Waves Observed in the Planetary Boundary Layer using an Array of Acoustic Sounders

Abstract

Three acoustic sounders, with antennas having vertically-pointed beams located at the vertices of a triangle about 300 m on a side, have been used successfully to calculate horizontal phase velocities of gravity waves in the lowest 1000 m of the atmosphere. The wave parameters obtained were compared with those obtained by an array of micrographs. The results from the two independent techniques agreed well in all cases where the waves were detected by both methods. However, the acoustic-sounder array was also able to detect gravity waves propagating in an inversion overlying the convective boundary layer that were undetected by the microbarograph array because of wave attenuation in the convective region. Wave-associated vertical-velocity fluctuations inside the undulating structure were measured using Doppler techniques to an accuracy of about ±0.1 m sec−1. Vertical-velocity fluctuations of about ±0.5 m sec−1 were measured inside one wave with displacement amplitude of 120 m and wavelength of 5.5 km. From wave-associated vertical-velocity fluctuations, displacement amplitude and wave period, we could calculate the wind speed component along the wave propagation direction. This calculated wind speed component agreed reasonably well with the value derived independently from radiosonde measurements.