With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct? 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. 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. Select the correct using the code given below:
Contents15
- A1 only
- B2 only
- CBoth 1 and 2
- DNeither 1 nor 2
Show answer
Answer: (B) 2 only
Ocean Mean Temperature (OMT) is a newer, more reliable parameter for weather prediction.
Statement 1 (26°C isotherm at 129 meters in SW Indian Ocean) — NOT CORRECT: The 26°C isotherm depth varies from 50-100 metres generally, and in the Southwestern Indian Ocean during January-March, the mean depth is only 59 metres — not 129 metres.
Statement 2 (OMT is a better predictor of monsoon than SST) — CORRECT: Traditional Sea Surface Temperature (SST) has only 60% success rate in predicting Indian summer monsoon. OMT, developed by scientists at Pune's IITM, has 80% success rate. This is because SST only measures the top few millimetres of the ocean and is easily affected by winds, evaporation, and clouds. OMT measures temperature down to the 26°C isotherm depth, making it more stable and reliable.
Answer: B (2 only).
Key Takeaway: OMT (80% accuracy) > SST (60% accuracy) for monsoon prediction. OMT measures deeper ocean temperature, making it more stable. The 26°C isotherm is at 50-100m depth, not 129m.
OMT has 80% accuracy in predicting monsoons compared to traditional Sea Surface Temperature which has only 60% accuracy.
Scientists at IITM Pune developed OMT as a more reliable alternative because it measures temperature down to the 26°C isotherm depth rather than just the surface layer affected by winds and evaporation.
The question tests understanding of specific depth measurements and the practical application of OMT in monsoon forecasting.
Ocean Mean Temperature (OMT)
Geography Ocean Mean Temperature OMT 26°C isotherm
Ocean Mean Temperature (OMT): Definition, Measurement & UPSC Facts
OMT is ocean temperature measured from surface down to 26°C isotherm depth
26°C isotherm is typically at 50-100 metres depth (not 129m as in Statement 1)
In SW Indian Ocean during Jan-Mar, 26°C isotherm is at 59 metres depth
Developed by scientists at IITM Pune for better weather prediction
What is OMT
Ocean Mean Temperature (OMT) is the average temperature of ocean water from the surface down to the depth where water temperature reaches 26°C (called the 26°C isotherm). Unlike traditional methods that only measure surface temperature, OMT captures the thermal profile of the upper ocean layer.
OMT vs SST Comparison
Parameter | Ocean Mean Temperature | Sea Surface Temperature |
|---|---|---|
Measurement Depth | Surface to 26°C isotherm (50-100m) | Top few millimetres only |
Stability | More stable - less affected by daily variations | Less stable - easily affected by wind, clouds |
Monsoon Prediction Success | 80% accuracy | 60% accuracy |
Developed By | IITM Pune scientists | Traditional method |
Key Advantage | Captures thermal structure of upper ocean | Quick surface reading |
26°C Isotherm Facts
26°C isotherm = the depth where ocean temperature drops to exactly 26°C
Typical depth range: 50-100 metres across different ocean regions
In SW Indian Ocean during January-March: average depth is 59 metres
Depth varies by season, location, and ocean currents
Deeper 26°C isotherm indicates warmer upper ocean = more energy for weather systems
Why OMT Works Better
OMT is superior for monsoon prediction because it measures the thermal energy content of the upper ocean layer. This thermal energy directly influences evaporation rates, atmospheric heating, and monsoon circulation patterns. SST only captures surface conditions which change rapidly due to wind and solar heating.
Statement 1 trap: 26°C isotherm at 129 metres in SW Indian Ocean - actual depth is 59 metres
Don't confuse OMT depth range (50-100m) with the specific SW Indian Ocean depth (59m)
OMT ≠ SST - OMT measures deeper, SST measures surface only
80% vs 60% success rates - OMT is more accurate than SST for monsoon prediction
Monsoon Prediction Methods
Geography monsoon rainfall long-term mean
Monsoon Prediction: Traditional vs Modern Methods
Sea Surface Temperature (SST) has 60% accuracy in monsoon prediction
Ocean Mean Temperature (OMT) has 80% accuracy - newer, better method
Indian summer monsoon prediction uses ocean temperature as key indicator
IITM Pune developed OMT method for improved forecasting
Ocean-Monsoon Connection
Ocean temperatures directly influence monsoon strength because warmer oceans provide more moisture and thermal energy for monsoon circulation. The Indian Ocean's thermal state during pre-monsoon months (Jan-Mar) sets up conditions for the upcoming southwest monsoon (Jun-Sep).
Monsoon Prediction Methods
Method | What it Measures | Success Rate | Key Limitation |
|---|---|---|---|
Sea Surface Temperature | Top few mm of ocean | 60% | Too variable, affected by wind/clouds |
Ocean Mean Temperature | Surface to 26°C isotherm | 80% | Newer method, needs more validation |
El Niño/La Niña | Pacific Ocean temperatures | Moderate | Regional focus, doesn't capture Indian Ocean |
Statistical Models | Multiple atmospheric parameters | Variable | Complex, requires extensive data |
Why OMT is Superior
Thermal stability - deeper measurement is less affected by daily weather changes
Heat content - captures actual energy available for monsoon circulation
Pre-monsoon assessment - Jan-Mar OMT helps predict Jun-Sep monsoon strength
Reduced noise - filters out surface fluctuations that mislead SST-based predictions
How OMT Predicts Monsoon
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Measure OMT**
January-March OMT data from Indian Ocean`"]
s2["`**Compare with Long-term Mean**
Check if current OMT is above or below historical average`"]
s3["`**Thermal Energy Assessment**
Higher OMT = more ocean heat = stronger monsoon potential`"]
s4["`**Monsoon Forecast**
Predict whether upcoming monsoon will be above/below normal`"]
s1 --> s2
s2 --> s3
s3 --> s4Don't reverse the accuracy rates: OMT = 80%, SST = 60% (not the other way)
January-March timing is crucial - this is when OMT is measured for monsoon prediction
OMT predicts monsoon strength, not exact rainfall amounts or dates
IITM Pune developed OMT method - don't confuse with other meteorological institutes
Southwestern Indian Ocean
Geography south-western Indian Ocean January–March
Southwestern Indian Ocean: Location & Thermal Characteristics
SW Indian Ocean region is crucial for monsoon prediction studies
26°C isotherm depth is 59 metres during Jan-Mar (not 129m)
Bounded by East Africa, Madagascar, and Mauritius region
Geographic Definition
The Southwestern Indian Ocean encompasses waters off East Africa, around Madagascar, Mauritius, Réunion, and extending towards the Seychelles. This region is critical for monsoon studies because it influences the moisture supply and thermal conditions for the Indian monsoon system.
Regional Map
Source: Britannica — Indian Ocean | History, Map, Depth, Islands, & Facts | Britannica · www.britannica.com
Thermal Characteristics
Warm tropical waters throughout the year due to equatorial location
26°C isotherm depth varies seasonally - shallower in winter, deeper in summer
January-March period represents pre-monsoon thermal state
Ocean heat content in this region influences monsoon circulation patterns
26°C Isotherm Depths by Region
Ocean Region | Typical Depth Range | SW Indian Ocean (Jan-Mar) | Significance |
|---|---|---|---|
Global Average | 50-100 metres | 59 metres | Within normal range |
Arabian Sea | 40-80 metres | Variable | Affects monsoon onset |
Bay of Bengal | 60-120 metres | Variable | Influences monsoon intensity |
Equatorial Indian | 80-150 metres | Deep thermocline | Warm pool region |
Key trap: Statement 1 claims 129 metres depth - actual depth is 59 metres
SW Indian Ocean ≠ entire Indian Ocean - it's a specific southwestern region
January-March timing is specific to pre-monsoon thermal assessment
Don't confuse with Arabian Sea or Bay of Bengal depth measurements