1 Institut für Physikalische Geodäsie INTERGEO 07 Integrated use of GRACE, Altimetry and Models...

Institut für Physikalische Geodäsie INTERGEO 07

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Integrated use of GRACE, Altimetry and Models for the Assessment

of Interannual Mass Variation in the Mediterranean Sea and Black Sea

L. Fenoglio, M. Becker Institut für Physikalische Geodäsie, TU Darmstadt

J. Kusche, R. RietbroekGeoForschungsZentrum Potsdam

S. Grayek, E. StanevICBM Universität Oldenburg

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• Motivation

• Basin-averaged watermass change from

Grace & steric-corrected altimetry (BAMV)

• Accuracy of annual & inter-annual BAMV estimation

• Closing the Water Budget

• Black Sea: Water balance & numerical modelling of 3D circulation

• Conclusion

OUTLINE

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MED (2.5 106 km2)

WEST-MED (0.5 106 km2)

EAST-MED (2.0 106 km2)

BLACK SEA(0.48 106 km2)

Motivation Data Method Results Conclusions

STREMP PROJECT AREA

seawater mass GRACE .NE. a-s (in coastal oceans(in coastal oceans) ) h! h! a – s = G – h (both terms filtered)a – s = G – h (both terms filtered)

•Closing the balance: dm/dt = P-E+R+FG+B (MED) dm/dt = P-E+R-FB (BS)

•smoothing (de-striping) to reduce spatially correlated noise & RE-SCALE

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G: GRACE :- L2 GSM (GFZ rl04), GSM 2002.04-2006.9 (2-90,

400 km)- atmosphere and ocean response restored (GAD)

A: ALTIMETRY single & multi-mission (T/P, J1, E2, Envisat 02-07)

O: STERIC(T,S) oc: ECCO/JPL, MFSTEP (MED)cl: Medar, WOA05, Ishii (MED), Black Sea

H: HYDROLOGY (LAD/Fraser, WGHM)

0.5x0.5, 1x1 grids R: River Run-off (Climatology, Water Gap)E: Evaporation (ECMWF, NCEP)P : Precipitation (ECMWF, NCEP)F: Flow at Straits (Bosphoro, Gibraltar)

Integration


Grace

R

P

FG

Altimetry

E

FB

Steric

Hydrology

9 components:

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• Reduction of correlated GRACE noise:• Gaussian filter• Anisotropic filter (Kusche 2007)

• Center of mass correction to compare with altimetry: annual model from GPS loading inversion (Jansen et al., 2006, see JIGOG Presentation)Annual amplitude eq. Water height= 2 cm

G: GRACE


Example: annual Sine/Cosine

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A: ALTIMETRY / O: OCEANOGRAPHY


• Single-mission, multi-mission, objective analysed grids• IBC to be applied in agreement to GRACE processing and ocean modelling (DUACS grids, in Black Sea MOG2D correction not available)

• Correction of atmospheric forcing effects is an issue in semi-closed basins !

Med Sea: MFSTEP / steric component

Black Sea: 3-D modelling with the “best” water balance terms

PARAMETRISATION: • Horizontal tracer diffusion: geopotential laplacian operator • Horizontal dynamic viscosity: geopotential bilaplacian operator • Vertical viscosity/diffusivity: TKE closure scheme, enhanced vertical diffusion.• Horizontal: 1/9° x 1/12°, Vertical: 31 levels

FORCING: Meterological forcing: bulk aerodynamic formulas using atmospheric temperature and humidity, winds, and simulated SST

ASSIMILATION of SLA from altimetry (“Cooper and Heins” scheme)

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BASIN AVERAGE


Basin Average Kernel

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GRACE – hydrology* Altimetry* – steric*

COMPARISON G-h and a-s (filtered time-series)

The worst The best

&


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Altimetric SLA 83 +/- 2 284 +/- 2Steric 55 +/- 4 251 +/- 4Grace filtered 43 +/- 7 8 +/- 7H filtered 26 +/- 3 29 +/ - 7 G – h / a-s filtered 24 +/- 3 301 +/- 6 8.8 mm/yr

steric 25% SLAhydrology 80% GRACE

2002.6-2004.6steric 60% SLA, hydrology 30% GRACE

MED BASIN AVERAGE: Annual Amplitude &Phase, trend (eq. water height)

Field MED

Amp

(mm)

MED

Phase

(mm)

MED

Trend (mm/y)

BS

Amp.

(mm)

BS

Phase(deg

BS

Trend

(mm/y)

altimetry 83 +/- 2 284+/-2 1.1 +/- 0.5 - - -

Steric 55 +/ 4 251+/-4 -1.6+/-0.2 29 +/- 4 238+/-4 0.0

Hydrology 26 +/- 3 29 +/- 7 - 64 +/- 5 59 +/- 5 -

Grace filt. 43 +/- 7 8 +/-7 - 56 +/- 7 75 +/- 7 -

a-s 45 +/- 4 301+/- 5 - - -

A-s_filt 24 +/- 3 301+/- 6 3.2 +/- 2.2

G-h 28 +/- 6 327+/ 13 5.4 +/- 2.6 - - -

G-h_scaled 52 +/- 11 327+/ 12 - - -

22002.6-2006.6


(02-04 in Fenoglio et al. GRL2006, JGR in press)

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MED BASIN AVERAGE:G-h ~ a-s with : GRACE, LAD, J1, ECCO

rms=14 mm, corr=0.8, N=475.4 +/- 2.6 mm/yr

3.2 +/- 2.2 mm/yr2002.6-2006.7


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Error estimates for monthly means, annual component and trend (from RMS and Error Propagation) in 2002.6 – 2004.6

1 cm (*1-2)!

--1013Grace – h_filt

-

-

-

10

10

2

Annual Phase error(d)

3715WM from a-s

-715WM GRACE

-310GRACE_filt

-911Hydrology

5613Steric

148altimetry

Trend

(mm/yr)

Annual Amplitude

error (mm)

Eq. water

Monthly

error(mm)

Field

1-2 cm (*2-4)

ACCURACY OF ESTIMATION FOR MED BASIN AVERAGE

** (Fenoglio et al. GRL2006, JGR in press)


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ACCURACY of ESTIMATION: BASIN DETAILS


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WATER BUDGET IN THE MEDITERRANEAN SEA

Hydrological cycle: water thickness change (mm/mon)

MED

EP

RE-P-R

E-P

FG = (E-P-R-B) + dm/dt

P-E(mm/mon)

R(mm/mon)

FG (a-s)(mm/mon)

FG (G-h) (mm/mon)

16-30 5 39+/-7 60+/-7

48 +/-7

R~ B


dm/dt = P-E+R+FG+B (MED)

Annual Amplitude

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BS: A DIFFICULT REGION?

-H: huge contribution to GRACE -A: strong interannual, ibc not realistic- S: small ~ constant- large water fluxes


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Seasonal Range 2002-2007 [m]river run-off precipitation evaporation strait heat flux

0,05 0,06 0,13 0,14 0,07

Interannual Range 2002-2007 [m]total water flux heat flux

0,07 0,01

Mean yearly water fluxes


Contribution of individual terms to BS level change

- P: from atmospheric analyses (large errors).

- E: computed by model using bulk formulas (big errors)

- R: for some rivers only, input statistically generated

- B: Bosporus transports reconstructed (linearly from R)

FOR BS NUMERICAL MODELLING of 3D CIRCULATION

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Problem in reconstructing BS Water balance: SENSITIVITY TO STRAIT TRANSPORTS (ST)

Still problems with theoretical/statistical reconstruction

Constraining the balance by altimetry (0D) –> consistently close water balance

a) ST Statistically reconstructed from R

b) ST Computed as a residual (use of satellite data)


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COMPARING RESULTS


Integrated P-E+R-B watermass change from a-s

dm/dt = P-E+R-FB (BS)

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Simulated Mean Sea Level 0D/3D

Linear equation of state0D (mean area) forcing fields

Unesco eq. of state (non linear)2D forcing fields

BEST (Presently) FIT OF SEA LEVEL TO DIFFERENT DATA


Model captures well the vertical structure of thermohaline fields (known from observations)

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• In MED the water-mass signal could be recovered (both seasonal and long-term variations), in the BS it is more difficult.

•Basin averages: smoothed spatial averaging kernel (isotropic and anisotropic), small improvement with anisotropic

•MED : Basin average a-s and G-h with comparable error estimates (15 mm monthly, 1 cm Annual Ampl., 2 mm/yr)

•Land hydrology contamination to be considered, dominant in Black Sea

•Closing the water balance in MED (Gibraltar estimation ~ observations)

•Closing the water balance in BS is necessary for realistic modelisation. BS is complex system (LARGE sensitivity to water fluxes & errors in WF components, straits flows inaccurate, numerical parameterizations of straits transport not solved).


CONCLUSION

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Oceanography:

Improve modeling :

• Physical (not by residuals) closing of water budgets,

• More appropriate assimilation scheme, focus on absolute sea level analysing its role for the evolution of baroclinic structure and circulation

Geodesy:

• Improve filtering of GRACE data

• reduce leakage of hydrology in watermass estimation

Overall:

• Budget Closure & separation of components


OUTLOOK

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1 Institut für Physikalische Geodäsie INTERGEO 07 Integrated use of GRACE, Altimetry and Models...

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