Geophysical Research Letters最新文献

In positive leader discharge, the channel evolution process during pause period significantly impacts the subsequent discharge behavior accompanied by sudden elongation and intense reillumination of the discharge channel. The discontinuous discharge phenomenon is widely observed in the intermittent positive leader of natural lightning and laboratory positive long air gap discharge. In this study, direct optical photography and schlieren observation system were designed to acquire the time-resolved morphology images of optical and thermal plasma channel during pause period of positive leader discharge. The synchronized propagation of luminous and thermal channels within pause duration is experimentally characterized. Besides, it is confirmed that the secondary streamer triggering leader inception bursts in front of the residual channel within pause duration and further reactivates the discharge channel, providing insight into the stepped propagation mode of positive leader discharges in nature lightning and restrike phenomenon.

This study compares the vertical tilt and potential vorticity $��\left(��P�V��\right)�$ structure of average and extreme extra-tropical cyclones (ETCs) in the Northern Hemisphere during the cold season (October–March) in ERA5 reanalysis. Vertical tilt is quantified using a novel two-component (directional and lateral, aligned with and across cyclone motion) horizontal offset between the near-surface and upper-level ETC centers. Compared to average ETCs, extreme ETCs exhibit an amplified tilt magnitude during the intensification phase and a change in the sign of the lateral tilt prior to maximum intensity. Accounting for the tilted vertical structure, this study shows that average ETCs are associated with an upper-level positive $��P�V�$ anomaly, which is constant through the ETC lifecycle, while the $��P�V�$ intensifies from the bottom up. In contrast, extreme ETCs are characterized by a growing magnitude of upper-level $��P�V�$ anomaly, and a simultaneous intensification throughout the lower levels.

Precipitation from marine boundary layer clouds is a critical yet highly uncertain feature of post-frontal conditions over the Southern Ocean (SO), where shallow convection dominates. This study evaluates whether satellite retrievals (GPM-IMERG and CloudSat) and reanalysis (ERA5) represent the contrasting precipitation between open and closed mesoscale cellular convection (MCC) observed over the SO, from limited in situ records. Substantial discrepancies are found across data sets. While ERA5 captures the expected contrast, GPM-IMERG underestimates precipitation, especially from open MCCs, and fails to reflect morphological distinction. Both CloudSat products detect higher mean precipitation for open MCCs, though with differences in intensity distribution. Using observed precipitation rates and occurrence frequencies, open MCCs are estimated to contribute 9%–13% and closed MCCs 1%–11% of the annual precipitation between 40°S and 50°S. These results highlight the importance of improving the representation of marine atmospheric boundary layer cloud morphologies in models and observational data sets to better constrain the SO water cycle.

Most CMIP6 climate models simulate a Pacific SST warming pattern through the 20th and 21st centuries that is “El Niño-like,” with a weakened zonal equatorial gradient. However, observed trends are “La Niña-like,” displaying a strengthened zonal equatorial gradient, raising concerns about the accuracy of these projections. Here we explore multi-model ensemble variability in the projected Pacific warming pattern. This pattern variability is largely explained by two dominant patterns: one linked to hemispheric warming asymmetries, and the other to zonal equatorial gradients. Crucially, model differences in projected zonal equatorial gradients are strongly tied to the model representation of the mean state in the off-equatorial east and west Pacific. This implies that mean state biases partly control the projected warming pattern. Moreover, models with more realistic mean states tend to produce: (a) historical trends with stronger gradients, aligning better with observations, and (b) more “El Niño-like” future projections.

On 28 March 2025, a Mw 7.7 earthquake occurred on the Sagaing Fault in Myanmar. Security constraints prevented timely field investigations on its surface rupture, hindering analysis of seismotectonics and rupture dynamics. Using high-resolution satellite imagery, we mapped a ∼420 km surface rupture and measured 540 dextral offsets, revealing an average slip of 2.7 m and a maximum of 5.6 m. The rupture consists of two sections separated by a low-slip-zone that aligns with the refined epicenter and a previously unmapped stepover, suggesting the earthquake most likely nucleated at this structure and then propagate bilaterally. The rupture extends beyond the known seismic gap and overlaps with some recent historical rupture, highlighting contrasting earthquake recurrence cycles along different fault sections. Our mapping provides essential documentation of an ultra-long, multi-segment rupture on a major continental strike-slip fault under restricted field access, offering critical insights into the rupture behavior of similar faults worldwide.

Trifluoroacetic acid (TFA) is a persistent pollutant with potential long-term effects on the environment and on health. Recent studies using ice core records report large increases (up to tenfold) in Arctic TFA deposition since the 1970s, and trends suggest long-lived chlorofluorocarbon (CFC) replacements may be a major source. Here, we use a chemical transport model to examine the global TFA budget arising from CFC replacements–hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs)–and inhalation anesthetics. Global TFA deposition from these sources increased ∼3.5-fold from 6.8 (5.9–7.6) Gg/yr in 2000 to 21.8 (18.6–25.0) Gg/yr in 2022, with cumulative deposition reaching 335.5 Gg. We find HCFC-123, HCFC-124, and HFC-134a account for most modeled TFA production and that long-lived CFC replacements account for virtually all of the observed Arctic deposition trend. At lower latitudes, our analysis supports the recent emergence of hydrofluoroolefins (HFOs) as a TFA source. We conclude that increased TFA monitoring is required.

Myanmar's high seismic hazard is underscored by the 2025 M_w 7.7 earthquake on the Sagaing Fault, yet its seismicity patterns and underlying controls remain poorly understood. Using new seismic data from the 2nd-phase array of the China-Myanmar Geophysical Survey in the Myanmar Orogen, we construct a high-resolution catalog of 1,819 local-shallow earthquakes in central and southern Myanmar by combining deep-learning algorithms and manual phase-pick refinement, with 93 robust focal mechanisms. Integrated with a previous catalog further north, our analysis reveals that the Sagaing Fault dips eastward at ∼73° in the north, transitions to a nearly-vertical geometry at ∼20.5°N, and continues further south. This newly identified fault segmentation and associated geometric variations provide essential constraints for improving fine-scale rupture modelling of the 2025 earthquake. For the whole of Myanmar, our results suggest an abrupt along-strike north-south change of shallow seismicity across ∼20°N, with contrasting earthquake distributions and focal mechanisms.

The El Niño-Southern Oscillation has two warm phase flavors of Eastern Pacific (EP) and Central Pacific (CP) El Niños that exhibit seemingly distinct global teleconnections, but the limited observational sample leaves open whether and where these differences are robust. Coupled climate models are conventionally used to more robustly sample these teleconnections and their differences, yet they have persistent tropical sea surface temperature (SST) biases. To better understand teleconnection differences between EP and CP El Niño, we use atmosphere-only ensemble simulations with both observed and realistic synthetic SSTs generated from a Linear Inverse Model. With a sufficient number of El Niño events, the perceived teleconnection differences weaken due to broader sampling of event patterns, event strengths, and intrinsic atmospheric variability. However, biases in the atmospheric model's teleconnection caveat these conclusions. With CP event frequency projected to increase in the future, associated global impacts have the potential to become stronger, too.

The Southern Annular Mode (SAM) is the dominant mode of atmospheric variability in the Southern Hemisphere extratropics. While its long-term positive trend is well-documented, changes in the amplitude of SAM variability remain poorly understood. Based on reanalysis data and surface-station observations, we demonstrate that the amplitude of SAM variability has substantially increased over the past eight decades, which is associated with more frequent and severe weather extremes. A simple model and idealized climate experiments reveal that this amplification is primarily driven by enhanced stochastic eddy momentum flux, which is linked to a strengthened meridional temperature gradient. State-of-the-art climate model projections indicate that SAM variability will likely continue to intensify throughout the 21st century, driven by a further increase in the meridional temperature gradient. These findings highlight a critical but previously overlooked response of large-scale circulation to climate change, with important implications for assessing and mitigating future climate risks across the Southern Hemisphere.

Observations show that the drag coefficient (C_D) increases rapidly as wind speed decreases under low-wind conditions, contradicting Monin-Obukhov similarity theory (MOST). Analysis of multi-year station data reveals that wind speed has a stronger influence on this anomalous C_D increase than atmospheric stability. High-resolution WRF-LES simulations demonstrate that while moderate winds conform to MOST, the constant-flux-layer assumption fails under low winds: momentum flux varies by 378% within 25 m. Applying MOST under these conditions yields height-increasing C_D, explaining the excessively large C_D in observations. Additionally, turbulent kinetic energy (TKE) is significantly lower under low winds, and the mean momentum flux reverses to upward. Further analysis identifies hundred-meter-scale eddies causing counter-local-gradient transport, with spectral analysis confirming their dominance in momentum flux. The near-surface momentum flux is primarily generated by pressure perturbations and transported upward via vertical gradient terms.