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Evaluation of two global HYCOM 1/12º hindcasts in the

Mediterranean Sea

Cedric Sommen1

In collaboration with Alexandra Bozec2 and Eric Chassignet2

1 The French Military Academy of Saint-Cyr, Guer, France

2 Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL/ 25

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OutlineOutline

• The Mediterranean Sea• Presentation of the HYCOM global ocean

prediction system• Experimental set-up• Circulation• Temperature and Salinity• Transport• Comparison with ARGO profile• Summary

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The Mediterranean SeaThe Mediterranean Sea

The Mediterranean Sea is a mid-latitude marginal sea connected to the Atlantic Ocean by the Gibraltar Strait. It has the particularity to produce dense (warm and salty) water that spreads into the Atlantic Ocean and thus can potentially have an impact on the global thermohaline circulation (Mauritzen and McCartney, 2001).

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The Mediterranean OutflowThe Mediterranean Outflow

http://hycom.coaps.fsu.edu/thredds/dodC/gbl_simulation

1/12º Global HYCOM Hindcast for April, 16th 2007

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Presentation of the HYCOM Presentation of the HYCOM global ocean prediction systemglobal ocean prediction system

Horizontal grid: 1/12° equatorial resolution 4500 x 3298 grid points, ~6.5 km spacing on average, ~3.5 km at

poleMercator 79°S to 47°N, then Arctic dipole patch

Vertical coordinate surfaces: 32 for σ2*

KPP mixed layer model

Thermodynamic (energy loan) sea-ice model

Surface forcing: FNMOC NOGAPS 0.5° wind stress, wind speed, thermal forcing, and NOGAPS 1.0° precipitation

Monthly river runoff (986 rivers)

Initialized from January climatology (GDEM3) T and S, then SSS relaxation from PHC 3.0

No subsurface relaxation to climatology

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Presentation of the HYCOM Presentation of the HYCOM global ocean prediction systemglobal ocean prediction system

Sequential Incremental Update Cycle Analysis-Forecast-Analysis

MVOI - simultaneous analysis 6 ocean variables temperature, salinity, geopotential, layer pressure, velocity (u,v)

HYCOM Model

Ocean QC

3D MVOI

Ocean Obs

SST: GAC/LAC MCSST, GOES, Ship, Buoy Profile: XBT, CTD, ARGO Floats, Fixed Buoy, Drifting Buoy Altimeter SSHA SSM/I Sea Ice

Innovations

Increments

Forecast Fields Prediction Errors

First Guess

Navy Coupled Ocean Data Assimilation (NCODA)

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Goal of my studyGoal of my study

The main goal of this study is to determine if the 1/12º Hybrid Coordinate Ocean Model (HYCOM) global configuration is able to reproduce the main features of the Mediterranean circulation and its outflow in the Atlantic Ocean. In particular, we

evaluate the ability of two hindcast simulations on the period June 2007 to September 2008

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EXPERIMENTAL SET-UPEXPERIMENTAL SET-UP

• Hindcast 1– Spin-up with climatological atmospheric reanalysis ERA15 1979-

1993. – Hindcast with 3-hourly 0.5º NOGAPS from Nov 2003-present. – Vertical projection of observed SSH using Cooper and Haines

(1996).

• Hindcast 2 – Spin-up with climatological atmospheric reanalysis ERA40 1979-

2002 + winds scaled to Quikscat wind speed.– Hindcast with 3-hourly 0.5º NOGAPS + winds scaled to Quikscat

wind speed from June 2007- present. – Vertical projection using synthetics temperature profiles from the

Modular Ocean Data Assimilation System (MODAS) database.

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CIRCULATIONCIRCULATION

• In the eastern basin

Hindcast 1 Hindcast 2

(Hamad et al. 2005)

Winter 2008

Current on Kinetic energy (m2/s2)

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CIRCULATIONCIRCULATION

• In the western basin

Hindcast 1 Hindcast 2

(Millot et al. 1999)

Current on Kinetic energy (m2/s2)

Winter 2008

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TEMPERATURE and SALINITYTEMPERATURE and SALINITY

Temperature

averaged over the whole water column

• Positive bias in Hindcast 1

• Hindcast 2 stays closer to GDEM3 than Hindcast 1

EASTERN BASIN

WESTERN BASIN

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TEMPERATURE and SALINITYTEMPERATURE and SALINITY

Temperature

Vertical sections:

Eastern basin

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TEMPERATURE and SALINITYTEMPERATURE and SALINITY

Salinity

averaged over the whole water column

•Positive bias of Hindcast 1 in the eastern basin

•Slight positive bias in Hindcast 2

WESTERN BASIN

EASTERN BASIN

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TEMPERATURE and SALINITYTEMPERATURE and SALINITY

Vertical sections:

Eastern basin

Salinity

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TRANSPORTTRANSPORT

ExperimentsTransport

(1Sv=106m3/s)Salinity In/out

(psu)Temperature In/Out

(C)

Observations ~ 0.7-0.8 36.2/38.4 16.2/13.

Gibraltar H1 0.63/-0.62 36.2/38.0 16.6/13.8

Gibraltar H2 0.77/-0.71 36.1/37.8 16.5/13.4

Observations 1.10+/-0.58 38.70/37.5 13.8/15.4-16

Sicily H1 1.60/-1.77 38.6/37.8 14.5/18.1

Sicily H2 1.0/-1.02 38.3/37.65 15.1/16.9

Gibraltar strait Sicily strait

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COMPARISON WITH ARGO COMPARISON WITH ARGO PROFILESPROFILES

In the eastern basin

Temperature Anomaly

•GDEM3/ARGO: slight bias

•Hindcast 1/ARGO:worse than GDEM3

•Hindcast 2/ARGO: improvement compared with GDEM3

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COMPARISON WITH ARGO COMPARISON WITH ARGO PROFILESPROFILES

In the eastern basin

Salinity Anomaly

•GDEM3/ARGO: fresh bias

•Hindcast 1/ARGO: too salty at the surface

•Hindcast 2/ARGO: improvement compared with GDEM3

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COMPARISON WITH ARGO COMPARISON WITH ARGO PROFILESPROFILES

In the western basin

Temperature Anomaly

•GDEM3/ARGO: slight cold bias

•Hindcast 1/ARGO:too warm

•Hindcast 2/ARGO:stays slightly too cold

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COMPARISON WITH ARGO COMPARISON WITH ARGO PROFILESPROFILES

In the western basin

Salinity Anomaly

•GDEM3/ARGO: fresh bias

•Hindcast 1/ARGO: too fresh

•Hindcast 2/ARGO: improvement compared with GDEM3

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SUMMARYSUMMARY

The assimilation method using MODAS synthetics gives better results in the

Mediterranean Sea than the Cooper-Haines assimilation method in terms of:

•large-scale Circulation pattern•transport at the strait

•large and small scale T/S properties

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QUESTIONSQUESTIONS??????