From synoptic to interdecadal variability in southern African rainfall: towards a unified view across timescales

Benjamin Pohl, Bastien Dieppois, Julien Cretat, Damian Lawler, Mathieu Rouault

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

During the austral summer season (November–February), southern African rainfall, south of 20°S, has been shown to vary over a range of timescales, from synoptic variability (3-7 days, mostly Tropical-Temperate Troughs) to interannual variability (2-8 years, reflecting the regional effects of El Niño Southern Oscillation). There is also evidence for variability at quasi-decadal (8-13 years) and interdecadal (15-28 years) timescales, linked to the Interdecadal Pacific Oscillation and the Pacific Decadal Oscillation, respectively. This study aims to provide an overview of these ranges of variability, their influence on regional climate and large-scale atmospheric convection, and quantify uncertainties associated with each timescale. We do this by applying k-means clustering onto long-term (1901–2011) daily Outgoing Longwave Radiation anomalies derived from the 56 individual members of the 20th Century Reanalysis. Eight large-scale convective regimes are identified.

Results show that: (i) the seasonal occurrence of the regimes significantly varies at the low-frequency timescales mentioned above; (ii) these modulations account for a significant fraction of seasonal rainfall variability over the region; (iii) significant associations are found between some of the regimes and the aforementioned modes of climate variability; and (iv) associated uncertainties in the regime occurrence and convection anomalies strongly decrease with time, especially the phasing of transient variability. The short-lived synoptic anomalies and the low-frequency anomalies are shown to be approximately additive, but even if they combine their respective influence at both scales, the magnitude of short-lived perturbations remains much larger.
LanguageEnglish
Pages5845–5872
Number of pages28
JournalJournal of Climate
Volume31
Issue number15
Early online date29 Jun 2018
DOIs
Publication statusPublished - Aug 2018

Fingerprint

timescale
anomaly
rainfall
atmospheric convection
Pacific Decadal Oscillation
longwave radiation
regional climate
El Nino-Southern Oscillation
trough
convection
oscillation
perturbation
climate
summer
effect

Keywords

  • Africa
  • Rainfall
  • Climate classifaction/regimes
  • Climate variability
  • Decadal Variability
  • Interannual variability

Cite this

From synoptic to interdecadal variability in southern African rainfall: towards a unified view across timescales. / Pohl, Benjamin; Dieppois, Bastien; Cretat, Julien; Lawler, Damian; Rouault, Mathieu.

In: Journal of Climate, Vol. 31, No. 15, 08.2018, p. 5845–5872.

Research output: Contribution to journalArticle

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