Geophysical Research Letters最新文献

Earthquakes occur through repeated cycles of locking and slip. What is the relationship between transiently locked patches and the size, location, and timing of the subsequent slip events? Here we use an experimental fault made of transparent rubber to image the slip history of over 18,000 events. The soft elastic system allows for contained ruptures and thus a natural evolution of stress heterogeneity over multiple earthquake cycles. We observe a precursory locking phase preceding slip nucleation for events of all sizes. The integrated locking distance increases linearly with the moment of the eventual event. The most intense (largest slip deficit) locking events are spatially and temporally correlated with the hypocenters of the largest rupture events. These results show that the transient locking is statistically, but not deterministically, predictive of the location, timing, and size of the eventual slip event.

Hudson Bay seasonal sea-ice cover plays an important role in marine ecosystems and human activities. Spring 2024 witnessed a uniquely early southeastern opening, leading to basin-wide sea ice extent falling 5$��\sigma �$ below the 1979–2023 average. Here, we show that a strong pressure gradient between high pressure over the Canadian Archipelago and low pressure to the south led to unusually strong and persistent winds from the east during May 2024. Consequently, the median sea ice opening date in the southeast was 31 days earlier than the 1979–2023 median, while sea ice opening in the west was delayed by 13 days. Early opening and warmer than average sea surface temperatures have extended the ice-free period to 202 days in southeastern Hudson Bay, with potentially dramatic consequences on the local marine ecosystem and contributed to the record low Arctic-wide sea ice extent by December 2024.

Marine geodetic references, such as the mean sea surface (MSS), are currently limited by the spatial resolution of conventional satellite altimeters. We analyze the new swath-altimetry data from the Surface Water and Ocean Topography (SWOT) satellite, to determine the performance of SWOT for mapping the static ocean topography, and possible benefit of inclusion in future reference models. By determining how well SWOT observes the static features in the ocean surface during SWOTs fast-sampling phase, we have determined the expected performance during the science phase of the mission. We observe a 50% reduction in variability of the static surface compared with Sentinel-3, whilst resolving up to 36% shorter wavelengths (down to $��\sim �$8 km) compared to the current state-of-the-art Hybrid23 MSS reference model. Comparisons with Sentinel-3 show that SWOT will benefit the current altimetry record.

To better understand rapid radiation belt losses, this statistical study examines dropouts, defined as a phase-space density (PSD) decrease by a factor of $��\ge �5�$ within 8 hr. The relationship between dropouts, storm parameters, solar-wind drivers, geomagnetic indices, and MeV electron precipitation is analyzed. Four years of data from the Van Allen Probes, measuring electron density, the CALorimetric Electron Telescope on the International Space Station, measuring MeV electron precipitation, and solar-wind/magnetic indices from the OMNI dataset are utilized. Our investigation reveals that electron loss in PSD increases with disturbance intensity. However, about one-third of dropouts occur during small geomagnetic disturbance periods, some involving precipitation, while approximately 40% of storms do not lead to dropouts. Superposed epoch analysis identifies solar-wind density and dynamic pressure as the main dropout drivers, while precipitation becomes more likely with higher trapped electron flux and stronger substorms. Dropouts do not require a negative southward magnetic field component.

Cyclone-generated cold wakes enhance productivity and impact local air-sea interaction, paths and intensities of subsequent storms in the region. However, in-situ observations of recovery across such wakes are rare. A cold wake in the Arabian Sea was surveyed using multiple shipboard instruments approximately 10 days after the passage of Cyclone Biparjoy in 2023. The wake, nearly 30 km wide, had a stronger (weaker) buoyancy gradient at its eastern (western) edge and assumed a downfront (upfront) orientation relative to the southwesterly monsoon winds. This resulted in notable asymmetry in the vertical structure of temperature, salinity and velocity at the edges of the wake, indicating the importance of Ekman Buoyancy Fluxes and Mixed Layer Eddies. While the wake recovery following a cyclone is often attributed to one-dimensional diurnal heating and cooling, these observations underscore the role of interactions between monsoon winds and underlying three-dimensional submesoscale processes for a slow-moving cyclone wake recovery.

In May 2024, southern Brazil experienced a severe flood that caused widespread devastation, particularly in the metropolitan area of Porto Alegre. This disaster resulted from a rare combination of atmospheric conditions: a heatwave stalled a cold front, leading to prolonged and intense rainfall. The flood claimed 183 lives, left 27 missing, and displaced many more. Notably, the flood's peak coincided with satellite observations from both SWOT and Sentinel-2, providing a valuable snapshot of the disaster. To assess the flood's scope, and volume, we integrate these satellite data with FABDEM topography. SWOT's water height measurements, evaluated with in situ data, underscore its flood monitoring potential. The estimated floodwater volume was $��\sim �$ 1.5 billion $��m^3�$. While primarily damaging croplands, the flood directly affected $��\sim �$ 420,000 individuals in the study region, with $��\sim �$ 16% identified as socially vulnerable. These findings offer insights into floodwater distribution and contribute to future flood dynamics research, mitigation strategies, and disaster preparedness.

The intricate flow processes in nano-pores pose limitations on the extraction of resources such as shale gas and gas hydrates. To observe water/gas two-phase flow in nano-pores, we employed molecular dynamics simulations on water/methane two-phase flow in a hydrophilic SiO₂ nanoslit, and obtained high-quality data by applying the “pump method” and “nano-manometer.” This study revealed the variation in phase distribution during flow process, and assessed the impact of water phase distribution on methane gas flow. We proposed the “Deformed Water Layer (DWL) model” based on physical mechanisms, which can precisely describe methane relative permeability and forecast the critical water saturation for forming water lock. Our results suggest a two-stage transition in methane gas permeability with increasing water saturation within nano-pores, governed by spatial deformation of water phase. This phenomenon underscores that maintaining a reduced groundwater saturation is imperative to facilitate superior gas permeability and enhance recovery efficacy.

We use the coupled atmosphere-ocean model MIROC4m to investigate the effect of mid-Pliocene boundary conditions on the Atlantic Meridional Overturning Circulation (AMOC), studying the impact of increased $��{\text{CO}}_2�$, reduced ice sheets and altered orography and vegetation. We find that a higher $��{\text{CO}}_2�$ concentration and smaller ice sheets both weaken the AMOC with respect to the pre-industrial. The stronger mid-Pliocene AMOC is therefore a consequence of mid-Pliocene orography and vegetation, where the closed Arctic gateways are responsible for approximately 80% of the AMOC strengthening. The main mechanism for mid-Pliocene AMOC strengthening is reduced transport of freshwater from the Arctic into the North Atlantic, enhanced by a decrease of surface freshwater flux into the high-latitude North Atlantic.

The extreme positive Indian Ocean Dipole (pIOD) in 2019 was followed by tropical Indian Ocean (TIO) basin-wide warming in summer 2020, which contributed to severe flooding in the Yangtze River basin. Here, the potential relationship between extreme pIOD and subsequent summer TIO basin-wide warming is explored using observations and model outputs, revealing that this sequential co-occurrence is significantly influenced by Pacific SST conditions. Extreme pIODs that coincide with El Niño tend to be followed by TIO basin-wide warming, whereas those cooccurring with neutral or La Niña conditions are comparatively less likely to do so. This is because El Niño can trigger anomalous anticyclone over the southeastern TIO, thereby maintaining and reinforcing the extreme pIOD-related warm SST anomalies over the southwestern TIO, which subsequently induces SST warming over the northern TIO in summer. Our findings highlight the important modulation role of Pacific SST conditions, with significant implications for regional climate predictions.

The Coupled Model Inter-comparison Project Phase 6 (CMIP6) multi-models predict future warming over Antarctica under five different scenarios, but their uncertainties remain high and have not been well constrained. Here we find that the projected Antarctic warming robustly correlates with simulated averaged temperature trends during 1958–2012 across the CMIP6 multi-models under each scenario, which is thereby used to refine future air temperature projections using observation-based temperature reconstruction. The median of future warming projections under the five scenarios reduces by 24%, 19%, 18%, 21%, and 21%, respectively. The constrained uncertainty ranges are narrowed down, with the likely range by the end of the century relative to 1850–1900 baseline declining from 4.2°C–6.8°C to 3.2°C–6.1°C under the highest emission scenario. The application of ERA5 for the same constraint shows an increase in future warming and constrained uncertainty ranges. This suggests a key role of observational data set uncertainties in the performance of emergent constraints.