Presenter: Changhoon Ko (KAIST)

Description:
We investigated spatial and temporal variability of island-induced submesoscale eddies and overturning instability in the Korea Strait, based on hourly and 2- km spatial resolution velocity data of the global sub-mesoscale numerical simulation outputs (MITgcm llc4320). We quantified the generation frequency of the island-induced submesoscale eddies with analyses of times series of surface vorticity. Also, we examined the spatial and temporal structures of the surface circulation associated with island wakes using empirical orthogonal function analysis. The second mode principal components revealed a consistent generation frequency ranging from 0.2 to 0.5 cycles per day (2–5-day period). The frequency of island-induced submesoscale eddies varies along seasons due to seasonal mixed layer depth differences. We used Richardson criterion analysis to identify the overturning instability of the regional circulation. Regional overturning instability is described with (1) dominant gravitational instability near the surface due to inverse density gradient and (2) symmetric instability in the mixed layer (20m to 100m depth) during winter. Richardson number criterion shows stability below 100m depth because of the intense density gradient at the thermocline.