Geophysical Research Letters最新文献

We studied the characteristics of ultra-low-frequency (ULF) waves associated with dipolarization in the near-Earth plasma sheet for substorms and pseudosubstorms, employing superposed epoch analysis of data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft. We find exponential intensification of ULF waves before dipolarization for both substorms and pseudosubstorms, highlighting Pi2 waves' appearance before Pi1 waves. After rapid growth, the high-frequency portion of the Pi2 waves and the Pi1 waves in a tailward region for pseudosubstorms are notably weaker and decrease faster than those for substorms. These results suggest that instabilities related to high-frequency Pi2 and Pi1 waves are essential for a full-fledged substorm and auroral poleward expansion.

Surface mixed-layer dynamics play a crucial role in modulating the climate as it is the oceanic layer that directly communicates with the atmosphere. The resolution of global ocean models is, however, often restricted to $��O��\left(��1�/�4�°��\right)��$; this is too coarse to adequately resolve mixed-layer processes, and we depend on parametrizations. One of such parametrizations is the mixed-layer eddy (MLE) parametrization. Here, we compare the performance of two MLE parametrizations [Fox-Kemper et al. (2011, https://doi.org/10.1016/j.ocemod.2010.09.002 hereon BFF11) and Bodner et al. (2023, https://doi.org/10.1175/jpo-d-21-0297.1 hereon BOD23)], and document their impact in three global ocean simulations. Upon tuning, and diagnosing submesoscale-permitting truth simulations, the MLE efficiency coefficient in BOD23 ranges between the values of 0.003–0.038, while 0.06 to 0.07 for BFF11. We find that the spatial distribution of mixed-layer depth and ventilation of the abyssal ocean, using the ideal-age tracer and Atlantic Meridional Overturning Circulation as its proxy, are sensitive to the interaction between MLE parametrizations and ocean surface boundary-layer mixing schemes.

California, as a transform plate boundary, provides a distinctive tectonic setting and an ideal natural laboratory for investigating tectonic tremors and the slow deformation associated with plate motion. By analyzing continuous seismic records across multiple stations with an envelope correlation method, we identified ∼83,000 tremor events from 2000 to 2025. These events exhibit waveform characteristics consistent with tectonic tremors observed elsewhere. Beyond the previously documented central section of the San Andreas fault, we identify several new tremor clusters, primarily concentrated near the Mendocino Triple Junction and within the Big Bend segment. Our results suggest that tremor events near the Mendocino Triple Junction may mark the southern edge of the Cascadia subduction zone, while tremor events in the Big Bend region, located within the rupture zone of the 1857 M7.9 Fort Tejon earthquake, could have implications for regional seismic hazard.

Biomass burning aerosols significantly contribute to atmospheric composition and radiative forcing, with black carbon (BC) mixing states critically influencing optical properties and climate impacts. Recent field observations reveal a systematic three-phase evolution in BC coating thickness during plume aging: rapid initial growth, quasi-equilibrium, and gradual coating loss. Current models misrepresent this evolution due to oversimplified treatment of organic aerosol volatility. Here we demonstrate that incorporating semi-volatile organic partitioning through the MATRIX-VBS model fundamentally improves simulation accuracy compared to traditional non-volatile approaches. Evaluation against four field campaigns spanning fresh to aged plumes shows MATRIX-VBS successfully captures the observed three-phase pattern, and global application reveals universal three-phase evolution with substantial regional variations. These advances address critical gaps in aerosol mixing state representation and provide essential improvements for climate model predictions in wildfire-affected regions.

During Galileo's closest (“E12”) flyby of Europa, a brief burst of wave activity was recorded by the plasma wave instrumentation, PWS. This was speculatively interpreted by Jia et al. (2018, https://doi.org/10.1038/s41550-018-0450-z) as a 2,100 cm⁻³ spike in plasma densities from a water plume encounter. While the plasma instrument, PLS, could have provided an independent density measurement and resolved ambiguity in the PWS analysis, calibrated PLS data were never published from E12. Here we present high-resolution (∼18 s) PLS moments and velocity distributions from E12. Plasma densities near closest approach were between $��398�\pm �72��{\text{cm}}^{�-�3�}�$ (assuming $��m�/�q�=�16�$) and $��563�\pm �103��{\text{cm}}^{�-�3�}�$ (assuming $��m�/�q�=�32�$), in agreement with the original interpretation of PWS densities by Kurth et al. (2001, https://doi.org/10.1016/s0032-0633(00)00156-2). We thus discount a plume encounter. PLS measurements near Europa imply a highly asymmetrical and inhomogeneous ionosphere (as expected). Europa's Alfvén Wings were more compact than expected, implying stronger electrical currents than predicted by existing models.

Previous observations have demonstrated that rocket exhaust can trigger ionospheric electron density holes and cause electron temperature enhancements during launches. Using high-precision measurements from the Sanya incoherent scatter radar, we discovered a previously overlooked decrease in electron temperature. We report a daytime event and a nighttime event. During daytime, the electron temperature first decreased sharply by ∼650 K within 5.5 min, then increased by ∼1000 K before gradually recovering over ∼1 hr. Multi-beam observations indicated that this cooling was localized near the rocket trajectory, much narrower than the accompanying electron density depletion. Moreover, the ion temperature increased by 550 K. The nighttime electron and ion temperatures decreased by ∼450 and ∼150 K, respectively, without subsequent electron temperature increase. Analysis indicated that these temperature perturbations resulted from the initial expansion cooling following the exhaust injection and the subsequent hole formation, which disrupted the thermal equilibrium in the ionosphere.

Reconstructions and simulations disagree on whether the Holocene exhibited a long-term cooling or warming signal. Anthropogenic land-use could be an important forcing regionally, but available population-based estimates differ widely. We examine transient Holocene climate model simulations forced with three population-based disturbed-land reconstructions and compare this with a fourth scenario derived entirely from fossil pollen records. The direct biophysical temperature effects are broadly similar across the scenarios but the pollen-based product suggests an earlier onset of disturbance, particularly in China and accounting for its limited spatial coverage, falls closer to the upper limit of the existing uncertainty range. Impacts in many areas begin during the mid-Holocene but emergence of a signal varies spatially with earliest impacts over Europe, China and the North Atlantic. Significant uncertainties remain, and these could be tackled by improving the representation of land-use effects in climate models or by merging different information sources related to Holocene land-use.

Nonlinear interactions between internal tides (ITs) and near-inertial waves (NIWs) generate the “third waves” at frequencies corresponding to the sum of IT and NIW frequencies. The third waves drive oceanic energy cascade, yet under what conditions these waves are generated remain poorly quantified. This study employs an integrated approach combining multi-mooring observations, causality analysis, and high-resolution regional simulations (i.e., 2 km, 60 levels) in the Northern South China Sea (NSCS) to address this knowledge gap. Both field observations and numerical simulations reveal that at stations near the tropical cyclone (TC) track, third-wave kinetic energy doubled after TC passage, while vertical penetration depths dramatically shoaled. Causality analysis demonstrates that NIWs dominate third-wave generation at these sites, exceeding IT contributions by a factor of 9.4. In contrast, tide-dominated stations farther from TC path showed slight energy increases with balanced NIW-IT contributions. This study provides the first three-dimensional, causality-constrained perspective on how TC and ITs selectively control third-wave generation through nonlinear interactions.

Cloud vertical overlap has important implications for cloud radiative effects in climate models. Due to its spatiotemporal complexity, it is difficult to simulate cloud overlap in climate models. Decorrelation length ($��L�$) is crucial for depicting the vertical overlap of clouds in climate models. This study introduces a scale-adaptive $��L�$ parameterization scheme, which can be integrated into climate models. The study considered three atmospheric statistics and dynamic factors: latitude, wind vertical shear, and horizontal grid scale, to develop an $��L�$ parameterization scheme by deep neural network (DNN). For different resolutions, the simulation accuracy of this parameterization scheme can basically be maintained at $��R^2�$ above 0.9, which significantly surpasses that of other traditional overlap schemes. The parameterization scheme can be seamlessly integrated into the climate model and has the potential to improve the simulation accuracy of cloud vertical overlap, thereby enhancing the model's capability to accurately depict cloud radiation effects.