Michelle Simões Reboita

Regimes de precipitação na América do Sul: uma revisão bibliográfica

Como a America do Sul se estende por diferentes latitudes e possui formas de relevo variadas, proporciona a atuacao e o desenvolvimento de diferentes sistemas atmosfericos, os quais contribuem para a nao homogeneidade climatica da regiao. Portanto o objetivo deste estudo e apresentar uma revisao dos sistemas atmosfericos que atuam nos diferentes setores do continente sul-americano e que contribuem para a precipitacao.

Precipitation over eastern South America and the South Atlantic Sea surface temperature during neutral ENSO periods

The dominant mode of coupled variability over the South Atlantic Ocean is known as “South Atlantic Dipole” (SAD) and is characterized by a dipole in sea surface temperature (SST) anomalies with centers over the tropical and the extratropical South Atlantic. Previous studies have shown that variations in SST related to SAD modulate large-scale patterns of precipitation over the Atlantic Ocean. Here we show that variations in the South Atlantic SST are associated with changes in daily precipitation over eastern South America. Rain gauge precipitation, satellite derived sea surface temperature and reanalysis data are used to investigate the variability of the subtropical and tropical South Atlantic and impacts on precipitation. SAD phases are assessed by performing Singular value decomposition analysis of sea level pressure and SST anomalies. We show that during neutral El Niño Southern Oscillation events, SAD plays an important role in modulating cyclogenesis and the characteristics of the South Atlantic Convergence Zone. Positive SST anomalies over the extratropical South Atlantic (SAD negative phase) are related to increased cyclogenesis near southeast Brazil as well as the migration of extratropical cyclones further north. As a consequence, these systems organize convection and increase precipitation over eastern South America.

Climatological features of cutoff low systems in the Southern Hemisphere

Abstract This study presents the first multidecadal climatology of cutoff low systems in the Northern Hemisphere. The climatology was constructed by using 41 yr (1958–98) of NCEP–NCAR reanalysis data and identifying cutoff lows by means of an objective method based on imposing the three main physical characteristics of the conceptual model of cutoff low (the 200-hPa geopotential minimum, cutoff circulation, and the specific structure of both equivalent thickness and thermal front parameter fields). Several results were confirmed and climatologically validated: 1) the existence of three preferred areas of cutoff low occurrence (the first one extends through southern Europe and the eastern Atlantic coast, the second one is the eastern North Pacific, and the third one is the northern China–Siberian region extending to the northwestern Pacific coast; the European area is the most favored region); 2) the known seasonal cycle, with cutoff lows forming much more frequently in summer than in winter; 3) the short ...

Relationship between the southern annular mode and southern hemisphere atmospheric systems

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.

Subtropical Cyclones over the Southwestern South Atlantic: Climatological Aspects and Case Study

AbstractHurricane 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 (ERA-Interim) 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 sub...

Climate Projections for South America: RegCM3 Driven by HadCM3 and ECHAM5

This study shows climate projections of air temperature and precipitation over South America (SA) from the Regional Climate Model version 3 (RegCM3) nested in ECHAM5 and HadCM3 global models. The projections consider the A1B scenario from Intergovernmental Panel on Climate Change (IPCC) and three time-slices: present (1960–1990), near- (2010–2040), and far-future (2070–2100) climates. In the future, RegCM3 projections indicate general warming throughout all SA and seasons, which is more pronounced in the far-future period. In this late period the RegCM3 projections indicate that the negative trend of precipitation over northern SA is also higher. In addition, a precipitation increase over southeastern SA is projected, mainly during summer and spring. The lifecycle of the South American monsoon (SAM) was also investigated in the present and future climates. In the near-future, the projections show a slight delay (one pentad) of the beginning of the rainy season, resulting in a small reduction of the SAM length. In the far-future, there is no agreement between projections related to the SAM features.

Precipitation in tropical America and the associated sources of moisture: a short review

Abstract Understanding of the relationship between precipitation and the associated sources of moisture is essential to the improvement of our comprehension of the global water cycle. The observation of precipitation is one of the major challenges in the study of climate, as is the proper assignment of the sources of moisture that account for that precipitation. A stark contrast in the amounts of available information on precipitation may be seen in the cases of Central America and the northern part of South America. The main areas of precipitation in tropical America are described, and the moisture sources for these areas are identified by means of a Lagrangian approach presented with an example application. A strong relationship exists between the identified sources of moisture and the distribution of precipitation in the locations in question. The Caribbean Sea and the tropical Atlantic are highlighted as the main sources of moisture for the regions of highest precipitation in tropical America. Regional low-level winds play a major role in transport of moisture from the adjacent oceanic regions. Editor Z.W. Kundzewicz Citation Durán-Quesada, A.M., Reboita, M. and Gimeno, L., 2012. Precipitation in tropical America and the associated sources of moisture: a short review. Hydrological Sciences Journal, 57 (4), 612–624.

Analysis of a semi-stationary cyclone on the coast of southern Brazil associated to an atmospheric blocking.

On the first week of May 2008, during four days, a semi-stationary surface cyclone acted over the coast of southern Brazil. This system was responsible for large amount of rain and strong near surface winds over Rio Grande do Sul and Santa Catarina causing many damages (fallen trees, floodings and landslides). This work evaluated cyclone development process to understand the reasons for its slow displacement, once most cyclones developed in this region move faster. The Sutcliffe development equation showed that cyclonic absolute vorticity advection in middle troposphere, and positive thermal advection in layer between 1000-500 hPa were important mechanisms for cyclogenesis processes. In this same period, diabatic heating also contributes to cyclogenesis as far as it was opposite to adiabatic cooling due to strong upward movement. Cyclonic absolute vorticity advection which propitiated cyclogenesis was associated with an Upper Level Cyclonic Vortex (ULCV) developed in a potential vorticity anomaly region. The ULCV was semi-stationary and part of a blocking dipole pattern. This blocking intensified a surface anticyclone at south/east of the cyclone, contributing to the cyclone staying semi-stationary near the coast of southern Brazil. The slow and unusual surface cyclone movement to south and sometimes to southwest was associated with middle level cyclonic absolute vorticity and warm air advections in their southern sector. Only when middle levels blocking and middle/high levels potential vorticity anomaly weakened, surface cyclone moved away from the coast of Southern Brazil.

Surface Cyclones over Austral Latitudes: Part I - Bibliographic Review

Abstract The purpose of this study is to summarize the main synoptic features of four types of cyclones: extratropical cyclone fol-lowing Bjerknes and Solberg model, extratropical cyclone following Shapiro and Keyser model, tropical and subtropi-cal. We present some conceptual models and mechanisms of cyclogenesis, intensification and cyclolisis of each cyclonekind.Themaindifferencesbetweenthefourtypesofcyclonesinsurfacearethehorizontalandverticalstructuresoftem-perature and relative vorticity fields. Keywords: extratropical cyclones, subtropical cyclones, tropical cyclones, life cycle, Southern Hemisphere. 1. Introducao O termo ciclone e usado para fazer referencia aossistemas de tempo com rotacao associada a areas de baixapressao na superficie (Petterssen, 1956). A nomenclaturaextratropical distingue os ciclones formados nosextratropicos dos formados nos tropicos, cuja genese ediferente. O processo de formacao ou intensificacao de umciclone e denominado ciclogenese, enquanto que sua dissi-pacao, ciclolise.A formacao e o comportamento dos ciclones extra-tropicais vem sendo estudados desde o seculo XIX, devidoas alteracoes nas condicoes de tempo que esses sistemasprovocam nas regioes onde atuam. O primeiro modeloconceitual mais realistico dos ciclones extratropicais foiproposto por Bjerknes (1919) e Bjerknes e Solberg (1922).Nestes estudos, a formacao dos ciclones extratropicais foiassociada a presenca de gradientes horizontais de tempe-ratura em superficie (isto e, associado a uma zona barocli-nica) e o aprofundamento do ciclone ocorre com a rotacaoda frente fria em torno do centro de baixa pressao ate que amesma alcance a frente quente, que tem menor velocidadede deslocamento do que a frente fria. Na decada de 1990,Shapiro e Keyser, estudando casos de ciclogeneses comrapida intensificacao, verificaram que em alguns ciclones afrente fria deslocava-se perpendicular a frente quente deforma que essas, geralmente, nao se encontravam. Comisso, surgiu outro modelo conceitual de ciclones, o cha-mado modelo de Shapiro e Keyser. E importante ressaltarque o modelo desses autores nao substitui o modelo de

PROCESSOS FÍSICOS ASSOCIADOS À GÊNESE DE UM VCAN ENTRE O OCEANO PACÍFICO E A AMÉRICA DO SUL EM ABRIL DE 2013

Esse estudo teve como objetivo avaliar, por meio das equacoes da tendencia da vorticidade e da temperatura, os processos fisicos associados a genese de um vortice ciclonico de altos niveis (VCAN) subtropical proximo a costa oeste da America do Sul (35o-40oS) entre os dias 30 de marco a 1o de abril de 2013. Entre os resultados tem-se que as adveccoes horizontais de vorticidade (300 hPa) e temperatura (500 hPa) sao processos importantes para aprofundar o cavado em 300 hPa levando a genese do VCAN.