GFDL, NCEP, & SODA Upper Ocean Assimilation Systems

Transcription

1 GFDL, NCEP, & SODA Upper Ocean Assimilation Systems Jim Carton (UMD) With help from Gennady Chepurin, Ben Giese (TAMU), David Behringer (NCEP), Matt Harrison & Tony Rosati (GFDL) Description Goals Products Some results from examining the current products

2 NCEP Global Ocean Data Assimilation System (GODAS) Model: GFDL MOM3 Grid: Quasi-global domain extending from 75 o S to 65 o N; zonal resolution is 1 o poleward of 30 o increasing to 1/3 o within 10 o of the equator; 40 vertical levels; 10 meter resolution in the top 200 meters. Physics: KPP mixing; GM isoneutral mixing of tracers; nonlinear horizontal viscosity; explicit free surface; variable thickness bottom cell Forcing: wind stress, heat flux, E-P (NCEP Reanalysis 2 or operational GDAS); SST relaxed to NCEP SST analysis; SSS relaxed to Levitus climatology Method: 3D Var; background error variance varies geographically and temporally Data: Temperature (XBTs, Argo floats, TAO/Triton moorings), synthetic salinity profiles Period: pres

3 NCEP GODAS OGCM Global MOM v.3 Surface Fluxes: Momentum Heat E - P Data Assimilation 3D VAR Analyzed Fields: Temperature Salinity Observations: XBTs TAO P-Floats Altimetry Oceanic I.C.for Coupled Model Statistical Models CCA, Markov ENSO Monitoring

4 Longer term goals, such as improvements to the current assimilation system and its eventual replacement, will be accomplished through partnerships with other organizations. NCEP Goals Replacement of the present Pacific Ocean data assimilation system and Pacific Ocean - global atmosphere coupled forecast model. GODAS becomes operational in September It is currently running in parallel mode. The new coupled forecast model (CFM) becomes operational within the next year. It couples the global ocean model as used in GODAS with the atmospheric model from the current version of NCEP s Global Forecast System (GFS). The CFM is currently being used to generate hindcasts for present.

5 NCEP GODAS products An ocean reanalysis extending from 1979 through the present has been completed. It is forced by daily fluxes from the NCEP Reanalysis 2 and saved at 5-day intervals. Operational ocean analyses are forced by daily fluxes from the NCEP GDAS and saved at daily intervals.

6 GFDL (see previous talk) Model: MOM3 MOM4 Grid: Quasi-global domain extending from 75 o S to 65 o N; zonal resolution is 1 o poleward of 30 o increasing to 1/3 o within 10 o of the equator; 40 vertical levels; 10 meter resolution in the top 200 meters. Physics: KPP& MY mixing; GM isoneutral mixing of tracers; nonlinear horizontal viscosity; Forcing: wind stress, heat flux, E-P (NCEP Reanalysis 2 or operational GDAS); SST relaxed to NCEP SST analysis; SSS relaxed to Levitus climatology Method: 3D VAR Data: XBT, SSH PERIOD: present

7 Simple Ocean Data Assimilation (SODA) Model: POP-2 Grid: Global displaced pole with 0.4 o x 0.25 o tropical resolution, 25km resolution in Western North Atlantic, 50 levels (5m nearsurface) Physics: KPP, nonlinear viscosity Forcing: NCEP/NCAR reanalysis, ECMWF ERA40, GPCP precip, WMO river discharge, microwave Sea ice Method: sequential estimation, flow-dependent covariance, explicit bias analysis including bias model Data Hydrography (MBTs, XBTs, CTDs, ARGO, Moored thermistor chains, stations, ship intake) Altimetry (Geosat, T/P, ERS1/2, Jason) Radiance SST Period: 1940s-pres Availability: Latest release ~ December 2003

8 SODA grid (actual resolution is 4x)

9 SODA flowdependent background error

10 SODA Goals and Products Goal Reanalysis of the global ocean focusing on the upper 1000m 1940s pres Products Renalyses available through DODS, IRI, IPRC, etc.

11 What we can learn from comparing analyses Western tropical Atlantic April 15, 1991

12 Data coverage differences Data missing from GFDL TAO Data missing from SODA

13 SODA zonal vel. 0N, 140W SODA 10m 50m OBS 100m 150m

14 SODA meridional vel. 0N, 140W SODA OBS

15 Zonal velocity at 0N, 110W SODA GFDL

16 Gulf Stream in SODA Hydro Observations Sea level

17 RMS sea level Altimeter variability SODA GFDL

18 NCEP may have some problems with AAIW Temperature salinity characteristics SODA lacks precip

19 Forecast Bias f < w w t o > Errors in forcing Errors in initial conditions Errors in physics parameterizations Errors in numerics

20 Time-mean temperature forecast error along 0N SODA GFDL < w f w o t > NCEP

21 SODA annual cycle bias in the mixed layer (without bias correction algorithm) Histogram of < w In the North Pacific f w o > Annual cycle of ML bias June amp Dec phase The summer mixed layer is too cold, the winter mixed layer is too warm

22 SODA impact of bias correction algorithm Without bias correction algorithm With bias correction algorithm amp phase

23 Questions: What resolution in space and time is needed to reasonably represent climate? The coupled system supports a variety of unstable modes. Which of these really need to be resolved? Can we use theory to help us focus on those aspects that really count? (EK) How consistent are the fluxes from atmospheric and oceanic analyses? What do imbalances say about our understanding? What are the causes of different forecast biases? What can we learn from examination of error statistics? E Res

24 For the white paper: Explore data set differences Further algorithm development Mixed layers FWPF (fix worst problem first) Forecast bias (mean, annual, etc.) Flow-dependent covariances Eddy-permitting resolution

25 The End