The ECMWF coupled data assimilation system

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1 The ECMWF coupled data assimilation system Patrick Laloyaux Acknowledgments: Magdalena Balmaseda, Kristian Mogensen, Peter Janssen, Dick Dee August 21, 214 Patrick Laloyaux (ECMWF) CERA August 21, / 24

2 Outline ECMWF has started to develop a coupled assimilation system in 213 Joint effort between Reanalysis and Marine Prediction sections A first prototype has been implemented: CERA system (Coupled ECMWF ReAnalysis) Table of contents: 1 Description of the CERA system 2 Single observation experiments 3 Comparison with an uncoupled assimilation system 4 Impact on medium-range forecast skill 5 Influence of scatterometer data Patrick Laloyaux (ECMWF) CERA August 21, / 24

3 Table of Contents 1 Description of the CERA system 2 Single observation experiments 3 Comparison with an uncoupled assimilation system 4 Impact on medium-range forecast skill 5 Influence of scatterometer data Patrick Laloyaux (ECMWF) CERA August 21, / 24

The ECMWF coupled model The CERA system is based on the ocean-wave-atmosphere coupled model used at ECMWF in seasonal forecasting medium-range/monthly ensemble forecasting Sequential calling of each

4 The ECMWF coupled model The CERA system is based on the ocean-wave-atmosphere coupled model used at ECMWF in seasonal forecasting medium-range/monthly ensemble forecasting Sequential calling of each component within the same executable Coupling frequency is set to one hour Prescribed sea-ice using an external analysis (work in progress to include a sea-ice model) Patrick Laloyaux (ECMWF) CERA August 21, / 24

5 The CERA system Incremental variational approach: A common 24-hour assimilation window Coupled model to compute observation misfits Increments computed separately and in parallel Separate background-error covariance model Sea Surface Temperature: SST relaxation scheme towards a daily SST analysis product Model resolution: Atmosphere: horizontal grid with 137 levels Ocean: 1 horizontal grid with 42 levels (first layer of 1 meters) Wave: 1.5 horizontal grid Experiments: Run successfully on short recent periods Patrick Laloyaux (ECMWF) CERA August 21, / 24

6 Observations assimilated in the CERA system (September 21) Ocean observation type Ocean variable Number of daily assimilated observations CTD/ARGO/Moorings Temperature 25k Salinity 25k XBT Temperature 1k Atmospheric observation type Atmospheric variable Weather stations Surface pressure 1k Ships and buoys Surface pressure 22k 1m wind direction/force 7k Radiosondes and profilers upper air wind direction/force 23k upper air temperature 55k Specific humidity 3k Aircraft report Upper air wind direction/force 3k Temperature 15k Satellite sounding Radiance 26k Radio occultation bending angle 4k 1m wind direction/force 7k Atmospheric motion winds 2k Wave observation type Wave variable Altimeters Wave height 6k Land observation type Land variable Weather stations 2m Temperature 3k 2m relative humidity 3k Snow depth 1k Satellite sounding Snow cover 2k Patrick Laloyaux (ECMWF) CERA August 21, / 24

7 Table of Contents 1 Description of the CERA system 2 Single observation experiments 3 Comparison with an uncoupled assimilation system 4 Impact on medium-range forecast skill 5 Influence of scatterometer data Patrick Laloyaux (ECMWF) CERA August 21, / 24

8 Model level Ocean single observation experiment Time step : h atmospheric temperature increment Experiment setup: No atmospheric assimilation No SST nudging One temperature observation at 5-meter depth ( N,14 W) with an innovation of 3 C tn Z mean 2 4 Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -.1, Max=.39, Int= ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

9 Model level Ocean single observation experiment Time step : 6h atmospheric temperature increment Experiment setup: No atmospheric assimilation No SST nudging One temperature observation at 5-meter depth ( N,14 W) with an innovation of 3 C tn Z mean 2 4 Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -.1, Max=.39, Int= ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

10 Model level Ocean single observation experiment Time step : 12h atmospheric temperature increment Experiment setup: No atmospheric assimilation No SST nudging One temperature observation at 5-meter depth ( N,14 W) with an innovation of 3 C tn Z mean 2 4 Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -., Max=.39, Int= ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

11 Model level Ocean single observation experiment Time step : 18h atmospheric temperature increment Experiment setup: No atmospheric assimilation No SST nudging One temperature observation at 5-meter depth ( N,14 W) with an innovation of 3 C tn Z mean 2 4 Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -., Max=.38, Int= ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

12 Model level Ocean single observation experiment Time step : 24h atmospheric temperature increment Experiment setup: No atmospheric assimilation No SST nudging One temperature observation at 5-meter depth ( N,14 W) with an innovation of 3 C tn Z mean 2 4 Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -.1, Max=.33, Int= ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

13 Model level Ocean single observation experiment Time step : 24h atmospheric temperature increment Experiment setup: No atmospheric assimilation No SST nudging One temperature observation at 5-meter depth ( N,14 W) with an innovation of 3 C Depth (m) tn Z mean W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -.1, Max=.33, Int=.1 Ocean observations affect: the second atmospheric trajectory the second atmospheric increment the atmospheric analysis The CERA system generates ocean-atmosphere correlations within the incremental variational approach ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

Atmospheric single observation experiment Experiment setup: No ocean assimilation No SST nudging Single location ( N,14 W) - hourly measurements of

14 Atmospheric single observation experiment Experiment setup: No ocean assimilation No SST nudging Single location ( N,14 W) - hourly measurements of a 1m/s westward wind Background surface wind Observations are stronger to affect the atmosphere Patrick Laloyaux (ECMWF) CERA August 21, / 24

15 Model level Atmospheric single observation experiment Time step : h Zonal wind increment Experiment setup: No ocean assimilation No SST nudging 24 wind observations - hourly measurements ( N,14 W) 1m/s westward wind tn Z mean Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min=.e+, Max=.e+, Int= 5.e ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

16 Model level Atmospheric single observation experiment Time step : 6h Zonal wind increment Experiment setup: No ocean assimilation No SST nudging 24 wind observations - hourly measurements ( N,14 W) 1m/s westward wind tn Z mean Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -2.1e-2, Max= 7.8e-3, Int= 1.e ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

17 Model level Atmospheric single observation experiment Time step : 12h Zonal wind increment Experiment setup: No ocean assimilation No SST nudging 24 wind observations - hourly measurements ( N,14 W) 1m/s westward wind tn Z mean Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -4.e-2, Max= 2.e-2, Int= 1.e ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

18 Model level Atmospheric single observation experiment Time step : 18h Zonal wind increment Experiment setup: No ocean assimilation No SST nudging 24 wind observations - hourly measurements ( N,14 W) 1m/s westward wind tn Z mean Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -.8, Max=.6, Int= ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

19 Model level Atmospheric single observation experiment Time step : 24h Zonal wind increment Experiment setup: No ocean assimilation No SST nudging 24 wind observations - hourly measurements ( N,14 W) 1m/s westward wind tn Z mean Depth (m) W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -.8, Max=.8, Int= ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

20 Model level Atmospheric single observation experiment Time step : 24h Zonal wind increment Experiment setup: No ocean assimilation No SST nudging 24 wind observations - hourly measurements ( N,14 W) 1m/s westward wind Depth (m) tn Z mean 18 16W 14W 12W 1W 8W latitudes in [-1., 1.] - (7 points) (): Min= -.8, Max=.8, Int=.1 Atmospheric observations affect: the second ocean trajectory the second ocean increment the ocean analysis The CERA system generates ocean-atmosphere correlations within the incremental variational approach ocean temperature increment Patrick Laloyaux (ECMWF) CERA August 21, / 24

21 Table of Contents 1 Description of the CERA system 2 Single observation experiments 3 Comparison with an uncoupled assimilation system 4 Impact on medium-range forecast skill 5 Influence of scatterometer data Patrick Laloyaux (ECMWF) CERA August 21, / 24

22 Baseline for comparison Coupled assimilation system [CERA] ECMWF operational-like assimilation system [OPER] Same resolution (1 grids) and model version Same assimilation window (24 hours) Same number of outer and inner iterations Different dynamical model in the variational method Different treatment of the atmospheric boundary condition Patrick Laloyaux (ECMWF) CERA August 21, / 24

Atmospheric temperature over land (September 21) Distribution of conventional temperature observations (surface - 7 hpa) CERA compared to OPER - Analysis RMSE (dashed lines) and background RMSE

23 Atmospheric temperature over land (September 21) Distribution of conventional temperature observations (surface - 7 hpa) CERA compared to OPER - Analysis RMSE (dashed lines) and background RMSE (solid lines) Extra-tropical Northern Hemisphere Tropics Extra-tropical Southern Hemisphere The CERA analysis is consistent with the OPER system About the same number of assimilated observations The CERA background is better in the Tropics and in the Extra-tropical Southern Hemisphere Patrick Laloyaux (ECMWF) CERA August 21, / 24

Atmospheric temperature over sea (September 21) AMSU-A Microwave radiometer provides brightness temperature observations over ocean Extra-tropical Northern Hemisphere Tropics Extra-tropical Southern

24 Atmospheric temperature over sea (September 21) AMSU-A Microwave radiometer provides brightness temperature observations over ocean Extra-tropical Northern Hemisphere Tropics Extra-tropical Southern Hemisphere Reduction in the CERA background RMSE with respect to AMSU-A channel 5 (%) Significant benefit over Tropical oceans Neutral impact in Extra-tropical regions Negative impact in some locations Patrick Laloyaux (ECMWF) CERA August 21, / 24

Ocean temperature (September 21) Distribution of temperature profiles (ARGO, moorings, CTD, XBT and seals) CERA compared to OPER - Analysis RMSE (dashed lines) and background RMSE (solid lines) Ocean

25 Ocean temperature (September 21) Distribution of temperature profiles (ARGO, moorings, CTD, XBT and seals) CERA compared to OPER - Analysis RMSE (dashed lines) and background RMSE (solid lines) Ocean depth Extra-tropical Northern Hemisphere () 5467 () 5795 (7) 5164 () 5285 () 4775 (1) 7222 (4) 764 (1) 6295 (-6) 1676 (-8) 8755 () Ocean depth Tropics (6) (11) (11) 2236 (7) (11) 1933 (4) 2642 (22) (22) (12) (18) (21) Ocean depth Extra-tropical Southern Hemisphere () 1873 () () 9873 () 1179 () 8549 (1) (1) (1) 156 (9) (18) (5) (-1) (18) (15) (9) The CERA system reduces significantly the analysis and background RMSE About the same number of assimilated observations (15) (1) Patrick Laloyaux (ECMWF) CERA August 21, / 24

26 Table of Contents 1 Description of the CERA system 2 Single observation experiments 3 Comparison with an uncoupled assimilation system 4 Impact on medium-range forecast skill 5 Influence of scatterometer data Patrick Laloyaux (ECMWF) CERA August 21, / 24

27 Impact of the coupled model on the SST forecast (September 21) Uncoupled forecast initialized by OPER Analysis: SST prescribed Forecast: persisted SST anomaly Coupled forecast initialized by OPER Analysis: SST from ocean component (relaxation) Forecast: SST evolves in the coupled model North Atlantic North Pacific Tropics Extra-tropical Southern Hemisphere Initial RMSE larger in the coupled forecast, but smaller error growth Patrick Laloyaux (ECMWF) CERA August 21, / 24

A larger initial RMSE with a smaller error

21, 214 14 / 24 Impact of the coupled model on

RMSE with a large error growth RMSE evolution

28 A larger initial RMSE with a smaller error growth Patrick Laloyaux (ECMWF) CERA August 21, / 24 Impact of the coupled model on the SST forecast RMSE evolution in the Uncoupled forecast initialized by OPER Forecast + h Forecast + 24h A small initial RMSE with a large error growth RMSE evolution in the Coupled forecast initialized by OPER Forecast + h Forecast + 24h

29 Impact of the coupled analysis on the SST forecast Uncoupled forecast initialized by OPER Analysis: SST prescribed Forecast: persisted SST anomaly Coupled forecast initialised by CERA Analysis: coupled analysis (SST relaxation) Forecast: SST evolves in the coupled model North Atlantic Coupled forecast initialized by OPER Analysis: ocean component (SST relaxation) Forecast: SST evolves in the coupled model North Pacific Tropics Extra-tropical Southern Hemisphere Coupled CERA forecast are consistent with the coupled OPER forecast CERA coupled analysis has small impacts on the SST forecast Patrick Laloyaux (ECMWF) CERA August 21, / 24

Impact of the coupled analysis on the temperature forecast (at 1 hpa) Coupled forecast initialised by CERA and Coupled forecast initialized by OPER Extra-tropical Northern Hemisphere Tropics

30 Impact of the coupled analysis on the temperature forecast (at 1 hpa) Coupled forecast initialised by CERA and Coupled forecast initialized by OPER Extra-tropical Northern Hemisphere Tropics Extra-tropical Southern Hemisphere CERA coupled analysis has small impacts on the temperature forecast No evidence that the OPER uncoupled analysis is unbalanced, producing initialisation shocks Coupled hindcast shocks and drifts following uncoupled initialisation by David Mulholland (SCI-POW137) initialisation shocks are sensitives to model versions used for analysis vs forecasts Patrick Laloyaux (ECMWF) CERA August 21, / 24

31 Table of Contents 1 Description of the CERA system 2 Single observation experiments 3 Comparison with an uncoupled assimilation system 4 Impact on medium-range forecast skill 5 Influence of scatterometer data Patrick Laloyaux (ECMWF) CERA August 21, / 24

Impact of scatterometer data Coupled assimilation system [CERA] ECMWF operational-like assimilation system [OPER] 4 different systems: CERA - All the ocean and atmospheric observations are

32 Impact of scatterometer data Coupled assimilation system [CERA] ECMWF operational-like assimilation system [OPER] 4 different systems: CERA - All the ocean and atmospheric observations are assimilated CERA/NOSCATT - CERA system withholding scatterometer data OPER - All the ocean and atmospheric observations are assimilated OPER/NOSCATT - OPER system withholding scatterometer data Patrick Laloyaux (ECMWF) CERA August 21, / 24

33 Experiment setup Timeline of scatterometer data assimilated at ECMWF ASCAT-B OSCAT ASCAT-A QuickSCAT ERS-2 ERS Impact study carried out from September 213 to November 213 Patrick Laloyaux (ECMWF) CERA August 21, / 24

34 Mean 1m wind (Sep-Nov. 213) CERA/NOSCATT analysis OPER/NOSCATT analysis Impact of scatterometer assimilation on 1m wind CERA analysis - CERA/NOSCATT analysis OPER analysis - OPER/NOSCATT analysis Similar patterns in both systems Patrick Laloyaux (ECMWF) CERA August 21, / 24

Verification against buoys wind observations (Sep-Nov.

assimilation (%) RMSE(CERA/NOSCATT)=2.157 RMSE(CERA)=2.15 REDUCTION=.

25% Reduction in the 1m meridional wind background RMSE due to scatterometer

75% RMSE(OPER/NOSCATT)=2.111 RMSE(OPER)=2.97 REDUCTION=.

35 Verification against buoys wind observations (Sep-Nov. 213) Reduction in the 1m zonal wind background RMSE due to scatterometer assimilation (%) RMSE(CERA/NOSCATT)=2.157 RMSE(CERA)=2.15 REDUCTION=.35% RMSE(OPER/NOSCATT)=2.153 RMSE(OPER)=2.148 REDUCTION=.25% Reduction in the 1m meridional wind background RMSE due to scatterometer assimilation (%) RMSE(CERA/NOSCATT)=2.126 RMSE(CERA)=2.88 REDUCTION=1.75% RMSE(OPER/NOSCATT)=2.111 RMSE(OPER)=2.97 REDUCTION=.65% Positive impact of scatterometer assimilation in the two systems Slightly larger RMSE reduction in the CERA system Patrick Laloyaux (ECMWF) CERA August 21, / 24

36 Impact on the surface ocean currents (Nov. 213) Impact of scatterometer assimilation on zonal speed (surface) Latitude 3N 2N 1N 1S 2S 3S CERA/SCATT - CERA/NOSCATT vozocrtx - monthly mean E 16W 6W (m/s): Min= -.27, Max=.42, Int=.5 Latitude 3N 2N 1N 1S 2S 3S OPER/SCATT - OPER/NOSCATT vozocrtx - monthly mean E 16W 6W (m/s): Min= -.15, Max=.43, Int= Impact of scatterometer assimilation on meridional speed (surface) Latitude 3N 2N 1N 1S 2S 3S CERA/SCATT - CERA/NOSCATT vomecrty - monthly mean E 16W 6W (m/s): Min= -.32, Max=.32, Int=.5 Latitude 3N 2N 1N 1S 2S 3S OPER/SCATT - OPER/NOSCATT vomecrty - monthly mean E 16W 6W (m/s): Min= -.23, Max=.21, Int=.5 out_map1) Aug out_map1) Aug Larger ocean feedback in the CERA system (due to the coupled model) Patrick Laloyaux (ECMWF) CERA August 21, / 24

37 E 16W 6W 1E 16W 6W Impact on the ocean temperature (Meridional section at 5 N Nov. 213) latitudes in [4., 6.] - (6 points) (deg C): Min=.81, Max= 3.2, Int= latitudes in [4., 6.] - (6 points) (deg C): Min=.81, Max= 3.2, Int= 2. CERA/NOSCATT OPER/NOSCATT votemper - monthly mean votemper - monthly mean Depth (m) 2 25 Depth (m) E 16W 6W latitudes in [4., 6.] - (6 points) (deg C): Min=.81, Max= 3.23, Int= E 16W 6W latitudes in [4., 6.] - (6 points) (deg C): Min=.81, Max= 3.25, Int= out_section1) Aug CERA - CERA/NOSCATT votemper - monthly mean out_section1) Aug OPER - OPER/NOSCATT votemper - monthly mean Depth (m) 2 25 Depth (m) E 16W 6W latitudes in [4., 6.] - (6 points) (deg C): Min= -1.69, Max= 1.4, Int= E 16W 6W latitudes in [4., 6.] - (6 points) (deg C): Min= -1.2, Max= 1.73, Int= Temperature feedback follows the thermocline in the two systems Larger temperature feedback in the CERA system Patrick Laloyaux (ECMWF) CERA August 21, / 24

38 Verification against ocean EN3 temperature observations (Nov. 213) CERA compared to OPER - analysis NOSCATT (solid lines) and analysis (dashed lines) Ocean depth Tropical Indian.6.8 CERA NOSCATT CERA OPER NOSCATT OPER (;;) 5421 (;;) 5539 (;;) 518 (;;) 4919 (;;) 423 (;;) 5465 (;;) 5313 (;;) 3743 (;;) 5449 (;;) Ocean depth Tropical West Pacific CERA NOSCATT CERA OPER NOSCATT OPER (;;) 5768 (;;) 657 (;;) 5681 (;2;) 5567 (;;) 5278 (;;) 685 (-2;-5;-5) 6662 (;;) 5174 (;;) 797 (;;) The CERA system reduces significantly the analysis and background RMSE (as in September 21) 5 Tropical East Pacific 2411 (;;) 4693 (4;5;6) 4978 (1;4;6) 4799 (;-2;-2) 5 Tropical Atlantic 166 (;;) 2283 (;;) 247 (;;) 2249 (;;) Similar improvement in the two systems due to scatterometer assimilation Ocean depth (;-1;-1) 475 (2;;2) 5364 (4;-6;-2) 5329 (4;-8;-8) Ocean depth (;;) 293 (;1;1) 2742 (;1;1) 243 (;;) CERA NOSCATT CERA OPER NOSCATT OPER (;;) 6547 (;;) CERA NOSCATT CERA OPER NOSCATT OPER (;;) 33 (;;) Patrick Laloyaux (ECMWF) CERA August 21, / 24

39 Conclusions and perspectives The CERA system performs well in technical and scientific assessments over short periods: small improvements in the atmosphere compared to the OPER-like system significant improvements in the ocean compared to the OPER-like system Challenges: illustrate the possible reduction in initialisation shocks due to the coupled analysis illustrate the better use of near-surface observations Future productions: Production of an extended climate reanalysis spanning the 2th-century (1 resolution) Production of a reanalysis of the satellite era (.25 resolution) Patrick Laloyaux (ECMWF) CERA August 21, / 24

The Coupled Earth Reanalysis system [CERA]

The Coupled Earth Reanalysis system [CERA] Patrick Laloyaux Acknowledgments: Eric de Boisséson, Magdalena Balmaseda, Dick Dee, Peter Janssen, Kristian Mogensen, Jean-Noël Thépaut and Reanalysis Section