1. L. Gourdeau (LEGOS/IRD-Noumea)
South Pacific Ocean and SPICE: Jets around Vanuatu and New Caledonia from an inverse box model A. Ganachaud JISAO/PMEL/NOAA LEGOS / IRD Nouméa-Toulouse Laboratoire d’Etudes Géophysiques et d’Océanographie Spatiale
Bonjour je vais présenter aujourd’hui une expérience d’océanographie que nous mettons en place sur la Mer de Corail, mon équipe et moi-même, en collaboration avec les pays de la région. Cette expérience se base sur des études de prospection, en cours, menées par l’UR65 depuis deux ans.
Nous nous intéressons essentiellement à la circulation océanique des eaux de thermocline, c’est-à-dire entre la surface océanique et 500 mètres, et nous allons voir pourquoi. Cette carte qui date de 150 ans.
This old picture provides the basis of the oceanic circulation in the south west Pacific, and it is surprinzingly correct. A westward flow which splits northward and southward when arriving at the Australian coast, ans a branch going directly in the Salomon sea.
Black (1851)
L. Gourdeau (LEGOS/IRD-Noumea)
W. Kessler (PMEL)

2. Thanks to:
Billy Kessler Eddie Bernard Dennis Moore Vallapha, Ansley, Ryan and Tracy, ...and MANY dear friends and colleagues

3. Outline South Equatorial Current, jets and climate
The SECALIS cruise series
An inverse model of SECALIS-2 and SECALIS-3
SPICE
PNG
SOLOMON IS.
Solomon
Sea
Coral
Sea
Fiji
VANUATU
N. CALEDONIA
AUSTRALIA
Tasman
Sea
NEW
ZEALAND

4. The Southwest Pacific Atmosphere
SPCZ
Trade winds
Trade winds A A

5. Decadal influences: Thermocline water connection between the subduction zone of the South East Pacific and the equator
Lines show geostrophic streamlines on the isopycnal (courtesy B. Kessler)

6. Decadal influences: Thermocline water connection
SST
TO WBC
TO EAST
8°S, East to West
Equator
Giese et al. 2002:
T on sigma=25
AUSTRALIA
UPWELLING
A temperature anomaly on sigma=25 (EUC core) from the Southeast Pacific preceeds Nino-3 by 7 years
Giese et al. 2002, Schneider 2004, Luo et al. 2005
Izumo et al., 2002: Origins of Nino 3 waters

7. The South Pacific "Thermocline" waters
Equatorial Current
Salinity maximum Z=100:300m
Temperature/salinity diagram

8. Southwest Pacific Topography
PNG
SOLOMON IS.
Solomon
Sea
Coral
Sea
Fiji
VANUATU
N. CALEDONIA
AUSTRALIA
Tasman
Sea
NEW
ZEALAND

9. Thermocline water currents: 0-300m
~25 Sv

10. Thermocline water currents 0-300m
70 % EUC waters
~15 Sv
~25 Sv

11. Thermocline water currents 0-300m
~15 Sv
~25 Sv
~10 Sv

12. Jets in numerical models
OCCAM model, Webb, JPO, 2000

13. The South West Pacific Ocean: poorly sampled and poorly understood
Sokolov and Rintoul (2000)
Qu and Lindstrom (2002)
Ridgway and Dunn (2003)
The data in the South west Pacific are very sparse and by example there is big area in the Coral sea without Argo floats. By consequence the circulation in this area is very little documented and the papers have focused on the mean circulation.
Active Argo floats on 08/17/2007
Distribution of the (T,S) casts (Ridgway and Dunn, 2003)

14. The South West Pacific Ocean: poorly sampled and poorly understood
Sokolov and Rintoul (2000)
Qu and Lindstrom (2002)
Ridgway and Dunn (2003)
The data in the South west Pacific are very sparse and by example there is big area in the Coral sea without Argo floats. By consequence the circulation in this area is very little documented and the papers have focused on the mean circulation.
Active Argo floats on
March 4, 2008
Distribution of the (T,S) casts (Ridgway and Dunn, 2003)

15. The SEC-ALIS cruises S E C ??? RV ALIS
VANUATU
???
NEW
CALEDONIA
RV ALIS
Transport between New Caledonia and Vanuatu:
Andrew and Clegg (1989): southeastward (!)
Sokolov and Rintoul (2000): 41 Sv
Climatology: Sv
Island Rule: Sv
Numerical models: Various
Existence of a boundary current to the northwest?
To the southeast ?

16. The SEC-ALIS cruises ??? RV ALIS SECALIS-1: Jul 2003
SECALIS-4: Nov 2006
SECALIS-2: Dec 2004

17. Cruise Secalis-2
December 2004 : snapshot of the circulation, chasing the jets
Terrible winch but good mechanics
Closed box, inverse box model by requiring mass, heat and salt conservation within isopycnal layers
2000-db reference level
GUESS

18. SECALIS-2: Water mass
SLW
AAIW

19. South Pacific Tropical Water (SPTW)/ Subtropical Lower Water
200m
In the core of the EUC, in the lower salinity maximum (S=24.3/24.5)
Warm SPTW (21°C)
COLD SLW (16/20°C)
S=25.5

20. Subantarctic Mode Water (SAMW)
formed north of the ACC
(S=27)

21. Antarctic Intermediate Water (AAIW)
salinity minimum
formed in the southeast PF (50°S-60°S)
(S=27.2)
northern limit

22. "Oxygen minimum" water (Wyrtki 1962)
formation ??
(S=27.6)

23. Inverse model formulation

24. Inverse model formulation
Define vertical layers;
Write cons. Equation for:
Mass
Heat (anomaly)
Salt (anomaly)
Including Ekman
transports

25. Inverse model estimate for the velocity field:
North Caledonian JET
NCJ
GUESS
Inverse model estimate for the velocity field:
50cm/s,
15±2.6 Sv,
deep shear

26. Oceanic circulation in Dec 2004
Ganachaud, Gourdeau, Kessler,
JPO, 2008
Inverse model
OCCAM 1/12° 2004 average
above σ=26
below σ=26

27. Oceanic circulation in Dec 2004
Ganachaud, Gourdeau, Kessler,
JPO, 2008
Transport m
14 Sv
20 Sv
OCCAM 1/12° 2004 average 9
6.5
above σ=26
below σ=26

28. Net transports in Dec 2004 and July 2005
Net transports (Sv)
December 2004
Net transports (Sv)
July 2005 5
195
396
143
104
204
215 5 9 9

29. Upper 300m transports in Dec 2004 and July 2005
Upper layer transports (Sv)
December 2004
Upper layer transports (Sv)
July 2005
4.51
151
222
8.51
6.51
9.51
4.4
2.5
above σ=26
1.6
below σ=26

30. 0.70.2 Net Heat transports 2.60.3PW above σ=26 below σ=26
Net transports (Sv)
December 2004
Net transports (Sv)
July 2005
0.70.2
2.60.3PW
above σ=26
below σ=26

31. Glider measurements, 2005 (Gourdeau, Kessler, Davis, Sherman)
U, T and S
Prototype, Scripps OI, San Diego
Dropped July 17th, 2005
Recovered october 18th, 2005
C. Maes, IRD

32. Glider measurements, 2005 (Gourdeau, Kessler, Davis, Sherman)
cruise
Gourdeau et al. 2007
Transport is similar to CTD-LADCP estimate

33. Conclusions on SECALIS program
A regional picture of the SEC splitting and jet formation east of New Caledonia is emerging:
2004 cruise: NCJ, SCJ characterized
2005/2006 cruise: NCJ, NVJ and Glider feasibility (July/November)
The NCJ shear is deep (700m-1500m) so that XBTs miss it
Ongoing work:
Mean circulation and variability from Secalis, glider surveys and models
XCTD/XBT/Argo monitoring
SPICE

34. Interests in the Coral and Tasman Sea circulation
Rotschi, Legand, Hamon
R/V ORSOM III, 1956 interisland flows
Cronulla, August 1958 Conference on the Coral and Tasman Sea Oceanography
Cairns, August 2005 Workshop on the Southwest Pacific Ocean Circulation and its relation with Climate

35. Southwest PacIfic Ocean Circulation and Climate Experiment: SPICE
W. Kessler (PMEL/NOAA)
G. Brassington(BOM)
R. Mechoso (UCLA)
S. Wijffels, K. Ridgway, W. Cai (CSIRO)
N. Holbrook (MU)
P. Sutton, M. Bowen (NIWA)
B. Qiu, A. Timmermann (UH)
D. Roemmich, J. Sprintall (SIO),
D. Neelin, B. Lintner (UCLA)
H. Diamond (NOAA/NCDC)
S. Cravatte, L. Gourdeau (LEGOS)
P.Eastwood (SOPAC, Fiji)
T. Aung (USP/Fiji)
Black (1851)

36. Southwest PacIfic Ocean Circulation and Climate Experiment
Objectives: 1-Understand the SW Pacific in climate / CGCM incl. SPCZ 2-Measure air-sea fluxes and currents in the -Coral, -Solomon -and Tasman seas
Objectives: 3-Combine obs with modeling to elaborate a monitoring plan 4-Determine local oceanic environment influences

37. Southwest PacIfic Ocean Circulation and Climate Experiment
Objectives: 1-Understand the SW Pacific in climate / CGCM incl. SPCZ 2-Measure air-sea fluxes and currents in the -Coral, -Solomon -and Tasman seas
Objectives: 3-Combine obs with modeling to elaborate a monitoring plan 4-Determine local oceanic environment influences

38. South Pacific Convergence Zone
COADS cloudiness
20th century climate model
High convective activity, precipitation, wind convergence -Dominant convective feature in the Southern Hemisphere -Substantial variability: (intra) seasonal; interannual;Equatorward shift Unresolved southward bend, poorly modelled -Strong local effects (SSS, oceanic heat content)

39. Thermocline water currents 0-300m
3-Solomon Sea
1-Inflows
2-Tasman Sea

40. Relation w/ climate/ENSO
2-EAC and EAUC
South
Equatorial Current
Equatorial upwelling
East Australian Current
Tasman Front
Equatorial Undercurrent
The second issue of SPICE concerns the EAC.
EAC variability:
Relation w/ climate/ENSO
Eddy generation
Air-Sea fluxes

41. SWPacific and Climate EAC and the Tasman Front
The Southward Pacific WBC which closes the subtropical gyre (Ridgway and Dunn, 2003)
Looking at more to the South, the East Australian Current is the western boundary current which returns the main gyre flow to the South. It separates from the coast as a series of filament and in the Tasman front at 32°S before to reattaches the East Auckland Current north of New Zeland.
The EAC extension to the south reattaches the Tasman outflow and EAC can be seen as another throughflow to connect the PAcific and Indian Ocean gyres.
The three southern gyres are connected forming a supergyre. This supergyre is an important piece in the modelisation of global warming where the EAC is seen to shift southward.
Alex:. The EAC is the South Pacific western boundary current which returns the main gyre flow to the south. Formed south of the bifurcation and separates from the coast as a series of filaments, the main flow is at ~32°S (Tasman Front, B). Reattaches to coast north of NZ > East Auckland Current & sequence of quasi-permanent eddies

42. Solomon Sea: A WBC pathway to feed the EUC and ITF
South
Equatorial Current
Equatorial upwelling
East Australian Current
Tasman Front
Equatorial Undercurrent
Solomon Sea
The next issue concerns the north Coral sea

43. Solomon Sea: A WBC pathway to feed the EUC and ITF
GEORGES ST
SOLOMON
VITIAZ
CARS dynamic Ht relative to 2000m (C. W. Kessler)
NVJ
NCJ
Quasi undocumented circulation
WEPOCS cruises, 1985
(Lindstrom et al., 1987; Tsuchiya et al., 1989; Fine et al., 1994)

44. 3-North Coral Sea: A WBC pathway to feed the EUC and ITF
Narrow straits, difficult to model
Strong WBC, mixing
Strong variability: monsoon, ENSO
0-200m SADCP currents, May 1993
Blue: 2007 glider trajectory (C. W. Kessler)

45. Solwara Pilot study Accomplished: Flusec cruise (inflow)
Glider (inflow)
To do:
Mooring in key straits
Glider monitoring
Plans in the NQC/Papua Gulf
SOLWARA project (IRD-PMEL-SIO-CSIRO, submitted

46. Ocean and climate impacts on environment in the southwest Pacific
Consequences of ocean and climate fluctuations:
Biodiversity, Coral reefs
Freshwater-agriculture and health
Tropical cyclones
Sea surface height
PIC High sensitivity to the oceanic environment
Pacific Island Countries:
Fragile ecosystems, low-lying populated areas, isolated places
Australia and New Zealand:
Climate depends on heat content in the Tasman Sea
Freshwater resources critical
Important changes in biodiversity
SST Trend (°C/century)
ERSST data ( )

47. Interannual influences: ENSO and cyclones
Courtesy J. Salinger
La Niña - Tropical Cyclone Density

48. Downscaling climate and ocean models
Les îles du Pacifique sud-ouest sont particulièrement sensibles à l’environnement océanique de par la fragilité de leur environnement, leur vulnérabilité aux changements climatiques (montée des eaux, par exemple), leur isolement et leurs ressources naturelles limitées. Le programme Pacific Islands' Global Ocean Observing System (PI-GOOS, Fidji, a pour mission d’effectuer l’interface entre les programmes internationaux d’étude du climat et de l’océan et les gouvernements et populations insulaires, pour consolider les capacités des gouvernements insulaires aux prises de décisions dans le cadre d’un développement durable. Sarah Grimes, coordinatrice PI-GOOS, est impliquée dans l’élaboration de SPICE et nous souhaitons impliquer l’IRD sur cet aspect. Les moyens mis en œuvre pour les actions de recherche du LEGOS-Nouméa pourront être utilisés à des fins applicatives. Un poste d’accueil sera demandé pour cette action, complémentaires aux thématiques du LEGOS, et demandée à l’IRD par les communautés insulaires.
J. Lefevre, IRD
Need to link between large-scale oceanography, coastal island oceanography, and impacts on climate and environment
New Caledonia Upwelling
(A. Vega, M. Despinoy)

49. Towards a regional field experiment
2010
2007+
2007+
2005+
2004+
2008
2007+
2008
running
TBS
TBS

50. Modelling strategy: regional zooms
Help to design observation / monitoring program
Sensitivity experiments
Regional applications
CSIRO/BOM
UH/LOCEAN
UH/LEGOS
IRD/NIWA
IRD/CNRS/CNES/IFREMER/METEO-FRANCE/SHOM

51. Towards a regional field experiment: Existing large scale programs
UW/CSIRO/IRD
IRD
SIO/CSIRO/IRD
BOM/MF
BOM/IRD
IMOS/Bluewater and climate

52. Au revoir
et merci !!

53. Tentative timetable

54. Glider measurements, 2005 (Gourdeau, Kessler, Davis, Sherman)
580 CTD profiles down to 600 meters
Absolute geostrophic velocity field
Temperature
NVJ
Salinity
Gourdeau et al. 2007
NJC

55. 1-Modeling strategy: regional zooms
Help to design observation then monitoring program
Sensitivity experiments
Regional applications
High resolution global/regional ocean, atmosphere and climate models
Blue Link (CSIRO/BOM)
ROMS/Mercator (IRD Nouméa)

56. Towards a large scale field experiment Existing observations
Sokolov and Rintoul (2000)
Qu and Lindstrom (2002)
Ridgway and Dunn (2003)
Maximenko (2005)
Active Argo floats on 08/17/2007
Distribution of the (T,S) casts (Ridgway and Dunn, 2003)
Sattelite-derived surface currents

57. 2: EAC and the Tasman Front
Interannual Variability
(Sea level anomaly)
1996
2000
In this area, variability are observed at interannual time scale as shown here by looking at sea level anomaly around Australia between 1994 and 2005.
Also, with regard to global warming, a SST/trend south east of Australia is observed reaching 2°C in the last 60 years and this warming is corroborated by global climate forecast.
SST Trend (°C/century)
Global Climate Model Forecast
Mk Surface Temperature
ERSST data ( )
O’Farrell, 2005

58. Interannual influences: thermocline transport modulation
The next three slides illustrated the variability in the South west Pacific at different time scale.
At interannual time scale, there is a strong influence of El Nino. We look at the transport computed from XBT lines between New Caledonia and Salomon Islands. For the period, there is a strong relationship between the variability of the zonal transport from the South equatorial current in black and the South Oscillation Index of ENSO in red.
Courtesy B. Kessler
Interannual time scale:
El Niño influences the SW Pacific Circulation
(Delcroix and hénin, 1989; Sprintall et al., 1995; Gouriou and Delcroix, 2002)

59. 1-Thermocline water inflow to the Coral Sea
162.5°E zonal velocity (blue=westward)
TO EAC
TO NQC
NVJ
NCJ
SCJ
Bifurcation:
Qu and Lindstrom 2002
Kessler and Gourdeau 2006, 2007
Formation of 3 "jets"
Bifurcation (northward bias in GCM/CGCMs)
Outflows and budget

60. 2: EAC and the Tasman Front: Critical issues
Need to describe the Tasman Sea variability in the climate system:
EAC inflow and outflow component: robust estimates of the mean & seasonal cycle
Mechanism of EAC eddy generation
Tasman Sea heat balance and effects on air-sea fluxes and regional climate
Southward shift of the EAC associated with Global change
A this stage, there is a need to describe the EAC region variability in the climate system,
To estimate the mean and seasonal cycle of each inflow and outflow component
To understand the mechanism of eddy generation
To define accuratly the air/sea fluxes
About the maximum SST in global warming at 40°S, we don’t know how the south Pacific gyre redistributes this warming signal and if there are significant atmosphere-ocean feedbbacks?
There is a clear need in longer term monitoring and appropriate modeling experiment.

61. 3-North Coral Sea Critical issues
Flows in Solomon Sea need explanation from models and observations
Structure of the SEC inflow components
Structure and monitoring of WBCs
Straits transport monitoring and modeling (need ~1/20° resolution).
Dynamical response: WBCs adjustment to meridional and vertical variations
(western boundary influence on Equator is crucial, and we do not know where it originates).
Need a pilot study

62. Downscaling…and upscaling
ROMS, 1/12°, nested (Courtesy A. Vega, IRD)
J. Lefevre, IRD

63. SPICE Challenges

64. SPICE Challenges Modelling strategy Existing programs
Ocean field experiment
SPCZ process study (?)

65. Towards a regional field experiment
2005+
2004+
2008

66. Towards a regional field experiment
2010
2007+
2007+
2005+
2004+
2008

67. SPICE and CLIVAR
A. Ganachaud, W. Kessler, G. Brassington, S. Wijffels, K. Ridgway, W. Cai, N. Holbrook, M. Bowen, P. Sutton, A. Timmermann, B. Qiu, D. Roemmich, J. Sprintall, H. Diamond, S. Cravatte, L. Gourdeau, T. Aung
Relevance
1-Identify key features and their impact on climate simulation on seasonal to decadal timescales
2-Understand pertinent air-sea fluxes and oceanic currents (LLWBCs) to improve climate modelling and prediction
Legacy
1- Long term monitoring of selected features (SST, straits…)
2-Training and transition to local benefits (application of data or operational products)
"Add-on" Costs
1-Fieldwork:
Shiptime: 1.5month/yr
Wet measurements: $1.6M/yr
HRXBT, Air-sea fluxes: funded
2-Modelling:
Infrastructures exist
Specific analyses costs

68. Main objectives and timetable
A. Ganachaud, W. Kessler, G. Brassington, S. Wijffels, K. Ridgway, W. Cai, N. Holbrook, M. Bowen, P. Sutton, A. Timmermann, B. Qiu, D. Roemmich, J. Sprintall, S. Cravatte, L. Gourdeau, T. Aung
Objective
1-Role of the southwest Pacific in CGCMS (SPCZ, …)
2-Air-sea fluxes and currents
3-Monitoring key quantities
4-Local impacts
-SEC inflow (cruise and glider)
-Gyre dynamics and jets
-Experimental monitoring Solomon Sea
-Model downscaling (ROMS-type)
-Operational prototypes
-SSS-based analyses
-Modelling experiments -Major SPCZ experiments ?
-SEC infow monitoring
-Solomon Sea exploration (model, cruise, moorings, gliders)
-EAC monitoring
-VOS with AWS Hull SST
-Experimental monitoring SEC and Solomon Straits
-Regionally oriented applications and training
SPCZ/ocean
Session AGU 2007

69. 2-EAC and EAUC
Ridgway and Dunn, (2003); Cai et al. (2003); Bowen et al. (2005)
Distri-bution of the (T,S) casts

70. 2-EAC and EAUC 1.Variability dominates mean flow
Ridgway and Dunn, (2003); Cai et al. (2003); Bowen et al. (2005)
Distri-bution of the (T,S) casts
SSH variability
C. Ken Ridgway
1.Variability dominates mean flow
Similar SSH variability as other WBCs
2.Highly influenced by:
Non-linear flow instabilities
Upper-ocean topographic coupling
3.Tasman Box: Ocean heat transport changes influence regional climate (Sprintall et al. 1995, Roemmich et al., 2005