El Niño/Southern Oscillation (ENSO)-related patterns of monthly reanalyzed upper-level circulation data and monthly rainfall time series over South America are revised for the 1948-1999 period considering the phases of the Pacific interDecadal Oscillation (PDO). The El Niño (EN) related composites show differences relative to the PDO phases as well as seasonal differences. EN signals in the South American rainfall are more conspicuous for the warm PDO (WPDO) regime, when seasonal differences are more pronounced, than for the cold PDO (CPDO). Differences for the 200-hPa stream function composites seem to determine the precipitation composite differences. In fact, the negative precipitation anomalies over northeast Brazil and the excessive rainfall to the south are explained respectively by a cyclonic center over eastern and northeastern Brazil and a weak anticyclonic center over southeastern South America for the WPDO regime. Positive precipitation anomalies over southeastern South America are located in a southern position for the CPDO regime when compared to those for the WPDO regime. These anomalies might be related to a strengthened upper-level subtropical jet stream associated with strong cyclonic circulation extending over southern South America for the CPDO regime. With regard to the linear and nonlinear parts of the precipitation anomaly patterns related to the ENSO, the nonlinear component is considerably smaller than the linear component, in particular, over northern and southeastern South America. This suggests that the linear approach of the South American precipitation response to the ENSO seems to be appropriated.

Abstract:The anomaly patterns of rainfall in South America for El Niño/Southern Oscillation (ENSO) extreme conditions stratified according to the high, low, and normal Pacific (inter-) Decadal Oscillation (PDO) phases (HPDO, LPDO and NPDO) are examined for the three bi-months of the season from November to April. El Niño (EN) and La Niña (LN) composites as well as the linear (EN − LN) and nonlinear (EN + LN) components of the precipitation anomaly patterns relative to ENSO show substantial differences among the three PDO phases. The differences in the strength of ENSO teleconnections for the South American rainfall might be related to the PDO, which creates a background for these teleconnections acting constructively (destructively) when ENSO and PDO are in the same (opposite) phase. An interesting aspect is the occurrence of robust structures of the nonlinear component, which are due to the same sign rainfall anomalies for EN and LN composites. This is particularly conspicuous for the HPDO over eastern Brazil in the South Atlantic Convergence Zone (SACZ) region during Nov/Dec and Jan/Feb, for the HPDO over northern/northwestern South America during Mar/Apr, and for the NPDO over northeastern Brazil during Mar/Apr. The results presented here might have relevant implications for climate monitoring purposes.

ABSTRACT:The impacts of El Niño (EN) on the rainfall over South America are investigated considering three EN types differing in the locations of the maximum sea surface temperature (SST) anomalies in the equatorial Pacific: the Central-Pacific (CP), Eastern-Pacific (EP) and the Mixed (MIX) types. The largest positive (SST) anomalies for the EP and CP types occur, respectively, in the eastern and central sectors of the tropical Pacific during all seasons. The SST anomaly pattern for the MIX-EN resembles that of the EP-EN during its onset stage, and of the CP-EN during its mature and demise stages. The different SST anomaly patterns affect the large-scale (Walker circulation and the tropospheric Rossby-wave trains) and local (South American low-level jet -SALLJ) atmospheric circulation patterns in different ways and lead to distinct precipitation anomaly patterns over South America. Variations in the position and longitudinal extension of the downward motions of the EN-related eastward-displaced Walker circulation explain the differences in the dryness over equatorial South America. For the CP-EN, a double Walker cell defines a more zonal configuration of the equatorial dryness over South America during the first three analysed seasons. This feature is not noted for the other two EN types. The Rossby-wave train pattern path depends on the EN types and seasons. In consequence, the associated local atmospheric circulation patterns depend also on the season and EN types. In all seasons, an intense SALLJ for the EP EN contrasts with weak or inexistence SALLJ for the other two EN types. Thus, a wetter condition over southeastern South America, southern and eastern Brazil occurs for the EP EN in relation to the other EN types. The results shown here, in particular considering the MIX EN type, have not been discussed before and might be useful mainly for climate monitoring purposes.

[1] In this paper, sea surface temperature (SST) and sea level pressure variability modes associated with climate extremes (droughts and floods) over northeastern Brazil (NEB) stratified according to the El Niño-Southern Oscillation (ENSO) phases (El Niño, La Niña, and neutral) are reexamined. The analyses indicate that only 36% of the time an ENSO-based forecast for the NEB climate would be right. This relatively low percentage is mostly because the interannual variations of the NEB climate are more closely tied to the tropical South Atlantic SST variability modes than to the tropical Pacific variability mode. An interesting aspect revealed in the present analysis is that hints of the FebruaryApril SST anomaly patterns in the tropical Atlantic for dry and wet cases which are not directly related to the ENSO can be found months prior to the NEB rainy season. Since these hints are particularly strong in the tropical South Atlantic, the SST variations in this sector during months prior to the rainy season should be carefully monitored in the diagnostic activities.Citation: Kayano, M. T., and R. V. Andreoli (2006), Relationships between rainfall anomalies over northeastern Brazil and the El Niño -Southern Oscillation,

From April 2014 to January 2015, ozone (O 3) dynamics were investigated as part of GoAmazon 2014/5 project in the central Amazon rainforest of Brazil. Just above the forest canopy, maximum hourly O 3 mixing ratios averaged 20 ppbv (parts per billion on a volume basis) during the June-September dry months and 15 ppbv during the wet months. Ozone levels occasionally exceeded 75 ppbv in response to influences from biomass burning and regional air pollution. Individual convective storms transported O 3-rich air parcels from the mid-troposphere to the surface and abruptly enhanced the regional atmospheric boundary layer by as much as 25 ppbv. In contrast to the individual storms, days with multiple con

This paper analyses the relations between the El Niño/Southern Oscillation (ENSO) mode in the tropical Pacific and the sea surface temperature (SST) modes in the South Atlantic for the 1900-2006 period. In the South Atlantic, two modes are analysed in more detail: the South Atlantic dipole (SAD) mode, with centres at (15°S, Greenwich longitude) and at (37.5°S, 25°W) and the southwestern South Atlantic (SWSA) mode, with centres at (30°S, 40°W) and at the southern midlatitudes. The ENSO and SAD modes are lagged or lead connected depending on the period of analysis. An El Niño (a La Niña) precedes by up to 6 months the establishment of a positive (negative) SAD mode during the 1920-1930 and 1940-1980 periods. Otherwise, a positive (negative) SAD mode precedes by up to 1 year the establishment of a La Niña (El Niño) during the 1975-2000 period. On the other hand, the SWSA is strongly driven by the ENSO. The effects of both the SAD and SWSA modes on the South American rainfall are also discussed on a seasonal basis. In general, the SAD (ENSO) mode has a weak influence on the ENSO-related (SAD-related) rainfall anomalies over South America. On the other hand, in general, the SWSA and ENSO modes have a combined effect on rainfall of the southern and southeastern regions of South America. A particularly important result of the present analysis for climate monitoring and forecasting purposes seems to be the changing relations between the SAD and ENSO modes.

The present paper reexamines the relative role of the tropical Pacific and tropical South Atlantic (TSA) on the rainfall over Northeast Brazil (NEB). For several variables, El Niño-Southern Oscillation (ENSO) and TSA-related anomalous patterns are obtained. These patterns are then compared to the combined ENSO and TSA-related patterns to infer the relative importance of the two oceanic basins on the rainfall over NEB. Analyses are done for austral summer and autumn seasons. Considering the composite technique, six cases are examined: El Niño and neutral conditions in the TSA, La Niña and neutral conditions in the TSA, ENSO neutral conditions and warm TSA, ENSO neutral conditions and cold TSA, El Niño and warm TSA, and La Niña and cold TSA. The most important result comes from the cases with competing influences of the tropical Pacific and the TSA. In some of these cases, the SST variability in the TSA is the determining factor of the NEB climate. The result of this study might be useful mainly for regional climate monitoring purposes.

The intercontinental transport of aerosols from the Sahara desert plays a significant role in nutrient cycles in the Amazon rainforest, since it carries many types of minerals to these otherwise low-fertility lands. Iron is one of the micronutrients essential for plant growth, and its long-range transport might be an important source for the iron-limited Amazon rainforest. This study assesses the bioavailability of iron Fe(II) and Fe(III) in the particulate matter over the Amazon forest, which was transported from the Sahara desert (for the sake of our discussion, this term also includes the Sahel region). The sampling campaign was carried out above and below the forest canopy at the ATTO site (Amazon Tall Tower Observatory), a near-pristine area in the central Amazon Basin, from March to April 2015. Measurements reached peak concentrations for soluble Fe(III) (48 ng m−3), Fe(II) (16 ng m−3), Na (470 ng m−3), Ca (194 ng m−3), K (65 ng m−3), and Mg (89 ng m−3) during a time period of dust transport from the Sahara, as confirmed by ground-based and satellite remote sensing data and air mass backward trajectories. Dust sampled above the Amazon canopy included primary biological aerosols and other coarse particles up to 12 µm in diameter. Atmospheric transport of weathered Saharan dust, followed by surface deposition, resulted in substantial iron bioavailability across the rainforest canopy. The seasonal deposition of dust, rich in soluble iron, and other minerals is likely to assist both bacteria and fungi within the topsoil and on canopy surfaces, and especially benefit highly bioabsorbent species. In this scenario, Saharan dust can provide essential macronutrients and micronutrients to plant roots, and also directly to plant leaves. The influence of this input on the ecology of the forest canopy and topsoil is discussed, and we argue that this influence would likely be different from that of nutrients from the weathered Amazon bedrock, which otherwise provides the main source of soluble mineral nutrients