California Institute of Technology

Abstract Classical theories for axisymmetric, nearly inviscid Hadley circulations typically neglect processes such as vertical momentum advection to obtain analytical solutions. Using simple 1.5- and 2-layer axisymmetric inviscid models, we clarify the relative significance of these processes, with particular focus on seasonally varying dry Hadley cells. We show that vertical momentum advection strongly modifies the strength, extent, and seasonal response of the circulation. Including nonzero surface zonal winds in a two-layer model only produces a negligible weakening of the solstitial circulation. Building on these results, we introduce a semianalytical theory for the meridional structure of dry, nearly inviscid Hadley cells that explicitly incorporates vertical momentum advection. This theory accurately explains the strength and extent of seasonally varying Hadley circulations simulated in axisymmetric GCMs. Importantly, the theory shows that axisymmetric Hadley circulations do not undergo the rapid nonlinear strengthening with seasonality predicted by earlier models. Meridional variations in gross stability observed in the simulations can, in principle, lead to deviations from the theory. We explain the cause of these variations and show that their impact is limited: While the mass transport streamfunction is very sensitive to these variations, the heat transport profile, along with the meridional profiles of zonal wind and temperature, remains relatively invariant due to angular momentum constraints. Finally, we assess the influence of vertical momentum diffusion on the axisymmetric GCM simulations and discuss implications for eddying and moist atmospheres, as well as for regime transitions of the Hadley circulation and connections to monsoons.

BackgroundHyperosmotic shock and the resulting cell volume compression are commonly experienced by organs such as the kidneys, causing rapid formation of hyperosmotic phase separation (HOPS) condensates in the cytoplasm and nucleoplasm. Although the causal relationship between hyperosmotic shock and condensation has been characterized, the diffusion dynamics of biomolecular condensates in hyperosmotically compressed cells and their underlying mechanisms remain largely unknown.ResultsWe systematically characterize the dynamics of HOPS condensates formed by model protein mRNA decapping enzyme 1A (DCP1A) through live-cell fluorescent single-particle tracking (SPT) across timescales. We find that HOPS condensates predominantly exhibit sub-diffusion rather than free diffusion, while a small fraction undergo bursts of super-diffusion. Using imaging to measure spatial accessibility inside cells and fluorescence labels for specific cellular organelles, we show that sub-diffusion arises from endoplasmic reticulum (ER) attachment, whereas super-diffusion reflects microtubule-dependent active transport. We further reconstruct spatial accessibility within hyperosmotically compressed cells using trajectories of genetically encoded multimeric nanoparticles (GEMs) and find that, despite compression, the cytoplasm remains accessible via diffusion and does not exhibit physical corralling. This indicates that restricted condensate mobility arises primarily from specific molecular interactions rather than from physical barriers.ConclusionsOur findings challenge the view that the cytosol becomes static and constrained during hyperosmotic compression. Instead, it remains dynamic, while condensates are spatially organized through docking to membrane structures with intermittent episodes of long-range transport. This model reshapes our understanding of the physical environment within stressed cells and provides a framework for how condensates achieve spatiotemporal organization through interactions with cellular structures and active processes.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13059-026-04042-w.

International audience

Giant megathrust earthquakes typically occur above the upper-plate Moho or the 350°C isotherm in warm subduction zones. However, large earthquakes also occur within the mantle wedge corner at 35-55 km depth at cold subduction zones, such as the Kermadec, Japan Trench, and Chilean margins. Here we investigate the frictional behavior of lawsonite blueschist metagreywacke, potentially found in cold subduction channels, to better understand the control of metamorphic grade on such first-order variations in seismogenic depth. We perform velocity-step experiments on metagreywacke gouge from room temperature to 500°C and effective normal stresses from 50 MPa to 320 MPa, capturing the unstable friction regime and the brittle-to-flow transition. The constitutive behavior of metagreywacke indicates a potential seismogenic behavior at high temperatures below the Moho. Large megathrust earthquakes in the mantle wedge corner may develop in the lawsonite blueschist metasediment channel of cold subduction slabs.

Abstract The most general searches for gravitational wave transients (GWTs) rely on data analysis methods that do not assume prior knowledge of the signal’s waveform, direction, and arrival time on Earth. These searches provide data-driven signal reconstructions that are crucial both for testing available GW emission models and for discovering yet-to-be-unveiled sources. Here, we discuss the progresses in detection performances of the coherent WaveBurst second generation pipeline (cWB-2G), which is highly adaptable to minimally–modeled as well as model–informed searches for GWTs. Several search configurations for GWTs are examined using approximately 14.8 d of observation time from the third observing run by LIGO-Virgo-KAGRA (LVK). Recent enhancements include a ranking statistic fully based on multivariate classification with eXtreme gradient boosting, a thorough validation of the accuracy of the statistical significance of GWT candidates, and the measurement of the correlations of false alarms and simulated detections between different concurrent searches. For the first time, we provide a comprehensive comparison of cWB-2G performances on data from networks made of two and three detectors, and we demonstrate the advantage of combining concurrent searches for GWTs of generic morphology in a global observatory. This work offers essential insights for assessing our data analysis strategies in the ongoing and future LVK searches for generic GWTs.

Stratospheric aerosols play a crucial role in atmospheric chemistry and climate through heterogeneous chemical reactions and radiative forcing. Although sulfate aerosols in the stratosphere have been extensively studied, the organic fraction remains poorly characterized, despite its potential importance for both climate and chemical processes.The Stratospheric Aerosol Processes, Budget, and Radiative Effects (SABRE) 2023 campaign deployed the WB-57 high-altitude aircraft with a payload designed to improve characterization of stratospheric aerosols. Aerosol particles with aerodynamic diameters between 0.18 and 3.2 μm were collected using a cascade impactor (Mini-MOUDI 135, MSP) for offline analysis. We apply Scanning Transmission X-ray Microscopy coupled with near-edge X-ray absorption fine structure (STXM-NEXAFS) to characterize the composition and morphology of individual stratospheric aerosol particles. Carbon K-edge spectra are used to classify particles by organic carbon, elemental carbon, and inorganic content, enabling investigation of aerosol mixing state, morphology, and carbon functional group distributions. NEXAFS analysis also measures potential tracers, such as potassium associated with biomass burning, and other anthropogenic organic species. Using a radial distance shell-based classification scheme, we present preliminary results highlighting the complexity and diversity of particle morphologies. These microphysical properties help constrain the impacts of stratospheric aerosols on radiative forcing and ozone chemistry. We compare results across multiple flights, distinguishing aerosols sampled within and outside the polar vortex. Together, these observations advance our understanding of the chemical and radiative roles of stratospheric aerosols in Earth’s atmosphere.

With air temperature anomalies already reaching +3°C, Switzerland is undergoing rapid environmental change, particularly in the Swiss Alps, experiencing alpine greening and an upward shift of the tree line. However, the consequences of these changes for soil carbon storage, turnover, and lateral export remain poorly constrained. Using the national Radiocarbon Inventories of Switzerland database (RICH, rich.ethz.ch), we combine highly informative 13C and 14C isotopic data with a coupled soil–rock–water model to investigate carbon cycle dynamics across spatial scales, from individual sites to entire catchments. At the local scale, isotopic measurements of soil density fractions provide detailed insights into carbon stabilization mechanisms and turnover times. Meanwhile at the catchment scale, riverine ion concentrations and carbon isotopic signatures integrate signals across landscapes. Long-term continuous monitoring of river carbon and solute fluxes over the past 50 years reveal significant changes across both the Swiss Plateau and Alps, reflecting shifts in weathering, hydrology, and soil carbon cycling. By jointly calibrating site-scale soil processes and catchment-scale riverine fluxes using isotopic constraints, our approach enables cross-scale inference of carbon turnover and pathways. With this integrated framework, we aim to improve our understanding of the coupling between vegetation dynamics, soil carbon turnover, bedrock weathering, and lateral carbon export in vulnerable landscapes undergoing change.