A Comparison of the Turbulent Fluctuations in Clear Air Convection Measured Simultaneously by Aircraft and Doppler Radar

Abstract

A comparison between the fluctuations in the horizontal component of velocity measured simultaneously by Doppler radar and aircraft has been made in clear air convective conditions. This experiment is the first in which such a comparison was attempted where the radar return was from fine-scale refractivity fluctuations due to turbulent mixing and not from precipitation particles or artificial scatterers. Good agreement was found between the velocity spectra obtained from Doppler measurements of the variations in the mean wind field and the spectra of velocity fluctuations measured by a hot-wire anemometer. Although the velocity spectrum from Doppler radar measurements is limited to those scales larger than the dimensions of the pulse volume, the comparison with the hot-wire data shows that the spectrum of wind variations for scales smaller than the pulse volume may be confidently estimated by extrapolating the velocity spectrum along a ?5/3 slope. This result is further supported by the good agreement found between the predicted level of the velocity spectrum based on the variance of the individual Doppler spectra and the measured velocity spectra from the mean Doppler fluctuations and hot-wire anemometer data.