Orlanski, I., 1973: Trapeze instability as a source of internal gravity waves. Part I. Journal of the Atmospheric Sciences, 30 (6), 1007-1016.

Abstract: We can identify the diurnal oscillation of the atmospheric boundary layer as an important source of mesoscale internal gravity waves in the lower atmosphere.
The oscillation period of these waves is a function of latitude. A definitive two-day period may be found in the equatorial regions with scales on the order of a few hundred kilometers. In particular, for a situation in which the mean stratification at any time of the day is unstable, the wavelength could be on the order of 100 km. This result suggests that some cloud clusters may be originated by this process.