GFDL ODA ACTIVITIES for CLIMATE

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GFDL ODA ACTIVITIES for CLIMATE

• A.Rosati
• T.Delworth
• M.Harrison
• S.Zhang

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ODA and CLIMATE

• Produce forecasts (SI, decadal) from ODA
  initialization
• Improve climate variability analysis (Carbon/heat
  uptake, circulation, )
• Climate change detection
• Model parameter estimation
• Observing system design
• Model Validation

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GFDLs CM2.x Coupled Climate Models Efforts in
Support of the IPCC AR4 the US CCSP
In 2004, following several years of intensive
development efforts, a new family of GFDL climate
models (the CM2.x family) was first used to
conduct climate research. The CM2.x models are
being applied to decadal-to-centennial time scale
issues (including IPCC-style multi-century
control experiments, climate of the 20th century
runs, climate change projections), as well as
to seasonal-to-interannual problems, such as El
Niño research and forecasts.
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GFDLs Coupled Data Assimilation System Using
Multi-Coupled Climate Models
GHGNA
Radiative Forcings
ADA Component
Atmospheric models
tobs, psobs
B-grid differencing dynamical core u,v,t,q,ps
Finite-Volume dynamical core u,v,t,q,ps
ODA Component
Land model
tx,ty
(Qt,Qq)
Sea-Ice model
Ocean model (MOM4)
T,S,U,V
Tobs, Sobs?obs
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How much can we retrieve the trend of climate
change in the 20th century?

• Assimilation Idealized twin experiments
• Truth 20th Century climate simulation forced by
  time-varying
• green-house-gas radiation (IPCC
  run)
• Observations Projecting the IPCC simulation
  onto 20th Century ocean temperature observational
  network (XBT, CDT, MBT, OSD, MRB )
• Model CM2 control run -- without GHG forcing
• Initialize the model from arbitrary initial
  conditions (75 years ago, for instance)

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Temperature Errors
CTL
ODA
(OA)DA

• vertical mean
  lt200S-200Ngt

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TEMPERATURE (0250m)
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Wind Stress Errors
ctl
oda
(oa)da

• tau-x
  tau-y

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WIND STRESS
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Temperature lt0500mgt

• ctl
• truth
• assim

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Salinity lt0500mgt
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Ongoing experiments for climate detection at GFDL

• Idealized experiments to uncover issues and
  advance the understanding
• Ocean temperature observational network in the
  20th century (basically, XBT)
• Ocean temperature and salinity observational
  network in the 20th century
• Present ocean observational network (XBT Argo
  Altimetry) applied to the 20th century
• Real data to reconstruct the history of climate
  changes in the 20th century

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ARGO Array for Real-time Geostrophic
Oceanography JASON A hero in Greek mythology
ARGO JASONs ship
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ARGO deploy 3000 autonomous profiling floats
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Comparison of T-S relationships in the North
Atlantic
62.5N-C 47.5N-B 22.5N-A
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Comparison of T-S relationships in the North
Atlantic
22.5N-A
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Comparison of T-S relationships in the North
Atlantic
62.5N-C
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Atlantic Decadal Climate Variability and Change

• The Atlantic Multidecadal Oscillation (AMO)
• Diagnostic Analyses of Atlantic variability
• Future behavior of the Atlantic

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Pathways of Atlantic Ocean Circulation
1.2 Petawatts of ocean heat transport
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Atlantic Ocean Temperature
(80oW-0oW,0oN-60oN)
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Multidecadal variability plus greenhouse gas
induced trend can combine to yield oceanic
temperature response IDEALIZED ILLUSTRATION
(a) Long term trend in Atlantic temperatures
(c) Ocean temperature time series


(b) Multidecadal warmings and coolings
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Atlantic Ocean Temperature
(80oW-0oW,0oN-60oN)
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Sea Surface Temperature (SST) Differences 1941-19
60 minus 1965-1984
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Mechanisms of AMO
The AMO is thought to be driven by multidecadal
variability of the Atlantic thermohaline
circulation (THC) (Bjerknes 1964 Folland
1984 Delworth et al., 1993 Delworth and Mann
2000 Latif et al 2004) Enhanced THC strength
enhances the poleward transport of heat in the
North Atlantic, driving the large-scale positive
SST anomalies. Changes in vertical and
horizontal density gradients in the North
Atlantic alter the THC (enhanced density
gradients strengthen the THC)
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AMO associated with major climatic anomalies

• African summer rainfall Sahelian drought
• Indian summer rainfall
• United States summer temperature and rainfall
• European summer temperature
• Intense hurricanes

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To address issues such as this, we use GFDLs
newly developed global climate model, CM2.
Does the AMO CAUSE these climate anomalies?

• CM2.1 State of the art climate model
• Atmosphere AM2, 20 horizontal resolution, 24
  vertical levels
• Ocean OM3, 10 horizontal resolution, 50
  vertical levels
• Newly developed land, sea ice component models
• Used in ongoing IPCC climate assessment process
• Routinely used for seasonal to interannual
  forecasting
• Used for a wide variety of research projects
• CM2.1 is among the best models in the world, as
  judged by several recent independent assessments

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Measure of fidelity of Atlantic simulation
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How will the Atlantic change in the future?

• Two primary influences
• Natural variability of the Atlantic (AMO)
• From known initial state, use models
• to predict the decadal-scale evolution of the
  system.
• Response to anthropogenic forcing
• a. Direct thermal response
• b. Ocean circulation response (thermohaline
  circulation)
• c. Other factors (Atmospheric circulation
  changes
• Greenland ice sheet etc.)

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Atlantic decadal predictability

• Two complementary pathways are being pursued at
  GFDL using our CM2.1 global coupled model
• Use perfect predictability experiments to
  characterize
• potential predictability in the system, and its
  physical basis.
• 2. Use assimilated ocean state for decadal scale
  projections

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Predictability of North Atlantic Thermohaline
Circulation
5 ensemble members with perturbed atmospheric
conditions and ocean initial conditions beginning
every 100 yrs from 2000 yr coupled model run
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CM2.1 simulations of 20th century change
Subtropical N Atlantic
Tropical N Atlantic
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CO2 time series in SRES runs
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North Atlantic Thermohaline Circulation Index
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Summary

• The Atlantic Multidecadal Oscillation (AMO) is a
  prominent mode of Atlantic variability with
  significant climate links (hurricanes, rainfall,
  temperature)
• Observed Atlantic behavior is a combination of
  the AMO and a long term warming trend, with the
  trend likely a response to increasing greenhouse
  gases.
• 3. Vigorous research efforts aimed at improving
  our understanding and predictive capabilities for
  Atlantic change
• a. Diagnostic analyses of Atlantic variability
• b. Simulating climatic impacts of Atlantic
  variability
• c. Predictions of Atlantic change (both internal
  variability
• component as well as forced anthropogenic
  change)