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The influence of climate variability on Eastern Boundary Upwelling Ecosystems (EBUEs) is evident through changes in productivity and shifts in species' distributions, yet to date, metrics of upwelling variability appropriate for comparative ecosystem studies have yet to be implemented. Here, we present synoptic-scale upwelling indices to quantify inter-annual to decadal variations in Ekman transport, at temporal and spatial scales relevant to the biota of EBUEs, and apply them to the Benguela Upwelling System (BUS). From 1979 to 2015, interannual, decadal-scale, and unidirectional variability in upwelling was observed, including a significant recent decrease in upwelling in the northern BUS, and a significant increase on the Agulhas Bank. These trends are associated with changes in the number of upwelling days and events in these regions, and correspond to a shift in the meridional positioning of the South Atlantic High pressure system.

A circulacao de brisa maritima e continental tem importância expressiva na Regiao Metropolitana de Sao Paulo (RMSP), influenciando a direcao predominante do vento na escala diurna e podendo ocasionar transporte de poluentes. No verao de 2014, o ozonio ultrapassou os Padroes de Qualidade do Ar da CETESB durante 43 dias, quando a Alta Subtropical do Atlântico Sul se fortaleceu sobre a regiao Sudeste do Brasil. Buscou-se compreender como a brisa maritima e continental influenciaram o transporte dos poluentes CO, NO, NO2 e O3 na area de estudo, utilizando o modelo WRF/Chem, no periodo 28/01-01/02/2014. Foram construidos dois cenarios: CTRL – emissoes veiculares baseadas em inventarios atuais de emissao de poluentes, e SENS – retirada de cerca de 75% das emissoes na RMSP. A analise dos resultados, por meio de mapas com a distribuicao espacial dos poluentes no dominio, demonstrou a importância da circulacao de brisa para o transporte de poluicao. A analise do campo de divergencia mostrou-se util para a identificacao das frentes de brisa. Concentracoes de O3 mais altas foram simuladas na regiao pre-frontal devido a estagnacao e acumulo de poluentes trazidos das areas mais poluidas por onde a frente de brisa passou, ocasionando o transporte de ozonio para areas distantes a noroeste durante a tarde. Ocorre tambem transporte de poluentes para sul durante o inicio da manha com a brisa continental. O movimento ascendente do ar na regiao pre-frontal ocasionado pela convergencia propicia o transporte vertical de ozonio durante a tarde.

This study examines for the first time the changing characteristics of summer and winter southern African rainfall and their teleconnections with large-scale climate through the dominant time scales of variability. As determined by wavelet analysis, the austral summer and winter rainfall indices exhibit three significant time scales of variability over the twentieth century: interdecadal (15–28 years), quasi-decadal (8–13 years), and interannual (2–8 years). Teleconnections with global sea surface temperature and atmospheric circulation anomalies are established here but are different for each time scale. Tropical/subtropical teleconnections emerge as the main driver of austral summer rainfall variability. Thus, shifts in the Walker circulation are linked to the El Nino–Southern Oscillation (ENSO) and, at decadal time scales, to decadal ENSO-like patterns related to the Pacific Decadal Oscillation and the Interdecadal Pacific Oscillation. These global changes in the upper zonal circulation interact with asymmetric ocean-atmospheric conditions between the South Atlantic and South Indian Oceans; together, these lead to a shift in the South Indian Convergence Zone and a modulation of the development of convective rain-bearing systems over southern Africa in summer. Such regional changes, embedded in quasi-annular geopotential patterns, consist of easterly moisture fluxes from the South Indian High, which dominate southerly moisture fluxes from the South Atlantic High. Austral winter rainfall variability is more influenced by midlatitude atmospheric variability, in particular the Southern Annular Mode. The rainfall changes in the southwestern regions of southern Africa are determined by asymmetrical changes in the midlatitude westerlies between the Atlantic and Indian Oceans.

We study the annual patterns and linear trend of satellite sea level anomaly (SLA) over the southwest South Atlantic continental shelf (SWACS) between 54ºS and 36ºS. Results show that south of 42°S the thermal steric effect explains nearly 100% of the annual amplitude of the SLA, while north of 42°S it explains less than 60%. This difference is due to the halosteric contribution. The annual wind variability plays a minor role over the whole continental shelf. The temporal linear trend in SLA ranges between 1 and 5 mm/yr (95% confidence level). The largest linear trends are found north of 39°S, at 42°S and at 50°S. We propose that in the northern region the large positive linear trends are associated with local changes in the density field caused by advective effects in response to a southward displacement of the South Atlantic High. The causes of the relative large SLA trends in two southern coastal regions are discussed as a function meridional wind stress and river discharge. Finally, we combined the annual cycle of SLA with the mean dynamic topography to estimate the absolute geostrophic velocities. This approach provides the first comprehensive description of the seasonal component of SWACS circulation based on satellite observations. The general circulation of the SWACS is northeastward with stronger/weaker geostrophic currents in austral summer/winter. At all latitudes, geostrophic velocities are larger (up to 20 cm/s) close to the shelf‐break and decrease toward the coast. This spatio‐temporal pattern is more intense north of 45°S., Key Points: Trends, annual patterns, and currents are analyzed with altimetry dataAnnual changes in sea level over the Patagonian shelf are mostly due to steric effectsThe general circulation in the region is northeastward with seasonal variability

Observed and simulated climate trends across South Africa in the period 1980–2014 are studied. Observed CRU3/CAMS (Climate Research Unit v3 / Climate Analysis and Monitoring System) air temperatures have increased by 0.02°C·yr −1 while NOAA/SODA sea temperatures have risen by 0.03°C·yr −1 in the Agulhas Current. A poleward expansion of the South Atlantic high in NCEP2/MERRA (National Center for Environmental Prediction v2 / Modern-Era Retrospective analysis for Research and Applications) has produced a trend toward south-easterly flow which contributes to a moist-east/dry-west pattern. Observed CHIRPS2 rainfall and NDVI vegetation fraction show no appreciable trend except near Cape Town where drier conditions in the period 1980–2014 correspond with enhanced coastal upwelling. CMIP5 model projections for rainfall up to 2050 reflect drying, except in the eastern coastal plains. While inter-annual fluctuations of South African rainfall overshadow linear trends, temperature increases account for 32% of observed variance. Keywords : South Africa, climate change, satellite era

This paper evaluates the influence of the El Niño - Southern Oscillation on the wave climate variability in the central region of Rio de Janeiro’s coastal zone. The regional climate of the area was characterized using the WAVEWATCH III wave data model, obtained from NOAA, organized as a 35 year time series (1979-2013). These data were validated for the study area and a characterization and analysis performed by focusing on years with occurrence of strong El Niño/La Niña events. The correlation between the interannual variability of significant wave height and Oceanic Niño Index showed a slight reduction in significant wave height during El Niño years and the opposite pattern during La Niña years, with a lag of four months. This decrease could be attributed to the intensification of the South Atlantic High with a corresponding increase in the occurrence of subtropical jets during periods of El Niño. This weather change causes the blocking of cold fronts in the southern region of Brazil and the consequent reduction in the percentage of waves from the south along the southeast coast. Este artigo busca avaliar a influência do fenômeno El Niño - Oscilação Sul na variabilidade do clima de ondas da porção central da zona costeira do Rio de Janeiro. Para tanto, a climatologia regional da área foi caracterizada a partir de dados de ondas do modelo WAVEWATCH III disponibilizado pela NOAA, organizados numa série temporal de 35 anos (1979 - 2013). Esses dados foram validados para a área de estudo e, realizada sua caracterização e análise com enfoque em anos de acentuada ocorrência de eventos de El Niño/La Ninã. A correlação da variabilidade interanual da série de altura significativa de ondas e Índice de Niño Oceânico mostrou padrão de leve redução das alturas significativas em anos de El Niño e, o inverso para anos de La Niña, com defasagem temporal de quatro meses na região. Essa redução na altura significativa das ondas pode ser atribuída à intensificação da Alta Subtropical do Atlântico Sul e aumento na ocorrência de jatos subtropicais nos períodos de El Niño. Essa alteração no padrão meteorológico causa o bloqueio de frentes frias na região Sul do Brasil e consequente redução da porcentagem de ondas de sul na região sudeste.

The inner shelf circulation on the Abrolhos Bank is investigated using four years (2002–2005) of moored current and bottom pressure observations from two sites in conjunction with wind data from a nearby meteorological station. This is one of the longest projects monitoring current and sea level along the Brazilian coast. The time variability of the local circulation and main forcings are described. For the first time, both the seasonal and the interannual variabilities are addressed, as are the impact of remote forcing. The cross-shore pressure gradient in the region is mostly set up by along-shore winds, whereas the sub-inertial cross-shore momentum balance is essentially geostrophic, with smaller contributions from the cross-shore wind stress. The along-shelf momentum balance is ageostrophic and mainly occurs between the wind and bottom stresses. South-southwestward along-shore currents occur between October and January, whereas stronger north-northeastward currents are observed in fall and winter. This seasonal cycle is driven by the N–S migration of the South Atlantic High between the seasons. An increasing frequency of the southern winds and, consequently, northward currents are observed between 2002 and 2005 and are related to both the number of fronts reaching the region and the remote effect of fronts that did not cross the area. The cross-shore circulation is weak and mainly forced by the tides. It is suggested that long-period shelf waves that propagate into the region change the inner shelf current field and sea level.

Two sea surface temperature (SST) products, Pathfinder version 5.0 and MODIS/TERRA are evaluated and used to study the seasonal and the inter-annual variability of sea surface temperature (SST) together with local SST and wind data in the vicinity of False Bay (Western Cape, South Africa). At the monthly scale, differences of up to 3 °C are detected between the two products in the bay. In the northern half of the bay, SST is fairly well explained by seasonality. In contrast, the southern half exhibits a higher inter-annual variability in SST. The southern half of the bay and the Western Cape upwelling system (Cape Agulhas to Cape Columbine) share most of their variance. Furthermore, the inter-annual variability of SST in False Bay is correlated with both the Nino 3.4 index and local wind speed anomalies. El Nino (La Nina) events induce an equatorward (poleward) shift in the South Atlantic High pressure system leading to a weakening (strengthening) of upwelling favourable south-easterly. Those changes induce a warm (cold) SST anomaly along the West Coast of Southern Africa.

Coastal and oceanic sea surface temperature (SST) trends were analyzed in the Benguela upwelling ecosystem from the seventies on. Monthly SST data were obtained from the UK Meteorological Office, Hadley Center at two transects in front of the Namibia coast and the western coast of South Africa. A positive SST trend (0.06 °C dec−1) is observed at open sea locations and a negative one (−0.13 °C dec−1) near shore. The observed negative ΔSST (SSTcoast−SSTocean) trend (−0.18 °C dec−1) is linked to the strengthening of upwelling (87 m3 s−1 km−1 dec−1) during the same period. For this purpose, Ekman transport was directly obtained from the Pacific Fisheries Environmental Laboratory in the area under study and calculated from reanalysis wind data from NCEP/NCAR at six locations in front of the Namibia coast and the western coast of South Africa. This coastal upwelling enhancement is in good agreement with changes in the intensity and location of the South Atlantic High, which are also reflected in the Southern Annular Mode (SAM) index.

A sediment core from the Cabo Frio coastal shelf (−23.19 S, −41.8 W; 117 m depth), was analyzed for TOC, C/N ratio, organic petrography and planktonic foraminiferal content to evaluate variations in local productivity caused by changes in upwelling intensity and its relation to regional and global climatic variations during the last millennium. The Cabo Frio core recorded the last 1200 years of sedimentation, with rates varying from 0.11 to 0.32 mm yr−1. Foraminiferal and organic geochemical analyses indicate the occurrence of three distinct periods of productivity. From 850 AD until 1070 AD, foraminifera fluxes consisting primarily of Turborotalita quinqueloba indicate stronger South Atlantic Central Water (SACW) transport onto the shelf, which induced high biological productivity that was also recorded by high TOC and marine palynomorphs content and a low C/N atomic ratio. This period coincided with a northward displacement of the atmospheric Intertropical Convergence Zone (ITCZ) and South Atlantic High (SAH) systems driven by positive temperature anomalies in the North Atlantic Ocean during the Medieval Climate Anomaly (MCA). From 1070 until 1500 AD, low TOC flux and planktonic foraminifera fluxes and high C/N atomic ratios suggest a reduction in marine productivity, probably driven by reduced transport of SACW associated with the southward displacement of the SAH and weakening of northeasterly winds. The period between 1500 and 1830 AD, which corresponds to the Little Ice Age, is marked by increased fluxes of planktonic foraminifera, principally of Globigerina bulloides and Globigerinita glutinata. These species mark an increase in productivity linked to SACW upwelling, supported by the enhancement of northeasterly winds and southward displacement of the ITCZ and SAH.

Since 2015 the greater Cape Town area (~3.7 million people) has been experiencing the worst drought of the last century. The combined effect of this prolonged dry period with an ever-growing demand for water culminated in the widely publicized 'Day Zero' water crisis. Here we show how: (i) consecutive significant decreases in rainfall during the last three winters led to the current water crisis; (ii) the 2015–2017 record breaking drought was driven by a poleward shift of the Southern Hemisphere moisture corridor; (iii) a displacement of the jet-stream and South Atlantic storm-track has imposed significantly drier conditions to this region. Decreasing local rainfall trends are consistent with an expansion of the semi-permanent South Atlantic high pressure, and reflected in the prevalence of the positive phase of the Southern Annular Mode. Large-scale forcing mechanisms reveal the intensification and migration of subtropical anticyclones towards the mid-latitudes, highlighting the link between these circulation responses and the record warm years during 2015–2017 at the global scale.

Baric troughs were studied over the Alagoas State, Brazil, in 2003. The relationship between these synoptic systems, weekly sea surface temperature anomaly and adverse meteorological phenomena in the Alagoas State, was analyzed. The maximum trough frequency occurred at low levels during the wetter and colder season in the investigated region (June and July). Most of the troughs were observed at 1200 UTC. It was also noted that 87% of the troughs was associated with wavy disturbance in the trade winds on the northwestern periphery of the subtropical South Atlantic High. These troughs were associated with meteorological phenomena in a stable and an unstable atmosphere. Copyright © 2010 Royal Meteorological Society

This is an analysis of the atmospheric structure of a particular rainy day in January 1985, a month of well-above-normal rainfall in the Northeast Brazil semi-arid region. Close attention is given to 24 January 1985, with a focus on the rain structures that are most indicative of the mesoscale convective systems (MCSs) within a radar coverage area centred at Petrolina (9 24′S, 40 30′W), situated in the semi-arid lower-middle portion of the Sao Francisco River Valley. The contribution of the synoptic environment to the development of these systems is also investigated. C-band meteorological radar, along with surface rain-gauge data (intensities and 24-hour totals), has made possible a diagnosis of the mesoscale structure of the rain systems. Surface data, upper-air data, NCEP/NCAR reanalyses and Meteosat satellite images are employed as well. On the synoptic scale, the results reveal that during the greater part of the month, the area of study was largely influenced not only by the western sector of the South Atlantic upper-tropospheric trough but also by a weak South Atlantic subtropical high, as indicated by surface winds in Petrolina over all quadrants of the wind rose, except for the typical southeasterly winds. On day 24, the upper trough showed high amplitude, whereas the South Atlantic high was weak, as demonstrated by less intense subsidence inversion, high moisture content, and light and variable winds in the mid-to-lower troposphere. Extensive (meso-β-scale), long-lasting stratiform rain areas with embedded convection that became intensified in the mid-to-late afternoon indicated the presence of MCSs. These precipitation areas were dynamically supported by low-level moisture convergence and upward motion on the mesoscale and larger scales, while surface heating due to solar radiation may have been an additional factor for convection growth in the afternoon. A large number of rain-gauge stations reporting rain and surface rain rates (5-minute duration) higher than 60 mm h−1 gave additional evidence of widespread light (stratiform) and localized intense (convective) rainfall, indicating the presence of MCSs. Copyright © 2007 Royal Meteorological Society

Two years of drought in Southeast Brazil have led to water shortages in Sao Paulo, the country's most populous city. We examine the observed drought during austral summers of 2013/2014 and 2014/2015 and the related large-scale dynamics. The 2013-2014 precipitation deficits were more concentrated in the state of Sao Paulo, while in 2014-2015 moderate deficits were seen throughout the region. We find that a persistent warm sea surface temperature (SST) anomaly in the western tropical Pacific Ocean was an important driver of drought via atmospheric teleconnection in the two December-February seasons. The warm SST and associated convective heating initiated a wave train across the South Pacific. The resulting anticyclonic geopotential height anomaly over the southwest Atlantic expanded the westward margin of the South Atlantic high and prevented low-pressure systems from entering southeast Brazil from midlatitudes. This mechanism suggests a hemispheric symmetry to that proposed for the recent California drought.

A database synthesized from 19 oceanographic expeditions conducted by the former Soviet Union was used to analyse interannual patterns in copepod species diversity in the tropical Atlantic. Mesozooplankton was collected predominately in vertical hauls through the upper 100 m with Juday nets. The samples from 744 oceanographic stations were identified and enumerated to the species level. To assess species diversity, the Shannon diversity index was used. On the interdecadal scale, no statistically confirmed trend was found in species diversity change over the years sampled (1963–89). Multiple regression analysis indicated that interannual fluctuations of the South Atlantic High (pressure and latitude), the Azores High longitude and El Nino–Southern Oscillation (ENSO) index could explain 87% of species diversity fluctuations. Possible mechanisms that drive interannual fluctuations of species diversity are discussed.

We describe the rainfall and circulation anomalies of the South American summer monsoon (SASM) during December–January–February (DJF) of 1997–98 (El Nino) and 1998–99 (La Nina). The most pronounced rainfall signals in DJF 1997–98 include (a) excessive rainfall over northern Peru and Ecuador, (b) deficient rainfall over northern and central Brazil, and (c) above-normal rainfall over southeastern subtropical South America. The rainfall anomalies in (a) and (b) are associated with the excitation of an anomalous east–west overturning cell with rising motion and low-level westerlies over the equatorial eastern Pacific, coupled to sinking motion and low-level easterlies over northern Brazil. The easterlies turn sharply southeastward on encountering the steep topography of the Andes, enhancing the summertime low-level jet (LLJ) along the eastern foothills of the Andes near 15–20° S, possibly contributing to the increased rainfall in (c). During DJF 1997–98, the sea-surface temperature-induced warming spreads and expands over the entire tropical troposphere. The eastward expansion of a warm upper tropospheric geopotential and temperature ridge from the Nino-3 region, across subtropical South America to the southeast Atlantic, enhances warming over the Altiplano Plateau, hydrostatically strengthening the Bolivia high. Similar to previous warming events, the South Pacific high is weakened, and the South Atlantic high is strengthened. During DJF 1998–99, as cold water develops over the equatorial central Pacific, the SASM anomalies in the tropics are weaker and less organized and appear to be in transition to the opposite phase to those found in DJF 97–98. In the subtropics, notable features include a weakening of the LLJ, a rainfall pattern associated with a poleward shift of the South Atlantic convergence zone, and development of the Pacific–South America teleconnection pattern. Published in 2003 by John Wiley & Sons, Ltd.

This paper presents some additional results on the use of an automatic scheme for tracking surface cyclones and anticyclones. The Southern Hemisphere (SH) total amount of synoptic tracks (every 12 h) was analyzed for the 1973–96 period using sea level pressure from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis. Composites for seven El Nino (EN) and La Nina (LN) years were constructed in order to analyze the association between the hemispheric cyclone and anticyclone propagation and the phase of the El Nino–Southern Oscillation (ENSO) phenomenon. A climatological view of cyclone and anticyclone tracks and orphan centers superposed on the same map is presented and analyzed. A large area with overlapped cyclone and anticyclone tracks is seen between 30° and 60°S, which is approximately the climatological position of the SH transient activity. To the north of 30°S, the subtropical South Atlantic high is embedded in a region with just...

The observed large-scale circulation mechanisms associated with summertime precipitation variability over South America are investigated. Particular attention is paid to the Altiplano where a close relationship has been observed between rainfall and the position and intensity of the Bolivian high. Empirical orthogonal function (EOF), correlation, and composite analyses suggest that on intraseasonal timescales (typically 5–20 days), rainy periods on the Altiplano are associated with at least three types of circulation anomalies, involving either extratropical cyclones, cold-core lows, or the westward enhancement of the South Atlantic high. In each instance, the primary support for high rainfall rates is a moist, poleward flow at low levels along the eastern flank of the central Andes in association with the South Atlantic convergence zone (SACZ). The warm, low-level flow along the SACZ also inflates the overlying atmospheric column, resulting in an intensification and southward shift of the Bolivi...

Bermejo River Basin is located in the Chaco Plains in northern Argentina. The river has an extension of 1450 km and the basin area covers 16048 km2, comprising the north of Salta and the entire Formosa and Chaco provinces. Its principal tributary is San Francisco River which brings mountain waters. Two different sections can be detected in Bermejo River: the upper and the middle-low Bermejo. Vegetation is wooded with more plains to the east and with the presence of isolated yungas. The worst areas are historically inhabited by indigenous communities with extensive farming practice. Historical data show that the region has been the scene of frequent hydro-meteorological disasters (floods and droughts) and the impacts of these events have had a strong impact on the welfare of the population, productive activities and infrastructure. There is ample evidence that climate change impacts are already being observed today and that policies that seek the best ways to meet them are essential for the development and welfare of the community. The Chaco region is one of the regions that, as a result of the change in land use, presents “hotspot "or critical areas in recent times (from 1980). They are the result of the implementation of deforestation as a technology for the advancement of agriculture and intensive farming. In this region the climate is subtropical with a mean annual rainfall cycle showing a minimum in winter, which is more pronounced in the west, with dry conditions prevailing from May to September. The Andes chain lies along the west of Argentina and prevents the access of humidity from the Pacific Ocean. Therefore, the flow is governed by the South Atlantic High and as a consequence, winds prevail from the north and the east. The great interannual rainfall variability generates the requirement to understand the large circulation patterns associated with different hydric situations. Some remote sources affect the mentioned interannual variability. Subtropical South America is known to be one of the regions of the world with an important El Niño-Southern Oscillation (ENSO) signal in the precipitation field. This signal varies along each of the ENSO phases, and it differs between sub-regions. Although ENSO is the most important remote forcing without a doubt, the variability originated by other regional or remote sources cannot be disregarded. The scientific basis of the seasonal climate predictability lies in the fact that slow variations in the earth’s boundary conditions (i.e. sea surface temperature or soil wetness) can influence global atmospheric circulation and thus precipitation. As the skill of seasonal numerical prediction models is still limited, it is essential the statistical study of the probable relationships between some local or remote forcing and rainfall. In this paper an example of seasonal rainfall prediction is presented for Bermejo River basin. As the maximum rainfall season was summer, from January until March (JFM), this period was used to study interannual rainfall variability and predictors in the previous December could be defined, for each one of two sub-basin (Lower-Middle Bermejo and Upper Bermejo). Athough it is a small area, some differences were detected all over the basin. Therefore, two mean rainfall series were constructed as the average of monthly precipitation of nineteen stations in the upper Bermejo river basin (UB) during the period 1982-2007 and fourteen stations in the lower and middle Bermejo River Basin (LB) during the period 1968-2007, in order to be representative as from the precipitation over each one of the basin regions. Different period were considered in each sub-basin because of the availability of data. Simultaneous and one month lagged correlations were calculated to find the existing relation between summer (JFM) rainfall in LB and UB and sea surface temperature, 1000 Hpa, 500 Hpa and 200 Hpa geopotential height SST and 850 Hpa zonal and meridional wind. The results allowed to define some predictors in previous December, which were used to develop a statistical forecast model using the forward stepwise regression method, which retained only the variables, correlated with a 95% significance level. Forward stepwise regression is a model-building technique that finds subsets of predictor variables that most adequately predict responses on a dependent variable by linear regression, given the specified criteria for adequacy of model fit. The basic procedures involve identifying an initial model, then predictors are added one-by-one with the remaining candidate predictor that reduces the size of the errors, and this process continues until the errors cannot be significantly reduced. Linear regression models were developed for both, UB and LB. The correlation between observed and forecast rainfall time series derived from cross-validation was 0,6 and the linear regression model explained the 49% of the variance of EFM LB rainfall. However, the summer rainfall in UB depended mainly of Pacific and Indian Ocean sea surface temperatures. The final model explained the 46% of the variance of JFM rainfall in UB and the correlation between observed and forecast series was 0,49. Results indicate that the two mayor factors that influence summer precipitation in Lower Bermejo were the South Antarctic Oscillation and the weaken Atlantic High. In Upper Bermejo it depends mainly on Pacific and Indian Ocean sea surface temperatures. The efficiency of the method was proved by calculating some statistics like the hit rate, the probability of detection and the false alarm ratio. Results in LB are better than in UB. The probability of above normal rainfall events is in general, better than the probability to detect below normal rainfall ones. The probability to give a false alarm in a below normal rainfall event is greater than in the above normal cases. Additionally, the probability functions resulting from estimated and observed JFM rainfall resulted similar at the 95% confidence level and reveal that the method underestimates the most extreme cases. These results are promising and encourage further work in order to examine new techniques to better estimate rainfall, especially the extremes, and to investigate other predictors which could affect precipitation in summer. Fil: González, Marcela Hebe. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina Fil: Murgida, Ana Maria. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Most of South Africa’s climate is dominated by semi-permanent high pressure cells controlling the major upper-air circulation patterns. Through the combined effects of a stable relatively persistent South Atlantic anticyclone and the cold Benguela current, the west coast experiences arid conditions. While the South Atlantic high pressure cell exhibits small irregular longitudinal fluctuations, the South Indian oceanic anticyclone moves substantially eastward in summer and shifts westward towards the east coast in winter. These differences in stable anticyclonic control produce a decline in precipitation from east to west. Recent studies have established a strong correlation between rainfall anomalies in parts of the southern Africa summer rainfall zone since 1820 and extreme high and low phases of the Southern Oscillation. High phases of the latter, cold event summers, broadly correlate with above average rainfall; while low phases, warm event summers, are associated with drought in southern Africa. Dry as opposed to wet conditions over Southern Africa result from weakening of the tropical easterlies and strengthening of expansion equatorwards of westerlies.

High resolution hydrographic observations of temperature and salinity are used to analyse the subsurface circulation along the coast of North Brazil, off the Amazon mouth, between 2° S and 6° N. Observations are presented from four cruises carried out in different periods of the year (March–May 1995, May–June 1999, July–August 2001 and October–November 1997). Numerical model outputs complement the results of the shipboard measurements, and are used to complete the descriptions of mesoscale circulation. The Salinity Maximum Waters are here analyzed, principally in order to describe the penetration of waters originating in the Southern Hemisphere toward the Northern Hemisphere through the North Brazil Current (NBC)/North Brazil Undercurrent (NBUC). Our results show that, if the Equatorial Undercurrent (EUC) is fed by Northern Atlantic Waters, this contribution may only occur in the ocean interior, east of the western boundary around 100 m depth. Modeling results indicate a southward penetration of the Western Boundary Undercurrent (WBUC) below the thermocline, along the North Brazilian coast into the EUC or the North Equatorial Undercurrent (NEUC) (around 48° W–3° N). The WBUC in the region does not flow more south than 3° N. The northern waters are diverted eastward either by the NBC retroflection or by the northern edge of the associated clockwise rings. The existence of subsurface mesoscale rings associated to the NBC retroflection is evidenced, without any signature in the surface layer, so confirming earlier numerical model outputs. These subsurface anticyclones, linked to the NBC/NBUC retroflection into the North Equatorial Undercurrent and the EUC, contribute to the transport of South Atlantic high salinity water into the Northern Hemisphere.

[1] The rainfall anomalies over South America are found to be influenced by the Indian Ocean Dipole (IOD). Between subtropical La Plata Basin and central Brazil, the IOD excites a dipolar pattern in rainfall anomalies; rainfall is reduced (enhanced) over latter (former) during austral-spring, when IOD reaches its peak phase. A Rossby wave train extends from the subtropical south Indian Ocean to the subtropical South Atlantic. The associated anomaly in surface circulation suggests an intensification of the South Atlantic High. The anomalous anticyclone in the lower troposphere causes anomalous divergence (convergence) of moisture over central Brazil (subtropical La Plata Basin). These results based on the University of Delaware precipitation analysis and the NCEP-NCAR reanalysis data are corroborated by that of the Scale Interaction Experiment-Frontier version 1 (SINTEX-F1) coupled general circulation model.

We investigate, for the first time, the response of the North African summer monsoon to separate precession and obliquity forcings using a high-resolution state-of-the-art coupled general circulation model, EC-Earth. Our aim is to better understand the mechanisms underlying the astronomical forcing of this low-latitude climate system in detail. The North African monsoon is strengthened when northern hemisphere summer insolation is higher, as is the case in the minimum precession and maximum obliquity experiments. In these experiments, the low surface pressure areas over the Sahara are intensified and located farther north, and the meridional pressure gradient is further enhanced by a stronger South Atlantic high pressure area. As a result, the southwesterly monsoon winds are stronger and bring more moisture into the monsoon region from both the northern and southern tropical Atlantic. The monsoon winds, precipitation and convection also extend farther north into North Africa. The precession-induced changes are much larger than those induced by obliquity, but the latter are remarkable because obliquity-induced changes in summer insolation over the tropics are nearly zero. Our results provide a different explanation than previously proposed for mechanisms underlying the precession- and, especially, obliquity-related signals in paleoclimate proxy records of the North African monsoon. The EC-Earth experiments reveal that, instead of higher latitude mechanisms, increased moisture transport from both the northern and southern tropical Atlantic is responsible for the precession and obliquity signals in the North African monsoon. This increased moisture transport results from both increased insolation and an increased tropical insolation gradient.

The anthropogenic CO2 in the Atlantic Ocean is separated from the large natural variability of dissolved inorganic carbon using the method developed by Gruber et al. [1996]. Surface concentrations of anthropogenic CO2 are found to be highest in the tropical to subtropical regions and to decrease toward the high latitudes. They are very close to what is expected from thermodynamic considerations assuming that the surface ocean followed the atmospheric CO2 perturbation. Highest specific inventories (inventory per square meter) of anthropogenic CO2 occur in the subtropical convergence zones. Large differences exist between the North and South Atlantic high latitudes: In the North Atlantic, anthropogenic CO2 has already invaded deeply into the interior; north of 50°N it has even reached the bottom. By contrast, waters south of 50°S contain relatively little anthropogenic CO2, and hence specific inventories are very low. An anthropogenic CO2 inventory of about 22 ± 5 Gt C is estimated for the Atlantic north of the equator for 1982, and 18 ± 4 Gt C is estimated for the Atlantic south of the equator for 1989. The Princeton ocean biogeochemistry model predicts anthropogenic CO2 inventories of 20.0 Gt C (North Atlantic, 1982) and 17.7 Gt C (South Atlantic, 1989) for the same regions in good agreement with the observed inventories. Important differences exist on a more regional scale, associated with known deficiencies of the model.

Four current-meter moorings placed in False Bay between February and May 1985 revealed a tendency towards cyclonic motion, but with poleward flow along the western boundary. Data from six anemometers situated around the Bay showed periodic acceleration of northward air flow associated with south-easterly wind events during ridging of the South Atlantic high pressure cell round the continent. A clear pattern of cooling and warming of water at the current-meter sites was observed, corresponding to the acceleration and decay phases of south-easterly wind over periods of a few days. There was a suggestion of subsidence of warm water along the western boundary when the wind relaxed.

Meteorological conditions along the west coast of Africa between 30° and 35°S were monitored by means of an instrumented aircraft flown at a height of 150 m over the continental shelf and coastal margin. Case studies, selected from 600 h of aerial survey data encompassing a variety of weather conditions, are used to illustrate mesoscale gradients in the wind, air and sea temperature fields forced by local topographic features. These results focus on the summer season, when the periodic eastward ridging of the South Atlantic high pressure cell gives rise to pulses in SE trade wind flow of variable depth. A composite of four grids describes many of the summer mesoclimatic features found along the west coast, including: divergence of southerly wind flow over the continental shelf in response to friction and seabreezes over the coast; low-level wind jets off the mountainous capes at 33° and 34°S; and wind shadows leeward of the capes where subsidence is enhanced. Topographic channeling is contrasted ...

An upper-air climatology of tropical South America is presented using objectively analysed geopotential height, temperature and wind data from various radiosonde stations for the common period 1970-1974. In the lower troposphere the South Atlantic high dominates the geopotential height patterns extending deeply into interior Brazil in Southern winter. In the upper troposphere, contour gradients are concentrated around the subtropical region in winter. Temperature analysis shows the steep meridional gradient in winter. In summer, the Peruvian-Bolivian Altiplano heating effect is manifested in the mid-tropospheric temperature fields and also in the thickness field. Lower-tropospheric flow throughout the year is marked by an anticyclonic turning of easterlies over much of eastern Brazil. Easterlies originating from the South Atlantic high penetrate further inland in Southern winter. Upper-tropospheric flow changes dramatically from mainly westerly in winter to a well-defined anticyclone over the Altiplano and a trough downstream over northeast Brazil in summer. Thickness and temperature patterns indicate that the upper anticyclone is maintained by a warm-core system whereas the trough is marked by a relatively cold temperature. Upper tropospheric flows are equivalent barotropic in nature over tropical South America. The map discussion of summer and winter circulation is complemented by cross-sections of meridional wind component along approximately 60°W.