Intensity of the IOD is represented by anomalous SST gradient between the western equatorial Indian Ocean (50E-70E and 10S-10N) and the south eastern equatorial Indian Ocean (90E-110E and 10S-0N). This gradient is named as Dipole Mode Index (DMI). When the DMI is positive then, the phenomenon is refereed as the positive IOD and when it is negative, it is refereed as negative IOD.
Since IOD is a coupled ocean-atmosphere phenomenon, it can also be represented by any other atmospheric (pressure, OLR) or oceanographic (sea surface height) as well.
SST DMI dataset (monthly from 1870 to present) derived from HadISST dataset
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