UPSC Prelims 2012 · Question 49 of 98
UPSC Prelims 2012 question on Temperature Lapse Rate
- ExamUPSC CSE
- Year2012
- PaperGeneral Studies Paper I
- SubjectGeography
- TopicClimatology
- DifficultyMedium
- TypeStatement
Normally, the temperature decreases with the increase in height from the Earth’s surface, because
1. The atmosphere can be heated upwards only from the Earth’s surface.
2. There is more moisture in the upper atmosphere.
3. The air is less dense in the upper atmosphere.
Select the correct answer using the codes given below.
Show answer
Answer: C. 1 and 3 only
Verdict
Correct Answer: 1 and 3 only
Analysis
Temperature generally decreases with altitude in the troposphere due to the normal lapse rate.
On average, temperature falls by about 6.5°C for every 1,000 metres of ascent.
Statement by statement
1. The atmosphere can be heated upwards only from the Earth’s surface — Correct
The atmosphere is mainly heated from below by terrestrial radiation emitted by the Earth’s surface.
Since lower layers are closer to the heated surface, they are warmer than upper layers.
2. There is more moisture in the upper atmosphere — Incorrect
This is scientifically incorrect.
Water vapour and dust particles are concentrated mainly in the lower atmosphere. These help absorb and retain heat, while their scarcity at higher altitudes contributes to lower temperatures.
3. The air is less dense in the upper atmosphere — Correct
As altitude increases, air pressure decreases and air becomes thinner.
Less dense air has fewer molecules to absorb and retain heat, so temperature decreases with height.
Extra UPSC info
* Normal lapse rate is about 6.5°C per 1,000 metres in the troposphere.
* The troposphere is the lowest layer of the atmosphere and contains most weather phenomena.
* Temperature inversion is an exception where temperature increases with height.
* Inversion is common during long winter nights, clear skies and calm winds.
* Temperature inversion traps pollutants near the ground and causes smog, especially in urban areas.
* It can also cause fog, frost and poor visibility.
How to crack it
Temperature decreases with altitude because the atmosphere is heated from the Earth’s surface and upper air is thinner, while moisture is not greater in the upper atmosphere.