Observing system simulation experiments reveal that subsurface temperature observations improve estimates of circulation and heat content in a dynamic western boundary current

Abstract. Western boundary currents (WBCs) form the narrow, fast-flowing poleward return flows of great subtropical ocean gyres and are sources rapidly varying mesoscale eddies. Accurate simulation vertical structure, separation latitude, heat content WBCs is important for understanding transport in global ocean. However, state estimation forecasting WBC regions, such as East Australian Current (EAC), South Pacific gyre, challenging due to their dynamic nature lack observations at depth. Here we use observing system experiments show that subsurface temperature a high eddy kinetic energy region yield large improvement representation key EAC circulation features, both downstream ∼ 600 km upstream location. These (in concert with sea surface height measurements) also critical correctly representing along length EAC. Furthermore, find more latitude leads an field represented far reduced error, compared when separates closer Equator. Our results demonstrate importance accurate can lead marine heatwaves. provide useful suggestions design under different oceanographic regimes, example, adaptive sampling target states low fewer observations.