Geophysical Research Letters最新文献

Central America faces increasing risks from climate variability and extreme weather events. Limited observational records and model biases have constrained our ability to understand the ocean–atmosphere dynamics that influence precipitation variability in the region over longer timescales. Paleoclimate proxies, including the stable oxygen isotope ratio of the cellulose of tropical trees, can extend the climate record, allowing recent trends and variability to be evaluated in a long-term context and improving our understanding of forced and unforced variability of the climate system. Here, we present a new multidecadal record of tree-ring $��{\delta }^{18}�O�$ from Abies guatemalensis (Guatemalan Fir) from Guatemala and Honduras. We demonstrate that this proxy records boreal summer rainfall and is tightly coupled to neotropical ocean–atmosphere dynamics. This precisely dated, high-resolution proxy can be used for multicentury hydroclimate reconstructions of the Intertropical Convergence Zone dynamics and its interactions with the eastern Pacific Ocean and Caribbean Sea.

Physics-based atmosphere-land models with prescribed sea surface temperature have notable successes but also biases in their ability to represent atmospheric variability compared to observations. Recently, AI emulators and hybrid models have emerged with the potential to overcome these biases, but still require systematic evaluation against metrics grounded in fundamental atmospheric dynamics. We evaluate the representation of four atmospheric variability benchmarking metrics in a fully data-driven AI emulator (ACE2-ERA5) and hybrid model (NeuralGCM). The hybrid model and emulator can capture the spectra of large-scale tropical waves and extratropical eddy-mean flow interactions, including critical levels. However, both struggle to capture the timescales associated with quasi-biennial oscillation (QBO, ∼28 months) and Southern annular mode propagation (∼150 days). These dynamical metrics serve as an initial benchmarking tool to inform AI model development and understand their limitations, which may be essential for out-of-distribution applications (e.g., extrapolating to unseen climates).

Density-driven flow and fluid inertia jointly shape solute transport in fracture networks, with implications for hydrogeology and subsurface engineering. While their individual effects are well recognized, their coupled impact remains underexplored. We integrate pore-to-network-scale dye visualization experiments and numerical simulations to investigate solute trapping at fracture intersections. At the network scale, 3D flume experiments show localized tracer retention caused by density-induced convection and inertia-driven vortices. Millifluidic experiments and simulations reveal that density contrast, flow imbalance, and fluid inertia govern these dynamics. Maximum trapping occurs when bottom fracture flow is ∼10% greater than the top, maximizing mass entry while minimizing loss. This imbalance promotes vortex-driven retention and extended solute residence, leading to breakthrough curve tailing. Simulations in smooth and rough-walled fractures confirm that roughness alters trapping locations but not the underlying mechanisms. These findings highlight the central role of coupled pore-scale processes in controlling network-scale transport and subsurface reactivity.

A recent theory–originally proposed for tropical depression (TD)-type waves–is extended to the Madden-Julian Oscillation (MJO) and convectively-coupled equatorial Rossby (ER) waves across the Indo-Western Pacific region using reanalysis and Coupled Model Intercomparison Project Phase 6 (CMIP6) data. This framework posits that waves grow from a Hadley Cell-linked instability, quantified by a metric tied to the product of the meridional gradient of background vertical velocity and planetary vorticity. Results show that wave activity, diagnosed via wave-filtered moisture variance and poleward eddy moisture fluxes, is strongest in MJO and ER waves when the instability metric peaks. CMIP6 models with a higher instability metric exhibit stronger Southern Hemisphere MJO and ER waves. While significant in both, the correlations are stronger for ER waves. These results suggest that ER waves are driven by the same mechanisms as TD-type waves, whereas other processes not accounted for in this framework are also important for the MJO.

Accurate data on curvature-induced water-surface superelevation are important for understanding complex patterns of fluid motion in meandering rivers. Nevertheless, superelevation has been studied primarily in the laboratory because field measurements are difficult to obtain. This study assesses whether the Surface Water and Ocean Topography (SWOT) satellite can detect superelevation in meander bends. Plots of lateral water-surface slope (LWS) reveal distinct superelevation in three sets of Mississippi-River bends. As expected, the magnitude and direction of LWS are strongly correlated with channel curvature. Superelevation can also be detected on comparatively narrow Wabash-River bends, but levels of noise are more pronounced than for the Mississippi bends. Mean flow velocities estimated from LWS based on theoretical considerations agree closely with gauge-based estimates (±7%–35%). These findings confirm that SWOT data can be used to reliably detect superelevation in large river bends, providing the basis for global assessments of hydrodynamics in large meandering rivers.

The Laguna del Maule volcanic field in Chile has been uplifting at exceptional rates since 2007, offering a unique opportunity to examine the interplay between crustal deformation and magma dynamics. To understand this relationship, we integrate GNSS with local seismic observations from 2013 to 2024 to model the reservoir strain field, relocate earthquakes, and determine focal mechanisms. Our preferred model identifies a shallow spheroidal reservoir at ∼4 km depth that underwent ∼15 MPa of overpressure and a volume change increase of ∼0.23 km³. Seismicity clusters align with dilatational strain, and focal mechanisms are dominated by strike-slip faulting consistent with the regional NE–SW tectonic stress regime. We distinguish two phases of unrest: 2013–2018, when seismicity concentrated in dilatational faults, and 2018–2024, when swarms became more energetic with increased magma flux and strain rates. These results demonstrate how magma input, crustal deformation, and faulting interact during prolonged volcanic unrest.

The ocean absorbs most of the excess heat induced by anthropogenic greenhouse gas emissions. Among the different processes, a key role has been attributed to the Atlantic Meridional Overturning Circulation (AMOC), both for heat uptake and redistribution among basins, yet a comprehensive view remains elusive. In this study, we investigate how a weakening of the AMOC would influence ocean heat storage in a warming climate by comparing two idealized experiments with two different AMOC evolutions from the global climate model EC-Earth3, after abrupt carbon dioxide quadrupling. We find that AMOC weakening influences both vertical and inter-basin heat redistribution. For a stronger AMOC decline, more heat is stored in the Indo-Pacific Ocean and in the intermediate ocean layers above 700 m, while less heat accumulates in the deeper ocean layers, especially in the Atlantic. Globally, we find a 3% increase in cumulated ocean heat uptake at the end of the simulations.

This study investigates the spectral and dynamic characteristics of turbulent fluctuations in the electric field within equatorial plasma bubbles using data from the Electric Field Detector aboard the China Seismo-Electromagnetic Satellite-01. We applied a novel analysis method, developed within the framework of dynamical systems theory, to high-resolution electric field data, allowing us to resolve spatial scales down to just a few meters. This method evaluates the system's persistence in specific states and the instantaneous dimension of fluctuations. Our findings reveal a significant increase in the instantaneous dimension $��d�$ and a decrease in the extremal index $��\theta �$, which measures local persistence, within the plasma bubbles. These results suggest a complex interplay of structures at different scales driven by turbulent dynamics characterizing these ionospheric plasma depletions. This study provides new insights into the turbulent processes within equatorial plasma bubbles, advancing our understanding of their underlying mechanisms.