Arquivo do Trabalho - IAG - USP

1690 JOURNAL OF CLIMATE VOLUME 22FIG. 7. Same as in Fig. 5, but for composites of 200-hPa zonal wind (m s 21 ). First contour is 1.0 m s 21(21.0 m s 21 ) and second is 2.0 m s 21 (22.0 m s 21 )withinterval2.0ms 21 .(Fig. 8d). The center of this anomaly is located approximatelyat 308S and is associated with easterlyanomalies over SEBr and northerly anomalies oversouth Brazil. An intensification of the poleward flowoccurs south of WAtl whereas the equatorward flowintensifies north of the region collocated with easterlyupper-level zonal wind anomalies (Fig. 7e). As postulatedby Kodama (1992), these features inhibit the organizationof the subtropical convergence zones.5. Wet and dry events on intraseasonal time scalesThe objective of this section is to examine in detail therole of the MJO in modulating extreme precipitationanomalies on intraseasonal time scales. Jones et al. (2004),Carvalho et al. (2004), and Liebmann et al. (2004)provided insights into understanding the role of the MJOin modulating extreme precipitation over broad areasof tropical and subtropical South America. The noveltyof the present analysis is the focus on wet and dryintraseasonal anomalies (and not total precipitation) inthe region of large intraseasonal variance over SouthAmerica and the southeastern Atlantic (Fig. 2) and adetailed examination of the relationships of extremeevents with the MJO.Extreme anomalies on intraseasonal time scales aredefined as discussed in section 3b. Figure 9 shows thepatterns of wet and dry extreme precipitation anomaliesover each region. The striking aspect of the spatialorganization of precipitation anomalies on intraseasonaltime scales is the seesaw pattern previouslydocumented in some studies (e.g., Casarin and Kousky