Atmosphere

The Earth functions as an integrated system in which the ocean, land, and atmosphere are connected through complex exchanges of matter and energy [...]

Stratocumulus clouds are cloud systems composed of stratiform clouds with embedded convective clouds, possessing strong catalytic potential and serving as key target cloud systems for weather modification operations. In this study, the parameterization of ice nucleation for silver iodide (AgI) particles was applied to the Thompson microphysics scheme in the WRF model. Numerical experiments were designed for a stratocumulus cloud that occurred over the Hulunbuir region, northeastern China, on 31 May 2021, to investigate how the structure and evolution of cloud macro- and microphysical properties and precipitation formation respond to glaciogenic seeding. The simulation results indicate that AgI nucleation increased ice concentrations at 4–5 km altitude, enhancing ice crystal formation through condensation–freezing and deposition nucleation and the growth of ice particles through auto-conversion and riming, leading to increased precipitation. The results also show that owing to the non-uniform distribution of supercooled water within this stratocumulus cloud system, the consumption of AgI and the enhanced ice nucleation release latent heat more strongly in regions with higher supercooled water content. This leads to more pronounced isolated updrafts, altering the structure of shear lines and subsequently influencing regional precipitation distribution after silver iodide seeding concludes. These findings reveal that seeding influences both the microphysical and dynamic structures within clouds and highlight the non-uniform seeding effects within cloud systems. This study contributes to a deeper understanding of the effects of artificial seeding on stratocumulus clouds in high-latitude regions and holds significant reference value for artificial weather modification efforts in mixed-phase stratiform clouds.

This study investigates inflow turbulence strategies for large-eddy simulations (LES) of urban boundary layers under time-varying atmospheric conditions. A combined approach integrating a digital-filter-based synthetic turbulence generator (STG) with the cell perturbation method (CPM) is proposed to reduce turbulence adjustment distance and improve vertical mixing. Using the PALM model, 24 h simulations were conducted over a real urban domain in Seoul, capturing diurnal transitions in stability and wind direction. Six experiments were compared: two reference runs with extended upstream fetch, and four analysis runs without fetch, applying different inflow strategies (NOT, STG, CPM, and CPM + STG). Results indicate that CPM + STG mitigates abrupt structural transitions and sustains turbulence kinetic energy (TKE) more consistently than STG alone, while requiring lower computational cost than extended-fetch configurations. Under unstable daytime conditions, CPM + STG enhanced vertical mixing and preserved local boundary-layer height closer to background values, whereas nighttime performance was dominated by building-induced shear regardless of inflow strategy. These findings suggest that the combined CPM + STG approach achieves a balance between physical realism and computational efficiency, demonstrating its potential as a robust inflow strategy for time-varying urban LES within limited domain sizes.

Substantial black carbon (BC) emissions in China have raised serious concerns owing to their significant influence on climate change and health. However, knowledge around the relative contributions of emissions and meteorological conditions to BC dynamics is limited but essential for air pollution management. Therefore, emission-driven (BC_EMI) and meteorology-driven (BC_MET) BC concentrations in China during 2000–2019 were quantified by a machine learning framework, focusing on five regions (NC: North China, YRD: Yangtze River Delta, PRD: Pearl River Delta, SCB: Sichuan Basin, and CC: Central China). Furthermore, driving mechanisms of key meteorological factors were investigated using Shapley Additive Explanation (SHAP). Results show a dominant role of emissions in shaping BC variability, with ratios of regional average BC_EMI changes to total changes ranging from −140.50% to 76.40%. Especially, the most pronounced decrease occurred in NC during 2013–2019, with BC_EMI dropping by 1.56 μg/m³. Even so, the impact of extremely adverse meteorological conditions on BC variations cannot be ignored. The highest annual mean BC_MET in YRD (0.17 μg/m³) and PRD (0.30 μg/m³) was observed in 2004, while positive BC_MET in NC, SCB, and CC peaked in 2013, with values of 0.26, 0.18, and 0.18 μg/m³, respectively. Regarding SHAP values of each feature, meteorological effects in NC, YRD, SCB and CC were dominated by boundary layer height and temperature, whereas those in PRD were mainly regulated by precipitation and wind. These findings provide a new perspective for attributing BC variability and offer valuable insights for optimizing regional BC control strategies and air quality models.