# Presentation: 546446

## The Global Ocean Data Assimilation System (GODAS) at NCEP

- D W Behringer (EMC), A Vinzileos (EMC), I Fukumori (JPL), R Miller (OSU)

- 4th Annual CTB SAB Meeting
- September 11-12, 2008
- ESSIC
- University of Maryland
- College Park, MD

## Current Operational GODAS

- Operational in 2003.
- Based on MOMv3 (1o x 1o, 1/3o in the tropics, 40 lvls) and a 3DVAR assimilation scheme.
- The assimilation data are temperature profiles (XBT, Argo, TAO, TRITON, PIRATA), synthetic salinity profiles derived from a climatological T-S relation and Jason-1 altimetry (March 2007). The data window extends from 2-weeks before to 2-weeks after the analysis date.
- Atmospheric forcing from the NCEP Reanalysis-2, surface relaxation to Reynolds weekly OIv2 SST, Levitas climatological SSS.
- Ocean reanalysis (1980-present) providing initial conditions for retrospective CFS forecasts used for calibration.
- Two versions associated with the CFS: 14-day lag, 1-day lag.
- A third stand-alone version with a 14-day lag.

**Notes:**
All operational versions of GODAS are updated daily.  The 1-day lag version is reinitialized each time by the 14-day lag analysis and brought forward using an asymmetric data window.

The CFS versions are essentially frozen with the CFS and updated with the CFS.  The stand-alone version can be updated more frequently (e.g. in 2009 it will be switched to MOM4) without upsetting the CFS S-I forecast calibration.

## Seasonal to Interannual Prediction at NCEP

## GODAS in the CFSRR

- To become operational in 2010.
- Based on MOMv4 (1/2o x 1/2o, 1/4o in the tropics, 40 lvls) and an updated 3DVAR assimilation scheme.
- Assimilation data are temperature profiles (XBT, Argo, TAO, TRITON, PIRATA), synthetic salinity profiles derived from a seasonal T-S relation and TOPEX/Jason-1 Altimetry. The data window is asymmetrical extending from 10-days before the analysis date.
- Surface temperature relaxation to (or assimilation of) Reynolds new daily, 1/4o OIv2 SST, surface salinity relaxation Levitas climatological SSS.
- The analysis system is coupled to the CFS in the sense that the first guess for the assimilation is provided by the CFS. After each analysis cycle the ocean model is stepped forward as a fully coupled component of the CFS.
- The current stand-alone operational GODAS will be upgraded in 2009 to the higher resolution MOMv4 and be available for comparison with the coupled version.

## CFSRR at NCEP

- Climate Forecast System

## GODAS-M4 1⁄2o x 1⁄2o resolution

**ave: 0.05**
**rms: 0.13**

**ave: 0.05**
**rms: 0.20**

- GODAS-M4 1⁄2o x 1⁄2o resolution
-  assimilating Reynolds 1⁄4o daily
-                        vs
- GODAS-M3 1o x 1o resolution
-  relaxing to Reynolds 1⁄2o weekly

## GODAS-M4 1⁄2o x 1⁄2o resolution

- Warm Pool

- Cold Tongue

**ave: 0.08**
**rms: 0.10**

**ave: 0.04**
**rms: 0.10**

- GODAS-M4 1⁄2o x 1⁄2o resolution
-  assimilating Reynolds 1⁄4o daily
-                        vs
- GODAS-M3 1o x 1o resolution
-  relaxing to Reynolds 1⁄2o weekly

## Comparison of GODAS/M4 and GODAS/M3

- Comparison of GODAS/M4 and GODAS/M3
- with TAO temperature and zonal velocity

- In the thermocline both GM4 and GM3 are warm at 140w, while GM4 is warm and GM3 is cold at 110w.

- The undercurrent is stronger than observed in GM4 and weaker in GM3. The vertical structure at 165e is better in GM4 than in GM3.

## Collaborations

- Impact of the GODAS mixed layer analysis on subseasonal forecasting with the CFS. Augustin Vintsileos (EMC)
- Improved estimates of representation errors for observations. Bob Miller (OSU)
- Alternative assimilation method. An adaption of the ECCO Kalman Filter (a partitioned, reduced-state, time-asymptotic filter) to MOM4. Ichiro Fukumori (JPL)

## Comparison of GODAS/KF and GODAS/3DVAR

- with TAO temperature and zonal velocity anomalies

- Re = [model explained variance] / [data variance]

- in collaboration with I Fukumori (JPL)

- For points toward the top (GKF) and toward the right (G3DV) the models are closer to the data. For points above (below) the diagonal GKF (G3DV) is closer to the data.