A climatic oscillation similar to ENSO also occurs in the Indian Ocean (IO).
The Indian Ocean Dipole (IOD) is an oscillation between the SST of the western
IO off the coast of Somalia and the SST over the eastern IO off the coast of
Indonesia (Figure 2). When the western IO SSTs are higher than normal and the
eastern IO SSTs are lower than normal, the IOD is in a positive phase. The
negative phase is defined by the opposite SST anomaly pattern. Saji et al.
(1999) defined this phenomenon and formation. Low SSTs tend to appear off the
coast of Java in the late spring. By late summer, the low SST and easterly low
level-wind surface anomalies intensify while the western tropical IO warms
(Figure 2). The temporal scale over which the IOD varies is smaller than for
ENSO. It is common for the phases of the IOD to oscillate several times a year
(Saji et al. 1999).