Alternating Wet and Dry Conditions over South America during Summer

Nogués-Paegle, Julia; Mo, Kingtse C.

doi:10.1175/1520-0493(1997)125<0279:awadco>2.0.co;2

Cited by 454 publications

(361 citation statements)

References 22 publications

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“…Inversely, in southern South America and the adjacent subtropical Pacific there is an upper-level cyclonic circulation anomaly with diffluent moisture and suppressed convection below (Figure 8(a), (b)). This meridional convective dipole resembles the SACZ features that are well documented in the literature (Nogues- Paegle and Mo, 1997;Liebmann et al, 1999;Paegle et al, 2000;Carvalho et al, 2004) but with its climatological position slightly shifted northward. These regional mechanisms observed during the peak of the intraseasonal rainfall events over tropical Brazil are dynamically embedded within the eastward-propagating MJO-related large-scale convective envelope along tropical South America/the Atlantic Ocean.…”

Section: Regional Mechanisms Over South America/the Atlantic Oceansupporting

confidence: 78%

“…Other studies with a regional focus were able to detect significant intraseasonal variability over tropical (Kousky and Kayano, 1994;Carvalho et al, 2002;Souza et al, 2005) and subtropical South America with emphasis on the South Atlantic Convergence Zone (SACZ) (Casarin and Kousky, 1986;Nogues-Paegle and Mo, 1997;Liebmann et al, 1999;Grimm et al, 2000;Paegle et al, 2000;Todd et al, 2003;Carvalho et al, 2004), which is dynamically linked with MJO events (Kiladis and Weickmann, 1992;Grimm and Silva Dias, 1995). In addition, Jones et al (2004) reported unambiguous and robust signals of an increased frequency of precipitation extremes in the eastern part of South America during active MJO events.…”

Section: Introductionmentioning

confidence: 99%

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Modulation of the intraseasonal rainfall over tropical Brazil by the Madden–Julian oscillation

Souza¹,

Ambrizzi

2006

Int. J. Climatol.

101

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Fifteen years (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) of rain gauge-based data are used to describe the intraseasonal rainfall variability over tropical Brazil and its associated dynamical structure. Wavelet analysis performed on rainfall time series showed significant peaks centered roughly in periods of 30-70 days, particularly in the eastern southeastern Amazon and northern northeast Brazil. A significant enhancement of precipitation with maximum anomalies in a northeastward oriented band over tropical Brazil is evidenced from empirical orthogonal function (EOF) analysis of 30-70-day filtered rainfall anomalies during rainy season (January to May). Lagged/lead composites revealed that, on a global scale, the Madden-Julian oscillation (MJO) is the main atmospheric-mechanism modulator of the pluviometric variations on intraseasonal timescale in the eastern Amazon and northeast Brazil. A coherent northward expansion of rainfall across tropical Brazil is evident during the passage of MJO over South America. Regionally, the establishment of a quasi-stationary deep convection band triggered by the simultaneous manifestation of south Atlantic convergence zone (SACZ) and intertropical convergence zone (ITCZ) explains the intensified rainfall over these regions. Such regional mechanisms are dynamically embedded within the eastward-propagating MJO-related large-scale convective envelope along tropical South America/the Atlantic Ocean. These features occur in association with a significant intraseasonal evolution of the lower-level wind and seasurface temperature (SST) patterns, particularly in the Atlantic Ocean, including a coherent dynamical connection with atmospheric circulation, deep convective activity over South America and rainfall over tropical Brazil.

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Section: Regional Mechanisms Over South America/the Atlantic Oceansupporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Modulation of the intraseasonal rainfall over tropical Brazil by the Madden–Julian oscillation

Souza¹,

Ambrizzi

2006

Int. J. Climatol.

101

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“…8, third panel) indicate the existence of a tropical-subtropical dipole in convective activity as noted by Nogués-Paegle and Mo (1997) and Liebmann et al (1999). The pattern of 200-hPa geopotential height anomalies (Fig.…”

Section: Oceanic Sacz Categorysupporting

confidence: 53%

The South Atlantic Convergence Zone: Intensity, Form, Persistence, and Relationships with Intraseasonal to Interannual Activity and Extreme Rainfall

2004

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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 versus 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 (MJO) modulates intense SACZ events with persistence longer than 3 days. Interannual variability of persistent 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 centraleastern 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 northnortheastern Brazil, whereas opposite features are observed for the phase of the MJO characterized by the enhancement of convection over Indonesia and suppression over the central Pacific.

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“…Extratropical Rossby wave trains are the main forcing for the intraseasonal variability of the SACZ (Casarin and Kousky 1986;Grimm and Silva Dias 1995;Nogues-Paegle and Mo 1997;Liebmann et al 1999;Jones and Carvalho 2002;Carvalho et al 2004). Some of these wave trains have been shown to be associated with the eastward propagation of the MJO ).…”

Section: Characterization Of Sams and Saczmentioning

confidence: 99%

Moisture transport and intraseasonal variability in the South America monsoon system

et al. 2010

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This paper examines moisture transport on intraseasonal timescales over the continent and over the South Atlantic convergence zone (SACZ) during the South America (SA) summer monsoon. Combined Empirical Orthogonal Function analysis (EOFc) of Global Precipitation Climatology Project pentad precipitation, specific humidity, air temperature, zonal and meridional winds at 850 hPa (NCEP/NCAR reanalysis) are performed to identify the large-scale variability of the South America monsoon system and the SACZ. The first EOFc was used as a large-scale index for the South American monsoon (LISAM), whereas the second EOFc characterized the SACZ. LISAM (SACZ) index showed spectral variance on 30-90 (15-20) days and were both band filtered (10-100 days). Intraseasonal wet anomalies were defined when LISAM and SACZ anomalies were above the 75th percentile of their respective distribution. LISAM and SACZ wet events were examined independently of each other and when they occur simultaneously. LISAM wet events were observed with the amplification of wave activity in the Northern Hemisphere and the enhancement of northwesterly cross-equatorial moisture transport over tropical continental SA. Enhanced SACZ was observed with moisture transport from the extratropics of the Southern Hemisphere. Simultaneous LISAM and SACZ wet events are associated with cross-equatorial moisture transport along with moisture transport from Subtropical Southwestern Atlantic.

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Alternating Wet and Dry Conditions over South America during Summer

Cited by 454 publications

References 22 publications

Modulation of the intraseasonal rainfall over tropical Brazil by the Madden–Julian oscillation

Modulation of the intraseasonal rainfall over tropical Brazil by the Madden–Julian oscillation

The South Atlantic Convergence Zone: Intensity, Form, Persistence, and Relationships with Intraseasonal to Interannual Activity and Extreme Rainfall

Moisture transport and intraseasonal variability in the South America monsoon system

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