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Climate Dynamics

, Volume 48, Issue 7–8, pp 2529–2540 | Cite as

Modulation of the Southern Africa precipitation response to the El Niño Southern Oscillation by the subtropical Indian Ocean Dipole

  • Andrew Hoell
  • Chris Funk
  • Jens Zinke
  • Laura Harrison
Article

Abstract

The climate of Southern Africa, defined as the land area bound by the region 15°S–35°S; 12.5°E–42.5°E, during the December–March rainy season is driven by Indo-Pacific sea surface temperature (SST) anomalies associated with the El Niño Southern Oscillation (ENSO) and the Subtropical Indian Ocean Dipole (SIOD). The observed December–March 1979–2014 Southern Africa precipitation during the four ENSO and SIOD phase combinations suggests that the phase of the SIOD can disrupt or enhance the Southern Africa precipitation response to ENSO. Here, we use a large ensemble of model simulations driven by global SST and ENSO-only SST to test whether the SIOD modifies the relationship between Southern Africa precipitation and ENSO. Since ENSO-based precipitation forecasts are used extensively over Southern Africa, an improved understanding of how other modes of SST variability modulate the regional response to ENSO is important. ENSO, in the absence of the SIOD, forces an equivalent barotropic Rossby wave over Southern Africa that modifies the regional mid-tropospheric vertical motions and precipitation anomalies. El Niño (La Niña) is related with high (low) pressure over Southern Africa that produces anomalous mid-tropospheric descent (ascent) and decreases (increases) in precipitation relative to average. When the SIOD and ENSO are in opposite phases, the SIOD compliments the ENSO-related atmospheric response over Southern Africa by strengthening the regional equivalent barotropic Rossby wave, anomalous mid-tropospheric vertical motions and anomalous precipitation. By contrast, when the SIOD and ENSO are in the same phase, the SIOD disrupts the ENSO-related atmospheric response over Southern Africa by weakening the regional equivalent barotropic Rossby wave, anomalous mid-tropospheric vertical motions and anomalous precipitation.

Keywords

Southern Africa Precipitation El Nino-Southern Oscillation Subtropical Indian Ocean Dipole 

Notes

Acknowledgments

The authors thank Dave Allured for completing the ECHAM5.4 simulations and Tao Zhang for completing the GFSv2 simulations. The authors are grateful for support from the Famine Early Warning Systems Network (FEWS NET).

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Copyright information

© Springer-Verlag (outside the USA)  2016

Authors and Affiliations

  1. 1.NOAA Earth System Research Laboratory Physical Sciences DivisionBoulderUSA
  2. 2.Department of GeographyUniversity of California Santa BarbaraSanta BarbaraUSA
  3. 3.Earth Resources Observation and Science CenterU.S. Geological SurveySioux FallsUSA
  4. 4.Institut für Geologische WissenschaftenFreie Universität BerlinBerlinGermany
  5. 5.Department of Environment and AgricultureCurtin University of TechnologyBentleyAustralia
  6. 6.Australian Institute of Marine ScienceCape FergusonAustralia
  7. 7.School of Geography, Archaeology and Environmental StudiesUniversity of WitwatersrandJohannesburgSouth Africa

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