Physical Chemistry 2 CH4003 Dr. Erzeng Xue CH4003 Lecture Notes 1 (Erzeng Xue)
Operational NCEP Global Ocean Data Assimilation System: The Link, Validation, and Application Part I...
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Transcript of Operational NCEP Global Ocean Data Assimilation System: The Link, Validation, and Application Part I...
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.