Geophysical Research Letters

Tropical cyclones (TCs) are an important source of turbulent mixing for the upper ocean at low latitudes, causing sea surface cooling and subsurface warming. A new estimate of annually accumulated sea surface cooling and upper ocean diapycnal diffusivity induced by TCs is obtained by using quantified cold wake sizes, which were largely ignored by previous studies. Both the annually accumulated tropical cyclone‐induced sea surface cooling and upper ocean diffusivity on a global scale show a significant decreasing trend over the period of 1982–2016, at a rate of −0.09 ± 0.03 °C/decade and −0.03 ± 0.01 cm²/s/decade respectively. The strengthening of ocean stratification with global warming contributes to the decrease of sea surface cooling and mixing, while the changes of tropical cyclone characteristics (such as translation speed, intensity, number, lifetime and size) contribute differently in various ocean basins.

Plain Language Summary Mass redistributions occurring in the Earth's interior, for example, when a magma batch is displaced through the feeding system of an active volcano, may induce tiny changes in gravity over time, measurable on the ground. Measurement of such changes requires high‐precision devices, namely, the gravimeters, which can detect variations as small as one part in 10⁹ of the gravity acceleration on Earth. However, standard gravimeters are not ideally suited for use in harsh field conditions, especially when continuous measurements are the target. Recent advances in quantum technology have allowed the development of a portable gravimeter which can successfully operate under field conditions. Here we present the world's first application of this quantum gravimeter for monitoring and studying an active volcano. The device was deployed only 2.5 km away from the summit active craters of Mt. Etna volcano (Italy) and has provided a high‐quality gravity time series. Inspection of this time series highlighted gravity changes which are reflective of bulk volcanic processes, involving magma and exsolved gas in the upper part of Mt. Etna's plumbing system.

The daily variation of ground‐level ozone (O3), a harmful pollutant, is positively correlated with air temperature (T) in many midlatitude land regions in the summer. The observed temporal regression slope between O3 and T (dO3/dT) is referred to as the “ozone‐climate change penalty” and has been proposed as a way to predict the impact of future climate warming on O3 from observations. Here, we use two chemical transport models to show that the spatial variation of dO3/dT is primarily determined by simultaneous meridional advection of O3 and T. Furthermore, the sign and magnitude of dO3/dT can be approximated by their climatological meridional gradient ratio (O3 gradient divided by T gradient). Consideration of expected changes in the meridional gradients of T and O3 due to climate change indicates that dO3/dT will likely change. Caution is needed when using the observed climate penalty to predict O3 changes.

Plain Language Summary The exchange of contaminants and nutrients between surface and subsurface water in the hyporheic zone of rivers and wetlands controls water quality as well as the metabolism of benthic microbes and the associated biogeochemical cycle. Vegetation, which is ubiquitous in aquatic ecosystems, has been found to affect the surface‐subsurface exchange and as such impact water quality and stream biogeochemical cycle. However, how vegetation impacts this exchange remains unclear, making it difficult to predict the contaminant transport and biogeochemical cycle in streams, lakes, and coastal areas with vegetation. In this study, we directly visualized the release of a fluorescent dye from the transparent sediment into the surface water in a water‐recirculating tank filled with translucent vegetation. We discovered that vegetation can significantly increase the exchange in the hyporheic zone. Furthermore, we proposed a model to predict the impacts of vegetation on hyporheic exchange. We believe that this finding will help improve predictions of contaminant transport and biogeochemical cycle in streams and other aquatic ecosystems. The results of this study will also help ecologists design stream restoration projects that use vegetation to increase the retention and degradation of contaminants in sediment.

Plain Language Summary Earthquakes are among the most destructive natural hazards known to humankind. While earthquakes can not be predicted, it is possible to record them in real‐time and provide warnings to locations that the shaking has not reached yet. Warning times usually range from few seconds to tens of seconds. For very large earthquakes, the rupture itself, which is the process sending out the seismic waves, can have a similar duration. Whether the final size of the earthquake, its magnitude, can be determined while the rupture is still ongoing is an open question. Here we show that this question is inherently probabilistic ‐ how likely is an event to become large? We develop a formulation of rupture predictability in terms of conditional probabilities and a framework for estimating these from data. We apply our approach to two observables: moment rate functions, describing the energy release over time during a rupture, and seismic waveforms at distances of several thousand kilometers. The final earthquake magnitude can only be predicted after the moment rate peak, at approximately half the event duration. Even then, it is impossible to foresee future subevents. Our results suggests that ruptures exhibit a universal initiation behavior, independent of their size.

Carbonyl sulfide (COS) plays an important role in the sulfur cycle and climate change. Yet, much remains unknown about the photochemical mechanisms of COS in nutrient‐rich seawater. We measured the photochemical production rates of COS in the surface seawater of the Indian Ocean under sunlight irradiation. The photochemical production of COS was mainly initiated by ultraviolet (UV) radiation with UVA contributing approximately 68% to the total COS production. Using cysteine, a typical proxy of dissolved organic sulfur, the effect of enhanced nitrate concentration on COS formation was conducted in authentic seawater during simulated sunlight irradiation, indicating the enhancement of the COS formation with increasing nitrate concentrations. This result revealed that the generation of hydroxyl radical with nitrate photolysis plays a key role in the COS formation process. These findings improve our understanding of the marine COS photoproduction cycle and the impact of nitrate on the COS photochemical production in surface seawater.

Plain Language Summary The destructiveness of tropical cyclones (TCs) is mainly caused by their strong winds. The maximum wind speed, namely TC intensity, and its evolution has been intensively studied, including rapid intensification (RI). However, the extent of strong winds and its growth remains little‐explored. We investigate, for the first time, the rapid growth (RG) of the gale‐force wind radius (R34) for Atlantic hurricanes. We define RG by the 90th percentile of R34 changes, which is equivalently at least 75 km/24 hr. This threshold is supported by an objective anomaly detection algorithm, the isolation forest. There are 88% of the TCs (15/17) with large lifetime maximum size (larger than 400 km) undergoing RG. Among the 11 TCs with high destructive potential (kinetic energy higher than 82TJ), nine show RG, while only five undergo RI. The TCs with RG also show a more discernible size life cycle than those without RG. Our analysis highlights the crucial role of the rapid growth of TC outer size in changing the TC overall destructive potential, which is found to be at least as important as the widely recognized TC rapid intensification.

Medium energy electron (MEE) (30–1,000 keV) precipitation enhances the production of nitric (NOx) and hydrogen oxides (HOx) throughout the mesosphere, which can destroy ozone (O3) in catalytic reactions. The dynamical effect of the direct mesospheric O3 reduction has long been an outstanding question, partly due to the concurrent feedback from the stratospheric O3 reduction. To overcome this challenge, the Whole Atmosphere Community Climate Model version 6 is applied in the specified dynamics mode for the year 2010, with and without MEE ionization rates. The results demonstrate that MEE ionization rates can modulate temperature, zonal wind and the residual circulation affecting NOx transport. The required fluxes of MEE to impose dynamical changes depend on the dynamical preconditions. During the Northern Hemispheric winter, even weak ionization rates can modulate the mesospheric signal of a sudden stratospheric warming event. The result provides a first step in a paradigm shift for the understanding of the MEE direct effect.

Plain Language Summary Electromagnetic ion cyclotron (EMIC) waves and Magnetosonic (MS) waves are commonly observed in the Earth's magnetosphere and play important roles in energetic electron dynamics. Usually, EMIC waves and MS waves scatter electrons at different energies and pitch angles. The peak frequency of the H⁺ band EMIC wave is usually much lower than the equatorial proton gyrofrequency. Recently, a different type of H⁺ band EMIC waves, named unusual high‐frequency EMIC waves since their peak frequency is close to the equatorial proton gyrofrequency, has been reported. Studies on the unusual high‐frequency EMIC waves found that these waves are capable of scattering sub‐MeV and MeV electrons that can also be influenced by MS waves. Moreover, observations confirm that unusual high‐frequency EMIC waves can be well connected with MS waves. In the present study, we quantitatively investigate the combined scattering effect of both wave modes on radiation belt electrons and simulate the evolution of the electron phase space densities under the impact of both waves. The simulation results show similar evolution trends as the observations, indicating the importance of incorporating these two waves and evaluating their combined effects on radiation belt particle dynamics.

Plain Language Summary Tectonic processes in the geologic past, such as the formation and breakup of supercontinents, modified the deep structures of the crust and upper mantle beneath eastern North America. In this study, we use a seismic imaging technique based on scattered wavefield back‐projection to investigate deep structures beneath southern New England. This imaging technique, which relies on seismic wave energy from distant earthquakes, is capable of resolving km‐scale structures when applied to data from closely spaced seismometers (∼10 km station spacing). We image an abrupt, step‐like change of the crustal thickness beneath southern New England; the details of this feature suggest a complicated tectonic history during the formation of the Appalachian Mountains. A west‐dipping interface in the upper mantle suggests the presence of a relict slab beneath southern New England, associated with a past subduction event. A region of low seismic velocity in the upper mantle beneath southeastern New England may reflect past impingement of a mantle plume or modern upwelling of asthenospheric mantle.

The compound of late winter snow droughts and early spring heatwaves (CSDHW) could dramatically affect ecosystems and water availability, but has not been systematically investigated. Here we present a comprehensive assessment of CSDHW events and possible driving mechanisms. We find that 7% of the snow-covered area experiences significant (p < 0.05) CSDHW events, and an average of 35% of snow droughts are followed by heatwaves during 1981–2020. The spatial extent of CSDHW is asymmetrically enlarging, with a significant increase in Eurasia and a relatively high fluctuation in North America. Specifically, the warm-type CSDHW (i.e., snow drought with normal or above-average precipitation followed by heatwave) occurs more frequently, with spatial coverage increasing faster than the dry-type CSDHW (i.e., snow drought with below-average precipitation followed by heatwave). In comparison, dry snow drought is more likely to be followed by heatwave due to intensified soil drought and atmospheric aridity.

CO2‐driven cold‐water geysers periodically ejecting cold water are rare. Although coalescence and expansion of ascending CO2 bubbles can explain the eruption process, the triggering conditions and eruption cycle remain unclear. To clarify the triggering conditions, hydrostatic pressure in the well was decreased by pumping to induce eruptions. All four pumping tests successfully induced eruptions by decreasing the pressure of ∼10⁴ Pa. In the absence of artificial perturbations, similar reductions in pressure were observed during the intervals between two consecutive eruptions (IBEs). During IBE, the atmospheric pressure (Pair) and temperature (Tair) controlled the generation of the CO2 bubbles which directly induced the pressure reduction in the well. Especially under the persistent low Pair and high Tair, the length of IBE showed a minimum value of 3.90 hr during field observations. We suggest that the atmospheric perturbations are the causes of the changes in geyser periodicity, given consistent geological and hydraulic conditions.

Plain Language Summary Electron acceleration and thermalization in the plasma sheet (PS) of the Earth's magnetotail are fundamental research topics of magnetospheric physics. Theoretical analyses and numerical simulations have revealed that beam electrons can be accelerated and thermalized by the structure of double layer (DL). Direct observation of PS electron acceleration and thermalization is essential to demonstrate the theoretical prediction. Due to the low time and energy resolutions of observing electrons on previous satellites, it was very difficult to display the detailed evolutionary processes of electron acceleration and thermalization by DL structures. Using 3D electron phase‐space distributions with a time resolution of 30 ms and electric field data in burst mode by the magnetospheric multiscale satellites, for the first time, we provide a complete and direct observation of the detailed evolution of the acceleration and thermalization of magnetotail beam electrons by a DL structure, which indicates the energy exchange process between nonlinear electric field structures and electrons in the Earth's PS.

Plain Language Summary Eddy kinetic energy has been increasing in the Southern Ocean over the past few decades. These changes in the eddy field are of great importance because they play a crucial role in modulating the ocean circulation response to surface forcing. However, the EKE changes are inhomogeneous in the Southern Ocean. To understand the pattern of these changes, we analyze the satellite altimeter record over a period of 28 years since 1993 and carry out a set of idealized simulations. We find that the change of EKE is more related to the mean-flow than to localized wind changes. The increasing wind stress contributes to increasing EKE by intensifying the circumpolar mean flow, with local wind stress playing a minor role in the pattern of EKE changes. Strong EKE variations are generally confined downstream of major topographic features, suggesting strong modulation by topography. This study indicates the change of EKE depends on the combination of wind stress, mean-flow and topography in the Southern Ocean.

The flux Richardson number Rf, also called the mixing efficiency of stratified turbulence, is important in determining geophysical flow phenomena such as ocean circulation and air-sea transports. Measuring Rf in the field is usually difficult, thus parameterization of Rf based on readily observed properties is essential. Here, estimates of Rf in a strongly turbulent, sediment-stratified estuarine flow are obtained from measurements of covariance-derived turbulent buoyancy fluxes (B) and spectrally fitted values of the dissipation rate of turbulent kinetic energy (ε). We test scalings for Rf in terms of the buoyancy Reynolds number (Reb), the gradient Richardson number (Ri), and turbulent Froude number (Frt). Neither the Reb-based nor the Ri-based scheme is able to describe the observed variations in Rf, but the Frt-based parameterization works well. These findings support further use of the Frt-based parameterization in turbulent oceanic and estuarine environments.

Large-scale CO2 sequestration into geological formations has been suggested to reduce CO2 emissions from industrial activities. However, much like enhanced geothermal stimulation and wastewater injection, CO2 sequestration has a potential to induce earthquake along weak faults, which can be considered a negative impact on safety and public opinion. This study shows the physical mechanisms of potential seismic hazards along basement faults driven by CO2 sequestration under variation in geological and operational constraints. Specifically we compare the poroelastic behaviors between multiphase flow and single-phase flow cases, highlighting specific needs of evaluating induced seismicity associated with CO2 sequestration. In contrast to single-phase injection scenario, slower migration of the CO2 plume than pressure pulse may delay accumulation of pressure and stress along basement faults that may not be mitigated immediately by shut-in of injection. The impact of multiphase flow system, therefore, needs to be considered for proper monitoring and mitigation strategies.

Understanding the partitioning of snow and rain contributing to either catchment streamflow or evapotranspiration (ET) is of critical relevance for water management in response to climate change. To investigate this partitioning, we use endmember splitting and mixing analyses based on stable isotope (18 O) data from nine headwater catchments in the East River, Colorado. Our results show that one third of the snow partitions to ET and 13% of the snowmelt sustains summer streamflow. Only 8% of the rainfall contributes to the summer streamflow, because most of the rain (67%) partitions to ET. The spatial variability of precipitation partitioning is mainly driven by aspect and tree cover across the sub-catchments. Catchments with higher tree cover have a higher share of snow becoming ET, resulting in less snow in summer streamflow. Summer streamflow did not contain more rain with higher rainfall sums, but more rain was taken up in ET.

Climate change threatens biodiversity through global alteration of habitats, but efficient conservation responses are often hindered by imprecise downscaling of impacts. Besides thermal effects, warming also drives important ancillary environmental changes, such as when river hydrology evolves in response to climate forcing. Earlier snowmelt runoff and summer flow declines are broadly manifested in snow‐dependent regions and relevant to socioeconomically important cold‐water fishes. Here, we mechanistically quantify how climate‐induced summer flow declines during historical and future periods cause complex local changes in Chinook salmon (Oncorhynchus tshawytscha) habitats for juveniles and spawning adults. Changes consisted of large reductions in useable habitat area and connectivity between the main channel and adjacent off‐channel habitats. These reductions decrease the capacity of freshwater habitats to support historical salmon abundances and could pose risks to population persistence in some areas.

Plain Language Summary Lightning is one of the most impressive, commonly experienced geophysical phenomena, driven by the propagation of positively and negatively charged, thermally‐ionized plasma channels, known as positive and negative leaders. Leaders propagate in a continuous or stepwise manner. Knowledge of leader steps is critical to understanding the radio‐frequency electromagnetic radiation and even the high energy physical phenomenon. Based on natural or triggering lightning observations, laboratory‐scale discharge experiments, and numerical simulations, some important insights (like the spontaneous emergence of space stems and the bi‐directional development of the space leaders) about negative leader steps have been given by researchers. Positive leader steps are more mysterious. We investigate positive leader steps by performing laboratory spark discharge experiments. Using a high‐speed video camera and a synchronized electrical parameter measurement system, two types of steps were distinguished in the positive leader continuous development process based on the current pulse features. One type of step exhibits a bell‐shaped current, while the other type of step exhibits a steep current rise. The former type vanishes when the rising rate of the ambient electric field increases, whereas the latter type, which could be led by a floating luminous formation, does not.

In the Katha Range of central Myanmar, lithologic tracers and pressure‐temperature‐deformation‐time data identify Cambro‐Ordovician, Indian‐affinity Tethyan Himalaya Series, located ∼700 km from their easternmost outcrop in S‐Tibet, and ∼450 km from Himalayan rocks in the Eastern Himalayan Syntaxis. Metamorphism began at ∼65 Ma, peaked at ∼45 Ma (∼510°C, 0.93 GPa), and exhumation/cooling (∼25°C/Myr) occurred until ∼30 Ma in a subduction‐early collision tectonic setting. When the Burma microplate—part of the intra‐Tethyan Incertus arc—accreted to SE‐Asia, its eastern boundary, the southern continuation of the Indus‐Yarlung suture (IYS), was reactivated as the Sagaing fault (SF), which propagated northward into Indian rocks. In the Katha rocks, this strike‐slip stage is marked by ∼4°C/Myr exhumation/cooling. Restoring the SF system defines a continental collision‐oceanic subduction transition junction, where the IYS bifurcates into the SF at the eastern edge of the Burma microplate and the Jurassic ophiolite‐Jadeite belts that include the Incertus‐arc suture.

The ocean is inhomogeneous in hydrographic properties with diverse water masses. Yet, how this inhomogeneity has evolved in a rapidly changing climate has not been investigated. Using multiple observational and reanalysis datasets, we show that the spatial standard deviation (SSD) of the global ocean has increased by 1.4 ± 0.1% in temperature and 1.5 ± 0.1% in salinity since 1960. A newly defined thermohaline inhomogeneity index, a holistic measure of both temperature and salinity changes, has increased by 2.4 ± 0.1%. Climate model simulations suggest that the observed ocean inhomogeneity increase is dominated by anthropogenic forcing and projected to accelerate by 200%–300% during 2015–2100. Geographically, the rapid upper‐ocean warming at mid‐to‐low latitudes dominates the temperature inhomogeneity increase, while the increasing salinity inhomogeneity is mainly due to the amplified salinity contrast between the subtropical and subpolar latitudes.

In June of 2021 the southwest United States experienced a record-breaking heatwave. This heatwave came at a time when the region was in severe drought. As drought alters the surface energy budget in ways that affect lower atmosphere temperature and circulations, it is possible that the combined drought-heat event was a cascading climate hazard, in which preexisting drought exacerbated the heatwave. We apply satellite observation and numerical experiments with the Weather Research and Forecasting (WRF) model to test for land-atmosphere feedbacks during the heatwave consistent with drought influence. We find a modest positive drought-heat effect, as WRF simulations that include the drought have marginally higher air temperatures than those that exclude the initial drought conditions, with more substantial effects in wetter, forested areas. Evidence of drought-heat-drought coupled feedbacks was similarly modest in our simulations, as accounting for drought preconditioning led to a small reduction in simulated precipitation in the region.

The ocean floor makes up the majority of the Earth's surface and yet, its geomorphology is not fully understood. Recent debate has focused on whether sea level changes—driven by Milankovitch glacial cycles—generate the abyssal hill fabric of the ocean floor by modulating mid‐ocean ridge magma supply. However, periodicities longer than Milankovitch cycles are prominent in the ocean bathymetry. Using crustal thickness estimates from two‐phase flow simulations of ridge magma transport, I show that persistent melt‐rich porosity waves could be responsible for the ocean floor fabric at periods of 100 kyr and longer, except in the case of fast‐spreading ridges. For periods longer than 100 kyr, spectral energy is notably present at large mantle permeabilities regardless of spreading rates. Therefore, two‐phase flow models can provide constraints on elusive mantle parameters such as permeability and viscosity when directly linked to the ocean floor fabric produced.

Plain Language Summary How the Tibetan Plateau grows outward and deformed remains controversial. A large‐scale crustal flow model has been favored for the expansion of the southeast Tibetan Plateau, arguing that crustal materials could flow hundreds of km resulting in crustal thickening and uplift. Detailed geochemical and isotopic investigations on the largest intrusion (Gongga‐Zheduo) in the eastern margin of the Tibetan Plateau show that their magmatic source is local crustal rocks of the Songpan‐Ganzi terrane without the input of crustal materials from central Tibet. Thermodynamic and trace element modeling results show that the Cenozoic magma is derived from ∼30 to 40 km depth, similar to the depth of postulated crustal flow. The results are inconsistent with the large‐scale eastward crustal flow model. A repeated shifting of magmatic sources during the Cenozoic is correlated with crustal uplift. Mantle‐crust interaction plays a primary role in the formation of magmatism and modifying crustal rheology. The continued collision between the Indian and Asian blocks and upwelling of the asthenosphere contribute to the crustal deformation and uplift.

Plain Language Summary The enigmatic and active Changbaishan volcano located at the border between China and North Korea is an ideal laboratory for investigating the origin and evolution of continental intraplate volcanism. However, the seismic structures related to the magma plumbing system beneath this volcano are still debated and not well resolved. In this study, we build a high‐resolution seismic velocity model at Changbaishan volcanic region combining seismic data from both China and North Korea. We find significant low velocities in the lower crust of Changbaishan volcano, which is interpreted to be a deep crustal melt‐bearing zone with an estimated melt fraction of ∼1.5%–3.6%. Three narrow channel‐like low‐velocity anomalies observed in the uppermost mantle below Changbaishan, Longgang, and Jingpohu volcanoes are suggested to reflect magma ascending passages that transport deep‐sourced mantle melts upward. Our detailed tomographic images provide tight seismic constraints and deepen our understanding on the magma generation and evolution dynamics associated with the young intraplate volcanism in northeast China.

Plain Language Summary Land‐use change (LUC) is considered the second anthropogenic source of climate change after fossil fuel combustion. However, significant uncertainties remain in the estimate of radiative forcing (RF) induced by LUC, partially attributable to the lack of reliable LUC data with a high spatiotemporal resolution. This study incorporated a new LUC data set with a high spatiotemporal resolution into a compact earth‐system model OSCAR to quantify the response of RF to LUCs from 1982 to 2010 in China. We assessed changes in RF for this period subject to the altered surface albedo and carbon emission associated with human‐disturbed land‐use transitions. We compared estimated RF values with those obtained using previously adopted LUC data with a low spatiotemporal resolution, which failed to identify detailed LUCs occurring in China for the past four decades. We show that the updated LUC data set weakens the cooling effect featured by negative RF‐induced by surface albedo variation but significantly enhances positive RF due to CO2 emissions from LU transition. We identify that the LU transition between grassland and cropland and between cropland and forest made the most significant contribution to the changes in RF, attributable to China's national strategies for urbanization, conservation of agricultural resources, and forest expansion.

Plain Language Summary Radiation belt electrons have various pitch angle distributions in response to global/local processes arising in the magnetosphere. Butterfly pitch angle distribution is a characteristic feature of the electron pitch angle distribution, which has the maximum flux intensity at a pitch angle lower than 90°. Wave‐particle interactions have been proposed as a driver for the butterfly distribution in the heart of the radiation belt. However, it is in debate how the wave‐particle interactions contribute to the formation of the butterfly distribution of multi‐megaelectron (MeV) volt electrons that is “killer electrons.” In this Letter, we report that lower band whistler chorus waves play an important role for the electron butterfly distribution at MeV energies. A numerical simulation was carried out and showed that electrons nonlinearly scattered by the whistler chorus waves produce the butterfly distribution at MeV energies. The simulation also showed the upper limit of the rapid electron acceleration in the formation of the butterfly distribution. The simulation results advance our understanding of a formation mechanism of MeV electron butterfly distribution driven by whistler chorus waves.

Lake ice loss has been detected worldwide due to recent climate warming, yet spatially and temporally detailed information on the changes inglobal ice phenology does not exist. Here, we build a global lake ice phenologydatabase comprising three lake ice phenologies –freeze-up, break-up, and ice duration –for each year acrosstwocenturies (1900-2099). The timing ofall three phenologies experienced mild but statistically significant warming trends in the 20thcentury; continued warming trends were detected in ~60% of the lakes from 2001 to 2020. Under a high emissions scenario (RCP 8.5), future global median ice duration would be shortened by 49.9 days by the end of the 21stcentury; such changecan be substantially reduced under lower emission scenarios. We revealed continuous loss of global lake ice during the observed period, our generated database provides critical baseline information to evaluate the consequences of historical and future lake ice changes.

Plain Language Summary Incision in bedrock rivers sets the pace of landscape evolution by controlling the rate of geomorphic responses to climatic and tectonic signals, yet the processes driving incision occur at much finer scale than those captured by landscape evolution models. Local bedrock river incision is driven by flow structures that are not well understood. Rivers typically flow fastest near the surface and slowest near the bed, but many bedrock rivers have channel morphologies that cause this velocity/depth relation to invert. The fastest‐flows submerge toward the bed enhancing near‐bed velocities, sediment transport, and consequently the potential for bedrock incision by particle impacts. However, the first observations of these “plunging flows” were from relatively low discharges and it is not clear if they persist during floods. Here we show that plunging flows get stronger during floods, which clears sediment cover that protects the underlying bedrock and increases bedrock incision potential. The length of the plunging flows matches their coincident pools which are common features of bedrock rivers, explaining why these pools exist. Formation of deep scour pools by complex flow structures in bedrock‐confined rivers is the mechanism that drives incision, begging for a re‐examination of the models used to explore landscape evolution.

We present a novel and robust method for estimating moment magnitudes (Mw) of large earthquakes with long‐period and long‐lasting coda energy. Fitting the energy with a simple decay model, we derive a straightforward relationship between the coda energy and the Mw. Tests with both real and synthetic data of 10 globally distributed large earthquakes (Mw > 8) verify the method and the results are stable and reliable even with a fast calculation of synthetics for a 1D model. Tests also show that the method is applicable for earthquakes with Mw above 7.5–8.0 with energy sufficiently greater than the ambient noise. The method removes or reduces the effects of geometric spreading, focal mechanism, source rupture process, and the actual Earth structure, making it advantageous for estimating the magnitudes of large earthquakes. The new long‐period coda moment magnitude (Mwo) estimations are similar to the conventional solutions but are slightly larger (by 0.04 on average).

Geological hydrogen storage in depleted gas fields represents a new technology to mitigate climate change. It comes with several research gaps, around hydrogen recovery, including the flow behavior of hydrogen gas in porous media. Here, we provide the first‐published comprehensive experimental study of unsteady state drainage relative permeability curves with H2‐Brine, on two different types of sandstones and a carbonate rock. We investigate the effect of pressure, brine salinity, and rock type on hydrogen flow behavior and compare it to that of CH4 and N2 at high‐pressure and high‐temperature conditions representative of potential geological storage sites. Finally, we use a history matching method for modeling relative permeability curves using the measured data within the experiments. Our results suggest that nitrogen can be used as a proxy gas for hydrogen to carry out multiphase fluid flow experiments, to provide the fundamental constitutive relationships necessary for large‐scale simulations of geological hydrogen storage.

Plain Language Summary Previous observations and models have shown that current sheets are associated with plateaus in plasma density, which result in dynamic pressure increases and potentially impact the Earth's magnetosphere. Thus, the evolution of solar wind current sheets in the magnetosheath and their potential effects in the magnetosphere are examined based on the in‐situ observations of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes and the Geostationary Operational Environmental Satellites (GOES) satellites. Since these solar wind current sheets are associated with magnetic field changes, they can also control the appearance and disappearance of foreshock ions which, in turn, may modulate the geoeffectiveness of solar wind current sheets. In this study, we found that the current sheets without foreshock‐ion modulations generated dynamic pressure plateaus, which further evolved to dynamic pressure plateaus in the magnetosheath and likely induced waves in the magnetosphere. Some current sheets were modulated by foreshock ions. These foreshock ions enhanced the perturbations within the current sheets, which further compressed the magnetosphere and caused more oscillations than the current sheets without foreshock‐ion modulations. Thus, we conclude that solar wind current sheets can be geoeffective and their geoeffectiveness can be amplified by foreshock ions inside their structure.

Plain Language Summary The loss of thick multiyear sea ice in the Arctic leads to weaker sea ice that is more easily broken up by strong winds. As a consequence, extreme sea ice breakup events may become more frequent, even during the middle of winter when the sea ice cover is frozen solid. This can lead to an earlier onset of the melt season and potentially accelerate Arctic sea ice loss. Such extreme breakup events are generally not captured by climate models, potentially limiting our confidence in projections of Arctic sea ice. We investigated the driving forces behind sea ice breakup events during winter and how they change in a future climate. Our sea ice model is the first to reproduce such breakup events and reveals that the combination of strong winds and thin sea ice is a key factor for these breakups. We found that winter breakups have a large effect on local heat and moisture transfer and cause enhanced sea ice production, but also increase the overall movement of the sea ice cover, making it more vulnerable. Finally, we show that if the Arctic sea ice continues to thin, these extreme breakup events could become even more frequent.

Plain Language Summary Understanding the spatial pattern of burn severity is crucial for fire‐related ecological research and effective fire management. The Canadian Rocky Mountain region is characterized by mixed‐severity fires, which makes fine‐scale burn severity investigation a challenge. This study used random forest models to establish the relationships between observed burn severity and various environmental predictors (fuel type, fire cause, management zone, topography, vegetation, and climate) and identify key drivers of burn severity in three Canada's mountain national parks (Banff, Kootenay, and Yoho). The prediction models were applied to predict the burn severity potentials by human‐ and lightning‐caused fires for all forest locations in the study area in 2002 and 2012, that is, the 2 years with available data. The results contribute to a more comprehensive understanding of regional fire behavior. The estimated important influences of fuel type, topography, vegetation, and climate on regional burn severity indicate the complex mechanism of environmental controls on fire behavior. The predictions of burn severity in the parks showed an overall consistent spatial pattern over time, which provide a baseline for relevant fire ecology research and useful information for park conservation.

Plain Language Summary The Arctic is warming more rapidly than the rest of the world. This warming has had an especially profound impact on Greenland's ice cover. Only 4% of Greenland's ice cover are small peripheral glaciers that are distinct from the ice sheet proper. Despite comprising this relatively small area, these small peripheral glaciers are responsible for 11% of the ice loss associated with Greenland's recent sea level rise contribution. Using the satellite laser platforms Ice, Cloud, and land Elevation Satellite (ICESat) and ICESat‐2, we estimate that ice loss from these Greenland glaciers increased from 27 ± 6 Gt/yr (2003–2009) to 42 ± 6 Gt/yr (2018–2021). We find that the largest acceleration in ice loss is in North Greenland, where we observe ice loss to increase by a factor of four between 2003 and 2021. In some areas, it appears that recent increases in snowfall at high altitudes have partially counteracted recent increases in melt at low altitudes. While many recent Greenland ice loss assessments have focused on only the ice sheet, the recent sharp increase in ice loss from small peripheral glaciers highlights the importance of accurately monitoring Greenland's small peripheral glaciers. These small peripheral glaciers appear poised to play an outsized role in Greenland ice loss for decades to come.

End of century projections from Coupled Model Intercomparison Project (CMIP) models show a decrease in precipitation over subtropical oceans that often extends into surrounding land areas, but with substantial intermodel spread. Changes in precipitation are controlled by both thermodynamical and dynamical processes, though the importance of these processes for regional scales and for intermodel spread is not well understood. The contribution of dynamic and thermodynamic processes to the model spread in regional precipitation minus evaporation (P − E) is computed for 48 CMIP models. The intermodel spread is dominated essentially everywhere by the change of the dynamic term, including in most regions where thermodynamic changes drive the multi‐model mean response. The dominant role of dynamic changes is insensitive to zonal averaging which removes any influence of stationary wave changes, and is also evident in subtropical oceanic regions. Relatedly, intermodel spread in P − E is generally unrelated to climate sensitivity.

Plain Language Summary Western boundary currents are major ocean currents located on the western side of the world's oceans. These currents transport warm water toward the poles, which influences regional weather and climate. However, despite their importance, the fast speeds, high variability, and narrow width of these currents makes them difficult to observe. Here we examine the western boundary currents (WBCs) of the Indian Ocean (Agulhas Current) and Pacific Ocean (East Australian Current and Kuroshio) using measurements from three different ocean observing networks. The same method is applied to each current, allowing us to compare variability in the three currents. Between the start of 2004 and end of 2019 we find that transport of water has decreased in the Kuroshio but has not changed in the Agulhas or East Australian Current. We find changes in the path of the Kuroshio on interannual time scales, and shorter and irregular changes in the path of the Agulhas. On annual time periods, all three currents transport more water in summer than winter, which is related to faster speeds during the summer. These long subsurface time series can help us better understand how WBC variability impacts society at the western boundaries of the ocean.

By using a database of 4,634 cold patches (high density and low electron temperature) and 4,700 hot patches (high density and high electron temperature) from Defense Meteorological Satellite Program F16 in 2005–2018 winter months (October–March), we present a statistical survey of the distributions of polar cap patches for different interplanetary magnetic field (IMF) orientations and ionospheric convection geometries. We investigate the dependence of cold and hot patches on local plasma transport and soft‐electron precipitation. Our results indicate that: in winter, (a) more cold and hot patches occur in the stronger anti‐sunward flow organized by different IMF orientations. (b) cold patches are frequent near the central polar cap, while hot patches are closer to the auroral oval. (c) enhanced anti‐sunward flow (E × B drift) mainly contributes to cold patch occurrence under Bz < 0, and soft‐electron precipitation contributes to hot patch occurrence both under southward and northward IMF.

Modeling experiments reducing surface temperatures via an idealized reduction of the solar constant have often been used as analogs for Stratospheric Aerosol Injection (SAI), thereby implicitly assuming that solar dimming captures the essential physical mechanism through which SAI influences surface climate. While the omission of some important processes that otherwise operate under SAI was identified before, here we demonstrate that the imposed reduction in the incoming solar radiation also induces a different stratospheric dynamical response, manifested through a weakening of the polar vortex, that propagates from the upper stratosphere down to the troposphere. The coupled stratospheric‐tropospheric response exerts a previously overlooked first‐order influence on southern hemispheric surface climate in the solar dimming experiments, including on the position of the tropospheric jet and Hadley Circulation and thus, ultimately, precipitation patterns. This perturbation, opposite to that expected under SAI, highlights the need for caution when attributing responses in idealized experiments.

Single‐frequency microseisms (SFMs) have been revealed to be only generated in shallow water for decades, while some recent studies reported them in a deep ocean. Using the continuous waveform data recorded by ocean bottom seismometers, we investigate the deep ocean SFMs in the northern Philippine Sea. Based on the spectrum analysis, we find that the SFMs can be detected in deep ocean and the detection is time variable. To determine the source locations of SFMs, we perform polarization analysis and calculate the cross‐correlation coefficients between SFMs on vertical components and ocean wave energy spectra considering the attenuation of SFMs. Both the polarization and correlation results show that the sources nearby stations dominate the observed Rayleigh‐wave SFMs though distant sources also contribute. Our investigation suggests that the SFMs can be generated in a deep ocean likely by infragravity ocean waves interacting with seafloor topography, which is strengthened by strong ocean storms.

The Earth's solid inner core (IC) is generally believed to rotate relative to the mantle, but the proposal remains controversial. Here we use seven waveform doublets in the South Sandwich Islands region with time lapses of 5.8–17.0 years that are recorded by two close stations in Kyrgyzstan with virtually the same epicentral distance. The fortuitous geometry allows precise measurements of the IC temporal changes and the underlying local structure at the same time. The remarkable observations in waveforms and spatial‐temporal measurements show unequivocally that the IC must have shifted (rotated) eastward in 1991–2010 and help determine accurately the average rotation rate as 0.127 ± 0.006°/yr at 95% confidence level during the time span.

Short‐duration precipitation extremes (PE) increase at a rate of around 7%/K explained by the Clausius‐Clapeyron relationship. Previous studies show uncertainty in the extreme precipitation‐temperature relationship (scaling) due to various thermodynamic/dynamic factors. Here, we show that uncertainty may arise from the choice of data and methods. Using hourly precipitation (PPT) and daily dewpoint temperature (DPT) across 2,905 locations over the United States, we found higher scaling for quality‐controlled data, all locations showing positive (median 6.2%/K) scaling, as compared to raw data showing positive (median 5.3%/K) scaling over 97.5% of locations. We found higher scaling for higher measurement precision of PPT (0.25 mm: median 7.8%/K; 2.54 mm: median 6.6%/K). The method that removes seasonality in PPT and DPT gives higher (with seasonality: median 6.2%/K; without seasonality: median 7.2%/K) scaling. Our results demonstrate the importance of quality‐controlled, high‐precision observations and robust methods in estimating accurate scaling for a better understanding of PE change with warming.

Plain Language Summary Phytoplankton fluorescence is a relatively easy and consistent measurement that can be made in the ocean. The measured fluorescence stems directly from the chlorophyll contained in phytoplankton cells and is therefore very specific to the tiny plants. Great oceanic coverage of fluorescence measurements is achieved because fluorometers can be mounted on autonomous platforms such as gliders and floats, yielding reliable data for years without human intervention. But there is a problem with this measurement: fluorescence does not equal chlorophyll, and the factor for the conversion of fluorescence to chlorophyll varies almost 10‐fold across the world's oceans. The largest conversion factors, with the highest variability, are observed in the Southern Ocean. We know that things such as phytoplankton species composition, nutrient status, and acclimation to light all affect the conversion factor. Using data from biogeochemical Argo floats and from laboratory studies, we show in this study that iron limitation also significantly increases the fluorescence‐chlorophyll conversion factor, and that iron limitation may indeed be a key driver for the high conversion factors observed in the Southern Ocean.

Plain Language Summary Ionospheric plasma are known to be highly irregular, with fluctuations evolving both in space and time. Irregular structures can reach hundreds of kilometers to a few meters and, despite being common and having space weather impacts, the details of their source(s) and behavior are still unclear, especially at smaller scales. In this work, we investigate small‐scale plasma density and electric field fluctuations observed by a sounding rocket where ground‐based instruments also detected irregularities. To circumvent ambiguities of interpreting measurements made by single probes, we take advantage of the fact that the fluctuations were detected by spatially separated probes and use multi‐point analysis techniques to separate the spatial and temporal scales of the observed structures. The analysis allows to estimate the phase velocities and wavelengths of the fluctuations and reveals spatial irregularities from tens of meters to a meter, that is, irregularities that are slow in the plasma frame. Additionally, we show that these small‐scale structures are concentrated outside of regions where most electrons are precipitating downward along the Earth's magnetic field and discuss the observations in the context of irregularity creation. Altogether, this study provides new insights into the sources and behavior of high‐latitude ionospheric irregularities.

Plain Language Summary The entire global N budget remains out of balance, with total N inputs exceeding N losses. Streams and rivers serve as substantial recipients and processors of reactive N transported from terrestrial landscapes. The benthic zone is traditionally identified as a hotspot for N processing in fluvial systems. However, the role of the water column is poorly understood. Here, we found that the water column area‐basis production rates of N2 and N2O increased with stream order although volumetric‐basis production rates did not change significantly with stream order through 4‐year observations across six river networks in China. The water column contribution increased with stream order and became dominant in large rivers. The increase in the contact area of SPS‐water caused by higher SPS concentrations and water volume accounted for the shift as river size increased. The current estimates would underestimate riverine N removal and N2O emissions by approximately 50% if neglecting water column processes based on the upscaling results for the six large river networks ranging from first to eighth order. Thus, our findings provide insight into the understanding of riverine N dynamics and highlight the important role of water column processes in N upscaling for closing regional and global N budgets.

Blue electric streamer discharges in the upper reaches of thunderclouds are observed as flashes of 337.0 nm (blue) with faint or no emissions of 777.4 nm (red). Analyzing 3 years of measurements by the Atmosphere‐Space Interactions Monitor on the International Space Station, we find that their distribution in rise time falls into two categories. One with fast rise times of 30 μs or less that are relatively unaffected by cloud scattering and emanate from within ∼2 km of the cloud tops, and another with longer rise times from deeper within the clouds. 50% of cells generating shallow events are associated with overshooting tops compared to 34% of cells generating deeper events. The median Convective Available Potential Energy of the cells is ∼70% higher for the shallow events and ∼38% higher for the deeper events than for lightning cells, suggesting the discharges are favored by strongly convective environments.

Radium isotopes are powerful proxies in oceanography and hydrology. Radium mass balance models, including assessments of submarine groundwater discharge (SGD), often overlook particle scavenging (PS) as a pathway for dissolved radium removal from the world ocean. Here, we build a global ocean ²²⁶Ra mass balance model and reevaluate the potential importance of PS. We find that PS is the major ²²⁶Ra sink for the upper ocean, removing about 96% of the total input from various sources. Aside from vertical exchange with the lower ocean, SGD is the largest ²²⁶Ra source into the upper ocean. The biological pump transfers particles to the deep ocean, resulting in a major but often overlooked impact on the global ²²⁶Ra marine budget. Our findings suggest that radium mass balance models should consider PS in systems with high siliceous algae production and export fluxes and long water residence times to prevent underestimation of large‐scale SGD fluxes.

Plain Language Summary The Humboldt Upwelling System is a fishery‐important region. A common assumption is that a certain amount of phytoplankton supports a proportional amount of fish. However, we find that a small seasonal change in phytoplankton can trigger a larger variation in zooplankton. This implies that one may underestimate changes in fish solely based on phytoplankton. Using ecosystem model simulations, we investigate why changes of phytoplankton are not proportionally reflected in zooplankton. The portion of phytoplankton that ends up in zooplankton is controlled by the changing depth of the surface ocean “mixed layer.” The “mixed layer” traps both the phytoplankton and zooplankton in a limited amount of space. When the “mixed layer” is shallow, zooplankton can feed more efficiently on phytoplankton as both are compressed in a comparatively smaller space. We conclude that in the Humboldt System, and other “food‐rich” regions, feeding efficiently, determined by the “mixed layer,” is more important than how much food is available.