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)

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

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

The Southwest Pacific Atmosphere SPCZ Trade winds Trade winds A A

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)

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

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

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

Thermocline water currents: 0-300m ~25 Sv

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

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

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

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)

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)

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: 10-12 Sv Island Rule: 10-11 Sv Numerical models: Various Existence of a boundary current to the northwest? To the southeast ?

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

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

SECALIS-2: Water mass SLW AAIW

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

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

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

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

Inverse model formulation

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

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

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

Oceanic circulation in Dec 2004 Ganachaud, Gourdeau, Kessler, JPO, 2008 Transport 0-2000m 14 Sv 20 Sv OCCAM 1/12° 2004 average 9 6.5 above σ=26 below σ=26

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

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

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

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

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

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

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

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)

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

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

South Pacific Convergence Zone COADS cloudiness 1960-1970 20th century climate model High convective activity, precipitation, wind convergence -Dominant convective feature in the Southern Hemisphere -Substantial variability: (intra) seasonal; interannual;Equatorward shift 1976 -Unresolved southward bend, poorly modelled -Strong local effects (SSS, oceanic heat content)

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

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

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

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

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)

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)

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

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 (1944-2005)

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

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, www.sopac.org), 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)

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

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

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

Au revoir et merci !!

Tentative timetable

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

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)

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

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 Mk3 2070 Surface Temperature ERSST data (1944-2005) O’Farrell, 2005

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 1985-2002 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)

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

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.

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

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

SPICE Challenges

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

Towards a regional field experiment 2005+ 2004+ 2008

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

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 2008-2011 1-Fieldwork: Shiptime: 1.5month/yr Wet measurements: $1.6M/yr HRXBT, Air-sea fluxes: funded 2-Modelling: Infrastructures exist Specific analyses costs

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 2004-2007 -SEC inflow (cruise and glider) -Gyre dynamics and jets -Experimental monitoring Solomon Sea -Model downscaling (ROMS-type) -Operational prototypes -SSS-based analyses 2008-2010 -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

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

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