Journal articles on the topic 'South Tropical Atlantic'
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SOUZA, Everaldo B. de, Mary T. KAYANO, Julio TOTA, Luciano PEZZI, Gilberto FISCH, and Carlos NOBRE. "On the influences of the El Niño, La niña and Atlantic Dipole Paterni on the Amazonian Rainfall during 1960-1998." Acta Amazonica 30, no. 2 (June 2000): 305–18. http://dx.doi.org/10.1590/1809-43922000302318.
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The influence of the large-scale climatic variability dominant modes in the Pacific and in the Atlantic on Amazonian rainfall is investigated. The composite technique of the Amazon precipitation anomalies is used in this work. The basis years for these composites arc those in the period 1960-1998 with occurrences of extremes in the Southern Oscillation (El Niño or La Niña) and the north/south warm (or cold) sea surface temperature (SST) anomalies dipole pattern in the tropical Atlantic. Warm (cold) dipole means positive (negative) anomalies in the tropical North Atlantic and negative (positive) anomalies in the tropical South Atlantic. Austral summer and autumn composites for extremes in the Southern Oscillation (El Niño or La Niña) and independently for north/south dipole pattern (warm or cold) of the SST anomalies in the tropical Atlantic present values (magnitude and sign) consistent with those found in previous works on the relationship between Amazon rainfall variations and the SST anomalies in the tropical Pacific and Atlantic. However, austral summer and autumn composites for the years with simultaneous occurrences of El Niño and warm north/south dipole of the SST anomalies in the tropical Atlantic show negative precipitation anomalies extending eastward over the center-eastern Amazon. This result indicates the important role played by the tropical Atlantic in the Amazon anomalous rainfall distribution.
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Gordon, Arnold L., and Kathryn T. Bosley. "Cyclonic gyre in the tropical South Atlantic." Deep Sea Research Part A. Oceanographic Research Papers 38 (1991): S323—S343. http://dx.doi.org/10.1016/s0198-0149(12)80015-x.
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Muñoz, Ernesto, Wilbert Weijer, Semyon A. Grodsky, Susan C. Bates, and Ilana Wainer. "Mean and Variability of the Tropical Atlantic Ocean in the CCSM4*." Journal of Climate 25, no. 14 (July 15, 2012): 4860–82. http://dx.doi.org/10.1175/jcli-d-11-00294.1.
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Abstract This study analyzes important aspects of the tropical Atlantic Ocean from simulations of the fourth version of the Community Climate System Model (CCSM4): the mean sea surface temperature (SST) and wind stress, the Atlantic warm pools, the principal modes of SST variability, and the heat budget in the Benguela region. The main goal was to assess the similarities and differences between the CCSM4 simulations and observations. The results indicate that the tropical Atlantic overall is realistic in CCSM4. However, there are still significant biases in the CCSM4 Atlantic SSTs, with a colder tropical North Atlantic and a hotter tropical South Atlantic, that are related to biases in the wind stress. These are also reflected in the Atlantic warm pools in April and September, with its volume greater than in observations in April and smaller than in observations in September. The variability of SSTs in the tropical Atlantic is well represented in CCSM4. However, in the equatorial and tropical South Atlantic regions, CCSM4 has two distinct modes of variability, in contrast to observed behavior. A model heat budget analysis of the Benguela region indicates that the variability of the upper-ocean temperature is dominated by vertical advection, followed by meridional advection.
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Rodrigues, Regina R., Reindert J. Haarsma, Edmo J. D. Campos, and Tércio Ambrizzi. "The Impacts of Inter–El Niño Variability on the Tropical Atlantic and Northeast Brazil Climate." Journal of Climate 24, no. 13 (July 1, 2011): 3402–22. http://dx.doi.org/10.1175/2011jcli3983.1.
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Abstract In this study, observations and numerical simulations are used to investigate how different El Niño events affect the development of SST anomalies in the Atlantic and how this relates to the Brazilian northeast (NE) precipitation. The results show that different types of El Niño have different impacts on the SST anomalies of the equatorial and tropical South Atlantic but a similar SST response in the tropical North Atlantic. Strong and long (weak and short) El Niños with the main heating source located in the eastern (central) Pacific generate cold (warm) anomalies in the cold tongue and Benguela upwelling regions during boreal winter and spring. When the SST anomalies in the eastern equatorial and tropical South Atlantic are cold (warm), the meridional SST gradient across the equator is positive (negative) and the ITCZ is not allowed (allowed) to move southward during the boreal spring; as a consequence, the precipitation is below (above) the average over the NE. Thus, strong and long (weak and short) El Niños are followed by dry (wet) conditions in the NE. During strong and long El Niños, changes in the Walker circulation over the Atlantic and in the Pacific–South Atlantic (PSA) wave train cause easterly wind anomalies in the western equatorial Atlantic, which in turn activate the Bjerknes mechanism, establishing the cold tongue in boreal spring and summer. These easterly anomalies are also responsible for the Benguela upwelling. During short and weak El Niños, westerly wind anomalies are present in the western equatorial Atlantic accompanied by warm anomalies in the eastern equatorial and tropical South Atlantic; a positive phase of the South Atlantic dipole develops during boreal winter. The simulations highlight the importance of ocean dynamics in establishing the correct slope of the equatorial thermocline and SST anomalies, which in turn determine the correct rainfall response over the NE.
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Seager, Richard, Naomi Naik, Walter Baethgen, Andrew Robertson, Yochanan Kushnir, Jennifer Nakamura, and Stephanie Jurburg. "Tropical Oceanic Causes of Interannual to Multidecadal Precipitation Variability in Southeast South America over the Past Century*." Journal of Climate 23, no. 20 (October 15, 2010): 5517–39. http://dx.doi.org/10.1175/2010jcli3578.1.
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Abstract Observations, atmosphere models forced by historical SSTs, and idealized simulations are used to determine the causes and mechanisms of interannual to multidecadal precipitation anomalies over southeast South America (SESA) since 1901. About 40% of SESA precipitation variability over this period can be accounted for by global SST forcing. Both the tropical Pacific and Atlantic Oceans share the driving of SESA precipitation, with the latter contributing the most on multidecadal time scales and explaining a wetting trend from the early midcentury until the end of the last century. Cold tropical Atlantic SST anomalies are shown to drive wet conditions in SESA. The dynamics that link SESA precipitation to tropical Atlantic SST anomalies are explored. Cold tropical Atlantic SST anomalies force equatorward-flowing upper-tropospheric flow to the southeast of the tropical heating anomaly, and the vorticity advection by this flow is balanced by vortex stretching and ascent, which drives the increased precipitation. The 1930s Pampas Dust Bowl drought occurred, via this mechanism, in response to warm tropical Atlantic SST anomalies. The atmospheric response to cold tropical Pacific SSTs also contributed. The tropical Atlantic SST anomalies linked to SESA precipitation are the tropical components of the Atlantic multidecadal oscillation. There is little evidence that the large trends over past decades are related to anthropogenic radiative forcing, although models project that this will cause a modest wetting of the climate of SESA. As such, and if the Atlantic multidecadal oscillation has shifted toward a warm phase, it should not be assumed that the long-term wetting trend in SESA will continue. Any reversal to a drier climate more typical of earlier decades would have clear consequences for regional agriculture and water resources.
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Cabré, A., J. L. Pelegrí, and I. Vallès‐Casanova. "Subtropical‐Tropical Transfer in the South Atlantic Ocean." Journal of Geophysical Research: Oceans 124, no. 7 (July 2019): 4820–37. http://dx.doi.org/10.1029/2019jc015160.
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Córdova, Mario, Rolando Célleri, and Aarnout van Delden. "Dynamics of Precipitation Anomalies in Tropical South America." Atmosphere 13, no. 6 (June 15, 2022): 972. http://dx.doi.org/10.3390/atmos13060972.
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In this study, precipitation in Tropical South America in the 1931–2016 period is investigated by means of Principal Component Analysis and composite analysis of circulation fields. The associated dynamics are analyzed using the 20th century ERA-20C reanalysis. It is found that the main climatic processes related to precipitation anomalies in Tropical South America are: (1) the intensity and position of the South Atlantic Convergence Zone (SACZ); (2) El Niño Southern Oscillation (ENSO); (3) the meridional position of the Intertropical Convergence Zone (ITCZ), which is found to be related to Atlantic Sea Surface Temperature (SST) anomalies; and (4) anomalies in the strength of the South American Monsoon System, especially the South American Low-Level Jet (SALLJ). Interestingly, all of the analyzed anomalies are related to processes that operate from the Atlantic Ocean, except for ENSO. Results from the present study are in agreement with the state of the art literature about precipitation anomalies in the region. However, the added strength of the longer dataset and the larger study area improves the knowledge and gives new insights into how climate variability and the resulting dynamics are related to precipitation in Tropical South America.
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Kishcha, P., A. M. da Silva, B. Starobinets, C. N. Long, O. Kalashnikova, and P. Alpert. "Meridional distribution of aerosol optical thickness over the tropical Atlantic Ocean." Atmospheric Chemistry and Physics Discussions 14, no. 16 (September 10, 2014): 23309–39. http://dx.doi.org/10.5194/acpd-14-23309-2014.
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Abstract. Previous studies showed that, over the global ocean, there is hemispheric asymmetry in aerosols and no noticeable asymmetry in cloud fraction (CF). In the current study, we focus on the tropical Atlantic (30° N–30° S) which is characterized by significant amounts of Saharan dust dominating other aerosol species over the North Atlantic. Over a limited area such as the tropical Atlantic, our study showed that strong meridional asymmetry in dust aerosols was accompanied by meridional CF asymmetry, by contrast to the global ocean. During the 10 yr study period (July 2002–June 2012), NASA Aerosol Reanalysis (aka MERRAero) showed that, when the meridional asymmetry in dust aerosol optical thickness (AOT) was the most pronounced (particularly in July), dust AOT averaged separately over the tropical North Atlantic was one order of magnitude higher than dust AOT averaged over the tropical South Atlantic. In the presence of such strong meridional asymmetry in dust AOT in July, CF averaged separately over the tropical North Atlantic exceeded CF averaged over the tropical South Atlantic by 20%. In July, along the Saharan Air Layer, Moderate Resolution Imaging Spectroradiometer (MODIS) CF data showed significant cloud cover (up to 0.8–0.9), which contributed to above-mentioned meridional CF asymmetry. Both Multi-Angle Imaging SpectroRadiometer (MISR) measurements and MERRAero data were in agreement on seasonal variations in meridional aerosol asymmetry. Meridional asymmetry in total AOT over the Atlantic was the most pronounced between March and July, when dust presence over the North Atlantic was maximal. In September and October, there was no noticeable meridional asymmetry in total AOT over the tropical Atlantic.
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Haarsma, Reindert J., Edmo Campos, Wilco Hazeleger, and Camiel Severijns. "Influence of the Meridional Overturning Circulation on Tropical Atlantic Climate and Variability." Journal of Climate 21, no. 6 (March 15, 2008): 1403–16. http://dx.doi.org/10.1175/2007jcli1930.1.
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Abstract The influence of the meridional overturning circulation on tropical Atlantic climate and variability has been investigated using the atmosphere–ocean coupled model Speedy-MICOM (Miami Isopycnic Coordinate Ocean Model). In the ocean model MICOM the strength of the meridional overturning cell can be regulated by specifying the lateral boundary conditions. In case of a collapse of the basinwide meridional overturning cell the SST response in the Atlantic is characterized by a dipole with a cooling in the North Atlantic and a warming in the tropical and South Atlantic. The cooling in the North Atlantic is due to the decrease in the strength of the western boundary currents, which reduces the northward advection of heat. The warming in the tropical Atlantic is caused by a reduced ventilation of water originating from the South Atlantic. This effect is most prominent in the eastern tropical Atlantic during boreal summer when the mixed layer attains its minimum depth. As a consequence the seasonal cycle as well as the interannual variability in SST is reduced. The characteristics of the cold tongue mode are changed: the variability in the eastern equatorial region is strongly reduced and the largest variability is now in the Benguela, Angola region. Because of the deepening of the equatorial thermocline, variations in the thermocline depth in the eastern tropical Atlantic no longer significantly affect the mixed layer temperature. The gradient mode remains unaltered. The warming of the tropical Atlantic enhances and shifts the Hadley circulation. Together with the cooling in the North Atlantic, this increases the strength of the subtropical jet and the baroclinicity over the North Atlantic.
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Fröhlich, Luise, Peter Knippertz, Andreas H. Fink, and Esther Hohberger. "An Objective Climatology of Tropical Plumes." Journal of Climate 26, no. 14 (July 12, 2013): 5044–60. http://dx.doi.org/10.1175/jcli-d-12-00351.1.
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Abstract The first global objective climatology of tropical plumes (TPs), obtained from a novel algorithm based on gridded 10.8-μm brightness temperatures Tb, is presented for 1983–2006. TPs are defined as continuous cloud bands (>2000 km) crossing 15°N or 15°S with Tb anomalies of less than −20 K and a lifetime of at least 3 h. A minimum length-to-width ratio of 3 filters out elongated features. Numbers of identified TPs are sensitive to the chosen thresholds but not their geographical distribution and seasonal cycle. TPs are an important indicator of tropical–extratropical interactions with impacts on radiation and moisture. TP occurrence during boreal winter is largely confined to oceanic regions with main maxima over the South Pacific and South Atlantic as well as the eastern North Atlantic and Pacific Oceans. The geographical distribution during boreal summer is similar, but with lower frequencies, except for monsoon-influenced regions. Interannual variations over the Indo-Pacific region are strongly related to El Niño. TPs often develop downstream of extratropical upper-level troughs propagating into low latitudes, particularly over the wintertime eastern North Pacific and North Atlantic, but also in regions where mean upper-level easterlies do not generally favor equatorward Rossby wave propagation. Synoptic-scale variations in the quasi-permanent cloud bands associated with the South Pacific and South Atlantic convergence zones frequently produce TP-like anomalies, which are climatologically associated with downstream upper-level troughs. Some regions also feature TPs associated with mesoscale tropical disturbances. The new TP algorithm will serve as a basis for more in-depth studies in the future.
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Nobre, Paulo, Roberto A. De Almeida, Marta Malagutti, and Emanuel Giarolla. "Coupled Ocean–Atmosphere Variations over the South Atlantic Ocean." Journal of Climate 25, no. 18 (April 18, 2012): 6349–58. http://dx.doi.org/10.1175/jcli-d-11-00444.1.
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Abstract The impact of ocean–atmosphere interactions on summer rainfall over the South Atlantic Ocean is explored through the use of coupled ocean–atmosphere models. The Brazilian Center for Weather Forecast and Climate Studies (CPTEC) coupled ocean–atmosphere general circulation model (CGCM) and its atmospheric general circulation model (AGCM) are used to gauge the role of coupled modes of variability of the climate system over the South Atlantic at seasonal time scales. Twenty-six years of summer [December–February (DJF)] simulations were done with the CGCM in ensemble mode and the AGCM forced with both observed sea surface temperature (SST) and SST generated by the CGCM forecasts to investigate the dynamics/thermodynamics of the two major convergence zones in the tropical Atlantic: the intertropical convergence zone (ITCZ) and the South Atlantic convergence zone (SACZ). The results present both numerical model and observational evidence supporting the hypothesis that the ITCZ is a thermally direct, SST-driven atmospheric circulation, while the SACZ is a thermally indirect atmospheric circulation controlling SST variability underneath—a consequence of ocean–atmosphere interactions not captured by the atmospheric model forced by prescribed ocean temperatures. Six CGCM model results of the Ensemble-based Predictions of Climate Changes and their Impacts (ENSEMBLES) project, NCEP–NCAR reanalysis data, and oceanic and atmospheric data from buoys of the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) Project over the tropical Atlantic are used to validate CPTEC’s coupled and uncoupled model simulations.
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Hounsou-Gbo, Gbèkpo Aubains, Jacques Servain, Moacyr Araujo, Guy Caniaux, Bernard Bourlès, Diogenes Fontenele, and Eduardo Sávio P. R. Martins. "SST Indexes in the Tropical South Atlantic for Forecasting Rainy Seasons in Northeast Brazil." Atmosphere 10, no. 6 (June 19, 2019): 335. http://dx.doi.org/10.3390/atmos10060335.
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May-to-July and February-to-April represent peak rainy seasons in two sub-regions of Northeast Brazil (NEB): Eastern NEB and Northern NEB respectively. In this paper, we identify key oceanic indexes in the tropical South Atlantic for driving these two rainy seasons. In Eastern NEB, the May-to-July rainfall anomalies present a positive relationship with the previous boreal winter sea surface temperature anomalies (SSTA) in the southeast tropical Atlantic (20°–10° S; 10° W–5° E). This positive relationship, which spread westward along the southern branch of the South Equatorial Current, is associated with northwesterly surface wind anomalies. A warmer sea surface temperature in the southwestern Atlantic warm pool increases the moisture flux convergence, as well as its ascending motion and, hence, the rainfall along the adjacent coastal region. For the Northern NEB, another positive relationship is observed between the February-to-April rainfall anomalies and the SSTA of the previous boreal summer in the Atlantic Niño region (3° S–3° N; 20° W–0°). The negative remote relationship noticeable between the Northern NEB rainfall and the concomitant Pacific Niño/Niña follows cold/warm events occurring during the previous boreal summer in the eastern equatorial Atlantic. The southeastern tropical Atlantic and Atlantic Niño SSTA indexes may, then, be useful to predict seasonal rainfall over the Eastern and Northern NEB, respectively, for about a 6 month leading period. The ability of both southeastern tropical Atlantic and Atlantic Niño SSTA indexes to forecast the Eastern and Northern NEB rainfall, with about a 6 month lead time, is improved when these indexes are respectively combined with the Niño3 (5° S–5° N; 150°–90° W) and the northeast subtropical Atlantic (20° N–35° N, 45° W–20° W), mainly from the 1970’s climate shift.
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Shaman, Jeffrey, Steven K. Esbensen, and Eric D. Maloney. "The Dynamics of the ENSO–Atlantic Hurricane Teleconnection: ENSO-Related Changes to the North African–Asian Jet Affect Atlantic Basin Tropical Cyclogenesis." Journal of Climate 22, no. 9 (May 1, 2009): 2458–82. http://dx.doi.org/10.1175/2008jcli2360.1.
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Abstract The nature of the teleconnection linking ENSO variability with Atlantic basin tropical storm formation is investigated. Solutions of the linearized barotropic vorticity equation forced with August–October El Niño event divergence produce upper-tropospheric vorticity anomalies over the Sahel and at the mouth of the North African–Asian (NAA) jet over the tropical Atlantic. These responses are similar in magnitude and orientation to observed ENSO vorticity variability for this region. Further investigation reveals that the vorticity anomalies over the subtropical Atlantic develop primarily in response to very low wavenumber, westward-propagating stationary Rossby waves excited by El Niño–related convective activity over the equatorial Pacific Ocean. However, the dynamics of this teleconnection change as the Atlantic basin hurricane season progresses. In August and September the response is dominated by the westward-propagating stationary Rossby waves that alter vorticity within the NAA jet and to its south. The upper-tropospheric nondivergent zonal wind anomalies produced by these vorticity anomalies are similar in pattern to observed zonal wind and vertical zonal wind shear anomalies, which suppress Atlantic basin tropical cyclogenesis. By October, eastward-propagating signals also develop over the tropical Atlantic Ocean in response to El Niño conditions. Over the main development region of Atlantic basin tropical cyclogenesis, these eastward-propagating Rossby waves appear to destructively interfere with the vorticity changes produced by the westward-propagating Rossby waves within the NAA jet. In addition, the NAA jet has shifted south by October. Consequently, the resultant upper-tropospheric nondivergent zonal wind perturbations for October are weak and suggest that ENSO should have little effect on rates of Atlantic basin tropical cyclogenesis during October. Statistical analyses of monthly ENSO-related changes in Atlantic basin tropical storm formation support this hypothesis.
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Joyeux, J. C., S. R. Floeter, C. E. L. Ferreira, and J. L. Gasparini. "Biogeography of tropical reef fishes: the South Atlantic puzzle." Journal of Biogeography 28, no. 7 (July 7, 2008): 831–41. http://dx.doi.org/10.1046/j.1365-2699.2001.00602.x.
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Wang, Hui, and Rong Fu. "The Influence of Amazon Rainfall on the Atlantic ITCZ through Convectively Coupled Kelvin Waves." Journal of Climate 20, no. 7 (April 1, 2007): 1188–201. http://dx.doi.org/10.1175/jcli4061.1.
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Abstract Using outgoing longwave radiation (OLR) and Tropical Rainfall Measuring Mission (TRMM) daily rain-rate data, systematic changes in intensity and location of the Atlantic intertropical convergence zone (ITCZ) were detected along the equator during boreal spring. It is found that the changes in convection over the tropical Atlantic may be induced by deep convection in equatorial South America. Lagged regression analyses demonstrate that the anomalies of convection developed over the land propagate eastward across the Atlantic and then into Africa. The eastward-propagating disturbances appear to be convectively coupled Kelvin waves with a period of 6–7.5 days and a phase speed of around 15 m s−1. These waves modulate the intensity and location of the convection in the tropical Atlantic and result in a zonal variation of the Atlantic ITCZ on synoptic time scales. The convectively coupled Kelvin wave has substantial signals in both the lower and upper troposphere. Both a reanalysis dataset and the Quick Scatterometer (QuikSCAT) ocean surface wind are used to characterize the Kelvin wave. This study suggests that synoptic-scale variation of the Atlantic ITCZ may be linked to precipitation anomalies in South America through the convectively coupled Kelvin wave. The results imply that the changes of Amazon convection could contribute to the large variability of the tropical Atlantic ITCZ observed during boreal spring.
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Finke, Kathrin, Bernat Jiménez-Esteve, Andréa S. Taschetto, Caroline C. Ummenhofer, Karl Bumke, and Daniela I. V. Domeisen. "Revisiting remote drivers of the 2014 drought in South-Eastern Brazil." Climate Dynamics 55, no. 11-12 (September 3, 2020): 3197–211. http://dx.doi.org/10.1007/s00382-020-05442-9.
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Abstract South-Eastern Brazil experienced a devastating drought associated with significant agricultural losses in austral summer 2014. The drought was linked to the development of a quasi-stationary anticyclone in the South Atlantic in early 2014 that affected local precipitation patterns over South-East Brazil. Previous studies have suggested that the unusual blocking was triggered by tropical Pacific sea surface temperature (SST) anomalies and, more recently, by convection over the Indian Ocean related to the Madden–Julian Oscillation. Further investigation of the proposed teleconnections appears crucial for anticipating future economic impacts. In this study, we use numerical experiments with an idealized atmospheric general circulation model forced with the observed 2013/2014 SST anomalies in different ocean basins to understand the dominant mechanism that initiated the 2014 South Atlantic anticyclonic anomaly. We show that a forcing with global 2013/2014 SST anomalies enhances the chance for the occurrence of positive geopotential height anomalies in the South Atlantic. However, further sensitivity experiments with SST forcings in separate ocean basins suggest that neither the Indian Ocean nor tropical Pacific SST anomalies alone have contributed significantly to the anomalous atmospheric circulation that led to the 2014 South-East Brazil drought. The model study rather points to an important role of remote forcing from the South Pacific, local South Atlantic SSTs, and internal atmospheric variability in driving the persistent blocking over the South Atlantic.
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Stockdale, Timothy N., Magdalena A. Balmaseda, and Arthur Vidard. "Tropical Atlantic SST Prediction with Coupled Ocean–Atmosphere GCMs." Journal of Climate 19, no. 23 (December 1, 2006): 6047–61. http://dx.doi.org/10.1175/jcli3947.1.
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Abstract Variations in tropical Atlantic SST are an important factor in seasonal forecasts in the region and beyond. An analysis is given of the capabilities of the latest generation of coupled GCM seasonal forecast systems to predict tropical Atlantic SST anomalies. Skill above that of persistence is demonstrated in both the northern tropical and equatorial Atlantic, but not farther south. The inability of the coupled models to correctly represent the mean seasonal cycle is a major problem in attempts to forecast equatorial SST anomalies in the boreal summer. Even when forced with observed SST, atmosphere models have significant failings in this area. The quality of ocean initial conditions for coupled model forecasts is also a cause for concern, and the adequacy of the near-equatorial ocean observing system is in doubt. A multimodel approach improves forecast skill only modestly, and large errors remain in the southern tropical Atlantic. There is still much scope for improving forecasts of tropical Atlantic SST.
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Hu, Zeng-Zhen, and Bohua Huang. "The Predictive Skill and the Most Predictable Pattern in the Tropical Atlantic: The Effect of ENSO." Monthly Weather Review 135, no. 5 (May 1, 2007): 1786–806. http://dx.doi.org/10.1175/mwr3393.1.
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Abstract This work investigates the predictive skill and most predictable pattern in the NCEP Climate Forecast System (CFS) in the tropical Atlantic Ocean. The skill is measured by the sea surface temperature (SST) anomaly correlation between the predictions and the corresponding analyses, and the most predictable patterns are isolated by an empirical orthogonal function analysis with a maximized signal-to-noise ratio. On average, for predictions with initial conditions (ICs) of all months, the predictability of SST is higher in the west than in the east. The highest skill is near the tropical Brazilian coast and in the Caribbean Sea, and the lowest skill occurs in the eastern coast. Seasonally, the skill is higher for predictions with ICs in summer or autumn and lower for those with ICs in spring. The CFS poorly predicts the meridional gradient in the tropical Atlantic Ocean. The superiority of the CFS predictions to the persistence forecasts depends on IC month, region, and lead time. The CFS prediction is generally better than the corresponding persistence forecast when the lead time is longer than 3 months. The most predictable pattern of SST in March has the same sign in almost the whole tropical Atlantic. The corresponding pattern in March is dominated by the same sign for geopotential height at 200 hPa in most of the domain and by significant opposite variation for precipitation between the northwestern tropical North Atlantic and the regions from tropical South America to the southwestern tropical North Atlantic. These predictable signals mainly result from the influence of the El Niño–Southern Oscillation (ENSO). The significant values in the most predictable pattern of precipitation in the regions from tropical South America to the southwestern tropical North Atlantic in March are associated with excessive divergence (convergence) at low (high) levels over these regions in the CFS. For the CFS, the predictive skill in the tropical Atlantic Ocean is largely determined by its ability to predict ENSO. This is due to the strong connection between ENSO and the most predictable patterns in the tropical Atlantic Ocean in the model. The higher predictive skill of tropical North Atlantic SST is consistent with the ability of the CFS to predict ENSO on interseasonal time scales, particularly for the ICs in warm months from March to October. In the southeastern ocean, the systematic warm bias is a crucial factor leading to the low skill in this region.
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da Cunha, L. C., and E. T. Buitenhuis. "Riverine influence on the tropical Atlantic Ocean biogeochemistry." Biogeosciences 10, no. 10 (October 9, 2013): 6357–73. http://dx.doi.org/10.5194/bg-10-6357-2013.
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Abstract. We assess the role of riverine inputs of N, Si, Fe, organic and inorganic C in the tropical Atlantic Ocean using a global ocean biogeochemistry model. We use a standard model scenario and three sensitivity tests to investigate the role of total river nutrient and carbon inputs, as well as the western (South American) and eastern (African) river inputs on the tropical Atlantic Ocean biogeochemistry, between 20° S–20° N and 70° W–20° E. Increased nutrient availability from river inputs in this area (compared to a sensitivity scenario without river nutrient inputs, NO_RIVER) leads to an increase in primary production (PP) and export production (EP), mainly in the coastal ocean area (modeled ocean area with bathymetry <200 m). Model results suggest an enhanced N-fixation by diazotrophs on the tropical Atlantic mainly in open ocean areas. The increased rate of N-fixation in the TODAY scenario is proportional to the increase in PP and EP relative to the NO_RIVER scenario, and may support up to 14% of the coastal ocean export production. Inputs from South American rivers have an impact in coastal PP and EP two times higher than those from African rivers. On the other hand, results suggest that the contribution of African and South American rivers to the total increase in open ocean PP and EP is similar. Considering the amount of delivered nutrients (2–3 times less nutrients and carbon inputs by African rivers) one concludes that African riverine inputs may have a larger impact on the whole tropical Atlantic Ocean biogeochemistry. This is probably due to a combination of nutrient trapping in upwelling areas off the large rivers' outflows and shallow mixed layers in the eastern tropical Atlantic, concomitantly to the differences in delivered nutrient ratios leading to alleviation in limitation conditions, mainly for diatoms. When river inputs are added to the model, we estimate a modest decrease in open ocean sea-air CO2 fluxes (−5.2 Tg C a−1) and an increase in coastal ocean CO2 fluxes, mainly provoked by the remineralization of riverine organic matter delivered by the South American rivers.
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Liu, Xiaojuan, David S. Battisti, Rachel H. White, and Paul A. Baker. "South American Climate during the Early Eocene: Impact of a Narrower Atlantic and Higher Atmospheric CO2." Journal of Climate 33, no. 2 (January 15, 2020): 691–706. http://dx.doi.org/10.1175/jcli-d-19-0170.1.
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AbstractThe Cenozoic climate of tropical South America was fundamental to the development of its biota, the most biodiverse on Earth. No previous studies have explicitly addressed how the very different atmospheric composition and Atlantic geometry during the early Eocene (approximately 55 million years ago) may have affected South American climate. At that time, the Atlantic Ocean was approximately half of its current width and the CO2 concentration of Earth’s atmosphere ranged from ~550 to ~1500 ppm or even higher. Climate model simulations were performed to examine the effects of these major state changes on the climate of tropical South America. Reducing the width of the Atlantic by approximately half produces significant drying relative to modern climate. Drying is only partly offset by an enhancement of precipitation due to the higher CO2 of the early Eocene. The main mechanism for drier conditions is simple. Low-level air crosses the tropical Atlantic from North Africa in much less time for a narrower Atlantic (2 days) than for the modern Atlantic (~6 days); as a result, much less water is evaporated into the air and thus there is far lower moisture imported to the continent in the Eocene simulation than in the modern control. The progressive wetting (during the mid- to late Cenozoic) of the Amazon due to the widening Atlantic and the rising Andes, only partly offset by decreasing CO2 values, may have been partly responsible for the accumulating biodiversity of this region.
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Piecuch, Christopher G., and Rui M. Ponte. "Buoyancy-Driven Interannual Sea Level Changes in the Tropical South Atlantic." Journal of Physical Oceanography 43, no. 3 (March 1, 2013): 533–47. http://dx.doi.org/10.1175/jpo-d-12-093.1.
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Abstract Linear models of dynamical ocean adjustment to wind field changes, local atmospheric driving, and eastern boundary forcing are often invoked to explain observed patterns of interannual regional sea level variability. While skillful in some regions, these processes alone cannot explain low levels of interannual sea level variability observed in the tropical Atlantic. In this study, through a set of modeling approaches, interannual sea level changes in the tropical South Atlantic are attributed and the dynamical influence of buoyancy forcing is elucidated. Similar to recent findings in the southeast tropical Pacific, sea level patterns in the tropical South Atlantic (as estimated from a data-constrained ocean general circulation model) are found to result from the action of both surface wind and buoyancy forcing; in addition to static local effects, the buoyancy-driven changes comprise important nonlocal ocean dynamical processes. It is shown that the buoyancy-driven sea level changes can be understood within the framework of a linear first baroclinic mode Rossby wave model forced by atmospheric fields and variability along the eastern boundary. To lowest order, the linear model framework also reproduces qualitative patterns of basinwide compensation between wind- and buoyancy-driven sea level changes, which are mostly tied to the anticorrelation of both surface and boundary forcing. Results suggest that the ocean’s dynamical adjustment to buoyancy forcing exerts an important influence on interannual sea level changes across all tropical oceans.
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Cotrim da Cunha, L., and E. T. Buitenhuis. "Riverine influence on the tropical Atlantic Ocean biogeochemistry." Biogeosciences Discussions 9, no. 2 (February 17, 2012): 1945–69. http://dx.doi.org/10.5194/bgd-9-1945-2012.
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Abstract. We assess the role of riverine inputs of N, Si, Fe, organic and inorganic C in the tropical Atlantic Ocean using a global ocean biogeochemistry model. We use two sensitivity tests to investigate the role of the western (South American Rivers) and eastern (African Rivers) riverine nutrient inputs on the tropical Atlantic Ocean biogeochemistry (between 20° S–20° N and 70° W–20°). Increased nutrient availability from river inputs in this area (compared to an extreme scenario with no river nutrients) leads to an increase in 14 % (0.7 Pg C a−1) in open ocean primary production (PP), and 21 % (0.2 Pg C a−1) in coastal ocean PP. We estimate very modest increases in open and coastal ocean export production and sea-air CO2 fluxes. Results suggest that in the tropical Atlantic Ocean, the large riverine nutrient inputs on the western side have a larger impact on primary production and sea-air CO2 exchanges. On the other hand, African river inputs, although smaller than South American inputs, have larger impact on the coastal and open tropical Atlantic Ocean export production. This is probably due to a combination of nutrient trapping in upwelling areas off the Congo River outflow, and differences in delivered nutrient ratios leading to alleviation in limitation conditions mainly for diatoms.
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Trzaska, Sylwia, Andrew W. Robertson, John D. Farrara, and Carlos R. Mechoso. "South Atlantic Variability Arising from Air–Sea Coupling: Local Mechanisms and Tropical–Subtropical Interactions." Journal of Climate 20, no. 14 (July 15, 2007): 3345–65. http://dx.doi.org/10.1175/jcli4114.1.
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Abstract Interannual variability in the southern and equatorial Atlantic is investigated using an atmospheric general circulation model (AGCM) coupled to a slab ocean model (SOM) in the Atlantic in order to isolate features of air–sea interactions particular to this basin. Simulated covariability between sea surface temperatures (SSTs) and atmosphere is very similar to the observed non-ENSO-related covariations in both spatial structures and time scales. The leading simulated empirical coupled mode resembles the zonal mode in the tropical Atlantic, despite the lack of ocean dynamics, and is associated with baroclinic atmospheric anomalies in the Tropics and a Rossby wave train extending to the extratropics, suggesting an atmospheric response to tropical SST forcing. The second non-ENSO mode is the subtropical dipole in the SST with a mainly equivalent barotropic atmospheric anomaly centered on the subtropical high and associated with a midlatitude wave train, consistent with atmospheric forcing of the subtropical SST. The power spectrum of the tropical mode in both simulation and observation is red with two major interannual peaks near 5 and 2 yr. The quasi-biennial component exhibits a progression between the subtropics and the Tropics. It is phase locked to the seasonal cycle and owes its existence to the imbalances between SST–evaporation and SST–shortwave radiation feedbacks. These feedbacks are found to be reversed between the western and eastern South Atlantic, associated with the dominant role of deep convection in the west and that of shallow clouds in the east. A correct representation of tropical–extratropical interactions and of deep and shallow clouds may thus be crucial to the simulation of realistic interannual variability in the southern and tropical Atlantic.
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Knippertz, Peter. "Tropical–Extratropical Interactions Associated with an Atlantic Tropical Plume and Subtropical Jet Streak." Monthly Weather Review 133, no. 9 (September 1, 2005): 2759–76. http://dx.doi.org/10.1175/mwr2999.1.
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Abstract Tropical plumes (TPs) are elongated bands of upper- and midlevel clouds stretching from the Tropics poleward and eastward into the subtropics, typically accompanied by a subtropical jet (STJ) streak and a trough on their poleward side. This study uses ECMWF analyses and high-resolution University of Wisconsin–Nonhydrostatic Modeling System trajectories to analyze the multiscale complex tropical–extratropical interactions involved in the genesis of a pronounced TP and STJ over the NH Atlantic Ocean in late March 2002 that was associated with extreme precipitation in arid northwest Africa. Previous concepts for TP genesis from the literature are discussed in the light of this case study. Analysis of the upper-level flow prior to the TP formation shows a northeastward propagation and a continuous acceleration of the STJ over the Atlantic Ocean equatorward of a positively tilted upper-level trough to the west of northwest Africa. Both dynamic and advective processes contribute to the generation of the accompanying cloud band. The northern portion of the TP consists of parcels that exit a strong STJ streak over North America, enter the deep Tropics over South America, and then accelerate into the Atlantic STJ, accompanied by strong cross-jet ageostrophic motions, rising, and cloud formation. The southern portion is formed by parcels originating in the divergent outflow from strong near-equatorial convection accompanying the TP genesis. A local increase in the Hadley overturning is found over the tropical Atlantic and east Pacific/South America and appears to be related to low inertial stability at the outflow level and to low-level trade surges associated with the cold advection, sinking, and lower-level divergence underneath two strong upper-level convergence centers in the eastern portions of both a subtropical ridge over North America and an extratropical ridge over the North Atlantic Ocean. Evidence is presented that the convective response lags the trade surge by several days.
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Figueiredo Prado, Luciana, Ilana Wainer, and Pedro Leite da Silva Dias. "Tropical Atlantic Response to Last Millennium Volcanic Forcing." Atmosphere 9, no. 11 (October 27, 2018): 421. http://dx.doi.org/10.3390/atmos9110421.
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Climate responses to volcanic eruptions include changes in the distribution of temperature and precipitation such as those associated with El Niño Southern Oscillation (ENSO). Recent studies suggest an ENSO-positive phase after a volcanic eruption. In the Atlantic Basin, a similar mode of variability is referred as the Atlantic Niño, which is related to precipitation variability in West Africa and South America. Both ENSO and Atlantic Niño are characterized in the tropics by conjoined fluctuations in sea surface temperature (SST), zonal winds, and thermocline depth. Here, we examine possible responses of the Tropical Atlantic to last millennium volcanic forcing via SST, zonal winds, and thermocline changes. We used simulation results from the National Center for Atmospheric Research Community Earth System Model Last Millennium Ensemble single-forcing experiment ranging from 850 to 1850 C.E. Our results show an SST cooling in the Tropical Atlantic during the post-eruption year accompanied by differences in the Atlantic Niño associated feedback. However, we found no significant deviations in zonal winds and thermocline depth related to the volcanic forcing in the first 10 years after the eruption. Changes in South America and Africa monsoon precipitation regimes related to the volcanic forcing were detected, as well as in the Intertropical Convergence Zone position and associated precipitation. These precipitation responses derive primarily from Southern and Tropical volcanic eruptions and occur predominantly during the austral summer and autumn of the post-eruption year.
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Grodsky, Semyon A., James A. Carton, Sumant Nigam, and Yuko M. Okumura. "Tropical Atlantic Biases in CCSM4." Journal of Climate 25, no. 11 (June 2012): 3684–701. http://dx.doi.org/10.1175/jcli-d-11-00315.1.
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This paper focuses on diagnosing biases in the seasonal climate of the tropical Atlantic in the twentieth-century simulation of the Community Climate System Model, version 4 (CCSM4). The biases appear in both atmospheric and oceanic components. Mean sea level pressure is erroneously high by a few millibars in the subtropical highs and erroneously low in the polar lows (similar to CCSM3). As a result, surface winds in the tropics are ~1 m s−1 too strong. Excess winds cause excess cooling and depressed SSTs north of the equator. However, south of the equator SST is erroneously high due to the presence of additional warming effects. The region of highest SST bias is close to southern Africa near the mean latitude of the Angola–Benguela Front (ABF). Comparison of CCSM4 to ocean simulations of various resolutions suggests that insufficient horizontal resolution leads to the insufficient northward transport of cool water along this coast and an erroneous southward stretching of the ABF. A similar problem arises in the coupled model if the atmospheric component produces alongshore winds that are too weak. Erroneously warm coastal SSTs spread westward through a combination of advection and positive air–sea feedback involving marine stratocumulus clouds. This study thus highlights three aspects to improve to reduce bias in coupled simulations of the tropical Atlantic: 1) large-scale atmospheric pressure fields; 2) the parameterization of stratocumulus clouds; and 3) the processes, including winds and ocean model resolution, that lead to errors in seasonal SST along southwestern Africa. Improvements of the latter require horizontal resolution much finer than the 1° currently used in many climate models.
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Handoh, Itsuki C., Grant R. Bigg, Adrian J. Matthews, and David P. Stevens. "Interannual variability of the Tropical Atlantic independent of and associated with ENSO: Part II. The South Tropical Atlantic." International Journal of Climatology 26, no. 14 (2006): 1957–76. http://dx.doi.org/10.1002/joc.1342.
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Brierley, Chris, and Ilana Wainer. "Inter-annual variability in the tropical Atlantic from the Last Glacial Maximum into future climate projections simulated by CMIP5/PMIP3." Climate of the Past 14, no. 10 (October 1, 2018): 1377–90. http://dx.doi.org/10.5194/cp-14-1377-2018.
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Abstract. Tropical Atlantic variability (TAV) plays an important role in driving year-to-year changes in rainfall over Africa and South America. In this study, its response to global climate change is investigated through a series of multi-model experiments. We explore the leading modes of TAV during the historical, Last Glacial Maximum, mid-Holocene, and future simulations in the multi-model ensemble known as PMIP3/CMIP5. Despite their known sea surface temperature biases, most of the models are able to capture the tropical Atlantic's two leading modes of SST variability patterns – the Atlantic Meridional Mode (AMM) and the Atlantic zonal mode (also called the Atlantic Niño or ATL3). The ensemble suggests that AMM amplitude was less during the mid-Holocene and increased during the Last Glacial Maximum, but is equivocal about future changes. ATL3 appears stronger under both the Last Glacial Maximum and future climate changes, with no consistent message about the mid-Holocene. The patterns and the regions under the influence of the two modes alter a little under climate change in concert with changes in the mean climate state. In the future climate experiment, the equatorial mode weakens, and the whole Northern Hemisphere warms up, while the South Atlantic displays a hemisphere-wide weak oscillating pattern. For the LGM, the AMM projects onto a pattern that resembles the pan-Atlantic decadal oscillation. No robust relationships between the amplitude of the zonal and meridional temperature gradients and their respective variability was found.
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Huang, Huei-Ping, Andrew W. Robertson, Yochanan Kushnir, and Shiling Peng. "Hindcasts of Tropical Atlantic SST Gradient and South American Precipitation: The Influences of the ENSO Forcing and the Atlantic Preconditioning." Journal of Climate 22, no. 9 (May 1, 2009): 2405–21. http://dx.doi.org/10.1175/2008jcli2569.1.
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Abstract Hindcast experiments for the tropical Atlantic sea surface temperature (SST) gradient G1, defined as tropical North Atlantic SST anomaly minus tropical South Atlantic SST anomaly, are performed using an atmospheric general circulation model coupled to a mixed layer ocean over the Atlantic to quantify the contributions of the El Niño–Southern Oscillation (ENSO) forcing and the preconditioning in the Atlantic to G1 in boreal spring. The results confirm previous observational analyses that, in the years with a persistent ENSO SST anomaly from boreal winter to spring, the ENSO forcing plays a primary role in determining the tendency of G1 from winter to spring and the sign of G1 in late spring. In the hindcasts, the initial perturbations in Atlantic SST in boreal winter are found to generally persist beyond a season, leaving a secondary but nonnegligible contribution to the predicted Atlantic SST gradient in spring. For 1993/94, a neutral year with a large preexisting G1 in winter, the hindcast using the information of Atlantic preconditioning alone is found to reproduce the observed G1 in spring. The seasonal predictability in precipitation over South America is examined in the hindcast experiments. For the recent events that can be validated with high-quality observations, the hindcasts produced dryness in boreal spring 1983, wetness in spring 1996, and wetness in spring 1994 over northern Brazil that are qualitatively consistent with observations. An inclusion of the Atlantic preconditioning is found to help the prediction of South American rainfall in boreal spring. For the ENSO years, discrepancies remain between the hindcast and observed precipitation anomalies over northern and equatorial South America, an error that is partially attributed to the biased atmospheric response to ENSO forcing in the model. The hindcast of the 1993/94 neutral year does not suffer this error. It constitutes an intriguing example of useful seasonal forecast of G1 and South American rainfall anomalies without ENSO.
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Jenkins, G. S., and J. H. Ryu. "Space-borne observations link the tropical Atlantic ozone maximum and paradox to lightning." Atmospheric Chemistry and Physics Discussions 3, no. 6 (November 13, 2003): 5725–54. http://dx.doi.org/10.5194/acpd-3-5725-2003.
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Abstract. The causes of high tropospheric column ozone values over the Tropical Atlantic Ocean during September, October, and November (SON) are investigated by examining lightning during 1998–2001. The cause for high tropospheric column ozone in the hemisphere opposite of biomass burning (tropical ozone paradox) is also examined. Our results show that lightning is central to high tropospheric column ozone during SON and responsible for the tropical ozone paradox during December, January, and February (DJF) and June, July and August (JJA). During SON large numbers of flashes are observed in South America, Central and West Africa enriching the tropospheric column ozone over the Tropical Atlantic Ocean. During JJA the largest numbers of lightning flashes are observed in West Africa, enriching tropospheric column ozone to the north of 5° S in the absence biomass burning. During DJF, lightning is concentrated in South America and Central Africa enriching tropospheric column ozone south of the Equator in the absence of biomass burning.
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Knippertz, Peter, Heini Wernli, and Gregor Gläser. "A Global Climatology of Tropical Moisture Exports." Journal of Climate 26, no. 10 (May 8, 2013): 3031–45. http://dx.doi.org/10.1175/jcli-d-12-00401.1.
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Abstract In a recent paper, a climatology of tropical moisture exports (TMEs) to the Northern Hemisphere (NH) was constructed on the basis of 7-day forward trajectories, started daily from the tropical lower troposphere, which were required to reach a water vapor flux of at least 100 g kg−1 m s−1 somewhere north of 35°N. It was shown that TMEs contribute significantly to regional precipitation. Here, the authors complement and extend this work by (i) using 6-hourly European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) data from 1979 to 2010 instead of the earlier 40-yr ECMWF Re-Analysis (ERA-40), (ii) extending the climatology to the Southern Hemisphere (SH), and (iii) relating TME events to atmospheric rivers (ARs) previously discussed in the literature. The main conclusions are as follows: First, the TME climatology is not sensitive to the reanalysis dataset. Second, SH TME shows four activity centers: the central and eastern Pacific Ocean (170°–90°W, near the South Pacific convergence zone), eastern South America and the adjacent Atlantic Ocean (60°W–0°, near the South Atlantic convergence zone), the western Indian Ocean (30°–80°E), and western Australia (110°–140°E). Third, TME activity in the SH peaks in austral summer because of higher moisture contents and possibly because of increased Rossby wave activity from the NH. Fourth, El Niño warm events are associated with reduced activity over the South Pacific and increased activity over the South Atlantic and around Australia, while correlations with the southern annular mode are generally weak. Finally, around 90% of all ARs affecting the U.S. West Coast during December–May are connected to TME events, revealing their importance for heavy rain and flooding.
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Pisera, Andrzej, and Shirley A. Pomponi. "New data on lithistid sponges from the deep Florida shelf with description of a new species of Theonella." Journal of the Marine Biological Association of the United Kingdom 95, no. 7 (February 18, 2015): 1297–309. http://dx.doi.org/10.1017/s0025315414001477.
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Most lithistids occur worldwide in deep-water environments, but can be found in some places in shallow water. They are not well known in the tropical western Atlantic, despite the fact that they were first described in the late 1800s. We report here two species of poorly known theonellid demosponges (Astrophorina), Discodermia dissoluta and Theonella atlantica, and one new species, Theonella wrightae, from the north-west, south-west and south Florida shelf. There is considerable variability in habitus, colour and spiculation in this species. If samples are taken randomly from different specimens and from functionally and structurally different locations on the sponge, the specimens could be mistakenly identified or individuals of the same species could be described as different species. This report increases the number of lithistid sponges reported from the tropical western Atlantic region to 30 species, but our unpublished data suggest a much higher number of species present in this region. It is also the second report of the relatively deep-water (81 m) occurrence of D. dissoluta that is mostly known from depths as shallow as 10–30 m.
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Donners, J., S. S. Drijfhout, and W. Hazeleger. "Water Mass Transformation and Subduction in the South Atlantic." Journal of Physical Oceanography 35, no. 10 (October 1, 2005): 1841–60. http://dx.doi.org/10.1175/jpo2782.1.
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Abstract The transformation of water masses induced by air–sea fluxes in the South Atlantic Ocean is calculated with a global ocean model, Ocean Circulation and Climate Advanced Modeling (OCCAM), and has been compared with several observational datasets. Air–sea interaction supplies buoyancy to the ocean at almost all density levels. The uncertainty of the estimates of water mass transformations is at least 10 Sv (Sv ≡ 106 m3 s−1), largely caused by the uncertainties in heat fluxes. Further analysis of the buoyancy budget of the mixed layer in the OCCAM model shows that diffusion extracts buoyancy from the water column at all densities. In agreement with observations, water mass formation of surface water by air–sea interaction is completely balanced by consumption from diffusion. There is a large interocean exchange with the Indian and Pacific Oceans. Intermediate water is imported from the Pacific, and light surface water is imported from the Indian Ocean. South Atlantic Central Water and denser water masses are exported to the Indian Ocean. The air–sea formation rate is only a qualitative estimate of the sum of subduction and interocean exchange. Subduction generates teleconnections between the South Atlantic and remote areas where these water masses reemerge in the mixed layer. Therefore, the subduction is analyzed with a Lagrangian trajectory analysis. Surface water obducts in the South Atlantic, while all other water masses experience net subduction. The subducted Antarctic Intermediate Water and Subantarctic Mode Water reemerge mainly in the Antarctic Circumpolar Current farther downstream. Lighter waters reemerge in the eastern tropical Atlantic. As a result, the extratropical South Atlantic has a strong link with the tropical Atlantic basin and only a weak direct link with the extratropical North Atlantic. The impact of the South Atlantic on the upper branch of the thermohaline circulation is indirect: water is significantly transformed by air–sea fluxes and mixing in the South Atlantic, but most of it reemerges and subducts again farther downstream.
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Leão de Moura, Rodrigo, Matheus Oliveira Freitas, Ronaldo Bastos Francini-Filho, and Carolina Viviana Minte-Vera. "Spawning patterns of commercially important reef fish (Lutjanidae and Serranidae) in the tropical western South Atlantic." Scientia Marina 75, no. 1 (February 4, 2011): 135–46. http://dx.doi.org/10.3989/scimar.2011.75n1135.
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Penland, Cécile, and Ludmila Matrosova. "Studies of El Niño and Interdecadal Variability in Tropical Sea Surface Temperatures Using a Nonnormal Filter." Journal of Climate 19, no. 22 (November 15, 2006): 5796–815. http://dx.doi.org/10.1175/jcli3951.1.
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Abstract A dynamically based filter is used to separate tropical sea surface temperatures (SSTs) into three components: the evolving El Niño signal, the global tropical trend, and the background. The components thus isolated are not independent. On the contrary, this procedure allows us to see the importance of the interdecadal signal to the predictability of El Niño. The data filtered in this way reveal El Niño signals in the equatorial Indian Ocean and in the north tropical Atlantic Ocean that are remarkably similar. A signature of El Niño in the south tropical Atlantic leads Niño-3.4 SST anomalies by about 9 months. The time series of a global tropical trend is found to have a very smooth parabolic structure. In unfiltered data, this trend conspires with El Niño to obscure a meridional tropical Atlantic dipole, which is significant in the filtered background SST data.
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Handiani, D., A. Paul, M. Prange, U. Merkel, L. Dupont, and X. Zhang. "Tropical vegetation response to Heinrich Event 1 as simulated with the UVic ESCM and CCSM3." Climate of the Past 9, no. 4 (July 31, 2013): 1683–96. http://dx.doi.org/10.5194/cp-9-1683-2013.
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Abstract. We investigated changes in tropical climate and vegetation cover associated with abrupt climate change during Heinrich Event 1 (HE1, ca. 17.5 ka BP) using two different global climate models: the University of Victoria Earth System-Climate Model (UVic ESCM) and the Community Climate System Model version 3 (CCSM3). Tropical South American and African pollen records suggest that the cooling of the North Atlantic Ocean during HE1 influenced the tropics through a southward shift of the rain belt. In this study, we simulated the HE1 by applying a freshwater perturbation to the North Atlantic Ocean. The resulting slowdown of the Atlantic Meridional Overturning Circulation was followed by a temperature seesaw between the Northern and Southern Hemispheres, as well as a southward shift of the tropical rain belt. The shift and the response pattern of the tropical vegetation around the Atlantic Ocean were more pronounced in the CCSM3 than in the UVic ESCM simulation. For tropical South America, opposite changes in tree and grass cover were modeled around 10° S in the CCSM3 but not in the UVic ESCM. In tropical Africa, the grass cover increased and the tree cover decreased around 15° N in the UVic ESCM and around 10° N in the CCSM3. In the CCSM3 model, the tree and grass cover in tropical Southeast Asia responded to the abrupt climate change during the HE1, which could not be found in the UVic ESCM. The biome distributions derived from both models corroborate findings from pollen records in southwestern and equatorial western Africa as well as northeastern Brazil.
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Chen, Tsing-Chang, Shih-Yu Wang, and Adam J. Clark. "North Atlantic Hurricanes Contributed by African Easterly Waves North and South of the African Easterly Jet." Journal of Climate 21, no. 24 (December 15, 2008): 6767–76. http://dx.doi.org/10.1175/2008jcli2523.1.
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Abstract A majority of tropical cyclones in the North Atlantic develop from African easterly waves (AEWs), which originate along both the southern and northern flanks of the midtropospheric African easterly jet (AEWS and AEWn, respectively). The purpose of this note is to identify the contribution of AEWSs and AEWns to North Atlantic tropical cyclones that develop from AEWs. Applying a manual backtracking approach to identify the genesis locations of AEWS, it was found that the population ratio of tropical cyclones formed from AEWSs to those formed from AEWns is 1:1.2. Because the population ratio of AEWSs to AEWns is 1:2.5, the conversion rate of the former AEWS to tropical cyclones is twice as effective as the latter waves. In addition, it was found that AEWns travel farther and take longer to transform into tropical cyclones than AEWSs, which is likely because the AEWns are drier and shallower than AEWSs. An analysis of various terms in the moisture and vorticity budgets reveals that the monsoon trough over West Africa provides moisture and enhances low-level vorticity for both AEWns and AEWSs as they move off the West African coast. The monsoon trough appears to be of particular importance in supplying AEWns with enough moisture so that they have similar properties to AEWSs after they have traveled a considerable westward distance across the tropical Atlantic.
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Richter, Ingo, Carlos R. Mechoso, and Andrew W. Robertson. "What Determines the Position and Intensity of the South Atlantic Anticyclone in Austral Winter?—An AGCM Study." Journal of Climate 21, no. 2 (January 15, 2008): 214–29. http://dx.doi.org/10.1175/2007jcli1802.1.
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Abstract The South Atlantic anticyclone is a major feature of the austral winter climatology. An atmospheric general circulation model (AGCM) is used to study the dynamics of the South Atlantic anticyclone by means of control simulations and experiments to investigate sensitivity to prescribed orography, sea surface temperatures, and soil wetness. The South Atlantic anticyclone in the first control simulation is unrealistically zonally elongated and centered too far west—errors typical of coupled ocean–atmosphere GCMs. Results of the sensitivity experiments suggest that these deficiencies are associated with another family of systematic model errors: the overprediction of convection over the tropical land surfaces, particularly over eastern tropical Africa and India, and the concurrent large-scale westward shift in the divergence center at upper levels and the convergence center at lower levels. The results also confirm the important role of South American and African orography in localizing the South Atlantic anticyclone over the ocean. Other factors, however, like the regional zonal gradients of sea surface temperatures, are found to have only a minor impact on the anticyclone. To further substantiate these findings, the wintertime anticyclone is examined using a revised version of the atmospheric GCM. Improvements are found in both the anticyclone as well as the Asia–African summer monsoon circulations. The results demonstrate the existence of links between intensity and structure of the wintertime South Atlantic anticyclone and the major summer monsoons in the Northern Hemisphere.
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Evangelista, Heitor, Marcio Gurgel, Abdelfettah Sifeddine, Nivaor Rodolfo Rigozo, and Mohammed Boussafir. "South Tropical Atlantic anti-phase response to Holocene Bond Events." Palaeogeography, Palaeoclimatology, Palaeoecology 415 (December 2014): 21–27. http://dx.doi.org/10.1016/j.palaeo.2014.07.019.
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Gomes, Helber B., Tércio Ambrizzi, Bruce F. Pontes da Silva, Kevin Hodges, Pedro L. Silva Dias, Dirceu L. Herdies, Maria Cristina L. Silva, and Heliofábio B. Gomes. "Climatology of easterly wave disturbances over the tropical South Atlantic." Climate Dynamics 53, no. 3-4 (February 15, 2019): 1393–411. http://dx.doi.org/10.1007/s00382-019-04667-7.
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Capel, K. C. C., B. Segal, P. Bertuol, and A. Lindner. "Corallith beds at the edge of the tropical South Atlantic." Coral Reefs 31, no. 1 (September 4, 2011): 75. http://dx.doi.org/10.1007/s00338-011-0818-3.
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Rouault, Mathieu, Pierre Florenchie, Nicolas Fauchereau, and Chris J. C. Reason. "South East tropical Atlantic warm events and southern African rainfall." Geophysical Research Letters 30, no. 5 (March 2003): n/a. http://dx.doi.org/10.1029/2002gl014840.
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Barimalala, Rondrotiana, Annalisa Bracco, Fred Kucharski, Julian P. McCreary, and Alessandro Crise. "Arabian Sea ecosystem responses to the South Tropical Atlantic teleconnection." Journal of Marine Systems 117-118 (May 2013): 14–30. http://dx.doi.org/10.1016/j.jmarsys.2013.03.002.
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Nobre, P., J. A. Marengo, I. F. A. Cavalcanti, G. Obregon, V. Barros, I. Camilloni, N. Campos, and A. G. Ferreira. "Seasonal-to-Decadal Predictability and Prediction of South American Climate." Journal of Climate 19, no. 23 (December 1, 2006): 5988–6004. http://dx.doi.org/10.1175/jcli3946.1.
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Abstract The dynamical basis for seasonal to decadal climate predictions and predictability over South America is reviewed. It is shown that, while global tropical SSTs affect both predictability and predictions over South America, the current lack of SST predictability over the tropical Atlantic represents a limiting factor to seasonal climate predictions over some parts of the continent. The model’s skill varies with the continental region: the highest skill is found in the “Nordeste” region and the lowest skill over southeastern Brazil. It is also suggested that current two-tier approaches to predict seasonal climate variations might represent a major limitation to forecast coupled ocean–atmosphere phenomena like the South Atlantic convergence zone. Also discussed are the possible effects of global climate change on regional predictability of seasonal climate.
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Drumond, A., J. Marengo, T. Ambrizzi, R. Nieto, L. Moreira, and L. Gimeno. "The role of the Amazon Basin moisture in the atmospheric branch of the hydrological cycle: a Lagrangian analysis." Hydrology and Earth System Sciences 18, no. 7 (July 11, 2014): 2577–98. http://dx.doi.org/10.5194/hess-18-2577-2014.
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Abstract. We used a Lagrangian model (FLEXPART) together with the 1979–2012 ERA-Interim reanalysis data to investigate the role of the moisture in the Amazon Basin in the regional hydrological budget over the course of the year. FLEXPART computes budgets of evaporation minus precipitation by calculating changes in the specific humidity along forward and backward trajectories. The tropical Atlantic is the most important remote moisture source for the Amazon Basin. The tropical North Atlantic (NA) mainly contributed during the austral summer, while the contribution of the tropical South Atlantic (SA) prevailed for the remainder of the year. At the same time, the moisture contribution from the Amazon Basin itself is mainly for moisture supplying the southeastern South America. The 33-year temporal domain allowed the investigation of some aspects of the interannual variability of the moisture transport over the basin, such as the role of the El Niño Southern Oscillation (ENSO) and the Atlantic Meridional Mode (AMM) on the hydrological budget. During the peak of the Amazonian rainy season (from February to May, FMAM) the AMM is associated more with the interannual variations in the contribution from the tropical Atlantic sources, while the transport from the basin towards the subtropics responds more to the ENSO variability. The moisture contribution prevailed from the SA (NA) region in the years dominated by El Niño/positive AMM (La Niña/negative AMM) conditions. The transport from the Amazon towards the subtropics increased (reduced) during El Niño (La Niña) years.
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Wainer, I., A. Lazar, and A. Solomon. "Tropical extra-tropical thermocline water mass exchanges in the Community Climate Model v.3 Part I: the Atlantic Ocean." Ocean Science 2, no. 2 (October 10, 2006): 137–46. http://dx.doi.org/10.5194/os-2-137-2006.
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Abstract. The climatological annual mean tropical-extra-tropical pathways of thermocline waters in the Atlantic Ocean are investigated with the NCAR CCSM numerical coupled model. Results from three numerical experiments are analyzed: Two are fully coupled runs with different spatial resolution (T42 and T85) for the atmospheric component. The third numerical experiment is an ocean-only run forced by NCEP winds and fluxes. Results show that the different atmospheric resolutions have a significant impact on the subduction pathways in the Atlantic because of how the wind field is represented. These simulation results also show that the water subducted at the subtropics reaching the EUC is entirely from the South Atlantic. The coupled model ability to simulate the STCs is discussed.
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Wainer, I., A. Lazar, and A. Solomon. "Tropical Extra-tropical thermocline water mass exchanges in the community climate model v.3 Part I: the Atlantic Ocean." Ocean Science Discussions 3, no. 3 (May 10, 2006): 55–84. http://dx.doi.org/10.5194/osd-3-55-2006.
Full textAbstract:
Abstract. The NCAR CCSM numerical coupled model is used to understand the tropical-extra-tropical pathways of thermocline waters in the Atlantic Ocean. Climatological annual mean simulation results from three numerical experiments are analyzed. Two are fully coupled runs with different spatial resolution (T42 and T85) for the atmospheric component. The third numerical experiment is an ocean-only run forced by NCEP winds and fluxes. Results show that the different atmospheric resolutions have a significant impact on the subduction pathways in the Atlantic because of how the wind field is represented. These simulation results also show that the water subducted at the subtropics reaching the EUC is entirely from the South Atlantic. The coupled model ability to simulate the STCs is discussed.
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Lin, Zhongda, and Yun Li. "Remote Influence of the Tropical Atlantic on the Variability and Trend in North West Australia Summer Rainfall." Journal of Climate 25, no. 7 (March 28, 2012): 2408–20. http://dx.doi.org/10.1175/jcli-d-11-00020.1.
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Abstract Rainfall in North West Australia (NWA) has been increasing over the past decades, occurring mainly in the austral summer season (December–March). A range of factors such as decreased land albedo in Australia and increasing anthropogenic aerosols in the Northern Hemisphere, identified using simulations from climate models, have been implicated in this wetting trend. However, the impact of land albedo and aerosols on Australian rainfall remains unclear. In addition, previous studies showed that dominant sea surface temperature (SST) signals in the Pacific–Indian Ocean including El Niño–Southern Oscillation (ENSO), ENSO Modoki, and the Indian Ocean dipole mode have no significant impact on the NWA rainfall trend. The present study proposes another viewpoint on the remote influence of tropical Atlantic atmospheric vertical motion on the observed rainfall variability and trend in NWA. It is found that, with the atmospheric ascent instigated by the warming of SST over the tropical Atlantic, a Rossby wave train is emanating southeastward from off the west coast of subtropical South America to the midlatitudes of the South Atlantic Ocean. It then travels eastward embedded in the westerly jet waveguide over the South Atlantic and South Indian Oceans. The eastward-propagated Rossby wave induces an anticyclonic anomaly in the upper troposphere over Australia, which is at the exit of the westerly jet waveguide. This leads to an in situ upper-tropospheric divergence, ascending motion and a lower-tropospheric convergence, and the associated increase in rainfall in NWA. Thus, the increasing trend in atmospheric upward motion induced by the warming trend of SST in the tropical Atlantic may partially explain the observed rainfall trend in NWA.
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Reboita, Michelle Simões, Kelvem Rodrigo De Oliveira, Pedro Ygor Carvalho Corrêa, and Renan Rodrigues. "Influência dos Diferentes Tipos do Fenômeno El Niño na Precipitação da América do Sul." Revista Brasileira de Geografia Física 14, no. 2 (June 16, 2021): 729. http://dx.doi.org/10.26848/rbgf.v14.2.p729-742.
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Nesse estudo foi aplicada uma metodologia de classificação dos eventos de El Niño em seus diferentes tipos (Central, Leste e, quando ambos ocorrem concomitantemente, MIX) no período de janeiro de 1950 a março de 2019. Além disso, os tipos de El Niño foram separados por estação do ano e considerando as diferentes condições de anomalias de temperatura da superfície do mar no oceano Atlântico Tropical Sul (neutras quando ocorrem anomalias de temperatura entre -0,5º e 0,5ºC; quentes quando as anomalias são superiores a 0,5ºC e frias quando as anomalias são inferiores a -0,5ºC). Com base nas combinações de ocorrência de cada tipo de EN e anomalias de temperatura da superfície do mar no Atlântico Tropical Sul, foram determinadas as anomalias de precipitação na América do Sul. Os diferentes tipos de El Niño são mais frequentes quando há condições neutras no Atlântico Tropical Sul. Com relação às anomalias de precipitação na América do Sul, os eventos de El Niño Leste e MIX, em geral, mostram padrão similar na distribuição espacial das anomalias, mas com os eventos MIX mostrando sinal mais fraco. As anomalias de temperatura da superfície do mar no Atlântico Tropical Sul quando negativas ajudam a fortalecer as condições secas entre o norte das regiões norte e nordeste do Brasil propiciadas pelos eventos de El Niño. Influence of the Different Types of El Niño in the Precipitation over South America A B S T R A C TIn this study, a specific methodology was applied to classify El Niño events into their different types (Central, East and when both occur at the same time, MIX) from January 1950 to March 2019. In addition, the types of El Niño were separated by season and considering the conditions of sea surface temperature anomalies on the South Tropical Atlantic Ocean (neutrality: temperature anomalies between -0.5º and 0.5ºC, warm: anomalies above 0.5ºC and cold: anomalies below -0.5ºC). Based on in the combination of different types of El Niño and sea surface temperature anomalies on the South Atlantic Tropical Ocean, precipitation anomalies over South America were computed. The different types El Niño occur, in general, under neutral conditions on the Atlantic Ocean. The events of El Niño - East and MIX, in general, present a similar pattern in the spatial distribution of the precipitation anomalies over South America, but with the MIX events showing weaker signal. Sea surface temperature anomalies in the Tropical South Atlantic when negative, they help to strengthen the dry conditions between the north of the north and northeast regions of Brazil caused by the El Niño events.Keywords: atmospheric circulation, anomaly conditions, tropical oceans, climate
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Wu, Lixin, Chun Li, Chunxue Yang, and Shang-Ping Xie. "Global Teleconnections in Response to a Shutdown of the Atlantic Meridional Overturning Circulation*." Journal of Climate 21, no. 12 (June 15, 2008): 3002–19. http://dx.doi.org/10.1175/2007jcli1858.1.
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Abstract The global response to a shutdown of the Atlantic meridional overturning circulation (AMOC) is investigated by conducting a water-hosing experiment with a coupled ocean–atmosphere general circulation model. In the model, the addition of freshwater in the subpolar North Atlantic shuts off the AMOC. The intense cooling in the extratropical North Atlantic induces a widespread response over the global ocean. In the tropical Atlantic, a sea surface temperature (SST) dipole forms, with cooling north and warming on and south of the equator. This tropical dipole is most pronounced in June–December, displacing the Atlantic intertropical convergence zone southward. In the tropical Pacific, a SST dipole forms in boreal spring in response to the intensified northeast trades across Central America and triggering the development of an El Niño–like warming that peaks on the equator in boreal fall. In the extratropical North Pacific, a basinwide cooling of ∼1°C takes place, with a general westward increase in intensity. A series of sensitivity experiments are carried out to shed light on the ocean–atmospheric processes for these global teleconnections. The results demonstrate the following: ocean dynamical adjustments are responsible for the formation of the tropical Atlantic dipole; air–sea interaction over the tropical Atlantic is key to the tropical Pacific response; extratropical teleconnection from the North Atlantic is most important for the North Pacific cooling, with the influence from the tropics being secondary; and the subtropical North Pacific cooling propagates southwestward from off Baja California to the western and central equatorial Pacific through the wind–evaporation–SST feedback.