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atmosphere The envelope of air surrounding the earth and bound to it more or less permanently by virtue of the earth's gravitational attraction. The earth's atmosphere extends from the solid or liquid surface of the earth to an indefinite height, its density asymptotically approaching that of interplanetary space. At heights of the order of 80 kilometers (50 statute miles) the atmosphere is barely dense enough to scatter sunlight to a visible degree. The atmosphere may be subdivided vertically into a number of atmospheric shells, but the most common basic subdivision is that which recognizes a troposphere from the surface to about 10 kilometers, a stratosphere from about 10 kilometers to about 80 kilometers, and an ionosphere above 80 kilometers. Most weather that affects us on the surface lies within the troposphere. See also standard atmosphere and lapse rate. WXT G157 is a diagram of the vertical structure of the atmosphere.

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