Improving GODAE products for IMBER applications Summary of
Improving GODAE products for IMBER applications (Summary of break-out group #1) IGST-XII meeting, St. John’s, Newfoundland, Aug. 7 -9, 2007 Tony Lee NASA Jet Propulsion Laboratory, California Institute of Technology Three proposed actions: 1. Evaluate the quality of GODAE-derived vertical fluxes by using GODAE products to drive IMBER models. 2. Examine the impact of volume conservation in GODAE products on ecosystem variables. 3. Assess the reliability of forcing fields estimated by GODAE systems.
1. Evaluate the quality of GODAE-derived vertical fluxes by using GODAE products to drive IMBER models Background: • Abrupt temporal “shocks” caused by sequential assimilation methods result in spurious convective adjustment of the model state. • Some evidence that this problem cause unrealistic vertical fluxes, which degrade the simulation of IMBER variables.
An example of spurious vertical exchange due to sequential update of model state: problems may be hidden in the physical state, but emerges in biogeochemical applications. CO 2 flux during ENSO inferred from a Kalman filter estimation (physically inconsistent) is unrealistically large (left), but that based on Kalman filter-smoother (physically consistent) is reasonable (right). Kalman Filtered estimate Kalman-filter/smoother estimate Mc. Kinley et al. , 2002
Is this a common problem for systems based on sequential assimilation methods? Prompt for a systematic evaluation of the vertical fluxes in GODAE systems in the context of IMBER: • GODAE provides 3 D velocity, temperature, salinity, and vertical diffusivity on a common grid to drive IMBER models offline. • Prior states (before assimilation) also needed to evaluate impact of assimilation. • All products should be accompanied by meta data info. • NETCDF format preferred. • Regional high-res evaluation + global coarse-res evaluations. • IMBER interested in offline tracer codes of GODAE systems (potential issues: advection and grid schemes).
A web-based tool forward and adjoint tracer simulation
Horizontal distribution of source waters for the Pacific cold tongue as a function of years backward in time estimated using ECCO adjoint tracer (Fukumori et al. 2004) IMBER need such tools
Strategy to improve vertical fluxes in GODAE systems • Ad-hoc approach: spread out the assimilation correction over a certain time window as opposed to at a single-time step. • Use a smoother in addition to sequential filter. • Use assimilation methods that allow estimated state to satisfy model equations (e. g. , Green’s function, 4 D-VAR).
2. Examine the impact of volume conservation in GODAE products on ecosystem variables Background: • Many GODAE products do not satisfy volume conservation. • May impact diagnostic studies of IMBER. Proposed approach to evaluate impact on IMBER: Analyze budget imbalance on IMBER variables.
3. Assess the reliability of forcing fields estimated by GODAE systems Background: IMBER scientists need forcing fields that are consistent with the GODAE state estimates to perform diagnostic studies. Issues: Only 2 of the GODAE systems have forcing fields that are consistent with the state estimation (ECCO and Japan K-7). Potential drawback: These forcing estimates may be model dependent.
- Slides: 9