Atmospheric Layers Temperature Profile Analysis

The Earth's atmosphere is divided into several layers, each with unique characteristics, including how temperature changes with altitude. This question asks us to identify the atmospheric layers where the temperature *decreases* as the *height increases* from the Earth's surface.

Troposphere Temperature Profile

The Troposphere is the layer closest to the Earth's surface, extending up to about 7-20 km. It's where most weather phenomena occur.

• In the Troposphere, the temperature generally decreases with an increase in height.
• This happens because the primary source of heat is the Earth's surface, which absorbs solar radiation and warms the air above it through conduction and convection. As you move higher, you get further from this heat source, and the air becomes less dense, expands, and cools.

Stratosphere Temperature Profile

The Stratosphere is the layer above the Troposphere, extending up to about 50 km.

• In the Stratosphere, the temperature generally increases with an increase in height.
• This temperature inversion is caused by the presence of the ozone layer (O₃), which absorbs harmful ultraviolet (UV) radiation from the sun. This absorption process heats the Stratosphere.

Mesosphere Temperature Profile

The Mesosphere is the layer above the Stratosphere, extending up to about 85 km.

• In the Mesosphere, the temperature once again decreases with an increase in height.
• This happens because there are very few molecules in this layer to absorb solar radiation, and the air is extremely thin. It's the coldest layer of the atmosphere, with temperatures reaching as low as -90°C.

Thermosphere Temperature Profile

The Thermosphere is the layer above the Mesosphere, extending to about 600 km or more.

• In the Thermosphere, the temperature increases sharply with an increase in height.
• This is due to the absorption of high-energy X-rays and UV radiation from the sun by the few gas molecules present (mostly oxygen and nitrogen). While the temperature is very high, the air is so thin that it would feel very cold to us.

Identifying Layers with Decreasing Temperature

Based on the analysis of each layer:

• Troposphere (A): Temperature decreases with height.
• Stratosphere (D): Temperature increases with height.
• Mesosphere (B): Temperature decreases with height.
• Thermosphere (C): Temperature increases with height.

Therefore, the layers where the temperature decreases with the increase in height are the Troposphere and the Mesosphere.

This corresponds to options (A) and (B) only.