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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 Review Silver Spring, Maryland, April 25-27, 2005. - PowerPoint PPT Presentation
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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
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