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 1
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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?
4DJF climatological mean precipitation
(CMAP)
SACZSouth
Atlantic Convergenc
e zone
LPBLa Plata
Basin
Leading pattern of year-to-year variability of DJF precipitation anomalies (CMAP)
EOF1 - domain A
EOF1 - domain B
A
B
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•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
OBJECTIVES
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• 18 models from (WCRP/CMIP3) dataset for IPCC-AR4 are used.
• For each model, EOF analysis of DJF precipitation anomalies from XXI century simulations is performed over southeastern South America.
Data and Methodology
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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
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Increment of wetter than
normal DJFs in the la Plata Basin
Decrease of dryier than normal DJFs
in the la Plata Basin
Mean number of positive
and negative EOF1-SE
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 .
iii) an increase of the frequency of positive EOF1 events and adecrease of negative EOF1 events during the 21st century
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DJF rainfall difference between (2050-2099) and (2001-2049)
EOF1-SE years(~30% of year total)
no EOF1-SE years
9-model ensemble
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All years
The differences in the three panels are
standardized by the total number of years
Temporal evolution of the DJF normalized rainfall anomalies in LPB (38°S-26°S,64°-50°W) from 9-model
ensemble
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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)
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
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(B) –(A)
Composites of standardized SST anomalies for positive and negative EOF1 events over the central Tropical Pacific Ocean from 9-model
ensemble
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Warmer than normal Central Pacific
conditions associated to an increment of wetter than normal summers in the la
Plata Basin
Composite differences of DJF geopotential height anomalies at 500 hPa between positive and
negative EOF1events 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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•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?
Discussion
Annual mean anomalies of precipitation in Posadas (Northeastern Argentina)
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•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?
Discussion
Strategy•Analysis of CMIP5 multi-model ensemble simulations•New sensitivity studies performing numerical simulations with global and regional models at specific conditions
