Interaction Between Atmospheric and Oceanic Dynamics at Mesoscale and Small Scale

1. Introduction

The exchange of momentum and heat between ocean dynamic processes at meso- and small scales is an interesting issue for the oceanography community [1]. Against the background of climate change, air–sea interaction plays an important role in economic activities [2]. Moreover, with the development of artificial intelligence (AI), the promotion of AI-based oceanography could deepen the understanding of multiscale air–sea interactions [3,4]. With this background, the newly launched Special Issue “The Interaction between Atmospheric and Oceanic Dynamics at Mesoscale and Small Scale” is founded. This Special Issue present relevant research on the interaction between atmospheric and oceanic dynamics at meso- and small scales utilizing traditional techniques, i.e., remote sensing [5] and numerical models [6,7,8]. Moreover, it is worthwhile to research these dynamics using AI.

2. An Overview of Published Articles

This Special Issue focuses on the interaction between atmospheric and oceanic dynamics in complex conditions, containing 11 published articles. The main contributions are delineated below.

Contribution 1 investigated how the semi-enclosed Sea of Japan (SJ) influenced Typhoon Songda’s (TY-0418, 4–8 September 2004) intensity changes using high-resolution three-dimensional Weather Research and Forecasting (3D-WRF)/UM-KMA models and Geostationary Operational Environmental Satellite (GOES)-IR imagery. The approach identified key mechanisms, i.e., terrain-induced friction, enhanced latent heat release over warm currents, moisture convergence, and orographically modulated vorticity, explaining the typhoon’s structural evolution, and rapid intensification within the confined SJ basin.

To understand the seasonal variability and long-term trends of Sea Surface Temperature (SST) fronts in Zhoushan and adjacent seas (1982–2021) and their driving mechanisms, Contribution 2 employed frontal intensity (SST horizontal gradient) and frequency analysis using a defined threshold (0.03 °C/km). This quantified frontal activity and linked it to river discharge, wind, upwelling, and currents. The method effectively revealed distinct seasonal patterns (strong winter bands, summer hotspots), key drivers (e.g., Changjiang Diluted Water), and significant winter intensification trends over decades.

To understand the mesoscale eddy regulation of Subsurface Chlorophyll Maximum Depth (SCMD) seasonality in the Kuroshio–Oyashio confluence, composite averaging and normalization of satellite altimetry and reanalysis data isolated SCMD responses to cyclonic and anticyclonic eddies. Contribution 3’s superiority lies in effectively quantifying distinct eddy-induced SCMD monopole patterns (shallow/deep centers), revealing asymmetric seasonal correlations and demonstrating eddy-driven westward Chl-a transport over differing distances.

Addressing severe local scour at monopile foundations in the central Bohai Sea, an integrated numerical–experimental approach was proposed by Contribution 4, analyzing two decades of tidal currents, sediment transport, and scour. Results quantified minimal background erosion (<0.02 m/year), revealed 80% of scour occurs initially, and demonstrated that collar protection reduces scour depth by 50%, providing a crucial basis for design and mitigation in similar regions.

Spatiotemporal variations in NW Pacific tropical cyclones (frequency, genesis, Accumulated Cyclone Energy (ACE)) and links to warm pool/monsoon trough were resolved using wavelet analysis, correlation, and Mann–Kendall tests on typhoon, SST, and wind data. This method proposed by Contribution 5 specifically detects trends, mutation points (e.g., 1996 frequency shift), and periodicities in cyclone behavior. Its superiority lies in revealing divergent trends (rising frequency vs. declining ACE), quantifying how warm pool thermal states inversely modulate monsoon trough intensity and genesis locations, and identifying synchronized multiscale climate oscillations driving cyclone activity.

The characterization of complex wind–wave dependence for deep-sea floating structure design employed elliptical, Archimedean, and vine copula models with 20-year hindcast data. Modeling trivariate distributions quantified tail dependencies, demonstrating C-vine copula’s optimal performance for asymmetry. The approach in Contribution 6 reduced engineering costs by 20–30% via contour-based extreme value identification and provided robust environmental criteria aligned with actual sea conditions.

In Contribution 7, siltation challenges at Binhai Port’s entrance were addressed by integrating field data with a 2D tidal sediment model. Quantifying hydro-sedimentary dynamics and typhoon impacts (e.g., Lekima/Muifa) revealed critical mechanisms: tidal asymmetry-driven transport and lagged sedimentary responses. Predicting extreme-event siltation (e.g., 1.0 m during Muifa) provides actionable insights for port management and sustainable mitigation strategies.

Accurate wind stress parameterization in air–sea coupled models, critical under typhoons, was addressed by systematically evaluating five momentum flux partitioning schemes in Contribution 8. Analyzing how drag coefficient formulations alter feedback and surge predictions showed that wave-state-aware schemes outperform wind-speed-dependent approaches in surge accuracy. Higher drag coefficients weaken winds while amplifying currents/surges, providing guidelines to improve forecasting fidelity and reliability.

Regulatory mechanisms of Wyrtki Jets (WJs) under Indo-Pacific climate (ENSO/IOD) interactions were analyzed by partitioning events into distinct phases. Contribution 9 isolated phase-locked responses (e.g., spring-positive anomalies during El Niño decay; fall-negative anomalies during dipole events), revealing opposing seasonal patterns governed by ENSO stages and amplified fall anomalies under IOD, providing insights for predicting Indian Ocean heat/matter redistribution.

In Contribution 10, accurate extreme wind–wave estimates for Bohai Sea engineering were generated using a chained 30-year (1993–2022) WRF-SWAN simulation. Applying the Gumbel distribution to 100-year return periods revealed a ring-shaped spatial pattern (offshore peaks: 37 m/s winds, 6 m waves) and steep nearshore gradients (20–25 m/s winds, 2–3 m waves), providing robust design criteria unattainable via observations.

Drivers of anomalous sea-level rise in the Bohai Sea were quantified using a coupled WRF-FVCOM-SWAVE model, validated against satellite/tide-gauge data. In Contribution 11, sensitivity experiments identified tides as the primary driver, with wind/elevation forcing and Stokes transport amplifying extremes (e.g., 1.1 m surges). This prioritizes essential processes (marginalizing boundary currents) for coastal hazard prediction.

3. Conclusions

The 11 contributions in this Special Issue systematically quantified the complex mechanism of air–sea interaction through multiscale coupling models, long-term data mining, and innovative statistical methods, providing scientific basis for typhoon prediction, coastal engineering protection, port management, and climate response strategies. These significantly improve the risk prevention and control capabilities of extreme environmental events. Major conclusions reveal how semi-enclosed basins like the Sea of Japan modulate typhoon intensification via terrain friction, warm-core eddies, and moisture convergence (Contribution 1). Research quantifies the long-term intensification of winter SST fronts in East China Sea (linked to river discharge/upwelling) and demonstrates mesoscale eddies’ asymmetric seasonal control on chlorophyll distribution in the Kuroshio–Oyashio confluence (Contributions 2 and 3). For engineering applications, studies establish that collar protection reduces monopile scour by 50% in the Bohai Sea, while vine copula models optimize extreme wind–wave design criteria, cutting costs by 20–30% (Contributions 4 and 6). Climate analyses identify divergent NW Pacific tropical cyclone trends (rising frequency vs. declining intensity) governed by warm pool–monsoon trough interactions and reveal the phase-locked ENSO/IOD regulation of Wyrtki Jet anomalies. Methodologically, wave-state-dependent wind stress schemes improve storm surge forecasts, and chained model simulations enable robust extreme event estimation (e.g., 100-year Bohai Sea winds: 37 m/s) (Contributions 5, 8, 9, and 10). Port siltation dynamics are attributed to tidal asymmetry and typhoon lag effects, while Bohai sea-level rise is primarily tide-driven, amplified by wind and Stokes transport (Contributions 7 and 11). Collectively, these studies provide critical insights for predicting marine hazards and optimizing coastal resilience.