The California Current System (CCS) is an eastern boundary region with a very high biological productivity adjacent to one of the main population centers of the United States. This project will test the hypothesis, suggested by recent observational investigations, that synoptic ocean eddies in the region play a major role in controlling its low frequency variations.. Specifically, the work will (i) study the impacts of intrinsic and externally forced mesoscale eddy variability on the inter-annual and decadal changes of temperature, salinity and currents in the CCS, (ii) diagnose the dynamics of the synoptic ocean response (the eddy field) to transient local atmospheric forcing and to remote oceanic forcing associated with El Nino and the adjustments of the North Pacific gyre, (iii) identify the patterns of tracer distribution from and to the coastal upwelling system and (iv) explore the response of the North East Pacific thermocline to variations in the CCS.
The primary tools for these studies are high resolution, nested, ocean models (ROMS), augmented by their existing Adjoint and Tangent Linear codes. Model domains include the entire Pacific, to supply the large scale conditions, and regional nested areas of very high resolution in the CCS region. The regional simulations will selectively apply climatological or time dependent atmospheric and oceanic boundary conditions to isolate influences of ocean intrinsic variability, of atmospheric forcing and of remote ocean forcing. Of special note are the surface fresh water fluxes formulations, which will not use the unphysical feedback of surface relaxation to reference surface salinity. The comparison of these experiments will allow the identification of the impacts of the different forcing and the role of intrinsic ocean processes. Analysis of these runs will include (i) budget calculations for momentum, salinity and vorticity to determine the role of ocean synoptic variations in the low frequency changes of the CCS, (ii) EOFs and spectral analysis to statistically characterize the dynamical relationships in the budget terms and isolate the signature of oceanic processes, (iii) stability and sensitivity analysis with the tangent linear and adjoint models to diagnose the generating mechanisms and dynamics of the eddies during different circulation and forcing regimes and (iv) probability distribution functions for passive tracers to further clarify the stirring and mixing pathways from and to the upwelling system.
Intellectual Merits: This study aims to increase understanding of the role and dynamics of ocean intrinsic variations of the eastern boundary regions, and their role in energizing and affecting the regional and large-scale low-frequency climate variations. This is essential to the understanding and prediction of the physics, chemistry and biology of these highly productive coastal upwelling systems. In particular this study will focus on the California Current coastal upwelling system, a major economical resource for US fisheries.
Broader Impacts: The improvements in our ability to model observed long-term variability in the CCS will directly be available to a related NSF Long Term Ecological Research Site (LTER) sponsored program on Nonlinear Transitions in the California Current Coastal Pelagic Ecosystem at Scripps. Among the LTER tasks is the use of physical-biological models of the CCS to test hypothesis on ecosystem changes. The dynamical inferences on the changes eddy variance and mixing pathways, have direct application in the NSF-GLOBal Ecosystems studies (GLOBEC). The principal investigators communicate on a regular basis with some of the scientists involved in GLOBEC and will promptly share the results of this research. The investigator at the Georgia Institute of Technology will participate in K-12 educational outreach, to promote oceanography in a one day "hands on experience' for high school students during the summer camps activity organized by the Center for Education Integrating Science, Mathematics and Consulting (CEISMC). Two oceanography education sessions for 6th grade teacher from Fulton County, Atlanta, will also be held at Georgia Tech as part of this outreach activity.
