Question 68 from UPSC CSE 2020 - GEOGRAPHY

Question

With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct?
1. OMT is measured up to a depth of 26Â°C isotherm which is 129 meters in the south-western Indian Ocean during JanuaryâMarch.
2. OMT collected during JanuaryâMarch can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.

IASCODEX · Accepted Answer

Correct Option: B. 2 only

Strategy: - Evaluate statements by checking measurement parameters and contextual cues.
- Identify Statement 1's fixed depth of 129 meters for the 26°C isotherm in the s-w Indian Ocean (Jan-Mar) as a specific and uncommon figure, indicating a red flag.
- Recognize Statement 2's connection of OMT (measured Jan-Mar) to monsoon rainfall prediction as a well-established application.
- Reject Statement 1 and accept Statement 2 due to the technical detail mismatch.

Key Info: ## Ocean Mean Temperature (OMT) Details

OMT represents the average ocean temperature from the surface down to the depth of the 26°C isotherm. This isotherm's depth varies regionally and seasonally.

### Key Facts & Predictive Value
*   In the southwestern Indian Ocean, the average 26°C isotherm depth during January-March is approximately 59 meters, significantly shallower than 129 meters.
*   OMT is a more robust indicator than Sea Surface Temperature (SST) for large-scale climate analysis. It incorporates oceanic heat content from a larger volume and is less affected by transient atmospheric events.
*   Studies (e.g., IITM) show OMT from January-March has higher predictive value (approx. 80% success rate) for Indian summer monsoon rainfall forecasting compared to SST (approx. 60% success rate).
*   This is because OMT reflects the sub-surface heat reservoir crucial for monsoon development, whereas SST is limited to the ocean's thin upper layer and is easily altered.

### Broader Importance
OMT is also critical for understanding phenomena like cyclogenesis and heat transport. The intra-annual and regional variability of the 26°C isotherm depth must always be considered in measurements.

IASCODEX · Answer

Option A: 1 only

IASCODEX · Answer

Option C: Both 1 and 2

IASCODEX · Answer

Option D: Neither 1 nor 2