# Presentation: 012329

## The Operational NCEP GODAS:

**Evaluation and Application**
_**Yan Xue**_ Climate Prediction Center, NCEP/NOAA
-  **David Behringer** Environmental Modeling Center, NCEP/NOAA
- Thanks to Kyong-Hwan Seo
- NCEP CFS Assessment Meeting, Camp Spring, Maryland, November 16, 2004

## Slide 2

## GODAS

**Model**:** **
**    **MOM v.3
**Grid**:
- Quasi-global, 40 vertical levels.
**Physics**:
- KPP boundary layer mixing scheme,
- free surface.
**Forcing**:
- Wind stress, heat flux, E-P from
- Reanalysis 2, surface salinity
- relaxed to Levitus monthly SSS
- climatology.
**A****ssimilation method**:
- 3D VAR, analyzes **temperature** and
**salinity**, error covariance varies
- geographically and temporally.
**Assimilation data**:
- Temperature profile data from **XBTs**,
- profiling floats (**Argo**), moorings
- (**TAO**), **s****ynthetic sa****l****inity** from local
- Levitus T-S climatology.

**RA6****  **
**Model**:
**    **MOM v.1
**Grid:**
- Pacific basin, 27 vertical levels.
**Physics**:
- Richardson number based scheme,
- rigid lid.
**Forcing**:
- combining anomalies from FSU winds
- with Hellerman and Rosenstein climatology, no E-P flux, no constraint on SSS.
**A****ssimilation method**:
- 3D VAR, analyzes **temperature only**,
- fixed error covariance prior to
- TOPEX era.
**Assimilation data**:
- Temperature profile data from **XBTs**,
- profiling floats (**Argo**), moorings
- (**TAO**), **TOPEX sea level** since
- 1993.

## VERIFICATION

**Dependent Data:**
**TAO temperature profiles**
**Independent Data:**
**Tide Gauge ****(sea level)**
**Gregory Johnson’s CTD**** (salinity)**
**Gregory Johnson’s ship ADCP ****(velocity)**
**Peter Niiler’s drifter current ****(velocity)**
**TAO ADCP ****(velocity)**

**MODEL RUNS**

-     **GODAS**
**    ****RA6**
**    ****SIM**** (same as GODAS except no data assimilation)**

## Applications of GODAS at CPC

**CFS model uses GODAS as oceanic initial conditions.**
**“****Weekly ENSO Update”**** uses GODAS pentad temperature and sea level fields to monitor intraseasonal oceanic variability.**
**“****Climate Diagnostic Bulletin” uses GODAS monthly temperature and sea level fields to assess interannual oceanic variability. **
**Markov model**** uses GODAS monthly sea level field as predictor.**
**CCA ENSO model uses GODAS monthly sea level and depth of 20 degree as predictors.**

**Study relationship between ENSO and ****MJO-related oceanic Kelvin waves****.**
**Study coupled ocean-atmospheric modes in the Tropical Atlantic Ocean, and improve forecast skill of SST and precipitation there.**

## Slide 6

## Slide 7

## Slide 8

## Warm Biases in GODAS

## Guam

- Kwajalein

- Rabaul

## from 1992-2000 mean

## Slide 12

## Slide 13

## Slide 14

## Slide 15

## Slide 16

## Surface Current Errors in GODAS

## 6 hour

**Peter Niiler’s Drifter Current**

- daily

- pentad

**GODAS**

- pentad

- 5ox1o grid

## Slide 19

## EXPERIMENTAL RUNS

_**EXPERIMENTAL RUNS**_

-     **GODAS.v2**
** **pentad,** **1992-2001
- salinity in mixed layer was made closer to SIM than
-    to GODAS
**    ****GODAS_TJ**** **
-  pentad, 1993-2003
-  TOPEX/Jason1sea level assimilated
**    ****GODAS_EE**
-  pentad, 1996-2003
-  ERS2/Envisat sea level assimilated

## Slide 21

## Johnson et al. 2000, JGR

- 172 sections
- for 1985-2000
- gridded in y

- TAO cruises
- twice per year

## Salinity at Z=5m

- GODAS.v1

- GODAS.v2

## Slide 24

## Slide 25

## Slide 26

## Summary

**Assimilation of synthetic salinity seriously underestimated SSS variability, which contributes to large errors in surface currents. **
**Surface currents are slightly improved when more weights are given to model salinity than to synthetic salinity in the mixed layer. **
**Assimilation of altimetry appears to improve sea level analysis significantly in the Atlantic and Indian Ocean, but whether it improves other variables is unknown. **
**Assimilation of altimetry does not improve deficiencies in GODAS surface currents.**

## Future Works

**Impacts of geostrophic adjustment on GODAS**
**Impacts of boundary forcings on GODAS**
**Momentum fluxes: CDAS2, ERA40 and FSU winds**
**E-P fluxes: CDAS2, Xie-Arkin and GPCP Prec.**
**	**(Glen White shows that CDAS2 correlates with FSU at 0.3 in the eastern Pacific)
**Impacts of altimetry sea level on GODAS**
**Impacts of ARGO data on GODAS**
**Evaluation of Atlantic and Indian Oceans**
**Evaluation of intraseasonal variability**

## Ocean Observations for Seasonal Forecasting at NCEP

|  | RA6
(~opr) | GODAS (opr) | GODAS (dev) | Verify |
| --- | --- | --- | --- | --- |
| Temperature |  |  |  |  |
|  XBTs | X | X | X |  |
|  TAO | X | X | X |  |
|  Argo | X | X | X |  |
| Salinity |  |  |  |  |
|  Synthetic |  | X | X |  |
|  Argo |  |  | X | X |
| Altimetry |  |  |  |  |
|  TPX / Jason-1 | X |  | X | X |
|  ERS-2 / Envisat |  |  | X | X |
| Tide Gauges |  |  |  | X |
| Moored CMs |  |  |  | X |
| Drifters |  |  |  | X |
| Ocean SST is relaxed to the NCEP SST OI analysis.
Scatterometer winds enter the atmospheric wind-stress analysis |  |  |  |  |

**Ocean Observations for Seasonal Forecasting at NCEP**

## Slide 30

## TAO

**TAO**

**GODAS**

**SIM**

**RA6**

## SIM

**SIM**

**RA6**

**GODAS**

## Slide 33

## ~15ox1o grid

- ~15ox1o grid

## Salinity at Eq

- GODAS.v1

- GODAS.v2