GRL

A too-weak eddy feedback in models has been proposed to explain the signal-to-noise paradox in seasonal-to-decadal forecasts of the winter Northern Hemisphere. We show that the “eddy feedback parameter” (EFP) used in previous studies is sensitive to sampling and multidecadal variability. When these uncertainties are accounted for, the EFP diagnosed from CMIP6 historical simulations generally falls within the reanalysis uncertainty. We find the EFP is not independent of the sampled North Atlantic Oscillation (NAO). Within the same dataset, a sample containing larger NAO variability will show a larger EFP, suggesting that the link between eddy feedbacks and the signal-to-noise paradox could be due to sampling effects with the EFP. An alternative measure of eddy feedback, the barotropic energy generation rate, is less sensitive to sampling errors and delineates CMIP6 models that have weak, strong, or unbiased eddy feedbacks, but shows little relation to NAO variability.

We use multi-year observations of cross-track winds (u) from the CHAllenging Minisatellite Payload (CHAMP) and the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) to calculate third-order structure functions in the thermosphere as a function of horizontal separation (s). They are computed using the mean (〈δu 3〉) and the median 〈δu3〉med $\left({\langle \delta {u}^{3}\rangle }_{\text{med}}\right)$ and implemented over non-polar satellite paths in both hemispheres. On height averages, 〈δu 3〉 is shown to scale with s 2 for s ≃ 80–1,000 km, in agreement with equivalent estimates in the lower atmosphere from aircraft observations. Conversely, 〈δu3〉med ${\langle \delta {u}^{3}\rangle }_{\text{med}}$ follows an s 3 power law for almost the whole s range, consistent with the two-dimensional turbulence scaling law for a direct enstrophy cascade. These scaling laws appear independent of winds in distinct atmospheric regions. Furthermore, the functions are predominantly positive, indicating a preferential cyclonic motion for the wind.

The empirical rate- and state-dependent friction law is widely used to explain the frictional resistance of rocks. However, the constitutive parameters vary with temperature and sliding velocity, preventing extrapolation of laboratory results to natural conditions. Here, we explain the frictional properties of natural gouge from the San Andreas Fault, Alpine Fault, and the Nankai Trough from room temperature to ∼300°C for a wide range of slip-rates with constant constitutive parameters by invoking the competition between two healing mechanisms with different thermodynamic properties. A transition from velocity-strengthening to velocity-weakening at steady-state can be attained either by decreasing the slip-rate or by increasing temperature. Our study provides a framework to understand the physics underlying the slip-rate and state dependence of friction and the dependence of frictional properties on ambient physical conditions.

Amplification of sea surface temperature (SST) seasonality in response to global warming is a robust feature in climate model projections but season-dependent regional disparities in this amplification and the associated mechanisms are not well addressed. Here, by analyzing large ensemble simulations using Community Earth System Model version 2, we investigate detailed spatiotemporal characteristics of the amplification of SST seasonality focusing on the North Pacific and North Atlantic, where robust changes are projected to emerge around 2050 under SSP3-7.0 scenario. Our results indicate that atmosphere-ocean coupled processes shape regional changes in SST seasonality differently between warm (MAMJJAS) and cold seasons (ONDJF). During the warm season, the projected warming tendency is mainly due to increased net surface heat flux and weakening of vertical mixing. On the other hand, in the cold season, the projected cooling tendency is driven by strengthened vertical mixing over the North Pacific associated with the northward shift of storm tracks but weakened horizontal advection and mixing due to changes in ocean currents over the North Atlantic.

Compound wind and precipitation extremes (CWPEs) can severely impact natural and socioeconomic systems. However, our understanding of CWPE future changes, drivers, and uncertainties under a warmer climate is limited. Here, by analyzing the event both on oceans and landmasses via state-of-the-art climate model simulations, we reveal a poleward shift of CWPE occurrences by the late 21st century, with notable increases at latitudes exceeding 50° in both hemispheres and decreases in the subtropics around 25°. CWPE intensification occurs across approximately 90% of global landmasses, and is most pronounced under a high-emission scenario. Most changes in CWPE frequency and intensity (about 70% and 80%, respectively) stem from changes in precipitation extremes. We further identify large uncertainties in CWPE changes, which can be understood at the regional level by considering climate model differences in trends of CWPE drivers. These results provide insights into understanding CWPE changes under a warmer climate, aiding robust regional adaptation strategy development.

We validate the multiyear potential predictability of wintertime heavy precipitation potential in East Asia by combining initialized decadal hindcasts of the global climate model and large ensemble simulations from a high-resolution global atmospheric model. By analyzing a set of initialized hindcasts, the major predictive components of sea surface temperature (SST) variability beyond interannual timescales are identified as high-latitudes multidecadal variability and the so-called trans-basin variability (TBV). A set of 100 ensemble simulations using a high-resolution atmospheric model showed a significantly large signal-to-noise ratio for the wintertime heavy precipitation potential in East Asia, which is closely related to the TBV. When the SST around the maritime continent is higher, the anomalously low pressure in the northwestern Pacific enhances low-level cold air transport due to the winter monsoon. Consequently, the resultant weaker baroclinicity in the lower atmosphere reduces storm activity and wintertime heavy precipitation potential in East Asia.

Reservoirs exert a profound influence on the cycling of dissolved organic matter (DOM) in inland waters by altering flow regimes. Biological incubations can help to disentangle the role that microbial processing plays in the DOM cycling within reservoirs. However, the complex DOM composition poses a great challenge to the analysis of such data. Here we tested if the interpretable machine learning (ML) methodologies can contribute to capturing the relationships between molecular reactivity and composition. We developed time-specific ML models based on 7-day and 30-day incubations to simulate the biogeochemical processes in the Three Gorges Reservoir over shorter and longer water retention periods, respectively. Results showed that the extended water retention time likely allows the successive microbial degradation of molecules, with stochasticity exerting a non-negligible effect on the molecular composition at the initial stage of the incubation. This study highlights the potential of ML in enhancing our interpretation of DOM dynamics over time.

We study the sensitivity of South Asian Summer Monsoon (SASM) precipitation to Southern Hemisphere (SH) subtropical Absorbed Solar Radiation (ASR) changes using Community Earth System Model 2 simulations. Reducing positive ASR biases over the SH subtropics impacts SASM, and is sensitive to the ocean basin where changes are imposed. Radiation changes over the SH subtropical Indian Ocean (IO) shifts rainfall over the equatorial IO northward causing 1–2 mm/day drying south of equator, changes over the SH subtropical Pacific increases precipitation over northern continental regions by 1–2 mm/day, and changes over the SH subtropical Atlantic have little effect on SASM precipitation. Radiation changes over the subtropical Pacific impacts the SASM through zonal circulation changes, while changes over the IO modify meridional circulation to bring about changes in precipitation over northern IO. Our findings suggest that reducing SH subtropical radiation biases in climate models may also reduce SASM precipitation biases.

Modeling the nonlinear interactions between flow, sediment, and vegetation is essential for improving our understanding and prediction of river system dynamics. Using simple numerical models, we simulate the key flow-sediment-vegetation interaction where the disturbance is intrinsically generated by the presence of vegetation. In this case, biomass growth modifies the flow field, induces bed scour, and thus potentially causes vegetation uprooting when erosion exceeds root depth. Our results show that this nonlinear feedback produces deterministic chaos under a wide range of conditions, with complex aperiodic dynamics generated by a period-doubling route to chaos. Moreover, our results suggest relatively small values of Lyapunov time, spanning 2–4 growth-flood cycles, which significantly restrict the predictability of riverbed evolution. Although further spatial and temporal processes may add complexity to the system, these results call for the use of ensemble methods and associated uncertainty estimates in ecomorphodynamic models.

Extreme El Niño events have outsized global impacts and control the El Niño Southern Oscillation (ENSO) warm/cold phases asymmetries. Yet, a consensus regarding the relative contributions of atmospheric and oceanic nonlinearities to their genesis remains elusive. Here, we isolate the contribution of oceanic nonlinearities by conducting paired experiments forced with opposite wind stress anomalies in an oceanic general circulation model, which realistically simulates extreme El Niño events and oceanic nonlinearities thought to contribute to ENSO skewness (Tropical Instability Waves (TIWs), Nonlinear Dynamical Heating (NDH)). Our findings indicate a weak contribution of oceanic nonlinearities to extreme El Niño events in the eastern Pacific, owing to compensatory effects between lateral (NDH and TIWs) and vertical processes. These results hold across different vertical mixing schemes and modifications of the upper-ocean heat budget mixed layer criterion. Our study reinforces previous research underscoring the pivotal role of atmospheric nonlinearities in shaping extreme El Niño events.

The effects of generating pulsed radiation by a long spark discharge are important for the development of lightning models and applications related to lightning protection. In experiments with a Marx generator simulating a lightning discharge, we detected the radiation in the form of a single ultrawideband electromagnetic pulse (UWB EMP) about 200 ps in duration, and rising time about 100 ps. UWB EMP generation occurs during the breakdown of a “rod–rod” 4 m long gap. Pulses of almost unipolar shape are observed in more than half of all positive discharges. EMP emission occurs before the main stage, and corresponds to the start of the upward leader from a grounded electrode. In negative discharges, pulses are also observed, but less frequently and with a smaller amplitude. The UWB EMPs, given their large amplitude (more than 100 V/m at a distance of 90 m from the discharge), can be considered as possible new lightning damage factors.

Very low-frequency earthquakes (VLFs) are characterized by longer source duration and smaller stress drop than regular earthquakes of similar magnitude. Recent studies have shown their frequent correlation with low-frequency earthquakes (LFEs) on shared faults. The underlying source processes governing the occurrence of VLFs and their interaction with LFEs remain elusive. Here, we employ a slip-weakening model for slow earthquakes. By comparing the source parameters of simulations and observations, it is suggested that VLFs are slow self-arresting earthquakes that self-terminate within the nucleation patch. Additionally, we adopt a composite model to reproduce the records of the simultaneous occurrences of a VLF and an LFE in the Nankai area. Our results present the possibility that VLFs, LFEs, and regular earthquakes can be distinguished using a unified dynamic framework.

Convective Quasi-Equilibrium (CQE) is often adopted as a useful closure assumption to summarize the effects of unresolved convection on large-scale thermodynamics, while existing efforts to observationally validate CQE largely rely on specific spatial domains or sites rather than the source of CQE constraints—deep convection. This study employs a Lagrangian framework to investigate leading temperature perturbation patterns near deep convection, of which the centers are located by use of an ensemble of satellite measurements. Temperature perturbations near deep convection with high peak precipitation are rapidly adjusted toward the CQE structure within the [−2, 1] hours centered on peak precipitation. The top 1% precipitating deep convection constrains neighboring free-tropospheric leading perturbations up to 9°. Notable CQE validity beyond a 1° radius is observed when peak precipitation exceeds the 93rd percentile. These findings suggest that only a small fraction of deep convection with extreme precipitation shapes tropical free-tropospheric temperature patterns dominantly.

Mollisols are highly fertile soils and function as significant carbon reservoirs. However, determining their ages and formation processes is challenging due to extensive pedoturbation, which undermines conventional dating methods. Here, we employed luminescence, a light-sensitive property of minerals widely used in geological dating, to investigate and quantify soil mixing. We analyzed over 2,400 luminescence ages of individual K-feldspar grains from a Mollisol profile in Northeast China, and for the first time, we were able to determine the intensity of pedoturbation in the Mollisol profile over the past 50,000 years. The results showed that the current pedoturbation can penetrate to a depth of approximately 80 cm, with the intensity decreasing with depth. By identifying a significant intensification in historical pedoturbation, we inferred that the paleoenvironment might be suitable for the formation of Mollisols 16,400 years before present.

The Vietnam upwelling is a crucial circulation feature in the South China Sea. Although previous studies have shown that various coastal upwellings around the world may intensify under global warming, future changes in the Vietnam upwelling remain unclear. To address this knowledge gap, we analyzed the long-term trend in the Vietnam upwelling under a high-emission scenario for the period 2006–2100, using simulation results from a global eddy-resolving climate model. In this model, the summertime Vietnam upwelling is projected to intensify in the 21st century and is statistically significant between 12°N and 14°N. A volume flux budget analysis indicates that wind stress curl is the most important contributor to the intensification. The geostrophic flow, to some extent, may suppress the upwelling intensification. The projected increase in upwelling is shown to significantly reduce local ocean warming and freshening and thus may have vital impacts on the local climate and circulation.

Plateau pikas, small mammals native to the Qinghai-Tibet Plateau (QTP), create bare patches through burrowing. No previous assessment exists on their impact on permafrost. This study fills this gap by simulating hypothetical scenarios in the Three Rivers Headwaters Region of the QTP using the Noah-MP model for the plant growing seasons during 2015–2018. Our findings reveal a significant increase in soil temperature in the active layer due to pika-induced bare patches, particularly during July–August. The average temperature rise at 2.5 cm depth was 0.36°C in permafrost regions and 0.29°C in seasonally frozen ground regions during August. Minimal impact on unfrozen water content was observed, with a slight increase in deep soil layers in permafrost regions, and negligible in seasonally frozen areas. These findings underscore the previously unexplored influence of pika burrowing on permafrost temperature, suggesting a potential risk of accelerating permafrost degradation, especially in permafrost-dominated regions.

Elastic properties of Si0.95H0.21O2 with hydrogarnet substitution (4H+ = Si4+) across the post-stishovite transition (28–42 GPa) are determined up to 70 GPa using ab initio calculations and a pseudo-proper type Landau model. At 28 GPa, elastic coefficients C 11 and C 12 converge, and the average shear and compressional velocity (V S and V P ) decrease by a maximum of 25.5% and 5.2%, respectively. Hydrogarnet substitution reduces ambient elastic moduli and sound velocities, and shifts shear softening to lower pressure. 2%–13% Si0.95H0.21O2 may cause a V S anomaly of −0.5% to −2.6% at 700–820 km depth, explaining low V S layers beneath North America and the European Alps. Additionally, 20 vol % SiO2 in subducted basalt, with decreasing water content from 3.2 wt% to zero, could cause a V S anomaly of up to −7(4) % from 700 to 1,900 km depth, aligning with seismic scatterers identified in some subduction regions.

An unexpected Mw7.45 earthquake struck the Noto Peninsula on 1 January 2024, preceded by several long-living earthquake swarms, providing a valuable opportunity to study seismic and aseismic slips, as well as their interactions. We derived coseismic and 19-day postseismic slip distributions by inverting co- and post-seismic displacements from Global Navigation Satellite System (GNSS) data. The inverted coseismic slip distribution shows two slip patches, with a maximum slip of ∼4 m. The early postseismic afterslip is 0.1–0.25 m within coseismic slip asperity and 0.1–0.6 m northward of the rupture area. The afterslip within the rupture area is accompanied by numerous aftershocks and coincides with a ∼6 MPa stress drop, suggesting that aftershocks are likely driven by the afterslip. The pattern of poroelastic rebound implies a potential effect of fluid flow on aftershock triggering. This study sheds lights on the intricate interplay between seismic and aseismic processes following large earthquakes.

Although it is known that the frequency and intensity of heatwaves are affected by the El Niño–Southern Oscillation (ENSO), unknown are the ENSO modulations on the moving properties (e.g., moving distance and speed) of spatiotemporally contiguous heatwaves. Here, we investigate the relationship between ENSO and the moving patterns of contiguous heatwaves. We show that contiguous heatwaves are likely more frequent, more persistent, and longer-traveling, but slower-moving during El Niño than La Niña episodes. The differences in the tropical contiguous heatwaves between El Niño and La Niña are influenced by persistent high-pressure anomalies. During the following summers, El Niño can induce anomalous atmospheric circulation characterized by an intensified subsidence over the western North Pacific and ascending motion over the tropical Indian and Pacific Oceans. These features provide favorable conditions for the occurrence and maintenance of contiguous heatwaves.

Decadal predictions focus regularly on the predictability of single values, like means or extremes. In this study we investigate the prediction skill of the full underlying surface temperature distributions on global and European scales. We investigate initialized hindcast simulations of the Max Planck Institute Earth system model decadal prediction system and compare the distribution of seasonal daily temperatures with estimates of the climatology and uninitialized historical simulations. In the analysis we show that the initialized prediction system has advantages in particular in the North Atlantic area and allow so to make reliable predictions for the whole temperature spectrum for two to 10 years ahead. We also demonstrate that the capability of initialized climate predictions to predict the temperature distribution depends on the season.