impacts of ocean observations on ocean (re)analysis and
TRANSCRIPT
© ECMWF November 26, 2020
Impacts of ocean observations on ocean (re)analysis and coupled forecasts
Hao Zuo, Magdalena Alonso Balmaseda, Beena Balan-Sarojini, Christopher Roberts, Michael Mayer, Steffen Tietsche, Patricia de Rosnay
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 2
ECMWF Ocean and sea-ice (re)analysis systemOverview of the OCEAN5 setup
Zuo et al., 2019
OCEAN5 is the 5th generation ofECMWF ocean and sea-ice ensemblereanalysis-analysis system (Zuo et al.,2018, 2019).
• Ocean: NEMOv3.4
• Sea-ice: LIM2
• Resolution: ¼ degree with 75 levels
• Assimilation: 3DVAR-FGAT
• 5 ensemble member
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 3
Ocean in-situ observations used by ECMWF
Ocean in-situ observations in 5-days (After QC, Feb 2019)
0 150 300 450 600
Atmosphere
Ocean
Obs used (M) Obs received (M)
Ocean observation is about 1/1000 to 1/10000 smaller than Atmospheric observation
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 4
~1e6 /day
Sea-Level Anomaly (Altimeter)Sea-ice thickness
Sea-ice concentration
Ocean model
Nudging
SST (IR, PMW)
Nudging3DVar
3DVar
Satellite sea surface observations
~1e6 /day
~1e5 /day
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 5
Ocean observations impact: ocean reanalysis
Temperature RMSE: 0-1000m
MRB: moored buoyOSD: CTD sondeXBT: Expendable bathythermographPFL: Argo float
~65% of the total RMSE reduction comes from assimilating in-situ data
Assimilation of ocean in-situ observations helps to constrain the 3D ocean, therefore providing better estimation of the ocean initial condition for the coupled forecasting system
Model free run
ORAS5With DA
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 6
2.8 33.5
3.8
4.5
S1 S2 S3 S4 S5
Lead
Tim
e (m
onth
s)
Forecast lead month for correlation above 0.9 in NINO3.4 SST anomalies
2.8 33.5 3.8
4.5
3.2
S1 S2 S3 S4 S5 S5-NoOobs
• Gain about 1.3 months in ENSO prediction
• Without Ocean observation and DA, we would lose about 15 years of progress.
1997 2002 2006 2011 2017
OCEAN5 provides ocean and sea-ice initial conditions for all ECMWF coupled forecasting system: (ENS, HRES, seasonal-S5).
Ocean observations impact: ENSO prediction
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 7
Impact on ocean data assimilation system
Maps of normalized RMSD of Temperature (upper 700m) in OSEs
Zuo et al., 2019, Ocean Science
Remove Moored buoys
Remove all in-situ
Remove CTD/XBT/MBT
Remove Argo Remove in-situ only in Atlantic
RMSD w.r.t a reference reanalysis, in which all in-situ data are assimilated.
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 8
Significant degradation in ocean surface and subsurface variables when removing observationsFrom week 1 to week 4
Ocean observations impact: Extended Range
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 9
SIC DA and impact on sea-ice reanalysis
L4 OSTIA Sea-Ice Concentration (SIC) is
assimilated through outer-loop coupling in
NEMO-LIM2, with a 3DVar-FGAT scheme.
This has a positive impact on both SIC and
SIT analysis states.
SIC bias (1980-2016)Ref data: OSI-SAF 430
With SIC DAWithout SIC DA
In percent
In m
SIT bias (2011-2016)Ref data: CS2SMOS merged data
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 10
SIT DA and impact on sea-ice reanalysis
where 𝑆𝐼𝑇! is the nudged thickness, 𝑆𝐼𝑇" is the modelled thickness, 𝑆𝐼𝑇# is the observed thickness (CS2SMOS), tau is the nudging coefficient
No SIT nudging with SIT nudging
Balan Sarojini, et al. The Cryosphere, in review
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 11
SIT DA and impact on sea-ice forecasts
with SIT nudging – No SIT nudging
Spatially integrated SIC mean absolute error over lead month (72 forecasts each first of the month: 2011-2016, verified against OSI-401-b)
Difference in forecast Integrated Ice Edge Error (2011-2016, verified against OSI-401b)
Balan Sarojini, et al. The Cryosphere, in review
Mean absolute error in SIC forecasts
October 29, 2014WMO 7TH WORKSHOP ON THE IMPACT OF VARIOUS OBSERVING SYSTEMS ON NWP 12
Summary and conclusion
Assessments of ocean and sea-ice observation impacts on ocean reanalysis, and coupled reforecasts have also been carried out using the operational ECMWF system.
• Assimilation of ocean observations has a strong positive impact on the performance of ocean reanalysis, with almost 2/3 of the error reduction comes from in-situ data.
• Removal of all ocean observations leads to significant degradation in forecasted ocean states from week 1 to week 4, and has a negative impact (~2 month skill) on coupled forecasts of ENSO prediction.
• Adding sea-ice thickness constrain has reduced the biases in the sea-ice initial conditions, which then leads to improvement on predictive skill of pan-Arctic sea-ice for lead times of up to 7 months.
• Coordinated efforts on developing a experimental framework and analysis methodology for assessing observation impact in ODA and coupled forecasts are needed (see Fujii et al., 2019).
A consistent, homogenous and deep reaching global ocean observing network is absolutely essential for both operational NWP and climate monitoring services.