COLLABORATORS: P. Estrade, S. Herbette, C. Lett, A. Peliz, C. Roy, B. Sow, C. Roy
EDDY-DRIVEN DISPERSION IN COASTAL UPWELLING SYSTEMS
EDDY-DRIVEN DISPERSION IN COASTAL UPWELLING SYSTEMS
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
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
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]
Model
1 10
Resolution [km]
5 20
10
100
Ed
dy K
inet i
c E
nerg
y [
cm
2/s
2]
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
Model
SSH Standard Deviation
[cm]
For non-seasonal
variability
California
Sahara
Mesoscale ActivityIn California and Canary Systems
Model
SSH Standard Deviation
[cm]
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
California
Canary
Salinity profiles & Reduced Gravity
Potential density
JOINT I cruise, after Huyer(1976)
IMPACT
T’u’ = -Kx dT/dx
100km
T
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
New
Pro
d.
Excre
tion
Bre
akd
ow
n
Grazing
Aggregation
Mortality
Light
Sink
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
0
100
200
300
400
500
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
