Abstract Knowledge of crater degradation rates on the Moon is fundamental for dating individual craters, understanding material transport, and investigating crater equilibrium, with broader implications for water ice exploration, regolith evolution, and impact flux reconstruction. However, direct observational constraints on the degradation rates of hundred‐meter‐scale lunar craters remain scarce, and regional variations between mare and highland terrains are poorly quantified. Here, we measure the diameters and depths of 56,229 small impact craters across the Apollo, Luna, and Chang’E landing regions using high‐resolution optical and topographic data. We then systematically simulate the production and evolution of crater populations from geological unit emplacement to the present, accounting for both diffusive degradation and catastrophic obliteration. By comparing observations with forward simulations, we provide the most extensive observational constraints to date on the degradation rates and lifetimes of small craters with diameters of 50–500 m. At these scales, the estimated topographic diffusivities increase from 0.62 to 2.33 /Myr in the maria and from 2.27 to 4.54 /Myr in the highlands. Regional variations in degradation rates are most strongly associated with meter‐scale slope rather than adopted proxies for target properties. The inferred lifetimes imply that subhectometer micro cold traps are short‐lived (<100 Myr) and thus host only recently delivered water ice, whereas larger cold traps of several hundred meters can persist over geological timescales and are favorable for water ice accumulation. Our results further indicate that crater equilibrium at small diameters is achieved mainly through diffusive degradation rather than superposition, and that equilibrium crater abundance is expected to vary across the Moon.
Abstract Accurate short‐term tropical cyclone (TC) intensity forecasting remains challenging because rapidly evolving inner‐core structures are difficult to observe at sufficiently high temporal resolution. Here, we derive an area‐mean upper‐level vorticity indicator (VORm) from minute‐scale atmospheric motion vectors retrieved from the Fengyun‐4B Geostationary High‐speed Imager (FY‐4B/GHI) using the Single‐Plane Assumption–Fast Approximate Barnes Interpolation framework. Analysis of western North Pacific TCs shows that VORm closely follows the broad evolution of storm intensity while retaining substantial high‐frequency structural variability. VORm exhibits a strong contemporaneous association with TC intensity and retains information related to subsequent 6‐hr intensity change after accounting for the current intensity and preceding intensity tendency, indicating potential value for short‐term intensity prediction. Forecast experiments further demonstrate this predictive potential. In the linear framework, incorporating VORm reduced the pooled 6‐hr RMSE from 6.27 to 5.97 kt, indicating additional predictive information beyond conventional intensity and environmental predictors. In the nonlinear XGBoost framework, VORm further reduced the RMSE from 6.26 to 6.18 kt even when the preceding 6‐hr intensity tendency was explicitly included, indicating that VORm still provides additional predictive information beyond recent intensity evolution. Because FY‐4B/GHI winds and the derived vorticity can be obtained with very low latency, this approach offers a practical pathway for rapidly incorporating high‐frequency inner‐core structural information into short‐range TC intensity forecasting.
Abstract Ionospheric scintillation disrupts trans‐ionospheric radio signals and represents significant challenges for critical communication and navigation systems. Here we document that hot flow anomalies (HFAs), transient disturbances formed near Earth's bow shock, can contribute to scintillation near the cusp. We used coordinated multi‐instrument observations including GNSS receivers, SuperDARN, AMPERE, DMSP/SSUSI, MMS to link an upstream HFA to the scintillation in the polar ionosphere. During 10:47–10:57 UT on 19 November 2015, enhanced phase scintillation was observed, along with a convection vortex, enhanced field‐aligned currents (FACs) and nearby particle precipitation. An HFA and associated high‐speed jets (HSJs) were observed in the corresponding magnetic local time (MLT) region of the magnetosheath. Our analysis indicates that the HFA disturbs the magnetopause and enhances the FACs, causing the localized ionospheric density gradient instability, thereby triggering the ionospheric scintillation. These results show that the particle precipitation caused by HFAs can strongly affect the cusp plasma and trigger significant phase scintillation. Our results provided direct observational evidence that HFAs are a contributing source of polar space‐weather impacts on GNSS and radio systems.
Abstract Tropospheric ozone (O3) influences climate and poses risks to human health and crop productivity. Its distribution is shaped by complex interactions between chemical production, transport, and loss processes, including reactions with naturally occurring halogens. Recent studies have shown that mineral dust represents a catalyst for halogen activation, releasing chlorine and iodine radicals that destroy O3 yet these mechanisms are rarely represented in current atmospheric models. Here, using the Community Earth System Model with explicit chlorine and iodine activation on dust particles, we show that dust‐driven halogen chemistry substantially reduces O3 downwind of major dust source regions. This mechanism drives global annual mean decreases of ∼5% in ground‐level O3 and ∼3% in the tropospheric O3 column, consistent with observed 3%–6% tropospheric O3 column reductions over the tropical Atlantic during high‐dust conditions. Including this process improves the model's ability to detect the observed spatial pattern of tropospheric O3 suppression under high‐dust conditions, particularly in major dust outflow regions. Dust‐driven halogen activation reduces ozone over marine regions, with impacts that propagate inland into agricultural areas. These reductions lower accumulated ozone exposure and improve crop productivity, with the largest improvements (up to 9%) for wheat, rice, and soybeans in southern Asia and North America. Reduced ozone also lowers ozone‐attributable mortality, with the strongest benefits occurring in dust‐influenced regions of Asia. Our results identify that dust‐catalyzed halogen chemistry represents an underrepresented natural ozone sink, with implications for air quality, agricultural productivity, and human health. Projected future increases in dust emissions could further amplify this effect on regional and global ozone budgets.
Abstract In the dynamo region of the Martian ionosphere, a large‐scale current is generated by charge separation: ions collide with neutrals while electrons preferentially gyrate around local magnetic field lines. Using MAVEN magnetometer data and a physics‐informed neural network constrained by Ampère's law and Gauss's law for magnetism (the Neural‐Curlometer technique), we compute the first continuous and locally‐resolved model of ionospheric currents. The reconstructed dynamo currents are concentrated between 125 and 220 km, with a Hall‐to‐Pedersen transition near 160 km. The current density scales with the crustal magnetic field, with a dayside correlation of 0.89, and is mostly active over regions where the crustal field ranges between 130 and 450 nT at 150 km. The proposed approach allows us to model the currents over time, revealing clear seasonal variability partially related to dust storm events. Furthermore, the modeled currents exhibit a smooth hemispheric vortex pattern consistent with independently predicted atmospheric wind circulation and Coriolis‐driven transport associated with seasonal CO2 condensation at the poles. As such, we provide a data‐driven proxy for atmospheric circulation at ionospheric altitudes, providing new inputs for Martian general circulation models.
