The motion of that portion of the atmosphere that extends in altitude roughly from 10 to 100 km (6 to 60 mi). Interest in the middle atmosphere has been fueled by concerns over the Earth's environment, and in particular by the discovery of the ozone hole in the Antarctic lower stratosphere, together with predictions of greenhouse warming. Among the most difficult and important tasks in atmospheric science are unequivocal determinations of long-term changes in both amount of ozone and greenhouse-induced global temperature. Both are intimately related to the composition, structure, and dynamical motions in the middle atmosphere.