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Geological CO2 storage is an emerging topic in energy and environmental community, which is, as a commonly accepted sense, considered as the most promising and powerful approach to mitigate the global carbon emissions during the transition to net‐zero. Of the geological media which initially considered cover the saline aquifers, oil and gas reservoirs, coal beds, and potentially basalts, up to now only the first two choices have been proven to be the most capable storage sites and successfully implemented at pilot/commercial scales. Here, two tandem papers propose novel strategies for the first time, by synthesizing and utilizing new high‐dryness CO2 foam, to enhance geological CO2 storage capacity in saline aquifer and oil and gas reservoirs. In this paper, a new high‐dryness CO2 foam is synthesized and injected into the saline aquifers to explore the storage capacity enhancement, with the unique foam‐induced advantages of sweep area expansion and storage efficiency improvement. Such a new idea is specifically evaluated and validated through a series of static analytical and dynamic performance experiments. With the optimum surfactant concentration of 0.5 wt%, the foaming volume and quality are determined to be 521 mL and 80.81%, respectively, which also shows excellent salt tolerance with 45,000 ppm Na+, 25,000 ppm Ca2+, and 25,000 ppm Mg2+. Moreover, the water consumption for CO2 storage decreases from 464.31 g/mol at 25% foam quality to 67.38 g/mol at 85% foam quality by using the new CO2 foam. Overall, the newly synthesized CO2 foam could effectively enhance geological CO2 storage capacity and concurrently diminish water consumption, therefore realizing the win‐win environment and economic benefits. Plain Language Summary: Geological CO2 storage is an emerging topic in energy and environmental community, which is, as a commonly accepted sense, considered as the most promising and powerful approach to mitigate global carbon emissions amid the transition to net‐zero. The geological CO2 storage options initially included ocean storage, surface mineral carbonation, and geological storage, but currently only refer to the storage in geological media. Of the geological media which initially considered cover the saline aquifers, oil and gas reservoirs, coal beds, and potentially basalts, up to now only the first two choices have been proven to be the most capable storage sites and successfully implemented at pilot/commercial scales. Here, a paper proposes novel strategies for the first time, by synthesizing and utilizing new high‐dryness CO2 foam, to enhance geological CO2 storage capacity in saline aquifer and oil and gas reservoirs. Novel strategies, which effectively enhance geological CO2 storage capacity, are specifically evaluated and validated through a series of static analytical and dynamic performance experiments. Qualitative and quantitative analyses fill the knowledge gap or enhancing geological CO2 storage in saline aquifer and oil and gas reservoirs. Also, solid scientific analyses/supports are provided for future academic research and practical geological CO2 utilization and storage. Key Points: Novel strategies for the first time, by synthesizing and utilizing new high‐dryness CO2 foam, to enhance geological CO2 storage capacity in saline aquiferQualitative and quantitative analyses fill the knowledge gap of enhancing the geological CO2 storage in saline aquiferSolid scientific analyses/supports are provided for future academic research and practical geological CO2 utilization and storage [ABSTRACT FROM AUTHOR]

Gravity currents contribute to the transport of heat and mass in atmospheric and aquatic environments. In aquatic systems subject to daily surface cooling, gravity currents propagate through turbulent convective surroundings. Yet, the effects of thermal convection on aquatic gravity currents remain to be quantified. This paper demonstrates how the interaction between penetrative convection and downslope gravity currents impacts the fluid dynamics and transport across littoral aquatic systems. We performed field experiments in a wind‐sheltered lake experiencing differential cooling to resolve the dynamics of thermally driven gravity currents in convective environments. Our in situ observations reveal that convective plumes penetrate gravity currents, generating large vertical fluctuations that foster the erosion of the stratified layer. This enhanced vertical mixing destroys the stratified downslope flow and limits the basin‐scale transport. Our results demonstrate that the interaction between penetrative convection and downslope gravity currents controls the littoral‐pelagic connectivity in aquatic ecosystems. Plain Language Summary: Horizontal differences in fluid density generate flows called gravity currents. These currents transport heat and mass across environmental systems. The dynamics of gravity current and the resulting transport are well understood when the surroundings are quiescent, which is rarely the case in nature. In aquatic systems, turbulent processes such as convection energize the ambient water. Cooling‐driven convection occurs when the surface of aquatic systems loses heat to the atmosphere, which generates sinking thermal plumes. In this paper, we used a lake experiencing differential cooling as an ideal field‐scale laboratory to investigate the effects of convection on the dynamics of gravity currents. Our in situ observations reveal that convective plumes distort the upper interface of gravity currents and limit the flow intensity. These results demonstrate that convection constrains the horizontal transport induced by gravity currents in natural systems. Key Points: Convective plumes penetrate downslope gravity currents and generate vertical interface fluctuationsVertical convective mixing erodes the stratified downslope flow and limits lateral transportThe time of maximal lateral transport is delayed to the relaxation phase once penetrative convection weakens [ABSTRACT FROM AUTHOR]

This paper exploits triggered lightning as a point source for the basin‐scale electromagnetic tomographic survey to image 3‐D subsurface electrical properties in basins. This paper further develops a new temporal moment approach, overcoming the difficulties in forward and inverse modeling of 3‐D Maxwell's equations with heterogeneous parameter fields. Using this approach, we find that the influence of a single triggered lightning strike covers a radius of 20–70 km with detectable signals. The cross‐correlation analysis between the moment difference of the electric and electric/magnetic property field indicates that the approach is suitable for mapping subsurface electric conductivity (σ $\sigma $) heterogeneity. A numerical experiment with 3‐D spatially random parameter fields demonstrates that the method captures the spatial distribution of electric conductivity over large areas with a sparse monitoring network. It reveals the potential of using triggered lightning as a basin‐scale electric/magnetic tomography survey. Plain Language Summary: Triggered lightning experiments traditionally aim at adverse impacts of lightning phenomena on near‐surface structures (such as buildings, power, communication, and transportation networks). Magnetotellurics surveys have exploited electromagnetic (EM) waves from thunderstorm activities and the interaction of solar wind with the Earth's magnetosphere to map the subsurface structure, assuming that electromagnetic waves are planar and propagate vertically into the Earth. This paper, in contrast, explores the EM waves generated by flashes of lightning triggered by a lightning rocket at designated locations as EM point sources and their measurements at different depths and distances in the subsurface. Such experiments are tantamount to an EM tomographic survey, viewing the subsurface from different perspectives. This paper further develops a new stochastic methodology to analyze the propagation of EM waves in heterogeneous geologic media over hundreds of kilometers. These accomplishments permit harvesting the lightning signals to image the subsurface over greater depths and areas and address the image's uncertainty. Numerical experiments confirm the robustness of this proposed concept, which could be a new technology to explore subsurface processes and natural resources in basins and mountain terrains. Key Points: An efficient 3‐D forward and inverse model based on the temporal moment is developed to solve Maxwell's equations in random parameter fieldsTriggered lightning tomography yields an excellent subsurface electric conductivity spatial distribution in a basin of several kilometersDeep lightning rods in the subsurface improve vertical resolution and depth of investigation [ABSTRACT FROM AUTHOR]

The aerosol shortwave, direct radiative effects of smoke plumes from Chilean wildfires in 2017 and 2023 were derived from satellite observations in both cloud‐free and cloud scenes. At the top of the atmosphere, the aerosol DRE changes sign when aerosol overly clouds or open ocean, confirmed by both measurements and a simulation study. The cloud‐free daily‐mean DRE, computed using an offline radiative transfer model (RTM), was 66 W m−2 in 2023 and 42 W m−2 in 2017, due to absorption by smoke. However, the total radiative effects were larger in 2017 due to a larger plume size compared to 2023. The method presented here provides a new conceptual model to quickly assess the radiative effects of wildfire smoke plumes using satellite measurements and pre‐computed RTM results. The presented estimates are strongly affected by the uncertainty of aerosol optical thickness retrievals from satellite, which can be large in the presence of clouds. Plain Language Summary: From 30 January to the end of February 2023, central Chile experienced over 400 individual wildfires, consuming over 430,000 ha of native sclerophyllous forests, with 25 fatalities as of 14 February. Wildfires are common in central Chile during dry periods, but seem intensified due to the mega‐drought since 2010. Next to health effects, the smoke from these wildfires has important climatic impacts through the change of solar insolation in the atmosphere: smoke strongly absorbs solar radiation and heats the atmosphere, changing the vertical stability. In this paper, the horizontal and vertical smoke distribution in the atmosphere is presented using satellite observations, and the radiative effects in the atmosphere and at the surface are quantified for the recent fires and as well as for the record‐breaking wildfires in 2017, which were the most devastating in the modern history of central‐Chile. Our results show that the radiative effects of the smoke from the recent wildfires were stronger in magnitude during the first few days, but confined to a smaller area, reducing their overall effect. Key Points: The radiative effects of the recent 2023 Chilean wildfire smoke plumes are assessed and compared to the 2017 Chilean wildfires smoke plumesPre‐computed radiative transfer model results can provide readily available aerosol direct radiative effects in clear‐sky for smokeSatellite measurements can further improve the aerosol direct effect and direct forcing estimates for both clear sky and cloud scenes [ABSTRACT FROM AUTHOR]

The annular structure of Antarctic oscillation (AAO) is a research hotpot, but its asymmetry receives less attention. In this paper, the self‐organizing map method is employed to cluster the AAO patterns into symmetric and asymmetric modes in austral autumn. The asymmetry is mainly reflected in the Pacific‐Atlantic sector, and the AAO evolves toward asymmetric positive polarity, with the most pronounced asymmetry in May. Originating from near Australia, the asymmetry indicates a zonal wave train in the Pacific‐Atlantic sector. Both modeled and observed results demonstrate that the sea surface temperature anomaly in the equatorial western Pacific stimulates a local meridional circulation anomaly and induces anomalous Rossby wave sources near Australia subsequently. An anomalous wave train propagating toward the Antarctic Peninsula is formed, and the associated geopotential anomaly enhances the asymmetry of AAO. Asymmetric AAO is conducive to the Antarctic dipole, which modulates the air temperature and sea ice anomalies around Antarctica. Plain Language Summary: The zonal symmetry of the Antarctic oscillation (AAO; also named southern annular mode) is well known to researchers, while the zonal asymmetry has received less attention. We use a clustering method to cluster the AAO modes in austral autumn into symmetric modes and asymmetric modes. The asymmetry of AAO is mainly reflected in the Pacific‐Atlantic sector. The results show that the AAO mode evolves to a positive asymmetric mode, and the asymmetry is most obvious in May. Both simulations and observations suggest that this asymmetry stems from sea surface temperature anomaly in the equatorial western Pacific that stimulates an anomalous local meridional circulation near Australia, and in turn triggers an anomalous wave train propagating toward the Antarctic Peninsula. The associated geopotential anomalies enhance the asymmetry of AAO. The asymmetric AAO favors the Antarctic dipole, regulating the air temperature and sea ice anomalies around Antarctica. Key Points: Via a cluster method, we obtained the zonal asymmetric Antarctic oscillation (AAO) mode, and analyzed its trend and preferred monthThe source of its asymmetry is from the sea surface temperature anomaly in the tropical western PacificThe asymmetric AAO mode has a vital influence on the Antarctic dipole [ABSTRACT FROM AUTHOR]

Orbital precession has been linked to glacial cycles and the atmospheric carbon dioxide (CO2) concentration, yet the direct impact of precession on the carbon cycle is not well understood. We analyze output from an Earth system model configured under different orbital parameters to isolate the impact of precession on air‐sea CO2 flux in the Southern Ocean—a component of the global carbon cycle that is thought to play a key role on past atmospheric CO2 variations. Here, we demonstrate that periods of high precession are coincident with anomalous CO2 outgassing from the Southern Ocean. Under high precession, we find a poleward shift in the southern westerly winds, enhanced Southern Ocean meridional overturning, and an increase in the surface ocean partial pressure of CO2 along the core of the Antarctic Circumpolar Current. These results suggest that orbital precession may have played an important role in driving changes in atmospheric CO2. Plain Language Summary: Over the past one million years, Earth has experienced several glacial and interglacial periods. As a glacial period is ending, carbon in the atmosphere can rise by up to 50%. The cause for this change is currently unknown, but most theories suggest that this carbon is released from the deep ocean into the atmosphere. The Southern Ocean surrounding Antarctica is the location of a lot of carbon outgassing from the deep ocean into the atmosphere, so it could be responsible for some of this change in atmospheric carbon. One of Earth's orbital cycles, precession, has been shown to change circulation in the Southern Ocean, that can affect how much carbon is carried from the deep ocean to the surface and released into the atmosphere. This paper uses simulations of a climate model to show that high precession corresponds to a 20% increase in the release of carbon from the Southern Ocean into the atmosphere. These findings suggest that precession could have affected changes in past atmospheric carbon concentrations. Key Points: Increased insolation during austral summer due to orbital precession shifts the southern westerlies polewardPoleward shifted westerlies enhance CO2 outgassing due to increased turbulent exchange and vertical transport of carbon‐rich watersEnhanced transport of carbon‐rich waters is driven by a deepening of the overturning circulation in response to poleward shifted winds [ABSTRACT FROM AUTHOR]

Optical remote sensing observations have suggested that the top layer of Europa's icy surface is heavily affected by external weathering agents. To model and understand these effects, it is necessary to characterize the environment as fully as possible. In this paper, we focus on one agent in the environment (energetic electrons). We show Juno electron data from its 2022 Europa flyby and other time periods. While the Juno sensor used here (Jupiter Energetic Particle Detector Instrument) was not designed to obtain high quality electron data in an intense radiation environment, it is possible to extract information such as how Europa blocks energetic particles from accessing some of the surrounding space. The decrease in charged particle flux in Europa's wake provides an upper limit on the precipitation fluxes of the same particles. We also report that electron pitch angle distributions near Europa for the single energy channel considered here are time variable and not isotropic. Plain Language Summary: We present energetic electron data obtained when the Juno spacecraft crossed the plasma wake of the moon Europa in 2022. A major goal of this work is to estimate the amount of blockage of MeV electrons near the moon to inform radiation estimates for future Europa orbiters and landers. While the Jupiter Energetic Particle Detector Instrument does not directly detect particles between 1 and 20 MeV, using knowledge gained since the instrument began obtaining data we were able to estimate that about 80% of the particles in question are blocked by Europa in its wake at low altitude. Research on the weathering of Europa's surface by electrons is also discussed. Key Points: Jupiter Energetic Particle Detector Instrument electron data relevant to Europa are presentedWe estimate Europa's blockage causes an ∼80% reduction of ∼1–20 MeV electrons in the immediate plasma wakePitch angle distributions are computed from 70 keV electron data and show time variability [ABSTRACT FROM AUTHOR]

The flow‐induced dissolution of porous rocks governs many important subsurface processes and applications. Solute mixing, which determines pore‐scale concentration fields, is a key process that affects dissolution. Despite its importance, the effects of pore‐scale mixing on large‐scale dissolution patterns have not been investigated. Here, we use a pore network model to elucidate the mixing effects on macroscopic dissolution patterns and solute transport. We consider two mixing rules at pore intersections that represent two end members in terms of the mixing intensity. We observe that the mixing effect on dissolution is the strongest at moderate Damköhler number, when the reactive and advective time scales are comparable. This is the regime where wormholes spontaneously appear. Incomplete mixing is shown to enhance flow focusing at the tips of the dissolution channels, which results in thinner wormholes and shorter breakthrough times. These effects on passive solute transport are evident independent of initial network heterogeneity. Plain Language Summary: When a reactive fluid infiltrates the rock, the dissolution channels (wormholes) can spontaneously form, in which the flow and transport of reactant focus. The formation and growth of such channels is a complex phenomenon in which the processes taking place at the micro‐scale are strongly coupled with the macro‐scale patterns. One of these processes is the mixing of reactant‐saturated water at pore intersections. In this paper, we study how the intensity of the mixing process impacts the shapes and growth velocities of the dissolution channels. We find that when the mixing at pore intersections is relatively weak, the flow focuses more strongly in front of the wormhole tip, which reduces the width of the wormhole and leads to its faster propagation and early breakthrough. These effects are also evident from tracer breakthrough curves. Our findings contribute to the understanding of dissolution‐induced patterns, with implications to subsurface flow‐related processes such as karst formation and contaminant migration. Key Points: Mixing at pore intersections can have a major impact on macroscopic dissolution patterns and solute transportMixing effect is the strongest when reactive and advective time scales in the system are comparableMixing effect on dissolution increases as network heterogeneity decreases [ABSTRACT FROM AUTHOR]

This paper summarizes the results of the first investigation into the effect of particle‐laden plumes on glacier melting using laboratory experiments. We find that the melt rate, when the ice is exposed to a particle‐laden plume, can be larger than when exposed to an equivalent plume without particles. The increased melt rate is linked to an increase in the plume velocity in response to the presence of suspended particles. Including this increased velocity in a plume model improves melt rate predictions from the "three‐equation model" by approximately 45% for the range of particle concentrations used in this study. Plain Language Summary: Ice loss from the Greenland ice sheet is more rapid in locations where fresh water is released at the base of marine terminating glaciers. The fresh water forms a buoyant plume that rises vertically next to the ice face. Previous observations of these plumes have shown that they can contain significant concentrations of suspended sediment. We show, using laboratory experiments, that the melt rate of a vertical ice face can be increased by the presence of suspended particles in the vertically rising plume. This observation suggests that the effect of such plumes could be larger than current modeling studies predict. Key Points: Laboratory experiments show that melting of an ice face can be increased by the presence of sediment in a subglacial discharge plumeThe increased melting is linked to an increase in the plume velocity in response to the presence of suspended particlesAccounting for the increased plume velocity within the three‐equation model significantly improves predictions of the melt rate [ABSTRACT FROM AUTHOR]

A mass‐conserving method to downscale precipitation from global climate models (GCMs) using sub‐grid‐scale topography and modeled 700‐mb wind direction is presented. Runoff is simulated using a stand‐alone hydrological model, with this and several other methods as inputs, and compared to runoff simulated using historical observations over the western contiguous United States. Results suggest the mitigation of grid‐scale biases is more critical than downscaling for some regions with large wet biases (e.g., the Great Basin and Upper Colorado). In other regions (e.g., the Pacific Northwest) the new method produces more realistic sub‐grid‐scale variability in runoff compared to unadjusted GCM output and a simpler downscaling method. The presented method also brings the runoff centroid timing closer to that simulated with observations for all subregions examined. Plain Language Summary: Due to limitations in computing power which necessitates coarse spatial resolution, climate models do not include many details on mountains and their impact on precipitation. For this reason, it is difficult to estimate the impact of climate change on the availability of water for human consumption in places like the western United States, where mountain snowpack is an important source of water. This paper presents a way to adjust precipitation estimates from climate models by using some simple statistics about nearby mountains and valleys. The adjusted precipitation is then used in a hydrologic model to calculate the runoff that is simulated with different precipitation inputs. Results show that in most cases, the precipitation adjustment improves estimates of the resultant runoff relative to simulations with observed precipitation. The main exceptions are in very dry areas where the climate model produces far too much precipitation. With further work, the proposed adjustment may be integrated into the climate model itself to make it easier for those managing water resources (e.g., controlling reservoir levels) to use the model output to plan and adapt to climate change. Key Points: A mass‐conserving method for downscaling orographic precipitation improves modeled runoff from the CESM2Considering upwind topography further improves modeled runoff compared to simpler adjustmentsNot tuning to individual model grid points makes this method more generalizable than many existing statistical downscaling methods [ABSTRACT FROM AUTHOR]

Using new continuous geodetic time series, we identify five shallow slow slip events (SSEs) offshore and beneath the Osa peninsula in southern Costa Rica. An early event was detected by one station in 2013, and two events occurring in close succession in both 2018 and 2022 were detected by multiple stations, indicating a preliminary recurrence interval of ∼4–5 years. While SSEs have been observed to the northwest at Nicoya, this is their first documentation in southern Costa Rica. Modeled slip distributions of the 2018 and 2022 events indicate they likely ruptured the same or overlapping patches of the plate interface, near the trench, updip of the 1983 Mw 7.4 Osa event. Immediately offshore, estimated cumulative slip from the 2018 and 2022 events is sufficient to close the slip deficit from tectonic loading over the recurrence interval, potentially limiting the magnitude and spatial slip distribution of future large ruptures. Plain Language Summary: Slow slip events (SSEs), effectively slow earthquake ruptures, are a phenomena that have been observed in many subduction zones around the world. While SSEs in subduction zones are often observed at depth, this is likely due to our observational capability being better when the events occur under land. By contrast, shallow events are more difficult to observe because they often occur under the ocean, despite their potential relationship to large, damaging, and/or tsunamigenic earthquakes. In this paper, we present research that identifies shallow slow slip events in a location where they have not been previously observed, the Osa Peninsula in southern Costa Rica. In total we observe five shallow SSEs, sometimes occurring in pairs, that appear to rupture every ∼4–5 years. Additionally we suggest that the amount of slip in these events may be sufficient to account for all the tectonic convergence in some locations, potentially limiting the size of future large earthquakes. Key Points: We identify five slow slip events in southern Costa Rica, one in 2013, and two events occurring in close succession in both 2018 and 2022The recent four events likely ruptured the same shallow patch of the megathrust, extremely close to the Middle American TrenchEvents in 2018 and 2022 seem to release nearly all slip accumulated by plate motion over a ∼4 year recurrence interval in some locations [ABSTRACT FROM AUTHOR]

In Saturn's magnetosphere, the radially‐inward transport of magnetic fluxes is usually carried by localized flux tubes with sharply‐enhanced equatorial magnetic fields. The flux tubes also bring energetic particles inward, which are expected to drift azimuthally and produce energy‐dispersive signatures. Spacecraft observations, however, indicate the occurrence of energy‐dispersionless signatures for perpendicular‐moving particles. These unexpected features are attributed to the sharp magnetic gradient at the edge of the flux tubes, which significantly modifies the drift trajectories of perpendicular‐moving particles to enable their trapping motion within the flux tubes. The bouncing particles are less affected by the gradient, and therefore, still display energy‐dispersive signatures. It is the distinct particle behavior, together with different spacecraft traversal paths, that underlies the observational diversity. The results improve our understanding of particle dynamics in the magnetospheres of giant planets and indicate that pitch‐angle information should be considered in the extraction of flux‐tube properties from energetic particle observations. Plain Language Summary: The conservation of magnetic fluxes in Saturn's magnetosphere requires that the outward convection is compensated by a return process of magnetic fluxes, which has been observed in the form of localized flux tubes associated with sharply‐enhanced equatorial magnetic field and hot plasma population. The azimuthal drift of energetic particles within the flux tubes produces energy‐dispersive signatures, which have been utilized to estimate the age and starting position of the returning flux tubes. In this paper, we are motivated by Cassini observations of energy‐dispersionless signatures for perpendicular‐moving particles, to demonstrate that their drift paths can be significantly modified by the sharp magnetic gradient to cause their trapping within the flux tubes. The bouncing particles, on the other hand, are less affected by the gradient and, therefore, can leave the flux tubes to continue their drift around the planet. We further construct the magnetic configuration associated with the flux tubes, to illustrate the origin of the diverse observational signatures depending on particle pitch angle, spacecraft traversal path, and the trapping extent. These results have important implications for the interpretation of observational data in the injection flux tubes, and therefore improve our understanding of giant planet's magnetosphere and the associated particle dynamics. Key Points: In Saturn's injection flux tubes, charged particles often show distinct energy‐dispersive or dispersionless signals depending on pitch angleThe unexpected, energy‐dispersionless features for perpendicular‐moving particles are formed by their trapping motion within the flux tubesThe bouncing particles can hardly be trapped, and therefore, exhibit the characteristic energy dispersion and particle leaking signatures [ABSTRACT FROM AUTHOR]

The water table depth (WTD) in peatlands determines the soil carbon decomposition rate and influences vegetation growth, hence the above‐ground carbon assimilation. Here, we used satellite‐observed Solar‐Induced chlorophyll Fluorescence (SIF) as a proxy of Gross Primary Production (GPP) to investigate water‐related vegetation stress over northern peatlands. A linear model with interaction effects was used to relate short‐ and long‐term anomalies in SIF with WTD anomalies and the absolute WTD. Most locations showed the occurrence of drought and waterlogging stress though regions with exclusively waterlogging or drought stress were also detected. As a spatial median, minimal water‐related vegetation stress was found for a WTD of −0.22 m (short‐term) and −0.20 m (long‐term) (±0.01 m, 95% confidence interval of statistical uncertainty). The stress response observed with SIF is supported by an analysis of in situ GPP data. Our findings provide insight into how changes in WTD of northern peatlands could affect GPP under climate change. Plain Language Summary: Water table depth is an important variable influencing the carbon cycle and vegetation growth in northern peatlands. In this paper, the impact of changing wetness conditions on vegetation growth over peatlands was studied through satellite measurements of solar‐induced fluorescence (SIF), which is a radiation signal emitted by vegetation during photosynthesis. Previous studies over ecosystems on mineral soil, that is, not over peatland, suggested a response of SIF to drought conditions. In our study, it was shown that peatland vegetation experiences moisture‐related growth stress under both very wet and very dry conditions, which might reduce the photosynthesis efficiency and the ability to capture and store CO2. Stress due to drought conditions was detected for peatlands in the south of the Western Siberian Lowlands and the Boreal Plains. Stress due to prolonged wet conditions occurred for example, in the north of the Western Siberian Lowlands and the north of the Hudson Bay Lowlands. Key Points: Spaceborne Solar‐Induced Fluorescence (SIF) data was used to analyze soil moisture‐related vegetation stress regimes in northern peatlandsFor most locations, waterlogging as well as drought stress regimes occurred and alternated depending on peatland water level dynamicsThe SIF‐based stress response observations are supported by in situ data of Gross Primary Production [ABSTRACT FROM AUTHOR]

This paper investigates the relationship between the growth of the 34‐kt wind radius (R34) of tropical cyclones (TCs) and their fullness using best‐track data from 2001 to 2020. The storms were categorized into four groups based on a fullness scale: FS1 (fullness ≤ 0.4), FS2 (0.4 < fullness ≤ 0.6), FS3 (0.6 < fullness ≤ 0.8), and FS4 (fullness > 0.8). These groups exhibit unique spatial patterns of very deep convective clouds with infrared brightness temperatures <208 K. The mean R34 growth rates in 24 hr decrease from FS1 to FS4, which is linked to the higher coverage of very deep convection around R34 in storms with lower fullness. This study demonstrates that TC fullness can characterize the spatial distribution of deep convection in storms and serve as a representation of the growth of TC outer region size. These results have implications for understanding the mechanisms behind TC outer size growth. Plain Language Summary: The destructive potential of tropical cyclones (TCs) is primarily determined by two key factors: intensity and the size of the outer region. While the impact of TC wind structure on TC intensification rates has been extensively studied, little has been done to explore its effect on the growth of the outer region. This study finds that storms with lower fullness had larger growth rates in the radius of gale‐force winds (34 kt or 17 m/s; R34). TC fullness is defined as the ratio of the extent of the outer‐core wind skirt to the outer‐core size of the TC. This is associated with the higher coverage of very deep convective clouds with infrared brightness temperatures below 208 K around R34 in storms with lower fullness. These findings shed light on the importance of wind structure in the growth of the outer region in TCs, which helps improve our understanding of how these storms change in outer‐core size. Key Points: Tropical cyclone fullness can serve as a reliable indicator of the distribution of very deep convectionStorms with lower fullness have a higher mean R34 growth rate over a 24‐hr periodMore intense convection occurred around R34 in storms with lower fullness, which promotes the growth of R34 [ABSTRACT FROM AUTHOR]

The first orbits around Jupiter of the Juno spacecraft in 2016 revealed a symmetric structure of multiple cyclones that remained stable over the next 5 years. Trajectories of individual cyclones indicated a consistent westward circumpolar motion around both poles. In this paper, we propose an explanation for this tendency using the concept of beta‐drift and a "center‐of‐mass" approach. We suggest that the motion of these cyclones as a group can be represented by an equivalent sole cyclone, which is continuously pushed by beta‐drift poleward and westward, embodying the westward motion of the individual cyclones. We support our hypothesis with 2D model simulations and observational evidence, demonstrating this mechanism for the westward drift. This study joins consistently with previous studies that revealed how aspects of these cyclones result from vorticity‐gradient forces, shedding light on the physical nature of Jupiter's polar cyclones. Plain Language Summary: The Juno spacecraft arrived at Jupiter in 2016, revealing a unique atmospheric phenomenon. Each of the poles of Jupiter is inhabited by a symmetrically structured group of cyclones, where a ring of cyclones surrounds one cyclone close to the pole. The collective observations of these cyclones over 5 years show that although they are relatively stable, they generally drift in the westward direction a few degrees per year. Here, we investigate the mechanism driving this drift by examining the cyclones as a group. This "center‐of‐mass" approach masks the interactions between the cyclones and only considers trends that happen simultaneously on all cyclones. Using model simulations, we show that the motion of a group's "center of mass" can be captured by a sole equivalent cyclone, pushed poleward and westward by the "beta‐drift" effect, which is known to contribute to the motion of tropical cyclones on Earth. This westward force on the group as a whole is thus suggested as the driver of the observed westward drift. We conclude by presenting observational evidence supporting this hypothesis. Key Points: The mean westward circumpolar motion of Jupiter's northern and southern polar cyclones is analyzed and explained by the β‐drift effectSimulations show that the "center of mass" of a group of cyclones behaves like one equivalent cyclone, moving poleward‐westward under β‐driftThis center‐of‐mass approach is applied to the Juno data, implying that the cyclones' collective β‐drift drives their observed westward drift [ABSTRACT FROM AUTHOR]

Compared to interannual and interdecadal variations, inadequate attention has been given to intraseasonal changes in the summer northwest Pacific subtropical high (NWPSH). During 1981–2005, the north Indian Ocean (NIO) and NWPSH exhibit significant relationships from June to August, while the influences of the Boreal Summer Intraseasonal Oscillation 1 (BSISO1) in June and August differ from its impacts in July, resulting in a significant correlation between the NWPSH in June and August. The models capture NIO's roles but underestimate BSISO1's influences, leading to an underestimation (overestimation) of the relationship between NWPSH in June and August (adjacent two months). A dynamical‐statistical approach based on the close relationship between June and August NWPSH is proposed to improve models' prediction capabilities. Improved results show the mean correlation coefficients (root mean square errors) between prediction and observation for August precipitation and geopotential height increase by 57% and 21% (decrease by 0.27 mm/day and 1.61 m). Plain Language Summary: The Northwest Pacific Subtropical High (NWPSH) holds significant importance for the East Asian summer climate as it directly affects precipitation and temperature. Accurate predicting the NWPSH in advance is crucial, but it poses challenges at subseasonal scales as it requires considering both initial fields and external forcing factors. This study primarily evaluates and enhances the prediction capabilities of Seasonal‐to‐Subseasonal (S2S) models for the relationship between the summer NWPSH in different months. Due to the combined influences of the boreal summer intraseasonal oscillation 1 (BSISO1) and the north Indian Ocean (NIO), the NWPSH in June exhibits a strong correlation with the August NWPSH. Therefore, based on the connection between the June and August NWPSH, this paper proposes a dynamical‐statistical approach aimed at enhancing the prediction capabilities of S2S models for August precipitation and geopotential height. Key Points: Intraseasonal oscillation and north Indian ocean together cause high correlation between June and August northwest Pacific subtropical highThe models can only capture the influences of the north Indian ocean but not the intraseasonal oscillationThe models' prediction skills for August precipitation are markedly improved when referring to the June northwest Pacific subtropical high [ABSTRACT FROM AUTHOR]

Ocean swell activities excite body‐wave microseisms that contain information on the Earth's internal structure. Although seismic interferometry is feasible for exploring structures, it faces the problem of spurious phases stemming from an inhomogeneous source distribution. This paper proposes a new method for inferring seismic discontinuity structures beneath receivers using body‐wave microseisms. This method considers the excitation sources of body‐wave microseisms to be spatially localized and persistent over time. To detect the P‐s conversion beneath the receivers, we generalize the receiver function analysis for earthquakes to body‐wave microseisms. The resultant receiver functions are migrated to the depth section. The detected 410‐ and 660‐km mantle discontinuities are consistent with the results obtained using earthquakes, thereby demonstrating the feasibility of our method for exploring deep‐earth interiors. This study is a significant step toward body‐wave exploration considering the sources of P‐wave microseisms to be isolated events. Plain Language Summary: The ocean waves excite persistent and random ground motions called microseisms. Since this excitation is independent of seismic activities, this wavefield has information about seismic structures that earthquakes never have. For the deep structure, such as the mantle and core, body‐wave microseisms are more suitable than surface‐wave microseisms because body‐wave microseisms have better sensitivity. Previous studies using body‐wave microseisms mainly adopted the cross‐correlation analysis known as seismic interferometry. This method assumes that the microseisms are excited everywhere. However, the inhomogeneous source distribution of body‐wave microseisms causes artifacts for exploration by seismic interferometry. We developed a new method which circumvents this problem. Assuming that the body‐wave microseisms are spatially isolated, this method extracted the P‐s converted waves beneath receivers from body‐wave microseisms. The 3‐Dimensional imaging result of extracted P‐s converted waves shows both 410‐ and 660‐km mantle discontinuities, consistent with results using earthquakes. This study shows the potential of body‐wave microseisms for exploring the deep earth structure. Key Points: The P‐S waves at mantle discontinuities were extracted from the ambient noise excited by the ocean swellsWe developed the source deconvolution method to generalize a receiver function method to P‐wave microseismsThe migration result of P‐S waves was consistent with previous studies, showing the potential of P‐wave microseisms to seismic structures [ABSTRACT FROM AUTHOR]

Glacial isostatic adjustment (GIA) modeling is not only useful for understanding past relative sea‐level change but also for projecting future sea‐level change due to ongoing land deformation. However, GIA model predictions are subject to a range of uncertainties, most notably due to uncertainty in the input ice history. An effective way to reduce this uncertainty is to perform data‐model comparisons over a large ensemble of possible ice histories, but this is often impossible due to computational limitations. Here we address this problem by building a deep‐learning‐based GIA emulator that can mimic the behavior of a physics‐based GIA model while being computationally cheap to evaluate. Assuming a single 1‐D Earth rheology, our emulator shows 0.54 m mean absolute error on 150 out‐of‐sample testing data with <0.5 s emulation time. Using this emulator, two illustrative applications related to the calculation of barystatic sea level are provided for use by the sea‐level community. Plain Language Summary: Piecing together the history of ice sheet change during past glacial cycles is not only important for understanding past sea‐level change but also for predicting how ongoing glacial rebound contributes to future sea‐level change. Traditionally, a physics‐based "sea‐level model" is used to predict the sea‐level change associated with a particular reconstruction of past ice sheet change and compare the results with geological records of past sea level. However, a fundamental limitation of this approach is the need to compute sea‐level change for a large number of plausible ice histories, which is often prohibited by the computational resources required to repeatedly solve the complex physical equations. In this paper, we describe a machine‐learning‐based statistical model that can mimic the behavior of a physics‐based sea‐level model. This statistical model is computationally cheap and we demonstrate that it is able to accurately predict global sea‐level change for a suite of 150 "unseen" ice histories. Our statistical model predicts sea‐level change 100–1,000 times faster than a physics‐based model, making it an ideal tool for investigating and improving our understanding of global ice sheet change. Key Points: The first attempt to build a deep‐learning based Glacial isostatic adjustment (GIA) emulator that can accurately predict global sea‐level change based on a given ice modelThis emulator (GEORGIA) can predict global sea‐level change history within 0.5 s with minor emulation errorThis GIA emulator along with two illustrative applications are available for use by the wider sea‐level community [ABSTRACT FROM AUTHOR]

The estimation of cloud radiative forcing due to aerosol‐cloud interactions, RFaci (also known as the first indirect effect), relies on approximating the cloud albedo susceptibility to changes in droplet concentration, β. β depends on the cloud albedo and droplet concentration, both of which can be observed by satellites. Satellite observations are often spatially aggregated to coarser resolutions, typically 1 × 1° scenes. However, on such spatial scales, the cloud albedo tends to be heterogeneous, whereas the β approximation assumes homogeneity. Here, we demonstrate that the common practice of aggregating satellite data and neglecting cloud albedo heterogeneity results in an average overestimation of 10% in previous estimates of the RFaci. Additionally, we establish a relationship between the magnitude of the bias in β and Stratocumulus morphologies, providing a physical context for cloud heterogeneity and the associated bias. Lastly, we propose a correction method that can be applied to cloud albedo gridded data. Plain Language Summary: This paper explores the effect of cloud albedo morphology, which is a reflection of cloud heterogeneity, on radiative forcing due to aerosol‐cloud interactions (RFaci). The RFaci is estimated from satellite observations based on the assumption that clouds are homogeneous within a given scene. However, when satellite data is spatially aggregated to reduce the amount of data to a user‐friendly gridded format—a common practice—this assumption is no longer valid. Consequently, an overestimation of the RFaci occurs, particularly in heterogeneous scenes, where the overestimation can reach up to 50%. This means that the RFaci is lower than previously estimated. Our results also suggest that cloud albedo enhancement due to an increase in droplet concentrations would be most effective in homogeneous scenes. Therefore, marine cloud brightening strategies should take cloud albedo homogeneity into account to achieve the most effective albedo enhancement. Key Points: The common practice of spatial aggregation of satellite data into 1 × 1° scenes leads to an average 10% overestimation of the RFaciThe overestimation is due to neglecting cloud albedo heterogeneity, and is associated to different types of Stratocumulus morphologiesA correction is proposed, which calls for the incorporation of cloud reflectance statistics in Level 3 data [ABSTRACT FROM AUTHOR]

The electron butterfly distribution, characterized by pitch angles (PA) primarily at 45° and 135°, was rarely observed in Earth's magnetotail. Here using the high‐resolution measurements from Magnetospheric Multiscale mission, we present the observation of electron butterfly distribution in a contracting dipolarization front (DF), and propose a new physical mechanism to explain its formation. Specifically, we discover that the electron butterfly distribution only exhibited in the locally contracted DF and was observed above 1.7 keV. We infer that local contraction of the DF transformed its configuration from a magnetic bottle to an hourglass‐shaped magnetic structure, and the butterfly distribution was formed by the magnetic mirror effect of this magnetic hourglass. Additionally, the theoretically estimated loss cone of the magnetic hourglass fits well with the observations of electrons, validating our inference about the formation mechanism. These findings can improve our understanding of electron dynamics in Earth's magnetosphere. Plain Language Summary: Examining the pitch‐angle (PA) distribution of electrons can help us understand the electron dynamic process in space. In this paper, we present the observation of electron butterfly distribution, characterized by PA primarily around 45° and 135°, in Earth's magnetotail. We find that the electron butterfly distribution was observed only above 1.7 keV, and exhibited in a locally contracting dipolarization front (DF). We propose a new formation mechanism for this distribution, and perform the theoretical calculations to validate it. Our findings can significantly improve the knowledge of electron dynamics in Earth's magnetosphere. Key Points: The electron butterfly distribution was observed above 1.7 keV and only exhibited in the contracted dipolarization front (DF)The local contraction of the DF transformed its configuration from a magnetic bottle to an hourglass‐shaped magnetic structureThe butterfly distribution is formed by the magnetic mirror effect of the hourglass‐shaped structure [ABSTRACT FROM AUTHOR]

Previous studies showed that the Eratosthenian mare (Em) unit in the northern Mare Imbrium, which is the location of the Chang'e‐3 (CE3) landing site, was simply formed by one period of thick lava flow. However, the CE3 Yutu rover equipped with lunar penetrating radar (LPR) recognized multilayered Em basalts based on the Channel 1 data reprocessed in this paper, indicating that three subdivided thin Eratosthenian lava flows should exist. The spatial variation and thickness distribution of each layer are further estimated based on the location of interfaces recognized from the shallow radar profile. Finally, we build a three‐dimensional stratigraphic model of young mare basalts with filling directions beneath the Chang'e‐3 landing site. The result infers that these young lava flows in the northern Mare Imbrium probably erupted intermittently from the same source. Plain Language Summary: The Chang'e‐3 spacecraft, which landed on the northern Mare Imbrium on the near side of the Moon, was equipped with lunar penetrating radar (LPR) on the Yutu rover and detected subsurface structures around the landing site. The structure of the regolith and those underneath young periods (Eratosthenian) and old periods (Imbrian) of lava flow layers have been constrained. However, due to data quality limitations, further information about the young period lava materials that exist pervasively in the northern Mare Imbrium is still lacking. This paper reprocessed the shallow part of LPR Channel 1 data and then ascertained multilayered young mare basalts underlying the regolith, which are interpreted as three periods of thin Eratosthenian lava flows. The filling directions beneath the CE3 landing site were also constrained based on the spatial distribution of interfaces recognized from LPR data. Key Points: Multilayered shallow structures are recognized beneath the Chang'e 3 landing site based on lunar penetrating radar Channel 1 dataThree periods of Eratosthenian lava flows produced intermittent flooding in the northern Mare ImbriumA three‐dimensional stratigraphic model of young mare basalts is constructed in the area [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]

We calculate the aspect ratio of the electron diffusion region (EDR) during symmetric magnetic reconnection using magnetic field gradients measured by the Magnetospheric Multiscale (MMS) Mission. The technique introduced in this paper is validated using a particle‐in‐cell simulation and used to calculate the EDR aspect ratios for three MMS‐observed magnetotail EDRs which are compared with the EDR aspect ratio predicted by scaling dependencies on asymptotic upstream electron β. We then use the aspect ratio to calculate the normalized reconnection rate and show that it is within uncertainty of the normalized reconnection rate found by previous studies for three MMS‐observed EDRs. Because the magnetic field gradients are velocity‐frame independent and typically very well measured by MMS, the technique can be used to obtain the normalized reconnection rate with higher fidelity than established methods. Plain Language Summary: Magnetic reconnection is a plasma process which occurs throughout the universe. It accelerates and heats nearby particles, and can redistribute energy over vast scales. The rate at which it occurs, the reconnection rate, is one of the most important quantities describing reconnection. Reconnection occurs within an electron‐scale region where ions and electrons are decoupled from the magnetic field, known as the electron diffusion region (EDR). Theory and simulations have shown the dimensions of the EDR scale with the reconnection rate. In this paper, we introduce a new method to determine the aspect ratio of the EDR and use it to find the reconnection rate for three EDRs observed by the Magnetospheric Multiscale Mission. This new method has fewer sources of error than established methods for determining reconnection rate using spacecraft data, and could provide a simpler way of studying the mechanisms which control the reconnection rate. Key Points: A new technique is introduced to calculate the aspect ratio of the electron diffusion region (EDR) with magnetic field gradientsThe aspect ratio is determined within 20% uncertainty for a particle‐in‐cell simulation with added MMS‐like errorsThe reconnection rates from the aspect ratio and reconnection electric fields are within uncertainties during three magnetotail EDRs [ABSTRACT FROM AUTHOR]

In response to global warming, ozone is predicted to increase aloft due to stratospheric cooling but decrease in the tropical lower stratosphere. The ozone reductions have been primarily attributed to a strengthening Brewer‐Dobson circulation, which upwells ozone‐poor air. Yet, this paper finds that strengthening upwelling only explains part of the reduction. The reduction is also driven by tropospheric expansion under global warming, which erodes the ozone layer from below, the low ozone anomalies from which are advected upwards. Strengthening upwelling and tropospheric expansion are correlated under global warming, making it challenging to disentangle their relative contributions. Therefore, chemistry‐climate model output is used to validate an idealized model of ozone photochemistry and transport with a tropopause lower boundary condition. In our idealized decomposition, strengthening upwelling and tropospheric expansion both contribute at leading order to reducing tropical ozone. Tropospheric expansion drives bottom‐heavy reductions in ozone, which decay in magnitude into the mid‐stratosphere. Plain Language Summary: The ozone layer absorbs ultraviolet light otherwise harmful to life. Due to compliance with the Montreal Protocol, the ozone layer is generally recovering from depletion. But, at the same time, global warming is predicted to impact ozone, increasing ozone in the upper stratosphere and decreasing ozone in the tropical lower stratosphere. These decreases are typically argued to result from a strengthening of tropical stratospheric upwelling under global warming. Yet, this paper shows that in addition to contributions from strengthening upwelling, much of the ozone loss arises from a deepening of the troposphere under global warming. The deepening of the troposphere erodes the ozone layer from below, with the low ozone anomalies in the eroded region subsequently transported upwards by the background upwelling. Deepening of the troposphere therefore helps to explain the predicted ozone reductions throughout the tropical lower stratosphere. Key Points: Global warming reduces ozone in the tropical lower stratosphere, an effect typically attributed to strengthening stratospheric upwellingYet, global warming also deepens the troposphere, which erodes the ozone layer and reduces transport of ozone into the lower stratosphereAlong with strengthening upwelling, tropospheric expansion contributes at leading order to reductions in tropical lower stratospheric ozone [ABSTRACT FROM AUTHOR]

Blooms of various types of seaweeds have been reported worldwide, with recent expansions in surface waters. While most of the expansions have been attributed to eutrophication due mainly to human activities, any potential role of climate change is unclear. Here we show that, in the East China Sea and Yellow Sea, increased biomass of Sargassum horneri (S. horneri, brown seaweed) from 2000 to 2021 appears to be caused primarily by ocean warming, as S. horneri prefers a certain temperature range to grow. In contrast, while increases of Ulva prolifera (U. prolifera, green seaweed) in the same regions might also be related to ocean warming, during the same period, human activities such as coastal aquaculture or seaweed mitigation may muddle such effects. With the projected ocean warming in the next decades, we hypothesize that S. horneri blooms may occur earlier during the year and may continue to expand in the future. Plain Language Summary: Seaweed macroalgae blooms have been reported around the world in the last two decades, yet the exact reasons are often unclear. This paper attempts to solve this puzzle for the Sargassum and Ulva seaweeds in the East China Sea and Yellow Sea using long‐term observations and laboratory‐based seaweed physiology measurements. The paper shows not only how seaweeds have expanded in the two marginal seas in the past four decades, but also how a warming ocean (due to climate variability) and nutrient enrichment (due mainly to human activities) controlled such expansions. Among 63 large marine ecosystems (LMEs) in the world, the East China Sea (where seaweeds expanded) is one of the three LMEs that experienced "super‐fast" warming. Given the IPCC‐projected seawater temperature rise of 1.6°C by 2050, will these seaweeds continue to expand? Key Points: Multi‐sensor satellite data show significant and near‐synchronized expansions of Sargassum horneri and Ulva prolifera in the past 38 yearsOcean warming appears to be a main factor behind the recent expansions of S. horneri because of its physiological requirementOcean warming may also play a role in U. prolifera expansions, but the effect appears confounded by human mitigation efforts [ABSTRACT FROM AUTHOR]

Implementation of the hydrogen economy for emission reduction will require storage facilities, and underground hydrogen storage (UHS) in porous media offers a readily available large‐scale option. Lack of studies on multiphase hydrogen flow in porous media is one of the several barriers for accurate predictions of UHS. This paper reports, for the first time, measurements of hysteresis in hydrogen‐water relative permeability in a sandstone core under shallow storage conditions. We use the steady state technique to measure primary drainage, imbibition and secondary drainage relative permeabilities, and extend laboratory measurements with numerical history matching and capillary pressure measurements to cover the whole mobile saturation range. We observe that gas and water relative permeabilities show strong hysteresis, and nitrogen as substitute for hydrogen in laboratory assessments should be used with care. Our results serve as calibrated input to field scale numerical modeling of hydrogen injection and withdrawal processes during porous media UHS. Plain Language Summary: Hydrogen storage facilities will need a ramp‐up when the hydrogen share in the future energy mix increase. Large‐scale hydrogen storage can be implemented in empty hydrocarbon fields or ground water reservoirs. Hydrogen storage in such media involve complex interactions with native rocks and fluids, and injection and withdrawal are typically described by flow functions. Relative permeability is one of the key flow functions that describe how easily hydrogen can flow through porous media in the presence of other fluids. In underground storage, hydrogen is cyclically injected and withdrawn multiple times, and its relative permeability may differ between these two processes, described as hysteresis. In this paper, we investigate hydrogen relative permeability in the laboratory and match with results from numerical simulations. We find that hydrogen relative permeability is different for injection and withdrawal and is also different from that of nitrogen. Our results are directly applicable in computer simulators that predict hydrogen storage efficiency. Key Points: Steady state measurements of hydrogen‐water relative permeabilityNumerical history matching needed for extrapolationStrong hysteresis observed between drainage and imbibition [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]

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]

This paper revealed a physical connection between the antiphase variation in the preceding autumn Tibetan Plateau (TP) and Lake Baikal snow cover anomalies (TBSA) and the following winter North Atlantic Oscillation (NAO) on interannual time scales during 1979–2021. The antiphase variation in TBSA, accounting for 44% of the total years, has a dipole structure in autumn, which prolonged into the following winter. The persistent antiphase TBSA associated diabatic forcing, disturbances and transient eddies favor a double wave train structure spanning the TP (east of Baikal) and North Atlantic from autumn to winter. Amid the wave train, the circulation anomalies over the North Atlantic extract more energy from the basic flow due to the seasonal increase in the westerly jet, which further evolves into the winter NAO pattern. Our results provide new insights into the formation and projection of winter NAO from the perspective of subtropical and extratropical Eurasia snow. Plain Language Summary: A robust link exists in the preceding autumn antiphase Tibetan Plateau (TP) and Lake Baikal snow cover anomalies (TBSA) and the winter North Atlantic Oscillation (NAO) during 1979–2021. There are 44% years of antiphase variation in TBSA in autumn, which shows a dipole structure with one positive center over the TP and another negative center over the Baikal. Larger (smaller) snow cover over the TP (Baikal) stimulates a local low (high) pressure system via diabatic cooling (heating). Due to the jet waveguide effect, the antiphase TBSA associated diabatic forcing and perturbation along the subtropical westerly jet favor the atmospheric wave train spanning the TP and North Atlantic. The antiphase TBSA associated transient eddies along the extratropical belt contribute to the atmospheric wave train lying between the eastern Baikal and the North Atlantic owing to the eddy‐flow interaction. Along with the seasonal increase in the subtropical westerly jet from autumn to winter, the geopotential height anomalies in the double wave train associated with the antiphase TBSA gradually develop into the winter large‐scale NAO circulation through more energy extraction from the stronger basic flow. Key Points: A robust link of winter North Atlantic Oscillation (NAO) to the preceding fall antiphase Tibetan Plateau‐Baikal snow cover anomalies (TBSA)The antiphase TBSA associated diabatic forcing, disturbances and transient eddies favor a double wave train structure around 30°N and 60°NMore energy extracts over the North Atlantic due to the seasonal increase in the westerly jet, favoring the development of the winter NAO [ABSTRACT FROM AUTHOR]

Geomorphologists have long debated the relative importance of disturbance magnitude, duration, and frequency in shaping landscapes. For river‐channel adjustment by floods, some argue that the cumulative hydrograph, rather than magnitude or duration, matters most. However, studies of flood‐induced river‐channel change often draw upon small data sets. Here, we combine Sentinel‐2 imagery with flow data from laterally active rivers to address this question using a larger data set. We apply automated algorithms in Google Earth Engine to map rivers and detect their lateral shifting; we generate a large data set to quantify planform erosion during 175 floods at 34 selected sites. Erosion during these floods is best explained by their duration and then their cumulative hydrograph. We use a random forest regression model to predict flood‐induced erosion, with potential applications for hazard management. Ultimately, better global data on sediment supply and caliber would help us to understand flood‐driven change to river planforms. Plain Language Summary: Some rivers change their shape over time. In this paper, we explore how high‐flow events drive these river channels to reshape themselves. We use Google Earth Engine to automatically map the shapes of rivers in satellite images. We apply this method to pairs of satellite images before and after high‐flow events, to understand how the river shape is changed by the event. We compare the amount of channel widening measured to aspects of the high‐flow event, including its peak, duration, and total flow. We do so for 175 events, and find that the duration and total flow are most important for explaining how much a channel widens during the event. Finally, we build a statistical model to predict the average amount of channel widening for a given high‐flow event. This method has potential applications for hazard management in rivers that are known to change their shape. Key Points: We develop a method to quantify river planform change after flood events, using Google Earth EngineWe do so for a data set of 175 floods that exceeded the 80th percentile stage, at 34 flow gauging sites on laterally active riversPlanform erosion during these high‐flow events was most correlated with the event duration, and then the summed hydrograph [ABSTRACT FROM AUTHOR]

Though tropical cyclone (TC) models have been routinely evaluated against track and intensity observations, little work has been performed to validate modeled TC wind fields over land. In this paper, we present a simple framework for evaluating simulated low‐level inland winds with in‐situ observations and existing TC structure theory. The Automated Surface Observing Systems, Florida Coastal Monitoring Program, and best track data are used to generate a theory‐predicted wind profile that reasonably represents the observed radial distribution of TC wind speeds. We quantitatively and qualitatively evaluated the modeled inland TC wind fields, and described the model performance with a set of simple indicators. The framework was used to examine the performance of a high‐resolution two‐way nested Geophysical Fluid Dynamics Laboratory model on recent U.S. landfalling TCs. Results demonstrate the capacity of using this framework to assess the modeled TC low‐level wind field in the absence of dense inland observations. Plain Language Summary: Some of the biggest human impacts of tropical cyclone (TC) winds come after the TC makes landfall. A skillful prediction of the radial distribution of winds is essential for forecasting TC‐induced inland hazards. However, the forecast skill of numerical hurricane models on inland TC wind fields has rarely been evaluated since it is challenging to collect wind observations during landfall, and the network of regular weather observations is too spread out to capture the strongest winds associated with a TC. This inhibits the improvement of forecast models and limits our understanding of the TC's inland evolution. Our work combines available inland in‐situ wind observations over the southeastern U.S. with existing TC structure theory, and presents a new "optimal" estimate of the post‐landfall winds. Our framework is found to be useful for evaluating the post‐landfall TC winds in hurricane forecast models. In addition, the new evaluation technique can intuitively demonstrate how well the model simulates TC intensity and structure. Key Points: We introduce a new framework for evaluating modeled inland tropical cyclone (TC) wind fields with observation‐based, theory‐predicted wind profilesThe theory‐predicted wind profile well represents the observed radial distribution of inland TC wind speedsWe propose simple indicators to summarize the model performance on inland wind field predictions [ABSTRACT FROM AUTHOR]

We show that the return‐point memory of cyclic macroscopic trajectories enables the derivation of a thermodynamic framework for quasistatically driven dissipative systems with multiple metastable states. We use this framework to sort out and quantify the energy dissipated in quasistatic fluid‐fluid displacements in disordered media. Numerical computations of imbibition–drainage cycles in a quasi‐2D medium with gap thickness modulations (imperfect Hele‐Shaw cell) show that energy dissipation in quasistatic displacements is due to abrupt changes in the fluid‐fluid configuration between consecutive metastable states (Haines jumps), and its dependence on microstructure and gravity. The relative importance of viscous dissipation is deduced from comparison with quasistatic experiments. Plain Language Summary: Fluid flow into a porous material filled with another is not only an everyday process (gardening, stains in fabrics, or printing) but is also a key process affecting the water cycle, contamination in soils and storage of energy or hazardous waste in the subsurface. These flows are controlled by the energy of the fluids, and its dissipation during their advancement, making the knowledge of energy dissipation crucial to our ability to predict these phenomena. However, to date there is no rigorous way to evaluate this energy. This paper describes a novel method that overcomes this challenge, explaining how the properties of the medium affect dissipation and showing why even for very slow flows the viscous energy (i.e., related to rapid fluid motion) still makes a difference. Key Points: Rigorous account of the microscopic physics allows to compute the energy dissipated between consecutive two‐phase configurationsWe link the microscopic origins of hysteresis and dissipation to the macroscopic pressure‐saturation behaviorQuasistatic pressure‐driven experiments point to a secondary contribution of viscous dissipation during Haines jumps [ABSTRACT FROM AUTHOR]

The Pacific decadal oscillation (PDO) is a decadal variability phenomenon occurring in the North Pacific Ocean. It has substantial impacts on marine ecosystems and the global climate. Due to the high complexity and unclear evolution mechanism, the accurate long‐term prediction of PDO remains a challenge. In this paper, a deep spatiotemporal embedding network (DSEN) is proposed to extract the spatiotemporal features from historical climate data and achieve end‐to‐end forecasting of the PDO index. The spatiotemporal features are recursive in the continuous forecasting of the PDO index on seasonal time scales, thus the cumulative error is largely reduced. During the test period of 39 years (1982–2020), our model can skillfully predict the PDO index up to 1 year, outperforming six methods used as benchmark. By contrast with physically‐based methods, DSEN can accurately predict the PDO index from a data‐driven perspective. Plain Language Summary: A deep spatiotemporal embedding network (DSEN) is proposed to forecast the Pacific decadal oscillation (PDO) index from historical climate data. The spatial information can be well extracted and embedded in the network. The cumulative error is reduced during the continuous forecasting process. In a comparative test using a data set for the years 1982–2020, the DSEN model can predict the PDO index for up to 12 months more accurately than state‐of‐the‐art methods. Key Points: A deep spatiotemporal embedding network (DSEN) is developed to continuously forecast the Pacific decadal oscillation (PDO) indexThe DSEN model can extract spatial features and reduce the cumulative error of the forecastThe DSEN model outperforms state‐of‐the‐art models at forecasting the PDO index for up to 12‐month lead [ABSTRACT FROM AUTHOR]

We considered various non‐uniformities such as branch faults, rotation of stress field directions, and changes in tectonic environments to simulate the dynamic rupture process of the 6 February 2023 Mw 7.8 Kahramanmaraş earthquake in SE Türkiye. We utilized near‐fault waveform data, GNSS static displacements, and surface rupture to constrain the dynamic model. The results indicate that the high initial stress accumulated in the Kahramanmaraş‐Çelikhan seismic gap leads to the successful triggering of the East Anatolian Fault (EAF) and the supershear rupture in the northeast segment. Due to the complexity of fault geometry, the rupture speed along the southeastern segment of the EAF varied repeatedly between supershear and subshear, which contributed to the unexpectedly strong ground motion. Furthermore, the triggering of the EAF reminds us to be aware of the risk of seismic gaps on major faults being triggered by secondary faults, which is crucial to prevent significant disasters. Plain Language Summary: On 6 February 2023, the south‐central Türkiye was hit by two major earthquakes with magnitudes of Mw 7.8 and Mw 7.6 respectively. Among them, the complex rupture process and unexpected ground motion of the Mw 7.8 event attracted the attention of seismologists. In this paper, the 3D dynamic rupture process of this mainshock is simulated based on complex multi‐fault system and heterogeneous initial stress. And the simulation results are in good agreement with the observations. Our results show that high initial stress is required for the EAF to be triggered. The supershear rupture occurred only in certain fault segments and is unable to sustain itself in a significant area on the fault due to the along‐strike variations in fault geometry and strength. More importantly, the dynamic model suggests that we must be alert to the risk of major fault being triggered by earthquakes on nearby small faults, especially when there are seismic gaps on the major fault. Key Points: The high initial stress accumulated in the seismic gap leads to the successful triggering of the East Anatolian FaultThe change of fault geometry in the southwest segment prevented the sustained supershear ruptureThe risk of earthquake nucleation on the secondary fault triggering the major fault rupture and the related disaster was highlighted [ABSTRACT FROM AUTHOR]

Groundwater mixing dynamics play a crucial role in the biogeochemical cycling of shallow wetlands. In this paper, we conducted groundwater simulations to investigate the combined effects of evaporation and local heterogeneity on mixing dynamics in shallow wetland sediments. The results show that evaporation causes groundwater and solutes to upwell from deep sediments to the surface. As the solute reaches the surface, evaporation enhances the accumulation of the solute near the surface, resulting in a higher solute concentration than in deep sediments. Mapping of flow topology reveals that local heterogeneity generates spatially varied mixing patterns mainly along preferential flow pathways. The upwelling of groundwater induced by surface evaporation through heterogeneous sediments is likely to create distinct mixing hotspots that differ spatially from those generated by lateral preferential flows driven by large‐scale hydraulic gradients, which enhances the overall mixing in the subsurface. These findings have strong implications for biogeochemical processing in wetlands. Plain Language Summary: In shallow wetlands, groundwater mixing and exchange have been identified as critical factors affecting biogeochemical cycling and transformation in sediments. Our results for the first time demonstrate evaporation causes a significant upwelling of groundwater and solutes from deep sediments to the surface. As the solute reaches the surface, evaporation enhances the accumulation of the solute near the surface, resulting in a higher solute concentration than in deep sediments. Mapping of flow topology, including the Okubo‐Weiss parameter and dilution index, reveals that evaporation and local heterogeneity generates dynamic mixing patterns along preferential flow pathways. Such mixing mechanisms would strongly affect biogeochemical conditions in near‐surface sediments of shallow wetlands, which have strong implications for wetland ecosystems. Key Points: Evaporation causes groundwater and solutes to upwell from deep sediments to the surface, resulting in near‐surface solute accumulationHeterogeneity causes strain‐dominated and vorticity‐dominated flow regions to coexist at small spatial scales along preferential flow pathsUpwelling groundwater creates distinct mixing hotspots that differ spatially from those generated by large‐scale hydraulic gradients [ABSTRACT FROM AUTHOR]

This paper analyzes the effect of the Australian High (AH) on the seasonal phase locking of Indian Ocean Dipole (IOD) events. The anomalous strong AH associated with the positive phase of the Antarctic Oscillation can cause significant easterly wind anomalies and northward cross‐equatorial flow over the western Maritime Continent (MC) by strengthening the Australian winter monsoon during May–August. The AH‐associated easterly anomalies and northward cross‐equatorial flow can create thermodynamic air‐sea feedback and contribute to a significant cooling anomaly in the western MC and the tropical eastern Indian Ocean. Without considering the effect of ENSO, these processes contribute to the occurrence of positive IOD events, which begin in early summer, peak in late summer, and decay rapidly thereafter. The effect of ENSO can extend the peak period of IOD into the boreal autumn of that year. An anomalous weak AH corresponds to the occurrence and seasonal phase locking of negative IOD events. Through combined empirical orthogonal function analysis, we find that the effect of the AH can well explain the seasonal phase locking of 34 IOD events (40 in total), which provides an important theoretical basis for the prediction of IOD events. Plain Language Summary: Seasonal phase locking is a critical characteristic of typical Indian Ocean Dipole (IOD) events. The IOD usually develops in boreal summer, peaks in autumn, and decays rapidly in winter. Note that the Australian High (AH) plays a key role on the seasonal phase locking of IOD events. It is found that The anomalous strong AH associated with the positive phase of the Antarctic Oscillation (AAO) can cause significant easterly wind anomalies and northward cross‐equatorial flow over the western Maritime Continent by strengthening the Australian winter monsoon during May–August. Key Points: Investigate the effect of Australian High (AH) the on the seasonal phase locking of Indian Ocean Dipole eventsThe Antarctic Oscillation can strengthen AH and Australian winter monsoonThe AH induced easterlies and cross‐equatorial flow contribute to a significant cooling anomaly in the tropical eastern Indian Ocean [ABSTRACT FROM AUTHOR]

Interactions between whistler mode chorus waves and electrons are a dominant mechanism for particle acceleration and loss in the outer radiation belt. One form of this loss is electron microburst precipitation: a sub‐second intense burst of electrons. Despite previous investigations, details regarding the microburst‐chorus scattering mechanism—such as dominant resonance harmonic—are largely unconstrained. One way to observationally probe this is via the time‐of‐flight energy dispersion. If a single cyclotron resonance is dominant, then higher energy electrons will resonate at higher magnetic latitudes: sometimes resulting in an inverse time‐of‐flight dispersion with lower‐energy electrons leading. Here we present a clear example of this phenomena, observed by a FIREBIRD‐II CubeSat on 27 August 2015, that shows good agreement with the Miyoshi‐Saito time‐of‐flight model. When constrained by this observation, the Miyoshi‐Saito model predicts that a relatively narrowband chorus wave with a ∼0.2 of the equatorial electron gyrofrequency scattered the microburst. Plain Language Summary: Wave‐particle interactions are a ubiquitous phenomenon in plasmas. Around Earth, interactions between electrons and a plasma wave termed whistler mode chorus leads to both the acceleration of the outer Van Allen radiation belt electrons, and rapid precipitation of electrons into Earth's atmosphere. One form of this precipitation is called electron microbursts: a sub‐second and intense bursts of electrons most often observed by high altitude balloons and low Earth orbiting satellites. While microbursts have been studied since the dawn of the Space Age, fundamental details regarding how they are generated are largely unknown. One clue to the properties of the scattering mechanism comes from energy‐dependent time‐of‐flight dispersion signatures. Electrons with a larger kinetic energy move faster, and will therefore precipitate before the electrons with lower kinetic energy. However, in this paper we show observations made by the FIREBIRD‐II CubeSat mission of the opposite: lower‐energy electrons arriving first. This counter‐intuitive phenomena, termed inverse time‐of‐flight energy dispersion, together with models, is a powerful tool to sense the detailed nature of how plasma waves scatter electrons in Earth's near space environment. Key Points: FIREBIRD‐II observed a microburst whose 250 keV electrons arrived before the 650 keV electronsWe estimate that the observed inverse energy dispersion of 0.1 ms/keV is statistically significantOur observations are consistent with the inverse time‐of‐flight model of chorus waves resonating with 100s keV electrons [ABSTRACT FROM AUTHOR]

We report results from a self‐consistent global simulation model in which a large‐scale equatorial plasma bubble (EPB) forms during a midnight temperature maximum (MTM). The global model comprises the ionospheric code SAMI3 and the atmosphere/thermosphere code WACCM‐X. We consider solar minimum conditions for the month of August. We show that an EPB forms during an MTM in the Pacific sector and is caused by equatorward neutral wind flows. Although this is consistent with the theoretical result that a meridional neutral wind (V) with a negative gradient (∂V/∂θ < 0) is a destabilizing influence [Huba & Krall, 2013, https://doi.org/10.1002/grl.50292] (where a northward meridional neutral wind V is positive and θ is the latitude and increases in the northward direction), we find that the primary cause of the EPB is the large decrease in the Pedersen conductance caused by the equatorward winds. Plain Language Summary: The equatorial ionosphere often develops electron density irregularities at night in the altitude range 300–1,000 km. This phenomenon is known as equatorial spread F. A leading candidate to explain the generation of these irregularities is the generalized Rayleigh‐Taylor instability (GRTI). The phenomenon usually occurs after sunset but under certain conditions it can occur around midnight. In this paper, using the coupled ionosphere/thermosphere model SAMI3/WACCM‐X, we show that it can occur during a midnight temperature maximum where the neutral thermosphere temperature increases near the equator. This is associated with equatorward neutral wind flows that change the conductance of the ionosphere and leads to an increase in the growth rate of the GRTI and the development of a large equatorial plasma bubble. Key Points: An equatorial plasma bubble can develop during a midnight temperature maximum in the ionosphereEquatorward winds reduce the Pedersen conductance that enhances the growth rate of the generalized Rayleigh‐Taylor instabilityThe results are based on the coupled ionosphere/thermosphere model SAMI3/WACCM‐X [ABSTRACT FROM AUTHOR]

Wintertime precipitation, especially snowstorms, significantly impacts people's lives. However, the current forecast skill of wintertime precipitation is still low. Based on data augmentation (DA) and deep learning, we propose a DABU‐Net which improves the Global Forecast System wintertime precipitation forecast over southeastern China. We build three independent models for the forecast lead times of 24, 48, and 72 hr, respectively. After using DABU‐Net, the mean Root Mean Squared Errors (RMSEs) of the wintertime precipitation at the three lead times are reduced by 19.08%, 25.00%, and 22.37%, respectively. The threat scores (TS) are all significantly increased at the thresholds of 1, 5, 10, 15, and 20 mm day−1 for the three lead times. During heavy precipitation days, the RMSEs are decreased by 14% and TS are increased by 7% at the lead times within 48 hr. Therefore, combining DA and deep learning has great prospects in precipitation forecasting. Plain Language Summary: In this paper, we propose a deep learning‐based method to improve the forecast performance of Global Forecast System wintertime precipitation over southeastern China. Due to the imbalanced distribution of precipitation data, we use data from the three other seasons as an augmented data set for wintertime precipitation to train the deep neural network. The results show that the method can reduce the Root Mean Squared Error and improve the TS, a metric of precipitation forecast performance, of the precipitation. In particular, TS at the threshold of 20 mm day−1 are increased by 69.23%, 90.00%, and 100.00% at lead times of 24, 48, and 72 hr. The proposed method performs well during heavy precipitation days at lead times within 48 hr. Combining data augmentation with deep learning provides a successful approach to predicting precipitation. Key Points: A deep learning model based on data augmentation (DA) is proposed to improve the Global Forecast System wintertime precipitation forecastThe deep learning model improves the heavy precipitation forecast at lead times within 48 hrDA plays a critical role in the heavy precipitation forecast [ABSTRACT FROM AUTHOR]

Large‐scale seepage‐faces occur on small‐slope tidal flats. All previous studies assume that the seepage‐face has only one single exit point. Here we show via numerical simulations of tidally‐influenced groundwater flow that, in a two‐dimensional vertical, homogeneous transect of a tidal flat with gentle beach slope of 1‰, multiple seepage‐faces may occur with at most four unsaturated beach surface segments which separate four seepage‐faces. Salinity‐variation induced density‐dependent flow leads to this complex phenomenon. While the seepage‐faces are the groundwater discharging zones on the beach surface, the unsaturated zones are the recharging zones. The whole aquifer beneath the tidal flat is almost occupied by seawater and forms a wall blocking the horizontal seaward discharge of inland fresh groundwater so that inland freshwater discharges mainly occur near the high tide mark. This is in great contrast with the traditional results that inland freshwater discharge occurs mainly near low tide mark. Plain Language Summary: Tidal flat with very gentle‐slopes distributes extensively around the world, for example, the coastline of Bohai, the Yellow Sea of China, and Willapa bay of USA. Due to small slopes, the intertidal zone can be as wide as several kilometers, leading to large‐scale seepage‐faces (saturated beach surface with groundwater efflux) during ebbing and low tides. All previous studies assume that the seepage‐face has only at most one segment, the upper end of which is the exit point of water table and the other end is the intersection point of seawater and beach surface. Here, we found that in a tidal flat with gentle beach slope of 1‰, multiple seepage‐faces may occur with at most 4 unsaturated beach surface segments which separate 4 seepage‐faces during low and rising tides. The locations of these seepage‐faces and adjacent unsaturated zones are quite dynamic due to the complex, dynamic density‐dependent groundwater flow in the aquifer beneath the tidal flat. Seepage‐faces are kind of complex and important boundary for coastal groundwater flow in order to accurately model the groundwater flow and solute transport in intertidal aquifers, the complex nonlinear boundary conditions on the seepage‐faces should be strictly and accurately implemented. This paper made such an attempt. Key Points: Tidal groundwater flow with strict and explicit seepage‐face boundary conditions were numerically simulatedMultiple seepage‐faces were first found to develop on gentle tidal flat with slope around 1‰Multiple seepage‐faces imply multiple local density‐dependent groundwater‐seawater re‐circulations [ABSTRACT FROM AUTHOR]

Extricating histories of uplift and erosion from landscapes is crucial for many branches of the Earth sciences. An objective way to calculate such histories is to identify calibrated models that minimize misfit between observations (e.g., topography) and predictions (e.g., synthetic landscapes). In the presence of natural or computational noise, widely used Euclidean measures of similarity can have complicated objective functions, obscuring the search for optimal models. Instead, we introduce the Wasserstein distance as a means to measure misfit between observed and theoretical landscapes. Our results come in two parts. First, we show that this approach can generate much smoother objective functions than Euclidean measures, simplifying the search for optimal models. Second, we show how locations and amplitudes of uplift can be accurately recovered from synthetic landscapes even when seeded with different noisy initial conditions. We suggest that this approach holds promise for inverting real landscapes for their histories. Plain Language Summary: The shapes of Earth's landscapes tell us about how they were formed by processes like tectonic uplift and erosion. Mathematical models are used to predict how landscapes change over time due to these processes. However, identifying models that produce theoretical landscapes that resemble reality can be challenging. One way to do so is by comparing model predictions to actual landscapes we observe. To make this comparison, we need a way to measure how similar or different predicted and observed landscapes are. One common approach is to compare heights of land from both cases. However, this method can struggle because a small shift in the position of a theoretical valley, say, can dramatically change the outcome of a comparison. In this paper, we introduce an alternative approach that uses a metric called the Wasserstein distance from the field of "Optimal Transport." The Wasserstein distance is a measure of how different two probability distributions are from each other by considering how much "work" is needed to transform one distribution into the other. We show that this metric is effective for finding models to understand how landscapes were shaped by uplift over time. Key Points: The use of the Wasserstein distance for identifying optimal landscape evolution models is demonstratedThis approach can produce simple objective functions, simplifying the search for models that minimize data misfitAccurate amplitudes and locations of uplift can be retrieved from synthetic landscapes generated using different initial conditions [ABSTRACT FROM AUTHOR]

In this paper, we present the first high‐speed video observation of a cloud‐to‐ground lightning flash and its associated downward‐directed Terrestrial Gamma‐ray Flash (TGF). The optical emission of the event was observed by a high‐speed video camera running at 40,000 frames per second in conjunction with the Telescope Array Surface Detector, Lightning Mapping Array, interferometer, electric‐field fast antenna, and the National Lightning Detection Network. The cloud‐to‐ground flash associated with the observed TGF was formed by a fast downward leader followed by a very intense return stroke peak current of −154 kA. The TGF occurred while the downward leader was below cloud base, and even when it was halfway in its propagation to ground. The suite of gamma‐ray and lightning instruments, timing resolution, and source proximity offer us detailed information and therefore a unique look at the TGF phenomena. Plain Language Summary: This study provides the very first simultaneous observations of a downward‐directed terrestrial gamma‐ray flash (TGF) together with its associated cloud‐to‐ground lightning flash using a high‐speed camera in addition to gamma‐ray and radio measurements. The camera, running at 40,000 frames per second, allowed us to check the characteristics of the downward leader, the development stage of the lightning flash, and the luminosity variations in coincidence with TGF production. Key Points: Simultaneous recordings of a downward‐directed terrestrial gamma‐ray flash (TGF), high‐speed video images, and radio emissionsTGF events occurred while the leader was already branching below cloud base and even when it was halfway in its propagation to groundEnergetic downward‐directed TGFs were associated with fast downward leaders that produced high return stroke peak currents [ABSTRACT FROM AUTHOR]

The low‐latitude ionosphere is a dynamic region with a wide range of disturbances in temporal and spatial scales. The Giant Metrewave Radio Telescope (GMRT) situated in the low‐latitude region has demonstrated its ability to detect various ionospheric phenomena. It can detect total electron content (TEC) variation with precision of 10−3 TECU and also can measure TEC gradient with an accuracy of about 7 × 10−4 TECU km−1. This paper describes the spectral analysis of previously calculated TEC gradient measurements and validates them by comparing their properties using two bands. The analysis tracked individual waves associated with medium‐scale traveling ionospheric disturbances (MSTIDs) and smaller waves down to wavelengths of ∼10 km. The ionosphere is found to have unanticipated changes during sunrise hours, with waves changed propagation direction as the sun approached the zenith. Equatorial spread F disturbances during sunrise hours is observed, along with smaller structures moving in the same direction. Plain Language Summary: The Earth's ionosphere can limit exploring sub‐GHz frequencies of the sky and introduces an extra phase term that is difficult to calibrate. The same calibration data can be used to study the Earth's ionosphere more precisely than conventional probes. Radio interferometry is a technique for studying astronomical sources and Earth's ionosphere by measuring the spatial coherence function of multiple elements. The GMRT is a unique instrument for exploring the equatorial ionosphere region. This study used dual‐band observations of a bright radio source with the GMRT to explore the Equatorial Ionization Anomaly region. The GMRT can detect variations in total electron content and measure TEC gradient with high accuracy. Spectral analysis was performed on TEC gradient measurements to track individual waves associated with medium scales traveling ionospheric disturbances and smaller waves up to wavelengths of about ∼10 km. The results showed unexpected changes in the ionosphere during sunrise hours and observed large plasma irregularities and smaller structures moving in the same direction. Key Points: Giant Metrewave Radio Telescope (GMRT) can demonstrate an order of magnitude better sensitivity than GNSS‐based TEC measurements in characterizing ionospheric fluctuationsThe spectral analysis technique used with GMRT can detect multiple MSTIDs and smaller‐scale structures simultaneouslyGMRT can detect ionospheric variations as small as 10 km. The study also showed waves changing direction unexpectedly during sunrise time [ABSTRACT FROM AUTHOR]

We investigate the behavior of subaqueous barchans reaching dune‐size obstacles by carrying out experiments where we varied the obstacle shape and size, the flow strength, and the grains' properties. We found that a subaqueous barchan can pass over or bypass a dune‐size obstacle, or even be blocked, with some intermediate situations. In the bypass cases, the original barchan can split in two or more bedforms, redistributing sand in space. Finally, we propose a classification map in which the barchan behavior depends basically on two dimensionless parameters. Our results represent a step toward understanding how barchans behave in the presence of large obstacles, such as retaining walls, tubes and bridge pillars. Plain Language Summary: This paper is devoted to crescent‐shaped dunes, known as barchans, that are found on Earth, Mars and other celestial bodies, with roughly the same morphology but different scales. In some cases, barchans can approach an obstacle of comparable size, such as houses and buildings in the aeolian case, and bridge pillars and submarine structures in the aquatic case. In order to investigate that, we carried out experiments in a water channel where granular heaps developed into barchans that approached obstacles of different shape and size. We found that barchans can be blocked, bypass or pass over dune‐size obstacles, and that bypassing barchans can split in two or more bedforms, which means a significant redistribution of sand in space. Based on the experiments, we propose a classification map in which the barchan behavior depends on two dimensionless parameters. Our results shed light on how barchans behave in the presence of large obstacles, helping us to predict the outcomes of dunes interacting with objects in other environments, and design safer and eco‐friendly structures. Key Points: We show that subaqueous barchans can be blocked, bypass, or pass over dune‐size obstaclesIn some cases, barchans can split in two or more bedformsWe propose that the barchan behavior depends basically on two dimensionless parameters [ABSTRACT FROM AUTHOR]

In this study, we obtained the first leading mode and principal component 1 (PC1) of North Pacific sea surface temperature (SST). The PC1‐related SST anomalies, located relatively north/south, are referred to as North/South PC1 events. Model outputs, observations, reanalysis datasets and sensitivity experiments show that during the North PC1 events, an enhanced Aleutian low occurs and is located relatively north, favoring anomalous southerlies over western North America. The anomalous southerlies induce a strong warming anomaly over North America via warm advection of the anomalous southerlies and temperature advection of the climatological westerlies over North America. However, the Aleutian low anomaly and corresponding southerly anomaly associated with South PC1 events shift southward, favoring weakened effects of South PC1 events on atmospheric circulations and surface temperatures over North America. The meridional position of PC1 events deserves to be considered in the studies of the PC1 and its related climate changes. Plain Language Summary: Understanding of surface temperature variations is important since it largely affects human and society. This paper categorizes the North Pacific sea surface temperature anomaly events, which are associated with the first leading mode of North Pacific sea surface temperature, into North and South events according to their meridional positions. Using model outputs, observations, reanalysis datasets and sensitivity experiments, we found that the surface temperature anomalies over North America during the North events are quite different from those during the South events. During the North events, an enhanced Aleutian low occurs over high‐latitude North Pacific. The enhanced Aleutian low tends to induce anomalous southerlies over western North America. The anomalous southerlies favor warming anomalies over North America via the warm advection of anomalous southerlies and temperature advection of climatological westerly. However, the Aleutian low anomaly and meridional wind anomaly during the South events shift southward, leading to weakened effects of the South events on atmospheric circulations and surface temperatures over North America. Key Points: North American warming anomaly occurs during North Pacific sea surface temperature anomaly events located northThe warming anomaly is related to an enhanced Aleutian low anomaly located north and climatological westerlyDuring the events located south, North American surface temperature responses are weak due to a southward‐shift Aleutian low anomaly [ABSTRACT FROM AUTHOR]