EDDY-DRIVEN DISPERSION IN COASTAL UPWELLING SYSTEMS

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COLLABORATORS: P. Estrade, S. Herbette, C. Lett, A. Peliz, C. Roy, B. Sow, C. Roy

CaliforniaCanary

BenguelaHumbolt

Patrick Marchesiello

ROMS Meeting, VENEZIA

October 19 2004

Coastal Upwelling?

California Senegal

Divergencezone

Retentionzone

Eddy mixing zone

Coastal upwelling

Mitchum & Clark, 1978Lentz & Austin, 2002

Marchesiello et al., 2003

ROMS_AGRIF

• ROMS: HYDRODYNAMIC MODEL optimized for regional

and coastal high resolution, multi-scale, multidisciplinary

applications

• AGRIF: Online, synchronous nesting method (L. Debreu)

• ROMS_TOOL: Pre- and post-processing package (P.

Penven)

• DIAGNOSTIC TOOLS: Lagrangian tracers, budgets …

• APPLICATION MODELS: Ecosystem dynamics, Water

quality, Sediment transport

http://www.ird.brest.fr/Roms_tools

POG - 0.25 deg ROMS – 0.25 deg

Note on Regional Models

CALIFORNIA

APPLICATION TO THE CALIFORNIA CURRENT SYSTEM: CONFIGURATION AND STRATEGY

20km, 10km, 5km

20km, 10km, 5km, 2.5km

Volume Averaged KE (cm2/s2)

Surface Averaged KE (cm2/s2)

Nesting of the inner domain: on-line or off-line. Model integration: 10 years. Surface and lateral boundary forcing: Monthly climatologies.

Mesoscale Variability in the CCS

Realistic simulation of the Coastal Transition Zone More than 2/3 of the mesoscale variability is intrinsic, and produced through instabilities (baroclinic and barotropic) of the coastal currents generated in the upwelling process.

SST - AVHRRSST - Model

Marchesiello et al. (JPO, 2003)

Drifter Estimation [180]

Resolution [km]

inet i

Model Convergence

CANARY - COMPARISON

Canary Current System Configuration

ROMS – Canary 25 km

C. Vert

C. BlancC. Blanc

ROMS – Sahara 5 km

Mercator

Levitus

Clipper

SaharaCalifornia

8 20 17 26

Mesoscale ActivityIn California and Canary Systems

SSH Standard Deviation

For non-seasonal

variability

California

Sahara

Mesoscale ActivityIn California and Canary Systems

SSH Standard Deviation

For non-seasonal

variability

California

Sahara

AltimetryTopex/ERS from AVISO

California

Sahara

Wind Forcing

California Morocco

Units: Pascal

• The upwelling front results from upwelling of the thermocline (Mooers et al., 1976)

• Baroclinic instability:energy conversion from available potential energy to eddy kinetic energy varies with vertical shear of velocity (Pedlosky, 1986; Barth, 1989)

• U=(g’H0)1/2

where g’=g(ρ2-ρ1)/ ρ2

BAROCLINICITY: Two layer approach

•California g’=0.019

•Canary g’=0.008

Temperature relative to surface

Salinity relative to surface

Canary

California

Canary

Salinity profiles & Reduced Gravity

Potential density

JOINT I cruise, after Huyer(1976)

IMPACT

T’u’ = -Kx dT/dx

Offshore distance500km

Mixing

X 100 m2/s

Swenson and Niiler (1996) from drifting-buoy trajectories, 1985-1988: K = 1.1 - 4.6 103 m2/s with higher values for Kx compared to Ky

Model: Kx = 2.3 103 m2/s and Ky = 1.3 103 m2/s

MESOSCALE CROSS-SHORE DIFFUSION

Erosion of coastal properties

Nitrate

Chlorophyll A

Upwelling Nitrification

Grazing

Aggregation

Mortality

Zooplankton Phytoplankton

Large Detritus

HYDRODYNAMICS

Transport

Small Detritus

Ammonium

Reg. Prod.

THE ECOSYSTEM MODEL

LINEAR MODEL

(advection terms turned offin the momentum equation)

New Production NO3 transport

NON-LINEAR MODEL

Spring-time biology fluxesUnits: mmol N cm-2 a-1

Retention MapFrom Lagrangian Study

SSHStandard Deviation

Seawifs Annual Chl

BIOLOGICALLY ACTIVE AREA IN UPWELLING SYSTEMS BIOLOGICALLY ACTIVE AREA IN UPWELLING SYSTEMS

Californie Humbold Canaries Benguela

Biologically Active Area (1000 km2)

SeaWIFS estimations by M. Carr (2002) What drives the observed differences in cross-shore distribution of physical and biogeochemical properties?

Latitude (solar flux) Fe depositions from Sahara (Lene et al., 2001) Shelf width & nutrients (Johnson et al., 1997) Mesoscale physics (Marchesiello et al., 2003)

PERU-CHILICALIFORNIA CANARY BENGUELA

EDDY-DRIVEN DISPERSION IN COASTAL UPWELLING SYSTEMS

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