AGU Advances最新文献

The Van Allen radiation belts contain relativistic electrons trapped by Earth's magnetic field, posing serious risks to spacecraft. Chorus waves are known to accelerate these electrons via resonant interactions, but these interactions are inherently nonlinear and coherent. How such processes shape large-scale electron dynamics remains unresolved. Two competing paradigms, nonlinear advection and diffusive transport, have been debated for decades. Here, we address this controversy using large-scale first-principles simulations that self-consistently generate realistic chorus wave fields, coupled with test particle modeling. We find that electron motion is coherent on short timescales—comparable to or less than a bounce period—but becomes stochastic over longer timescales due to decorrelation. The resulting transport coefficients support the use of quasilinear diffusion theory for long-term evolution. This work bridges microscopic nonlinear physics with macroscopic modeling frameworks, offering a unified explanation of radiation belt dynamics and advancing the foundation for space weather forecasting.

Stable auroral red (SAR) arcs are luminous subauroral emissions produced by the collisional excitation of oxygen atoms during geomagnetically active times. While traditionally attributed to inner magnetospheric electron heating, recent observations and simulations challenge the exclusivity of this mechanism. Here, we resolve the ionospheric origin of SAR arcs using multi-instrument observations and numerical simulations during the March 2015 geomagnetic storm. Both magnetospheric heat flux and ion-neutral frictional heating, driven by subauroral plasma flows, independently generate SAR arcs with intensities surpassing background airglow by hundreds of Rayleighs. While thermal electron impact dominates red-line emissions in both cases, the vertical structures diverge: frictional heating localizes emissions to altitudes of 250–400 km, whereas magnetospheric heating extends emissions above ∼280 km with broader altitudinal coverage. These results redefine SAR arc generation as a product of competing magnetospheric and ionospheric energy pathways, advancing our understanding of cross-scale interactions in geospace.

Hydroclimatic extremes such as droughts and floods severely impact global livelihoods, economies, and ecosystems, yet their attribution remains challenging. This study evaluates global Terrestrial Water Storage (TWS) extremeness and climate linkages using GRACE and GRACE-FO data from 2002 to 2024. By examining upper and lower deciles of TWS anomalies representing wet and dry extremes and assessing spatial dependencies, we identify key patterns, trends, and driving factors through dimensional reduction and probabilistic modeling. Results show global TWS extremes are governed by a 2–3-year oscillatory cycle linked to El Niño–Southern Oscillation, which synchronizes drought and pluvial conditions across continents. Drought extremes show broader spatial coherence than pluvial events, indicating moisture deficits propagate more uniformly through the land–atmosphere system. A weaker quasi-decadal cycle (6–10 years) modulates these responses and underlies a shift around 2011–2012. Before 2011, wet extremes intensified, while after 2012, dry extremes became dominant, particularly in interior Asia, western United States, and southern Africa. Neither pluvial nor drought extremes show significant global trends in intensity; however, they remain phase-locked, with wet events twice as intense as dry ones, reflecting asymmetric hydrologic response to moisture surpluses versus deficits. We probabilistically reconstruct TWS extremeness during satellite data gaps using leading spatio-temporal patterns. The current record, spanning less than one multidecadal cycle, remains insufficient for robust attribution. Extending satellite gravimetry is essential to refine uncertainty in attributing global pluvial and drought extremes under climate change.

Great subduction earthquakes (M_w ≥ 8.0) can generate devastating tsunamis by rapidly displacing the seafloor and overlying water column. These potentially tsunamigenic seafloor offsets result from coseismic fault slip and deformation beneath or within the accretionary wedge. The mechanics of these shallow rupture phenomena and their dependence on subduction zone properties remain unresolved, partly due to the sparsity of offshore observations of shallow megathrust earthquake deformation. Here, we analyze how offshore structure influences shallow rupture mechanics and slip partitioning using 3D dynamic earthquake simulations of the Cascadia subduction zone (CSZ) megathrust with and without variably dipping seaward- or landward-vergent splay faults in the wedge that sole into the megathrust. Resulting tradeoffs between splay and megathrust slip reveal structural controls on rupture partitioning, with greater splay slip leading to less shallow megathrust slip updip. Gently dipping and seaward-vergent splays host more slip than those with steeper, landward-vergent splays. To isolate the underlying mechanisms, we compare models with Andersonian and plunging principal stresses. Results suggest distinct static and dynamic processes control the dip- and vergence-dependence of splay rupture: static (mis)alignment relative to far-field tectonic loading favors slip on more optimally oriented, shallowly dipping splay faults. In contrast, dynamic stress interactions of an updip-propagating megathrust rupture front with the free surface and potential branch faults favor forward branching onto seaward-vergent splays and inhibit backward branching onto landward-vergent splays. Resulting seafloor displacements suggest splay fault structure may influence coseismic tsunami source processes, highlighting the importance of dynamically viable rupture scenarios in subduction hazard assessments.

Recent studies have revealed strong trends in humid heat, including the nearing of human physiological limits in some regions. Understanding of past extremes and their meaningfulness for contextualizing future possibilities, especially in the near-term, is limited by the absence of a global analysis focused on the most extreme humid-heat-anomaly events. Here we identify record-setting humid-heat days for 216 global regions and assess the likelihood of these records being broken even under present-day climate forcing. We use several reanalyses as a historical catalogue, and large climate-model ensembles to represent other statistically plausible events. Unlike the spatial pattern of large temperature anomalies, we find that humid-heat anomalies are most intense, and most seasonally and interannually concentrated, in the deep tropics and arid subtropics. Many top events have attracted little if any prior attention. The eastern United States is especially susceptible to record-breaking humid heat due to modest current records (>1% inferred annual exceedance probability) contrasting with numerous simulated large-anomaly days. Australia and eastern China are also prone to locally exceptional episodes, with >40% of ensemble members simulating events exceeding the ERA5-based distribution maximum. Model biases for key characteristics, together with the observed record-setting day affecting its estimated return period by >2.5x in half of regions, underline several valuable aspects of a joint observation/model perspective on humid heat. This approach aids in evaluating the plausibility of as-yet-unseen extremes; identifying regions of concern that might otherwise be overlooked and underprepared; and gauging regionally specific correlations between event magnitudes and societal impacts.

Understanding how compound extremes affect terrestrial ecosystems is a major challenge in Earth system science. Although the combined effects of stressors are recognized, the manner in which the prestress state determines the basic response mechanism remains unclear. In this study, we used the “natural experiment” methodology to compare two major extreme events within a monsoon-influenced, low-latitude highlands setting to explain mechanistic changes in land-atmosphere interactions. By analyzing an extensive set of remote sensing and reanalysis data with nonlinear structural equation modeling, we show that the ecosystem response shifted from a traditional water-limited paradigm during the 2010 drought to an energy-governed paradigm during the 2019 heatwave. Our results suggest that this transition is governed by the antecedent root zone soil moisture status, which acts as a tipping point fundamentally shifting the impact of atmospheric factors on canopy evapotranspiration screens, such as temperature and vapor pressure deficit. This study highlights a possible threshold-type state dependence non-linearity, which is lacking in major Earth System Models. Incorporating this “hydrological memory” is crucial for minimizing uncertainties in climate projections and for correctly assessing the vulnerability of ecosystems in a warming world.

Magma and pressure transport between Kīlauea's summit reservoirs and along its East Rift Zone (ERZ) are dynamic even in the absence of surface eruptions. However, these processes do not always produce surface manifestations and may sometimes elude detection by current geological and geodetic monitoring. Here we monitor subsurface seismic velocity changes across Kīlauea's system from 2013 to 2018 and integrate these observations with concurrent measurements of ground deformation and lava lake elevation. We corroborate years-long seismic velocity decreases around the summit caldera, which are particularly pronounced at southern stations, consistent with sustained pressurization of the South Caldera reservoir (SCR) from a deep magma supply. Following the 2015 summit intrusion, accelerated rates of velocity decrease, summit inflation, and lava lake rise suggest an increased magma supply to the SCR. Notably, we identify an anomalous 7-month period (late 2016–mid 2017) of disrupted magma/pressure transfer between the SCR and Halema'uma'u magma reservoir (HMR), as evidenced by dropping lava lake levels despite continued summit inflation and SCR pressurization. This period coincided with pressurization observed beneath Pu'u'ō'ō, indicating pressure/magma diversion from the summit toward the ERZ and the episode terminated with a M5.3 flank earthquake in June 2017 that restored the connectivity between the SCR and HMR and triggered shallow crustal pressurization beneath the summit caldera for the subsequent 2–3 months. Our findings reveal significant perturbations in Kīlauea's magmatic plumbing system approximately one year before the catastrophic 2018 eruption, highlighting seismic velocity monitoring's value for detecting subtle changes of the volcano.

The challenge of distinguishing convective anvil cirrus from in situ cirrus has long limited the quantification of their distinct roles in regulating upper-tropospheric moisture and modulating Earth's energy budget. In this study, we address this ambiguity by introducing a physically constrained classification framework that applies advanced computer vision techniques to CloudSat-CALIPSO observations. By tracking the complete physical evolution of cloud systems from their convective origins, this method enables a robust global separation of anvil and in situ cirrus. Our results illuminate stark contrasts in their macro- and micro-properties, governed by fundamentally different mechanisms. Anvil cirrus extent is tightly coupled to dynamic factors, whereas in situ cirrus, while linked to local tropopause thermodynamics, exhibits strong modulation by remote atmospheric influences from the opposite hemisphere. This identified linkage shows a previously unrecognized interhemispheric teleconnection: wherein large-scale deep convective systems in one hemisphere rapidly influence in situ cirrus formation in the other. We hypothesize that this coupling is mediated by planetary-scale waves—likely fast-propagating Kelvin waves that transmit energy across the equator, cooling the remote tropical tropopause layer, with subsequent interactions with the subtropical jet fostering mid-latitude in situ development. This newly quantified atmospheric coupling provides a pathway for improving representation of cirrus in climate models and suggests a mechanism by which regional shifts in convection under global warming could reshape global cirrus distributions and their radiative impact.

The Arctic Ocean double estuary is a “three-legged” overturning system in which inflowing waters are converted into both lighter and denser waters before being exported equatorwards. As the northern terminus of the Atlantic Meridional Overturning Circulation (MOC), it thus both affects, and is affected by, the Atlantic MOC. Here we quantify the magnitudes of the two overturning cells in density space, and then decompose the water mass transformation rates into net pan-Arctic contributions from surface forcing and diapycnal mixing. We use a high-resolution, quasi-synoptic ice and ocean hydrographic data set spanning the four main Arctic Ocean gateways—Fram, Davis and Bering Straits, and the Barents Sea Opening. Two surface flux reanalyses and a hydrographic climatology are used to generate estimates of surface water mass transformation rates by density class. A box model then determines the profiles of turbulent mixing transformation rates, and associated turbulent diffusivities. We show that turbulent mixing and surface forcing drive transformations of similar magnitudes, while mixing dominates in the upper cell and surface fluxes in the lower cell. Consideration of uncertainties and timescales leads to the tentative suggestion that our results might be representative of recent decades. We discuss the possible significance of tides and sea ice brine rejection as energy sources driving turbulent mixing. Finally, we speculate as to whether water mass transformation rates may change in future as ocean heat transport into the Arctic increases. As sea ice declines and the efficiency of atmosphere-to-ocean momentum transfer increases, the Arctic Ocean is expected to “spin up,” causing more intense turbulent mixing, with uncertain consequences.

Mid- to higher-latitude shallow marine environments are suggested to serve as refugia for organisms during intervals of rapid environmental change associated with hyperthermals. To understand the role of these environments during hyperthermals, we herein investigate the Permian–Triassic environmental crisis, which led to the most severe mass extinction event in the Phanerozoic. Our analysis of siliciclastic deposits from the Boreal Ocean from Lusitaniadalen, Svalbard, reveals a distinct increase of the lipid biomarkers C₃₃-n-alkylcyclohexane (C₃₃-n-ACH) and phytanyl toluene following the extinction event. This increase does not appear to reflect facies changes. Rather, it coincides with the extinction horizon, and persists into the lowermost Triassic (Griesbachian). Our findings suggest that neither C₃₃-n-ACH nor phytanyl toluene are linked to short periods of photic zone euxinia recorded at Lusitaniadalen, but rather are derived from a specific group of phytoplankton. This indicates that higher-latitude ecosystems may have supported regional blooms of unknown primary producers after the Permian–Triassic mass extinction, thus explaining the selective survival of some marine organisms. We also identify (albeit in lower abundance) C₃₃-n-ACH and its pseudohomologs in northern Italy, which is the first report of n-ACHs in the tropical Tethys region across the Permian–Triassic transition outside of South China, highlighting the wide paleogeographic distribution of this biomarker. Phytanyl toluene, however, is found exclusively in deposits recording higher-latitude ecosystems, and is likely linked to organisms occupying a similar ecological niche as the source organism of C₃₃-n-ACH in these settings.