Moore, A. M., H. G. Arango, E. Di Lorenzo,
A. J. Miller
and B. D. Cornuelle, 2009:
An adjoint sensitivity analysis of the
Southern California Current circulation and
Journal of Physical Oceanography, 39, 702-720.
Adjoint methods of sensitivity analysis were applied to the California Current using the Regional Ocean
Modeling Systems (ROMS) with medium resolution, aimed at diagnosing the circulation sensitivity to variations
in surface forcing. The sensitivities of coastal variations in SST, eddy kinetic energy, and baroclinic
instability of complex time-evolving flows were quantified. Each aspect of the circulation exhibits significant
interannual and seasonal variations in sensitivity controlled by mesoscale circulation features. Central California
SST is equally sensitive to wind stress and surface heat flux, but less so to wind stress curl, displaying
the greatest sensitivity when upwelling-favorable winds are relaxing and the least sensitivity during the peak
of upwelling. SST sensitivity is typically 2.4 times larger during summer than during spring, although larger
variations occur during some years.
The sensitivity of central coast eddy kinetic energy to surface forcing is constant on average throughout the
year. Perturbations in the wind that align with mesoscale eddies to enhance the strength of the circulation by
local Ekman pumping yield the greatest sensitivities.
The sensitivity of the potential for baroclinic instability is greatest when nearshore horizontal temperature
gradients are largest, and it is associated with variations in wind stress concentrated along the core of the
California Current. The sensitivity varies by a factor of ;1.5 throughout the year. A new and important
aspect of this work is identification of the complex flow dependence and seasonal dependence of the sensitivity
of the ROMS California Current System (CCS) circulation to variations in surface forcing that was
hitherto not previously appreciated.