Question

Which of the following is the coldest region of the atmosphere?
A.Thermosphere
B.Mesosphere
C.Troposphere
D.Stratosphere

Answer 1

Hint:The atmosphere is divided into layers on the basis of change of temperature with the altitude in that layer that is the layer’s temperature gradient. The temperature gradient of each layer will vary. There is an increase in temperature with altitude whereas in some layers it decreases too. The heat source of the layer helps to determine the temperature gradient of each layer.

Complete step by step answer:
The layers of the atmosphere starting from the surface of the earth is as follows: troposphere, stratosphere, mesosphere, thermosphere, ionosphere, and exosphere.
The thermosphere is the layer below the exosphere. It starts just above the mesosphere and it can extend upto height of 600 km. Aurora and satellites occur in this area. Its temperature increases with altitude due to the absorption of highly energetic solar radiation. The temperature can go as high as 2713 K.
The stratosphere lies below the mesosphere. It starts just above the troposphere and extends to 50 kilometers high. It consists of the ozone layer which also protects us from the harmful UV radiations. Here, the temperature increases with altitude because the ozone layer absorbs the UV radiation from the sun. The temperature ranges from 220 K to 260 K.
The troposphere starts at the earth’s surface and extends 14.5 kilometers high. In this region the increase in altitude leads to the decrease in temperature. The temperature varies from 290 K to 222 K.
The mesosphere starts just above the stratosphere and it can extend upto height of 85 kilometers. It lies below the thermosphere. The mesospheric temperature gradually decreases with increasing altitude. The temperature may decrease to as low as 100 K. Therefore, it is the coldest region of the atmosphere.
Hence, the correct answer is (B) Mesosphere.


Note:
Temperatures in the mesosphere decrease with altitude because there are only a few gas molecules in this region to absorb the sun’s radiation. The heat source is the stratosphere below. The heat source is the stratosphere below. The temperatures in the mesosphere can vary with the latitude and season. To be precise, it is the top of the mesosphere (known as mesopause) that is the coldest part of the atmosphere.