- A gaseous envelope gravitationally bound to a celestial body (e.g., a planet, its satellite, or a star).
Different atmospheres have very different properties. For instance, the atmosphere of Venus is very thick and cloudy and is responsible for producing the very high surface temperatures on that planet by virtue of its greenhouse effect. On the other hand, the Martian atmosphere is very sparse. Earth's atmosphere is intermediate between these two extremes. It is distinguished from all other known atmospheres by its very active hydrologic cycle. One need merely examine pictures of Earth from space to appreciate the intricate cloud structures. Water in Earth's atmosphere plays a very important energetic role. Because of its chemical composition, most incoming sunlight passes through Earth's atmosphere and is absorbed at the ground. This heat is transported to the atmosphere through sensible heat and moisture fluxes. Upon condensation, this heat is then released into the atmosphere. The thermodynamics of water vapor is the crucial factor to the existence of severe storms in Earth's atmosphere. Since more solar radiation is absorbed in the Tropics than at high latitudes, the atmosphere (and the ocean) transports heat poleward. These motions are heavily altered by the effects of planetary rotation to determine the atmospheric general circulation. Fluid dynamical instabilities play a large role in this circulation and are crucial in determining the fluctuations in this circulation that we call "weather."The atmosphere may be conceptually divided into several layers, according to its thermal and ionization structure. The region where the temperature decreases because of the upward heat flux is called the troposphere. Above it, there is a layer in which temperature increases upward because of ozone absorption of solar radiation, the stratosphere. Above this, the temperature decreases in the mesosphere, and above this, in the thermosphere, the extremely energetic radiation causes temperature to increase with height out to the outer reaches of Earth's atmosphere, the exosphere. Within the mesosphere and thermosphere, solar radiation is sufficiently energetic to ionize gases. This produces the ionosphere.
Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact firstname.lastname@example.org. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.