Kein Folientitel

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• The Indian Ocean
• Friedrich SchottInstitut für Meereskunde an der
  Universität Kiel, Germany
• with input from lots of people (much of it on
  posters here)
• Introduction The monsoon circulation and Indian
  Ocean specifics
• WOCE plans vs what was accomplished overview
• The shallow cross-equatorial exchange and
  upwelling
• Some regional results NW Arabian Sea Red Sea
  outflow, monsoon response Indonesian Throughflow
  and pathways in the Indian Ocean SW Indian Ocean
  and Mozambique Channel flow
• Deep circulation and overturning
• Climate modes
• Remaining challenges and outlook

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Circulation schematic for Southwest Monsoon

• Great Whirl and Southern Gyre
• Upwelling concentrated in wedges and filaments
• cyclonic domes both sides of Sri Lanka
  upwelling?
• Indonesian Throughflow max.
• Ekman transport southward in both hemispheres,
  but northward winds on equ.
• Subduction in southern subtropics

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Circulation schematic for Northeast Monsoon

• Somali Current and East African Coast Current
  merge into SECC
• Doming NE of Madagascar open-ocean uwelling?
• Indonesian Throughflow min.
• some subduction in northern Arabian Sea
• Ekman transport northward in both hemispheres

In between monsoon seasons eastward wind stress
causesWyrtki Jets along equator, that send out
coastal Kelvin waves
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WOCE sections, arrays(plan do sections north of
10S in each monsoon season)
deep
NL, 2000
Moorings
November - April
May - October
not deployed
not covered
post WOCE
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Mid-depth (1000m) float vectors mapped
R. Davis objectives of Ind. OceanWOCE float
program accomplished !

• 228 floats/ 1100 float yrs
• southw. flow in Mozambique Channel
• strong flow on equator
• see poster!!

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• Surface drifter currents for both monsoon seasons
• 180 WOCE drifters 1992-95
• 350 TOGA/ENSO drifters since 1995
• shows seasonal reversal of meridional Ekman
  transports

SW Monsoon
SEC
NE monsoon
SECC
Courtesy P. Niiler
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Meridional streamfunction for Indian Ocean north
of 8S(JAMSTEC model MOM-2, 55 levels, 1/4 deg.
resolution)

• Shallow cross-equatorial cell of about 6 Sv
  transport and upwelling at 5-15 N
• Equatorial roll (10Sv), northward at surface
  southward underneath (Ekman transports)first
  discussed by Wacongne Pacanowski (1996)

• Upwelling at 5-10S

Miyama et al. (DSR II, in press)
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Schematic diagram of shallow cross-equatorial
circulation

• Cross-equ. transport 6.5 Sv by--thermocline
  Somali C.--Sverdrup/Ekman tr.
• upwelling in models 1/3 in domes around India

Subduction from Karstensen, Quadfasel, 2002
Schott, Schoenefeldt, Dengler, 2002
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• Northern Somali upwelling
• outflow from Great Whirl
• which fraction of the 10 Sv of shallow offshore
  flow is transformed into surface water?
• which fraction slumps back into thermocline?

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Upwelling comes from up to 400m depth
Miyama et al (2002)
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Where does upwelling come from (Jamstec model)?

• Upwelling sources Southern subduction region
  Indonesian Throughflow

• Northern upwelling off Somalia, Arabia,in domes
  around India / Sri Lanka

Particles up to 400m deep underway
Miyama et al. (DSR II, 2002)
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Northern Indian Ocean upwellingannual basis (Sv)
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Red Sea outflowMurray Johns, 1997and
2002seas. outflow cycle
Red Sea outflow cycle max. in Feb.
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Oman upwelling wedge observations (A.Fischer,
K.Brink et al., (2002)...and JGOFs
Flux buoy(Weller et al., 2001)
8N MOC/heat/FW transport studiesBeal et al,
2002 1995 SW monsoon developmentStramma et al,
2002 SW vs. NE monsoon
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Seasonal cycle in Arabian Sea by Rossby wave
propagation
Remote forcing from Laccadive High or around
India (McCreary et al., 1993)? Amplitude of
annual harmonic of SSH from TOPEX/POSEIDON
altimetry and ship section
Phase of annual harmonic
Brandt et al., 2002Stramma et al.,2002 annual
Rossby wave explains density/geostrophy
difference in seasonal ship sections at 8N
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Seasonality of the meridionaloverturning
circulation of the Arabian Sea
seasonally reversing shallow overturning cell
deep overturning cell
Stramma et al., 2002 Beal et al., 2002
Heat transport -0.6 PW in Aug. 93, 0.2 PW in
Jan.98
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Interannual variability of Great Whirl
Observed ICM 7 large interannual differences of
location and transport of GW.
Model study by Wirth et al. (2002) interannual
GW variability dominantlyinternally generated
(instabilities) rather than externally (i.e.
wind stress variability)
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Depth of seasonal response in northern Somali
Basin
WOCE ICM-7
Amplitude of annual harmonic in cm s-1
Explained variance in
Dengler et al., 2002
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Indonesian Throughflow studies during WOCE

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Indonesian Throughflow studies during WOCE

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40 Sv -40
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Circulation of SW Ind. Ocean derived by Donohue
and Toole (DSR II, in press) and poster!
18 Sv through Mozambique Channel above 27.96
kg m-3 (about 2000m) 19 Sv East Madagascar
Current 4 Sv northward in DWBC east of
Madagascar 76 Sv Agulhas
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Float studies
Moz. Channel flow and eddies
Chapman, di Marco,Davis, Coward DSR II (in
press) see poster 117
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Is there a route to the Mozambique Channel from
south of Australia (lower thermocline)?
Tasmanleakage
ORCA model study of Speich et al. (2002)
backtracking of particles poster 24!
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Mean current field at 310m of global ECCO model
Courtesy D. Stammer
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Mozambique Channel eddies (1996-2001) Schouten et
al DSR II, in press

• Eddies propagate through Moz. Channel toward
  Agulhas and encourage pinch-off of Agulhas
  Rings
• are eddies triggered at northern Channel end by
  Rossby waves? And these in turn by
  equatorial/boundary Kelvin waves? (trans-
  Indian teleconection)? De Ruiter et al (2002)

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Deep inflow into the Australian Basin (and across
the 90E Ridge)
2.3Sv 6.7Sv
Warren and Johnson, 2002
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Inverse analysis results for the deep Indian Ocean
Ganachaud et al. (2000) deep flow
belowgn27.09 8 Sv at 32 S 10.5 Sv at 20S11
Sv at 10 S
Sloyan and Rintoul (2001)
23 Sv of deep overturning at 32S, only 4Sv at 18S
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Estimates on meridional overturning at 32S
Toole and Warren (1993) 27 Sv Robbins
and Toole (1998) 12 Sv Sloyan and Rintoul
(2001) 23 Sv Ganachaud et al. (2000) 8 Sv
(obtain similar structure as TW93
i.e. upwelling to shallower layers as
SR01) Difference Ganachaud et al vs.
SloyanRintouldue to different diapycnal flux
assumptions?(sections are partially the
same...)
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Is there enough deep mixing to a explain a 10 Sv
deep overturning cell?
Overturning and required eddy coeficients in
Ganachaud et al. (2000) solution
but poster by Talley/Reid/Sprintall
(19)concludes that only 5x10-4 m2s-1 is needed
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Deep overturning in assimilation of WOCE Ind.
Ocean lines

• Basin model with 10 Sv Indonesian Throughflow

• 18 Sv of deep inflow below 3200m
• 8 Sv of deep cell crosses equator
• strength of deep cell independent of Throughflow
• southward outflow at 1000-3200m
• only small heat transport (0.1 PW) by deep cell

0
4
10

• Equatorial roll present, southward near-surface
  (Ekman) transports
• upwelling at 5-10S

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Ferron and Marotzke, DSR II (in press)
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Comparison of regional and global assimialtion
results forIndian Ocean overurning transports
Note different sign convention!
Much weaker deep cell in ECCO model
0
4
10
18
Ferron and Marotzke (DSR II, in press)
Stammer et al., JGR 2002)
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SOC net heat fluxes (Wm-2) over Indian
Ocan(Josey et al., 1999) (global 30 Wm-2 net
heat gain!!As da Silva et al., 1994)
150 W m-2 -150
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Meridionalheat transport (PW)
SOC fluxes courtesy S. Josey
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Role of intraseasonal variability
27 day fluctuations (near-equatorial)
40-60 days
In early WOCE reproduced in seasonally driven
models i.e they were presumably due to
instabilities(Kindle Thompson, 1989 Woodbury
et al., 1989)
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Role of intraseasonal variability
15 day fluctuations
40-60 days
New observations (ICM-9) shorter periods (15
days) and meridional comp. well correlated with
local equ. winds (Yanai waves) East of
Madagascar 60 day variability resonant Rossby
waves (Warren et al., 2001)
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Difference in variance (cm2 s-2) between the run
driven by diurnal winds and the run driven by
smooth climatology. Intraseasonally forced energy
in equatorial band and in the west
Sengupta et al. (2001)and pers. comm.
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Role of interannual variability
Indian Ocean Dipole mode or Zonal Mode Saji
et al. (1999), Webster et al. (1999)
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Indian Ocean Dipole mode ensemble patternWind
stress and SST
Peak (SON)
Courtesy H. Annamalai
But, is it really a dipole or zonal mode?
After Saji et al. (1999)
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Indian Ocean Zonal Mode parameters
SST (west) and (east) in equ. Indian
Ocean SST-Diff W-Eand zonal windstress anomaly
in central equ. Indian Ocean SOI Index
(inverted)and windstress anomaly
BarsENs
Feng and Meyers (2002)
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T/P altimetry sea level anomalies during dipole
episodes of 1994 and 1997

• Ekman convergence at 5-10 S

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• EOF-1 of SSH-Anomaly (38 of variance)
• SSH (and SST) max northeast of Madagascar
• SSH (and SST) min west of Sumatra
• thermocline deepening in west
• shallowing in the east

Feng and Meyers, DSR II, in press
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Tropical cyclone days for Dec-Apr
Xie et al., 2002)
Climatological mean of number of cyclone days
(contours)difference between deep and shallow
mixed layer (shading)
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And beyond... Remaining WOCE challenges

• What happens to the net deep inflow (by 3
  western boundary currents) Is there a deep
  meridional overturning cell in the Indian Ocean?
  If so, what is the physical mechanism of water
  mass transformation and deep upwelling
• Where does upwelling occur really so much
  in offshore domes as suggested by models?
• Connection of Indian Ocean STC with Pacific and
  Atlantic and role in decadal variability
• Deep response to the monsoon variability (not
  studied in WOCE)
• Role of remote vs. local forcing in regional
  monsoon phenomena
• and the flux problem ...
• Indonesian Throughflow not directly measured in
  WOCE but our hopes are with the new program
  INSTANT (Sprintall et al.)

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INSTANT Indonesian Throughflow measurementsADCP
moorings 2003-2006 in the important
passages!!(AU/FR/INDON/NL/US)
A. Gordon, J. Sprintall,pers. communication
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And beyond...

• Oceans role in climate anomalies the Indian
  Ocean Zonal Mode use Rossby waves for
  predictability?

• Intraseasonal variability growing evidence
  relating coupled mode in Bay of Bengal to Indian
  monsoon breaks is there predictability?

• How to improve physical fields for improved
  ecosystem models Can we better quantify
  upwelling by combining observations? or more
  general benefit from increased WOCE/JGOFs type
  cooperation

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Drinks!!