Acoustic Sounder Observations of Atmospheric Turbulence Parameters in a Convective Boundary Layer

Abstract

Acoustic sounder observations of atmospheric turbulence parameters presented in this paper include estimates of the dissipation rate ?, estimates of turbulent scale lengths ?, and uncertainties in measurements of the variance of the vertical wind σ2w 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 ? and ?. Structure functions and the spectral variance of the echo are used to determine ?. The spectrum of vertical velocities are used to calculate ?m and the autocorrelation function is used to calculate ?e. Estimates of ? 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 ?m/?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 σ2w were found to be significant. In convective conditions, σ2w deduced from the Doppler shift of the echo can be underestimated by up to 25% and by greater amounts in other conditions.