Abstract The carbon dioxide (CO 2 )/argon (Ar) ratio is a useful tracer of atmospheric circulation on Mars, but it remains observationally poorly constrained in the middle atmosphere, where large‐scale circulation occurs. In this study, we infer the CO 2 /Ar ratio at the homopause, which marks the upper boundary of the well‐mixed Martian middle atmosphere, by extrapolating observations from NASA’s Mars Atmosphere and Volatile EvolutioN mission. The inferred ratio shows a double‐peaked seasonal variation, with minima near equinoxes and maxima near solstices, broadly consistent with simulations from a Mars General Circulation Model (GCM). However, we also identify pronounced high‐latitude enhancements of this ratio during L S ∼ 270°–300°, reaching ∼80–110 compared with ∼60 predicted by the GCM. These enhancements may indicate a transient atmospheric circulation pattern not captured by the model simulations. Our results provide a new observational constraint on composition near the Martian homopause and, consequently, on middle‐atmosphere circulation, and suggest that additional atmospheric processes remain to be understood.
Abstract Rapid infiltration influences rainfall partitioning, subsurface water movement, and freshwater availability, yet its large‐scale spatial organization remains poorly constrained by limited observations and the lack of scalable approaches for synthesizing infiltration measurements. Here, we identify rapid infiltration signatures from a global database using a dual‐mechanism modeling framework. Rapid infiltration signatures occurred in 26.6% of 4,992 valid curves. Occurrence varied among measurement methods, while rapid and non‐rapid signatures frequently coexisted within closely matched local contexts. At identical recorded locations, 74.7% of qualifying groups contained both rapid and non‐rapid signatures; for rapid‐classified curves, the fitted rapid component accounted for a median 41.2% of cumulative infiltration. Across 83 sites, rapid‐signature odds decreased by approximately 26% per 10° increase in absolute latitude. These findings provide a large‐scale observational basis for investigating rapid infiltration and highlight the importance of measurement context and independent physical evidence for improving its representation in hydrological and Earth system models.
Abstract Seasonal prediction of surface climate relies on influences external to the troposphere, of which the stratosphere is a key source. The October stratosphere is particularly important for predictability of the coming winter and summer seasons in the Northern and Southern Hemisphere respectively, as the seasonal transition in zonal winds creates an interhemispherically symmetric window of stratosphere‐troposphere coupling. Building on a recently identified teleconnection between the October upper stratospheric meridional wind and the December‐January‐February (DJF) North Atlantic Oscillation, we use reanalysis to demonstrate an analogous Southern Hemisphere teleconnection predicting the DJF Southern Annular Mode with skill comparable to current operational seasonal forecasts. We show that CMIP6 models fail to capture either teleconnection and that model skill is contingent on representation of the stratospheric pathway connecting the October meridional wind indices to the respective DJF polar vortex, a relationship that is poorly captured across models in both hemispheres.
Abstract Predicting the response of Antarctic ice to climate change requires detailed knowledge of its shallow structure, but direct measurements are challenging. Traditional seismic surveys are logistically demanding, and surface remote sensing provides limited information about subsurface layers. Here, we introduce uncontacted airborne seismology, a method that uses aircraft‐generated sounds and their conversion into seismic waves at the ice surface to probe the ice interior. Using a 36‐node seismic array during airborne passes, we captured multiple types of seismic waves and analyzed their propagation to extract dispersion patterns. Joint inversion of these observations reconstructs the elastic properties and porosity of the upper ∼100 m. This approach offers a rapid, scalable framework for mapping near‐surface ice structure and establishes a benchmark for future aerial or robotic exploration of polar regions, opening new possibilities for large‐scale, noninvasive monitoring of ice sheet dynamics.
Abstract Earthquakes affect surrounding fault systems through multiple mechanisms. Here, we examine a rare cessation of activity in 27 families of low‐frequency earthquakes (LFEs) that likely reflect fault creep at the southern edge of Cascadia subduction, near the Mendocino triple junction. These sources usually exhibit nearly daily activity but were shut off for ∼7–25 days following the December 2024 moment magnitude ( M w ) 7.0 Mendocino fault earthquake. Based on modeling, we infer that this cessation was not caused by induced shear stress, which was slightly encouraging of slip, but rather by combined clamping normal stress and reduced pore pressure. This mechanism, which isn't captured in the common effective friction simplification, may have strengthened the fault and inhibited creep, without requiring fluid outflow. Observed variations in LFE cessation times are not predicted by modeled stress changes alone and may instead reflect differing source dimensions or subtle variations in LFE fault geometry.
