ABSTRACT
The South Atlantic Convergence Zone: Intensity, Form, Persistence, and
Relationships with Intraseasonal to Interannual Activity and Extreme Rainfall
Leila M.V. Carvalho
Department of Atmospheric Sciences, Institute of Astronomy and
Geophysics, University of São Paulo, São Paulo, Brazil
Charles Jones
Institute for Computational Earth System Science, University of
California, Santa Barbara, Santa Barbara, California
Brant
Liebmann
NOAA-CIRES Climate Diagnostics Center, Boulder, Colorado
(Manuscript received 12 September 2002, in final form 7 July 2003)
Abstract
The characteristics of intensity, geographical location, and
persistence of the south Atlantic convergence zone (SACZ) during the
austral summer are investigated. Intensity and spatial features of the
SACZ are identified by performing a factor analysis of structural
properties of outgoing longwave radiation (OLR) data. The first two
leading factors explain 65% of the total variance of structural
properties and characterize the SACZ according to intensity and
location (oceanic vs continental). An index is constructed based on the
magnitude of the factor scores to identify intense(weak) and oceanic
(continental) SACZ. The intense SACZ category is associated with
negative OLR anomalies over a large area of tropical South America,
extending from the western Amazon to the Atlantic Ocean. The weak SACZ
category is observed with positive OLR anomalies over tropical South
America and negative OLR anomalies over southeastern South
America. Oceanic and continental aspects of the SACZ are related to a
midlatitude wave train pattern. The Madden-Julian oscillation (MJ0)
modulates intense SACZ events with persistence longer then 3
days. Interannual variability of persistenct events indicates that the
ratio of oceanic to continental SACZ as well as their frequency depends
on the phase of El Niño-Southern Oscillation (ENSO). Occurrence of
extreme rainfall in Brazil is discussed in the context of variations in
the SACZ and MJO. Intense (weak) SACZ increases (decreases) the 95th
daily rainfall percentile over central-eastern Brazil compared to the
climatology. Oceanic (continental) SACZ increases (decreases) the 95th
daily rainfall percentile over southeastern Brazil. The MJO phase
characterized by suppression of convective activity over Indonesia and
enhancement over the central Pacific increases the 95th daily rainfall
percentile over north-northeastern Brazil, wheras opposite features are
observed for the phase of the MJO characterized by the enhancement of
convection over Indonesia and suppression over the central Pacific