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Understanding the impact of various climate forcing agents, such as aerosols, on extreme precipitation is socially and scientifically vital. While anthropogenic absorbing aerosols influence Earth's energy balance and atmospheric convection, their role in extreme events remains unclear. This paper uses convective‐resolving radiative‐convective‐equilibrium simulations, with fixed solar radiation, to investigate the influence of absorbing aerosols on extreme precipitation comprehensively. Our findings reveal an underappreciated mechanism through which absorbing aerosols can, under certain conditions, strongly intensify extreme precipitation. Notably, we demonstrate that a mechanism previously reported for much warmer (hothouse) climates, where intense rainfall alternates with multi‐day dry spells, can operate under current realistic conditions due to absorbing aerosol influence. This mechanism operates when an aerosol perturbation shifts the lower tropospheric radiative heating rate to positive values, generating a strong inhibition layer. Our work highlights an additional potential effect of absorbing aerosols, with implications for climate change mitigation and disaster risk management. Plain Language Summary: Aerosols, particles suspended in the atmosphere, can interact with the incoming solar radiation by scattering or absorbing it. Aerosol species that absorb solar radiation generate local warming of the atmosphere. This local warming changes the vertical profile of temperature and by that affects cloud and precipitation development. In this paper we use idealized computer simulations to investigate the effect of absorbing aerosols on precipitation, and specifically on extreme precipitation events in the tropics. We demonstrate that under certain conditions, absorbing aerosols can strongly enhance extreme precipitation even despite reducing the mean. We show that this trend can be explained by a mechanism previously reported for much warmer climate conditions than currently found on Earth, involving heating by radiation of the lower part of the troposphere. These results have implications for climate change mitigation and disaster risk management. Key Points: The effect of absorbing aerosol on extreme precipitation is examined in idealized convective‐resolving radiative‐convective‐equilibrium simulationsAerosol perturbation that shifts the lower tropospheric radiative heating rate to positive values strongly enhances extreme precipitationThis trend is explained by a mechanism reported before for hothouse climate conditions involving a shift into an "episodic deluge" regime [ABSTRACT FROM AUTHOR]

Extracting balanced geostrophic motions (BM) from sea surface height (SSH) observations obtained by wide‐swath altimetry holds great significance in enhancing our understanding of oceanic dynamic processes at submesoscale wavelength. However, SSH observations derived from wide‐swath altimetry are characterized by high spatial resolution while relatively low temporal resolution, thereby posing challenges to extract the BM from a single SSH snapshot. To address this issue, this paper proposes a deep learning model called the BM‐UBM Network, which takes an instantaneous SSH snapshot as input and outputs the projection corresponding to the BM. Training experiments are conducted both in the Gulf Stream and South China Sea, and three metrics are considered to diagnose model's outputs. The favorable results highlight the potential capability of the BM‐UBM Network to process SSH measurements obtained by wide‐swath altimetry. Plain Language Summary: Oceanic dynamic processes can be classified into two categories: balanced geostrophic motions (BM), including large‐scale circulation, mesoscale and submesoscale eddy turbulence, and unbalanced wave motions (UBM), including barotropic tides, and inertia–gravity waves (IGWs). Both types of motions coexist and have respective contributions to the sea surface height (SSH). How to extract the BM from the total SSH observations obtained by satellite altimetry is the crucial problem to be solved in this paper. To tackle this issue, we propose a deep learning model named the BM‐UBM Network to establish the relationship between the total SSH and the BM component. The BM‐UBM Network can generate SSH estimations for the BM when provided with a well‐resolved SSH snapshot. Key Points: A Deep learning model is developed to extract balanced motions from sea surface height snapshot based on a realistic simulationDiagnostics of three metrics reveal the effectiveness of the model in extracting balanced motionsThe model exhibits remarkable advantages over the Gaussian filter (baseline) in capturing the gradient and Laplacian information [ABSTRACT FROM AUTHOR]

Air‐entraining whitecaps provide an important source of bubbles over the global oceans, yet the rate at which the associated air is entrained is not well known. This lack of understanding limits the ability to accurately parameterize bubble‐mediated gas exchange and sea spray aerosol flux. In this paper I present a model to predict the total volume of air entrained by individual whitecaps and extend it to estimate the rate at which air is entrained per unit sea surface area. The model agrees well with existing models and measurements and can be forced by the rate at which energy is dissipated by the wavefield which can be routinely provided by spectral wave models. I then use the model to present the first distributions of the estimated total volume of air entrained by individual whitecaps, as well as their rate of air entrainment and air degassing. Plain Language Summary: The amount of air in the oceans in the form of bubbles at any given time is not well known because of the difficulty associated with making in‐situ measurements. This lack of knowledge inhibits how well ocean‐atmosphere exchange processes that are driven by air and bubbles can be represented in climate models. In this paper, I present a new model to estimate the volume of air entrained by individual breaking waves called whitecaps, as well as how quickly the air is entrained into the oceans and how quickly it leaves the oceans when bubbles rise to the surface and burst. Key Points: A model for the entrainment of air by oceanic whitecaps is presented which agrees well with existing models and measurementsDistributions of the estimated volume of air entrained by individual oceanic whitecaps are presented for the first timeKey uncertainties in the air fraction and entrainment velocities of individual whitecaps remain due to a lack of measurements [ABSTRACT FROM AUTHOR]

The variability of Mars exosphere over monthly to solar‐cycle scales at 251 and 412 km altitude is quantified by analysis of 41‐Ls mean densities derived from precise orbit determination of the Mars Reconnaissance Orbiter (MRO) and Mars Odyssey (MO) satellites, respectively. The data encompass 2006–2020 (MRO) and 2002–2020 (MO). At both altitudes, most of the variance is captured by cos(Ls–ϕ), where ϕ ≈ 258°. This term represents the effects of solar heating changes due to the eccentricity of Mars orbit around the Sun, and climatological changes in heating due to lower‐atmosphere dust loading, which does not play a significant role. The remaining variability is connected with the "irregular" variability of solar flux over monthly time scales. For MO, the presence of Helium disrupts a clean correlation with these sources. Plain Language Summary: The force of continuous bombardment of atmospheric particles on a satellite slowly changes its orbit. By tracking the satellite, changes in its orbit can in turn be used to infer atmospheric particle densities. In this paper, we use tracking from NASA's Deep Space Network, an international array of giant antennas, to measure minute orbital changes of the Mars Reconnaissance Orbiter and Mars Odyssey satellite orbits (and thereby atmospheric densities) around Mars during the 2002–2020 time frame. These data are used to study how the outer regions of Mars atmosphere respond to changes in heating due to solar radation absorption by various chemical species, and by dust that is elevated into the atmosphere by strong winds near the surface. The major finding of this paper is that the variability of Mars outer atmosphere is mainly controlled by solar heating changes due to the eccentricity of Mars orbit around the Sun. Key Points: Densities from precise orbit determination of Mars Reconnaissance Orbiter and Mars Odyssey are used to quantify long‐term variability of Mars' exosphereThe annual term is the greatest contributor to total variance, followed by the irregular component of EUV/UV fluxDust‐induced inter‐annual variability is small, but the analysis method does suppress potentially important regional‐scale events [ABSTRACT FROM AUTHOR]

An array of atmospheric profile observations consists of three‐dimensional vectors representing pressure, temperature, and humidity, with each profile forming a continuous curve in this three‐dimensional space. In this paper, the Signature method, which can quantify a profile's curve, was adopted for the atmospheric profiles, and the accuracy of profile representations was investigated. The description of profiles by the signature was confirmed with adequate accuracy. The machine‐learning‐based model, developed using the signature, exhibited a high level of annual accuracy with minimal absolute mean differences in temperature and water vapor mixing ratio (<2.0 K or g kg−1). Notably, the model successfully captured the vertical structure and atmospheric instability, encompassing drastic variations in water vapor and temperature, even during intense rainfall. These results indicate the Signature method can comprehensively describe the vertical profile with information on how ordered values are correlated. This concept would potentially improve the representation of the atmospheric vertical structure. Plain Language Summary: The atmospheric profile can be visualized as a three‐dimensional curve representing pressure, temperature, and humidity. By utilizing the Signature method, we can measure and quantify the profile's curve, allowing for comprehensive modeling of the atmosphere. In this paper, we confirmed the accuracy of atmospheric profile representation using signatures and introduced the characteristics of signatures revealed through machine‐learning models. The description of profiles by the signature was confirmed with adequate accuracy. Moreover, the model demonstrated robust annual accuracy, with minimal temperature and water vapor discrepancies. It effectively captured the vertical structure and instability of the atmosphere, even during heavy rainfall, characterized by significant temperature and water vapor content fluctuations. Key Points: The utilization possibility of the Signature method for atmospheric profiles was confirmedBy utilizing the Signature method, we can measure and quantify the profile's curve, allowing for comprehensive modeling of the atmosphereThe machine‐learning model developed with the signature can predict the profiles with high annual accuracy [ABSTRACT FROM AUTHOR]

Earthquake swarms are most commonly composed of small‐magnitude earthquakes. However, a recent study by Yoshida, Uchida, et al. (2023, https://doi.org/10.1029/2023GL106023) analyzed a swarm beneath the Noto Peninsula in Japan that, after more than two years of moderate‐magnitude seismicity, triggered the moment magnitude (Mw) 6.2 Suzu mainshock in May 2023. Based on high‐precision earthquake locations and a slip inversion of the mainshock, these authors found that the Mw 6.2 Suzu earthquake occurred on the updip extension of a fault that was active during the swarm, likely driven by increased fluid pressure. After publication of that paper, a much larger and more destructive Mw 7.5 event occurred nearby on 1 January 2024. These events underscore the potential for swarms to be precursors to large, damaging earthquakes. Forecasting the eventual evolution of swarms is currently very challenging but could be aided in the future by new observations and models. Plain Language Summary: Although earthquake swarms often only contain small earthquakes, occasionally they can trigger large, damaging earthquakes. Yoshida, Uchida, et al. (2023, https://doi.org/10.1029/2023GL106023) examined the triggering of a magnitude 6.2 earthquake in Japan, which caused extensive damage, following two years of smaller earthquakes. This sequence, like many swarms, may have been driven by elevated fluid pressure migrating upwards within the crust. After publication of that paper, a much larger and more destructive Mw 7.5 event occurred nearby. Forecasting the eventual evolution of ongoing swarms is currently very challenging but could be aided in the future by new observations and models. Key Points: Earthquake swarms can be precursors to damaging earthquakes, including the 1 January 2024, Mw 7.5 Noto Peninsula, Japan eventFluid pressure changes often drive swarm activity, and their degree of confinement may influence swarm evolutionDirect observations of fluids in fault zones combined with numerical modeling may aid swarm forecasting in the future [ABSTRACT FROM AUTHOR]

Coral reef islands are amongst the most vulnerable environments to sea‐level rise (SLR). Recent physical and numerical modeling studies have demonstrated that overwash processes may enable reef islands to keep up with SLR through island accretion. Sediment supply to these islands from the surrounding reef system is critical in understanding their morphodynamic adjustments, but is poorly constrained due to insufficient knowledge about sediment delivery rates. This paper provides the first estimation of sediment delivery rates to coral reef islands. Analysis of topographic and geochronological data from 28 coral reef islands indicates an average rate of sediment delivery of c. 0.1 m3 m−1 yr−1, but with substantial inter‐island variability. Comparison with carbonate sediment production rates from census‐based studies suggests that this represents one quarter of the amount of sediment produced on the reef platform. Results of this study are useful in future modeling studies for predicting morphodynamic adjustments of coral reef islands to SLR. Plain Language Summary: Low‐lying coral reef islands are under threat of sea‐level rise (SLR). However, when these islands are flooded, ocean waves can bring in sediment that can increase the island elevation. This would enable coral reef islands to better withstand flooding in the future. Knowing how much sediment is brought in will help in our understanding of future changes to these islands due to SLR. In this paper, we use data from 28 Indo‐Pacific coral reef islands to compute sediment supply to the islands. We find that on average 0.1 m3 of sediment (roughly 100 kg) is delivered each year for every meter of island shoreline. We further suggest that this implies that only one quarter of the sediments produced by the coral reef system is delivered to the island shoreline. Most of the sediment produced remains on the reef flat or is exported to the ocean or the lagoon. Our results will help future studies to predict more accurately how coral reef islands will adjust to SLR. Key Points: We provide the first estimates of carbonate sediment delivery rates to 28 coral reef islands using all data available from the literatureSediment delivery to the reef islands occurs at a rate of c. 0.1 m3 m−1 yr−1, but with substantial inter‐island variabilityWhere island building has been continuous through island history, long‐term delivery rates provide valuable estimates for contemporary rates [ABSTRACT FROM AUTHOR]

Lightning channel morphology depends on the thunderstorm cloud charge structure, which in turn is influenced by the thunderstorm dynamics. In this paper, based on three‐dimensional radiation source localization data from the Lightning Mapping Array and radar‐based data, our analysis shows that the overall morphology and detailed morphology of the lightning channel correspond to different eddy dissipation rate (EDR) characteristics. Lightning with complex channel morphology occurs in regions with large EDRs. In single lightning events, channels that extend directly within a certain height range without significant bifurcation and turning tend to propagate in the direction of decreasing EDRs, while channel bifurcations and turns usually occur in regions with large radial velocity gradients and large EDRs. This study shows the relationship between channel morphology and thunderstorm dynamics and provides a new method for the direct application of channel‐level localization data to understand thunderstorm dynamics characteristics. Plain Language Summary: Turbulence in thunderstorms affects the charge distribution, which in turn affects the lightning channel morphology. Thus, the lightning channel morphology can reflect the characteristics of turbulence. The current understanding of the correlation between the two is still limited to the relationship between macroscopic thunderstorm dynamic characteristics and lightning activity. In this paper, the relationship between the morphology of the lightning channel and turbulence characteristics is investigated based on the Lightning Mapping Array (LMA) localization data and the cube root of the eddy dissipation rate (EDR) estimated from KABX radar‐based data. The turbulence strength affects the overall morphology of lightning, and lightning with complex morphology tends to occur in regions with large EDRs. In single lightning events, channels extending directly within a certain altitude range tend to propagate in the direction of decreasing EDRs, and lightning channel bifurcation or turning tends to occur in regions with large EDRs. This paper establishes the relationship between thunderstorm electricity and thunderstorm dynamics by using lightning channel morphology as a bridge and provides a new method for the direct application of channel‐level localization data to understand thunderstorm dynamics characteristics. Key Points: The morphology of lightning channels can reflect the distribution of turbulence intensity, and a certain correlation between the two existDirectly extended lightning channels tend to propagate in the direction of decreasing eddy dissipation ratesThe location of the channel bifurcations or turns often corresponds to regions with high eddy dissipation rates [ABSTRACT FROM AUTHOR]

Changes in precipitation patterns with climate change could have important impacts on human and natural systems. Zhang et al. (2021, https://doi.org/10.1029/2020gl092293) report trends in daily precipitation patterns over the last five decades in the western United States, focusing on meteorological drought. They report that dry intervals (calculated at the annual or seasonal level) have increased across much of the southwestern U.S., with statistical assessment suggesting the results are statistically robust. However, Zhang et al. (2021, https://doi.org/10.1029/2020gl092293) preprocess their annual (or seasonal) averages to compute 5‐year moving window averages before using established statistical techniques for trend analysis that assume independence about some fixed trend. Here we show that the moving window preprocessing violates that independence assumption and inflates the statistical significance of their trend estimates. This raises questions about the robustness of their results. We conclude by discussing the difficulty of adjusting for spatial structure when assessing time trends in a regional context. Plain Language Summary: A recent paper reports trends in drought in the western United States, in particular increases in drought in the southwestern United States, based on changes in the lengths of time intervals without precipitation. In this "comment" we note that the preprocessing approach used in the paper artificially increases the apparent statistical signal in the data and caution that the evidence for the trends reported is not as strong as presented in the paper. We conclude by discussing the difficulty of estimating trends in a statistically rigorous fashion across multiple weather stations. Key Points: Statistical uncertainty about trends in droughts in the southwestern US is larger than reported in a recent GRL letter [ABSTRACT FROM AUTHOR]

Paciorek and Wehner raise important questions around our use of the Mann‐Kendall nonparametric trend test on smoothed data for analyzing long‐term hydrometeorological trends in Zhang et al. (2021, https://doi.org/10.1029/2020gl092293). We thank them for initiating this important conversation and their gracious cooperation in exploring the issues addressed in their comment. In this reply we confirm the inflation of significant p‐values by our choice to smooth, illustrate the relatively minor impacts on the main conclusions of our paper, and add our voices to those of Paciorek and Wehner in highlighting the lack of methodology for hypothesis testing across multiple stations that have spatial structure (i.e., testing for regionally consistent trends). Plain Language Summary: Our colleagues Drs. Paciorek and Wehner have raised concerns about our paper (Zhang et al., 2021, https://doi.org/10.1029/2020gl092293), which showed widespread increases in the duration of drought events over the last five decades in the western United States. They point out that our decision to smooth the data using a moving average inflated the number of weather stations at which the trends toward longer droughts were deemed significant by a statistical test. We agree with them on this point, and we have recomputed all our results using unsmoothed data to determine the impacts. We find that for most stations and regions, trend magnitudes remained largely unchanged, with many stations nearby one another often suggesting similar trends. Finally, we agree with Paciorek and Wehner that there is a lack of statistical methods to test such coherent regional patterns, and we caution that over‐reliance on p‐values limits the power of regional data to identify important climate trends. Key Points: We agree that smoothing to 5‐year moving windows introduced serial correlation into time series of annual statistics of daily rainfall data, inflating the number of weather stations individually showing significant trends (p < 0.05) with the Mann‐Kendall testRecomputation with unsmoothed values produced substantially the same dry intervals trend magnitude and direction at most stations individually and had only minimal impacts on dry interval trends computed for National Ecological Observatory Network domains using the Regional Kendall testNo perfect statistical approach leverages the capacity of coherent regional patterns among spatially correlated weather stations, and an over‐reliance on p‐values as a binary (significant vs. insignificant) determinant of trends limits the power of regional data [ABSTRACT FROM AUTHOR]

Whistler‐mode waves are commonly observed within the lunar environment, while their variations during Interplanetary (IP) shocks are not fully understood yet. In this paper, we analyze two IP shock events observed by Acceleration, Reconnection, Turbulence and Electrodynamics of the Moons Interaction with the Sun (ARTEMIS) satellites while the Moon was exposed to the solar wind. In the first event, ARTEMIS detected whistler‐mode wave intensification, accompanied by sharply increased hot electron flux and anisotropy across the shock ramp. The potential reflection or backscattering of electrons by the lunar crustal magnetic field is found to be favorable for whistler‐mode wave intensification. In the second event, a magnetic field line rotation around the shock region was observed and correlated with whistler‐mode wave intensification. The wave growth rates calculated using linear theory agree well with the observed wave spectra. Our study highlights the significance of magnetic field variations and anisotropic hot electron distributions in generating whistler‐mode waves in the lunar plasma environment following IP shock arrivals. Plain Language Summary: The surface of the Earth's Moon is frequently exposed to the incoming solar wind flow and IP shocks due to its lack of internal magnetic fields that can deflect the solar wind particles. Within the lunar environment, whistler‐mode waves, characterized by electromagnetic fluctuations with frequencies below the electron gyrofrequency, are commonly present. Interplanetary shocks that are often associated with significant disturbances in electron flux and magnetic field can potentially lead to anisotropic distributions of electrons, which are known to provide free energy source for whistler‐mode wave generation. To assess the whistler wave generation under shock conditions, we conduct an in‐depth analysis of two IP shock events. These events provide clear evidence of shock‐induced enhancements in electron pitch angle anisotropy and flux, as well as a potential rotation of magnetic field around the shock region, resulting in the intensification of whistler‐mode waves downstream of the shock. We calculated a timeseries of linear wave growth rate for the entire duration of shock events, which remarkably accounted for the observed whistler‐mode wave spectra both before and after the shock arrival. Our findings are important for understanding the associated physical process of whistler‐mode wave generation in the lunar plasma environment during IP shock events. Key Points: Two Interplanetary shock events in the lunar environment are analyzed to unveil whistler wave generation around shock regionLinear wave growth calculations show that whistler‐mode waves are generated locally due to enhanced electron anisotropy and fluxMagnetic field line connection to lunar surface is found to be important for enhancing whistler wave intensity [ABSTRACT FROM AUTHOR]

Fluid flow through fractured media is typically governed by the distribution of fracture apertures, which are in turn governed by stress. Consequently, understanding subsurface stress is critical for understanding and predicting subsurface fluid flow. Although laboratory‐scale studies have established a sensitive relationship between effective stress and bulk electrical conductivity in crystalline rock, that relationship has not been extensively leveraged to monitor stress evolution at the field scale using electrical or electromagnetic geophysical monitoring approaches. In this paper we demonstrate the use time‐lapse 3‐dimensional (4D) electrical resistivity tomography to image perturbations in the stress field generated by pressurized borehole packers deployed during shear‐stimulation attempts in a 1.25 km deep metamorphic crystalline rock formation. Plain Language Summary: Time‐lapse electrical geophysical sensing is used to image 3D changes in rock stress generated by an isolated and pressurized interval of a borehole in a deep, dense, fractured rock formation. Key Points: Remotely monitoring stress is challenging but important for relating geomechanical behavior to flow pathways during energy productionBulk electrical conductivity is sensitive to stress in crystalline rockTime‐lapse electrical resistivity tomography can be used to remotely monitor 3D changes in effective stress [ABSTRACT FROM AUTHOR]

The cloud feedback may result in amplification or damping of Arctic warming. Two common techniques used to diagnose the top‐of‐the‐atmosphere cloud feedback are the Adjusted Cloud Radiative Effect (AdjCRE) method and the Cloud Radiative Kernel (CRK) method. We apply both to CMIP5 and CMIP6 model data, finding that the AdjCRE calculated Arctic shortwave cloud feedback is twice as correlated with sea ice loss in CMIP5, and four times in CMIP6, as the CRK method. We find that the CRK method produces Arctic all‐sky residual percentages exceeding 20% in 15 of 18 models. We use the CRK method to decompose the feedback in CMIP5 and CMIP6 finding that its median value changed from negative to positive driven by a less‐negative cloud optical depth feedback. Despite its lack of closure, we conclude that the CRK method is better suited for Arctic SW feedbacks as it is less impacted by surface albedo changes. Plain Language Summary: The cloud feedback is the process by which cloud property changes in a warming climate can either further enhance warming or damp it. The Arctic is warming faster than the rest of the globe, and one of the largest sources of uncertainty in its climate projections is the cloud feedback. There are two popular methods to calculate the cloud feedback: the Adjusted Cloud Radiative Effect technique, and the Cloud Radiative Kernel technique. In this paper we compare the two methods in a suite of climate models by considering the extent to which changes in Arctic sea ice impact the cloud feedbacks. From this analysis we conclude that the Cloud Radiative Kernel method is less affected by sea ice loss. We then apply the Cloud Radiative Kernel technique to data from the two most recent generations of global climate models to investigate how polar day Arctic cloud feedbacks have changed between these generations. We find that the median value of these Arctic feedbacks is slightly positive in the newest generation of models, a change from slightly negative in the previous generation that is largely fueled by a weakening of the feedback associated with changes in cloud optical depth. Key Points: The Cloud Radiative Kernel method is less sensitive to surface albedo changes than the Adjusted Cloud Radiative Effect techniqueThe Cloud Radiative Kernel method provides poor radiative closure in a suite of global climate modelsThe median shortwave Arctic cloud feedback in recent climate models is slightly positive due to a weakened cloud optical depth feedback [ABSTRACT FROM AUTHOR]

Increasing snow accumulation over the Antarctic Ice Sheet may mitigate future sea level rise. However, current estimates of mitigation potential are poorly constrained due to limited records of past variability. We present an annually resolved reconstruction of Antarctic snow accumulation from 1801 to 2000 CE, employing a paleoclimate data assimilation methodology to integrate ice core records with a multi‐model ensemble of climate simulations. Our reconstruction correlates well with instrumental reanalysis, and we find that Antarctic accumulation rates increased over the 20th‐century, resulting in a modest amount (∼1 mm) of sea level mitigation. Mitigation is primarily driven by an accelerating trend since around 1970. Our results contrast with previous mitigation estimates of ∼10–12 mm; this discrepancy is due to poorly constrained baseline estimates of 19th‐century accumulation in East Antarctica. Our reconstruction suggests that the uncertainty of future sea level mitigation from increasing Antarctic accumulation has been underestimated. Plain Language Summary: Ice loss from Antarctica causes sea level to rise, but Antarctica can also mitigate sea level rise if snowfall on the continent increases faster than the ice loss. There is not currently a consensus on whether Antarctica will contribute to or mitigate sea level rise in the coming century, due to a lack of Antarctic snowfall records. In this paper, we merge information from ice core records with climate models to reconstruct annual Antarctic snowfall from 1801 to 2000. We find that snowfall on Antarctica increased during the 20th‐century, but only had a modest counteracting effect of 1 mm on sea level rise in the 20th‐century, much less than a previous estimate of 10 mm. The large discrepancy is due to uncertainty in East Antarctic accumulation in the 19th‐century. The potential for Antarctica to mitigate sea level is uncertain, affecting projections for future sea level rise. Key Points: Antarctic accumulation reconstruction using paleoclimate data assimilation finds modest (∼1 mm) 20th‐century sea level mitigationWe find similar 20th‐century trends to previous work; lower sea level mitigation (1 vs. 10 mm) is due to the 19th‐century baselineUncertainty in past East Antarctic accumulation limits confidence in future projections of Antarctic sea level mitigation [ABSTRACT FROM AUTHOR]

Herein, fast fracture initiation in glacier ice is modeled using a Material Point Method and a simplified constitutive law describing tensile strain softening. Relying on a simple configuration where ice flows over a vertical step, crevasse patterns emerge and are consistent with previous observations reported in the literature. The model's few parameters allows identification of a single dimensionless number controlling fracture spacing and depth. This scaling law delineates two regimes. In the first one, ice thickness does not play a role and only ice tensile strength controls the spacing, giving rise to numerous surface crevasses, as observed in crevasse fields. In this regime, scaling can recover classical values for ice tensile strength from macroscopic field observations. The second regime, governed by ice bending, produces large‐scale, deep fractures resembling serac falls or calving events. Plain Language Summary: In ice sheets and alpine glaciers, fast‐flowing sections are often characterized by crevasse fields that play a significant role in the cryo‐hydrologic system by facilitating meltwater flow, enhancing basal sliding, weakening the ice, and impacting glacier thermodynamics. Modeling these fractures at the glacier scale remains challenging and often necessitates integrating diverse models which hinders the straightforward consideration of physical issues associated with crevasse fields on a large scale. Here, a new numerical framework allows us to conduct field‐scale experiments and paves the way for a scaling law to elucidate the macroscopic factors influencing fracture fields and to easily incorporate crevasse depth and spacing into large‐scale models. A newly discovered scaling law highlights the transition between a mechanical behavior where the regular crevasse spacing is unaffected by geometry to a regime where geometry plays a significant role, particularly in large‐scale fracture processes like glacier calving. While the numerical experiments in this paper focus on glaciers, the model and conceptual framework is versatile and can address the mechanical behavior of fractures in broader geophysical contexts such as snow, rock or ice avalanches, tectonics and landslides. Key Points: Fractures in glacier flow are modeled using material point method with elastoplasticity and tensile strain softeningA dimensional analysis reveals a key dimensionless number characterizing two different regimes of fast fractureOne regime predicts acknowledged ice tensile strength from field observations and characterizes the regular crevasse spacing [ABSTRACT FROM AUTHOR]

Two ∼2‐week Ultra‐Fast Kelvin Wave (UFKW) events centered on days 158(203) during 2021 are investigated using winds, temperatures, plasma drifts and electron densities (Ne) measured by the Ionospheric CONnections (ICON) mission. Eastward‐propagating longitudinal wave‐1 (s = −1) structures with periods 2.5–4.0d, thought to mainly reflect Ultra‐Fast Kelvin waves (UFKWs), reveal ±45 ms−1 zonal winds (U) at 100 km for both events. Height‐latitude structures of the 3.0(3.5)d‐period UFKWs are obtained for the first time for both temperature (T, 94–120 km) and U (94–280 km) between 12°S and 39°N latitude. Maximum values of 36(29) ms−1 for U and 12(15)K for T occur at 102(106) km altitude and within ±3° latitude. The U‐T peak height displacement remains unexplained. Vertical wavelengths are in the range 36–43 km for both U and T during both events. Concurrent with the E‐region dynamo winds, topside (580 km) F‐region field‐aligned (±20–40 ms−1), meridional (±5–10 ms−1) and vertical (±5–10 ms−1) drift and Ne (±20–40%) 2.5–4.0d s = −1 variations are also measured. These key elements of atmosphere‐ionosphere (A‐I) coupling, contemporaneously measured for the first time, are relevant to testing the internal consistency of A‐I models. The mean wind propagation environment of the UFKWs is also quantified, showing no appreciable effects on the UFKW structures, consistent with modeling and theory. Plain Language Summary: Atmospheric Ultra‐Fast Kelvin waves (UFKWs) are eastward‐ and vertically propagating oscillations with periods less than 1 week that are centered on the equator and confined to low latitudes. They are part of a whole spectrum of waves forced by the spatial‐temporal variability of the heat of condensation ("latent heating") that is released when rising moist air forms rain droplets, mainly in the tropics. At high altitudes UFKW reach large amplitudes due to the decrease in ambient density with height. Their growth is curtailed by the viscosity of the atmosphere near 102 km altitude where they reach maximum amplitudes. Here they interact with ionized particles (the ionosphere) and generate electric fields that ultimately drive ionospheric variability at higher altitudes (>200 km), thus presenting an element of "space weather" to navigation and communications systems. In this paper, UFKWs measured in connection with the ICON mission are used to reveal, for the first time, the height and latitudinal structures of temperatures and winds associated with UFKWs in this dissipative regime, and their corresponding effect on the ionosphere. These results can thus serve to assess the internal consistency of models that seek to simulate atmosphere‐ionosphere coupling and related space weather effects induced by the wave spectrum excited in the lower atmosphere. Key Points: First coincident UFKW winds and temperature structures covering 94‐120 km,12°S‐39°N latitude are reportedFirst UFKW wind profiles in the 100‐280 km altitude dissipative regime are reportedFirst contemporaneous measurements of ionosphere response and driving UFKW E‐region dynamo winds are reported [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) significantly impact the hydrological cycle and associated extremes in western continental regions. Recent studies suggest ARs also influence water resources and extremes in continental interiors. AR detection tools indicate that AR conditions are relatively frequent in areas east of the Rocky Mountains. The origin of these ARs, whether from synoptic‐scale waves or mesoscale processes, is unclear. This study uses meteorological composite maps and transects of AR conditions during the four seasons. The analysis reveals that ARs east of the Rockies are associated with long‐wave, baroclinic Rossby waves. This result demonstrates that eastern North American ARs are dynamically similar to their western coastal counterparts, though mechanisms for vertical moisture flux differ between the two. These findings provide a foundation for understanding future climate change and ARs in this region and offer new methods for evaluating climate model simulations. Plain Language Summary: Atmospheric rivers (ARs) are a weather pattern that brings high amounts of atmospheric water and winds in a relatively narrow region. ARs are typically considered a "west coast" phenomenon, largely because the majority of the scientific research on ARs has focused on ARs in western coastal regions: particularly the western United States (US). ARs occur in continental interiors, but there has been some debate about whether these ARs represent the same type of weather as those in western coastal regions. This paper uses two objective methods for identifying ARs and finds times when ARs are present in three locations in the eastern half of the US: Norman, OK, Bloomington, IN, and Washington, DC. Examination of weather conditions during these AR times shows remarkable similarity to conditions associated with west coast ARs. This gives strong evidence that ARs do occur in the eastern half of the US. This result is important because it suggests that ARs may be important for water resources and extreme weather in the eastern half of the US, just as they are in the western US. This result also suggests that ARs may be important for water resources and extremes in other continental interiors. Key Points: Atmospheric rivers (ARs) east of the Rockies are associated with baroclinic wavesWestern coastal ARs and eastern/midwest ARs are dynamically similarSynoptic‐scale uplift, combined with convective instability, provide efficient mechanisms for generating precipitation [ABSTRACT FROM AUTHOR]

We present the first direct evidence of an in situ excitation of drift‐compressional waves driven by drift resonance with ring current protons in the magnetosphere. Compressional Pc4–5 waves with frequencies of 4–12 mHz were observed by the Arase satellite near the magnetic equator at L ∼ 6 in the evening sector on 19 November 2018. Estimated azimuthal wave numbers (m) ranged from −100 to −130. The observed frequency was consistent with that calculated using the drift‐compressional mode theory, whereas the plasma anisotropy was too small to excite the drift‐mirror mode. We discovered that the energy source of the wave was a drift resonance instability, which was generated by the negative radial gradient in a proton phase space density at 20–25 keV. This proton distribution is attributed to a temporal variation of the electric field, which formed the observed multiple‐nose structures of ring current protons. Plain Language Summary: During magnetic storms and substorms, energetic ions are sporadically injected into the geospace, which distorts the stable population and velocity distributions of ions in space. At these moments, various plasma instabilities lead to ultra‐low frequency (ULF) wave excitations. The lowest‐frequency waves in the ULF range have a wavelength comparable to the size of the Earth and are typically analyzed using magnetohydrodynamic principles. This approach considers the plasma environment using macroscale parameters such as pressure and density. In this paper, we report a spacecraft observation of a broadband compressional ULF wave that cannot be interpreted using magnetohydrodynamics. Such waves have rarely been reported and analyzed; however, their interaction with energetic ions is important to understand magnetospheric energy dynamics. The plasma conditions were described using the kinetic theory, which involves particle velocity distributions. We observed that a drift resonance occurred between the energetic protons and waves, while the gradient instability condition was satisfied for a part of time. Therefore, we concluded that the wave was in a drift‐compressional mode excited through drift resonance and gradient instability. The interpretation of compressional waves via satellite observations of energetic ions has been receiving increasing attention to understand their excitation mechanism. Key Points: Pc4–5 compressional ultra‐low frequency waves with an azimuthal wave number of −130 were observed in the nose structure on dusksideTheoretically predicted values of drift‐compressional mode frequency match the observed wave frequencyBoth radial ion temperature gradient and drift resonance of 20–25 keV protons serve as energy sources of the wave [ABSTRACT FROM AUTHOR]

This study addresses a critical gap in understanding anthropogenic influences on tropical climate dynamics by investigating the impact of aerosol‐cloud interactions on large‐scale circulation. Despite extensive research on greenhouse gas‐induced warming and its effects on tropical circulation, the impact of aerosols, particularly their interactions with clouds, on large‐scale circulation remains understudied. Utilizing large‐domain radiative convective equilibrium cloud‐resolving simulations, this research demonstrates that increasing aerosol concentration intensifies tropical overturning circulation, evaluated at the mid‐troposphere (I) $(\mathcal{I})$, strongly correlating with domain mean cloud and radiative properties. Employing a weak temperature gradient approximation, I attribute variations in I $\mathcal{I}$ to changes in clear‐sky radiative cooling rather than stability. These radiative cooling changes are linked to humidity changes driven by warm rain suppression by aerosols. This study's findings underscore the need to take into account microphysical changes, particularly aerosol concentrations, when studying anthropogenic effects on tropical circulation. Plain Language Summary: Clouds intricately couple with the large‐scale overturning circulation in the tropics. Aerosols, small particles suspended in the atmosphere, interact with clouds. Thus, changes in aerosols concentration (Na) have the potential to affect cloud properties and by that the large‐scale circulation, with important implications for tropical climate and climate change. Despite this crucial relationship, the subject has been insufficiently explored. In this paper, I use a simplified, yet realistic, representation of the tropical atmosphere—radiative convective equilibrium large‐domain cloud‐resolving simulations—to investigate the effect of aerosol‐cloud interaction on overturning tropical circulation. By varying Na under diverse sea surface temperatures, I demonstrate that the strength of the overturning circulation intensifies with increasing Na. Utilizing a semi‐analytical expression for subsidence strength in clear‐sky tropical regions, I show that the intensified overturning circulation with increased Na can be attributed to heightened humidity in the mid‐troposphere, leading to intense radiative cooling. This mid‐tropospheric humidification can be explained by warm rain suppression by aerosols, which fosters stronger humidity mixing between clouds and their surroundings. These findings underscore the need to consider aerosol concentration changes when examining anthropogenic impacts on tropical circulation. Key Points: The overturning tropical circulation intensifies with aerosol concentration in a radiative convective equilibrium modelChanges in circulation strength can be explained by changes in diabatic subsidence driven by radiative changesRadiative changes can be explained by increased humidity at the mid‐troposphere due to warm rain suppression [ABSTRACT FROM AUTHOR]

In the California Current System (CCS), changes in the phenology (i.e., seasonal timing) of coastal upwelling alter the functioning of this productive marine ecosystem. Recently developed coastal upwelling indices that account for upwelling strength and nutrient flux to the surface provide a more complete understanding of bottom‐up forcing in the region. Using these indices, we describe CCS upwelling phenological variability in vertical transport and nutrient flux. Physical and biogeochemical spring transitions generally co‐occur in winter or spring, followed by increased upwelling and nutrient flux. In the latter half of the year, upwelling continues but nutrient flux wanes as declining source nutrient concentrations limit the biological efficacy of coastal upwelling. Earlier spring transitions and higher season‐integrated upwelling intensity occur during strong La Niña events at all latitudes, driven largely by stronger alongshore wind stress. Understanding phenological changes in coastal upwelling is critical, as they could have significant ecosystem consequences. Plain Language Summary: In the California Current System (CCS), coastal upwelling carries nutrient‐rich waters to the surface, supporting primary production and driving the coastal ecosystem. This upwelling varies on a seasonal and interannual basis, as reflected in recently developed indices that account for the amount of water upwelled to the surface as well as the amount of nutrients carried in that water. Generally upwelling and nutrient transport are high in the first half of the year. Upwelling persists into the second half of the year, but nutrient transport decreases as the deep‐water sources of these nutrients are depleted. Upwelling in the CCS is also affected by the El Niño Southern Oscillation. During La Niña conditions, strong trade winds enhance upwelling and nutrient transport on the California coast. This paper presents regional, seasonal and interannual patterns of upwelling and nutrient delivery in the CCS, which are important drivers of change to this coastal ecosystem. Key Points: We define new upwelling phenology indices for the California Current System that include nutrient transportWe identify spatial, seasonal, and interannual patterns of upwelling and nutrient deliveryWe relate the physical mechanisms of coastal upwelling with its biological efficacy [ABSTRACT FROM AUTHOR]

How and when sedimentary rocks record Earth's magnetic field is complex. Most studies assume a time‐progressive lock‐in mechanism during sediment deposition called depositional remanent magnetization (DRM). However, magnetic minerals can also form in situ, recording a chemical remanent magnetization (CRM) that is discontinuous in time. Disentangling the two mechanisms represents a major hurdle, and differences in their recording efficiencies remain unexplored. Here, our theoretical solutions demonstrate that CRM intensities exceed DRM by a factor of six when acquired in the same magnetic field. Novel experiments growing greigite (Fe3S4) in sediments and subsequent redeposition under identical magnetic field conditions confirm the predicted difference in recording efficiency. Thus, if left unrecognized, CRM leads to overestimated paleointensity and deserves more attention when interpreting Earth's magnetic history from sedimentary records. Recognition of fundamental differences between CRM and DRM characteristics provide a way forward to distinguish the recording mechanisms through routine laboratory protocols. Plain Language Summary: Remanent magnetizations preserved in sedimentary rocks serve as a continuous record of Earth's magnetic field history and play a fundamental role in understanding the Earth system. It is commonly assumed that magnetic minerals align with the magnetic field as a particle settles through the water column, known as a depositional remanent magnetization (DRM). However, diagenesis can lead to chemical growth of magnetic minerals, known as a chemical remanent magnetization (CRM). CRM lacks stratigraphic continuity and can obscure or completely overprint the original magnetization any time after sediment deposition, leading to a magnetic record that is uncorrelated with the age of the rock. Yet, CRMs go largely unrecognized. Theory and experiments in our paper document that CRMs record the magnetic field six times more efficiently than DRMs. Our work provides a way to distinguish the two through routine laboratory protocols. Key Points: Recording efficiency of chemical remanent magnetization (CRM) is six times higher than depositional remanent magnetization (DRM)Undetected chemical remanences lead to overestimated relative paleointensity estimatesComparison of natural and laboratory magnetization and demagnetization behavior help identify chemical remanent magnetizations in sediments [ABSTRACT FROM AUTHOR]

As the world's glaciers recede in response to a warming atmosphere, a change in the magnitude and frequency of related hazards is expected. Among the most destructive hazards are glacier lake outburst floods (GLOFs), and their future evolution is concerning for local populations and sustainable development policy. Central to this is a better understanding of triggers. There is a long‐standing assumption that earthquakes are a major GLOF trigger, and seismic activity is consistently included as a key hazard assessment criterion. Here, we provide the first empirical evidence that this assumption is largely incorrect. Focusing on the Tropical Andes, we show that, of 59 earthquakes (1900–2021) the effects of which intersect with known glacier lakes, only one has triggered GLOFs. We argue that, to help develop climate resilient protocols, the focus for future assessments should be on understanding other key GLOF drivers, such as thawing permafrost and underlying structural geology. Plain Language Summary: Climate change is increasing glacier melt in high mountains and increasing the size and number of glacial lakes. Over time, these lakes may drain catastrophically to generate glacier lake outburst floods (GLOFs), which can devastate downstream communities and destroy valuable infrastructure such as roads, bridges, and hydroelectric power facilities. As a result, many risk assessments have been carried out to understand what the triggers of GLOFs might be, in order to better predict their occurrence. One of the main triggers has been assumed to be earthquakes, but this association has not been properly tested. In this paper, we use earthquake and GLOF data from the Peruvian and Bolivian Andes to test this and find that there is little association between earthquakes and GLOFs. We conclude by arguing that focus needs to be on other GLOF triggers, and earthquake activity should be used as a secondary – not primary – indicator in GLOF susceptibility studies. Key Points: Glacier lake outburst floods (GLOFs) are a major risk concern, with earthquakes being commonly considered effective triggers in hazard assessmentsOf 59 earthquakes (1900–2021), the effects of which intersect lakes in the Tropical Andes, only one triggered GLOFsWe suggest that earthquake activity should be used as a secondary – not primary – susceptibility indicator for GLOFs [ABSTRACT FROM AUTHOR]

The fundamental features of one kind of rarely known stratocumulus, which was termed as "Millipede Cloud," occurred over the Eastern Pacific Ocean in 2017 were first documented by using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. These clouds had long and meandering "central axes" extending from several hundreds to thousands kilometers, and a number of "radical cloud arms" extending several tens of kilometers in its two sides. Total 59 "Millipede Clouds," 4 and 55 of them, were formed over the Northern and the Southern Hemispheres, respectively. Their environmental backgrounds were analyzed by using ERA5 reanalysis data and MODIS sensor Level‐2 data. The cloud top pressures of these "Millipede Clouds" were between 850 and 800 hPa, and their top heights were about 1–2 km. There existed "inversion layer" of air temperature near the cloud tops at 800 hPa, which strongly suggested that these clouds were lower stratocumulus in essence. Plain Language Summary: "Millipede Cloud," one kind of rarely known stratocumulus which looks like "Millipede" shape, is termed for the first time in this paper. It has an obvious "central axis" and a number of well‐organized "radial cloud arms" in two sides of the "central axis" extending in several tens of kilometers length. This paper introduces the fundamental features of "Millipede Clouds" occurred over the Eastern Pacific Ocean in 2017 from the perspective of satellite image. Totally, 59 "Millipede Clouds" were found to occur over the Eastern Pacific Ocean. Their geographic distribution, cloud top features and vertical structure of one typical case on 16 July 2017 were documented. Key Points: The fundamental features of "Millipede Clouds" over the Eastern Pacific Ocean in 2017 were documented by using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imageryThe environmental backgrounds of these "Millipede Clouds" were analyzed by using ERA5 reanalysis data and MODIS dataThe cloud top pressures of these "Millipede Clouds" are between 850 and 800 hPa, and their top heights are about 1–2 km [ABSTRACT FROM AUTHOR]

This paper studies a new concept of using global navigation satellite system (GNSS) signals coherently reflected over relatively smooth ocean and ice surfaces from very low elevation angles (below ∼8°) and received by low Earth orbit (LEO) satellites to retrieve the tropospheric information. This approach can provide horizontal profiles of tropospheric zenith delay and total column water vapor (TCWV) with centimeter‐level high precision and spatial resolutions of tens of km by ∼1 km, depending on the elevation angle, with a sampling spacing of ∼100 m. This approach can potentially be applied to most sea ice and calm ocean areas and provide tropospheric sensing data, which can complement and augment existing observation systems. A few case studies are conducted in this paper using the Spire grazing‐angle GNSS‐R data. The retrieved TCWV is compared to ERA5 products and the Sentinel‐3 Ocean and Land Color Instrument measurements and shows promising performances. The errors associated with the GNSS‐R tropospheric measurements are also discussed. Plain Language Summary: The atmospheric water vapor is an important component for the weather and climate systems and is difficult to measure, especially over ocean and ice surfaces. This paper studies a new approach to measuring atmospheric water vapor using global navigation satellite system (GNSS) signals reflected off ocean and ice surfaces. If the reflection is from a low elevation angle (below ∼8°) and the reflected signal is coherent (all signal rays are reflected in the same direction), this approach can provide very high precision observation of the horizontal gradients of the tropospheric delay and the vertically integrated atmospheric water vapor with good spatial resolutions. This paper presents the methodology of the proposed approach and a few case studies to demonstrate the feasibility and performance by comparing the GNSS‐R retrieved water vapor measurements with models and the Sentinel‐3 satellite radiometry measurements. The errors associated with the GNSS Reflectometry (GNSS‐R) tropospheric measurements are also discussed. Key Points: A new tropospheric sensing concept is studied that relies on coherent‐reflection global navigation satellite system (GNSS) signals off ocean and ice surfacesAlgorithms are developed and demonstrated using Spire grazing‐angle GNSS‐R data to retrieve tropospheric delay and water vaporThe presented approach provides high‐precision tropospheric delay and total column water vapor horizontal profiles, as validated using the Sentinel‐3 Ocean and Land Color Instrument data [ABSTRACT FROM AUTHOR]

Heavy cold ions at Mars are gravitationally bound to the planet unless some process provides energy to them. Observations show that cold (<20 eV) and dense (∼>1 cm−3) O+/O2+ ions with bulk velocities equal to energies ∼1 keV can reach deep into the nightside Martian magnetosheath. These ions are co‐located with a change of the sign of the sunward component of the magnetic field. This magnetic field topology implies the persistence of a localized planetary ions escape channel associated with draped magnetic field lines that are convecting tailward. The observed ion populations propagate approximately in the same direction as surrounding magnetosheath flow and are likely to be almost unheated ionospheric ions from low altitudes. The paper discusses planetary ion energization via Hall electric field originated from ions and electron separation associated with magnetic field curvature. Plain Language Summary: In‐situ observations above the nightside of Mars show the presence of localized dense planetary ion fluxes at altitudes exceeding 2,000 km and escaping from the planet at high energies, comparable to that of the solar wind. These fluxes are accompanied by the reversal of sunward component of magnetic field. Unlike most atmospheric escape channels, the reported phenomenon is characterized by an increase in heavy to light ions density ratio with the distance from the planet at the observed altitudes up to nearly 5,000 km, as well as an increase in overall plasma number density inside this escape channel relative to the ambient sheath environment. This behavior is consistent with acceleration process initiated by a bent magnetic flux tube. Key Points: Ions of different species gain similar energies in the Martian magnetosheath by Hall electric fields associated with magnetic curvatureA high concentration of ionospheric ions correlates with a near void of shocked solar wind protons and a magnetic field reversalNumber density at the reversal increases with distance from Mars in comparison to the surrounding sheath at least till two Martian radii [ABSTRACT FROM AUTHOR]

Theoretical analysis has revealed a specific resonance that shares the same condition as Landau resonance, but instead involves wave electromagnetic fields rather than traditionally electrostatic fields. While this resonance, referred to as electromagnetic Landau resonance due to its properties, is considered significant for magnetospheric dynamics, rare reports or evaluations based on observations have been made thus far. Here, we present an event detected by the Magnetospheric Multiscale mission near the dayside magnetopause. During this event, ∼748‐eV protons are observed to be in resonance with a wave. Detailed data analysis demonstrates the resonant velocity closely matches the wave's parallel phase speed, which, combined with the significant work done by wave perpendicular electric field, confirms this interaction as electromagnetic Landau resonance. Further investigation indicates these protons are being secularly accelerated within this resonance. Consequently, our observations provide the first empirical evidence supporting the previously suggested theoretical importance of the electromagnetic Landau resonance. Plain Language Summary: The electromagnetic Landau resonance shares the same resonance condition as the normal Landau resonance, but differs in that it involves the electromagnetic components of wave fields instead of the electrostatic components found in the case of the latter. Although it has been examined in theories and confirmed to occur in space plasmas experimentally, this resonance, especially the accompanying evolution of particle velocity distributions, has yet to be evaluated quantitatively through spacecraft observations. In this paper, we report the first observation of this resonance obtained by the Magnetospheric Multiscale mission near the dayside magnetosphere. In the reported case, protons of ∼400–1,000 eV are found to be in resonance with a wave. A more detailed examination of the observed fields and protons shows the corresponding resonant velocity is nearly identical to the wave's parallel phase speed. This observation, combined with the significant work done by wave perpendicular electric field, conclusively confirms the observed interaction as the electromagnetic Landau resonance. Further investigation indicates the protons are secularly accelerated by the wave via this resonance. Hence, our observations provide empirical evidence supporting the previously suggested theoretical significance of the electromagnetic Landau resonance. Key Points: MMS observations of electromagnetic Landau resonance near the dayside magnetopause are presentedThis resonance follows the same condition as the Landau resonance, but modulates particles via the electromagnetic components of wave fieldsAnalysis of the observed fields and protons provide conclusive evidence for this resonance accelerating protons [ABSTRACT FROM AUTHOR]

As an update on the current NOAA/NCEP operational ocean reanalysis systems, a new system named GLobal Ocean Reanalysis (GLORe) is recently built up based on the JEDI‐SOCA 3DVar scheme. In this study, the quality of GLORe is assessed in initializing ENSO predictions using the NOAA Unified Forecast System (UFS). In details, initialized by GLORe, 9‐month ensemble hindcasts are conducted from each May/November during 1982–2021. The ENSO prediction skill is compared to the current NOAA operational system CFSv2, suggesting that UFS initialized with GLORe has an improved skill in ENSO predictions. By conducting another set of hindcasts with UFS and the same initializations as CFSv2, it is found that the skill improvement is largely attributed to the ocean initialization with GLORe, but with some contributions from model improvements as well. The effect of ocean initializations is further confirmed by the superiority of GLORe over CFSR as validated against an objective analysis. Plain Language Summary: The operational climate monitoring and outlooks heavily rely on ocean data assimilation systems. At NOAA/NCEP, there are two such systems running in real time—GODAS and CFSR. As two highly related systems, GODAS and CFSR share some common weaknesses, and are lagging to meet the latest operational requirements. In this study, a new ocean reanalysis system (GLORe) is built based on the latest scientific advances. As a first evaluation about GLORe, this work focuses on its performance in initializing dynamical ENSO predictions, a critical component of climate outlooks. In particular, we complete a set of 9‐month ensemble hindcasts initialized with GLORe, by using the NOAA Unified Forecast System as the forecast model. The hindcasts are compared to the present NOAA operational system CFSv2 that is initialized with CFSR, and significant skill enhancements in ENSO predictions are seen in our hindcasts. Further experiments and diagnostics suggest that the skill improvement is mostly attributed to the GLORe initialization, but with some contributions from model improvements as well. As the configurations for our hindcasts are highly relevant to a future operational Seasonal Forecast System (SFS) at NOAA, the hindcasts reported in this paper will serve as an important benchmark for its developments. Key Points: A newly developed ocean reanalysis (GLORe) is introduced and evaluated for its quality in initializing ENSO predictionsUFS initialized with GLORe presents a better performance in ENSO predictions than the current operational system at NOAAThe hindcasts will be a benchmark for the Seasonal Forecast System (SFS) development at NOAA [ABSTRACT FROM AUTHOR]

A fundamental problem in plasma turbulence is understanding how energy cascades across multiple scales. In this paper, a new weak turbulence theory is developed to explain how energy can be transferred from Langmuir and Upper‐Hybrid waves to ion‐acoustic waves. A kinetic approach is used where the Boltzmann equation is Fourier‐Laplace transformed, and the nonlinear term is retained. A unique feature of this approach is the ability to calculate power spectra at low frequencies, for any wavelength or magnetic aspect angle. The results of this theory explain how the predominant type of 150‐km radar echoes are generated in the ionosphere. First, peaks in the suprathermal electron velocity distribution drive a bump‐on‐tail like instability that excites the Upper‐Hybrid mode. This excited wave then couples nonlinearly to the ion‐acoustic mode, generating the ∼10 dB enhancement observed by radars. This theory also explains why higher frequency radars like ALTAIR do not observe these echoes. Plain Language Summary: The onset and evolution of turbulent flows is one of the most important outstanding questions in classical physics. When a fluid, gas, or plasma goes turbulent the flow can no longer be described with simple parameters such as speed and temperature. The fundamental problem is that these types of parameters describe the whole system, but during turbulence the flow is irregular and involves both microscopic and macroscopic motions. The research presented here shows how a macroscopic instability can drive microscopic changes at vastly different length and time scales. The approach taken falls into the category of weak‐turbulence theory, which is where the turbulence is not overpowering, and therefore can be described using some of the standard tools from gas dynamics. This new turbulence theory is applied to the problem of 150‐km echoes. These echoes are a plasma instability observed by radars in the lower ionosphere between 130 and 170 km in altitude. The mechanism of the plasma instability driving 150‐km radar echoes has previously been worked out, but the weak‐turbulence theory developed here is needed to fully explain the observations. The results provide an unprecedented description of plasma turbulence across multiple time and length scales. Key Points: A kinetic theory is developed to explain how Langmuir and Upper‐Hybrid waves couple nonlinearly to ion‐acoustic wavesNonlinear mode coupling solves the problem of how 150‐km radar echoes are generated in the lower ionosphereMode coupling explains why only lower frequency (30–50 MHz) radars observe the enhanced ion‐acoustic waves in 150‐km echoes [ABSTRACT FROM AUTHOR]

In this study, a method for assimilating FY4A advanced geostationary radiance imager (AGRI) cirrus‐effected radiances (CER) is investigated, and the impact of this method on water vapor analysis and rainstorm forecasting is examined through observing system simulation experiments and actual case experiments. The high proportion of inverted humidity profiles in the cirrus‐effected pixels is the main reason for the negative effect of assimilation in the mid‐to‐lower troposphere. To address this, relevant constraint conditions are incorporated into the cost function. The statistical results reveal that the addition of a CER assimilation improves the analysis increment of water vapor, with pattern correlation coefficients of 0.33, 0.35, and 0.20 at 200, 300, and 400 hPa, respectively, which are greater than those of a clear‐sky radiance assimilation (0.28, 0.33, and 0.17, respectively). Moreover, the inclusion of a CER assimilation greatly improves data utilization, and has a neutral to positive effect on precipitation forecasting. Plain Language Summary: Infrared all‐sky radiance assimilation is an attractive but challenging problem in satellite data assimilation. Is there an alternative approach to achieve the assimilation of infrared radiance for a certain type of cloud? It is found that cirrus clouds, which are loose ice clouds composed of ice crystals, can partially transmit infrared radiance and are large in number. Considering these advantages, a new direct assimilation method for FY4A advanced geostationary radiance imager (AGRI) cirrus‐effected radiances is proposed in this paper. The method addresses the uncertainty in the assimilation of cirrus‐effected radiances by adding weak constraints of inverse humidity. This research highlights the substantial increase in AGRI data usage when incorporating cirrus‐effected radiance data, as well as the neutral‐to‐positive impact on water vapor analysis and precipitation forecasting. This study also suggests that future endeavors could combine infrared channels with lower‐level microwave channels, which may have a more significant contribution to infrared radiance assimilation. Key Points: A high percentage of inverse humidity exists in the atmospheric profile corresponding to cirrus cloud fields of view over landThe assimilation of cirrus cloud pixels greatly improves the utilization rateAssimilating advanced geostationary radiance imager cirrus‐effected radiances has a neutral to positive effect on water vapor analysis and precipitation forecasting [ABSTRACT FROM AUTHOR]

In the prevailing form of the generalized Ohm's law (GOL), −me/e(J/en)⋅∇(J/en) ${-}\left({m}_{e}/e\right)\left[(\boldsymbol{J}/en)\cdot \nabla \right](\boldsymbol{J}/en)$ is often neglected. Because of the resemblance to the magnetic tension, we refer to this term as the current tension electric field (ECT). Our theoretical analysis reveals that ECT with a characteristic length of mi/me1/6λe ${\left({m}_{i}/{m}_{e}\right)}^{1/6}{\lambda }_{e}$ dominates the electron inertia terms in the electron diffusion region (EDR) and is comparable to the electron pressure term in low‐βe conditions. Using particle‐in‐cell simulations, we demonstrate that ECT can contribute significantly to the reconnection electric field and energy dissipation at the boundaries of the inner EDR and in the outer EDR. Positive and negative J ⋅ ECT can be used to identify inner and outer electron diffusion regions, respectively. Plain Language Summary: Magnetic reconnection is a fundamental physical process which allows for the explosive release of magnetic energy into thermal and kinetic energy. It underlies many dynamic phenomena in the universe, including solar eruptions, geomagnetic substorms and tokamak disruptions. In collisionless plasma, the generalized Ohm's law (GOL) introduces collisionless effects which break the frozen‐in constraint and enable reconnection to occur. The term, −me/e(J/en)⋅∇(J/en) ${-}\left({m}_{e}/e\right)\left[(\boldsymbol{J}/en)\cdot \nabla \right](\boldsymbol{J}/en)$, which is one of the electron inertia terms of GOL, is referred to as the current tension electric field (ECT) by us due to its mathematical resemblance to magnetic tension. In many classic textbooks and review papers, ECT is considered as a small quantity and thus is ignored. In this study, we present solid evidence from both theoretical studies and particle‐in‐cell (PIC) simulations to demonstrate that ECT dominates the electron inertia terms and plays important roles in providing reconnection electric field and energy dissipation in reconnection. Therefore, it should not be ignored. Based on our results, many classic textbooks in which ECT has been ignored must be modified. Key Points: ECT dominates the electron inertia terms in the electron diffusion region (EDR) and thus cannot be ignored in the generalized Ohm's lawECT contribute significantly to the reconnection electric field and energy dissipation in the inner and outer EDRsPositive and negative J · ECT can be used to identify inner and outer EDRs, respectively [ABSTRACT FROM AUTHOR]

Polythermal glaciers can trap considerable volumes of liquid water with the potential to generate devastating outburst floods. This study aims to identify water‐filled subglacial reservoirs from ambient seismic noise collected by moderate‐cost surveys. The horizontal‐to‐vertical spectral ratio technique is highly sensitive to impedance contrasts at interfaces, thus commonly used to estimate glacier thickness. Here, we focus on the inverse ratio, that is, the V/H spectral ratio (VHSR), whose high values indicate a low impedance volume beneath the surface, suggesting subglacial cavities. We analyze VHSR peaks from a seismic array of 60 nodes installed on the Tête‐Rousse Glacier (Mont Blanc massif, French Alps); data were gathered over 15 days. Mapping the VHSR amplitude over the free surface reveals the main cavity locations and the basal areas affected by melting within the glacier. Results obtained in the field are supported by a conceptual model based on 3D finite‐element simulations. Plain Language Summary: Considerable volumes of liquid water may be trapped within cavities in polythermal glaciers. If these cavities rupture, the resulting outburst flood has the potential to cause devastation in populated mountain areas. With the aim of testing methods to locate such cavities, we installed 60 small 3‐component seismic sensors on the Tête‐Rousse Glacier (Mont Blanc massif, French Alps), which is known to contain such cavities. We used these sensors to test a detection method based on ambient seismic noise. For 3 weeks, the sensors recorded vibrations within the glacier. On a glacier without cavities, these vibrations ought to be predominantly in the horizontal direction. In the presence of a cavity, we expect the ice above the cavity to vibrate mostly vertically—like a bridge. In this paper, we highlight areas on the glacier where vertical vibrations were stronger than horizontal vibrations. These areas fit well with the locations of the main known cavities in this glacier, and with areas affected by basal melting. We supported our field observations with modeling based on 3D simulations, paving the way to a new method to locate water‐filled cavities within glaciers. Key Points: Spectral analysis from ambient seismic noise is complementary to other geophysical methods for investigating glaciers at depthResults suggest that the vertical‐to‐horizontal spectral ratio is a reliable proxy to locate subglacial cavitiesExperimental results were confirmed using a simplified numerical model [ABSTRACT FROM AUTHOR]

Bicoherence analysis is statistically performed for the oxygen ion cyclotron harmonic (OCH) waves observed by Van Allen Probes. While OCH waves and so‐called electromagnetic ion cyclotron harmonics have indistinguishable spectral characteristics in observation, they are believed to be excited by different mechanisms with the latter being suggested to arise from nonlinear wave‐wave coupling. Our result reveals that most of the OCH wave events have small bicoherence indices, so they are unlikely excited by wave‐wave coupling. The result is not much affected by the parameter choice in the bicoherence analysis, although increasing the subinterval length and/or reducing the subinterval overlap increases the chance of getting large bicoherence index values. Furthermore, the examination of two special events with large bicoherence indices shows that the observed phase relationship among different wave components does not align with the expectation from wave‐wave coupling. The events cannot be convincingly confirmed to be generated through wave‐wave coupling. Plain Language Summary: This paper presents a statistical bicoherence analysis study of the oxygen ion cyclotron harmonic (OCH) waves observed by Van Allen Probes. OCH waves have apparent features similar to electromagnetic ion cyclotron (EMIC) harmonics in observation. Previous studies have suggested that OCH waves are excited through the oxygen ion Bernstein instability but EMIC harmonics are generated by nonlinear wave‐wave coupling. Bicoherence analysis is commonly employed for assessing wave‐wave coupling. The results of our bicoherence analysis indicate that most of the OCH events have bicoherence indices less than 0.5, so they are unlikely generated through wave‐wave coupling. The study also demonstrates that the parameter choice in bicoherence analysis affects the calculated index values, but the index values remain mostly less than 0.5 for the various reasonable parameter choices tested. In addition, a detailed analysis of the phase relationship among various electric and magnetic wave components in two specific OCH events reveals that, despite their large bicoherence indices, the observed phase relationship does not align with what would be expected if the waves are generated from wave‐wave coupling. This reminds us that having a large bicoherence index is a necessary but not sufficient condition to prove that waves are generated by wave‐wave coupling. Key Points: Most of the oxygen ion cyclotron harmonic (OCH) waves observed by Van Allen Probes have small bicoherence indicesIncreasing the subinterval length and/or reducing the subinterval overlap increases the chance of getting large bicoherence index valuesExamination of two special OCH wave events with large bicoherence indices does not support them being generated from wave‐wave coupling [ABSTRACT FROM AUTHOR]

Numerical modeling of ice sheet motion and hence projections of global sea level rise require information about the evolving subglacial environment, which unfortunately remains largely unknown due to its difficulty of access. Here we advance such subglacial observations by reporting multi‐year observations of seismic tremor likely associated with glacier sliding at Helheim Glacier. This association is confirmed by correlation analysis between tremor power and multiple environmental forcings on different timescales. Variations of the observed tremor power indicate that different factors affect glacial sliding on different timescales. Effective pressure may control glacial sliding on long (seasonal/annual) timescales, while tidal forcing modulates the sliding rate and tremor power on short (hourly/daily) timescales. Polarization results suggest that the tremor source comes from an upstream subglacial ridge. This observation provides insights on how different factors should be included in ice sheet modeling and how their timescales of variability play an essential role. Plain Language Summary: The Greenland Ice Sheet has lost ice increasingly in the past few decades, contributing significantly to global sea level rise. However, large uncertainties remain in computer simulations of such ice mass loss and hence sea level rise. This uncertainly is mainly attributed to the lack of information on what is happening at the bottom of the ice sheet and how that affects ice sheet movement. For example, how much water is there and whether it is in isolated pockets or is well distributed as a thin sheet can have an important effect on ice movement. In this paper, we observe small ground motions that are generated during glacier movement at a marine‐terminating glacier in Greenland. By analyzing the energy variation of the small ground motions over multiple years as well as observing the reasons that cause the variations, we learn that subglacial water pressure may control ice flow speeds on a seasonal/annual scale, and that ocean tides can change ice flow on an hourly/daily scale. This observation provides important constraints for computer simulations of future sea level rise in terms of the impacting factors and their respective timescales. Key Points: Multi‐year seismic records reveal glacial slip and tremor variability at Helheim GlacierTremor correlates with high effective pressure at tidal timescales, opposite to the expectation at longer timescalesThe tremor source points to an upstream subglacial ridge [ABSTRACT FROM AUTHOR]

Previous studies suggested that Atlantic Multidecadal Variability (AMV) modulations on pan‐Pacific sea surface temperature (SST) variability and prediction are model‐dependent. These results were mainly based on SST forcing experiments in which AMV‐related Atlantic SST anomalies were prescribed. However, the AMV itself is also model‐dependent, but its influences on the Pacific remain unclear. Here, we use multi‐model fully coupled experiments from the Coupled Model Intercomparison Project Phase 6 (CMIP6), along with observations, to study the model‐dependent AMV trans‐basin effects. We found that AMV strength is a key factor: Stronger (Weaker) model AMV than observations overestimates (underestimates) SST response and decadal prediction skills, mainly in the North Pacific. The reason is that stronger positive phased AMV, for example, leads to higher sea level pressure anomalies over the North Pacific, which lifts sea surface height and deepens thermocline to warm SST. Our study highlights the necessity to improve simulations of AMV strength. Plain Language Summary: Pacific sea surface temperature (SST) decadal variability and prediction are important for economy and environment. The Atlantic Multidecadal Variability (AMV) was thought to significantly influence Pacific SST variability and prediction. However, the results of previous studies were model‐dependent. In this paper, we use fully coupled experiments of the Coupled Model Intercomparison Project Phase 6 (CMIP6) models to study what contributes to the model dependency. We found that the strength of the AMV is a key factor influencing AMV trans‐basin modulations on SST variability and decadal prediction, mainly in the North Pacific Ocean. The related mechanisms are discussed. Our paper sheds light on the way to improve North Pacific SST decadal prediction. Key Points: Climate models show a strong inter‐model spread of Atlantic Multidecadal Variability (AMV) strengthModels with stronger (weaker) AMV than observations overestimate (underestimate) North Pacific sea surface temperature (SST) response and decadal predictionThe North Pacific SST response is primarily forced by AMV‐induced wind stress curl and ocean dynamics [ABSTRACT FROM AUTHOR]

Scafetta (2022, https://doi.org/10.1029/2022gl097716) purports to test Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models through a comparison of temperature changes over three decades. Unfortunately, the paper contains numerous conceptual and statistical errors that undermine all of the conclusions. First, no uncertainty is given for the observational temperature difference, making it impossible to assess compatibility with any model result. Second, the CMIP6 data are the ensemble means for each model, but the metric being tested is sensitive to the internal variability and so the full ensemble for each model must be used. When this is corrected, the conclusion that "all models with ECS > 3.0°C overestimate the observed global surface warming" is not sustained. Third, the statistical test in Section 2 would reject all models even in a perfect model setup given sufficient ensemble members, thus the second conclusion "that spatial t‐statistics rejects the data‐model agreement" is also not sustainable. Plain Language Summary: Comparisons of models and observations need to account from multiple sources of uncertainty in both the observations and due to the chaotic dynamics of the weather. The analyses in Scafetta (2022, https://doi.org/10.1029/2022gl097716) do not take either of these issues into account and thus the conclusions in that paper are not supportable. Key Points: Scafetta (2022) contains errors in both of the statistical tests used that make the conclusions unsupportable [ABSTRACT FROM AUTHOR]

Sea surface temperatures (SSTs) vary not only due to heat exchange across the air‐sea interface but also due to changes in effective heat capacity as primarily determined by mixed layer depth (MLD). Here, we investigate seasonal and regional characteristics of the contribution of MLD anomalies to the month‐to‐month variability of SST using observational datasets. First, we propose a metric called Flux Divergence Angle, which can quantify the relative contributions of surface heat fluxes and MLD anomalies to SST variability. Using this metric, we find that MLD anomalies tend to amplify SST anomalies in the extra‐tropics, especially in the eastern ocean basins, during spring and summer. In contrast, MLD anomalies tend to suppress SST anomalies in the eastern tropical Pacific during December‐January‐February. This paper provides the first global picture of the observed importance of MLD anomalies to the local SST variability. Plain Language Summary: Sea surface temperature (SST) is one of the important indicators as well as drivers of climate variability over the globe. SST varies not only due to changes in surface heat fluxes but also due to changes in effective heat capacity as mainly determined by mixed layer depth (MLD). However, the observed characteristics of the latter process associated with the MLD anomalies are limited. In this study, we propose a new metric called "Flux Divergence Angle (FDA)," which can quantify the relative importance of MLD and surface heat flux to the SST variability. Using this metric, we find that the MLD anomalies tend to amplify the local SST variability in the extra‐tropics during spring and summer. On the other hand, MLD anomalies tend to suppress the SST variability in the eastern tropical Pacific during December‐January‐February. This paper provides, for the first time, the global picture of relative importance of MLD anomalies to the SST variability based on observations. Key Points: Relative contributions of mixed layer depth (MLD) and surface heat flux anomalies to sea surface temperature (SST) variability are investigated using the Flux Divergence Angle metricMLD anomalies tend to amplify SST anomalies in the extra‐tropics, especially in eastern part of ocean basin, during the spring and summerMLD anomalies tend to suppress SST anomalies in the eastern tropical Pacific during December‐January‐February [ABSTRACT FROM AUTHOR]

The runoff change in a large river is significant for hydrological event monitoring, such as floods and droughts. In this paper, we attempt to invert the river flow change based on the surface displacements observed by the continuous global navigation satellite system (GNSS) stations in the Wuhan section of the Yangtze River (WYR). We establish a two‐dimensional model accounting for deformation from a line load in an elastic half‐space to estimate the annual water load change from the GNSS data. The results show that the inverted line load from the annual maximum displacement change observed by the GNSS is Ne=2.30×108N·m−1 ${N}_{e}=2.30\times {10}^{8}\mathrm{N}\cdot {\mathrm{m}}^{-1}$, which is in good agreement with the river load from the hydrological station. This paper demonstrates a low‐cost and practical method to river flow research in local areas, which is also a creative application for the GNSS. Plain Language Summary: The runoff change in large rivers is an important element for flood and drought monitoring. Hydrological stations are used to monitor the water load change. Because of the high cost of construction and maintenance, there are few hydrological stations in most areas, and the unpredictable noise of hydrological stations influences the stability and precision of the results. We use the vertical displacements observed by the global navigation satellite system (GNSS) to estimate the river load and find that the results agree with the calculated water load change from hydrological stations. Thus, the GNSS can be an alternative for runoff change research, with low cost and high efficiency. In this study, we find a new application for the GNSS to water runoff change in local areas. Key Points: We propose a new method for estimate the river load change using the continuous global navigation satellite system (GNSS) dataA simple two‐dimensional line load on Elastic half‐space can invert the river load with considerable accuracy in local areasThe forward modeling prove that the modeled displacement agrees with the observed displacement from the GNSS [ABSTRACT FROM AUTHOR]

The nature of the inner core (IC) temporal changes is of great importance in understanding the deep earth dynamics. The comment by Tian and Wen (2023, https://doi.org/10.1029/2023gl103173) on our previous paper (Yang & Song, 2022, https://doi.org/10.1029/2022gl098393) provided a new observation as evidence against the IC rotation and proposed that our observations are instead from localized rapid changes at the IC surface. Here we argue the opposite to its conclusions. The comment misinterpreted our logic and many of our observations and arguments. Its one new waveform does not contradict with the "rotation" model. The original evidence for the "surface" model is demonstrated to be an artifact from station clock errors and instrument changes. Additionally, the surface model lacks a solid physical and quantitative basis to explain existing seismic evidence. We conclude that the rotation model is currently the best interpretation and the surface model is not a viable alternative. Plain Language Summary: Seismic waves traversing the Earth's inner core (IC) from repeating earthquakes exhibit significant temporal changes in their arrival times. The intriguing observation has been generally considered as evidence of the IC rotation (relative to the mantle) shifting the IC's laterally varying structures, which is further supported by the compelling evidence in Yang and Song (2022, https://doi.org/10.1029/2022gl098393). In the comment by Tian and Wen (2023, https://doi.org/10.1029/2023gl103173) on our study, they made harsh criticisms of our research and argued against the IC rotation, and proposed instead that the seismic observations result from localized topographic changes at the IC surface. In response, we believe that they misunderstood our logic and misinterpreted a number of our observations and arguments. The only one new example they presented does not contradict with the IC rotation model. Moreover, the original evidence supporting the IC surface change (Wen, 2006, https://doi.org/10.1126/science.1131692) is actually an artifact caused by station clock errors and instrument changes. They neglected substantial evidence that contradicts their proposed model but supports the IC rotation. Their model also lacks a quantitative physical basis. In conclusion, their comment does not diminish our confidence in the rotation model in our original paper and their proposed alternative model is not viable. Key Points: The comment misinterpreted our logic and arguments and failed to consider a large body of disadvantageous evidence from previous studiesThe only one new waveform does not contradict with the inner core (IC) rotation, while all the data from 10 doublets are consistent with itThe model of IC surface change can be ruled out, which is based on misinterpreted evidence and lacks a physical and quantitative basis [ABSTRACT FROM AUTHOR]

The variation of Tropical cyclone azimuthal wind speed (V) with distance from storm center (r) is a fundamental aspect of storm structure with important implications for risk and damages. The theoretical model of Emanuel (2004, https://doi.org/10.1017/CBO9780511735035.010), which applies outside the rainy core of the storm, matches radiatively‐driven subsidence and Ekman suction rates just above the boundary layer to obtain a nonlinear differential equation for dV/dr. This model is appealing because of its strong physical foundation, but lacks a known analytic solution for V(r). In this paper, I obtain an analytic solution to V(r) for the Emanuel (2004, https://doi.org/10.1017/CBO9780511735035.010) outer wind model. Following previous work, I then use this solution to explore properties of merged wind models that combine the outer model with an inner model, which applies to the rainy core of a storm. Plain Language Summary: The swirling winds of hurricanes extend far away from their centers, fading away into background weather. Previous work proposed a theoretical model to explain how these swirling winds decrease with distance from the storm center for areas outside the rainy core of the storm. But this model has not previously been solved with pencil‐and‐paper methods. Here, I find a new mathematical formula that solves the model for how winds weaken away from the center of a hurricane. I then use the solutions to examine how hurricane winds near the center of a storm relate to the winds far from the center, and what this implies about how hurricanes behave. Key Points: Analytic solutions are derived for the previously unsolved outer wind model of Emanuel (2004, https://doi.org/10.1017/CBO9780511735035.010)Analytic wind profile calculations enable faster merged wind profile calculations, following Chavas et al. (2015, https://doi.org/10.1175/jas-d-15-0014.1)Scaling of merged wind profiles suggests decreases in the radius of maximum wind with warming, at constant outer size [ABSTRACT FROM AUTHOR]

It is shown that a recently developed hybrid modeling approach that combines machine learning (ML) with an atmospheric global circulation model (AGCM) can serve as a basis for capturing atmospheric processes not captured by the AGCM. This power of the approach is illustrated by three examples from a decades‐long climate simulation experiment. The first example demonstrates that the hybrid model can produce sudden stratospheric warming, a dynamical process of nature not resolved by the low resolution AGCM component of the hybrid model. The second and third example show that introducing 6‐hr cumulative precipitation and sea surface temperature (SST) as ML‐based prognostic variables improves the precipitation climatology and leads to a realistic ENSO signal in the SST and atmospheric surface pressure. Plain Language Summary: This paper introduces and tests schemes for efficiently enabling significant expansion of the utility and scope of a recently introduced hybrid modeling technique that combines machine learning with an atmospheric global circulation model (AGCM). Simulation experiments are carried out with an implementation of the approach on a low resolution simplified AGCM. An examination of the simulated atmospheric circulation suggests that the hybrid model can capture dynamical process not captured by the AGCM. Moreover, the addition of precipitation and sea surface temperature (SST) as machine learning predicted physical quantities to the model improves the precipitation climatology and leads to a realistic El Niño‐La Niña signal in the SST and atmospheric surface pressure. Key Points: A hybrid system combining an atmospheric global circulation model (AGCM) with a machine‐learning component can capture processes not captured by the AGCMMachine learning provides a flexible framework to introduce additional prognostic variables into the hybrid modelThe prototype hybrid model tested in the paper is stable and has a realistic climate in decades‐long simulation experiments [ABSTRACT FROM AUTHOR]

This paper expands on work showing that the winter North Atlantic Oscillation (NAO) is predictable on decadal timescales to quantify the skill in capturing the North Atlantic eddy‐driven jet's location and speed. By focusing on decadal predictions made for years 2–9 from the sixth Coupled Model Intercomparison Project over 1960–2005 we find that there is significant skill in jet latitude and, especially, jet speed associated with the skill in the NAO. However, the skill in the NAO, jet latitude and speed indices appears to be sensitive to the period over which it is assessed. In particular, skill drops considerably when evaluating hindcasts up to the present day as models fail to capture the recent observed northern shift and strengthening of the winter eddy‐driven jet, and more thus positive NAO. We suggest that the drop in atmospheric circulation skill is related to reduced skill in North Atlantic sea surface temperatures. Plain Language Summary: Climate models have the capability to predict the evolution of mean atmospheric circulation over long timescales, from annual to decadal and longer. However, models are overestimating the chaotic, unpredictable component of the climate's variability and, although model predictions follow the observed oscillations of the climate, the strength of these oscillations is critically underestimated. While climate models have demonstrated skill in predicting the North Atlantic Oscillation (NAO), this paper assesses model skill in predicting the evolution of the wintertime North Atlantic eddy‐driven jet, with the aim to highlight how much of the predictive skill of the NAO is derived from accurate predictions of the jet's state. We find levels of skill similar to that for the NAO, with slightly higher skill for the jet's strength (speed) over its location (latitude of maximum speed). We also notice a drop in skill over the last decade, as models fail to capture the latest trends in the NAO and jet's evolution, and suggest that it might be related to degradation in skill at predicting surface temperature variability. Key Points: The winter North Atlantic eddy‐driven jet is predictable on decadal time‐scales with skill in jet speed comparable to that for the North Atlantic Oscillation (NAO)Anomalies in the jet are substantially smaller than expected from skill alone and so suffer from noise overestimationSkill drops significantly in the last decade, as hindcasts do not capture the return to positive NAO conditions post‐2010 [ABSTRACT FROM AUTHOR]

On 7 January 2014, a solar storm erupted, which eventually compressed the Earth's magnetosphere leading to the generation of chorus waves. These waves enhanced local wave‐particle interactions and led to the precipitation of electrons from 10 s eV to 100 s keV. This paper shows observations of a low energy cutoff in the precipitation spectrum from Van Allen Probe B Helium Oxygen Proton Electron measurements. This low energy cutoff is well replicated by the predicted loss calculated from pitch angle diffusion coefficients from wave and plasma observations on Probe B. To our knowledge, this is the first time a single spacecraft has been used to demonstrate an accurate theoretical prediction for chorus wave‐induced precipitation and its low energy cutoff. The specific properties of the precipitating soft electron spectrum have implications for ionospheric activity, with the lowest energies mainly contributing to thermospheric and ionospheric upwelling, which influences satellite drag and ionospheric outflow. Plain Language Summary: On 7 January 2014, a large storm erupted from the Sun. This storm encountered the Earth and compressed the magnetosphere a few days later. The compression of the magnetosphere led to the creation of chorus waves, a wave‐type known to interact only with electrons with specific energies. In this case, the waves interacted with electrons in the magnetosphere's outer radiation belt. They caused the loss of electrons from 10 s eV to 100 s keV into the ionosphere and upper atmosphere. This paper uses theory to determine which energies we expect will interact with the observed chorus wave. We use the Helium Oxygen Proton Electron instrument from the Van Allen Probes to see if our predictions are correct. We care about these processes because the loss of these electrons can affect ionospheric activity. Key Points: Upper band chorus waves can have a minimum resonant energy in the 10 s eV energy rangeChanges in the minimum resonant energy can change the cut off for what lower energy particles will be lostThe lower energy cut off can be observed in the Van Allen Probes Helium Oxygen Proton Electron data [ABSTRACT FROM AUTHOR]

Observations of a quiet electrostatic auroral arc by the ALIS network on 5 March 2008 are used to infer a two‐dimensional map of the flux of precipitating energy. Among a family of numerical solutions of a stationary magnetosphere—ionosphere coupling model in which the origin of the arc is a magnetospheric generator interface, we find which generator interface properties best fit the observed precipitating energy flux. The procedure finds that the plasma populations in the generator are colder and more rarefied on one side of the interface and warmer and denser on the other side, similar to a transition between plasma trough and plasma sheet plasmas. The increase of the arc's brightness, the decrease of its thickness and its slight spatial undulation may be driven by an increase of plasma sheet electron temperature in the tailward direction, tangential to the interface, and a local spatial indentation in the dawn‐ward direction. Plain Language Summary: Optical observations of aurora provide information about the local electromagnetic and plasma conditions in the ionosphere where the impact of energetic electrons produces auroral light emissions. The electrons gain energy through acceleration by static or dynamic electric fields along their path from the magnetospheric source to the upper ionized atmosphere where they collide with various atomic species, like oxygen and nitrogen, which emit light at various wavelengths. In this paper we use optical observations of a steady electrostatic auroral arc to identify the conditions in the magnetospheric source that best fit these observations in the context of an electrostatic auroral acceleration model. This way, optical auroral observations from the ground are used as a remote sensing tool to probe the magnetospheric source of the arc. Key Points: A new application using tomographic imaging of electrostatic auroral arcs with ALIS estimates the magnetospheric generator stateThe generator of the arc observed by ALIS appears to be a plasma interface at the contact between trough and plasma sheet‐like plasmasThe arc's longitudinal changes are linked to a tailward increase of electron temperature and dawnward indentation of the generator interface [ABSTRACT FROM AUTHOR]

Previous studies suggested that tropical sea surface salinity (SSS) can influence tropical Pacific sea surface temperature (SST) through mixing and entrainment and thus it may be a signal for El Niño‐Southern Oscillation (ENSO) prediction. This paper explores the influence of SSS on ENSO spring predictability barrier (SPB) using an empirical dynamic model ‐ Linear Inverse Model (LIM). By coupling and decoupling SSS in the LIM, we find that tropical Pacific SSS plays a significant role in weakening both Central‐Pacific and Eastern‐Pacific ENSO SPB. The evolution of optimal initial structure also shows the importance of SSS dynamics in ENSO. We found an SSS mode that plays the dominant role in SSS impacting ENSO prediction. By the analysis of lead‐lag correlation, we find that this mode can induce easterlies during the spring, which finally leads to a La Niña‐like SST pattern in the winter through zonal advective and thermocline feedbacks. Plain Language Summary: The spring predictability barrier (SPB) is a phenomenon of forecast skill reduction of the El Niño‐Southern Oscillation (ENSO) when it comes to the boreal spring, regardless of the initial month. Sea surface salinity (SSS) can influence sea surface temperature by altering sea surface density and thus it may be a signal for ENSO prediction. Using a linear dynamical model, we find that SSS plays an important role in improving the forecast skill of ENSO and weakening SPB. We further find that SSS can induce the easterlies during the spring, which finally leads to a La Niña‐like SST pattern. Our study suggests that SSS can be used to predict ENSO about 1 year later. Key Points: A linear dynamical model suggests that taking sea surface salinity (SSS) into consideration can strongly weaken Central‐Pacific and Eastern‐Pacific El Niño‐Southern Oscillation (ENSO) spring predictability barrier (SPB)A new SSS mode is found to be important for weakening ENSO SPBThe SSS mode can predict ENSO events about 1 year earlier by inducing sea surface temperature and wind anomalies in the early spring [ABSTRACT FROM AUTHOR]

Field Line Resonances (FLRs) are a critical component in Earth's magnetospheric dynamics, associated with the transfer of energy between Ultra Low Frequency waves and local plasma populations. In this study we investigate how the polarisation of FLRs are impacted by cold plasma density distributions during geomagnetic storms. We present an analysis of Van Allen Probe A observations, where the spacecraft traversed a storm time plasmaspheric plume. We show that the polarisation of the FLR is significantly altered at the sharp azimuthal density gradient of the plume boundary, where the polarisation is intermediate with significant poloidal and toroidal components. These signatures are consistent with magnetohydrodynamic modeling results, providing the first observational evidence of a 3D FLR associated with a plume in Earth's magnetosphere. These results demonstrate the importance of cold plasma in controlling wave dynamics in the magnetosphere, and have important implications for wave‐particle interactions at a range of energies. Plain Language Summary: Earth's space environment is home to electrons and ions across a wide range of energies, trapped in the region by our global geomagnetic field. Energy can be transferred to and from the trapped particles through oscillations in the magnetic field, and these processes are responsible for the extreme energization of trapped electrons to hazardous levels for local spacecraft. In this paper we explore a type of magnetic field oscillation termed Field Line Resonances (FLRs): standing waves on a field line analogous to the oscillatory motion of guitar strings. We use spacecraft observations to show that the direction of the field line oscillations changes significantly depending on the density of the background plasma. The results confirm previous modeling work, and are the first observational evidence of 3D FLRs at a plume. The findings have important consequences for how FLRs transfer energy between the electrons and ions. Key Points: We present the first observational evidence of a 3D Field Line Resonance at the sharp density gradient of a plume edgeThe observed polarisation change confirms magnetohydrodynamic modeling results and predictions made by Elsden and Wright (2022)The presence of 3D Field Line Resonances during storm times has impacts for how Ultra Low Frequency waves couple and interact with local plasma [ABSTRACT FROM AUTHOR]

The responses of atmospheric kinetic energy (KE) spectra to three convective parameterizations (CPs) in global high‐resolution simulations are revealed. The results show that the KE spectra exhibit high sensitivity to the CPs, mainly at mesoscales in the middle and upper troposphere. The New Tiedtke scheme produces the steepest mesoscale slope, followed by the Kain‐Fritsch scheme and then the Grell‐Freitas scheme. In general, there is a compensating relationship between latent heat released by the CP and microphysics parameterization (MP). The less latent heat released by the CP is compensated by the more latent heat released by the MP. The shallowest mesoscale spectra for the Grell‐Freitas scheme are related to the strongest downscale cascade dominated by the rotational component of the flow, and this is attributed to more latent heat released from MP enhancing the intensity of vorticity in the troposphere and producing more gravity wave activities in the lower stratosphere. Plain Language Summary: At the current horizontal resolution level of the atmospheric models, convective parameterization (CP) is crucial for representing convective clouds unresolved by model mesh and thus is still an important model component. Exploring the impacts of different CP schemes on global high‐resolution simulations is an important subject of modeling. Energy spectra have become a useful diagnostic for validating and comparing atmospheric models. Their sensitivity to CP is an important and not‐well‐studied part of this subject. This paper investigates the impact of CPs on atmospheric mesoscale kinetic energy spectra with global simulations from the Model for Prediction Across Scales. We found that the energy spectral slope and energy cascade are sensitive to the CP schemes. This is related to the complementary relationship between CP and microphysical parameterization (MP), which is also important for moist convection development and evolution. The less latent heat released by the CP, the more released by the MP. This leads to stronger vertical motion, accompanied by stronger convergence/divergence in the troposphere, thereby enhancing vortex motion. As a result, more energy is transferred from the synoptic scale to the mesoscale and more gravity waves are vertically propagated into the lower stratosphere, leading to the shallower spectra at mesoscales. Key Points: The kinetic energy (KE) spectra exhibit high sensitivity to the convective parameterizations (CPs) mainly at mesoscalesThe more latent heat released from CP, the steeper KE spectra at mesoscalesThe shallowest mesoscale KE spectra generated by the Grell‐Freitas scheme are attributed to the strongest RKE downscale cascades [ABSTRACT FROM AUTHOR]

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

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

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

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