Climate index




Antarctic Oscillation


Normalized difference in the zonal mean sea-level pressure pattern between 60˚S and 40˚S. It is a measure of equator-ward/pole-ward shifts in the southern mid latitude storm track; therefore, a measure of atmospheric circulation rather than SSTs, but we include it here because it is such a dominant descriptor of southern mid-latitude circulation. Source:

[28] [29] [30]

Indian Ocean Dipole


A shift of SST between positive, neutral and negative phases over the western and eastern Indian Ocean. Constructed from SST variability over the Indian Ocean for 35˚E - 115˚E and 25˚S - 20˚N domain using the methodology of [34] . It describes the center of the Walker circulation ascending branches over the eastern Indian Ocean and the south eastern corner of the South Atlantic Ocean.

[31] [32] [33]

Multivariate ENSO Index


Measure of combined atmosphere-ocean phenomena, representing shifts of warm surface waters and associated atmospheric convection back and forth across the tropical Pacific Ocean. Synonymous with El Nino-Southern Oscillation (ENSO) phenomena. ENSO has influence on South African rainfall anomalies which may occur through modulation of the local Walker circulation and SSTs in the neighboring Indian and Atlantic Oceans. Source:

[20] [21] [22] [23] [35] [36] [37]

Tropical Southern Atlantic


A measure of SST gradient over the southern parts of equatorial Atlantic Ocean. Several idealized climate model experiments shows that TSA exhibits a self-evident boost in daily rainfall and rainfall extremes over southern Africa, via locally-based effects such as increased convection and remotely-based effects such as an adjustment of the Walker-type circulation. Source:

[38] [39]

Benguela Nino


BGN dataset is similar to those of TSA described by [38] . It is a measure of SST anomaly gradient over the south-eastern Equatorial Atlantic. The influence of the tropical south-eastern Atlantic SST anomalies on the western Southern African rainfall and temperature may be enhanced if the easterly inflow of moisture from the western Indian Ocean is greater than average. Therefore, local evaporation, coupled with enhanced instability, over the south-eastern Atlantic Ocean act to supplement the precipitation derived from the Indian Ocean source rather than providing a dominant source of moisture. Its construction is however restricted to SST anomalies over the South Atlantic Ocean rectangular domain 15˚E - 0˚E and 30˚S - 5˚S in this study.

[38] [39] [40] [41] [42]

South Indian Ocean Index


SIO dataset, described by [43] , is akin to IOD dataset. The exception is that SIO is strictly constructed from SST variability over the Southern Indian Ocean rectangular domain 50˚E - 115˚E and 35˚S - 0˚S, also, using the methodology of [34] .

[31] [43]

Southwest Indian Ocean Index


SWI dataset is very similar to SIO except that SWI is constructed from SST variability over the Southwestern Indian Ocean rectangular domain 35˚E - 70˚E and 40˚S - 20˚S. Warm and cold conditions over the Southwest Indian Ocean have been linked, respectively, with wet and dry conditions over South Africa and vice versa. This is regardless of the atmospheric and oceanic mechanisms by which they arise.

[41] [44]