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 El Nino's impact on the monsoon. Select the correct answer using the code given below:
2 only
Understanding the Indian Ocean Dipole (IOD) and its Impact on Indian Monsoon
The question asks about the Indian Ocean Dipole (IOD) and its characteristics, specifically how it relates to forecasting the Indian monsoon and its interaction with El Nino.
Let's analyze each statement carefully.
Analyzing Statement 1: IOD Definition
Statement 1 says: IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
This statement describes a key characteristic of the IOD, which is based on sea surface temperature differences. However, it incorrectly mentions the tropical Eastern Pacific Ocean. The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperatures between two areas (poles) in the tropical Indian Ocean:
- A western pole in the Arabian Sea (western tropical Indian Ocean)
- An eastern pole in the eastern Indian Ocean south of Indonesia and west of Australia (eastern tropical Indian Ocean)
The difference in temperature between these two poles drives the IOD phenomenon. The tropical Eastern Pacific Ocean is associated with the El Nino-Southern Oscillation (ENSO) phenomenon, not the Indian Ocean Dipole (IOD).
Therefore, Statement 1 is incorrect because it refers to the Eastern Pacific Ocean instead of the Eastern Indian Ocean.
Analyzing Statement 2: IOD and El Nino Interaction
Statement 2 says: An IOD phenomenon can influence an El Nino's impact on the monsoon.
This statement discusses the interaction between IOD and El Nino. Both IOD and El Nino-Southern Oscillation (ENSO) are major climate patterns that originate in the tropical oceans and significantly affect weather patterns globally, including the Indian monsoon. While distinct phenomena, they can occur simultaneously and interact with each other.
For example:
- A positive IOD is associated with warmer-than-average sea surface temperatures in the western Indian Ocean and cooler-than-average temperatures in the eastern Indian Ocean.
- El Nino is associated with warmer-than-average sea surface temperatures in the central and eastern tropical Pacific Ocean.
El Nino is generally associated with below-average monsoon rainfall in India. However, a simultaneous positive IOD event can sometimes counteract or reduce the negative impact of El Nino on the Indian monsoon, potentially leading to more favourable monsoon conditions than would occur with El Nino alone. Similarly, a negative IOD could potentially amplify the negative effects of El Nino or El Nino-like conditions.
Because the IOD can occur concurrently with El Nino and influence its effects on the Indian monsoon, Statement 2 is correct.
Conclusion
Based on the analysis:
- Statement 1 is incorrect as IOD involves the tropical Indian Ocean, not the Eastern Pacific Ocean.
- Statement 2 is correct as IOD can indeed influence the impact of El Nino on the Indian monsoon.
Therefore, only Statement 2 is correct.
Understanding Indian Ocean Dipole (IOD) Phases and Monsoon Link
The IOD has three main phases:
- Positive IOD: Warmer SSTs in the western Indian Ocean, cooler SSTs in the eastern Indian Ocean. Often associated with increased rainfall in the western Indian Ocean region and over India during the monsoon season, and reduced rainfall over Indonesia and Australia.
- Negative IOD: Cooler SSTs in the western Indian Ocean, warmer SSTs in the eastern Indian Ocean. Often associated with reduced rainfall in the western Indian Ocean region and over India, and increased rainfall over Indonesia and Australia.
- Neutral IOD: Near-average SSTs across the tropical Indian Ocean. Less significant impact on rainfall patterns compared to positive or negative phases.
These phases play a crucial role in forecasting the Indian monsoon rainfall.
Revision Table: Comparing IOD and ENSO
| Feature | Indian Ocean Dipole (IOD) | El Nino-Southern Oscillation (ENSO) |
|---|---|---|
| Ocean Basin | Indian Ocean | Pacific Ocean |
| Key Areas Involved | Tropical Western Indian Ocean vs. Tropical Eastern Indian Ocean | Tropical Central/Eastern Pacific Ocean vs. Western Pacific Ocean/Indonesia |
| Impact on Indian Monsoon (Typical) | Positive IOD: Favourable for monsoon Negative IOD: Unfavourable for monsoon |
El Nino: Unfavourable for monsoon La Nina: Favourable for monsoon |
| Interaction | Can interact with ENSO, modifying its impact. | Can interact with IOD, influencing its impact. |
Additional Information: Climate Variability and Indian Monsoon
The Indian monsoon is a complex climate phenomenon influenced by various factors, including sea surface temperatures in the Indian and Pacific Oceans, atmospheric pressure systems, and land surface conditions. Climate patterns like IOD and ENSO are significant drivers of inter-annual variability in monsoon rainfall, making their monitoring and forecasting essential for agriculture, water management, and disaster preparedness in India and surrounding regions. Understanding these climate teleconnections helps improve long-range monsoon forecasts.
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