GODAE Final Symposium, 12 – 15 November 2008, Nice, France Ocean State Estimation for Climate Research Tong Lee, NASA JPL Toshiyuki Awaji, Kyoto University Magdalena Balmaseda, ECMWF Eric Greiner, CLS Detlef Stammer, Universität Hamburg

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Three streams of GODAE efforts Operational ocean analysis and forecast (presentations by Hurlburt et al. & Kamachi et al.) Initialization of seasonal-interannual prediction (presentation by Balmaseda et al.) State estimation for climate research (this presentation)

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Estimation Systems Models: MOMx, POP, MITOGCM, OPA/NEMO, etc. Data constraints: SSH, T/S profiles, SST, SSS, velocity data, … elephant-seal data. Assimilation methods: OI, 3D-VAR, Kalman filters (and smoother), adjoint (4D-VAR). Presentations by Dombrowsky et al. by Cummings et al. for further individual descriptions.

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Science Applications A large number of applications over a wide range of subjects (from physical oceanography & climate to biogeochemistry & geodesy). Examples (physical oceanography related) Meridional overturning circulation (MOC) (e.g., Lee & Fukumori ‘03, Schoenefeldt & Schott ‘06, Schott et al. ‘07 & ‘08, Wunsch & Heimbach ‘06, Balmadeda et al. ‘07, Cabanes et al. ‘08, Köhl & Stammer ’08, Rabe et al. ‘08) Water-mass pathways (e.g., Fukumori et al. ‘04, Wang et al. ‘04, Masuda et al. ‘06, Toyoda et al. ‘08) Heat budget (e.g., Kim et al ‘04, ‘06, ‘07, Halkides & Lee ’08-a & ‘08-b) Sea level (SSH) variability (e.g., Carton et al. ‘05, Wunsch et al. ‘07, Köhl & Stammer ‘08) Intercomparison

3-D structure of the anomalous subtropical cell (STC) of the Pacific Ocean Pacific Ocean STC Conventional bird’s eye view Poleward Ekman flow Equatorward thermocline flow N 10S10N Tradewind anomaly Conventional 2-D view via meridional transport stream function Poleward Ekman flow Interior thermocline flow Poleward Ekman flow LLWBC flow New view: 3-D structure Lower branch of the STC has a zonal structure characterized by anti-correlated anomalies of boundary & interior flows, thus opposite roles in regulating tropical heat content (Lee & Fukumori 2003, Schott et a. 2007) Poleward Ekman flow Equatorward thermocline flow Poleward Ekman flow

GODAE Final Symposium, 12 – 15 November 2008, Nice, France How do satellite data help constrain estimates of the anti-correlated boundary & interior flows Observed SSHA suggest local recirculation in w. Pacific causing anti-correlated boundary & interior flows (Lee & Fukumori 2003, Lee & McPhaden 2008). Need to monitor LLWBCs, which are not well sampled by existing in-situ systems. Trend of SSH

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Anti-correlated anomalies of boundary & interior flows in G-ECCO product Schott, Wang, & Stammer (2007) confirms finding of Lee & Fukumori (2003) (shorter period) 10°N 10°S

GODAE Final Symposium, 12 – 15 November 2008, Nice, France The North Atlantic Meridional Overturning Circulation (MOC) Picture from

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Interannual variation of MOC in subtropical N. Atl. is correlated with pycnocline depth difference Δh between west & east coasts Pycnocline depth difference across basin MOC anomaly at 1000 m Δh variation dominated by W.B. (mainly due to near local wind) Interannual variation of N. Atl. MOC: mechanism & fingerprinting (Cabanes, Lee, and Fu 2008) Normalized time series (by std. dev.) ΔSSH is not indicative of subtropical N. Atl. MOC variation because of dominant steric contribution in the upper 200 m

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Decadal change of N. Atl. MOC at 26N estimated by an ECCO-GODAE product (Wunsch & Heimbach 2006) Complex vertical structure: Weakening northward transport above 1000 m Strengthening southward transport of NADW Strengthening northward transport of abyssal water No significant decrease of northward heat transport (upper-ocean warming enhances vertical temperature gradient to offset weakening of upper MOC). Opposite trends of MOC strength at 26N & 50N.

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Decadal change of N. Atl. MOC at 26N estimated by ECMWF ocean reanalysis product (Balmaseda, Smith, and Haines, et al. 2007) Assimilation improves comparison with observational analysis Bryden et al. (2005) Cunningham et al. (2007) Large month-to-month variability and related uncertainty in model & data. Complex structure of trends (both in vertically & meridionally). Upper-ocean warming enhances vertical T gradient to offset weakening MOC.

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Using passive tracer adjoint to study water-mass pathways Origin of “NINO-3” waters: Fukumori, Lee, Cheng, & Menemenlis 2004) Other Other examples: Wang et al. (2004): cause for interannual co-variability of T & S in the cold tongue. Toyoda et al. (2008): interannual variation of subtropical Pacific mode water.

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Global sea level rise in SODA ocean reanalysis (Carton, Giese, and Grodsky 2005) The apparent acceleration of sea level rise in1990s was explainable to by fluctuations in warming and thermal expansion of the oceans (upper 1000 m) Levitus et al Miller & Douglas 2004

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Studying patterns of decadal trend ( ) of SSH in an ECCO-GODAE product (Wunsch, Ponte, & Heimbach 2007) Zonal sums of trends in ρ (a), T (b) and S (c) over various depth ranges showing non-negligible contributions from below 850 m (a) (b) (c) Observational errors & potential impact on state estimation

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Physically consistent state estimation allows budget closure – important to climate diagnostic analysis Mixed-layer temperature (MLT) budget: Kim, Lee, & Fukumori (2004): N. Pac. SST warming during Budget for MLT interannual anomaly Ocean dynamics contributed to the mid-latitude warming significantly.

GODAE Final Symposium, 12 – 15 November 2008, Nice, France CLIVAR/GODAE global ocean reanalysis product evaluation: the ability to detect climate signals. Many thanks to various groups for providing a large number of indices & participate the discussion; several analysts for performing the intercomparison; APDRC/IPRC (Peter Hacker’s group) for assistance. Examples … Intercomparison - climate time scales (presentation by Hernandez et al. for shorter time scales)

Comparison for anomaly of ITF volume transport among 13 ocean reanalysis products ( ) r.m.s. diff. 1 Sv r.m.s. diff. 2 Sv r.m.s. diff. 1 Sv

Ensemble mean: 13.8 r.m.s. difference of time mean: 3.7 Averaged temporal variability (>monthly) of different products: 3.6 r.m.s. difference of anomalies: 1 - seasonal, 2 - non-seasonal, 1 - interannual r.m.s. diff. for time mean larger than that for anomaly. “Signal-to-noise” ratio > 1 Requirements for observational accuracy (e.g., from INSTANT observations) to distinguish different products (also have statistics for T & S fluxes). Statistics of ITF volume transport comparison for the 13 products (all in Sv)

GODAE Final Symposium, 12 – 15 November 2008, Nice, France EQPAC EQATL EQIND TRPAC TRATL NPAC NATL GLOBAL T300: T300: S300: S300: Signal/Noise ratio of upper 300m averaged T & S in various regions for 20 products (Balmaseda & Weaver 2008) How well do ocean reanalysis detect climate variability? --- Signal/Noise Ratio

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Time evolution & ensemble spread of upper 300m mean T & S for 20 products (Balmaseda & Weaver’08) The colored envelopes (or their differences) indicate the spread due to different forcing, model, or assimilation methods

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Challenges ahead Model physics Model & data errors Physical consistency for sequential/filter methods Control space for adjoint & Green’s function methods Coupled assimilation Resources issues

GODAE Final Symposium, 12 – 15 November 2008, Nice, France Summary Significant advancement in ocean state estimation for climate research has been achieved in the past decades. Global ocean synthesis evaluation help identify pros & cons. Ongoing challenges require sustained resources and effort & collaboration with a broader community.