CLIVAR Pacific panel Report to OOPC-12, IOC/UNESCO, 2-5 May 2007 prepared by Axel Timmermann, presented/edited by Toshio Suga

Science questions of Pacific Panel Identified at the Panel meeting, Feb 2006 Why do CGCMs do a poor job in simulating cold tongue? Why do CGCMs do a poor job in simulating southeast Pacific climate What is the role of eastward-propagating WWB-SST interactions for ENSO? What determines the variations of ENSOs? How does the interaction between annual cycle and ENSOs work? What is the origin of Pacific multidecadal variability? What is the predictability of decadal variability in the Pacific? Vulnerabilities of present observing systems? What new observations are needed? How to observe and monitor LLWBCs, assess their climate relevance?

Contents Major science questions of Pacific Panel and observational requirements –ENSO Sensitivity to climate change –ENSO-WWB interactions –Understanding of SPCZ –Improving model biases in the eastern tropical Pacific –Interbasin connections on interannual to multidecadal timescales ENSO metrics SPICE South Pacific Observing network Workshop on Western Tropical Pacific: Hatchery for ENSO and Global Teleconnections (China, Nov 2007)

ENSO sensitivity to climate change Background state => MJO  ENSO Background state => annual cycle  ENSO Background state  ENSO  Orbital and millennial timescales => meridional control of ENSO  Greenhouse warming => meridional, zonal, subsurface control of ENSO and annual cycle  Decadal timescales => subsurface and meridional control of ENSO (footprinting)

ENSO sensitivity to climate change: Observational requirements ENSO sensitivity to climate change: Observational requirements Monitoring of SST, thermocline depth, boundary and interior transports Monitoring of Walker circulation (see Vecchi and Soden, Nature 2006) Monitoring of ENSO-MJO relationship Monitoring of subsurface anomalies (Argo, TAO, altimeter) Monitoring of heat flux convergences via drifter data, Argo data

ENSO-WWB interactions WWB activity modulates and is modulated by ENSO (Eisenman, Jin, Lengaigne) WWB is modulated by the annual cycle (Hendon and Zhang) Nature and Dynamics of these interactions still unclear Evidence for intensification of WWB and WWB- ENSO interactions (Jin et al. 2007) What background conditions make this interaction favorable?

East-ward propagating coupled instabilities Eisenman et al WWB modulation by temperature ENSO-WWB interactions

ENSO-WWB interactions: observational requirements Monitoring of zonal temperature advection Monitoring of MJO and warm pool heat budget “Precise” knowledge of WWB initial conditions (Lengaigne shows large loss of seasonal predictability if initial conditions are not well determined) => Pacific island data, PI-GCOS Monitoring of MJO-warm pool front propagation (satellites) and subsurface response (TAO, altimetry)

Understanding the South Pacific Convergence Zone Why is there a SPCZ? How is it connected to the ITCZ? How does the SPCZ interact with the MJO? How does the SPCZ interact with the SST How does the SPCZ respond to tropical and extratropical SST forcing on interannual to decadal timescales? What influence does the SPCZ wind convergence and its modulation have on southwest Pacific boundary currents?

Understanding the SPCZ Clouds and temperatures in observations (left) and NCAR CCSM3 model

Understanding the SPCZ Figure 1: Schematic of hypothesised mechanism for the development of convection along the SPCZ during an MJO. Convection over Indonesia (1) associated with the passage of a MJO leads to an upper tropospheric anticylone (2). Poleward of the anticyclone, there is a large PV gradient, associated with the subtropical jet and the tropopause (3). Equatorward advection of ``high'' PV air on the eastern flank of the anticylone leads to an upper tropospheric trough (4), which induces deep ascent to the east (5). This region of deep ascent, to the southeast of Indonesia, is over the SPCZ, an area susceptible to deep convection. Hence strongly enhanced convection can be triggered by the deep ascent and convection develops from Indonesia into the SPCZ (6). Matthews et al 2000 QJR

Understanding the SPCZ: observational requirements Series of detailed process studies needed (a la TOGA-COARE) focusing on cloud formation, boundary layer dynamics, atmosphere-ocean interactions Relationship between SST, SPCZ, Rain and Salinity using satellite data (Aquarius, SMOS) Response of ocean to variations in SPCZ (Argo, drifter data) SPCZ and subduction and mode-water formation (Argo, Repeat hydrography)

Improving model biases in the eastern tropical Pacific, cold bias and warm bias, SPCZ bias Possible origin of cold bias in coupled models (missing ocean biology, under-representation of TIWs, mixing, missing diurnal cycle of insolation, under-representation of Galapagos effect, uncertainties in convective parameterizations) Possible origin of warm bias in stratus regions (problems with cloud parameterizations and cloud-aerosol interactions, missing Tsuchiya jets, lack of horizontal resolution, under- representation of eddies in AR4 CGCMs)

Improving model biases in the eastern tropical Pacific, cold bias and warm bias Clouds and temperatures in observations (left) and NCAR CCSM3 model

Improving model biases in the eastern tropical Pacific, cold bias and warm and SPCZ bias: observations needed Vertical chlorophyll profiles => bio-optical feedbacks Better estimates of eddy-induced heat transports in the southeastern Pacific (VOCALS) Better observations of Tsuchiya Jets and their variability Observational estimates of TIW heat budgets Focused process study on SPCZ needed!

Interbasin connections on interannual to multidecadal timescales ACY ENSO AMO A weakened MOC leads to a reduction Of the meridional asymmetry in the eastern Tropical Pacific, hence a weakening of The annual cycle and an intensification of ENSO Whether the AMO reflects variations of the AMOC is still unclear, although modeling Results suggest a strong influence of the AMOC on Atlantic SST Challenge for ocean data assimilation to Establish a closer link between observed AMO and AMOC variability AMO: Atlantic Multidecadal Oscillation AMOC: Atlantic Meridional Overturning Circulation ACY: Annual cycle

Interbasin connections on interannual to multidecadal timescales, “observational requirements” Establish better statistical evidence for interbasin linkages using paleo-reconstructions of AMO (speleothems, drought indices), ENSO and annual cycle strength (corals, speleothems, varved lake sediments) Monitoring of MOC and AMO and their linkages with ENSO on decadal and longer timescales Monitoring of cross-central America moisture transport, stability of AMOC

ENSO metrics Societal relevance, application indices Standard Nino X indeces Rainfall over Peru and Ecuador, northern Australia Wave heights along Californian Coast Subsurface temperature around Galapagos Number of tropical cyclones in western tropical Pacific Chlorophyll concentration in Nino 3, and Nino 1 regions Upwelling indices in eastern equatorial Pacific, along the South and North American coast Seasonal forecasts not only of SST but also of primary productivity in Nino X regions (desirable, but not yet available) Coral bleaching indices from NOAA’s Reef watch Scientific relevance, advancing our understanding and prediction Standard Nino X indeces Standard warm water indices (PMEL web- site) MJO variance index (BMRC web-site) Second and third order statistics (including spectra) BJ index Transport indices (boundary and interior transports) SST-lead-lag correlation between east and west SSTA Growth rate and variance of ENSO as a function of calendar month Composite of annual cycle strength for El Nino and La Nina years TIW variance and heat transport Individual heat budget terms Moisture transport Atlantic-Pacific in atmosphere, interannual variations

Southwest PacIfic Ocean Circulation and Climate Experiment Goal: Observe, Model, and understand the role of the SW Pac Ocean in the: -Large scale decadal climate modulation- ENSO -Tasman Sea area -Generation of local climate signatures A. Ganachaud, W. Kessler, S. Wijffels, K. Ridgway, W. Cai, N. Holbrook, M. Bowen, P. Sutton, B. Qiu, A. Timmermann, D. Roemmich, J. Sprintall, S. Cravatte, L. Gourdeau, T. Aung

The Southwest Pacific Ocean SPCZ A A South Equatorial Current A A SPCZ

Thermocline water currents

SPICE Field Experiment Overview CTD section SPICE cruise XBT section Mooring array Glider section Mooring line A-Existing large scale programs B-Pilot studies C-Sustained observations Outset for a large scale field experiment 2-EAC variability monitoring 1-Monitoring inflow and bifurcation 3-North Coral Sea Pilot study

SPICE – issues on sustainable observations Argo floats are not numerous in the region because of the risk of getting stranded with strong Trade winds pushing the floats while they are transmitting their data at the surface. …expecting some Iridium floats Sattelite altimetry is being used, with some adaptation to improve the resolution near the coast/around islands. There are a few stations of surface ocean temperature monitoring (e.g. Noumea, Chersterfield, Wallis) that could be enhanced. HR XBT are a major repeat database, with the Tasman Box. We have in mind the possibility of improving the Noumea-Solomon Islands line for SPICE purposes (presently low resolution). Deployment of gliders 3/4 times/year to monitor the flow into the Solomon Sea from the South has been proposed. This would provide monitoring for 4 years. Deployment of moorings in the Solomon Straits is being proposed. This will be a 1-2 year monitoring, and we might consider continuous measurements in the future because those straits are the chokepoint of the southern EUC sources.

SPICE Implementation plan in progress Based on existing infrastructures and research groups Need for a process study in the SPCZ

South Pacific observing network High density XBT coverage - blue lines Low density XBT coverage - red lines and green region High density XBT coverage - blue lines Low density XBT coverage - red lines and green region

South Pacific observing network GCOS Surface Network (GSN)

South Pacific observing network; NEEDS Integrated data products for South Pacific needed Monitoring of South Pacific ocean currents and heat and salinity transports needed Monitoring of surfaces heat, momentum and freshwater fluxes needed Monitoring of boundary currents, heat transports and extratropical-tropical linkages => SPICE

Workshop on Western Tropical Pacific: Hatchery for ENSO and Global Teleconnections Guangzhou CHINA, November 2007 Objectives To address key science questions, such as: –does the South China Sea play an important role in the climate system or is it merely responding to Pacific/Indian forcing –How important is the South China Sea Throughflow in draining heat out of the Pacific? –What triggered the 2006/07 El Nino event? –What were the global impacts of the 2006/2007 El Nino? –How good was the forecast skill of the 2006/2007 El Nino? –How does the longterm Indian ocean warming affect the global climate system (including ENSO)? –What is the origin of the longterm Indian ocean warming? –How does the warm pool respond to anthropogenic climate change (atmospheric versus oceanic feedbacks)? To further engage the Chinese oceanographic and climate research community in CLIVAR To link the Chinese observational activities to other international field programs To seek international coordination in terms of field experiment timing and infrastructure (sharing ships, common XBT lines,...), large scale modeling projects, ocean, atmosphere and coupled.