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Transcript
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
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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
• 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 WWBENSO interactions (Jin et al. 2007)
• What background conditions make this
interaction favorable?
ENSO-WWB interactions
WWB modulation by temperature
Eisenman et al. 2005
•East-ward propagating coupled instabilities
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
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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
Matthews et al 2000 QJR
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).
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, underrepresentation 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
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
ENSO
ACY
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
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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
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Standard Nino X indeces
Standard warm water indices (PMEL website)
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 modulationENSO
-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
SPCZ
A
A
South
Equatorial
Current
Thermocline water currents
SPICE Field Experiment
Overview
Outset for a large scale
field experiment
3-North Coral Sea
Pilot study
1-Monitoring
inflow
and bifurcation
2-EAC variability
monitoring
A-Existing large scale
programs
B-Pilot studies
C-Sustained observations
CTD section
SPICE cruise
XBT section
Mooring array
Glider section
Mooring line
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
www.ird.nc/UR65/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
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, 26-28 November 2007
Objectives
• To address key science questions, such as:
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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.