With reference to ‘Indian Ocean Dipole (IOD)’ sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?

1. IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
2. An IOD phenomenon can influence an EI Nino’s impact on the monsoon.

Select the correct answer using the code given below:

[UPSC Civil Services Exam – 2017 Prelims]

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer: (b)

Explanation:

• The Indian Ocean Dipole (IOD) is a climate phenomenon characterized by the difference in sea surface temperature between two poles in the Indian Ocean – an eastern pole in the eastern Indian Ocean near Indonesia and a western pole in the Arabian Sea. This creates a dipole pattern, hence the name IOD.
• The IOD affects the climate of countries surrounding the Indian Ocean Basin, such as India and Australia, and plays a significant role in rainfall variability in the region.
• Similar to El Nino-Southern Oscillation (ENSO), the IOD is a coupled ocean and atmosphere phenomenon in the equatorial Indian Ocean. It is believed that the IOD is linked to ENSO events through the extension of the Walker Circulation to the west and the Indonesian throughflow, which is the flow of warm tropical ocean water from the Pacific into the Indian Ocean.
• Negative IOD events are often associated with La Nina, while positive events are associated with El Nino, making statement 2 correct.
• However, statement 1 is not correct as the IOD involves sea surface temperature differences between the eastern and western poles, rather than a north-south difference.

Therefore, option (b) is the correct answer.