Transcript Understanding physical processes linked to climate variability and

Understanding physical
processes linked to climate
variability and change in the South
America Monsoon System
Carolina Vera1, C. Junquas 1,2, H. Le Treut 2, L. Li 2
1CIMA/CONICET-University of Buenos Aires and DCAO/FCEyN,, Buenos Aires, Argentina
2 LMD/IPSL, Paris, France
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Precipitation
changes as
depicted by the
WCRP/CMIP3
multi-model
ensemble
(IPCC-AR4, 2007)
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Which are the physical
mechanisms explaining an
increase of summer precipitation
in southeastern South America
under GHG increment scenario?
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SACZ
South Atlantic
Convergence
zone
LPB
La Plata Basin
DJF climatological mean precipitation (CMAP)
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Leading pattern of year-to-year variability of DJF
precipitation anomalies (CMAP)
EOF1 - domain A
EOF1 - domain B
A
B
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OBJECTIVES
•To explore changes in the leading pattern of
precipitation year-to-year variability in South
America in the context of a climate change
induced by GHG increment.
•To explore how much of those changes
account for the trends projected for austral
summer precipitation in southeastern South
America
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Data and Methodology
• 18 models from (WCRP/CMIP3) dataset for IPCCAR4 are used.
• For each model, EOF analysis of DJF precipitation
anomalies from XXI century simulations is
performed over southeastern South America.
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Leading pattern
(EOF1) of DJF rainfall
anomaly variability
from the 18 models
Period: 2001-2099
Scenario: SRESA1B
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Principal Components (PC1)
of EOF1 from two of the
models
•Blue (red) : PC1 larger (smaller)
than 1 (-1) standard deviation
Positive(Negative) EOF1-SE.
•Positive (negative) EOF1-SE are
associated with positive
(negative) precipitation
anomalies in LPB
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Changes in the number of positive and negative EOF1-SE
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Mean number
of positive and
negative
EOF1-SE
Increment of wetter
than normal DJFs in
the la Plata Basin
Decrease of dryier
than normal DJFs in
the la Plata Basin
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9 models were
selected that show:
i) a realistic representation of the
dipole-like structure associated to
EOF1 events in the present (not
shown) as in the future
ii) an increase of the projected
summer rainfall in LPB by the
end of the 21st century .
Mean
number of
positive and
negative
EOF1-SE
iii) an increase of the frequency
of positive EOF1 events and a
decrease of negative EOF1
events during the 21st century
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DJF rainfall difference between (2050-2099) and (2001-2049)
9-model
ensemble
EOF1-SE years
(~30% of year total)
no EOF1-SE years
The differences in the
three panels are
standardized by the total
number of years
All years
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Temporal evolution of the DJF normalized rainfall anomalies
in LPB (38°S-26°S,64°-50°W) from 9-model ensemble
Blue (red) dots correspond to the rainfall anomalies associated to each
of the positive (negative) EOF1 events identified for each of the
models (the corresponding linear trends are depicted in dashed lines)
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Composite differences of mean DJF SST
anomalies between positive and negative EOF1
events from the 9-model ensemble mean
(A) 2001-2049
(B) 2050-2099
(B) –(A)
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Composites of standardized SST anomalies for positive
and negative EOF1 events over the central Tropical
Pacific Ocean from 9-model ensemble
Warmer than normal
Central Pacific conditions
associated to an
increment of wetter than
normal summers in the la
Plata Basin
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Composite differences of DJF geopotential height
anomalies at 500 hPa between positive and negative EOF1
events from 9-model ensemble
2001-2049
2050-2099
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Composite differences of moisture fluxes (arrows) and their
divergence (contour) at 850 hPa between positive and negative
EOF1 events from 9-model ensemble
2001-2049
2050-2099
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Discussion
•How much of the results are related to the ability of current
climate models in correctly reproducing the tropical ocean
dynamics not only in the Pacific but also in the Atlantic basins?
•Which is the role of other sources of climate variability (Indian
Ocean, SAM) in explaining such trends?
•Which is the combined effect of GHG increment and land use
change on the regional climate change?
•How will natural climate variability signal combine with that
associated to climate change in the next decades?
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Annual mean anomalies of precipitation
in Posadas (Northeastern Argentina)
Discussion
•How much of the results are related to the ability of current
climate models in correctly reproducing the tropical ocean
dynamics not only in the Pacific but also in the Atlantic basins?
•Which is the role of other sources of climate variability (Indian
Ocean, SAM) in explaining such trends?
•Which is the combined effect of GHG increment and land use
change on the regional climate change?
•How will natural climate variability signal combine with that
associated to climate change in the next decades?
Strategy
•Analysis of CMIP5 multi-model ensemble simulations
•New sensitivity studies performing numerical simulations with
global and regional models at specific conditions
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