Geophysical Research Letters最新文献

In 2022–2023, three local-magnitude (M_L) 4.8–5.6 earthquakes shook the Peace River oilsands area of Alberta, Canada. Previous studies statistically linked the seismicity to nearby disposal activities but lacked in-depth investigation into triggering mechanisms, including subsurface fluid migration and earthquake interaction. Here, we identify the seismicity as a directional, cascading rupture process initiated by wastewater disposal and sustained by tectonic fault interplay. Our findings highlight the role of regional geologic framework, a combination of a capped fringing-reef formation and a truncated fault, in channeling injected fluids. Injection above this architecture was effectively isolated, whereas fluids entering the reef formation progressively destabilized the fault, culminating in the M_L 5.6 event on 30 November 2022. This mainshock triggered a southeastward rupture cascade, including two M_L 4.8+ events on 16 March 2023. Earthquake swarms were primarily nucleated by the nearest reef-targeted disposal well, with secondary contributions from wells located 20–35 km away.

Organic-rich mangrove soils release CH₄, partially offsetting the climate benefits of high organic carbon sequestration. However, the local and global drivers and variability of mangrove CH₄ emissions remain poorly understood. Here, we quantify water-atmosphere CH₄ emissions over hourly, daily, and weekly time scales in an Australian mangrove ecosystem. We then combine our new observations with earlier data sets to link temperature and mangrove CH₄ emissions on the global scale. The water-atmosphere CH₄ emissions were partially controlled by temperature on both local and global scales. One degree warming increased mangrove water-atmosphere CH₄ emissions by ∼23% locally and ∼13% globally. Globally scaled water-atmosphere CH₄ emissions (0.07–0.10 Tg C yr⁻¹) currently offset 6%–8% of mangrove carbon burial. CH₄ emissions are predicted to increase by 10%–33% by 2100 under global warming scenarios and tropicalization. Therefore, mangrove CH₄ emissions should be considered in blue carbon assessments in the context of global warming.

The migration of fluids, such as aqueous fluids and melts, is often channelized and crucial for trace element transport. However, trace elements typically migrate slower than the fluid due to partitioning between solid and fluid phases, known as retardation. The influence of channelization intensity on trace element retardation remains poorly quantified. Here, we use two-dimensional numerical simulations to investigate trace element transport during compaction-driven flow involving porosity waves and channelization caused by decompaction weakening. We employ a small-amplitude porosity perturbation to study fluid segregation. A data collapse of systematic numerical results quantifies how the increase in channelization intensity cancels out the decrease in trace element transport caused by retardation, showing that channelized porosity waves enable segregated trace element mass transport. We illustrate changes of trace element distributions during fluid migration using multi-element (spider) and ternary diagrams as well as trace element profiles across channels.

The Labrador Sea is a key formation site for dense waters that contribute to the lower limb of the Atlantic meridional overturning circulation (AMOC). Recent observations have revealed a distinctly weak overturning in this basin, attributed to compensating effects of temperature and salinity anomalies on density. However, it remains unclear whether these effects are consistent under varying hydrographic conditions and whether they subsequently impact overturning variability. By combining moored observations and historical hydrographic data, we demonstrate a coherent response of the Labrador Sea overturning to salinity anomalies over recent decades. Notably, a strengthened overturning in the late 2010s can be attributed to subsurface fresh anomalies advected into the basin by the boundary currents, which are linked to large-scale freshening that began in the late 2000s. Our findings underscore the necessity of continuously monitoring boundary salinity and temperature anomalies to capture ongoing changes in the Labrador Sea.

Upward Illumination (UI) strokes are a subtype of cloud-to-ground (CG) return strokes characterized by two concurrent branches striking the ground a few milliseconds apart. The luminous channel of an UI stroke does not connect to the main channel, which gives this phenomenon its name. Since concurrent branches in positive CG strokes are not usual, positive UI (+UI) strokes were never reported yet. This study presents the first observations of +UI strokes. They were recorded in Utah, USA, using high-speed cameras. Although +UI strokes share similarities with negative UI strokes, their initiation mechanisms are fundamentally different. +UI strokes result from intense recoil leader activity with their positive leader speed one order of magnitude slower than the average of typical CG downward positive leaders. Additionally, multiple +UI strokes can occur within the same flash. Finally, we gather all the information learned from the case studies to propose the basic formation mechanisms of +UI strokes.

Assessing local climate change impacts often requires downscaling coarse global climate model (GCM) output to finer resolution. Two main approaches exist: dynamical downscaling using high-resolution regional climate models, and statistical downscaling based on historical relationships between large-scale and local variables. In a recent analysis of five dynamically downscaled simulations over the western United States, Koszuta et al. (2024, https://doi.org/10.1029/2023gl107298) found that warming weakens orographic influence on winter precipitation, damping increases on windward slopes and amplifying them in rain-shadowed regions. Here we show that this effect is robust across seasons and multiple dynamically downscaled ensembles, and is more pronounced at higher model resolutions. However, it is absent in projections from a widely used statistical model (LOCA2), even when trained on high-resolution future simulations (LOCA2-Hybrid). This highlights a key limitation of many statistical downscaling methods: their preservation of parent GCM trends, which usually fail to capture emergent changes in orographic precipitation patterns.

This article evaluates Entraining CAPE (ECAPE) as a thunderstorm proxy in climate studies using Global Precipitation Measurement satellite observations. ECAPE modifies traditional CAPE to account for the dependence of entrainment on the vertical wind shear, the lifted condensation level (LCL) height, and the properties of a cloud's surrounding atmosphere. ECAPE shows stronger pattern correlations with global regions of intense thunderstorms than previous metrics for updraft speed. In these regions, large CAPE, large shear, and high LCLs conspire to produce wide updrafts that are shielded from the negative effects of dry-air entrainment. ECAPE more skillfully discriminates intense thunderstorms from their less intense counterparts than other metrics commonly used in climatology and climate change studies of thunderstorms. We provide evidence that the well-known land-sea contrast in thunderstorm intensity is a consequence of larger CAPE and higher LCL heights over land than over the ocean.

Intensity forecast errors of tropical cyclones (TCs) over the western North Pacific are investigated using forecast records from the Hurricane Weather Research and Forecasting (HWRF) model. Intensity errors increase with the lead time, growing most rapidly during the first 36 hr. Predicted intensity of intense (weak) TCs is generally underestimated (overestimated). The biases mainly stem from the initial intensity bias and the predicted TC fullness (TCF) bias, as well as from the actual intensity change. Initial intensity bias dominates during the first day, explaining 19% of intensity forecast bias. Actual intensity change exhibits a persistent negative correlation with intensity forecast bias, accounting for 16% of the bias within 5 days. In contrast, the influence of TCF forecast bias increases over time and contributes 13% to intensity forecast bias during 4–5 days. Additionally, TC initial intensity, position, and TCF, together with track errors, also affect intensity forecast errors.

The structure and properties of mature upper oceanic plates may evolve through mechanisms such as magmatism, hydrothermal circulation, and faulting. However, high-resolution constraints, especially those involving both P- and S-waves, remain scarce, limiting our ability to detect these processes and assess their impacts on crustal properties. We present high-resolution P- and S-wave velocity models from traveltime tomography of downward-continued long-offset streamer data acquired along a margin-parallel profile in the outer rise of the Sumatra subduction zone. The data reveal high-quality, doubly converted S-wave arrivals from the upper crust. Layer 2A (uppermost crust) exhibits high and laterally uniform Poisson's ratios (0.3–0.35), whereas the underlying Layer 2B is more heterogeneous with lower Poisson's ratios (0.26–0.33). We interpret Layer 2B heterogeneity as reflecting widespread deformation within the Wharton Basin. In contrast, the more uniform and elevated Poisson's ratio in Layer 2A likely indicates the opening of cracks by plate bending in the outer rise.

Compound wind and precipitation extremes (CWPEs) pose significant threats to natural resources and the socio-economic security. This study investigates the projected changes and driving factors of CWPEs over Southeast Asia (SEA) based on Coupled Model Intercomparison Project Phase 6 outputs. Results show that the frequency of CWPEs during 2070–2099 is projected to increase by 56.6% (62.2%) under the SSP2-4.5 (SSP5-8.5) scenario, while intensity is expected to increase by 11.9% (25.5%). These changes are primarily driven by variations in precipitation, which account for 54.9%–85.7% of the total contribution under the two scenarios mentioned. We further revealed that the probability of high-frequency (high-risk) CWPEs will increase by a factor of 2.3 (1.6), with 56.2% (37.3%) of the risk increase is attributable to anthropogenic activities. These findings emphasize the high sensitivity of CWPEs to climate change over SEA, and underscores the importance in informing adaptation strategies for vulnerable regions.