Airborne Hot-Film Measurements of the Small-Scale Structure of Atmospheric Turbulence During GATE

Abstract

Fluctuations of temperature, horizontal velocity and vertical velocity were measured at scales from 50 m to 5 cm with airborne hot-film anemometers at altitudes of 150 and 900 m in clear air, and in subcloud air with and without rainfall. Although nearly inertial subrange spectral behavior was often present at scales smaller than 20 m, significant regions existed where inertial behavior did not appear until scales smaller than a few meters were reached. The energy dissipation rate varied intermittently by two orders of magnitude or more over scales ranging from 100 m to several kilometers. High Reynolds number intermittency effects were observed in the temperature spectra. In an anomalous region, here called a ?dry hole,? the microstructure of the velocity and temperature fields was radically different from that of the surrounding environment. Spectral intensity decreased by an order of magnitude and spectral shape was definitely non-inertial. Despite these changes, the probability distribution of the energy dissipation seemed to remain close to log-normal as did the distribution in the surroundings.