Intraseasonal variability in subtropical South America as depicted by precipitation data

Abstract

Daily precipitation data from three stations in subtropical Argentina are used to describe intraseasonal variability (20–90 days) during the austral summer. This variability is compared locally and regionally with that present in outgoing longwave radiation (OLR) data, in order to evaluate the performance of this variable as a proxy for convection in the region. The influence of the intraseasonal activity of the South American Seesaw (SASS) leading convection pattern on precipitation is also explored. Results show that intraseasonal variability explains a significant portion of summer precipitation variance, with a clear maximum in the vicinity of the SASS subtropical center. Correlation analysis reveals that OLR can explain only a small portion of daily precipitation variability, implying that it does not constitute a proper proxy for precipitation on daily timescales. On intraseasonal timescales, though, OLR is able to reproduce the main features of precipitation variability. The dynamical conditions that promote the development of intraseasonal variability in the region are further analyzed for selected summers. Seasons associated with a strong intraseasonal signal in precipitation variability show distinctive wet/dry intraseasonal periods in daily raw data, and are associated with a well defined SASS-like spatial pattern of convection. During these summers, strong large-scale forcing (such as warm El Niño/Southern Oscillation (ENSO) events and/or tropical intraseasonal convective activity), and Rossby-wave-like circulation anomalies extending across the Pacific Ocean, are also observed.

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Acknowledgments

The authors thank Gilbert Compo for his scientific inputs, and the anonymous reviewers for their valuable comments. This work was supported by University of Buenos Aires (X264) and ANPCyT (BID 1728/OC-AR—PICT25269).

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Correspondence to P. L. M. González.

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González, P.L.M., Vera, C.S., Liebmann, B. et al. Intraseasonal variability in subtropical South America as depicted by precipitation data. Clim Dyn 30, 727–744 (2008). https://doi.org/10.1007/s00382-007-0319-9

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Keywords

  • Intraseasonal variability
  • South America
  • Precipitation
  • Convection
  • Warm season