Eddy Velocities in the Planetary Boundary Layer as Obtained from Tetroon Flights at Idaho Falls

Abstract

Tetroon flights made at the National Reactor Testing Station, Idaho Falls, during the past few years have provided values of eddy velocity within the planetary boundary layer. In this desert-like terrain the root mean square (rms) values of longitudinal, lateral and vertical velocity tend to increase with height based on daytime observations throughout the year. The respective turbulence intensities, however, decrease with height. The mean values of rms velocity increase by factors of 2–3 between winter and summer. On the basis of an extensive tetroon experiment in summer, when lapse-rate data were available, the rms vertical velocity increases markedly with increase in height, lapse rate and wind speed during the day, whereas the rms lateral velocity is proportional chiefly to wind speed. The average vertical turbulence intensity is more than twice as large as the year-average value obtained by Pasquill in England, but decreases with height in a similar manner. The variation with height, stability and wind speed of both the vertical momentum flux and the rate of production of eddy kinetic energy from the mean sheared flow are indicated.