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<br />distributed and that they may playa much more important role t.han <br />previously thought. Analysis of ATS-3 satellite film loops from June <br />1972 to July 1973 has shown that 37 percent of the 395 days observed <br />had distinctive cloud motion typical of gravity waves. These c:loud <br />patterns are readily identified by par'allel bands of 1 ight and dark <br />oriented normal to the propagation. Upward motion along the waive is <br />associated with local condensation where saturation is possible, <br />whereas the dark banks are associated with sinking motion which <br />results in evaporation and cloud dissipation (see figure 1). <br /> <br />II. Theoretical Description <br /> <br />Gravity waves are internal atmospheric waves which develop along <br />strong density stratification boundaries under both gravitational <br />and Coriolis forces. They are disturbances in which buoyancy acts <br />as the restoring force on parcels displaced from hydrostatic equilib- <br />rium. There is, thus, a direct oscillatory conversion between <br />potential and kinetic energy in the wave motion. Gravity waves can <br />be produced in the atmosphere under conditions of heterogeneity due <br />to static stability that develops when the environmental lapse rate <br />is less than the adiabatic lapse rate.. The atmosphere can support <br />short internal gravity waves and long external gravity waves. Short <br />waves (~ !: 10 km) have been associ ated with 1 ee waves and <br />billow clouds. These waves have sign'ificant vertical motion upwards <br /> <br />2 <br />