World and Physical Geography

With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct ?

• OMT is measured up to a depth of 26°C isotherm which is 129 meters in the south-western Indian Ocean during January – March.
• OMT collected during January – March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.

Select the correct answer using the code given below :

[amp_mcq option1=”1 only” option2=”2 only” option3=”Both 1 and 2″ option4=”Neither 1 nor 2″ correct=”option2″]

The correct option is B, as statement 2 is correct regarding the use of OMT in monsoon prediction, while statement 1 contains specific details that may not be universally accurate or precisely phrased.

Ocean Mean Temperature (OMT) represents the average temperature of the upper ocean layer, typically down to the depth where the temperature is 26°C. This measure reflects the heat content of the upper ocean and is considered a better predictor of the Indian Summer Monsoon than Sea Surface Temperature (SST) alone.

1. **Depth and Measurement:** OMT is measured up to the depth of the 26°C isotherm. The depth of the 26°C isotherm is not fixed at 129 meters but varies geographically and seasonally. While it might be around 129 meters in the specific region (south-western Indian Ocean) and time (January-March) mentioned, stating it as a fixed depth “which is 129 meters” can be misleading, as the OMT is defined by the varying depth of the isotherm, not a fixed depth. Therefore, this statement is likely inaccurate or too specific/poorly phrased for a general description.
2. **Monsoon Prediction:** Studies have shown a strong correlation between the Ocean Mean Temperature in the southeastern equatorial Indian Ocean and the southwestern Bay of Bengal during the pre-monsoon period (January-March or April-May) and the subsequent Indian Summer Monsoon rainfall. Higher OMT in this region is generally associated with a better monsoon. This statement is correct.

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:

[amp_mcq option1=”1 only” option2=”2 only” option3=”Both 1 and 2″ option4=”Neither 1 nor 2″ correct=”option2″]

Statement 2 is correct, while statement 1 is incorrect.

– Statement 1 is incorrect. The Indian Ocean Dipole (IOD) is an irregular oscillation of sea surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean. It is characterised by a difference in sea surface temperature between a western pole in the Arabian Sea (western tropical Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia. The statement incorrectly mentions the Eastern Pacific Ocean, which is associated with El Niño-Southern Oscillation (ENSO).
– Statement 2 is correct. The IOD is a significant climate driver for countries around the Indian Ocean, including influencing the Indian monsoon. IOD and ENSO are two separate climate phenomena, but they can interact and influence each other’s impact on regional weather patterns, including the Indian monsoon. A positive IOD, for instance, is often associated with a good monsoon in India and can sometimes counteract the negative impact of an El Niño event.

A ‘positive IOD’ occurs when the western Indian Ocean is warmer and the eastern Indian Ocean is colder than average. A ‘negative IOD’ is the opposite. The IOD is often called the “Indian Niño” because of its similarity to the Pacific El Niño phenomenon.