions if the ground surface complexity is matched by similar complexity at depth, or conversely, if the strike‐slip geometry at depth is smoother. In this paper Chu et al. (2021), (https://doi.org/10.1029/2021GL095271) bring additional evidence of the fault structural complexity. Such evidence could be related to other independent observations pointing in a similar direction of the existence of a specific spatial scaling for strike‐slip fault structures. Such scaling should be considered in the development of seismic hazard models. Key Points: Chu et al. (2021) interpret high‐frequency in earthquake spectrum as fault geometry signatureIndependent observations from various earthquake research fields hint at spatial structure of strike‐slip faultsThe spatial structure of strike‐slip fault should be included in earthquake rupture scenario [ABSTRACT FROM AUTHOR]

A paleogeographic affinity of the south China craton (SCC) with India in the Neoproterozoic has long been advocated based on lines of geological evidence. However, the lack of coeval paleomagnetic data renders the putative connection ambiguous. Here we report new paleomagnetic results obtained from seven ca. 770 Ma mafic sills in SCC that provide new critical constraints on the issue. The data quality is assured by a positive regional tilt test, a reversal test, and by adequately averaging‐out paleosecular variation. Our data, together with coeval poles from the global paleomagnetic database, support a reconstruction in which the SCC was connected with India at ca. 770 Ma via linkages with smaller continental blocks. The SCC‐India landmass was located at high‐to‐mid latitudes and far from Laurentia and Australia, which were located at low latitudes at ca. 770 Ma. Plain Language Summary: Multiple lines of geological evidence may suggest a close paleogeographic relationship between the south China craton (SCC) and India. Their specific connection, including the alignment of tectonic features, if had ever existed in any way, can be tested and determined through the use of coeval high‐quality paleomagnetic data from the two cratons. In this paper, we report a new paleomagnetic pole obtained from seven ca. 770 Ma mafic sills in the SCC, which is coeval to the pole obtained from the Malani igneous suite in India. The data quality of both poles is assured by robust paleomagnetic field tests. Our reconstruction based on the updated paleomagnetic database and geological data demonstrates that the SCC was connected with India at ca. 770 Ma via linkages with other smaller Asian blocks. Furthermore, the SCC‐India landmass was located at high‐to‐mid latitudes and far from the core of Rodinia, for example, Laurentia and Australia, which were located at low latitudes at ca. 770 Ma. Key Points: A new paleomagnetic pole (25.6°N, 116.8°E, A95 = 9.9°) was obtained from ca. 770 Ma mafic sills in South ChinaSouth China was connected to India via Indochina and small Asian blocks at ca. 770 MaThe South China‐India landmass was located at high‐to‐mid latitudes and far away from the core of Rodinia at ca. 770 Ma [ABSTRACT FROM AUTHOR]

We present Van Allen Probes observations of periodic chorus wave emissions in the troughs of compressional ultralow frequency (ULF) waves. During this event, the spectral gap of chorus waves gradually widens as the spacecraft moves from the equatorial source region towards higher latitudes. Moreover, chorus wave intensity increases and frequency range widens after a substorm injection. We show that the periodic occurrence of chorus waves is attributed to the modulation of threshold amplitude for nonlinear growth of chorus waves by the second spatial derivative of ULF compressional magnetic field. The widening gap can be interpreted in terms of the nonlinear damping mechanism. A good agreement is also found between the nonlinear wave growth theory and the observations regarding the influence of substorm injection on the chorus. These findings support the applicability of the nonlinear theory in describing the chorus wave generation and damping, together with their modulations by ULF waves. Plain Language Summary: In Earth's magnetosphere, plasma waves play a key role in the acceleration, transport, and loss of energetic particles in the Van Allen radiation belts. These waves usually coexist and interact with one another. For example, whistler waves in the kHz range are often modulated by ultralow frequency (ULF) waves in the mHz range, which leads to fascinating phenomena such as pulsating auroral patches. In this paper, we report a representative case study of long‐duration modulation of whistler‐mode chorus emissions by ULF waves, in which chorus waves appear periodically at the trough of the ULF compressional magnetic field. There are two other interesting phenomena including the gradual widening of the chorus wave‐power gap near half of the electron cyclotron frequency and the abrupt enhancement of the chorus wave intensity and frequency range after a substorm injection. We utilize the nonlinear growth theory of chorus emissions to propose, for the first time, that the latitudinal configuration of the compressional ULF waves plays an important role in the modulation process. The nonlinear theory is also used to investigate the effect of substorm injection on chorus emissions and to understand the widening of the wave‐power gap. They both show good agreement with the observations. Key Points: The observed modulation of chorus emissions by ultralow frequency waves is explained in nonlinear theory by the periodic distortion of field configurationThe chorus waves also show a widening gap as the spacecraft moves away from the equator, which agrees with the nonlinear damping scenarioThe intensity and frequency range of the chorus waves increase abruptly due to the substorm injection of energetic electrons [ABSTRACT FROM AUTHOR]