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Tropical Atlantic (TASI) SST index

The TASI SST anomaly index is an indicator of the meridional surface temperature gradient in the tropical Atlantic Ocean. It is calculated as the difference of the NAT and SAT indices.

The TASI index was defined in a paper by Chang, Ji, and Li (Nature, 1997), where it were associated with a potential decadal 'dipole' mode of coupled variability in the tropical Atlantic.

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 07-SEP-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 two component indices that make up the difference. For the surface indices, it is generally small compared to the value of the index.   more details »