UC Santa Cruz

The California Current System (CCS) is undoubtedly one of the most well studied regions of the world ocean. The seasonal variability of equatorward

upwelling winds allow for the development of a complex set of dynamical features while also sustaining a rich diversity of marine organisms.

With use of the state-of-the-art Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation system,

the circulation of the CCS is explored in varying capacities over the time period 1980-2010.

Methods for improving the accuracy of circulation estimates provided during ROMS 4D-Var model integrations are explored through

quantification of a source of intrinsic model error that arrises from unavoidable numerical inaccuracies in the model and which is systematic to all oceanic and atmospheric forecast models.

Accounting for this source of model error in a model of the CCS leads to demonstrable improvements to the circulation estimates

compared to those computed without use of these techniques (Section 2).

Additionally, an in depth investigation of the low-frequency modulation of the circulation in a 31-year historical analysis of the CCS

computed using the ROMS 4D-Var system is presented and helps to elucidate the complex evolution of the 3-dimensional ocean state, as well as, assisting to

link local variations with basin scale climate modes; including the Pacific Decadal Oscillation, North Pacific Gyre Oscillation

and El Niño/Southern Oscillation (Section 3). Using a linear inverse model, estimates of the dynamical modes governing the temporal evolution

of the CCS circulation are computed. The dynamical modes capture the role ENSO plays in modulating the temperature, salinity and velocity structure in the CCS (Section 4) and the potential for decadal variability in the CCS to be dominated by forcing by basin scale climate modes (Section 5).