Interannual variability Interannual variability in the Mediterranean Seain the Mediterranean Sea

OBSERVATIONS and MODELLING of the variability in the Mediterranean at basin, sub-basin and local

scale

Joaquín Tintoré, Vicente Fernández and co-workers

IMEDEA (CSIC-UIB)

CLIVAR seminarMadrid, 14-15 Febrero

IndexIndex

1. IMEDEA modeling capabilities at different scales

2. IMEDEA observational capabilities at different scales

3. IMEDEA scientific examples of contributions on the ocean variability at different scales

4. Interannual variability of the Mediterranean circulation

Interannual variability in the Interannual variability in the MediterraneanMediterranean

IMEDEA modeling capabilities at different IMEDEA modeling capabilities at different scalesscales

DieCAST - DIEtrich Center for Air Sea Technology (Dietrich, 1997).

DieCAST is a 3D, PE, control-volume-based, z-level and fourth order accuracy model. The main characteristic of this model is the robustness with a low general dissipation.

HOPS - Harvard Ocean Prediction System (Robinson, 1996, 1999).

HOPS is a flexible, portable and generic system for ocean nowcasting and forecastin. The heart of HOPS is a primitive equation dynamical model, which can be coupled to biological models. Data assimilation.

Wang Coastal Ocean 3D PE Model: long term collaboration with IMEDEA in coastal ocean modelling since 1989.

Work is also in progress on wave modeling, wave induced coastal currents, interaction with wind induced currents and sediment re-suspension and transport (since 2003).

Three circulation models are now implemented at IMEDEA: at basin, sub-basin and local scale

IMEDEA observational capabilities at different IMEDEA observational capabilities at different scalesscales

Oceanographic cruises at sub-basin scale using different types of research vessels.

Deployment and maintenance of currentmeter moorings in deep ocean.

XBT’s lines using Ships of Opportunity

Argos tracked drifters release and monitoring at basin and sub-basin

scale and GSM tracked drifters at local and beach scale

Gliders and AUV’s (MERSEA EU funded project)

From basin to beach scale:

Large scale (> 5 km), since 1995 (*): large scale circulation, air-sea interaction, transport in detailed sections, etc.

Sub-Basin regional scale (51 km), since 1992: mesoscale/mean flow interactions, blocking basin scale circulation in specific sub-basins, circulation Alboran and Balearic Seas, etc.

Local (1 km500m), since 1993: sub-basin-local interaction through canyons, shelf/slope exchanges, circulation in bays, residence times, etc.

Towards… beach (50010m), since 2004: fine sediment resuspension by waves and recirculation and sediment transport by wind induced coastal currents in bays and beaches, (only still with PE non hydrostatic models and towards integration with wave models).

(*) indicates year of the first paper published in the subject in peer reviewed journals

Research examples at IMEDEAResearch examples at IMEDEA

Large scale variability – thermohaline circulationLarge scale variability – thermohaline circulation

Box model’s study (Stommel)

Evaporation Energy (heating) Precipitatio Energy (cooling)

1(S1,T1) 2(S2,T2)

Equator Pole

Q/2

Q/2

Total flux F/2

Total Flux F/2

(Velez, Alvarez, Colet, Tintoré, Geophys. Res. Lett., 2001)

This transitions can be due to Estochastic resonance:

Periodic perturbation plus ambient noise

Research examples at IMEDEAResearch examples at IMEDEA

The Palamós CanyonThe Palamós Canyon

Local scale variability - CanyonsLocal scale variability - Canyons

Main result: characteristic time scale for shelf-slope exchange 2 months

(Jordi et al, Prog. In Oceanog., 2004)

Study of canyon induced shelf/slope exchange. Canyons play an important role enhancing the coastal-open ocean transport

2 km

33 km18 km

Research examples at IMEDEAResearch examples at IMEDEA

• WIW (T < 13 C) are present

• Blocking of the Ibiza channel

No presence of WIW and no blocking

Interannual variability in the Interannual variability in the MediterraneanMediterranean

Observations

• Evidences of variability at different scales

• Coupling between sub-basin and basin scale circulation through mesoscale interactions.

• Coupling between mesoscale, sub-basin and basin scale circulation. Nonlinear effects and interannual variability.

Mediterranean Sea complexity

MW (WIW)

AW

Interannual variability in the Interannual variability in the MediterraneanMediterranean

• Atmospheric (external) forcing:

Seasonal cycle; synoptic episodes; changes in wind stress…

• Internal forcing (independent of the atmopheric state):

Non-linear chaotic nature of the ocean: free evolution of instabilities and mesoscale eddies at the scales of the internal Rossby radius of deformation: Ro=NH/f ~ 10 -100 Km in the ocean

We have to use numerical ocean models

Sources of ocean variability

Interannual variability in the Interannual variability in the MediterraneanMediterranean

Main objectives

Simulation and understanding of the observed variability

of the Mediterranean Sea circulation at different time

scales (seasonal, intraseasonal and interannual)

Study how many (observed) variability in the real ocean

can be due to internal (non-forced) dynamics?

Interannual variability in the Interannual variability in the MediterraneanMediterranean

Method: model simulations driven by a seasonal atmospheric forcing

.30 years simulation - no surface temperature or salinity drift – correct parameterization of air-sea thermohaline fluxes

Fernández, V., D. E. Dietrich, R. L. Haney y J. Tintoré. Progress in Oceanography. 2004

Interannual variability in the Interannual variability in the MediterraneanMediterranean

The same day two consecutive years

Complex circulation with mesoscale structures.

Seasonal, perpetual year forcing + interannual response!

Fernandez, Dietrich, Haney, Tintoré, Prog. Oceanogr., 2003

Interannual variability of the Interannual variability of the Mediterranean Mediterranean

Observations: Nortward intrusion of 0.2 to 0.7 Sv in the

summer

Southward transport of 1 to 1.5 in winter

(Pinot et al., 2002)

Seasonal and interannual variability

Southward

Northward

Fernandez, Dietrich, Haney, Tintoré, Prog. Oceanogr., 2003

Interannual variability in the Interannual variability in the MediterraneanMediterranean

Volume transports

Observations ~ 1-1.5 Sv (geostrophic transport)

( Font et al. 1995)

Southward

February

Interannual variability in the Interannual variability in the MediterraneanMediterranean

Fernandez, Dietrich, Haney, Tintoré, Prog. Oceanogr., 2003

Volume transports

The interannual variability occurs at mesoscale

Algerian sub-basin

cm2

Interannual variability in the Interannual variability in the MediterraneanMediterranean

Variance of surface pressure at interannual scales (cm2)

Surface variability

Conclussions

It has been reproduced, in a a long run simulation, the general circulation of the Mediterranean Sea and its seasonal variability.

It has been found a signal of interannual variability (observed) being non-forced (eddy) associated with the ocean internal dynamics.

Interannual variability in the Interannual variability in the MediterraneanMediterranean

Study the importance of anomalous heat fluxes (deep water formation in the Gulf of Lions, etc.) in the north-south water transport in the western Mediterranean.

Implication for global thermohaline circulation