Recent studies have shown that global warming and associated sea-surface temperature (SST) changes may trigger an important rainfall increase in southeastern South America (SESA) during the austral summer (December-January-February, DJF). The goal of this paper is to provide some insight into processes which may link global and SESA changes. For this purpose, a two-way nesting system coupling interactively the regional and global versions of the LMDZ4 atmospheric model is used to study the response to prescribed SST changes. The regional model is a variable-grid version of the global model, with a zoom focused over South America. An ensemble of simulations forced by distinct patterns of DJF SST changes has been carried out using a decomposition of full SST changes into their longitudinal and latitudinal components. The full SST changes are based on projections for the end of the twenty-first century from a multi-model ensemble of WCRP/CMIP3. Results confirm the presence of a major rainfall dipole structure, characterized by an increase in SESA and a decrease in the South Atlantic Convergence Zone region. Rainfall changes found in the WCRP/CMIP3 models are largely explained as a response of this dipole structure to the zonally-asymmetric (or longitudinal) component of SST changes. The rainfall response to the zonal-mean (or latitudinal) SST changes (including the global warming signal itself) shows an opposite contribution. The processes explaining the role of zonally-asymmetric SST changes involve remote effects of SST warming over the equatorial Indian and Pacific oceans inducing an atmospheric wave-train extended across the South Pacific into South America.
- South America climate
- Rainfall changes
- Two-way nesting system
- Sea surface temperature projections
- Climate change
- SURFACE TEMPERATURE ANOMALIES
- LOW-LEVEL CIRCULATION
- TROPOSPHERIC CIRCULATION
- INTERANNUAL VARIABILITY
- TROPICAL PRECIPITATION
- ATMOSPHERIC MODEL
[Junquas, C.; Li, L.; Le Treut, H.] UPMC, CNRS, Lab Meteorol Dynam, Inst Pierre Simon Laplace, Paris, France; [Junquas, C.; Vera, C. S.] UBA, CONICET, CIMA, DCAO,FCEN,UMI,IFAECI,CNRS, Buenos Aires, DF, Argentina
Junquas, C (reprint author), UPMC, CNRS, Lab Meteorol Dynam, Inst Pierre Simon Laplace, Paris, France.
- Institut Pierre-Simon Laplace (IPSL), FR636
- Laboratoire de météorologie dynamique (LMD), UMR8539