Presenter: Yuhong Zhang (SCSIO, CAS)

Description:
Direct measurement of the global ocean surface current is of great scientific interest and application value for understanding multiscale ocean dynamics, air-sea interaction, ocean mass and energy balance, and their variabilities under climate change. Presently, measurements of global ocean surface currents, which are mainly geostrophically derived from satellite altimeter data, are only available to resolve quasi-geostrophic current at large- to meso- scale in the off-equatorial open ocean. Ocean Surface Current multiscale Observation Mission (OSCOM) will launch a satellite equipped with a Doppler Scatterometer to directly measure ocean surface currents with a very high horizontal resolution of 5–10 km and a 3-day global coverage. OSCOM will provide an in-depth picture of non-equilibrium ocean state and air-sea interaction from mesoscale to submesoscale, and helps to construct the fine structure of deep ocean current through a combination with Argo profiling. Those direct measurements and derived dynamic parameters will further provide a novel and improved pathway to data assimilation and coupling of GCMs for ocean prediction and climate change. OSCAR current and the surface drifters indicate that the non-geostrophic currents in the global ocean account for ~14% of the total current. Especially, the non-geostrophic currents determine the directions of the total currents in the near-equatorial trade winds and mid-latitude westerly winds prevailing regions, where the maximum non-geostrophic speed can reach twice the geostrophic speed and exceed 60% of the total current. The present current reanalysis cannot reveal the non-geostrophic processes in these regions and underestimate the weakening effect of the non-geostrophic process in the strong western boundary currents and the Antarctic Circumpolar Current. The influence of the non-geostrophic processes in the real world will be more significant, and the OSCOM is expected to reveal these processes in the future.