The Global Ocean Data Assimilation System (GODAS) at NCEP: Introducing new data sets

David Behringer Environmental Modeling Center, NCEP/NOAA

Yan Xue Climate Prediction Center, NCEP/NOAA

Office of Climate Observation (OCO) Annual System ReviewSilver Spring, Maryland, April 25-27, 2005

Outline

•The standard operational GODAS

•Assimilating satellite altimetry

•Assimilating Argo salinity profiles

•The effect of a changing ocean observing

system on CFS S/I forecasts

Seasonal to Interannual Forecasting at NCEP

Global OceanData AssimilationSystem (GODAS)

Coupled OceanAtmosphere Forecast

System (CFS03)

SST XBT TAO

Altimeter Argo

Scatterometer

Stress

E-P

Heat Fluxes

SST Anomaly Surface Temperature& Rainfall Anomalies

Official SST ForecastOfficial ProbabilisticSurface Temperature& Rainfall Forecasts

Seasonal Forecastsfor North America

with ClimateAtmosphere GCM

CCA, CAMarkov

CCA, OCNMR, ENSO

Forecasters

Ocean Initial Conditions

IRI

IRI

GODAS (MOM V.3)Operational since September 2003Grid:

Quasi-global, 40 vertical levels.Physics:

KPP boundary layer mixing scheme, free surface.

Forcing: Wind stress, heat flux, E-P fromReanalysis 2 (R2), surface salinity relaxed to Levitus monthly SSS climatology.

Assimilation 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), synthetic salinity constructed from temperature and local Levitus T-S climatology.

CFS03Operational since August 2004Atmosphere: T62/64-layer version of the current NCEP atmospheric Global Forecast System (GFS) with the same configuration as used in R2Ocean: GFDL Modular Ocean Model (MOM V. 3) with the same configuration as used in GODASCoupling: Direct coupling with no flux correction, accomplished daily

GODAS

• Assimilation data sets

Standard temperature and synthetic salinity

Satellite altimetry data

Argo salinity

Ocean Observations Used in NCEP S/I Forecasting

GODAS

• Assimilation data sets

Standard temperature and synthetic salinity

Satellite altimetry data

Argo salinity

Assimilation of altimetry data• 2 Data sets

TOPEX / Jason-1, 10-day period

ERS-2 / Envisat, 35-day period

Both acquired from AVISO through John Lillibridge (NESDIS)

• 4 Experiments

GTSE - assimilates temperature, synthetic salinity

and TOPEX / Jason-1, 1993-2003

GTSEn - assimilates temperature, synthetic salinity

and ERS-2 / Envisat, 1996-2003

GTS - assimilates temperature and synthetic salinity

GSIM - control, no assimilation

12 / 28 / 1997 - 1 / 07 / 1998

12 / 14 / 1997 - 1 / 18 / 1998

SIM 9.96 0.54GTS 4.88 0.88GTSE 3.27 0.93GTSEn 2.87 0.96

SIM 6.65 0.54GTS 4.50 0.82GTSE 3.22 0.90GTSEn 3.42 0.90

SIM 4.85 0.80GTS 2.94 0.93GTSE 2.22 0.96GTSEn 2.30 0.97

RMS COR

SIM 5.06 0.85GTS 5.30 0.81GTSE 4.38 0.88GTSEn 4.02 0.93

SIM 5.35 0.81GTS 3.58 0.91GTSE 3.07 0.94GTSEn 3.17 0.96

SIM 4.38 0.88GTS 2.73 0.96GTSE 2.10 0.97GTSEn 1.97 0.98

RMS COR

GODAS

• Assimilation data sets

Standard temperature and synthetic salinity

Satellite altimetry data

Argo salinity

Assimilation of Argo salinity

• Each temperature profile (XBT, mooring, Argo) is paired with a salinity profile

• XBT and mooring profiles are paired with synthetic salinity profiles

• Most Argo profiles are paired with observed salinity profiles

• Synthetic salinity profiles are assigned larger errors based on the statistics of the synthetic - observed profile differences

• The experiment runs from the beginning of 2000 through the end of 2004

Operational SI prediction

• GODAS runs daily producing a daily mean file and a restart file that lag the current date by 8 days.

• CFS runs 2x daily, initialized by the GODAS restart file and the R2 atmospheric analysis.

• Each forecast extends out to 9 months.

• The ensemble forecast is built from the forecasts run on 20 consecutive days for a total of 40 members.

Courtesy ofDr Peitao Peng

Courtesy of Dr Peitao Peng

Summary

• Assimilation of new data sets

→ Altimetry assimilation leads to general improvement in GODAS sea level. It’s impact on CFS predictions is to be determined.→ Assimilation of Argo salinity leads to a general improvement in GODAS salinity. There is less improvement in western tropical Pacific and near river outflows.• S/I forecasting

→ The CFS S/I forecasts show higher skill in the 1990s than in the 1980s.→ The likely cause is a shift in the GODAS climatology that in turn is due changes in the assimilation data set.

Data Availability on the Internet

• GODAS Analyses

→ Operational GODAS fields (5-day and monthly ave) sea surface height surface temperature and salinity surface isothermal and mixed layer depths heat content of upper 300 meters temperature, salinity and currents at 40 levels surface forcing (wind-stress, heat flux, E-P)→ Reanalysis, 5-day averages, 1979-present

→ Operational, weekly, rotating archive,

ftp://ftpprd.ncep.noaa.gov:cmb/Products/G3R2TSo

The End