Adjoint sensitivities to local and remote forcing in the Central California region

Milena Veneziani, Christopher A. Edwards, and Andrew M. Moore
(Ocean Sciences Dept, University of California Santa Cruz)

We have used the ROMS adjoint model to study the sensitivity of the Central California circulation to different driving mechanisms. The region is characterized by complex dynamics driven both by internal instability processes and by external and boundary factors such as the wind forcing, open boundary conditions, steep bathymetry and coastline shape. Understanding the relative contribution of these factors is relevant not only for theoretical reasons, but also for planning observational strategies and for data assimilation purposes.

We have defined a number of metrics that best represent the coastal upwelling processes and the energetics of the California Current System, and we have used the adjoint model to determine the sensitivity of these metrics to the model initial conditions and external forcing. The spatial distribution of the sensitivity fields has allowed us to investigate the relative contribution of local versus remote forcing, while the sensitivity temporal changes have identified the periods of major influence. By averaging the appropriately weighted sensititivity results over the whole model domain, we have also ranked the sensitivies to different factors with respect to each other.