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The relationship between the Antarctic oscillation and blocking events over the South Pacific and Atlantic Oceans

Authors

  • Monica Cristina Damião Mendes,

    Corresponding author
    1. Center for Weather Forecasting and Climate Studies/National Institute for Space Research (CPTEC/INPE), São Paulo, Brazil
    • Correspondence to: M. C. D. Mendes and I. F. A. Cavalcanti, Instituto Nacional de Pesquisas Espaciais, Centro de Previsão de Tempo e Estudos Climáticos, Rodovia Presidente Dutra, SN, Km 40, 12630-000 Cachoeira Paulista, São Paulo, Brazil. E-mails: monica.damiao@gmail.com.br; iracema@cptec.inpe.br

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  • Iracema Fonseca Albuquerque Cavalcanti

    Corresponding author
    1. Center for Weather Forecasting and Climate Studies/National Institute for Space Research (CPTEC/INPE), São Paulo, Brazil
    • Correspondence to: M. C. D. Mendes and I. F. A. Cavalcanti, Instituto Nacional de Pesquisas Espaciais, Centro de Previsão de Tempo e Estudos Climáticos, Rodovia Presidente Dutra, SN, Km 40, 12630-000 Cachoeira Paulista, São Paulo, Brazil. E-mails: monica.damiao@gmail.com.br; iracema@cptec.inpe.br

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ABSTRACT

It is known that blocking events have impacts on the behaviour of transient systems and affect the weather in southern continental regions of the Southern Hemisphere. Since the main mode of variability in Southern Hemisphere, the annular mode, or Antarctic Oscillation (AAO), changes the extratropical atmospheric circulation, the blocking characteristics over Pacific and Atlantic Oceans are analysed in this study, in terms of the two opposing phases of the AAO. The characteristics of atmospheric flow patterns and blocking events are analysed as a function of season during the period 1979–2000. The relative frequency of blocked days is different for each AAO phase. Maximum duration and number of events over the Southwestern Pacific and South Atlantic regions occur in the positive phase, while the blocking activity over the Southeastern Pacific region is similar in the two phases but the persistence is higher in the negative phase. The atmospheric anomalous centres associated with middle latitude and polar AAO signals, as well as the behaviour of subtropical and polar jets are discussed in relation to the blocking characteristics. Convection over South America is analysed for blocking periods in each AAO phase and is discussed based on anomalous circulation in each phase. Wavetrain patterns over the South Pacific and variations in intensity of jet streams induce anomalous circulation over South America, which are associated with the track and persistence of transient systems over Southeastern South America and with convection over the continent.

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