Question

(a) How are the boundaries between the regions of the atmosphere determined? (b) Explain why the stratosphere, which is more than 20 miles thick, has a smaller total mass than the troposphere, which is less than 10 miles thick.

Short answer

(a) Atmospheric region boundaries are determined by changes in temperature and pressure with altitude, marked by boundary layers called pauses, where temperature and pressure profiles change from one region to another. (b) The troposphere has a higher total mass than the stratosphere, despite being less thick, due to its higher air density and pressure, with most of the atmosphere's mass concentrated near Earth's surface.

Step-by-step solution

Understanding the Earth's Atmosphere

The Earth's atmosphere is divided into several layers based on factors such as temperature and pressure. The primary layers are the troposphere, stratosphere, mesosphere, thermosphere, and the exosphere. Each layer has its unique characteristics, and the boundaries between these layers are determined by the changes in temperature and pressure.

Part (a): Determining the Atmosphere Region Boundaries

The boundaries between the atmospheric layers are mostly determined by the changes in temperature with altitude. These boundary layers are called pauses. For example, at the tropopause, which is the boundary between the troposphere and the stratosphere, the temperature stops decreasing with altitude and starts to increase as we move higher into the stratosphere. Similarly, the stratopause and mesopause mark the boundaries between the stratosphere and mesosphere, and the mesosphere and thermosphere, respectively.

Part (b): Mass of the Troposphere and Stratosphere

The atmosphere gets thinner the higher you go. This is because the Earth's gravity pulls air molecules closer to the Earth's surface, making the density of air greater near the surface. Most of the atmosphere's mass is concentrated near the Earth's surface within the troposphere. As we move upwards through the troposphere, the air pressure and density decrease markedly. In contrast, the stratosphere has lower air pressure and density compared to the troposphere. Although the stratosphere is much thicker than the troposphere, its air density is much lower. As a result, the overall mass of the stratosphere ends up being less than that of the troposphere. In summary,

Summary

(a) The boundaries between the regions of the atmosphere are determined by changes in temperature and pressure with altitude. The boundary layers, called pauses, are where the temperature and pressure profile changes from one region to another. (b) The troposphere, although less than 10 miles thick, has a higher total mass than the stratosphere, which is more than 20 miles thick. This is due to the higher air density and pressure in the troposphere compared to the stratosphere, with most of the atmosphere's mass concentrated near the Earth's surface.