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South Western Indian Ocean (SWIO) SST index

The SWIO SST anomaly index is an indicator of the surface temperatures in a region east of South Africa and south of Madagascar. It is calculated with SSTs in the box 31°E - 45°E, 32°S - 25°S. Above average austral summer rainfall over parts of subtropical southern Africa has been associated with periods of high SWIO.

This region has been identified as important in research by local scientists and others starting in the late 1980s. These include studies by Walker (1989), Walker (J. Geophys. Res., 1990), Jury et al. (J. Clim. Appl. Met., 1993), Mason and Tyson (J. Geophys. Res., 1992), Mason 1995 (Int. J. Clim., 1995), Rocha and Simmonds (Int. J. Clim., 1997), Reason and Mulenga (Int. J. Clim., 1999), Reason (J. Clim., 2001), Behera and Yamagata (Geophys. Res. Lett., 2001), Reason (Geophys. Res. Lett., 2001), Fauchereau et al. (Int. J. Clim., 2003), Hermes and Reason (J. Clim., 2005), and Washington and Preston (J. Geophys. Res., 2006).

Other sources of information (indices and forecasts) relevant to this region can be found at the: South African Weather Service site under 'Long Range Forecasts'; Near real-time monitoring page for the Indian and tropical and south Atlantic maintained by M. Rouault (University of Cape Town) and Ocean Analysis; and the NOAA African Desk.

The CLIVAR Variability in the African System (VACS) panel coordinates research on the variability and predictability of African climate, and its relationship to the global climate system.

Data source

The index is calculated using the Reynolds OIv2 SST analysis, made available through the IRI Data Library, and is updated weekly (last update 26-OCT-2016).   get series (netcdf 24kB) »  get error (netcdf 24kB) »

Calculation

The anomaly is calculated relative to a climatological seasonal cycle based on the years 1982-2005. The weekly series was linearly interpolated to a daily series to calculate the climatological seasonal cycle with daily resolution. The leap day (29 February) was treated as a special case and linearly interpolated between the climatology of 28 February and 1 March. Spatial averaging of the gridded analysis was weighted by surface area. The standard deviation of the index over the period 1982-2005 is indicated on the plot.

Uncertainty

The uncertainty in the estimate of the index is shown in gray, surrounding the zero x-axis, and is based on the uncertainty estimate of the analysis. For the surface indices, it is generally small compared to the value of the index.    more details »