Consider the following statements regarding Indian Ocean Dipole (IOD) :-
1. It is the difference of sea surface temperature between an eastern pole in the Arabian Sea and a western pole in the eastern Indian Ocean.
2. It is an independent phenomenon and does not have any link with El Niño–Southern Oscillation (ENSO).
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answers
Answer:
1.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.
2.El Niño–Southern Oscillation (ENSO) is an irregular periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics. The warming phase of the sea temperature is known as El Niño and the cooling phase as La Niña. The Southern Oscillation is the accompanying atmospheric component, coupled with the sea temperature change: El Niño is accompanied by high air surface pressure in the tropical western Pacific and La Niña with low air surface pressure there.[1][2] The two periods last several months each and typically occur every few years with varying intensity per period.[3]
Southern Oscillation Index timeseries 1876–2017.
Southern Oscillation Index correlated with mean sea level pressure.
The two phases relate to the Walker circulation, which was discovered by Gilbert Walker during the early twentieth century. The Walker circulation is caused by the pressure gradient force that results from a High-pressure area over the eastern Pacific Ocean, and a low-pressure system over Indonesia. Weakening or reversal of the Walker circulation (which includes the trade winds) decreases or eliminates the upwelling of cold deep sea water, thus creating El Niño by causing the ocean surface to reach above average temperatures. An especially strong Walker circulation causes La Niña, resulting in cooler ocean temperatures due to increased upwelling.
Mechanisms that cause the oscillation remain under study. The extremes of this climate pattern's oscillations cause extreme weather (such as floods and droughts) in many regions of the world. Developing countries dependent upon agriculture and fishing, particularly those bordering the Pacific Ocean, are the most affected.
3 Both 1 and 2
Option D - Neither 1 nor 2
- 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.
- Statement 2 is incorrect :- The IOD has a link with ENSO events through an extension of the Walker Circulation.
■ Explanation :-
- The IOD is a coupled ocean and atmosphere phenomenon, similar to ENSO but in the equatorial Indian Ocean.
- IOD has a link with ENSO events through an extension of the Walker Circulation to the west and associated Indonesian through flow (the flow of warm tropical ocean water from the Pacific into the Indian Ocean). Hence, positive IOD events are often associated with El Niño and negative events with La Niña.
- Positive IOD :- It is associated with cooler than normal sea-surface temperatures in the eastern equatorial Indian Ocean and warmer than normal sea surface temperatures in the western tropical Indian Ocean.
- Negative IOD :- It is characterised by warmer than normal sea-surface temperatures in the eastern equatorial Indian Ocean and cooler than normal sea-surface temperatures in the western tropical Indian Ocean.
- Walker circulation :- The longitudinal (east-west) circulation across the equatorial Pacific is known as the Walker cell or Walker circulation.
Hope It helps you
