UPSC Prelims 2020 Q93: Geography – Oceanography
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (b) 2 only
Explanation
Ocean Mean Temperature (OMT)
Ocean Mean Temperature is the average temperature of the sea from the surface down to the 26°C isotherm.
Scientists at the Indian Institute of Tropical Meteorology, Pune found that it predicts the monsoon better than sea surface temperature.
| Statement | Verdict | Reason |
|---|---|---|
| 1. OMT is measured up to a depth of 26°C isotherm which is 129 meters in the south-western Indian Ocean during January-March | Incorrect | The 26°C isotherm lies at 50 to 100 metres; in the south-western Indian Ocean in January to March it is at about 59 metres, not 129 |
| 2. 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 | Correct | This is the main finding of the study |
OMT compared with sea surface temperature (SST):
| Point | OMT | SST |
|---|---|---|
| What it measures | Heat in the upper ocean layer | Only the top few millimetres |
| Stability | Steady; little affected by wind and cloud | Changes quickly |
| Success in predicting the monsoon | About 80 per cent | About 60 per cent |
The first part of Statement 1 is right, but the depth is wrong.
Answer: (b) 2 only.
Why each option is right or wrong
- (a) Incorrect. Statement 1 gives the wrong depth; it is about 59 metres, not 129.
- (b) CORRECT. January to March OMT can show whether the monsoon will be above or below the mean.
- (c) Incorrect. Statement 1 fails on the depth of the 26°C isotherm.
- (d) Incorrect. Statement 2 is true; OMT is a useful monsoon predictor.
Key point
OMT: mean temperature down to the 26°C isotherm (50 to 100 m; about 59 m in the south-west Indian Ocean, January to March); better monsoon predictor than SST (IITM Pune).
Remember
OMT (January to March) predicts the monsoon; 26°C isotherm is at 50 to 100 m.
Common mistakes
- Accepting Statement 1 because the 26°C isotherm part is right; the number is wrong.
- Confusing OMT with sea surface temperature.
- Thinking OMT is about global warming; here it is a monsoon forecasting tool.
Exam tip
When a statement has an exact number, the number is what is being tested. Here 129 metres replaces 59.
Sources
- Indian Institute of Tropical Meteorology, Pune — study on Ocean Mean Temperature and Indian summer monsoon rainfall (Scientific Reports, 2018)
- The Hindu — 'Ocean mean temperature can better predict Indian summer monsoon' (2018)