1. Adjoint Sensitivity Analysis of the California Current Circulation and Ecosystem using the Regional Ocean Modeling System (ROMS)
Andy Moore,
Emanuele DiLorenzo, Hernan Arango,
Craig Lewis, Zack Powell,
Arthur Miller, Bruce Cornuelle

2. Outline The ROMS system The California Current Model configuration
Physical indices that characterize flow
Examples of sensitivities and variations
Summary

3. The Regional Ocean Modeling System (ROMS)
Hydrostatic, Boussinesq, primitive eqn
Free surface
Terrain following coordinates
Generalized, orthogonal, curvilinear coordinates in horizontal
Open boundaries
Nesting capabilities
All parallel applications

4. ROMS Versions myroms.org Nonlinear Perturbation tangent linear
Finite-amplitude tangent linear
Adjoint of tangent linear
myroms.org

5. Eigenmodes & Singular Value Decomposition (ARPACK-based)
Eigenmodes of
Singular vectors:
Forcing singular vectors:
Stochastic optimals:
Hankel singular vectors:
Pseudospectra

6. 4-Dimensional Variational Data Assimilation (4DVAR)
Strong constraint, incremental, 4DVAR
- Intra-Americas Sea (myroms.org/ias)
Weak constraint, representer-based, 4DVAR

7. Explorer of the Seas (Royal Caribbean CL)
We, however, are very fortunate to be aboard a far more luxurious and salubrious vessel which is also operates in a research capacity!

8. 4-Dimensional Variational Data Assimilation (4DVAR)
Strong constraint, incremental, 4DVAR
- Intra-Americas Sea (myroms.org/ias)
Weak constraint, representer-based, 4DVAR

9. Adjoint Sensitivity Analysis: Application to the California Current System

10. The California Current (CC)
High
CC circulation and biology controlled by upwelling, instability, topography
and bathymetry.
Sensitivity analysis can be used to unravel this complex system and
test hypotheses.

11. The ROMS SCB Domain Outer domain: 20km res, 20 levels. Inner domain:
Derives boundary
conditions from the
outer domain.
20km resolution; forced by NCEP climatological winds and surface fluxes
50 years outer, 10 years inner, last 5 years considered here..

12. Seasonal Circulation Index Regions
JSST
JKE
April Mean SST

13. Indices “Eady Index” An index of potential for baroclinic instability
NEW: We consider time integrals in our functionals which is not normally done – so we require time integrals of adjoint variables.
“Eady Index”
An index of potential
for baroclinic instability

14. What Physical Processes are likely to Influence J?
Signatures
visible in
time evolving
adjoint fields
Turbulence/
wave breaking
Advection
Long Rossby Waves
Instability
We can identify the influence of each of these processes on J by looking at different adjoint fields.
Q, P-E+R
Short Rossby Waves
Advection
Coastally
Trapped
Waves &
Tides

15. Adjoint Sensitivity Analysis
Forcing
Adjoint ROMS

16. Sensitivities of JSST to surface forcing
NEW: We consider sensitivity to time average forcings – so we must force the adjoint model appropriately.

17. Summary of Sensitivities
Spring
Summer
Autumn
Winter T T v v

18. Summary and Conclusions
The CC coastal SST, KE and baroclinic instability exhibit pronounced seasonal variations in sensitivity to surface forcing.
Sensitivities vary by a factor ~2-4 throughout the year, but some years variations are larger (~5-10).
CC typically most sensitive during the Summer-Fall transition.
Signatures of instability processes are apparent in many of the calculations.
Significant implications for data assimilation and predictability.