With reference to ‘Indian Ocean Dipole (IOD)’ sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?
- IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
- An IOD phenomenon can influence an El Nino’s impact on the monsoon.
Select the correct answer using the code given below:
- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
Explanation
Statement 1 is incorrect
- The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) ― a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia. Similar to ENSO, the atmospheric component of the IOD was later discovered and named as Equatorial Indian Ocean Oscillation (EQUINOO: oscillation of warm water and atmospheric pressure between the Bay of Bengal and the Arabian Sea).
Statement 2 is correct
- During positive IOD, winds over the Indian Ocean blow from east to west (from the Bay of Bengal towards the Arabian Sea). This results in the Arabian Sea (the western Indian Ocean near African Coast) being much warmer and the eastern Indian Ocean around Indonesia becoming colder and dry. In the negative dipole year (negative IOD), the reverse happens to make Indonesia much warmer and rainier.
- It was demonstrated that a positive IOD index often negated the effect of ENSO, resulting in increased Monsoon rains in several ENSO years like 1983, 1994 and 1997.
