WAVE NUMBER SPECTRA FROM TEMPERATURE-HUMIDITY INFRARED RADIOMETER 6.7-MICRON WATER VAPOR DATA


G. L. Manney(1), and J. L. Stanford, Department of Physics and Astronomy, Iowa State University, Ames, IA 50011

(1) Now at NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena.


J. Geophys. Res., 95, 909-913 (1990)


Abstract

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.