Geophysical Research Letters最新文献

The diurnal cycle of tropospheric Zenith Total Delays (ZTD) is critical for refining tropospheric models and understanding key geophysical and atmospheric processes. The fifth European Centre for Medium-Range Weather Forecasts reanalysis ERA5, with its unique 1-hr temporal resolution, provides valuable data for these purposes. However, we identified obvious discontinuities in ERA5-derived ZTD at 09:00 and 21:00 UTC. A comparison with 10-year GNSS data from 6,437 stations showed that 32.8% of the stations experienced discontinuities in mean diurnal anomalies of ERA5 ZTD, with an average magnitude of 2.2 mm, far exceeding the 0.3 mm hour-to-hour variations observed by GNSS. The discontinuities are more pronounced in summer and are primarily due to errors in ERA5's humidity modeling, with a few pressure-related issues limited to Antarctica. The discontinuity is attributed to the transition between ERA5's 12-hr assimilation windows and suggest that other ERA5 variables may also be impacted, warranting caution in ERA5-based diurnal cycle studies.

The destabilizing thermal gradient across the Earth's lithosphere drives convection in superconfined hydrothermal environments at mid-ocean ridges and geothermal reservoirs in the continental crust. Deep, hot waters rise in these regions and meet cold surface water that percolates through open fractures, creating complex and poorly understood mixing dynamics. This Letter explores the relationship between energy, convection, and mixing in analog hydrothermal systems. Leveraging energetics theory and lab-scale experiments, we present a scaling formulation for estimating the irreversible mixing boosted by convective flows occurring within faulted and fractured hydrothermal environments. These findings bear relevance to natural Earth processes and human-engineered applications, such as geothermal energy harvesting and geologic $��{\text{CO}}_2�$ sequestration.

On 10 May 2024, a super space storm—characterized by the Dst index plummeting to −412 nT and induced by a strong coronal mass ejection on the Sun—attacked the Earth's magnetosphere. This geomagnetic storm, according to the human record of Dst index, is the third-strongest one throughout history (only slightly lower than those in 1989 and 2003). In such an extreme condition, how the magnetopause evolves and reforms remains unclear, because only a few spacecraft measurements were available in the dayside magnetosphere during previous events. Here, by utilizing in-situ measurements of multiple spacecraft together with ground magnetometers, we for the first time determine the extreme compression of the magnetopause from higher than 10 R_E down to 5 R_E. This observation of such severe deformation is also consistent with the prediction of the theoretical model. This study provides crucial insights into the extreme behavior of the magnetopause during the influence of a superstorm.

A model for source-limited dust emission is proposed. The model accounts for the evolution of the supply of soil dust depleted by dust emission and enriched by the process of surface renewal, together with several other new developments. The model is tested with a field dataset. The impact of source limitation to dust emission is profound. Our tests show that by considering source limitation, the model predicted dust emission can reduce by one order of magnitude in a real-case simulation period of less than 20 days. We show that the process of dust emission is much more complex and variable than considered in previous dust models. Our findings have far-reaching implications, for example, to the global dust emission estimates. Because source-limited dust emission has so far not been represented in global dust models, the model estimated dust emission is only its potential and may be a substantial overestimate.

During its Grand Finale, the Cassini spacecraft collected crucial gravity data, revealing Saturn's low-degree gravity harmonics and large-scale zonal winds extending about 8,000 km deep. However, determining the high-degree gravity field, essential for understanding small-scale atmospheric dynamics, is challenging due to the limited spatial coverage of Cassini's periapses. To overcome this limitation, we employed Slepian functions, orthogonal within a bounded domain, to represent Saturn's localized high-degree gravity field. Focusing on latitudes from 32°S to 32°N, we estimated Slepian coefficients that represent short-scale latitudinal gravity variations. The reconstructed wind profile that explains low-degree harmonics can also reproduce these high-degree variations, assuming Saturn's atmosphere is, to first order, in thermal wind balance. Our findings suggest that small-scale winds may extend to depths between 7,000 km and 9,000 km, providing strong evidence that Saturn's zonal flows are oriented along coaxial cylinders, rotating at different angular velocities.

Changes in the Tibetan Plateau upper-level westerlies (TPUW) and El Niño-Southern Oscillation (ENSO) are crucial in regulating local hydrological cycles and large-range climate. Here we report a gradual disappearance of the cross-seasonal ENSO-TPUW teleconnection since the early-2000s, with correlation decreasing from 0.75 to near zero. Before the early-2000s, the anomalous western North Pacific (WNP) anticyclone (WNPAC) induced by ENSO can last from winter to summer under the maintenance of Indo-western Pacific surface seawater temperature gradient (IWPSSTG), prompting the WNP subtropical high to expand and strengthen toward South Asia, attracting the Tibet Plateau subtropical high southward, thereby causing the subtropical westerly jet to move southward and forming a cross-seasonal ENSO-TPUW teleconnection. However, given the prominent tropical WNP warming since the early-2000s, the early-summer outage of IWPSSTG and WNPAC disrupts the ENSO-TPUW chain. This discontinuity poses severe challenges to the improvement of short-term climate predictions in the Tibetan Plateau and surrounding areas.

Increasing urbanization causes urban heat island effects that might introduce significant biases into global warming estimates. Previous studies of urban warming signals and asymmetries remain a subject of debate. Here we comprehensively assess urban-induced warmings by investigating meteorological temperatures on 2,370 stations in China during 1980–2022. There are noticeable urban-induced annual warming biases and contributions ranging from 0.016 to 0.251°C decade⁻¹ and 0.3%–72.4%, primarily due to spatiotemporal heterogeneities and the criteria defining urban sites. Rapid urbanization tends to exacerbate diurnal and seasonal warming asymmetries, resulting in shrinking temperature differentials associated with urbanized areas and urbanization chronosequences. This study underscores that the specific definition of urban areas matters for warming biases in magnitude and complex nonlinear urbanization imprint on warming asymmetries.

The Gulf Stream transports heat from the tropics poleward and is an integral part of how the planet redistributes heat. Studies of the variability of the Gulf Stream have suggested that the seasonal cycle of ocean mixed layer heat content in the Gulf Stream may be driven by the local net atmospheric heat flux or by oceanic advection of heat in the strong western boundary current. Here we use sustained underwater glider observations of the Gulf Stream from 80$��°�$W to 67$��°�$W during 2015–2023 to show that oceanic advection heats the ocean mixed layer in spring when the upper ocean switches from cooling to warming. Estimated terms of the mixed layer temperature budget demonstrate that the net atmospheric heat flux cools the upper ocean in all seasons except summer and that mixed layer warming in spring is due to ocean advection of heat from farther south.

Electron beams are considered to be important free energy sources for the excitation of various plasma waves at quasi-perpendicular shocks. In this article, we perform a two-dimensional particle-in-cell simulation of a low-plasma-β quasi-perpendicular shock. The magnetic field at the shock ramp has a large gradient, where upstream electrons and ions are separated due to their different gyro-radius. This charge separation induces a sub-ion scale electric field at the shock ramp. The electric drift of electrons in this field can induce an electron shear flow, resulting in the excitation of Kelvin-Helmholtz instability and the generation of electron vortices. These vortices further cause charge separation at their centers, resulting in a large electrostatic field. The electrons trapped in these vortices can gain energy from the parallel component of the electric field, which eventually leads to field-aligned electron beams. Our results provide a novel process for generating electron beams at low-plasma-β quasi-perpendicular shocks.

Dikes can contribute to rifting, but the space-time behavior and role of magma in young and slowly extending continental rifts is unclear. We use InSAR and seismicity during the 2024 Fentale intrusion in the Main Ethiopian rift (MER) to understand magma-assisted rifting at slow extension rates (5 mm/yr). From 2021 to mid-2024, the Fentale Volcanic Complex (FVC) uplifted up to 6 cm. From mid-September 2024, upper crustal diking started northwards along the rift, initially with subdued seismicity. From late-September to early November, dike opening increased to ∼2 m and propagated a total of ∼14 km north, causing increased seismicity from normal faulting. The dike made ∼90% of the total geodetic moment, with the rest from faulting. The character of the event is similar to rifting episodes at mid-ocean ridges and demonstrates that episodic diking can occur in young, slow extending continent rifts but must be more infrequent.