Estimates of turbulent parameters in the lower stratosphere - upper troposphere by radar observations: A novel twist

The turbulence parameters in the upper troposphere - lower stratosphere are estimated from the backscattered power of a VHF radar located at the Observatoire de Haute-Provence (OHP). Under the classical framework of locally homogeneous and isotropic turbulence, we propose a slightly different method for estimating the turbulent diffusivity from radar measurements. The temperature structure parameter, C-T(2), and the vertical heat diffusivity, K-theta, are expressed as a function of the dissipation rate of the temperature variance, epsilon(theta) (and not from the dissipation rate of kinetic energy). This parameter appears weakly dependent on unknown quantities such as the mixing efficiency R-f/(1 - R-f) (R-f is the flux Richardson number) and the vertical stratification partial derivative<(theta)over bar>/partial derivative z. Our estimations of epsilon(theta) are of the same order as in situ measurements. The inferred diffusivity K-theta appears considerably weaker (one order of magnitude) than radar estimates using the bandwidth of the Doppler spectrum.