Question
With reference to the Earth's atmosphere, which one of the following statements is correct? (2023)
Correct Option
Infrared waves are largely absorbed by water vapour that is concentrated in the lower atmosphere.
Incoming solar radiation includes a significant portion of infrared radiation. However, the statement primarily refers to the longwave infrared radiation re-emitted by the Earth's surface after absorbing solar energy. This terrestrial infrared radiation is effectively absorbed by greenhouse gases present in the atmosphere. Water vapour is the most abundant and potent natural greenhouse gas, predominantly concentrated in the lower atmosphere (troposphere). Its absorption of terrestrial infrared radiation plays a crucial role in trapping heat and regulating Earth's surface temperature, contributing to the natural greenhouse effect.
Incorrect Options
1) The total amount of insolation received at the equator is roughly about 10 times that received at the poles.
While the equator receives significantly more insolation than the poles due to factors such as the higher angle of incidence and shorter atmospheric path length, the difference is not as high as 10 times. The ratio is generally estimated to be closer to 2.5 to 3 times, varying with seasons.
2) Infrared rays constitute roughly two-thirds of insolation.
Incoming solar radiation is composed of approximately 9% ultraviolet radiation, 41% visible light, and 50% infrared radiation. Therefore, infrared rays constitute roughly half of the insolation, not two-thirds. Visible light forms the largest single component.
4) Infrared waves are a part of visible spectrum of electromagnetic waves of solar radiation.
The electromagnetic spectrum comprises various types of radiation, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Infrared waves occupy the region of the spectrum with wavelengths longer than visible red light but shorter than microwaves. The visible spectrum is a narrow band that humans can perceive, ranging from approximately 400 nm (violet) to 700 nm (red). Infrared waves are distinct from and lie outside the visible spectrum.