Improvements in Ocean State Forecasts using

data assimilation in INCOIS

1

Arya Paul Indian National Centre for Ocean Information Services ( INCOIS ) India

Siva Reddy ( INCOIS ) Steve Penny ( Univ. of Maryland ) Eugenia Kalnay ( Univ. of Maryland ) Biswamoy Paul ( INCOIS ) Balaji B. ( INCOIS ) D. S. Banerjee ( INCOIS )

Collaborators:

GOVST - VII 2016

Acknowledgments:

Francis Pavanathara ( INCOIS ) Kunal Chakraborty ( INCOIS ) Abhisek Chatterjee ( INCOIS ) Arnab Mukherjee ( INCOIS )

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INCOIS-GODAS

ROMS (~ 9km)

INCOIS-GODAS (50km zonal & 25km meridional)

MULTI-MODEL “NESTING”

3

ROMS (~9km)

ROMS (2.5km)

ROMS (2.5km)

4

PRESENT STATUS OF ASSIMILATION IN INCOIS

• Global Ocean -- INCOIS – GODAS -- 3D VAR – In-situ T & S Profiles • Indian Ocean -- ROMS 1/12th -- NO ASSIMILATION • Coastal Ocean – ROMS 1/48th -- NO ASSIMILATION

UPCOMING

• Global Ocean -- INCOIS – HYBRID -- GODAS -- 3D VAR + LETKF – In-situ T & S, L2 SST, SSS & SLA • Indian Ocean -- ROMS 1/12th -- LETKF -- In-situ T & S Profiles, CHLA & O2, L2 SST, SSS & SLA • Coastal Ocean – ROMS 1/48th -- LETKF -- In-situ T & S Profiles, CHLA & O2 , L2 SST, SSS & SLA

5 Reference: Stephen Penny et al, Mon. Wea Rev, 143, 4660-4677, (2015)

HYBRIDIZATION

For more info: http://www.incois.gov.in/portal/GODAS

Operational set up of INCOIS-GODAS

References: 1) Ravichandran et al. , 2013, Ocean Modelling 2) Sivareddy et al., 2015, PhD thesis

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HOW DOES INCOIS-GODAS PERFORM ???

SST RMSD: TMIAMSRE vs Model NCEP-GODAS ECMWF-ORAS4

INCOIS-GODAS

Comparisons are based on 2004-2009

Correlation: Tropical Indian Ocean

ECMWF-ORAS4 NCEP-GODAS INCOIS-GODAS

Correlation: Temperature INCOIS-GODAS compares well with ECMWF-ORAS4 both at the surface and sub-surface layers. NCEP-GODAS poses serious issues at sub-surface layers

SSS Correlation: Argo-gridded vs Model NCEP-GODAS ECMWF-ORAS4

INCOIS-GODAS

Comparisons are based on 2004-2009

Tropical Pacific Ocean

ECMWF-ORAS4 NCEP-GODAS INCOIS-GODAS

Correlation: Salinity INCOIS-GODAS compares well with ECMWF-ORAS4 both at the surface and sub-surface layers. NCEP-GODAS poses serious issues at both surface and sub-surface layers

SLA RMSD: Altimeter vs Model

NCEP-GODAS ECMWF-ORAS4

INCOIS-GODAS

Comparisons are based on 2004-2009

INCOIS-GODAS compares reasonably well despite the absence of SLA assimilation.

Currents

Zonal currents at Eq, 80.5E

Correlation: OSCAR vs Model

Zonal currents in ECMWF-ORAS4 and INCOIS-GODAS are comparable to observations. Performance of NCEP-GODAS is inferior to other two

Monthly updates of climate indices are available by 10th of each month. Service is started in April, 2014. The information is being disseminated from the INCOIS web site www.incois.gov.in/portal/ElNino

Climate Indices from INCOIS-GODAS ocean analysis

SST (degC) Anomaly Temperature anomaly (deg C) averaged over 5S-5N latitudes

NiNO 3.4 SST anomaly

IOD index

De

g C

D

eg

C

De

pth

(m

)

Users of INCOIS-GODAS analysis

Analysis are used as initial and boundary conditions to

operational ROMS at INCOIS

Ocean initial conditions are provided to IITM, Pune for CFS-

V2

Global maps of SST and SST anomalies are provided to IMD-

Pune

Climate indices are used in MoES-ENSO bulletins

Researchers across globe

Local Ensemble Transform Kalman Filter

( LETKF )

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Observation Operator

LETKF

Initial background ensemble Observations

Ensemble “observations”

Ensemble analysis

• No model dependency • Each model grid point is simultaneously assimilated. • Very easily parallelized. • No requirement of adjoint.

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Observation based localization(R Localization)

• Data Assimilation is done in a local volume • All the observation within the circle is assimilated. • State is updated at the red dot.

Ref: Greybush et al, Mon. Wea. Rev., 139, 511-522, 2010

System Comparison

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INCOIS GODAS LETKF-MOM

Model MOM4.0 MOM4.1

Resolution 0.5 degree in zonal

0.25 degree in meridional

between 10S & 10N.

0.5 degree in zonal

0.25 degree in meridional

between 10S & 10N.

No. of levels 40 40

Features 1) River RunOff ON

2) Relaxed to REYNOLDS

SST

3) SSS not relaxed

1) River RunOff OFF

2) Relaxed to LETKF derived

SST

3) Relaxed to LETKF derived

SSS

Assimilation Scheme 3D VAR LETKF with 56 ensemble

members

Observations 1) In-situ temp & salinity 1) In-situ temp & salinity

2) Altimeter

3) L2 SST & L2 SSS

Initial Condition Well Trained 2003 IC pretended as 2010

Run Period 2002 onwards till date Jan 03, 2010 – June 15, 2010

Observations

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L2 SST

In-situ T & S L2 SSS

L2 SLA

TEMP Time Series Results

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80.5E,0N,40m

80.5E,8S,40m 90E,15N,40m

80.5E,1.5S,40m

GODAS

obs

Free run

LETKF

TEMP Vertical Profiles

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80.5E,0N,40m

80.5E,8S,40m 90E,15N,40m

80.5E,1.5S,40m

GODAS

obs

Free run

LETKF

SALT Time Series Results

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80.5E,0N,40m

80.5E,8S,10m 90E,15N,40m

80.5E,1.5S,40m

GODAS

obs

Free run

LETKF

SALT Vertical Profiles

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80.5E,0N,40m

80.5E,8S,40m 90E,15N,40m

80.5E,1.5S,40m

GODAS

obs

Free run

LETKF

SLA Correlations

with AVISO

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Free Model

LETKF-MOM

GODAS

SST Correlations with

REYNOLDS

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Free Model

LETKF-MOM

GODAS

System Comparison

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INCOIS GODAS LETKF-ROMS

Model MOM4.0 ROMS 3.6

Resolution 0.5 degree in zonal

0.25 degree in meridional

between 10S & 10N.

~ 10km

No. of levels 40 40

Features 1) River RunOff ON

2) Relaxed to REYNOLDS

SST

3) SSS not relaxed

1) River RunOff OFF

2) SSS relaxed to climatology

3) Fluxes are very coarse (

~200 km resolution )

Assimilation Scheme 3D VAR LETKF with 32 ensemble

members

Observations 1) In-situ temp & salinity 1) In-situ temp & salinity

2) Altimeter

Initial Condition Well Trained 2003 IC pretended as 2010

Run Period 2002 onwards till date Jan 03, 2010 – Nov 25, 2010

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OBSERVATIONS

SLA TRACKS In-situ T & S (Argo + Buoy)

Not many T & S observations in Indian Ocean in 2010!!!

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OBSERVATION FREE RUN

LETKF-ROMS INCOIS-GODAS

STANDARD DEVIATION IN SST

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RMSE of SST

Free LETKF-ROMS

INCOIS-GODAS

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FREE

LETKF-ROMS INCOIS-GODAS

SST CORRELATION WITH REYNOLDS SST

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OBSERVATION FREE RUN

LETKF-ROMS INCOIS-GODAS

STANDARD DEVIATION IN SLA

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Free LETKF-ROMS

INCOIS-GODAS

RMSE of SLA

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SPATIAL RMSE OF SLA ( in meters )

FREE

LETKF-ROMS INCOIS-GODAS

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SLA CORRELATION WITH AVISO

FREE

LETKF-ROMS INCOIS-GODAS

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Obs INCOIS-GODAS FREE LETKF-ROMS

D20

MLD

@ 12 N, 90 E

VERTICAL STRUCTURES

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@ 8S, 95 E

D20

MLD

Obs INCOIS-GODAS FREE LETKF-ROMS

Obs INCOIS-GODAS FREE LETKF-ROMS

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WHY IS LETKF-ROMS INFERIOR TO INCOIS-GODAS ?

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SPREAD IN SST SPREAD IN SSS

SPREAD IN TEMP at 50m SPREAD IN SALT at 50m

Conclusions

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• INCOIS-GODAS is at par with other data assimilation systems. • Hybrid-LETKF improves ocean states and should be explored. • LETKF-MOM is very promising and improves the ocean states as much as INCOIS-GODAS. • LETKF-ROMS performance is inferior to INCOIS-GODAS. • It may be due to (a) Ensemble Collapse (b) Bad Initial Condition (c) Forcings (d) SST relaxation in INCOIS-GODAS (e) Large Localization Radius of 720 km is smoothening out the fields. • Possible remedy lies in training the initial condition and using smaller localization radius

WE STILL HAVE SOME WAY TO GO !!!

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Local Ensemble Transform Kalman Filter ( LETKF )

Forecast Step: a

ktt

b

kt xMx ,1,

Analysis Step: b

k

bbbb

i

b

i

b

k

bbb

yyyYxHy

xxxX

~|...|~|~ ;

; ~|...|~|~

21

21

Localization : Choose the observations to be used for each grid point. Estimate the local error covariance and perturbations in ensemble space.

2/111 ~1 ; 1

~ aaTa PkWYRYIkP

Analysis Mean in the ensemble space : bTaa yyRYPw 01~

The new ensemble analysis in model space are stored in the columns of

bab

t

a

t xwXx

Add to each of the columns of awaW

SUB-SURFACE PERFORMANCE OF ROMS

Surface Salinity at (90E & 1.5S)

Sea level anomaly(cm) at (90E & 1.5S) Surface Temperature at (90E & 1.5S)

• 56 Ensemble Members. • In-situ T & S and satellite data of SST are assimilated. •SSS & SLA not assimilated.

-8

12

8

4

0

-4

Observation Free run Assim. Run.

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Real time (1-day delay) updates of the Global

Ocean from INCOIS-GODAS: 2D fields

SST TCHP

SSHA SSS

NOTE:Plots are of 13th Oct, 2016