Transcript Turbulent exchanges South of Africa S. Speich

Turbulent exchanges
South of Africa
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
A regional GCM configuration
Regional Ocean Modelling System
– ROMS (Haidvogel et al. 2000) –
bathymetry
CONTROL RUN:
1/6° resolution & CLIMATOLOGICAL
FORCINGS:
•
COADS heat & fresh water
•
QUICKSCAT climatology for wind
stress
•
OCCAM 1/4° climatology (19932000) at open boundaries & initial
conditions
OCCAM 1/4° at boundaries
Quickscat near Cape Columbine
meridonal component
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Simulated SST
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
Simulated SSH
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Ariane:
A quantitative Lagrangian tool
www.univ-brest.fr/lpo/ariane
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Agulhas-Benguela “connections”
Agulhas connections = fate Agulhas water
This has been computed with ARIANE
annual mean
SSH
5.5 Lagrangian fate of
Agulhas waters 67.5
21
11
30
Contour lines represent integrated diagnostic
of particle displacement (c.i. 1 Sv).
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Agulhas numerical sensitivity experiments
Simulation’s name
Topography
parameters
Geometry
parameters
Initial & Boundary
conditions
Control Run
r = 0.3
Real domain
OCCAM monthly means
Smooth Slope
r = 0.2
”
”
Very smooth slope
r = 0.1
”
”
Agulhas Bank
r = 0.3
No Agulhas Bank
”
LGM sea level
r = 0.3
– 130m of sea level
”
Agulhas Plateau
r = 0.3
No Agulhas Plateau
”
Beta zero
r = 0.3
=0
”
Tropical latitudes
r = 0.3
7°S≤  ≤ 27°S
”
Occam boundary
forcing every 5 days
r = 0.3
Real domain
OCCAM 5-day means
Levitus 98
Depthref = 2000m
r = 0.3
”
Levitus monthly means
Depth Vref = 2000m
Levitus 98
Depthref = 1000m
r = 0.3
”
Levitus monthly means
Depth Vref = 1000m
High Resolution 1/10°
r = 0.3
”
OCCAM monthly means
Large Domain 1/10°
r = 0.3
Larger domain
S. Speich
Levitus monthly means
Depth
Vref
= 2000m
South Atlantic Workshop, Estancia San Ceferino
8-10
May
2007
Effect of the slope steepness
Control run:
steep slope
r = 0.3
SSH
SST
5.5
21
fate
67.5
11
30
smooth slope
r = 0.2
6.5
22.5
66.7
13.2
very smooth
slope
r = 0.1
24.5
8
26
58.7
7
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
16.7
Slope steepness & Benguela
Upwelling
Origins of Southern Benguela Upwelling waters
steep slope
0.3 Sv
Very smooth slope
0.7 Sv
0.8 Sv
2.1 Sv
Lagrangian streamfunction depicting the origins of Southern Benguela
Upwelling waters
Upwelling water sources change with smoother slope
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Agulhas separation from the slope
Slope steepness, slope curvature & inertia
steep slope
slope
magnitude
surface
flow speed
smooth slope
slope
magnitude
surface
flow speed
Surface flow behaviour
along the 2000m isobath
slope steepness
Surface flow speed
barotropic flow
The WBC is stabilized (i.e., accelerated) by:
• the  effect
• the slope steepness
S. Speich
Separation occurs due to:
• isobath divergence
• isobath curvature
• inertial effect
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Ring shedding, the Agulhas Retroflection
and the sphericity of Earth
The spherical shape of Earth induces destabilization of equatorward EBC and
permits the existence of Rossby basin modes
When imposing  = 0, all Agulhas waters retroflect
0.7
SSH
fate
59
36
22.3
SSH for
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
=0
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Other topography related sensitivity of
Agulhas Leakage :
• Agulhas Plateau
• LGM Sea Level
Lagrangian Agulhas leakage into the Atlantic
Control run
No Agulhas Plateau
-130 m sea level
55 %
33 %
50 %
Lagrangian stream function depicting the mean fate of Agulhas waters
Agulhas leakage affected by presence of
Agulhas Plateau!
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Other sensitivity experiments :
• different thermohaline mean state (OCCAM vs Levitus
‘98)
• different
earthAgulhas
rotation leakage
rate for South
Africa
(f ~ 15°S)
Lagrangian
into the
Atlantic
Control run
55 %
Levitus clim. Dref=2000m
Levitus clim. Dref=1000m
42 %
26 %
f ~ 15°S
6%
Lagrangian stream function depicting the mean fate of Agulhas waters
Agulhas leakage affected by mean thermohaline
structure & f (tropics versus subtropics) !
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Comparing SST
Control run (OCCAM)
1/10° (OCCAM)
PATHFINDER
Levitus 2000m
S. Speich
Levitus 1000m
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Numerical/physical
sensitivity on the
Agulhas influence in
the Atlantic/South
Benguela Circulation
Slope smoothing
Benguela Sud
Total
transport
Agulhas
-130m
CTRL SSlope VSSlope AguBnk LGM
AguPlt  zero Tropic Occ5day Hres Lev2000 Lev1000
TOTAL
74,93
73,29
64,65
81,56 69,121
65,67
66,01
43,33
75,44 66,59
80,24
56,76
TOTAL Atlantic
% TOTAL Atlantic
41,31
55,14
44,15
60,24
41,08
63,54
56,23
68,94
35,14
50,83
33,50
51,01
3,57
5,41
6,78
15,64
35,11 25,2
46,54 37,84
34,21
42,63
14,85
26,16
2,81
3,74
6,79
3,52
4,80
7,96
3,57
5,53
8,70
3,32
4,07
5,90
0,80
1,16
2,28
2,59
3,95
7,74
0,45
0,68
12,61
0,66
1,52
9,72
2,26 0,47
3,00 0,71
6,45 1,87
3,44
4,29
10,06
2,43
4,28
16,36
UpBenguela
% Benguela
% Beng. Atl.
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Because of the complex SB upwelling
shelf-open ocean interaction a larger
regional study is necessary
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
A net southern source of water
0.2 Sv
5.3 Sv
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
MEAN EDDY KINETIC ENERGY
Ocean dynamics
around Southern of
Africa: highly
energetic nonlinear
processes
SNAPSHOT OF
SURFACE RELATIVE
VORTICITY
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Penetration of AAIW South
East of Africa :
a turbulent process ?
Evolution of the salinity in the lower
layer of an Agulhas ring in 6 months
Schmid et al. 2003
Mar.’97
Sep.’97
Mar.’97
Sep.’97
Mercier et al. 2005
z
s
S. Speich
N
South
May 2007
S Atlantic
N San Ceferino
S 8-10 N
S Estancia
N Workshop,
S
SSH
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
CAPITAL ROLE OF
EDDIES &
SUBMESOSCALE
PROCESSES IN
WATER MASS
TRANSFER
HOW CAN WE STUDY THE EDDIES
DYNAMICS, THE RELATED WATERMASS TRANSFERS &
THERMODYNAMICS PROCESSES?
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
1. We need to track/follow
accurately individual modelled
eddies
WAVELET ANALYSIS
2. We need to follow varying
properties and water-mass
transfer
LAGRANGIAN DIAGNOSTIC
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Wavelet Analysis – Eddy identification
Decomposition of an horizontal slice of relative vorticity
MATLAB tools using Wavelab library
Research Area
256 x 256 [gridcells]
[http://www-stat.stanford.edu/wavelab/]
depth= -200 m
Numbering and
Naming
Anticyclone
PANORAMIX
Cyclone
ASTERIX
Center definition
(ic,jc)=max(|z|)
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Wavelet Analysis – Time tracking
Anticyclone PANORAMIX
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Wavelet Analysis – Time tracking
Cyclone Asterix
Anticyclone PANORAMIX
END
(forward tracking)
BEGINNING
(backward tracking)
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Wavelet Analysis – 4D tracking
Anticyclone PANORAMIX
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Wavelet Analysis – 4D tracking
Cyclone ASTERIX
QuickTime™ et un
décompresseur GIF
sont requis pour visionner cette image.
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Wavelet Analysis – 4D tracking
Anticyclone PANORAMIX
Cyclone ASTERIX
January-June
Vel = 0.09 [ms-1]
Diam= 121 [km]
Vol=9.7 1012 [m3]
Boebel et al, 2003
Agulhas
Rings
Cyclones
January to October
Vel = 0.08[ms-1]
Diam = 75[km]
Van Ballegooyen et al.,1994
Vol=3.1 1012 [m3]
Cyclones
Anticyclones
Diameter [km]
120
200
160
190 – 320
Velocity [m/s]
0.036
0.038
0.046
0.04 – 0.09
Divergent
pathways
[Morrow et al., 2004]
Volume [1012South
m3]
11.2 - 33.8
Atlantic
Workshop,
Estancia- San Ceferino
8-10 May 2007
S. Speich
OUTLOOK
Wavelets & Lagrangian particles
Coherent eddies
Eddy-life
time integration
S. Speich
Remote Origins
Multiple-years
backward time integration
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
OUTLOOK
Swoddies
Bay of Biscay, NORTH ATLANTIC
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Good-Hope / Southern Ocean :
Monitoring the Indo-Atlantic connections
An international co-operative project
A process study and a contribution to CLIVAR
- Southern Ocean
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Southern Ocean
“Chokepoints”
Chokepoint #1 : Drake
Passage - SR1 line (UK)
Chokepoint #3 : TasmaniaAntarctica - SR3 line (AU & F)
Chokepoint #2 : S. Africa - Antarctica
- SR2 line : Nobody committed!!
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
GOODHOPE
Monitoring the SO along the SR2 line
• Mass, heat and salt fluxes along the GH
section & their correlation with the Atlantic
NADW export and import of cold, warm and
cool waters;
• How the ACC is modified in the Atlantic sector,
in terms of transport and water mass content
• To implement the estimate of mass, heat,
fresh-water, and biogeochemical budgets of
the Southern Ocean and South Atlantic
• Impact of interocean exchanges on the
local air-sea heat exchanges and their role
on the local climate of the African
continent and on the global heat budget
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
The GOODHOPE team
Name of involved scientists
MSU
S. Speich
Sabrina Speich (PI)
Michel Arhan (CO-PI)
Isa belle Ansorge (CO-PI)
Johann Lutjeharms
Chris Reason
Mathieu Rouault
William Froneman
Hans Rautenbach
Olaf Boebel (CO-PI)
Eberhard Fahrbach (CO-PI)
Mario Hoppema
Michael Schroeder
Deidre Byrne
Chris Duncombe Ray (CO-PI)
Silvia.Garzoli (CO-PI)
Gustavo Goni
Serguey Gladishev (CO-PI)
Marta Alvarez Rodriguez (CO-PI)
Aida Rios
Alexander Klepikov (CO-PI)
Brian King
Steve Cunningham
Sheldon Bacon
Sybren Drijfhout
Peter Jan van Leeuwen
Inst itution
LPO, France
UCT, South Africa
Rhodes Universi ty, SA
Pretoria University, SA
AWI, Germany
University of Maine,
USA
AOML-NOAA, USA
SIO, Russ ia
IIM-CSIC, Spain
AARI, Russi a
SOC, UK
KNMI, NL
IMAU, NL
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
POTENTIAL of GH line
• Partially covered by moorings
(ASTTEX & WECCON)
• TOPEX/POSEIDON - JASON1
ground track
• Use of “ferry” service to
Neumayer and SANAE
Antarctic stations (SA
Agulhas)
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
ARGO
Mars 2006
Fronts position, currents
transport, thermohaline
structure and water masses
budget via ARGO floats, full
depth hydrogrology, XBTs,
drifters, satellite altimetry, …
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
Speich
wartS.et
al., 2007
GOODHOPE
ACC dynamics and
variability
Fronts position, transport variability, thermohaline
structure using ARGO, CTDs, XBTs, & altimetry
(proxies + statistics - GEM, …)
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
S. Speich
Swart
et al., 2007
GOODHOPE
The subtropical-subpolar
exchanges
Dencausse et al., 2007
S. Speich
South Atlantic Workshop, Estancia San
Ceferino
8-10 May 2007
…and
modeling...
Marie BOYE (LEMAR, IUEM-Brest)
Sabrina SPEICH (LPO, UBO-Brest)
BONUS
GOODHOPE
INTERNATIONAL POLAR YEAR
S.
An international cooperative project
IPY-GEOTRACES,
ICED,
CASO &San
CLIVAR-Southern
Ocean
South to
Atlantic
Workshop,
Estancia
Ceferino 8-10
May
SpeichA contribution
2007
BONUS-GOODHOPE
IPY EoI#584
BONUS-GH
ZERO
&
DRAKE
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
BONUS-GOODHOPE
IPY EoI#584
228Ra
activity
226Ra activity
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
BONUS-GOODHOPE
IPY EoI#584
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
BONUS-GOODHOPE
IPY EoI#584
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007
The BONUS-GOODHOPE team
S. Speich
South Atlantic Workshop, Estancia San Ceferino 8-10 May 2007