Apresentao do PowerPoint

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• Evaluation of Model Simulation of 6k BP and
  present climate in South America
• Pedro L. Silva Dias (1)
• Maria Assunção F. Silva Dias (1)
• Pascalle Braconnot (2)
• Bruno Turc (3)
• Institute of Astronomy and Geophysics, University
  of São Paulo
• (2) Laboratoire des Sciences du Climat et de
  LEnvironnement
• (3) Paleotropique - IRD

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6k BP change with respect to present
Wm-2
Increased annual cycle
Decreased annual cycle
From Braconnot et al. 2000 J. Climate
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Description of PSL climate model

• Atmospheric component LMD version 5.3
• 3.6o latitude X 5.6o longitude resolution (50 x
  64)
• 11 sigma level in the vertical
• Oceanic component Océan Parallelizé Model
  LODYC
• 2.4o latitude X 3.9o longitude resolution (76 x
  92)
• 31 vertical levels with 10 in the upper 100m
• Once a day coupling between ocean and atmosphere
• River and coastal runoff (catchment for the 46
  major rivers)
• Vegetation/Soil BIOME1 - interactively coupled
  to atmosphere

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Experimental Design

•         OA0k - present day climate (taken from
  the average of a 150 year simulation). Ocean and
  atmosphere interact with each other and
  vegetation is taken from modern climatology
  TB1
•         OA6k Mid-Holocene climate (taken from
  the average of a 150 year simulation). Biome
  distribution prescribed at present conditions but
  Earths Orbital parameters prescribed as in the
  Paleoclimate Modeling Intercomparison Project
  (Joussaume and Taylor, 1995) TH1
•         OAV16k - 50 year simulation of the
  mid-Holocene climate with the biome distribution
  taken from interactive application of BIOME1 to
  model climate. TH3

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BIOME1 vegetation given present climate
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Based on climate produced by forcing model with
present vegetation but 6k BP orbital parameters
- TH1
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Iterative Application of BIOME1 TH3
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Present Day using BIOME1
6k BP TH3 BIOME1 applied interactively
6k BP TH1 BIOME1 interpretation
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Evaluation of Present Climate and comparison with
6K BP
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present
6kBP
From Braconnot et al. 2000 J. Climate
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Modern climatology
Model present climatology
difference
From Braconnot et al. 2000 J. Climate
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W
W
D
W
W
Observed Present Jagger climatology
Model present climatology - 6k BP
Model present climatology
mm/day ---- JANUARY
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SACZ
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Herdies et al. 2001
(shaded)
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D
D
W
D
Observed Present Jagger climatology
Model present climatology - 6k BP
Model present climatology
mm.day-1 July
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Model present
Model 6kBP

• SH summer LLJ East of Andes stronger today
• Observations indicate LLJ during winter and model
  does not!

Time x longitude cross section at 18oS
difference
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15
15S 50W
No indication of major changes in frontal activity
White present model Green 6kBP model
Meridional heat transport Transient eddies and
total heat transport
Indications of reduction in intensity of LLJ heat
transport in summer at 6kBP
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7.
11
11
Jan
Dec
24.
30.
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White present Green 6kBP
Precipitation (mm/day)
Jan
Dec
30.
4.
4
16.
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White present Green 6kBP
Dec
Jan
lkkl
Jan
Dec
Temperature (K)
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TB1 present - white TH1 6kBP - green
Smaller interannual variability at 6kBP
Present period is longer
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6kBP Precipitation
YEARS
Latitude
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TB1 present - white TH1 - 6k BP - green
Present higher extreme positive deviations Past
drier and larger negative deviations
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Teleconnections
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Streamfunction at 200 mb precipitation Differenc
e between 6kBP and present model
mm/day
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Velocity Potential at 200 mb precipitation Diffe
rence between 6kBP and present model
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th1)
Vegetation feedback drier SACZ, wetter NE
mm/day
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ENSO in the present climate and in 6k BP
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(No Transcript)
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Present model climate
6kBP model climate
years
Warm events
Longitude
Longitude
Time x longitude cross section of SSTa at the
Equator
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Niños
Niñas
Amplitude smaller than observations...
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Smaller amplitude than in the present climate
simulation
Niños
Niñas
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How about SST variability in the Atlantic??
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Main oscillation pattern of surface stress and
sea surface temperature
NE Brazil normalized precipitation
Nobre and Shukla 1996
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SST
SSTA
6k BP dominated by interannual scale
Present decadal is evident
years
years
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How about correlation between precipitation and
SST anomalies in present climate simulation and
6k BP??? (preliminary results...)
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Present model correlation between Precipitation
NE BRAZIL and SST
Equatorial Atlantic Dipole
ENSO
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6kBP model correlation between Precipitation and
SST
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Eastern Amazon Present Climate Model Simulation
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Conclusions

• SACZ precipitation present simulation gtgt than
  observations
• Amazon precipitation present simulation lt
  observed
• Present model correlation between Prec and SST
  consistent with obs.
• SACZ is drier in 6k BP simulation and more
  frequent low precipitation during wet season
• Southern Brazil wetter and colder (mainly summer)
  in 6k BP
• Amazon and NE Brazil slightly wetter and colder
  in the mean (shorter dry season in NE). Northern
  S.America longer dry season but wetter in the
  annual mean. Other important points
• Much larger extreme maximum monthly precipitation
  in current climate in interannual variability in
  the Amazon
• Larger negative deviation of normal in NE Brazil
  in 6k BP in interannual scale.

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• Amplitude of present ENSO SST signal lt
  observation
• Amplitude of 6k BP ENSO SST signal lt present
  simulation (i.e., weaker ENSO at 6k)
• Equatorial Atlantic SST interannual variability
  TH1 lt TB1
• (how can larger Precipitation interannual
  variability be reconciled with SST )??
• Higher latitude Atlantic SST variability TH1 gt
  TB1 (possible reason ???)
• Stationary meridional heat transport TB1 gt TH1
• Transient meridional heat transport TB1 TH1 (no
  indication of substantial changes in friagem
  events

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• Ongoing work
• Power spectra
• Correlation pattern between precipitation and
  SST
• Atlantic SST interannual and decadal variability
• ENSO and meridional heat transport
• Interaction with P. Braconnot to improve current
  climate