Como a América do Sul se estende por diferentes latitudes e possui formas de relevo variadas, proporciona a atuação e o desenvolvimento de diferentes sistemas atmosféricos, os quais contribuem para a não homogeneidade climática da região. Portanto o objetivo deste estudo é apresentar uma revisão dos sistemas atmosféricos que atuam nos diferentes setores do continente sul-americano e que contribuem para a precipitação.
found to be part of a large-scale teleconnection wave train linked with the subsidence branch of the Walker circulation in the tropical east Pacific, which in turn was generated by an anomalous tropical heat source in north/northeastern Australia. A regional Hadley circulation with an ascending branch to the south of the subsidence branch of the Walker circulation in the tropical east Pacific was identified as an important component connecting the tropical and extratropical circulation. The ascending branch of this Hadley circulation in the south Pacific coincided with an identified Rossby wave source region, which contributed to establishing the extratropical component of the large-scale wave train connecting the south Pacific and the Atlantic region surrounding southeast Brazil. This connection between the Pacific and the Atlantic was confirmed with Rossby ray tracing analyses. The local circulation response was associated to downward air motion (subsidence) over Southeast Brazil, contributing to the expressive negative precipitation anomalies observed during summer 2014, and leading to a major drought event in the historical context. The analysis of atmospheric and oceanic patterns of this event helped defining a schematic framework leading to the observed drought conditions in southeast Brazil, including the involved teleconnections, blocking high pressure, radiative and humidity transport effects.
Hurricane Catarina (2004) and subtropical storm Anita (2010) called attention to the development of subtropical cyclones (SCs) over the South Atlantic basin. Besides strong and organized storms, a large number of weaker, shallower cyclones with both extratropical and tropical characteristics form in the region, impacting the South American coast. The main focus of this study is to simulate a climatology of subtropical cyclones and their synoptic pattern over the South Atlantic, proposing a broader definition of these systems. In addition, a case study is presented to discuss the main characteristics of one weak SC. The Interim ECMWF Re-Analysis (ERAInterim) and NCEP-NCAR reanalysis are used to construct the 33-yr (1979-2011) climatology, and a comparison between them is established. Both reanalyses show good agreement in the SCs' intensity, geographical distribution, and seasonal variability, but the interannual variability is poorly correlated. Anomaly composites for austral summer show that subtropical cyclogenesis occurs under a dipole-blocking pattern in upper levels. Upward motion is enhanced by the vertical temperature gradient between a midtropospheric cold cutoff low/trough and the intense low-level warm air advection by the South Atlantic subtropical high. Turbulent fluxes in the cyclone region are not above average during cyclogenesis, but the subtropical high flow advects great amounts of moisture from distant regions to fuel the convective activity. Although most of the SCs develop during austral summer (December-February), it is in autumn (March-May) that the most ''tropical'' environment is found (stronger surface fluxes and weaker vertical wind shear), leading to the most intense episodes.
Cutoff lows (COLs) pressure systems climatology for the Southern Hemisphere (SH), between 10°S and 50°S, using the National Center for Environmental Prediction–National Center for Atmospheric Research (NCEP‐NCAR) and the ERA‐40 European Centre for Medium Range Weather Forecast (ECMWF) reanalyses are analyzed for the period 1979–1999. COLs were identified at three pressure levels (200, 300, and 500 hPa) using an objective method that considers the main physical characteristics of the conceptual model of COLs. Independently of the pressure level analyzed, the climatology from the ERA‐40 reanalysis has more COLs systems than the NCEP‐NCAR. However, both reanalyses present a large frequency of COLs at 300 hPa, followed by 500 and 200 hPa. The seasonality of COLs differs at each pressure level, but it is similar between the reanalyses. COLs are more frequent during summer, autumn, and winter at 200, 300, and 500 hPa, respectively. At these levels, they tend to occur around the continents, preferentially from southeastern Australia to New Zealand, the south of South America, and the south of Africa. To study the COLs at 200 and 300 hPa from a regional perspective, the SH was divided in three regions: Australia–New Zealand (60°E–130°W), South America (130°W–20°W), and southern Africa (20°W–60°E). The common COLs features in these sectors for both reanalyses are a short lifetime (∼80.0% and ∼70.0% of COLs at 200 and 300 hPa, respectively, persisting for up to 3 days), mobility (∼70.0% and ∼50% of COLs at 200 and 300 hPa, respectively, traveling distances of up to 1200 km), and an eastward propagation.
Seasonal relationship between the Southern annular Mode (SaM) and the spatial distribution of the cyclone systems over Southern hemisphere is investigated for the period 1980 to 1999. in addition, seasonal frontogenesis and rainfall distribution over South america and South atlantic ocean during different SaM phases were also analyzed. it is observed that during negative SaM phases the cyclone trajectories move northward when compared to the positive one, and in the South america and South atlantic sector there is intense frontogenetic activity and positive anomaly precipitation over the Southeast of the South america. in general, SaM positive phase shows opposite signals. Key-words: SaM, cyclones density, frontogenetic function, southeast South america ResuMo: RelaÇÃo entRe o Modo anUlaR SUl e oS SiSteMaS atMoSféRicoS no heMiSféRio SUl a relação sazonal entre o Modo anular Sul (Southern annular Mode -SaM) e a distribuição espacial dos sistemas ciclônicos sobre o hemisfério Sul foi investigada no período de 1980 a 1999. também foram analisados os padrões sazonais de frontogêneses e de distribuição de precipitação, sobre a américa do Sul e oceano atlântico Sul, durante as diferentes fases da SaM. na fase negativa da SaM foi observado que a trajetória dos ciclones em todo o hemisfério Sul move-se para norte, comparada à fase positiva, e que no setor da américa do Sul e atlântico Sul há intensa atividade frontogenética e anomalias positivas de precipitação na costa sudeste da américa do Sul. em geral, na fase positiva da SaM são observadas condições inversas. palavras-chave: SaM, densidade de ciclones, função frontogenética, sudeste da américa do Sul
The South Atlantic Subtropical Anticyclone (SASA) is the main feature of the atmospheric circulation over the South Atlantic Ocean, and its study is of great importance to explain many characteristics of the Brazilian weather and climate. Therefore, this study aims to present (1) a review of the literature on SASA including the drivers of the semi-permanent anticyclones and (2) the main features of the SASA in the future climate obtained through the projections of three global climate models (HadGEM2-ES, GFDL-ESM2M, and MPI-ESM-MR), from the Coupled Model Intercomparison Project (CMIP5), using the Representative Concentration Pathway 8.5 (RCP8.5) scenario. SASA is zonally wider in winter and retracted to the east in summer, when it presents a more circular format. These features of the SASA in the present climate (1979-2005) are well represented by the three global climate models, which also project this same SASA seasonal pattern for the future climate (2065-2095). Considering the projections, they indicate a slightly poleward expansion of the SASA, which is associated with the widening of the Hadley cell. At the SASA core, the pressure can be similar or slightly more intense than the present climate.
A principal fonte de energia do planeta Terra é o Sol. A energia que chega aquece primeiramente a superfície terrestre e depois, por intermédio de alguns processos físicos entre a superfície e a atmosfera, o ar adjacente também é aquecido. Entretanto, o aquecimento da Terra não ocorre de maneira uniforme entre polos e equador. Devido à forma da Terra, os raios solares atingem a região tropical IntroduçãoA América do Sul (AS) possui grande extensão latitudinal, ocupando desde áreas equatoriais até de latitudes médias; portanto, diferentes regimes climáticos são encontrados no continente.Assim, o objetivo deste trabalho é apresentar os conhecimentos meteorológicos básicos para o entendimento do tempo e clima vigentes no continente sul-americano. ABSTRACT Underrstanding Weather and Climate in South America: South America (SA) has a diversified geography that enables the development and action of different atmospheric systems. These systems contribute to the spatial and temporal non-homogeneity of precipitation patterns. This study has as purposes: (a) to provide basic concepts from weather and climate, (b) to present the precipitation climatology and (c) to describe the atmospheric systems that contribute to the diverse annual cycles of precipitation in each region
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