Predictability of Wind-Driven Coastal Ocean Flow Over Topography

The predictability of coastal ocean circulation over the central Oregon shelf is studied using ensembles of model forecasts from 50-day primitive equation ocean model simulations. The central Oregon shelf is a region of strong wind-driven currents and variable topography. The model configuration uses realistic topography, and simplified lateral boundary conditions. The forcing is an observed wind time-series representative of the summer upwelling season. The main focus on this study is on the balance between deterministic response to well-predicted forcing, uncertainty in initial conditions, and sensitivity to instabilities and topographical interactions. Simulated model forecasts are verified by standard statistics such as anomaly correlation coefficient and root mean squared error, and a new variant of relative entropy, the forecast relative entropy which quantifies the predictive information content in the forecast relative entropy relative to initial ensemble. The results suggest that the deterministic response is stronger than instability growth over the 3-7 day forecast intervals considered here. Therefore, when sufficiently accurate initializations are available, important elements of the coastal circulation should be accessible to predictive, dynamical forecasts on the nominal 7-day predictability timescale of the atmospheric forcing.