The Earth's atmosphere provides us with a multitude of phenomena whose complexity may make them seem beyond understanding. However, we can apply many of the basic physical ideas that we have already discussed for stars, such as hydrostatic equilibrium and energy transport, to form a reasonable understanding of those phenomena. With the aid of supercomputers, these ideas have been applied to the atmosphere in some detail. Also, the concepts that we develop in studying the Earth's atmosphere will be directly applicable to studying the atmospheres of other planets. In fact, one of the checks on computer models for the Earth's atmosphere is to see if they can predict the properties of the other atmospheres in the Solar System. In this section we look at some of the concepts common to all planetary atmospheres, and see how they apply to the Earth's atmosphere.
Though the Earth is a sphere, and the atmosphere is a spherical shell around it, the atmosphere is very thin (a few hundred kilometers) compared with the radius of the Earth (6380 km). This means that, if we stand on the ground, the effects of the curvature in the atmosphere are very small. This is shown in Fig. 23.10(a). This tells us that we can treat the atmosphere like a thin layer, and only worry about how things change as we go to higher altitudes. In studying the Earth's atmosphere, we want to understand how the pressure changes with altitude (the pressure distribution), how the temperature changes with altitude (temperature distribution), what the composition is, and how it changes with altitude, and how energy is transferred through the atmosphere.
In studying the atmosphere, it is convenient to divide it into layers, according to what conditions are prevalent. These layers are shown in part (b) of Fig. 23.10. Each of the layers has a different
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