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The role of synoptic and intraseasonal anomalies on the life cycle of rainfall extremes over South America: non-summer conditions

Abstract

Previous study showed that the interaction of synoptic disturbances with intraseasonal anomalies is important for heavy rainfall in the South Atlantic Convergence Zone and the La Plata basin during the austral summer. Here, we conduct similar analysis to study the evolution of rainfall extremes during austral spring (SON), fall (MAM) and winter (JJA). A relatively homogeneous region over southeastern South America, whose limits change little from season to season, is heavily affected by extreme precipitation events, as indicated by the value of the 95th percentile of daily rainfall, higher during the spring season (16.94 mm day−1) and lower in winter (13.79 mm day−1). From 1979 to 2013, extreme rainfall events are more frequent in spring (131 events) and less frequent in fall (112 events). Similar to summertime extreme events, synoptic-scale waves continue to be the main drivers of extreme precipitation over the region. The interaction between these waves and intraseasonal anomalies during the development of rainfall extremes over southeastern South America is observed especially during neutral ENSO and La Niña conditions. Warm ENSO phases tend to favor more frequent extremes in all three seasons and extreme events during El Niños are associated with synoptic waves, with no significant interaction with intraseasonal anomalies.

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Acknowledgments

This work was carried out with the support of the National Council for Scientific and Technological Development (CNPq-Brazil) Grant BJT 400547/2013-9, and with the aid of the Inter-American Institute for Global Change Research (IAI) Grant CRN3035, which is supported by the US National Science Foundation (Grant GEO-1128040).

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Correspondence to Fernando E. Hirata.

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Hirata, F.E., Grimm, A.M. The role of synoptic and intraseasonal anomalies on the life cycle of rainfall extremes over South America: non-summer conditions. Clim Dyn 49, 313–326 (2017). https://doi.org/10.1007/s00382-016-3344-8

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  • DOI: https://doi.org/10.1007/s00382-016-3344-8

Keywords

  • Rainfall Extreme
  • South Atlantic Convergence Zone
  • Synoptic Disturbance
  • Intraseasonal Anomaly
  • Intraseasonal Signal