Search

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Precise and timely rainfall nowcasting plays a critical role in ensuring public safety amid disasters triggered by heavy precipitation. While deep‐learning models have exhibited superior performance over traditional nowcasting methods in recent years, their efficacy is still hampered by limited forecasting skill, insufficient training data, and escalating blurriness in forecasts. To address these challenges, we present the Synthetic‐data Task‐segmented Generative Model (STGM), an innovative physical‐dynamic‐driven heavy rainfall nowcasting model. The STGM encompasses three key components: the Long Video Generation (LVG) model generating synthetic radar data from observed radar images and data provided by the Weather Research and Forecasting (WRF) model, MaskPredNet predicting the spatial coverage of various rainfall intensities, and SPADE determining rainfall intensity based on the coverage provided by MaskPredNet. The STGM has demonstrated promising skill for precipitation forecasts for up to six hours, and significantly reduce the blurriness of predicted images, thus showcasing advances in rainfall nowcasting. Plain Language Summary: Deep‐learning methods have proven superior to traditional techniques in rainfall nowcasting, but current models still face limitations such as low accuracy, insufficient training data, and a brief effective forecast period. To address these challenges, we've developed the STGM, a novel deep‐learning‐based architecture for predicting heavy rainfall. The STGM shows excellent performance by using a new design that breaks tasks into smaller parts and relies on AI‐generated data. Our results indicate that it excels in predicting heavy rainfall for up to 6 hr, accurately tracking the spatial and temporal evolution of storm cells over extended periods. Moreover, it significantly improves the clarity of the produced images compared to commonly used baseline models. Key Points: Our novel STGM model outperforms common baseline models, showcasing high proficiency in predicting precipitation up to 6 hr aheadBy integrating physical data from numerical weather prediction models, the performance of the STGM model is significantly enhancedThe use of synthetic data provides a substantial boost to the predictive capabilities of the STGM model [ABSTRACT FROM AUTHOR]

The temperature of the subsurface water entrained into the surface mixed layer plays a key role in controlling the sea surface temperature (SST) and its interannual variability in the equatorial Pacific. In this paper, we combine a hyperbolic tangent function bounded by the warm pool SST and centered at the thermocline depth with a variable sharpness parameter to describe the time‐space evolutions of the subsurface temperature. Under simple approximations of the sharpness parameter, this concise expression becomes remarkably efficient in capturing the observed and climate‐model simulated subsurface temperature variability in terms of anomalies of the thermocline depth and SST of the El Niño‐Southern Oscillation (ENSO) phenomenon. The formulations for the subsurface temperature and thermocline sharpness developed in this work should be useful tools for evaluating and understanding the role of the thermocline feedback in ENSO behaviors in both theoretical and comprehensive climate models. Plain Language Summary: While significant advances have been made in our ability to understand, simulate, and predict the El Niño‐Southern Oscillation (ENSO), its remarkable complexity is still not well understood. The subsurface ocean temperature in the equatorial Pacific is known to play a key role in controlling sea surface temperature and its interannual variations. An accurate description of its relationship with thermocline depth variability is of essential importance to understanding ENSO's complex dynamics in mechanistic studies. In this paper, we develop a concise expression which captures the observed relationship between anomalies of the subsurface temperature and thermocline depth remarkably well. This expression should be useful for ENSO mechanistic model studies and diagnostic investigations into climate models' performances in their ENSO simulations. Key Points: The equatorial Pacific subsurface temperature is expressed as a hyperbolic tangent function of thermocline depth and sharpnessEffective parameterizations for the subsurface temperature are derived by simple approximations of the thermocline sharpnessThese parameterizations can be useful tools for evaluating the impacts of thermocline feedback on ENSO [ABSTRACT FROM AUTHOR]

We present preliminary results from the field program Organization of Tropical East Pacific Convection (OTREC), with measurements during August and September of 2019 using the NSF/NCAR Gulfstream V over the tropical East Pacific and Southwest Caribbean. We found that active convection in this region has predominantly bottom‐heavy vertical mass fluxes, while decaying systems exhibit top‐heavy fluxes characteristic of stratiform rain regions. As in other regions that have been studied, a strong anti‐correlation exists between the low to mid‐level moist convective instability and the column relative humidity or saturation fraction. Finally, the characteristics of convection as a function of latitude differ greatly between the Southwest Caribbean and Colombian Pacific coast on one hand, and the intertropical convergence zone to the west. In particular, the strongest convection in the former is to the south, while it is to the north in the latter, in spite of similar latitudinal sea surface temperature distributions. Plain Language Summary: Understanding and modeling the physics of tropical atmospheric convection still poses a big challenge. Things are complicated over the tropical oceans because there is no easy way to gather data. Field projects such as the one presented in this paper, Organization of Tropical East Pacific Convection (OTREC2019) are of great importance to our scientific community for this reason. During OTREC, 22 research flights were performed over East Pacific and Southwest Caribbean gathering data from 13 km to surface. This paper presents early results that will help us understand the physics of convection and improve our weather and climate models. Key Points: Thermodynamic parameters instability index and saturation fraction show anti‐correlation, as explained by moisture quasi‐equilibrium theoryVertical mass flux profiles are generally bottom heavy for developing convection and top heavy for decaying convectionStrong differences exist between convection in the East Pacific ITCZ and in the Caribbean and Pacific coast of Colombia [ABSTRACT FROM AUTHOR]

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

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

Continuous monitoring of the atmospheric scattering phase function P(θ) $P(\theta)$ is difficult to perform since most observational techniques are limited to daylight hours. Among known aerosol optical properties, only atmospheric optical depth is measured routinely during clear nights at a few ground stations. In this paper we develop theoretical and experimental techniques to retrieve the scattering phase function from radiometry of a laser beam whose light is scattered in the lower nocturnal atmosphere. The field experiment we conducted in a night environment demonstrates the capability of the method to determine P(θ) $P(\theta)$ in real‐world settings. We show that extracting the scattering phase function from radiance data is realizable over a wide range of angles, which makes possible the use of an analytical extrapolation to approximate P(θ) $P(\theta)$ across the full range of scattering angles. Plain Language Summary: In order to understand how light moves through the Earth's atmosphere, we must measure it in real‐world circumstances. Only a few metrics characterizing the optical properties of the atmosphere are routinely measured, and generally only during the daytime. We aimed to extend the ability to measure the atmosphere's optical properties to nighttime using simple light‐scattering physics and inexpensive, off‐the‐shelf equipment with low electric power requirements. We developed a method to probe conditions in the part of the atmosphere nearest the Earth's surface by observing how light from a green laser beam scatters from both air molecules and small particles suspended in the air called aerosols. By measuring how much laser light scatters in various directions, we can better understand the distribution of aerosols in the lower atmosphere over times ranging from hours to years. Combined with well‐established daytime measurements, our method enables continuous monitoring of aerosols during both day and night. The portability of the equipment we use makes this possible in naturally dark places and also in light‐polluted environments, and under both clear and cloudy conditions. Here we describe our method and show results from an experiment conducted under field conditions. Key Points: The scattering phase function of the nighttime atmosphere is derived from ground‐based radiometry of a laser beam directed toward the skyThe experiment is designed to be carried out in arbitrary settings with the use of a low‐power laser operated in the continuous regimeThe nighttime scattering patterns complement daytime observations, providing an overall picture of the atmospheric optics [ABSTRACT FROM AUTHOR]

The geomagnetic activity index Kp is widely used but is restricted by low time resolution (3‐hourly) and an upper limit. To address this, new geomagnetic activity indices, Hpo, are introduced. Similar to Kp, Hpo expresses the level of planetary geomagnetic activity in units of thirds (0o, 0+, 1−, 1o, 1+, 2−, ...) based on the magnitude of geomagnetic disturbances observed at subauroral observatories. Hpo has a higher time resolution than Kp. 30‐min (Hp30) and 60‐min (Hp60) indices are produced. The frequency distribution of Hpo is designed to be similar to that of Kp so that Hpo may be used as a higher time‐resolution alternative to Kp. Unlike Kp, which is capped at 9o, Hpo is an open‐ended index and thus can characterize severe geomagnetic storms more accurately. Hp30, Hp60 and corresponding linearly scaled ap30 and ap60 are available, in near real time, at the GFZ website (https://www.gfz-potsdam.de/en/hpo-index). Plain Language Summary: The geomagnetic activity index Kp is a measure of planetary geomagnetic activity, expressed in units of thirds (0o, 0+, 1−, 1o, 1+, 2−, ...9o). Kp is widely used in the space physics community, as it is known to be a good proxy of the solar‐wind energy input into the magnetosphere‐ionosphere‐thermosphere system. Kp has two important limitations. One is the temporal resolution. Kp is a three‐hourly index, so that temporal features within 3 hr are not resolved. The other is the upper limit of the index. Kp does not exceed a maximum value of 9o, so that under extremely disturbed conditions, geomagnetic activity is not accurately represented. We introduce a group of new geomagnetic activity indices Hpo that overcomes these limitations. Hpo is designed to represent planetary geomagnetic activity in a similar way as Kp but with higher temporal resolution and without the upper limit at 9o. This paper describes the production of 30‐min (Hp30) and 60‐min (Hp60) indices, and demonstrates their properties in comparison with Kp. Hpo indices since 1995, including near‐real‐time values, are distributed through the GFZ website (https://www.gfz-potsdam.de/en/hpo-index). Key Points: New Kp‐like planetary geomagnetic activity indices, Hpo, are presentedHourly (Hp60) and half‐hourly (Hp30) indices are available from GFZ websiteHpo indices are open‐ended without the upper limit at 9o [ABSTRACT FROM AUTHOR]

Ice shelves regulate the stability of marine ice sheets. We track fractures on Pine Island Glacier, a quickly accelerating glacier in West Antarctica that contributes more to sea level rise than any other glacier. Using an on‐ice seismic network deployed from 2012 to 2014, we catalog icequakes that dominantly consist of flexural gravity waves. Icequakes occur near the rift tip and in two distinct areas of the shear margin, and TerraSAR‐X imagery shows significant fracture in each source region. Rift‐tip icequakes increase with ice speed, linking rift fracture to glaciological stresses and/or localized thinning. Using a simple flexural gravity wave model, we deconvolve wave propagation effects to estimate icequake source durations of 19.5–50.0 s and transient loads of 3.8–14.0 kPa corresponding to 4.3–15.9 m of crevasse growth per icequake. These long‐source durations suggest that water flow may limit the rate of crevasse opening. Plain Language Summary: Large shelves of floating ice strengthen glaciers in Antarctica, helping to protect against rapid sea level rise that can occur when glaciers flow into the ocean. Ice shelves can collapse through rapid cracking (synonym of fracturing), but it is difficult to directly observe cracking on ice shelves. In this paper, we track cracks on Pine Island Glacier, an ice shelf in Antarctica that is particularly vulnerable to collapse. We see cracks in pictures taken by satellites. Cracking causes the ice shelf to shake up and down, which we record using the same equipment that records earthquakes. We record shaking located at a set of cracks at the side of the ice shelf and at the tip of a single massive crack called a rift. Rift cracking seems related to the speed that the ice shelf is flowing. We also use a computer simulation of shaking to learn about the details of the crack process. Our simulation suggests that the crack process might be more complicated than a single crack opening evenly at a constant rate. Key Points: Fracture at Pine Island Glacier generates flexural gravity waves, a wave type related to interaction between a floating plate and supporting fluidRift‐tip seismicity rate increases with ice speed either due to changes in the underlying ice shelf stress state or localized thinningRecorded flexural gravity waves are consistent with a point load of ∼10 kPa applied over ∼30s, corresponding to ∼10m of vertical cracking [ABSTRACT FROM AUTHOR]

In situ conjugate electromagnetic ion cyclotron (EMIC) waves observed by the Swarm mission in both hemispheres are presented. A complex and unusual pattern of Alfvénic EMIC wave energy is observed, with a mid‐latitude peak close to the source at L =3.3, as well as a secondary lower L‐peak. A wave propagation model reveals that the secondary peak at L =1.7 may be explained by wave power being redirected equatorward due to the Buchsbaum resonance, crossing and interfering with the same EMIC wave power propagating equatorwards from the opposite hemisphere. This interference creates a coherent equatorial driver for a low‐L field line resonance at the secondary peak, and which is associated with strong shear‐to‐fast mode coupling in the ionosphere. This behavior complicates the interpretation of low‐Earth orbit EMIC data for applications assessing radiation belt loss. Combined low Earth orbit observations and modeling enable these novel and localized magnetosphere‐ionosphere EMIC wave propagation pathways to be identified. Plain Language Summary: Electromagnetic ion cyclotron (EMIC) waves are important in near‐Earth space due to their role in reducing the amount of radiation in the Earth's radiation belts following geomagnetic storms. They are also often observed during non‐storm times. They are studied using satellites and ground observatories. Our paper reveals how these waves can follow complicated and previously unknown pathways to reach the upper atmosphere where they can be detected on the ground. This study shows a new and unusual effect where some EMIC wave energy is reflected and diverted toward the equator, where it meets its opposite‐hemisphere counterpart, interferes with it and sets up a resonance. This resonance then creates a new signal peak in the upper atmosphere at lower latitudes, far away from the location of the initial source. This presents a new and hitherto unseen pathway for wave energy to travel from their generation region in near‐Earth space down to the ionosphere. Understanding such pathways is very important for correctly diagnosing the location of these wave populations in space, and assessing their role in causing reductions in the levels of space radiation. Key Points: Electromagnetic ion cyclotron wave propagation from the magnetosphere to the ionosphere is complicated by reflection from the Buchsbaum resonance and interferenceWaves reflected from the Buchsbaum resonance interfere to generate a coherent driver for a secondary lower latitude field line resonanceThis generates a field‐guided secondary lower‐latitude peak associated with strong shear‐to‐fast mode energy conversion in the ionosphere [ABSTRACT FROM AUTHOR]

This paper reports that there has been a significant relationship between the quasi‐biennial oscillation (QBO) in zonal wind at 50 hPa in summer and precipitation in August in northern China since the late 1970s. The correlation coefficient between them reaches up to −0.61 during 1979–2018. Associated with the easterly (westerly) phase of the QBO, there is a meridional dipole pattern of zonal wind from the stratosphere to troposphere over the Northwest Pacific in August with the easterly (westerly) anomalies in 25–50°N and westerly (easterly) anomalies in 50–65°N. This meridional zonal‐wind dipole favors the strengthening (weakening) of the tropospheric Japan Sea high in the QBO easterly (westerly) phase, causing an increase (decrease) of the water vapor transportation from the Northwest Pacific to northern China and thus more (less) precipitation in these regions. The finding of this study has import implications for predicting the summer precipitation in northern China in the future. Plain Language Summary: The quasi‐biennial oscillation (QBO) is a periodic phenomenon in the tropical stratosphere. It manifested as an alternation of easterly and westerly winds, with an average period of roughly 28 months. It has great influences on the Earth's surface via different pathways. But the previous studies mainly focused on winter. In this study, we are interested in the QBO's impact on the summer precipitation in Asia‐Pacific region. We find that the QBO does have a remarkable relationship with the August precipitation in northern China since the late 1970s. When the QBO is in its easterly phase, it can induce an easterly wind in 25–50°N and a westerly wind in 50–65°N over the Northwest Pacific from the lower stratosphere to lower troposphere, and causes a higher‐than‐normal high pressure over the Sea of Japan, which favors excessive rainfall to its west. Our study provides a direct evidence for the QBO's impact on the Earth's surface in summer. Meanwhile, it also provides potential ideas and methods for predicting the summer precipitation in northern China in the future. Key Points: The quasi‐biennial oscillation (QBO) at 50 hPa has a significantly negative correlation with summer precipitation in northern China since the late 1970sThe QBO can induce a meridional zonal‐wind dipole over the Northwest Pacific that extends from surface into the stratosphereThe enhanced Japan Sea high excited by the meridional zonal‐wind dipole in easterly QBO phase causes more precipitation in northern China [ABSTRACT FROM AUTHOR]

The eruption of the Hunga Tonga‐Hunga Ha'apai volcano on 15 January 2022 triggered atmospheric waves at all altitudes. The National Aeronautics and Space Administration Ionospheric Connection Explorer (ICON) and European Space Agency Swarm satellites were well placed to observe its impact on the ionospheric wind dynamo. After the Lamb wave entered the dayside, Swarm A observed an eastward and then westward equatorial electrojet (EEJ) on two consecutive orbits, each with magnitudes exceeding the 99.9th percentile of typically observed values. ICON simultaneously observed the neutral wind (90–300 km altitude) at approximately the same distance from Tonga. The observed neutral winds were also extreme (>99.9th percentile at some altitudes). The covariation of EEJ and winds is consistent with recent theoretical and observational results, indicating that the westward electrojet is driven by strong westward winds in the Pedersen region (∼120–150 km). These observations imply that the dynamo is a key mechanism in the ionospheric response to the Tonga disturbance. Plain Language Summary: The January 2022 Tonga volcanic eruption caused atmospheric impacts around the world. As a natural experiment, it can be used to test our understanding of how the lower atmosphere affects space weather. Researchers are only beginning to document the chain of events post‐eruption, and this paper focuses on its impact on the generator that drives electric fields in near‐Earth space, a key part of space weather. This generator is driven by the atmosphere pushing charged particles across Earth's magnetic field. This usually creates a strong eastward current above the equator. When the Swarm A satellite coincided with the wave from Tonga, it observed that this current strengthened dramatically, then reversed. Although reversals are not unusual, this was the strongest reversal observed by Swarm since its 2013 launch, except for one large geomagnetic storm in 2015. Another satellite, the Ionospheric Connection Explorer, was luckily at the right time and place to observe related motions of the upper atmosphere, which were similarly extreme. These observations are shown to be consistent with our theoretical understanding of the generator. This study is important because it represents a critical test of atmosphere‐space interactions and implies that the Tonga eruption caused a major space weather event. Key Points: Extreme thermospheric winds and ionospheric currents were observed in coordinated space/ground‐based measurements, 10 hours post‐eruptionThe westward electrojet current when the Lamb wave reaches the dayside is consistent with recent studies of the wind‐driven electrojetObservations of linked dynamo processes provide direct evidence of the space‐weather impacts of acute lower atmospheric forcing [ABSTRACT FROM AUTHOR]

We report observations of reconnection exhausts in the Heliospheric Current Sheet (HCS) during Parker Solar Probe Encounters 08 and 07, at 16 Rs and 20 Rs, respectively. Heliospheric current sheet (HCS) reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ∼3, due to the Alfvén speed being comparable to the solar wind flow speed at these near‐Sun distances. Furthermore, protons were energized to super‐thermal energies. During E08, energized protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field‐aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was not the local HCS reconnection exhaust. Plain Language Summary: Magnetic reconnection in current sheets is a universal plasma process that converts magnetic energy into particle energy. The process is important in many laboratory, solar, and astrophysical plasmas. The heliospheric current sheet (HCS), which originates from the Sun and extends throughout the heliosphere, is the largest current sheet in the solar system. One of the surprises of the Parker Solar Probe mission is the finding that magnetic reconnection is almost always active in the near‐Sun HCS, despite its enormous scales. In this paper, we report direct evidence showing that reconnection in the HCS close to the Sun can be a source of energetic protons observed in the solar wind. The reason protons can be accelerated to high energies (to tens of kilo‐electronvolts) is because the available magnetic energy per particle is high close to the Sun. This finding is important because the source of energetic protons in the heliosphere is unknown. Key Points: Large available magnetic energy per particle led to significant proton acceleration by reconnection in the near‐Sun heliospheric current sheet (HCS) at 16 and 20 RsProton beams and strahl electron dropouts in separatrices are evidence for HCS being a source of energetic protons seen outside the HCSEnergetic protons beams outside the HCS also exist without strahl electron dropouts. Their origin is unlikely to be the local HCS exhaust [ABSTRACT FROM AUTHOR]

The most important parameter driving the solar wind‐magnetosphere interaction is the southward (Bz) component of the interplanetary magnetic field (IMF). While the dawn‐dusk (By) component of the IMF is also known to play an important role, its effects are usually assumed to be independent of its sign. Here we demonstrate for the first time a seasonally varying, explicit IMF By‐dependence of the ring current and Dst index. Using satellite observations and a global magnetohydrodynamic model coupled with a ring current model, we show that for a fixed level of solar wind driving the flux of energetic magnetospheric protons and the growth‐rate of the ring current are greater for By < 0 (By > 0) than for By > 0 (By < 0) in Northern Hemisphere summer (winter). While the physical mechanism of this explicit By‐effect is not yet fully understood, our results suggest that IMF By modulates magnetospheric convection and plasma transport in the inner magnetosphere. Plain Language Summary: The magnetic field carried by solar wind is the most important driver of space weather. Aurora and other phenomena in the near‐Earth space are known to be stronger when the magnetic field on solar wind points to south than north. Usually the space weather response is expected to be equally strong for eastward and westward magnetic fields in solar wind. In this paper show that this is not the case. Using satellite measurements and computer modeling we show that electric currents in the near‐Earth space are stronger for westward than eastward magnetic field in solar wind in northern hemisphere summer, while the opposite is true in northern hemisphere winter. More studies are needed for understanding the physical mechanism of this phenomenon. Key Points: We show for the first time that there is an explicit By‐dependence in the ring current/proton precipitation and in the inner magnetosphereDuring Northern Hemisphere summer (winter) the ring current fluxes/proton precipitation and the rate of change of the Dst index are stronger for By < 0 (By > 0)The By‐dependence of the ring current and energetic proton fluxes is reproduced by a global coupled MHD‐ring current model [ABSTRACT FROM AUTHOR]

Ocean circulation receives its energy input at basin scales while dissipates at microscopic mixing scale. How this energy is transferred across different lengthscales is of paramount importance for understanding the ocean circulation equilibration and variability. Advancement in high‐resolution numerical simulations in recent years has significantly improved our understanding of kinetic energy (KE) cascades from basin to kilometer scales, although observational evidence to verify the simulated processes remains limited. Using repeat ship‐board velocity measurements along 165°E across the equatorial, subtropical and subarctic Pacific Ocean, we show that the length scale separating the inverse and forward cascades, LS, falls in the 8 ∼ 300 km range and it does not scale straightforwardly with the baroclinic deformation radius. Balanced and unbalanced oceanic motions co‐exist in this range but contribute oppositely to the directional energy cascades. LS is observed to depend on the relative strengths of these motions, as well as by their interaction. Plain Language Summary: This paper investigates how nonlinear interactions in the turbulent upper ocean transport kinetic energy (KE) across different spatial scales. This investigation is important because the energy input that drives the ocean circulation has scales at tens of thousand kilometers, whereas the oceanic mixing and dissipation take place below the centimeter scales. How oceanic KE is transported from one scale to another is neither fully understood nor adequately observed, and this is particularly true in the oceanic meso‐submesoscales in the 1 ∼ 300 km range. By using repeat shipboard Acoustic Doppler Current Profiler surveys from 2004 to 2020 in the western Pacific Ocean, we examined the cross‐scale KE transfers in dynamically different regimes of tropics, subtropics and high latitudes. We found that the KE can transfer both up‐scales and down‐scales due to the co‐existence of balanced geostrophic motions and unbalanced wave motions. The length scale that separates the bi‐directional KE transfers is geographically dependent. It is controlled by the relative strengths of co‐existing balanced and unbalanced motions, as well as by how the unbalanced wave motions are dynamically generated. Key Points: Nonlinear interaction in upper ocean transfers kinetic energy both up‐ and down‐scalesUpper ocean balance and unbalanced motions contribute oppositely to energy cascadeBi‐directional energy cascade depends on relative importance of balanced versus unbalanced motions and characteristics of the unbalanced motions [ABSTRACT FROM AUTHOR]

The major eruption of volcano Hunga Tonga‐Hunga Ha'apai in Tonga on 15 January 2022 generated atmospheric Lamb waves that propagated over the world. This seemed the first volcanic Lamb wave event that was clearly captured by the state‐of‐the‐art geostationary meteorological satellites. This paper provides visualization of the waves using thermal infrared images from geostationary satellite Himawari‐8. The second time derivatives of 10‐min interval images clearly illustrated the waves propagating at about 310 m s−1. The waves could be tracked for more than a week while they propagated five times round the earth. Automated wavefront identification illustrated nonuniform propagation speed. The signals in the satellite images well matched the surface pressure observations in Japan. Plain Language Summary: The major eruption of volcano Hunga Tonga‐Hunga Ha'apai in Tonga on 15 January 2022 generated atmospheric pressure pulses that propagated over the world. This seemed the first event that was clearly captured by the state‐of‐the‐art geostationary meteorological satellites, such as Himawari‐8. Taking the time difference of Himawari‐8's 10‐min interval images twice, the waves that propagated at about 310 m s−1 could be tracked for more than a week while they propagated five times round the earth. This was not possible with the previous‐generation geostationary meteorological satellites. Visualized waves also illustrated how the propagation speed changes in space and time. The signals in the satellite images well matched the surface pressure observations in Japan. Key Points: Lamb waves from an eruption were clearly visualized by the second time derivative of satellite infrared images every 10 minThe waves could be tracked for more than a week while they propagated at least five times round the earth at a speed of about 310 m s−1The signals in the satellite images matched the surface pressure changes quantitatively [ABSTRACT FROM AUTHOR]

Extremely persistent heavy rainfall (EPHR) events frequently occur in southern China. The mechanisms underlying their generation and development are not well understood, and this leads to difficulties in accurately forecasting these events. In this paper, hourly precipitation grid data and ERA‐5 reanalysis data are used to examine the relationships between precipitation, ageostrophic winds, and low‐level jets (LLJ). The results suggest that ageostrophic winds in the boundary layer mainly exhibit confrontational and asymptotic convergence, with the former being accompanied by double LLJ, which transport more vapor and provide favorable uplift conditions, thus producing stronger precipitation and wider rainbands. The different cooperated relationships between LLJ and ageostrophic winds play an important role in the development of EPHR events, and greater account needs to be taken of these relationships when forecasting. Plain Language Summary: Coastal extremely persistent heavy rainfall (EPHR), long‐duration heavy rainfall in local coastal area, occurs frequently in Southern China, and this kind of rainfall is usually accompanied by southwesterly in the lower atmosphere, which we call as the southwest low‐level jet. Generally, the occurrence and development of rainfall is accompanied by the convergence of the lower air flow. Since the divergence of the geostrophic wind component of the wind field is zero, the convergence situation is characterized by the ageostrophic wind component, which doesn't satisfy the geostrophic balance. In this type of coastal EPHR accompanied by the Southwest Jet, the ageostrophic wind is mainly manifested in two different convergence situations. One is that the ageostrophic wind presents several opposite branches of directions presenting a confrontational pattern around the rainfall area, and the other is an asymptotic convergence in which two similar wind directions, such as northeasterly and southeasterly, gradually converge to the rain area. The former has stronger lower‐level uplift, greater precipitation and wider rain bands, while the latter is relatively weak. This is an interesting phenomenon, of which the specific mechanisms need to be further studied. Key Points: About 74% of extremely persistent heavy rainfall cases along the coast of southern China are accompanied by southwest jets in the marine boundary layerAgeostrophic winds mainly exhibit confrontational and asymptotic convergence, and the former is accompanied by double low‐level jetsCases of ageostrophic winds with confrontational convergence have stronger precipitation and wider rainband [ABSTRACT FROM AUTHOR]

This paper investigates intense energy conversion events (IECEs) at the dayside magnetopause boundary layer (MBL) using high‐resolution data from the Magnetospheric Multiscale (MMS) spacecraft. Most events were detected by MMS in a duration less than 0.5 s, corresponding to a thickness below one ion inertia length. About three‐quarters of the events occurred in local reconnecting current sheets. Interestingly, there are more electron‐only reconnections than standard reconnections. Most of the reconnection IECEs are within the exhaust of the primary reconnection and the Kelvin‐Helmholtz vortices, suggesting that secondary reconnections are important building blocks for the overall energy conversion at the magnetopause. The nonreconnection events are also primarily within the reconnection exhaust and the Kelvin‐Helmholtz vortices, highlighting the importance of reconnection and Kelvin‐Helmholtz instability in regulating the energy conversion at the MBL. Plain Language Summary: Solar wind‐magnetosphere coupling is one of the long‐standing questions in magnetosphere physics. Part of the input energy from the solar wind is converted and dissipated at the magnetopause boundary layer. Identifying where does energy conversion occurs is valuable for understanding the solar wind‐magnetosphere coupling. Here we picked up hundreds of intense energy conversion events using high precision data from Magnetospheric Multiscale at the magnetopause boundary layer to study their locations and fundamental properties. It is found that most events are associated with magnetic reconnection and are more likely located in the reconnection exhaust and Kelvin‐Helmholtz vortices. An interesting finding is that most of these intense energy conversion events are associated with reconnection in which only electrons participate, that is, without ion coupling. Key Points: Hundreds of intense energy conversion events are examined at the dayside magnetopauseThere are more electron‐only reconnections than standard reconnections in these eventsThe exhaust of the primary reconnection and Kelvin‐Helmholtz vortices are two essential regions hosting the intense energy conversion [ABSTRACT FROM AUTHOR]

The global ocean overturning circulation, critically dependent on the global density stratification, plays a central role in regulating climate evolution. While it is well known that the global stratification profile exhibits a strong dependence to Southern Ocean dynamics and in particular to wind and buoyancy forcing, we demonstrate here that the stratification is also acutely sensitive to the mesoscale eddy energy dissipation timescale. Within the context of a global ocean circulation model with an energy constrained mesoscale eddy parameterization, it is shown that modest variations in the eddy energy dissipation timescale lead to significant variations in key metrics relating to ocean circulation, namely the Antarctic Circumpolar Current transport, Atlantic Meridional Overturning Circulation strength, and global ocean heat content, over long timescales. The results highlight a need to constrain uncertainties associated with eddy energy dissipation for climate model projections over centennial timescales and also for paleoclimate simulations over millennial timescales. Plain Language Summary: The ocean is populated by "eddies", analogous to weather systems in the atmosphere, but occurring on much smaller scales of typically 10–100 km. Recent advances in our understanding of the circulation of the Southern Ocean, which connects all of the major ocean basins to the north, have revealed a crucial role for the energy balance of Southern Ocean eddies. In this paper, we show that the timescale over which energy is removed from Southern Ocean eddies has a dramatic impact on the following: (a) the strength of the Antarctic Circumpolar Current, the largest current in the global ocean; (b) the strength of the Atlantic meridional overturning circulation, responsible in part for the relatively mild climatic conditions over northwestern Europe; and (c) global ocean heat content, a key parameter in the global climate system. These results have significant implications for both past and future climates, and highlight the importance of combining observational, theoretical and modeling efforts to better understand and constrain the energy balance of ocean eddies. Key Points: Key metrics of global ocean circulation (Antarctic Circumpolar Current transport, Atlantic Meridional Overturning Circulation strength, and Ocean Heat Content anomaly) acutely sensitive to an eddy energy dissipation timescaleModest variations in the dissipation timescale has a comparable effect to significant variations in the Southern Ocean wind forcingConstraints on the dissipation timescale critical to longtime integrations of ocean climate models such as paleoclimate scenarios [ABSTRACT FROM AUTHOR]

Despite a growing number of observations of whistler waves in/around the reconnection diffusion region, the origin of the whistler waves in the diffusion region and their role in reconnection remain elusive. This paper investigates the whistler‐mode waves within an electron‐scale reconnecting current sheet observed by the Magnetospheric Multiscale mission on 23 December 2016. These whistlers were observed in both the electron diffusion region (EDR) and the immediate inflow region of the electron‐scale magnetic reconnection site. The dispersion relation of these whistlers is measured and compared to predictions from linear theory for the first time in these regions. The comparison shows that the field‐aligned drifting electron component critically modifies the dispersion relation of whistlers in the EDR due to the Doppler‐shift effects. We demonstrate that these whistlers propagated into the EDR from outside rather than locally excited, however, they did not provide sufficiently large anomalous dissipation in this EDR. Plain Language Summary: Whistler‐mode waves are important plasma waves in the space plasma system, which can effectively interact with electrons to exchange energy. Whistler waves are frequently observed in various areas of magnetic reconnection, for example, outflow region, separatrix region, and diffusion region. However, the nature of whistler waves in the electron diffusion region (EDR), where the magnetic field line is broken and reconnected, is still unclear. Here, we present an observation of whistler waves in the EDR and the inflow region of magnetic reconnection. These whistler waves originate from the outside and propagate into the vicinity of the reconnection site. We measured the dispersion relation of these whistler waves for the first time within these regions and compare it with the dispersion relations predicted by linear theory. The results indicate that the effects from the drift velocity of electrons play a key role in modifying the dispersion relation of these whistlers in the EDR. Additionally, we find that these whistlers did not provide effective anomalous dissipation in this EDR. These results advance our knowledge of the source and features of whistlers in the vicinity of the reconnection site. Key Points: Observations confirm that whistler waves can propagate into the electron diffusion region (EDR) from outsideThe dispersion relation of the whistler waves is measured for the first time in the EDRThe observed whistler waves contributed to negligible anomalous effects in the EDR [ABSTRACT FROM AUTHOR]

Micrometeorite impacts and solar wind irradiation, the dominant space weathering (SW) processes, largely modified compositions and microtexture of soil materials on the Moon. Here, we report the SW characteristics of the Chang'e‐5 lunar soils from mid‐high latitude (43.06°N). All mineral phases exposed on the surface of a single basalt clast have a vapor deposit layer, whereas the textures of the solar wind irradiation‐damaged zone are dependent on the host mineral species. Nanophase Fe (npFe0) particles are spherical in the amorphized zone of pyroxenes, elongated in ilmenite, and irregular on the jagged surface of iron sulfide, but not found in Fe‐poor merrillite. Vesicles were found in the damaged zone of ilmenite and merrillite, but with different shapes. The observations were compared to Apollo samples and demonstrate no significant altitude‐dependent effects on the SW, which is important for decoding the reflectance spectra of the Moon. Plain Language Summary: The lunar surface has been suffering intense meteorite impacts and solar wind irradiation for billions of years, which heavily modifies its physical properties, chemical compositions and mineralogical features, and in turn, the optical reflectance spectra of the Moon. The meteorite impacts are random events, but the intensity of solar wind irradiation is latitude dependent. However, all Apollo and Luna missions landed in a narrow and low range of lunar latitude. The Chang'e‐5 (CE‐5) mission returned lunar soil samples from a middle latitude (43.06°N), providing unique samples for study of lunar space weathering (SW). In this paper, we report the SW features of various minerals from a single basaltic clast of the CE‐5 sample. Our observations reveal phase‐dependent effects on the SW. Furthermore, the CE‐5 lunar soil shows no significant differences from those of Apollo samples, suggestive of little latitude‐dependent effects on lunar SW. Key Points: The space weathering (SW) characteristics of lunar soils returned by Chang'e‐5 landing at the mid‐high latitude site are reportedMicroscopic textures of SW depend on mineral species but show no relationship with the latitude of sampling siteThe SW products by micrometeorite impacts and solar wind irradiation are distinguished [ABSTRACT FROM AUTHOR]

Quantification of velocity and pressure fields over streambeds is important for predicting sediment mobility, benthic and hyporheic habitat qualities, and hyporheic exchange. Here, we report the first experimental investigation of reconstructed water surface elevations and three‐dimensional time‐averaged velocity and pressure fields quantified with non‐invasive image techniques for a three‐dimensional free surface flow around a barely submerged vertical cylinder over a plane bed of coarse granular sediment in a full‐scale flume experiment. Stereo particle image velocimetry coupled with a refractive index‐matched fluid measured velocity data at multiple closely‐spaced parallel and aligned planes. The time‐averaged pressure field was reconstructed using the Rotating Parallel Ray Omni‐Directional integration method to integrate the pressure gradient terms obtained by the balance of all the Reynolds‐Averaged Navier‐Stokes equation terms, which were evaluated with stereo particle image velocimetry. The detailed pressure field allows deriving the water surface profile deformed by the cylinder and hyporheic flows induced by the cylinder. Plain Language Summary: This paper presents the first experiment that measured the pressure distribution around an object representing the stem of a plant placed over a rough surface made of irregular particles and barely covered by moving water using image analysis. Calculating the pressure distribution in moving water in a channel is challenging because the pressure caused by the weight of the water is much larger than that caused by the moving water. The presence of waves on the water surface and the irregular bed surface formed by sediment grains makes the analysis even more complex as the conditions near these locations are difficult to determine. Here, we used an object made of a transparent material that makes it invisible within water mixed with Epsom salt. This allows image analysis to measure water velocity from which we derived the pressure distributions everywhere in the water. By having the water surface within the image, we were able to reconstruct the water surface from the pressure field as pressure nears atmospheric value at that position. Knowing the near‐bed pressure distribution allowed us to predict the amount of water that is driven into the voids among the grains due to the presence of the object. Key Points: Non‐intrusive method to map the full three‐dimensional time‐averaged pressure field in full‐scale flume experimentsWater surface identification from reconstructed pressure distribution from measured velocity fieldHyporheic fluxes induced by a barely submerged single stem are stronger than those from dune‐like bedforms in equilibrium with the flow [ABSTRACT FROM AUTHOR]

This paper compares surface signatures of the zonally symmetric and asymmetric modes of stratospheric variability, which describe the strength of the polar vortex and a planetary wave‐1 pattern, respectively. Unlike a weak polar vortex followed by negative Arctic Oscillation–like anomalies, strong stratospheric wave activity features a polar vortex displacement with a deep planetary wave‐1 structure, resulting in positive North Atlantic Oscillation–like North American cooling in about 10 days. Moreover, the linkage between the stratosphere and surface is examined in two reanalyzes and four models of different configurations, which show more robust North American cooling following the displacement of the polar vortex due to strong stratospheric wave activity than the zonally symmetric weakening of the polar vortex. This suggests strong stratospheric wave activity acts as a better predictor for cold spells in the northern U.S. and Canada compared with a weak polar vortex. Plain Language Summary: A weak polar vortex in the winter stratosphere is likely associated with cold spells at the surface, yet there are large uncertainties in predicting surface cold events based on stratospheric signals. This study introduces a new method to separate stratospheric variability into the leading modes of zonally symmetric and asymmetric circulations. The zonally symmetric mode describes the strength of the polar vortex. A weak polar vortex is followed by cooling over northern Eurasia and midlatitude North America. In contrast, the zonally asymmetric mode characterizes a displacement of the polar vortex or a planetary wave‐1 pattern, with the positive phase featuring a high anomaly over North America and a low anomaly over Eurasia. This stratospheric wave pattern extends down to the surface, resulting in North American cooling and Eurasian warming in about 10 days. While both stratospheric modes are associated with surface cooling over North America, the linkage is more robust for the displacement than the zonally symmetric weakening of the polar vortex, based on analyses of several reanalyzes and models. This indicates that strong stratospheric wave activity serves as a better predictor for cold air outbreaks in the northern U.S. and Canada than the commonly used weak polar vortex events. Key Points: Distinct North American cooling signatures follow zonally symmetric and asymmetric modes of the stratosphereStrong stratospheric wave activity precedes positive North Atlantic Oscillation like North American coolingThe linkage between the stratospheric wave activity and the surface is robust in reanalyzes and models [ABSTRACT FROM AUTHOR]

Due to climate change, global oceanic dissolved oxygen (DO) has been decreasing, and oxygen minimum zones (OMZs) have been expanding. Here, we estimate the annual global and regional OMZ areas using geostatistical regression combined with Monte Carlo. From 1960 to 2019, annual global OMZ20 (DO < 20 μmol/kg) and OMZ60 (DO < 60 μmol/kg) areas cover 5%–14% and 15%–32% of the global ocean, respectively. The global and most regional OMZ areas after the late 2000s were all significantly larger than those in previous years. Most oceanic regions likely experienced significant expansions in OMZ areas, especially the North Pacific. However, the equatorial Pacific with the largest OMZ area showed insignificant horizontal expansion. The expanding OMZ areas of most oceans responded more quickly and effectively to the surrounding sea temperatures than to the sea surface temperatures. Our research highlights the need for marine resource management to account for the challenges from OMZs. Plain Language Summary: Expanding oxygen minimum zones (OMZs, low dissolved oxygen [DO] zones) in the open ocean have been the topic of intense interest. However, annual OMZ areas, trends in OMZ areas, and causes of OMZ expansions remain unclear. Our paper explores the locations and annual areas of global and regional OMZ areas based on observations from 1960 to 2019. Over the last six decades, annual global OMZ20 (DO < 20 μmol/kg) and OMZ60 (DO < 60 μmol/kg) areas cover 5%–14% and 15%–32% of the global ocean, respectively. The global OMZ areas show great interannual variability but remain stably large after the late 2000s. Most oceanic regions have experienced significant OMZ expansion, especially the North Pacific. The equatorial Pacific Ocean has the largest OMZ area, but shows insignificant expansion. Subsurface sea temperatures are more associated with the expanding OMZ areas than sea surface temperatures. Increasing sea temperature would substantially increase OMZ areas by the end of the century for the future societal development pathway (SSP585) scenario. Understanding how OMZs will change over the long‐term due to climate change is beneficial for the protection of marine resources. Key Points: From 1960 to 2019, most oceanic regions experienced significant horizontal expansions in oxygen minimum zone (OMZ) areas, especially the North PacificThe equatorial Pacific has the largest OMZ area but shows an insignificant increasing trendThe OMZ areas of most oceans respond more quickly and effectively to surrounding sea temperatures than to sea surface temperatures [ABSTRACT FROM AUTHOR]

This paper reports an observational study of lightning initial breakdown pulses (IBPs) using the low‐frequency array radio telescope and a broadband magnetic field sensor. The data show that the overall spatiotemporal evolution of the electrical breakdown causing an IBP is rather complex. During an IBP, spatially and temporally separated bursts of very high frequency (VHF) electromagnetic radiation occur in a volume on the order of 1003 m3, and they are coincident with brief magnetic field pulses, indicating that the location of the active breakdown region can change suddenly. Furthermore, recurrent breakdown activity is observed, especially at the location of the VHF burst. Interpreting each VHF burst as being generated by a corona burst, an IBP pulse appears to start off from an initial corona burst and subsequent corona bursts enhance it. We further suggest that the generation of IBPs likely involves multiple space stems/leaders and connections between them. Plain Language Summary: Lightning initiation is difficult to study because it occurs deep inside thunderclouds and in‐situ measurements are hard if not impossible. Strong low frequency radio pulses known as initial breakdown pulses (IBPs) are generated during the initiation stage of lightning. This study uses the LOFAR radio telescope to paint a picture of the electrical breakdown activity during IBPs. The picture shows that the breakdown activity is rather complex, involving sudden change of the active breakdown location and recurrent activity in a relatively large volume. Key Points: The electrical breakdown generating lightning initial breakdown pulses has complex spatial and temporal propertiesSpatially and temporally separated VHF bursts occur during an initial breakdown pulse, coincident with brief wideband magnetic field pulsesGeneration of initial breakdown pulses likely involves multiple corona bursts, and multiple space stems/leaders and their connections [ABSTRACT FROM AUTHOR]

In this paper, we investigate whether the relationship between the El Niño‐Southern Oscillation and tropical cyclone (TC) rain rate over the western North Pacific (WNP) changes between the global warming slowdown (2001–2012) and resumption (2013–2020) periods. Using high‐resolution satellite rainfall data, we show that the average TC rain rate increases by 9% but decreases by 14% during the recent El Niño and La Niña years (since 2013), respectively. During the El Niño years, the increase is related to higher TC track density at lower latitudes, where more water vapor and stronger convergence are present. On the other hand, the decrease in TC rain rate during the recent La Niña years is mainly related to an increase in track density at higher latitudes and a decrease in TC intensity. These changes in TC track density and intensity are both associated with the strengthening of the subtropical high since 2013. Plain Language Summary: The impacts on various weather phenomena associated with the global surface warming slowdown (or "hiatus": 1998–2012) and its subsequent resumption since 2013 have been extensively investigated. An unresolved issue is whether the tropical cyclone (TC) rain rate over the western North Pacific (WNP) basin has also changed, especially during the El Niño (or La Niña) years. Considering the availability of high‐resolution satellite rainfall data, we mainly focus on the period of 2001–2020 (slowdown period: 2001–2012; resumption period: 2013–2020). Our results show that, consistent with the increase in atmospheric water vapor after the global warming resumption, the average TC rain rate has increased by ∼2%. However, TC rain rate increases in El Niño years but decreases in La Niña years during the resumption period. This opposite change in TC rain rate is mainly influenced by the strengthened WNP subtropical high. Our findings suggest that it is necessary to properly consider the influence of the subtropical high on the projections in TC migration, intensity, and rain rate under global warming. Key Points: Compared with El Niño‐Southern Oscillation (ENSO) years in the global warming slowdown period, tropical cyclone (TC) rain rate increases and decreases in recent El Niño and La Niña yearsThis opposite change in TC rain rate in recent ENSO years is mainly affected by the changes in TC track density and TC intensityChanges in TC track density and intensity are both influenced by the extremely strengthened subtropical high since 2013 [ABSTRACT FROM AUTHOR]