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 Obser vatoire de Haute-Provence (OHP). Under the classical framework of locally h omogeneous and isotropic turbulence, we propose a slightly different method for estimating the turbulent diffusivity from radar measurements. The temp erature structure parameter, C-T(2), and the vertical heat diffusivity, K-t heta, are expressed as a function of the dissipation rate of the temperatur e variance, epsilon(theta) (and not from the dissipation rate of kinetic en ergy). This parameter appears weakly dependent on unknown quantities such a s the mixing efficiency R-f/(1 - R-f) (R-f is the flux Richardson number) a nd 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 w eaker (one order of magnitude) than radar estimates using the bandwidth of the Doppler spectrum.