Geophysical Research Letters最新文献

This study reveals that the onset of tropical Asian summer monsoon (TASM) experienced a pronounced interdecadal delay (about one week) after the late-2000s. Both the large-scale seasonal transition reflected by EOF analysis and the monsoon onset dates defined by local rainfall exhibited a clear interdecadal change. Correspondingly, there appears reduced rainfall and low-level easterly anomalies over tropical Asia in May, indicating that the monsoonal westerly winds and convective activities cannot be stably established. Further analysis suggests that the SST warming in the equatorial western Indian Ocean serves as a possible driver of the delayed TASM onset. The warm SST anomalies trigger a Kelvin wave-like response to the east, inducing anticyclonic circulation and easterly anomalies over tropical Asia, which hinder moisture transport and reduce rainfall. The reduced rainfall further strengthens anomalous easterly winds, thereby favoring the delayed onset of the summer monsoon.

Continental mantle earthquakes are uncommon but hold important clues for understanding lithospheric rheology. Few of these earthquakes (<10) have been documented in western North America, though it is likely more exist owing to difficulties in resolving focal depth for small earthquakes. Mapping their distribution in western North America is key to better characterizing cratonic evolution in this area. Here, we evaluate 25 nominally lower crustal and upper mantle earthquakes in the Milk River region of southwestern Alberta. We absolutely relocate each earthquake and compare depths to published estimates of Moho depth and find 17 earthquakes locate ∼8–16 km below the Moho. High-precision relative relocations and first-motions define a steeply west-dipping, Moho-crossing normal fault. We hypothesize these earthquakes are related to regional mantle flow patterns interacting with lithospheric edges and are part of a larger trend of upper mantle seismicity along the western edge of North American cratonic lithosphere.

For hydrogeological management of seasonally frozen soils, or permafrost, the quantification of ice and water content is key. Changes in electrical conductivity are commonly used to monitor ice-to-water ratios but hard rocks, ice and air are all highly resistive materials. The high-frequency polarization of ice (kHz range) offers a suitable alternative to the conductivity, but field investigations at such frequencies are still challenging. Here, we demonstrate the polarization of blank ice features in solid rocks at low frequencies (1–100 Hz). We identify two polarization effects: (a) an increase in the response due to the polarization of charges in the electrical double layer formed at the ice-water-rock interface; (b) an even larger response due to the non-equilibrium freezing potential taking place during ice formation. We demonstrate that these effects can be used to image ice features, for instance, during ground-ice formation and degradation.

We investigate the energy growth and dissipation of wind-forced breaking waves at high wind speed using direct numerical simulations of the coupled air–water Navier–Stokes equations. A turbulent wind boundary layer drives the growth of a pre-existing narrowband wave field until it breaks, transferring energy into the water column. Under sustained wind forcing, the wave field resumes growth. We separately analyze energy transfers during wave growth and breaking-induced dissipation. Energy transfers are dominated by pressure input during growth and turbulent dissipation during breaking. Wind input during growth is balanced with dissipation during breaking over an entire growing-breaking cycle. The wave growth rate scales with $��{\left(�u_{\ast }�/�c�\right)}^2�$, modulated by the wave steepness due to sheltering, and the energy dissipation follows the inertial scaling with wave slope at breaking, confirming the universality of the process. Following breaking, near-surface vertical turbulence dissipation profiles scale as $��z^{�-�1�}�$, with their magnitude controlled by the breaking-induced dissipation.

Polar amplification (PA) is a robust feature of contemporary climate change, but its state-dependence across different climate conditions is poorly understood despite potential relevance to paleoclimate records and future projections. Here we examine the state-dependence of PA across a wide range of climate states in an idealized moist general circulation model. We generate a phase space of climate states with different global-mean surface temperatures and equator-to-pole surface temperature contrasts then perturb each with longwave radiative forcing. We find that the state-dependence of PA is largely a superposition of two effects. Firstly, as a consequence of moist thermodynamics, latent energy transport drives stronger PA in climates with higher global-mean surface temperatures and stronger meridional surface temperature gradients. On top of this, the ice-albedo feedback amplifies PA in climates where the climatological ice edge sits within the polar cap.

The severe impacts of rain-on-snow (ROS) extreme events have been widely recognized and studied. However, unlike hydrological processes, flood inundation dynamics and the relative contribution of rainfall and snowmelt during ROS events remain under-investigated. We diagnosed and documented sub-kilometer spatio-temporal dynamics of flood inundation during the 2017 California ROS events, simulated by a 2-dimensional hydrodynamic model, River Dynamical Core (RDycore). RDycore shows good performance in capturing fine-scale flood inundation dynamics against gauge measurements (with a median correlation coefficient of 0.81) and satellite observations. On top of rainfall, snowmelt not only increases the mean maximum inundation depth (12.0%–25.1%), but also expands the total flooded area (19.9%–31.9%) and prolongs the mean flood duration (3.4%–7.1%) across the events. Our findings offer an explicit and accurate picture of when and where ROS flooding could occur and how snowmelt increases flood hazard, valuable for risk assessment and infrastructure planning.

Blind faults pose significant seismic hazards because they remain hidden beneath the surface and are often unrecognized until they generate large earthquakes. High-resolution shallow velocity models are essential for imaging these blind structures. We analyze seismic data from a dense linear array across the Chenghai Fault, buried beneath a thick basin in Yunnan, China. First, we obtain a high-resolution shallow velocity model using surface wave tomography with a three-station-interferometry-based denoising technique. Then we correct teleseismic S-wave delays with this model, and reveal a bi-material interface associated with the buried fault. Compared with previous regional tomography, the across-fault velocity contrast offers a higher-resolution view of the buried bi-material interface. These results highlight the importance of high-resolution shallow velocity models for detecting and characterizing blind faults. The model can be further exploited to remove wave propagation effects in shallow structures, aiding high-resolution imaging of blind faults in future studies.

The magnetic reconnection rate at the magnetopause is crucial for solar wind and magnetosphere coupling. However, direct measurement is challenging due to inherent uncertainties and limited electron diffusion region statistics, hindering understanding of the guide field's influence on the normalized reconnection rate. This study introduces a new statistical method using over 1 million in situ subsolar magnetopause measurements to estimate the normal magnetic field and plasma inflow velocity as a function of the interplanetary magnetic field (IMF) clock angle. Results show that both the normal components of the magnetic field and inflow velocity increase with IMF clock angle, as expected from ongoing magnetic reconnection. On average, their ratio to tangential components—used to derive four independent normalized reconnection rates—is shown to be relatively constant and about 0.14 $��\pm �$ 0.05 for all IMF clock angles larger than 60°, suggesting that the reconnection rate is independent of the guide field at the magnetopause.

We analyze Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) data to characterize ground deformation and dike opening associated with the May 2021 Nyiragongo eruption. Despite documented eruptions in 1977 and 2002, Nyiragongo's magmatic system and its interaction with regional rifting remain poorly understood. Here, we use Sentinel-1 (ESA Copernicus) and ALOS-2 (JAXA) InSAR data and GNSS observations from the KivuGNet network, that cover the period of the eruption and dike intrusion. Deformation is dominated by a co-eruptive dike intrusion extending over 25 km, accompanied by ground fissures of about 1.5 m opening in Goma (Democratic Republic of Congo) and Gisenyi (Rwanda). Joint inversions of four interferograms with GNSS data resolved a maximum dike opening near 10 m and a volumetric increase of about 180 Mm³. The inferred dike geometry aligns with observed ground deformation and seismicity, underscoring the coupling between magmatic and tectonic processes.

The Gravity Recovery and Climate Experiment (GRACE) satellite mission provides accurate observations of terrestrial water storage anomalies (TWSA), but their coarse spatial resolution (∼3°) limits sub-regional-scale applications. Existing downscaling methods rely on high-resolution hydrometeorological inputs, which often underestimate the full magnitude of GRACE signals. Here, we develop a machine-learning-based iterative downscaling method that reproduces TWSA at 0.25° resolution while retaining nearly all of the original GRACE signals, using ERA5 soil moisture, precipitation, and temperature as inputs. We find that the downscaled TWSA has improved agreement with in situ groundwater levels compared to the original GRACE data, with higher correlation at over 63% of wells and reduced RMSE at more than 83% globally. The downscaled TWSA also retains an average correlation of 0.99 with original GRACE data at the basin scale, outperforming a previously released downscaling product. The downscaled TWSA data set is publicly available at https://doi.org/10.5281/zenodo.17265162.