Observations of submesoscale turbulence using geostationary satellite images

Near-surface observations of submesoscale circulations play a crucial role in understanding physical/biological processes in the upper open oceans, but current observational platforms such as satellite altimetry and HR radar have limitations in resolution and coverage area. In this work, we introduce a way of studying submesoscale turbulence over an area of few hundred kilometers using Eulerian velocity observations. Geostationary satellite-based observations have extended the spatiotemporal scales down to submesoscales, at which local dispersion, ageostrophic circulation, vertical transport, and physical/biological interaction strongly occur. The movement of Chlorophyll-a distributions taken from the Geostationary Ocean Color Imager (GOCI) was processed by the method of Particle Image Velocimetry (PIV), from which we generated a submesoscale-permitting Eulerian velocity field around the Korean peninsula. The observations in the East/Japan Sea in April indicated two spectral regimes following k^-3 and k^-5/3 at scales larger and smaller than 50km, respectively. The spectral kink may represent a superposition of quasi-geostrophic (GQ) turbulence and surface quasi-geostrophic turbulence in an additive way, indicating a phase of increasing dominance of a QG flow in April.