# Presentation: 548084

## 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

## Outline

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

## 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

## ROMS Versions

- Nonlinear
- Perturbation tangent linear
- Finite-amplitude tangent linear
- Adjoint of tangent linear

- myroms.org

## Eigenmodes & Singular Value Decomposition (ARPACK-based)

- Eigenmodes of
- Eigenmodes of
- Singular vectors:
- Forcing singular vectors:
- Stochastic optimals:
- Hankel singular vectors:

## 4-Dimensional Variational Data Assimilation (4DVAR)

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

## Explorer of the Seas (Royal Caribbean CL)

**Notes:**
We, however, are very fortunate to be aboard a far more luxurious and salubrious vessel which is also operates in a research capacity!

## 4-Dimensional Variational Data Assimilation (4DVAR)

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

## Adjoint Sensitivity Analysis:Application to the California Current System

## The California Current (CC)

-  CC circulation and biology controlled by upwelling, instability, topography
-    and bathymetry.
-  Sensitivity analysis can be used to unravel this complex system and
-    test hypotheses.

## The ROMS SCB Domain

- 20km resolution; forced by NCEP climatological winds and surface fluxes
- 50 years outer, 10 years inner, last 5 years considered here..

- Outer domain:
- 20km res, 20 levels.
- Inner domain:
- 20km res, 20 levels.
- Derives boundary
- conditions from the
- outer domain.

## Seasonal Circulation Index Regions

- April Mean SST

## Indices

- “Eady Index”

- An index of potential
- for baroclinic instability

**Notes:**
NEW: We consider time integrals in our functionals which is not normally done – so we require time integrals of adjoint variables.

## What Physical Processes are likely to  Influence J?

- Advection

- Q, P-E+R

- Advection

- Instability

- Long Rossby Waves

- Short Rossby Waves

- Coastally
- Trapped
- Waves &
- Tides

- Turbulence/
- wave breaking

**Notes:**
We can identify the influence of each of these processes on J by looking at different adjoint fields.

## Adjoint Sensitivity Analysis

- Adjoint ROMS

- Forcing

## Sensitivities of JSST to surface forcing

**Notes:**
NEW: We consider sensitivity to time average forcings – so we must force the adjoint model appropriately.

## Summary of Sensitivities

- Spring

- Autumn

- Summer

- Winter

- T

- v

- T

- v

## 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.