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Current climate forecasting has advanced to the stage of investigating mesoscale air-sea interactions. Recent studies have identified significant structural differences between the cores and edges of mesoscale eddies; however, the effects of these structural variations on air-sea fluxes and the Marine Atmospheric Boundary Layer (MABL) remain underexplored. Traditional observations often fail to capture the detailed structures of eddies, necessitating enhanced observations at high spatiotemporal resolution for mesoscale eddies. To address this, efforts have been made to develop multi-agent platforms and expendable air-sea interface observation technologies. A task-oriented observation scheme was developed to monitor the spatial characteristics of mesoscale eddies. The South China Sea (SCS) is rich in mesoscale eddies with rapid motion changes, requiring enhanced observations of the air-sea interface using multi-agent mobile networking. An anticyclonic eddy was observed in the eastern region of the Xisha Islands in the SCS, and we examined variations in air-sea fluxes across different regions within the eddy. [ABSTRACT FROM AUTHOR]

This study investigates the dynamics and diurnal variations of submesoscale motions around an anticyclonic eddy with a cold core using observations and simulations. Glider observations reveal vigorous submesoscale motions within the mixed layer (ML) at the eddy periphery due to strong frontal structure. The main driving force behind these motions is external atmospheric forcing, especially down‐front wind, which injects negative Ertel potential vorticity (PV) into the ML, triggering frontal instability in the low‐PV layer. Observations indicate a regular diurnal cycle of submesoscale motions at the eddy periphery in the absence of strong daytime winds. During the night, cooling and winds inject negative PV, leading to instability, while daytime heating and weak winds contribute to restratification. However, the presence of strong down‐front winds during the day disrupts the regular diurnal cycle, causing frontal instability even during daylight hours. The observed eddy periphery is reconstructed in a turbulence‐resolving large‐eddy simulation, confirming and extending the observations. The combined results emphasize the crucial impact of atmospheric forcing, particularly down‐front wind, on the diurnal variations of submesoscale motions around abnormal anticyclonic eddies. Diurnal heat fluxes play a key role in maintaining the diurnal cycle of these motions, while transient strong down‐front winds are essential for breaking the regular cycle and rapidly triggering frontal instability. Plain Language Summary: In the vast ocean, swirling currents known as mesoscale eddies with scales around 100 km are widespread. Our study focuses on analyzing smaller‐scale currents, known as submesoscale motions, which have scales of about 1–10 km. These submesoscale motions accompany an anticyclonic eddy with a cold core and are investigated using observations and computer simulations. We found that the submesoscale motions are most intense in the surface layer at the periphery of the eddy. Surface cooling and winds from the atmosphere are identified as the main driving forces behind submesoscale motions. These submesoscale motions also exhibit temporal variations influenced by external atmospheric forcing. In the absence of strong winds, surface heating during the day suppresses submesoscale motions, while surface cooling at night leads to more active submesoscale motions. However, strong winds disrupt this pattern and cause active submesoscale motions even during the day. Overall, our study contributes not only to a deeper understanding of ocean dynamics but also to the understanding of how these currents interact with the atmosphere. Through observations and simulations, we gain insights into the intricate processes taking place in the ocean, shedding light on the complex relationship between the ocean and the atmosphere. Key Points: Submesoscale motions around anticyclonic eddy with a cold core are most vibrant at the eddy periphery, mainly driven by down‐front windsSubmesoscale motions at the eddy periphery exhibit regular diurnal variations when diurnal heat flux dominates atmospheric forcingStrong down‐front winds break the diurnal cycle at eddy periphery, triggering rapid submesoscale frontal instability even at daytime [ABSTRACT FROM AUTHOR]

The process of eddy shedding from the Kuroshio loop current (LC) into the South China Sea via the Luzon Strait is highly variable and significantly controlled by the uncertainties in the Western Pacific (WP) currents. This study investigates the forecast of a strong eddy shedding event from the Kuroshio LC during the winter 2016–2017 using the regional ocean modeling system and ensemble Kalman filter assimilation method. Experiments are conducted to explore the sensitivity of forecasts to the assimilation of satellite sea surface height anomaly data from different key regions of the WP, such as the subtropical countercurrent (STCC) and Northern Equatorial Current (NEC) regions. The results indicate that the improved forecast performance of the strong Kuroshio LC eddy shedding event is mainly attributed to assimilation in the STCC region and partly owing to assimilation in the NEC region. Specifically, assimilation in the STCC region reproduces a westward-propagating cyclonic eddy that collides with the Kuroshio in the Luzon Strait, blocking the Kuroshio northward flow and causing Kuroshio LC eddy shedding. Furthermore, assimilation in the NEC region enhances the simulation of the weak Kuroshio background current, which further facilitates the formation of a strong Kuroshio background LC and the occurrence of Kuroshio LC eddy shedding. • Strong eddy shedding into the SCS was predicted using EnKF data assimilation. • The improved forecast is mainly owing to a reproduced cyclonic eddy east of Luzon. • It is also partly owing to the reproduced weak Kuroshio background current. [ABSTRACT FROM AUTHOR]