Question 59 from UPSC CSE 2023 - Geography

Question

With reference to the Earth's atmosphere, which one of the following statements is correct?

IASCODEX · Accepted Answer

Correct Option: C. Infrared waves are largely absorbed by water vapour that is concentrated in the lower atmosphere.

Strategy: - Focus on the specific characteristics of insolation, infrared radiation, and the Earth's atmospheric absorption.
- **Statement C is correct:** Water vapor exists mostly in the lower atmosphere and is the main absorber of infrared radiation.
- **Incorrect options are ruled out because:**
    - The equator-pole insolation ratio is significantly less than 10:1.
    - Insolation is primarily visible and ultraviolet light, not two-thirds infrared.
    - Infrared radiation is not within the visible spectrum.

Key Info: Insolation refers to incoming solar radiation received at Earth's surface, predominantly as shortwave energy in the form of ultraviolet and visible light (wavelengths between 0.39 and 0.76 micrometres). The amount of insolation at the equator is about 4 to 5 times that at the poles, not ten times.

Infrared radiation, or longwave radiation (4-30 micrometres), is mostly re-emitted by the Earth's surface rather than delivered directly from the sun.

Water vapor, prevalent in the lower troposphere, is the most significant greenhouse gas and strongly absorbs infrared radiation, playing a key role in Earth's heat balance.

The visible spectrum covers 400-700 nanometres; infrared lies beyond this range and is not visible to the human eye. In Earth's energy budget, outgoing longwave infrared radiation is crucial for maintaining the greenhouse effect, and its absorption by water vapor results in atmospheric warming.

IASCODEX · Answer

Option A: The total amount of insolation received at the equator is roughly about 10 times that received at the poles.

IASCODEX · Answer

Option B: Infrared rays constitute roughly two-thirds of insolation.

IASCODEX · Answer

Option D: Infrared waves are a part of the visible spectrum of electromagnetic waves of solar radiation.