Under GODAE OceanView the operational ocean modelling community has developed a suite of global ocean forecast, reanalysis and analysis systems. Each system has a critical dependence on ocean observations – routinely assimilating observations of in-situ temperature and salinity, and satellite sea-level anomaly and sea surface temperature. Under GODAE OceanView (GOV), the Observing System Evaluation Task Team (https://www.godae-oceanview.org/science/task-teams/observing-system-evaluation-tt-oseval-tt/) regularly coordinates analyses from the GOV community to demonstration the value and impact of ocean observations on different global and regional data-assimilating forecast and reanalysis systems. Highlights of the latest suite of demonstrations will be presented here. Results show that Argo data are critically important – the most critical for seasonal prediction, and as critical as satellite altimetry for eddy-resolving applications. Most systems show that TAO data are as important as Argo in the tropical Pacific, and that XBT data have an impact that is comparable to other data types in the vicinity of XBT transects. It is clear that no currently available data type is redundant. On the contrary, the components of the global ocean observing system complement each other remarkably well, providing sufficient information to monitor and forecast the global ocean.

1. Assessing the impact of
observations on ocean forecasts
and reanalyses
Peter Oke and Gilles Larnicol
CSIRO and CLS
May 2015

2. Talk Outline
 GODAE OceanView and the OSEval Task Team
 OSEval-TT mission
 Examples of OSEval activities
 OSEval plans

3. Coastal Ocean and
Shelf Seas Task
Team (COSS-TT)
Pierre De Mey &
Villy Kourafalou
Intercomparison
and Validation Task
Team (IV-TT)
Fabrice Hernandez &
Greg Smith
Marine Ecosystem
Analysis and
Prediction Task
Team (MEAP-TT)
Katja Fennel & Marion Gehlen
Observing System
Evaluation Task
Team (OSEval-TT)
Peter Oke & Gilles Larnicol
Coupled
Prediction Task
Team (CP-TT)
Hal Richie & Chris Harris
Data Assimilation
Task Team (DA-TT)
Matt Martin & Andy Moore

4. OSEval Activities
 Capacity building;
 Routine monitoring;
 Community Observing
System Experiments; &
 Inter-comparisons of
observation impacts.
Co-Chairs:
Peter Oke (CSIRO)
Gilles Larnicol (CLS)
OSEval-TT mission
is to support observational
community by demonstrating
the impact of observations
on ocean forecast and
reanalysis systems
Associate members:
3Fabrice Hernandez (Mercator)
4Matt Martin (UKMet)
5Hans Bonekamp (EUMETSAT)
5Craig Donlon (ESA)
1CLIVAR GSOP rep.
2CGOV OSS-TT rep.
3GOV IV-TT rep.
4GOV DA-TT rep.
5GOV Patron rep.
TT Members:
1Magdalena Balmaseda (ECMWF)
Laurent Bertino (NERSC)
Pat Hogan (NRL)
Yosuke Fujii (JMA/MRI)
2Villy Kourafalou (UMiami)
Daniel Lea (UKMet)
Elisabeth Remy (Merc. Oc.)
Greg Smith (EnvC)
Clementa Tanajura (REMO)
Guimei Liu (NMEFC)

5. OSEval meetings
Paris – 2007 … OSEval-TT founded
Toulouse – 2009
Towards routine monitoring
Toulouse – 2014 … OSEval & E-AIMS & CLIVAR/GSOP
Santa Cruz – 2011 … OSEval & inter-comparisons

6. Some OSEval activities are simple
and practical – just involving model
inter-comparisons

7. Numberofbuoys
returningdata
Totaldatareturn
(%)
2010 2011 2012 2013
JMA example of inter-comparisons
demonstrating obs impacts
2010 2011 2012 2013

8. JAS 2010: Complete TAO array  agreement between systems  high confidence
JMA example of inter-comparisons
demonstrating obs impacts
TAO observations are essential for seasonal prediction
Fujii et al. (2014; QJRMS) – TPOS community paper
JAS 2013: Degraded TAO array  disagreement between systems  low confidence

9. Some diagnostics from data
assimilation systems quantify the
impacts of assimilated observations:
… they’re inexpensive to calculate
… but they’re not easily understood
… we’re working on making these
meaningful to everybody

10. TOPAZ example of obs-
impact diagnostics
 100-member EnKF;
 Assimilating SLA, SST, ice
concentration & drift, T/S - ~400K
obs/week
 We can compute inexpensive
diagnostics for every assimilation
cycle to show the impact of every
observation
 Helps identify bad observations or
under-sampling … where obs have
significant impact
SRF = Spread Reduction Factor …
quantifies how much each observation
reduces analysis error.
Higher SRF  greater impacts Sakov et al. 2012; Ocean Science
Impact of altimetry
Impact of SST
Impact of Ice Concentration
Impact of Ice velocity (u)
Impact of Ice velocity (v)
Impact of temperature (Argo)
Impact of salinity (Argo)

11. Some studies contribute to
discussions about options for
future observational arrays

12. Mercator OSSE example: application to wide-swath altimetry
M. Benkiran
and E. Remy
“Truth” – from a 3 km res
model “J1+J2+En” “7-km SWOT”
Step 1: 3-km model is treated as the true ocean
Step 2: sampling represents traditional and wide-swath altimetry
Step 3: assimilated synthetic “obs” back into model – and assess

13. Mercator OSSE example: application to wide-swath altimetry
M. Benkiran
and E. Remy
0.0 0.5 1.0 0.0 0.5 1.0
0.0 0.5 1.0
No assimilation “J1+J2+En” “7-km SWOT”
Correlation of SSH with “truth” …
Indicates that one SWOT altimeter is better than 3
traditional altimeters for high-resolution forecasting
R= 0.59 R= 0.80R= 0.72

14. Some studies exploit operational
forecasts systems and simply
withhold all, or some,
observations to quantify how the
forecasts degrade with the
missing observations

15. GIOPS example of
OSE: impact of loss
of all observations
Canadian operational ocean
forecast system simulating
the degradation in skill
following a complete loss of
observations …
The system reverts to
the skill of a free model
run over a 3 months
period.
All data: assimilates
altimetry, satellite SST, Argo,
XBT, and data from moorings.
Courtesy of Greg Smith

16. GOV OSEval-TT plans
1. Observation Impact
Statements
1. Annual Community Observing
System Experiments
1. Impact and exploitation of
satellite salinity observations
(proposal to ESA in preparation)

17. Summary
 OSEval-TT community is active – regularly undertaking studies
to assess past, present, or future observing systems
 OSEval-TT has promoted several practical approaches to
observing system evaluation
 Annual community OSEs are planned …
 Broader engagement with the observational community is sought
… how can we help?

18. Community OSEval papers
Fujii, Y., J. Cummings, Y. Xue, A. Schiller, T. Lee, O. Alves, M. Balmaseda, B. Cornuelle, M. Martin, S.
Masuda, P. R. Oke, E. Remy, G. Vernieres, X. Yang, 2015: Evaluation of the Tropical Pacific Observing
System from the Ocean Data Assimilation Perspective, Quarterly Journal of the Royal
Meteorological Society, in press.
Oke, P. R., G. Larnicol, E. M. Jones, V. Kourafalou, A. K. Sperrevik, F. Carse, C. A. S. Tanajura, B. Mourre, M.
Tonani, G. B. Brassington, M. Le Henaff, G. R. Halliwell, Jr., R. Atlas, A. M. Moore, C. A. Edwards, M. J.
Martin, A. A. Stellar, A. Alvarez, P. De Mey, M. Iskandarani, 2014: Assessing the impact of
observations on ocean forecasts and reanalyses: Part 2, Regional applications. Journal of
Operational Oceanography, in press.
Oke, P. R., G. Larnicol, Y. Fujii, G. C. Smith, D. J. Lea, S Guinehut, E. Remy, M. Alonso Balmaseda, T. Rykova,
D. Surcel-Colan, M. J. Martin, A. A. Sellar, S. Mulet, I. Pujol, 2014: Assessing the impact of
observations on ocean forecasts and reanalyses: Part 1, Global studies. Journal of Operational
Oceanography, in press.
Larnicol, G., P. R. Oke, GODAE OceanView Observing System Evaluation (OSEval) Task Team news, 2013:
Mercator Newsletters, 13, 3-5.
Oke, P. R., M. Balmaseda, M. Benkiran, J. A. Cummings, E. Dombrowsky, Y. Fujii, S. Guinehut, G. Larnicol,
P.-Y. Le Traon, and M. J. Martin, 2010: Observational requirements of GODAE Systems. In
Proceedings of OceanObs’09: Sustained Ocean Observations and Information for Society (Vol. 2),
Venice, Italy, 21-25 September 2009, Hall, J., Harrison, D. E. & Stammar, D., Eds., ESA Publication
WPP-306.
Oke, P. R., M. Balmaseda, M. Benkiran, J. A. Cummings, E. Dombrowsky, Y. Fujii, S. Guinehut, G. Larnicol,
P.-Y. Le Traon, and M. J. Martin, 2009: Observing System Evaluations using GODAE systems,
Oceanography, 22(3), 144-153.

19. Annual Community Observing System Experiments
 All GODAE OceanView partners perform a single OSE, once a
year, for community evaluation.
Preliminary schedule of Community OSEs:
Initial time End time Data with-held Due date
7/2013 12/2013 Degraded Argo array (-20%) 4/2015
7/2014 12/2014
X altimeter(s) of the
constellation (TBD)
4/2016
7/2015 12/2015 Tropical moorings 4/2017
7/2016 12/2016 X% of Argo (TBD) 4/2018
7/2017 12/2017
X altimeter(s) of the
constellation (TBD)
4/2019