Submesoscale Processes in the Upper Red Sea

Spatial‐temporal submesoscale variabilities in the upper Red Sea and their generation mechanisms, including frontogenesis, mixed‐layer instability (MLI), and symmetric instability (SI) are qualitatively investigated using high‐resolution simulations. The results suggest that submesoscales are critical hydrodynamic components and stirring at submesoscale has a clear signal in the Red Sea, enhanced in winter, particularly in the central and northern basins, and intensified toward the eastern coast. Frontogenesis and MLI energize submesoscales with winter peaks, when SI could also be triggered by the enhanced frontal gradients and buoyancy loss that reduce the surface potential vorticity. The MLI and SI have larger (smaller) scales in winter (summer). The seasonal submesoscale variability is governed by the vertical structure of the mixed layer forced by atmospheric conditions, significantly modulating the mesoscale eddies' seasonality via an inverse cascade. This study offers new insights into understanding the Red Sea submesoscales and have potential applications to other marginal seas. Plain Language Summary Oceanic submesoscale dynamics have small dimensions (1–10s km), and they are important in the variability of physical, biological and chemical processes. We used a high‐resolution numerical model to study the spatial‐temporal submesoscale variabilities in the upper Red Sea, as well as their driving force and energy budget. We found that submesoscales are critical components in the Red Sea dynamics and make important contributions to stirring and transport in the basin. The seasonal submesoscale variability is essentially driven by atmospheric conditions and can modulate the eddiesʼ seasonality by converting energy from smaller scales to larger scales. This study offers new insights into understanding the Red Sea submesoscales and has potential applications to other marginal seas in the global oceans. Key Points The Red Sea submesoscales are enhanced in winter and enhanced toward the northern and eastern basin due to buoyancy flux and Ekman effects Submesoscales are forced by seasonal atmospheric conditions and modulate the seasonality of the mesoscales via an inverse energy cascade Submesoscales may play a role in chaotic stirring in the Red Sea, although they are dominated by two‐dimensional structures