Geophysical Research Letters最新文献

We investigated the resonant interactions between Z-mode waves and radiation belt electrons at Saturn via constructing an empirical model of the frequency spectral and wave normal angle distributions of 5 and 20 kHz Saturnian Z-mode waves using Cassini observations. The results of the quasi-linear bounce-averaged diffusion coefficients show that Saturnian Z-mode waves efficiently scatter radiation belt electrons (with energies of up to several MeV), with the resonant pitch angle coverage narrowing with increasing L-shell. Compared with 20 kHz waves, 5 kHz wave-induced scattering occurs at higher electron energies with stronger efficiency. The results of Fokker-Planck simulations showed that Z-mode waves efficiently accelerate high-energy electrons at intermediate pitch angles, contributing to the formation of a butterfly electron pitch angle distribution. Our results further the current understanding of the role of Z-mode waves in the dynamics of Saturn's electron radiation belt.

Extensive dune fields nearly encircle the equatorial regions of Titan, Saturn's largest moon. Dunes evolve in response to environmental change, offering a record of recent geologic and climate history. A global analysis reveals that Titan's dunes become more narrowly spaced and increasingly more regular along a continuous eastward transport path, starting east of the Xanadu region, around the equator, and terminating abruptly at Xanadu's western margin. Xanadu is a rugged, tectonically active, water-ice-rich region with low topography and a thin layer of atmospherically deposited organic-rich material. Our results demonstrate that windblown grains must withstand long transport distances. Furthermore, environmental conditions along the eastern margin of Xanadu set a template over which dunes evolve, only gradually modified as sediment supply or availability increases downwind. Together, these results highlight the oversized impact that Xanadu has on Titan's dune fields, which in turn play a critical role in regulating Titan's sedimentary and carbon cycles.

Previous studies have verified that upward geomagnetic field-aligned electric fields (FAEFs) produce inverted-V signatures of precipitating electrons that generate discrete auroras in upward field-aligned currents (FACs). However, clear ion inverted-V signatures have rarely been reported in the polar magnetosphere. Plasma measurements with high time resolution at altitude of 630–670 km in the nightside auroral oval often detected inverted-V signatures of precipitating ions adjoining active electron inverted-Vs, suggesting downward ion acceleration by downward FAEFs associated with intense downward FAC. The energy-pitch angle distributions indicate that the altitudes of these FAEF accelerations producing ion inverted-V precipitation are estimated to be a few thousand kilometers, lower than those of electron inverted-Vs. The energies, fluxes, and latitudinal extents of ion inverted-Vs tend to be smaller than those of frequently observed electron inverted-Vs. However, their downward FAC densities are similar to or often larger than those of the upward FACs carried by inverted-V electrons.

We report, for the first time, the impact of interplanetary coronal mass ejections (ICME) on the recently discovered O(¹S) 557.7 nm dayglow emission in the Martian atmosphere. While there are a few studies on the seasonal variation of 557.7 nm dayglow emission available in the literature, the impact of ICME has not been investigated so far. Using the instruments aboard the ExoMars-TGO and Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, we show that the primary emission peak (75–80 km) remains unaffected during ICME events compared to quiet-times. However, an enhancement has been observed in the brightness of the secondary emission peak (110–120 km) and the upper altitude region (140–180 km). The enhancement is attributed to the increased solar electrons, X-ray fluxes and Solar Energetic Particles, augmenting the electron-impact processes causing the enhancement in the brightness. Thus, this study has an implication to the brightness of Martian upper atmosphere during intense solar transients like ICME.

We present the analysis of 2,152 electrostatic solitary waves observed aboard the Magnetospheric Multiscale in the Earth's magnetosheath. The electric field of the solitary waves is predominantly bipolar and parallel to the local magnetic field. In contrast to previous reports, we reveal similar occurrence rates of solitary waves of positive and negative polarity of the electrostatic potential. Both types of solitary waves have spatial half-widths of 10–150 m or 1–15 Debye lengths, amplitudes of the electrostatic potential of 0.01–1.5 V or 0.01%–1% of local electron temperature, and plasma frame speeds within ion thermal speed. We argue that the solitary waves are electron and ion holes produced separately in space or time by local processes, whose nature is, however, still elusive. We speculate that the solitary waves can mediate the energy between thermal electrons and ions in the Earth's magnetosheath and discuss other applications of the presented results.

The Interdecadal Pacific Oscillation (IPO) and Atlantic Multidecadal Variability (AMV) substantially affect global climate system. Model studies suggested a fast interaction between the IPO and AMV through atmospheric teleconnections, but observations exhibit a weak IPO–AMV contemporaneous correlation. To address this paradox, we apply linear inverse model (LIM) in observations to decode the interaction. We reveal that a cancel effect of the interaction lowers the observed IPO–AMV contemporaneous correlation. When only retaining the one-way modulation (the IPO forces the AMV or the reversed one) in the observational LIM, their correlation peaks nearly simultaneously, consistent with the fast IPO–AMV interaction in model experiments. We further demonstrate that the fast interaction is associated with both tropical and extratropical processes. Our study reconciles the discrepancy between observations and models on the IPO–AMV interaction.

Hydrogen fuel can help decarbonize the economy, but hydrogen leakage has indirect climate consequences. Atmospheric oxidation of hydrogen by hydroxyl radicals (OH) increases methane, ozone, and stratospheric water vapor concentrations. Current global 3-D atmospheric chemistry models estimate a global warming potential for hydrogen of 12 ± 3 over a 100-year horizon (GWP-100), but the models overestimate global OH concentrations and underestimate OH reactivity (OHR). These OH biases cause overestimates of the responses of methane and ozone to hydrogen. Here, we compare the hydrogen GWP-100 calculated from the standard GEOS-Chem model and from a modified version where OH and OHR biases are corrected with missing organic emissions and a terminal OH sink over continents. The hydrogen GWP-100 from the standard GEOS-Chem model agrees with previous studies, but the modified version is 20% lower. Better understanding of the factors controlling global OH concentrations and OHR is needed to refine hydrogen GWP estimates.

Conventional tsunami simulations rely on accurate bathymetric data, posing challenges in regions lacking such information. We introduce a novel approach using ambient noise interferometry to derive empirical Green's functions of infragravity waves from noise correlation functions (NCFs) extracted from a 10-year Deep-ocean Assessment and Reporting of Tsunamis data set in the Pacific Ocean. Our analysis reveals pronounced propagating behavior in NCFs, indicative of wave dispersion relationships. Long-period NCFs align with shallow-water wave dynamics, making them suitable for tsunami simulations. By eliminating the need for precise bathymetry, our method offers a practical solution for data-sparse regions. A case study of an Alaska tsunami demonstrates our NCFs effectively fit observed pressure data, outperforming conventional Cornell Multi-Grid Coupled Tsunami Model simulations. The fidelity of our results underscores the potential of ambient noise interferometry-derived NCFs to enhance tsunami predictions, even in complex environments. Our findings advance tsunami research and have significant implications for disaster preparedness and mitigation.

This study explores the response of Arctic sea ice to CO₂ removal and its subsequent effects on the winter Northern Hemisphere atmospheric circulation. Using multimodel ensembles from the Carbon Dioxide Removal Model Intercomparison Project, we find that most models display incomplete Arctic sea-ice recovery when CO₂ is stabilized back at preindustrial levels, with a deficit of sea-ice area of around 1 million km². This sea-ice deficit is associated with residual equatorward-shifted wintertime midlatitude jets. Sea-ice perturbation experiments from the Polar Amplification MIP provide evidence of a causal influence of residual sea-ice loss on the atmospheric circulation. Model uncertainty in the magnitude of the residual North Atlantic jet shift can be largely explained by the relative magnitudes of residual Arctic and tropical warming across the models. These findings suggest that Arctic sea-ice loss is not fully reversible after CDR, which leads to residual changes in the mid-latitude atmospheric circulation.

The investigation of chemical composition in hailstones offers valuable insights into cloud physics. Unique characteristics of heavy metals and water-soluble ions have been detected to provide a comprehensive perspective on their presence and behavior within hailstones. 34 hailstone samples were collected from 12 cities in China between 2016 and 2021. Regional differences in heavy metal concentrations between northern and southern China are influenced by anthropogenic pollution sources. Water-soluble ions are dominated by distant marine aerosol sources. The most notable distinction is that heavy metals display negligible correlation with PM₁₀, whereas water-soluble ions exhibit a statistically significant relationship. This suggests that chemical components contribute to hailstone formation through diverse pathways. Water-soluble ions with hygroscopicity primarily act as cloud condensation nuclei (CCN) to promote the formation of cloud droplets. Heavy metals are barely noticeable when attached to aerosol particles due to random collisions with various hydrometeors.