Subtropical Indian Ocean Dipole

Positive phase of Subtropical Indian Ocean Dipole is characterized by warmer-than-normal sea surface temperature in the southwestern part, south of Madagascar, and colder-than-normal sea surface temperature off Australia, causing above-normal precipitation in many regions over south and central Africa.

Also, Ekman transport accompanied with surface mixing process also plays a role in the formation of the SST dipole.

[1] Generally speaking, the Subtropical Indian Ocean Dipole mode develops in December–January, peaks in February, then decays in the following two months, and finally dies down in May–June.

[4] The spatial pattern of the dry(wet) composite SSTA shifted to the east of the spatial pattern of the positive(negative) Subtropical Indian Ocean Dipole event(previous definition of SIOD), and the calculation based on the Subtropical Indian Ocean Dipole Index may need re-consideration when the relationship between southwestern Australia rainfall and SIOD index is studied, which may require further work.

[4] Positive SIOD events also cause increased summer rains over large parts of southeastern Africa by bringing enhanced convergence of moisture.

(a)Regressed SIOD Index on detrended Sea Surface Temperature (SST) (1958-2007). The western and eastern box used to calculate SIOD Index are indicated. Water temperatures in the southwestern Southern Indian Ocean are significantly higher than water temperature in the eastern part of South Indian Ocean, off Australia. In this image blue areas are colder than normal, while red areas are warmer than normal. (b)The normalized SIOD index during 1958-2007. The values are normalized by standard deviation of 0.65. Blue line indicates the original time series and the red curve are after applying 1-2-1 smoothing by ten times.
the connection between Indian Ocean climate condition and (a) dry and (b) wet years over SWWA. SST anomalies are shown in colors. Wind anomalies are indicated as bold arrows, pressure anomalies are shown by H (high) and L (low), and rainfall anomalies are represented by sun/cloud symbols. Dry and wet years are from (England et al. 2006). [ 4 ]