PALEOCLIMATE STUDIES USING CSIRO Mk3L

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PALEOCLIMATE STUDIES USING CSIRO Mk3L
Matthew England with Agus Santoso, Willem Sijp,
Steven Phipps, Caroline Ummenhofer, Climate
Change Research Centre The University of New
South Wales www.maths.unsw.edu.au/matthew M.Engla
nd_at_unsw.edu.au
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Outline

• Role of the Indonesian throughflow in regional
  climate
• The Drake Passage Effect

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Dry years
Observed Sea Surface Temperature and winds
Wet years
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Indian Ocean Dipole
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Indian Ocean Dipole
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Contributions of Indian Ocean SST to enhanced
East African rainfall
Ummenhofer et al., J. Climate, 2008
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ALL IO
EI SI
WI only
EI WI
Ummenhofer et al., J. Climate, 2008
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Predictability experiments

• NCAR CCSM3 AGCM, 70 ensemble members
• Forced by underlying global SST
• Each run starts January 1-5, over successive
  years
• Each ensemble member integrated for 1 year

PDRY
PWET
SST perturbation anomalies (MJJAS)
Ummenhofer et al., J. Climate, 2008
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Total annual rainfall over Western Australia
(excluding tropical north)
PDRY
PWET
CNTRL
Ummenhofer et al., J. Climate, 2008
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Dry years
Observed Sea Surface Temperature and winds
Wet years
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Indonesian throughflow varies a lot. (2 18 Sv)
England and Huang (2005) J. Climate
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Model experiments

• Mk3L model in global configuration
• Dynamic ocean, atmosphere
• Dynamic/thermodynamic sea-ice
• Model solutions integrated for 800 yrs
• Experimental design
• Indonesian throughflow CLOSED
• Indonesian throughflow OPEN

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Past work ITF open vs. closed
Hirst and Godfrey (1993)
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Ocean-only ITF open vs. closed
Pacific cools
Indian warms
Hirst and Godfrey (1993)
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Ocean-only ITF open vs. closed
Hirst and Godfrey (1993)
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Coupled model response
England et al. (2009)
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ITFopen minus ITFclosed
Coupled model response
England et al. (2009)
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ITFopen minus ITFclosed
Coupled model response
England et al. (2009)
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ITFopen minus ITFclosed
Coupled model response
England et al. (2009)
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ITF clsd
ITF clsd
ITF open
ITF open
ITF open
ITF clsd
ITF open
ITF clsd
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CONCLUSIONS

• Indonesian throughflow fundamentally controls
  Indian Ocean climate via advection of warm water.
  
• Ocean currents temperatures, and atmospheric
  winds, SLP, cloud cover and rainfall all
  substantially affected.
• The opening of the ITF may have greened SWWA at
  the last deglaciation.

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Outline

• Role of the Indonesian throughflow in regional
  climate
• The Drake Passage Effect

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Background Goal

• Antarctica became isolated via the Southern Ocean
  approx 30 MYA
• Warmer and possibly ice-free conditions existed
  before isolation
• Coupled ocean-atmosphere-ice model is used to
  examine relation

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The numerical model

• Earth system climate model of intermediate
  complexity developed by Weaver et al. at the
  University of Victoria, Canada
• Global domain with resolution of 3.6 x 1.8
• Coupled components include
• An ocean general circulation model
• An atmospheric model
• Hydrological cycle
• Realistic topography
• A dynamic/thermodynamic sea-ice model
• Albedo from snow and sea-ice

See Weaver A.J., et al, 2001 The UVic Earth
System Climate Model Model description,
climatology, and applications to past, present
and future climates. Atmos.-Ocean, 39, 361-428.
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Weaver A.J., et al, 2001 The Uvic ESCM.
Atmos.-Ocean, 39, 361-428.
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The atmosphere model

• Based on Fanning Weaver (1996) energy-moisture
  balance model, featuring
• Vertically integrated thermodynamic energy
  balance equation
• Global, 3.6 x 1.8 horizontal grid, 1 vertical
  level
• Realistic orography, moisture advection/diffusion
  , heat diffusion (EBM)
• Realistic hydrological cycle
• Snow/ ice albedo feedbacks

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Experimental Design

• Model present day climate system
• Run model with shallow Drake Passage
• Run model with closed Drake Passage

• Other topographical features left unchanged.
• Steady states of 3500 year runs were examined for
  each run

Sijp and England, J. Phys. Oceanogr. (2004)
See also Gill and Bryan (1971), Cox (1989),
England (1992), Toggweiler and Samuels (1995),
and many others
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Meridional Overturning DP closed experiment
0 Sv NADW
50 Sv AABW
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Meridional Overturning DP closed experiment
PHT 2.5 PW PHT lt 0.5 PW
0 Sv NADW
50 Sv AABW
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Meridional Overturning DP shallow experiment
3 Sv NADW
35 Sv AABW
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Meridional Overturning DP shallow experiment
PHT 2.1 PW PHT lt 0.5 PW
3 Sv NADW
35 Sv AABW
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Meridional Overturning DP open experiment
20 Sv NADW
13 Sv AABW
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Meridional Overturning DP open experiment
PHT 1.5 PW PHT gt 1 PW
20 Sv NADW
13 Sv AABW
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Oceanic heat transport
How does the total oceanic poleward heat
transport change?
DP open
DP shallow
DP closed
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Sea surface temperatures

• Oceanic cooling occurs at mid latitudes in the
  South Atlantic
• Cooling is up to 10 degrees Celsius higher in
  both DP690 and DPopen
• North Atlantic up to 6 degrees Celsius warmer in
  DPopen due to NADW formation

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Sea surface temperatures

• Oceanic cooling occurs at mid latitudes in the
  South Atlantic
• Cooling is up to 10 degrees Celsius higher in
  both DP690 and DPopen
• North Atlantic up to 6 degrees Celsius warmer in
  DPopen due to NADW formation

SST warming due to increased Gulf Stream
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Air temperature difference
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Seasonality

• Air temperature (SAT) cooling is highly seasonal
• Area of maximum SH cooling shifts south-west in
  winter
• SAT differences of up to 17 degrees Celsius in
  winter
• SH SAT differences lowest in SH summer
• Results indicate changes in sea-ice cause
  seasonality

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Conclusions

• Southern Ocean changes are mostly achieved for a
  shallow DP cooler Antarctica, reduced AABW
  formation, and establishment of the ACC
• SAT cooling greater in winter but still large
  enough in summer to contribute to Antarctic
  glaciation (local summer SAT in SH up to 4C
  cooler)
• NADW formation does not appear until the DP is
  sufficiently deep
• Atmospheric changes are seasonal due to sea-ice
  feedback

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Experimental Design
Sijp and England, J. Climate (2005)

• Model present day climate system
• Run model with a variety of Drake Passage sill
  depths
• Run model with closed Drake Passage
• Hose/Salt to study possibility for multiple
  steady states

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Stable NADW
NADW not sustained
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Results
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Conclusions
Deepening the DP gt density contrast between AAIW
and NADW becomes more important than that between
AABW and NADW
The global circulation of NADW and its stability
depend not only on the existence of a
circumpolar SH ocean, but also on the depth of
sills in the SO
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But a dynamic atmosphere changes everything.
DP open
DP open
DP closed
DP closed
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PALEOCLIMATE STUDIES USING CSIRO Mk3L
Matthew England with Agus Santoso, Willem Sijp,
Steven Phipps, Caroline Ummenhofer, Climate
Change Research Centre The University of New
South Wales www.maths.unsw.edu.au/matthew M.Engla
nd_at_unsw.edu.au