One of the first applications proposed for earth-orbiting satellites was the observation of the atmosphere. A glance at any television weather report shows how far things have come. Pictures taken from geostationary orbit show cloud distributions over a large part of the globe, and credible forecasts utilizing satellite temperature soundings extend several days into the future. These data have had a profound influence on research as well. A recent article (“Breaking planetary waves in the stratosphere,” by M. E. Mclntyre and T. N. Palmer, Nature, vol. 303, pp. 593–600, 1983.) stated that “Satellite-borne IR radiometers are turning the Earth's stratosphere into one of the best available outdoor laboratories for observing the large scale dynamics of a rotating heterogeneous fluid under gravity.” Remote sounding data have revolutionized our understanding of the atmospheres of this and other planets.