Tropical Atlantic Climate Experiment

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Tropical Atlantic Climate Experiment
(TACE) TACE White Paper
http//www.clivar.org/science/atlantic.htm
Authors F. Schott, J. Carton, W. Hazeleger,
W. Johns, Y.
Kushnir, C. Reason, S-P. Xie
Contributors B. Bourles, D. Dommenget, M.
Latif, P.
Malanotte-Rizzoli, C. Zhang TACE
Synopsis http//www.clivar.org/science/atlantic.
htmNEWS
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• History leading up to TACE
• COSTA Workshop (May 1999, Miami)
• Subtropical Cells Workshop (Oct. 2000, Venice)
• CLIVAR Workshop on TAV (Sep. 2001, Paris)
• Tropical Atlantic Workshop (Aug. 2002, Kiel)
• TAV/AMMA meeting (ad hoc, Mar 2003, Miami)
• CLIVAR Atlantic Panel (Apr 2003) subgroup
  charged with drafting a TACE plan
• TAV/TACE meeting (June 2004, de Bilt)
• Review of TACE by CLIVAR Atlantic Panel (Oct.
  2004) Comments received from WGSIP
• TACE Implementation Workshop (Feb. 2005, Miami)

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• Key Climate Processes in the Tropical Atlantic
• The SST Meridional Gradient Mode
• The Atlantic Nino
• The Benguela Nino
• Western South Atlantic (SACZ,SITCZ) Variability

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SST Gradient Mode Atlantic Nino
Mode
First EOF (33) of the March-April rainfall from
GPCP 1979-2001 (contours in mm/day). March-April
SST anomaly (colors, in C white contours,
every 0.2) and surface wind anomaly (vector, in
m/sec) are determined by regression on the time
series of the rainfall EOF.
First EOF (23) of the June-August rainfall from
GPCP 1979-2001 (contours in mm/day). June-August
SST anomaly (colors, in C white contours,
every 0.2) and surface wind anomaly (vector, in
m/sec) are determined by regression on the time
series of the rainfall EOF.
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The Benguela Nino
The temporal history of sea surface temperature
anomalies (C) (left hand panel) spatially
averaged from 10 to 20S, and from 8E to the
coast of south-western Africa. The right hand
panel shows the standard deviation of OI-SST
anomalies from 1982 to 1999 (C). This area
corresponds to the location of sea surface
temperature anomalies associated with Benguela
Niños (Florenchie et al., 2003).
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Large-scale Ocean Circulation and its role in TAV

• Subtropical Cells (STCs)
• Supply of subducted waters to upwelling zones
  (EUC,NEUC,SEUC)
• Southern hemisphere branch is dominant
• Interannual variability - impacts on the
  equatorial thermocline?

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• TACE Objectives
• Enhance existing observing system to provide the
  data needed for research and operations.
• Improve coupled predictive systems, ocean
  synthesis, and transfer from science to
  operations.
• TACE is planned as 6 year (2007-2012) enhanced
  monitoring study, ultimately leading to
  specification of the sustained observations
  network in the tropical Atlantic needed to meet
  CLIVAR goals

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From Proceedings of the CLIVAR Workshop on
Atlantic Climate Predictability, April
2004 Overarching Challenge To realize
fully the potential of seasonal predictions for
the tropical Atlantic. The potential
skill and value of seasonal forecasts is highest
in the tropical Atlantic. The challenge is to
build a seasonal climate prediction system for
the tropical Atlantic region that is comparable
(in terms of data coverage, model fidelity, and
-subject to physical limits- forecast skill) to
that in the tropical Pacific.
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• Observational foci for TACE
• For seasonal predictions
• (i) in-situ surface and subsurface current,
  temperature and salinity measurements along the
  Atlantic equator,
• (ii) surface and subsurface temperature and
  salinity measurements in the eastern
  off-equatorial portions of the basin between 20ºS
  to 20ºN, including the coastal upwelling regions
  off NW Africa and SW Africa,
• (iii) in-situ surface measurements of
  temperature, air temperature, air humidity,
  radiative fluxes and winds north and south of the
  equator through the regions of dominant SST
  variability. Additionally, satellite measurements
  of SST (including microwave SST), sea surface
  height, wind stress, cloudiness, precipitation,
  and ocean colour are needed throughout the TA
  region.

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Observational foci for TACE For
interannual variability and longer time scales
(in addition to above)     (i) upper ocean
temperature and salinity throughout the tropical
Atlantic, (ii) moored time series sections
in the central/eastern equatorial band ( 5ºS to
5ºN) to monitor the equatorial wave system and
the supply of water masses to the eastern
equatorial thermocline and the Angola and Guinea
domes, (iii) surface drifters to monitor the
divergence at the equator from upwelling regions
to subduction regions, (iv) tracer
observations to monitor changes in ventilation
rates to the equatorial thermocline, and
(v) atmospheric soundings to study boundary
layer and air-sea interaction processes occurring
under the varying SST regimes.
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• Modeling foci for TACE
• Determine oceanic processes important in
  regulating SST in the tropical Atlantic and
  associated atmospheric responses
• Improve SST forecasts on seasonal to interannual
  time scales in the tropical Atlantic
• Provide parameterizations and model improvements
  to global and regional prediction centers
• Investigate response of tropical Atlantic region
  to global warming, including teleconnection
  patterns

• Promote synergy between research-mode models and
  operational centers

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Observing System Components
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Findings/Recommendations from the TACE Workshop
(1) Participants endorsed the TACE
initiative as timely and relevant. (2) A
critical mass of people and resources are focused
on the problem. Much of the observational plan is
already subscribed. (3) The overall
observational plan is suitable but needs
enhancements Recommended Observational
Enhancements - More focus on western equatorial
region to improve equatorial SST predictions
(recommended additional moorings across the
equatorial waveguide at 35ºW) - Address the
data void in the southwestern tropical Atlantic
(recommended extend the 23ºW array to at least
10ºS) - Better observational coverage is needed
of the eastern Gulf of Guinea, incl. south of the
equator (recommended enhance profiling float
coverage probably the best alternative due to
vandalism problems with PIRATA moorings in the
region)
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Findings/Recommendations from the TACE Workshop
(cont) (4) A more focused effort on model
development and intercomparison for the tropical
Atlantic (and Pacific) is needed. The Clivar
WGOMD charter is focused on mid-to-high
latitudes therefore the WGSIP may be the logical
place to coordinate this activity. An initial
step would be to organize a comparison experiment
of currently available high-resolution data
assimilation models of the region (MERCATOR,
HYCOM/GODAE, etc.) (5) A TACE data archive
(distributed mode) needs to be created to
facilitate and encourage full use of TACE
observations in synthesis experiments.
(6) Two TACE Working Groups should be
established - A TACE Observations Working
Group (coordinate observational logistics,
evaluate effectiveness of the observational
network, develop needed enhancements) - A TACE
Modeling and Synthesis Working Group (work with
WGOMD and WGSIP to coordinate modeling efforts,
encourage collaboration between research modelers
and operational centers, provide transitions to
operational centers)
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• TACE Next Steps
• Submit revised TACE plan (incorporating workshop
  recommendations) to CLIVAR Atlantic
  Implementation panel for final comment and
  endorsement.
• Draft Terms of Reference for TACE Working Groups
  appoint membership
• Follow-up at Tropical Atlantic Workshop (October
  2005)
• Implementation