(1) Now at NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
Wave number spectra from Nimbus 7 temperature-humidity infrared radiometer 6.7-micron water vapor data are analyzed using series 4800 km long, in regions free of high clouds and frontal zones. In these regions, the brightness temperatures approximate temperatures on a water vapor isosteric (constant density) surface, rather than averages over a broad vertical layer. Power above the noise can be extracted down to wavelengths of about 60 km. Fitting the power spectrum versus horizontal wave number k to a k^(-n) power law for wavelengths from 60 to a few hundred kilometers gives slopes of n= 2.7 to 3.0, depending on the exact wave numbers that are fitted. Thunderstorms and convective cloud systems may constitute an energy source for the reverse energy cascade which produces a -5/3 spectral slope. Our results suggest that when these features are not present a -3 slope may govern the motion at scales smaller than it has heretofore been observed.