Operational NCEP Global Ocean Data Assimilation System:

The Link, Validation, and Application

Part I

Yan Xue, Boyin HuangClimate Prediction Center, NCEP/NOAA

David Behringer Environmental Modeling Center, NCEP/NOAA

Office of Climate Observation Annual Review Meeting, May 10-11, 2006

Seasonal to Interannual Forecasting at NCEP

Global OceanData AssimilationSystem (GODAS)

Climate Forecast System (CFS)

SST XBT TAO

Altimeter Argo

Scatterometer

Stress

E-P

Heat Fluxes

SST Anomaly

Forecasters

Official SST Forecast

Official ProbabilisticSurface Temperature& Rainfall Forecasts

Seasonal Forecastsfor North America

CCA, CAMarkov

CCA, OCNMR, ENSO

Ocean Initial Conditions

IRI

IRI

VALIDATION

Dependent Data:• TAO temperature profiles• World Ocean Atlas 2001 (WOA01)

Independent Data:• Tide Gauge sea level (Hawaii Sea Level Center)• Drifter current velocity (Peter Niiler)• Ship-drift velocity (Arthur Mariano)• CTD and ADCP velocity from cruises (Gregory Johnson)• ADCP velocity from TAO moorings• Altimetry sea level

Drifter Current GODAS Currentlarge biases

Summary• The poor representation of salinity in RA6 has been

corrected in GODAS by assimilating a synthetic salinity using local climatological T-S relationship, but the method retains little salinity variability.

• Surface zonal velocity compares well with surface drifter velocity except in the equatorial Pacific where large biases exist in the western and central Pacific.

• Equatorial undercurrent is well simulated in the central-eastern Pacific, but poorly simulated in the western Pacific.

• Correlation with tide gauge observations is about 0.7-0.9 in tropical Pacific, and 0.4-0.7 in tropical Indian and Atlantic Oceans.

GODAS Web Site

Objectives: Monitor different aspects of oceanic climate

variability Assess benefits of NOAA’s extensive

investment in global ocean observing system Disseminate GODAS products to a broad user

community Involve research community in assessment and

improvement of GODAS

NOAA’s Office of Climate Observation sponsors CPC to host a web site for GODAS

http://www.cpc.ncep.noaa.gov/products/GODAS

1. Pentad products (archive past 3 months) Model output (SST, subsurface temperature, heat

content, depth of 20OC, mixed layer depth, ocean current, wind stress, total heat flux, total fresh water flux)

Model-data intercomparison

2. Monthly products (archive 1979-current years ) Model output Data distribution Model-data intercomparison

3. Climatology

4. Skill assessment

R2 Zonal Stress GODAS D20

Operational Applications of GODAS at NCEP

• Oceanic I.C. for Coupled Climate Forecast System

• Weekly ENSO Update

• Climate Diagnostic Bulletin

• Predictors for Markov and CCA ENSO models

Oceanic Kelvin Waves

Research Applications of GODAS at NCEP

• Study annual cycle of tropical Indian Ocean using GODAS products from NCEP, ECMWF and University of Maryland (SODA1.4.2)

• Study MJO-ENSO connection

• Study heat content redistribution that is critical for ENSO forecast

• Study coupled ocean-atmospheric modes in the tropical Indian and Atlantic Ocean and their interactions with ENSO, and use those modes to forecast global tropical SST using a Markov model

Eastern Dipole

SIO Dome

Eastern Dipole

SIO Dome

Annual Harmonic

Dec

Jul

Sep Mar

Dec

Jul

Sep Mar

Semi-annual Harmonic

Ship-drift

NCEP

SODA ECMWF

NCEP

Wyrtki Jet

NCEP’s mixed layer depth 5-10 m too deep

Summary• SODA simulates mean D20 very well except in southern middle latitudes.

NCEP has negative biases (5-10 m) in the eastern, south-western Indian Ocean and northern Bay of Bengal. ECMWF has large biases out of the equatorial belt.

• Annual harmonic of D20 is well simulated by all ocean analyses, which has maximum amplitude in Arabian Sea, western Bay of Bengal, and southern Indian Ocean near 12oS.

• Semi-annual harmonic of D20 is well simulated by all ocean analyses except it is underestimated by SODA and ECMWF.

• Wyrtki jet, dominated by semi-annual harmonic, is well simulated except its strength is too weak. NCEP has too strong westward jet during winter and summer and too weak eastward jet during fall. The annual harmonic is poorly simulated by all ocean analyses.

• Mean mixed layer depth is well simulated in the equatorial belt except NCEP and ECMWF have positive biases (5-10 m) in the central and eastern Indian Ocean respectively. Biases are generally large out of the equatorial belt.

THANKS!

00-05

79-01

79-01

00-05

Correlation

RMS Diff

# of pentads

SVKW: seasonal variance of Kelvin wave

Heat Content averaged in equatorial belt

NINO3.4

TAO data increases

sharply in 1993

XBT data increases

sharply in 1990

ARGO data come in

in 2000

ARGO

XBT TAO

SIMUL

SIMUL

60OE 140OW 30OW

Zonal Velocity

Meridional Velocity

10S 10S 10S10N 10N 10N

30N30N30N 30S30S30S

LEVITUS

SIMUL

RA6

GODAS

too fresh

Mean Salinity at 165oE

large biases SIMULTAO

Mean Zonal Velocity

RA6

GODAS

SIMUL

large improvement in Atlantic

• Assimilate more observations: Altimetry sea level, Argo salinity

• Reduce forward model errors: MOM4, sea level model

• Improve ocean data assimilation scheme: Geostrophic balance

Argo temp + Argo salinity

Argo temp + synthetic salinity

Developmental GODAS

MJO-related Oceanic Kelvin Waves and the ENSO Cycle: A Study with the NCEP Global Ocean Data Assimilation System

Kyong-Hwan Seo and Yan Xue, GRL, 2005

GODAS (MOM V.3)

Grid: Quasi-global, 40 vertical levels.

Physics: KPP boundary layer mixing scheme, free surface.

Forcing: Wind stress, heat flux, E-P fromReanalysis 2, 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.

RA6 (MOM V.1)

Grid:Pacific basin, 27 vertical levels.

Physics: Richardson number based scheme, rigid lid.

Forcing: combining anomalies from FSU windswith Hellerman and Rosenstein climatology, no E-P flux, no constraint on SSS.

Assimilation method: 3D VAR, analyzes temperature only, fixed error covariance prior toTOPEX era.

Assimilation data:Temperature profile data from XBTs,profiling floats (Argo), moorings(TAO), TOPEX sea level since1993.