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regional models (Christensen et al., 2007). However, it
should be mentioned that as South America is a data-sparse
region, the actual model skill is masked by existing
uncertainties in the observational-based datasets used to
evaluate models.
A collaborative research for studying the regional climate
with more detail as simulated by this CLARIS ensemble is
in progress.
3. Regional climate change experiment
In this section we examine a regional climate change
scenario carried out with RCA3. The model has a
continental-scale domain and is forced, for present climate
(1980-1999, 20C3M scenario, simulation hereafter called
RCA20) and future climate (2080-2099, IPCC SRES A1B
scenario, hereafter RCA21), with lateral boundary
conditions and SSTs updated every six hours from a coupled
global model, ECHAM5/MPI-OM (Jungclaus et al., 2006).
An additional 20-year experiment, where RCA3 is forced by
ERA40 reanalysis data (Uppala et al., 2005, hereafter
RCAERA), aids in the identification of the sources of the
biases for the present climate.
RCA3 does inherit certain large-scaleerrors from the driving
coupled model, in particular concerning the position of the
convergence zones in the Atlantic Ocean. As a consequence,
RCA20 presents spurious large rainfall and too cold surface
temperature over northeastern Brazil. In other regions such
as Southern Amazonia, the positive large precipitation bias
in RCAERA is attenuated in the global model driven
simulation. But in general, the geographical pattern of
precipitation is more correct in the reanalysis driven
simulation, except for the austral spring season (SON) when
both simulations show a reasonable pattern, and RCA20
actually is closer to the observed precipitation intensity.
The seasonal mean surface air temperature response to the
A1B scenario was found to be largest in the Amazon region,
especially during SON. The seasonal mean precipitation
response is largest during the monsoon seasons (SON and
DJF). However, when assessing the response, it should be
kept in mind that the present day biases are larger in
magnitude than the model’s response to large-scale changes
in circulation and SSTs for future climate. In SON the
precipitation response is negative, suggesting a longer dry
season and a delayed onset of the monsoon circulation in
austral spring while in the mature monsoon phase (DJF) the
response is positive in large areas of Western and Northern
Amazonia.
Changes in daily temperature are consistent with less cold
temperature extremes and more warm temperature extremes
throughout the continent. The distribution of precipitation on
different intensity classes shows a tendency toward an
increase in the number of dry days and a decrease in the
number of precipitation events in many regions during the
monsoon onset (SON). During the mature monsoon (DJF)
the amount of dry days decreases and the strong and heavy
precipitation events increases over most of the continent.
The Southern Amazonia and Southern Andes regions show
an increase of dry days for all seasons.
References
Assessment and Impact Studies. Climatic Change, in
press, 2009
Christensen, J.H. et al., Regional Climate Projections. In:
Climate Change 2007: The Physical Science Basis.
Contribution of Working Group I to the Fourth
Assessment Report of the Intergovernmental Panel on
Climate Change [Solomon, S., D. Qin, M. Manning,
Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and
H.L. Miller (eds.)]. Cambridge University Press,
Cambridge, United Kingdom and New York, NY,
USA, 2007
Jungclaus J. H., N. Keenlyside, M. Botzet, H. Haak, J.-J.
Luo, M. Latif, J. Marotzke, U. Mikolajewicz, and E.
Roeckner, Ocean Circulation and Tropical Variability
in the Coupled Model ECHAM5/MPI-OM. J. Clim.,
19, 3952–3972, 2006
Kjellström E., L. Bärring, S. Gollvik, U. Hansson, C.
Jones, P. Samuelsson, M. Rummukainen, A. Ullerstig,
U. Willén, K. Wyser, A 140-year simulation of
European climate with the new version of the Rossby
Centre regional atmospheric climate model (RCA3).
Reports Meteorology and Climatology No. 108,
SMHI, SE-60176 Norrköping, Sweden, 54pp, 2005
Menéndez C.G., M. de Castro, J.P. Boulanger, A.
D’Onofrio, E. Sanchez, A. A. Sörensson, J. Blazquez,
A. Elizalde, U. Hansson, H. Le Treut, Z. X. Li , M. N.
Núñez, S. Pfeiffer, N. Pessacg, M. Rojas, P.
Samuelsson, S. A. Solman, C. Teichmann,
Downscaling extreme month-long anomalies in
southern South America. Climatic Change, in press,
2009
New M, Hulme M, Jones P Representing twentiethcentury
space time climate variability. Part II:
Development of 1901-1996 monthly grids of
terrestrial surface climate. J. Clim 13, 2217-2238,
2000
Nuñez M.N., S.A. Solman, M.F. Cabré, Regional climate
change experiments over southern South America. II:
Climate change scenarios in the late twenty-first
century. Clim. Dyn., DOI 10.1007/s00382-008-0449-
8, 2008
Sörensson A.A., R. Ruscica, C.G. Menéndez, P.
Alexander, U. Hansson, P. Samuelsson, U. Willen,
South America’s present and future climate as
simulated by Rossby Centre Regional Atmospheric
Model. Extended abstracts of the 9th International
Conference on Southern Hemisphere Meteorology and
Oceanography. American Meteorological Society.
Melbourne, Australia, 9 to 13 February 2009 (a)
Sörensson A.A., C.G. Menéndez, P. Samuelsson, U.
Willén, U. Hansson, Soil-precipitation feedbacks
during the South American Monsoon as simulated by
a regional climate model. Climatic Change, in press,
2009 (b)
Uppala, S. M., et al., The ERA-40 re-analysis. Quart. J. R.
Meteorol. Soc., 131, 2961-3012, 2005
Boulanger J.P., G. Brasseur, A. F. Carril, M. Castro, N.
Degallier, C. Ereño, J. Marengo, H. Le Treut, C.
Menéndez, M. Nuñez, O. Penalba, A. Rolla, M.
Rusticucci, R. Terra, The European CLARIS Project: A
Europe-South America Network for Climate Change