western boundary circulation and the role of deep eddies in the tropical south atlantic overview...
TRANSCRIPT
![Page 1: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/1.jpg)
Western boundary circulation and the role of deep eddies in the tropical South Atlantic
Overview
• Western Boundary Circulation (Schott et al. 2004)- shipboard sections at 5°S (8 sections) and 11°S
(4 sections) - moored observations at 11°S (2000-2003)
• Deep Western Boundary Current Eddies
• Summary
Tropical Atlantic Workshop, June 2004
Marcus Dengler
Friedrich Schott, Peter Brandt, Jürgen Fischer, Lothar Stramma Carsten Eden, Rainer Zantopp, Karina Affler
Leibniz-Institut für Meereswissenschaften, Kiel, Germany
![Page 2: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/2.jpg)
Observational program (1990-2004)
8 sections
4 sections
Array 2000-2004 (gaps!)
![Page 3: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/3.jpg)
Mean salinity at 11°S and transport layer distinction
Boundary Circulation in the tropical South Atlantic
![Page 4: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/4.jpg)
10
• NBUC always at shelf edge
• DWBC sometimes reversed at slope
(new LADCP post-processing method)
Boundary Circulation at 5°S (8 Sections, 1990-2003)
Along-shore LADCP/ADCP velocity sections from 5°S
![Page 5: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/5.jpg)
NBUC=26.8 Sv
• 14.3 Sv in SACW layer
• offshore southward AAIW layer flow (5.2 Sv)
• net upper 21.5 Sv
DWBC= -28.1 Sv
• upper NADW -14.7Sv
• m/l NADW -5.3Sv
• net NADW -20.0 Sv
AABW = 1.3 Sv
Section total almost closed (10%)
Boundary Circulation at 5°S (8 Sections, 1990-2003)
![Page 6: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/6.jpg)
• NBUC welldeveloped
• AAIW counter current
• Large NADW transports and counter currents
Boundary Circulation at 11°S (4 Sections, 2000-2003)
![Page 7: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/7.jpg)
NBUC = 23.3 Sv
• 12.1 Sv in SACW layer
• southward offshore flow at AAIW level
• net upper 21.2 Sv
DWBC = 41.2 Sv
• 18.2 Sv return offshore
• net NADW -23.0 Sv
AABW = 1.4 Sv
Section nearly balanced (<1Sv).
Theat = 1.0 PW Tfresh = - 0.2 Sv
Boundary Circulation at 11°S (4 Sections, 2000-2003)
![Page 8: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/8.jpg)
• NBUC already fully established at 11°S (i.e. is part of the STC)
• Box 5-11°S requires westward flow in upper layer (but upper 20m uncertain due to extrapolation) and eastward flow in AAIW layer (300-1200m)
• EUC layer (main STC carrier): little inflow from east: good site!!
• Offshore southward flow in AAIW layer!
<24.5 24.5-26.8 26.8-32.15 total (Sv)
5°S sectionboundary 3.7 13.3 8.8 26.8
Offshore -- .2 -5.1 -4.9
net 3.7 13.9 3.0 20.6
Budget of upper circulation
11°S sectionboundary 1.5 12.1 9.7 23.3
Offshore -.4 1.1 -2.6 -1.9
net 1.1 11.0 7.1 19.2
![Page 9: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/9.jpg)
5°S section and AAIW-layer circulation in 1/12° Miami model
NBUC retroflection supplies recirculation
Budget of upper circulation
Courtesy of Z. Garaffo and E. Chassignet
![Page 10: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/10.jpg)
Western boundary circulation and the role of deep eddies in the tropical South Atlantic
Overview
• Western Boundary Circulation (Schott et al. 2004)- shipboard sections at 5°S (8 sections) and 11°S
(4 sections) - moored observations at 11°S (2000-2003)
• Deep Western Boundary Current Eddies
• Summary
Tropical Atlantic Workshop, June 2004
Marcus Dengler
Friedrich Schott, Peter Brandt, Jürgen Fischer, Lothar Stramma Carsten Eden, Rainer Zantopp, Karina Affler
Leibniz-Institut für Meereswissenschaften, Kiel, Germany
![Page 11: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/11.jpg)
Moored observations at 11°S (2000-2003)
100m level (large gaps)
![Page 12: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/12.jpg)
1900m level
Moored observations at 11°S (2000-2003)
Southward „DWBC“ aliasing during ship section times
![Page 13: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/13.jpg)
Box transports (Sv)
1: 12.52: 2.83. 9.84: 2.7
1-4: 27.8 (NBUC)(Ship NBUC was 23.3)
5:-3.0 (+0.7): (AAIW recirculation, -2.6 from ship obs. )
6: -18.7 (DWBC)(ship mean was –44 Sv)
Moored observations at 11°S (2000-2003)
Mean section and boxes (1-6) for time series
1 2
34
5
6
![Page 14: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/14.jpg)
Moored observations at 11°S (2000-2003)
NBUC transport variability (box 1-4)
• current records mapped using EOFs from all time series
• mode 1+2 explains NBUC variability
strong variability on different time scales
![Page 15: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/15.jpg)
Moored observations at 11°S (2000-2003)
DWBC transport variability (Box 6)
strong intraseasonal variability
![Page 16: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/16.jpg)
• Significant seasonal (semi+annual) cycle of NBUC and DWBC
• explains lower NBUC transport from ship-board observations
Moored observations at 11°S (2000-2003)
Annual and semi-annual cycle of transport time series
• NBUC variability at 11°S may be (partially) caused by SEC bifurcation migration (pers. comm. S. Huettl)
![Page 17: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/17.jpg)
Interannual differences and trends 2000-2003
Annual averages:
Time NBUC
3/00-3/01 23.6
3/01-3/02 23.7
3/02-3/03 26.4
NBUC Line fit: 1.5 Sv/year
Moored observations at 11°S (2000-2003)
![Page 18: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/18.jpg)
Correlation of NBUC and DWBC transport with alongshore currents of array
Moored observations at 11°S (2000-2003)
Variability in the upper ocean is not correlated to deep ocean variability.
![Page 19: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/19.jpg)
Western boundary circulation and the role of deep eddies in the tropical South Atlantic
Overview
• Western Boundary Circulation (Schott et al. 2004)- shipboard sections at 5°S (8 sections) and 11°S
(4 sections) - moored observations at 11°S (2000-2003)
• Deep Western Boundary Current Eddies
• Summary
Tropical Atlantic Workshop, June 2004
Marcus Dengler
Friedrich Schott, Peter Brandt, Jürgen Fischer, Lothar Stramma Carsten Eden, Rainer Zantopp, Karina Affler
Leibniz-Institut für Meereswissenschaften, Kiel, Germany
![Page 20: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/20.jpg)
Deep Western Boundary Current Eddies
along-shore velocity
Structure of DWBC similar to counter current structure
![Page 21: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/21.jpg)
Deep Western Boundary Current Eddies
Salinity distribution and contours of along-shore velocity
Oxygen distribution and contours of along-shore velocity
DWBC and offshore counter currents carry same water masses
![Page 22: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/22.jpg)
Deep Western Boundary Current Eddies
50-90d band-pass filtered time series
• EKE maximum largest at 1900m (K3,K4) and 2400m (K5)
• Maxima away from continental slope
![Page 23: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/23.jpg)
Deep Western Boundary Current Eddies
50-90 day band pass filtered velocities at 1900m (2400m) depth
Dengler et al., DSR, 2004
Sequence of anti-cyclonic sub-mesoscale eddies (about 6 per year)
cross-shore velocity
along-shore velocity
![Page 24: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/24.jpg)
20
20
20
2000
2000
H
)zz(
R
)tvtv())tt(ux(x(
0
0000eddy ee
R
))tt(ux(xAvV
20
20
20
2000
2000
H
)zz(
R
)tvtv())tt(ux(x(
0
0000eddy ee
R
tvtvAuU
alongshore component:
across-shore component:
Eddy fit to mooring data
Eddy model based on Gaussian-shaped density distribution
0000 tvy,tvy as array is one-dimensional
00 u,v
heightandradiusfoldingeH,R 00
eddyofcenterz,x 00
amplitudeA
- eddy translation
LACDP data Eddy fit
2000m
![Page 25: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/25.jpg)
Eddy fit to mooring data
Eddy model fit: min ])UU()VV[( 2eddyobs
2eddyobs
Data:
• 14 velocity time series
• 40h low-pass data
• 40-80 day ensembles
Explained Variance 46%
fit failed for two ensembles
![Page 26: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/26.jpg)
Average eddy parameters
Eddy translation
Along-shore = 3.8 cm/s
Cross-shore = 2.1 cm/s
3.9 cm/s westward drift > CR(3. mode)= 2.6 cm/s
1.8 cm/s southward drift
eddy translation not explainable by advection only
![Page 27: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/27.jpg)
Average eddy parameters
Eddy scale
Amplitude (gaussian)= 0.50 m/s Radius (e folding) = 60 km Eddy offshore center = 160 km Height (e folding) = 1100 m Depth of maximum = 2100 m
![Page 28: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/28.jpg)
Average eddy parameters
)s/cm1U,V(Volume eddyeddy Eddy Volume
average Volumeeddy = (13.9 +/- 5.9) x 1013 m3
DWBC- Volumeeddy = (10.5 +/- 3.6) x 1013 m3 (depth range: 1200-3800m)
![Page 29: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/29.jpg)
Box 6 transport from eddy sequence (-) and moorings (--)
- eddy scales could not be determined
Transport:
Box 6 (moorings) = -14.2 Sv
Eddies Box 6 = -15.2 Sv
total eddy DWBC transport (1200-3800m) = -17.9 Sv
Eddy Transport
DWBC array seesrectified eddy mean!
![Page 30: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/30.jpg)
Deep Western Boundary Current Eddies in Models
Eddy kinetic energy and mean kinetic energy at 1900m from FLAME model
FLAME Model
• 1/12° resolution
• Domain: 18°S-70°N, 100°W-16°E
• setup includes open boundary at 18°S
EKE distribution similar to distribution from 1/6° OPA model. (Trequier et al., JPO, 2003)
DWBC-EKE at 11°S only slightly enhanced in 1/12° Miami model.
![Page 31: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/31.jpg)
Deep Western Boundary Current Eddies in Models
FLAME Model eddy kinetic energy along 10°S
Deep EKE maximum similar to observations
Snapshot of along-shore and across-shore velocity
![Page 32: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/32.jpg)
Deep Western Boundary Current Eddies in Models
Velocity vectors and density perturbation
• Model suggests eddy generation near 8°S.
• Continental slope turns sharply to the west.
![Page 33: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/33.jpg)
Upper layers
• NBUC - average transport: at 5°S from 8 sections: 26.8 Sv, at 11°S from moorings: 27.8 Sv - 13 Sv as part of STC
- SEC bifurcation well south of 11°S - stable NBUC core at 5-11°S
- strong annual and semi-annual transport variability - significant interannual differences in NBUC (linear trend: 1.5 Sv/year)
- relation to STC variability? - how much near boundary vs. interior? (in Pacific: interior variability partially compensated by wbc)
• AAIW-Layer - offshore southward recirculation (5 Sv) - how does it connect? - Miami model: NBUC retroflection - - 800m RAFOS show inflow from east
Summary
![Page 34: Western boundary circulation and the role of deep eddies in the tropical South Atlantic Overview Western Boundary Circulation (Schott et al. 2004) - shipboard](https://reader035.vdocuments.us/reader035/viewer/2022070403/56649f2a5503460f94c44572/html5/thumbnails/34.jpg)
Deep circulation
• DWBC transports at 5-11S - at 5°S (8 sections): net southward flow –20 Sv
- at 11°S (4 sections): section net –23 Sv - DWBC transport from eddies: about –18 Sv
• DWBC Eddies - 5-6 DWBC eddies per year (similar to NBC rings) - carry water masses of the DWBC southward - westward translation agrees with eddy dynamics (southward translation?) - FLAME simulation indicate: - generation at ~7-8°S
- eddy size correlates with upstream DWBC transport - eddy existence implies no „classical DWBC“ south of °S
Summary