Retrieval of the Convective Clouds Turbulence Structure Using High-Resolution Vertically Pointed Doppler Radar Data

The high-resolution vertically pointed Doppler FMCW radar PARSAX was used for the investigation of turbulence in isolated convective clouds. The radar measures reflectivity, the mean Doppler velocity, and the spectrum width in clouds that are crossing the radar beam due to horizontal wind. The measured spectrum width is used to separate the air velocity from the sedimentation velocity of cloud drops in every reflecting volume. The transverse structure functions and the vertical velocity spectra were estimated for convective clouds which have different evolution stages and cloud top heights. The slopes of these structure functions and spectra, characterizing the kinetic energy transfer, were obtained. Three layers with different regimes of cascade energy transfer were found with an increase in the height. The first layer with a spectra slope of −1 was observed in the atmospheric boundary layer up to the height of 2 km. A layer with a classic Kolmogorov slope of -5/3 was observed above this layer, at a height of 2…5 km. At the upper part of the cloud appears a layer that tends to the Bolgiano-Obukhov slope of -11/5 generated by buoyancy forces influencing that part of the cloud. The measured spectra also made it possible to non-rigorously estimate the profiles of the turbulence kinetic energy, turbulent dissipation rate, and associated with velocity fluctuations turbulent diffusion coefficient.