HF processes assimilation in a 1/12° regional model (IBI12)godae-data/OceanView/Events/... ·...

HF processes assimilation in a 1/12° regional model (IBI12)

M. Benkiran, C. Dufau (CLS)

and Mercator Ocean Team

http://www.mercator-ocean.fr

[email protected]

Motivation

Mercator Ocean is working on the development of a global model which takes into account the forcing by Tide and Atmospheric pressure. To prepare the assimilation of altimeter data

in accord with these high frequency processes,

We are testing a new assimilation in the regional model which includes Iberia, Biscay and Ireland (IBI12).

Sea Surface Temperature snapshot

IBI12 : Iberia-Biscay-Ireland (1/12°)

• explicit free surface, « time splitting » + Variable volume formulation • k-ε : the Generic Length Scale (GLS) formulation (Umlauf and Burchard, 2003) • Atmospheric Forcing : 3-h ECMWF ; Wind + pressure • Tides (including potential) : • Open boundaries from GLORYS2V1 ¼° reanalysis (daily)

• In situ profiles ,T & S from CORA3.1 data base • Reynolds AVHRR ¼° SST • Along track SLA observations From CMEMS/AVISO , usual

corrections applied filtering of tides in the Observation Operator H

• Reduced order Kalman Filter (SEEK formulation) • 3D-VAR Bias corrections : for T and S • Incremental Analysis Updates (IAU) : Analysis J-2.5 • SST Correction in Bulk • Quality Control of in situ observation

IBI-1/12° NEMO:

Data Assimilation :

Assimilated Observations :

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SLA :Observation

SLA Observation (CMEMS/AVISO), Corrected from geophysical signal

Tide : GOT model (Goddard Ocean Tide model) DAC (Dynamic Atmospheric Correction):

• Objectives of the DAC remove high frequencies signals forced by the atmosphere (pressure and wind) and aliased in altimetric data because of bad temporal sampling of altimeters

• DAC

optimal combination of high frequencies of barotropic model (MOG2D model) and low frequencies of IB: cut-off freq= 20 days

DAC = MOG2D_HF + IB_LF

LWE (Long Wavelength Error) : Residual orbitER, IBER, Residual Tide Corr and Aliased HF signal

SLA = SLAsat - Tide - DAC - LWE


SLA = SLAsat - DAC - LWE - TIDE

-0.4 0 0.4

-0.4 0 0.4

S N

Sla & Correction along track J2(163)

-0.4 0 0.4

(DAC=IBLF+MOG2DHF)

Dac : not negligible; Large Scale Lwe is negligible compared to Dac

(GOT002 model)

-1.0 0 1.0

20

09


High frequency impact

We use a specific altimeter dataset dedicated to assimilation developed within CMEMS (“SLA-assim” issued from the TAPAS initiative). It provides at each along-track point the geophysical corrections We also adapt the model background for each experiment (2009)

Different experiences

LWETIDESLA SLA : Sim_Dac

DACLWETIDESLASLA : Sim_Ref

sat

obs

sat

obs






sat

obs

sat

obs

25h

To remove a DAC

like correction

Estimation of the correction large-scale high frequency (From barotropic part (wind reponse…))

Mean Dynamic

Topography (RIO; CLS)

Sim_Dac


Std (Innovation) in box (0.25x0.25), 2009

0. 8.0 12.0 20.0 Cm

Std(Innovation) in box (0.25x0.25), 2009

0. 8.0 12.0 20.0 Cm 0. 8.0 12.0 20.0 Cm

Impact of the assimilation of HF (SLA):

• Std(Innovation) :

Increase but this Std is not

calculated with the same data

Sim_Ref

Innovation = Data – Model Forecast

Mean = 5.88Cm Mean = 6.84Cm

Std(Innovation)/Std(Data) in box (0.25x0.25), 2009

0.4 0.8 1.2 1.6

Std(Innovation)/Std(Data) in box (0.25x0.25), 2009

0.4 0.8 1.2 1.6

Mean=0.80 Mean=0.51

• Std(Innovation)/Std(Data): The model is able to better

explain the observed signal with the HF data.

An improvement overall the basin In Open Ocean (Ratio <0.4 )

Sim_Dac


Impact on insitu data (T & S) Mean & Std (Innovation)

Mean Innovation(Temp,Sim_Ref )

-1.0 0.0 1.0

0 -50 -100 -150 -200

Mean Innovation (Temp, Sim_Dac )

-1.0 0.0 1.0

0 -50 -100 -150 -200

0 -50 -100 -150 -200

• Temperature : No Change for Mean and Std (over all domain)

Mean Innovation (Sal, Sim_Ref )

-0.4 0.0 0.4

0 -50 -100 -150 -200

Std Innovation (Sal, Sim_Ref)

0 -50 -100 -150 -200

0 0.25 0.5

Mean Innovation (Sal, Sim_Dac )

0 -50 -100 -150 -200

-0.4 0.0 0.4

Innovation = Data – Model Forecast; Data From CORA base

Std Innovation (Temp, Sim_Ref)

0 1.25 2.5

Std Innovation (Temp, Sim_Dac)

0 1.25 2.5

0 -50 -100 -150 -200

Std Innovation (Sal, Sim_Dac )

0 0.25 0.5

0 -50 -100 -150 -200

• Salinity : improvement in both Mean and Std especially near the surface (0-100m)


LWETIDEsat

SLAobsSLA

Std Sla Increment (Sim_Dac) in 2009

Sim_Dac

Std Sla Increment (Sim_Ref) in 2009

Impact LWE !!!

Role of LWE ? DAC contains residual errors ?

Impact of the assimilation of HF (SLA Increment):

DACLWETIDEsatSLAobsSLA

• Large increment in the highest-eddy-energy regions (present more variability): North Atlantic Drift….

• Position of the tracks

Sim_Ref

• It means that the assimilation step does not integrate the total difference (innovation) between the model and data

Increment = Result of analysis (correction)


Stddev LWE (2009)

Stddev Lwe (EN) in each point during 2009 Stddev Lwe (J2) in each point during 2009 Sttdev Lwe (J1g) in each point during 2009

0 4 8 Cm

• More variability in the barotropic region : North Sea • Important variabiliry for En (Med, Bob…)


LWE impact



Correction of Innovation in analysis

bubble (removing inter-tracks bias)

InnovationLWE

TIDESLA SLA : Sim_Lwe2

TIDESLASLA : Sim_Lwe1



sat

obs

sat

obs

sat

obs

sat

obs

We adapt the background model for each experiment (2009)


Std Sla Increment (Sim_Lwe1) in 2009

not apply LWE

TIDEsatSLAobsSLA

Sim_Lwe1

Std Sla Increment in 2009 Std Sla Increment (Sim_Dac) in 2009

Amplification the variability of increment sea level anomaly

DACLWETIDEsatSLAobsSLA LWETIDEsatSLAobsSLA

Impact LWE for assimilation (Sla Increment,2009)

Sim_Ref Sim_Dac


Std Sla Increment in 2009 Std Sla Increment (Sim_Dac) in 2009

DACLWETIDEsatSLAobsSLA LWETIDEsatSLAobsSLA

Impact LWE for assimilation (Sla Increment,2009)

Std Sla Increment (Sim_Lwe2) in 2009

not apply LWE apply LWEInnovation(bubble)

InnovationLWETIDE

satSLA

obsSLA

Significant reduction in variability of the (Sla) increments

Sim_Ref Sim_Dac Sim_Lwe2


Conclusion & prospects

• Improvement of DA diagnostic without the correction of the Dac in the model and data.

• More energy even at small scales

• Salinity improvement 0-100 m.

• On line Lwe correction (bubble, Innovation) gives better results….

Why it is more efficient to not applied the DAC correction in altimetry?

– the S1 S2 atmospheric waves are removed from the atmospheric pressure forcing used for DAC computation (while they are not removed for the IBI model forcing)

– ECMWF 6h analyses are used for DAC computation ( while ECMWF 3h analyses are used in the IBI model forcing)

– DAC = MOG2D_HF + IB_LF using a centered filter (cut-off =20 days) while a centered filtering is not possible with forecasting systems.

http://www.mercator-ocean.fr

[email protected]

Thanks for your attention

Multi-mission cross-calibration

Step 2 : Empirical reduction of Long-Wave Errors (LWE)

•Purpose : Correction of the long-wavelength errors (LWE) due to residual errors on tides, aliased HF residual signals, …

•Method : Reduction of the inter-track bias with Objective Analysis (Le Traon and al., 1998, JAOT 15)

Spatial scales considered for LWE : 300 to 800 km

A-priori mean LWE Variance : 8.5 (TP/J1) to 9 (EN) cm². Can locally reach 30-40 cm² or more

From SSH to altimeter products

LWE correction


Impact Sla(HF) on Surface Relative Vorticity…

DACLWETIDEsat

SLAobsSLA LWETIDEsat

SLAobsSLA

Vorticity (Sla With Dac) fro 05/12/2009 Vorticity (Sla Withou Dac) fro 05/12/2009

More energy : Eddies, filements we seem to increase the resolution of the model


Mercator-Ocean :

• Operational system (Global, Regional) • Reanalysis (GLORYS, IBIRYS)

Convential SLA Observations (e.g CMEMS/AVISO): VFEC : Verified, Filtered, SubSampled and Corrected)

LWEDACTIDESLASLA satvfec

“TAPAS” Sla Data Assimilation

Non along-track filtered

Non sub-sampled (i.e. 7km instead of 14Km)

Without Dynamical Atmospheric Correction (DAC= IBLF + MOG2DHF)

TAPAS : Tailored Altimetric Products for Assimilation Systems

LWEDACTIDESLASLA satvxxc

TAPAS SLA Observations, verified and Corrected

we use this data with different corrections

Residual orbitER, IBER, Residual Tide Corr and Aliased HF signals

HF processes assimilation in a 1/12° regional model (IBI12)godae-data/OceanView/Events/... ·...

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