ACOUSTIC SOUNDER OBSERVATIONS OF ATMOSPHERIC-TURBULENCE PARAMETERS IN A CONVECTIVE BOUNDARY-LAYER

Acoustic sounder observations of atmospheric turbulence parameters presented in this paper include estimates of the dissipation rate epsilon, estimates of turbulent scale lengths lambda, and uncertainties in measurements of the variance of the vertical wind sigma(w)2 caused by pulse volume filtering. The calculations are mainly restricted to periods when the convective regime is well established. Two techniques are used to determine epsilon and lambda. Structure functions and the spectral variance of the echo are used to determine epsilon. The spectrum of vertical velocities are used to calculate lambda(m) and the autocorrelation function is used to calculate lambda(e). Estimates of epsilon obtained from the spectral variance of the echo compare favorably with estimates from the structure function during convective regimes but the agreement is poor in other regimes. The autocorrelation function method for obtaining length scales yields results more reliably than the spectral method. The ratio lambda(m)/lambda(e) compares favorably with values reported in the literature except at low heights where it is markedly lower. The effects of pulse volume filtering on measurements of sigma(w)2 were found to be significant. In convective conditions, sigma(w)2 deduced from the Doppler shift of the echo can be underestimated by up to 25% and by greater amounts in other conditions.