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Dipole Mode Index (DMI)

The DMI index is an indicator of the east-west temperature gradient across the tropical Indian Ocean, linked to the Indian Ocean Dipole or Zonal Mode. It is calculated as the difference of the WTIO and SETIO indices. Extreme September-October-November rainfall in tropical East Africa has associated with periods of persistently high DMI (Black et al., Mon. Wea. Rev., 2003).

This index was defined by Saji et al. (Nature, 1999).

The Frontier Research Center for Global Change (JAMSTEC, Japan) hosts an Indian Ocean Dipole page with more information, including forecasts.

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 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 »