RAS question
The Indian Ocean Dipole (IOD) refers to:
Correct answer: (B) Temperature difference between western and eastern Indian Ocean.
The Indian Ocean Dipole refers to the temperature difference between the western and eastern Indian Ocean.
Explanation
The Indian Ocean Dipole, or IOD, is an ocean-atmosphere phenomenon marked by an irregular oscillation in sea-surface temperatures between the western and eastern Indian Ocean. IMD describes it as a pattern in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean. In a positive IOD, the tropical western Indian Ocean is warmer than normal while the tropical eastern Indian Ocean is cooler than normal. An east-west temperature difference is therefore the precise definition. The same pattern matters for RAS geography because a positive IOD is generally linked with a stronger Indian monsoon, while a negative IOD can suppress monsoon rainfall.
Why the other options are wrong
- (A) IOD is not defined as a pressure difference; IMD defines it through sea-surface temperature differences between the western and eastern Indian Ocean.
- (C) The Bay of Bengal-Arabian Sea comparison is too narrow and uses the wrong basins; IOD is an east-west Indian Ocean temperature contrast.
- (D) Salinity variation is not the defining feature of IOD; IMD defines it in terms of sea-surface temperature oscillation.
Concept
Indian monsoon teleconnections include the influence of ocean temperature patterns on Indian Summer Monsoon Rainfall. ENSO, IOD and related ocean-atmosphere links recur in RAS because they are standard tools for explaining monsoon variability.