Thursday, 7 August 2003: 11:30 AM
Deriving turbulent kinetic energy dissipation rate within clouds using ground based 94 Ghz radar.
A new technique is proposed to derive the turbulent kinetic energy dissipation rate within non-precipitating cloud using a vertically pointing 94GHz Doppler radar. The technique can be applied to both water clouds such as stratocumulus and ice clouds such as cirrus. The underlying hypothesis is that the radar targets (droplets or ice crystals) are good tracers of turbulence motions, that turbulence is isotropic and that the turbulent kinetic energy spectrum is Kolmogorov in form. The turbulent kinetic energy dissipation rate is then deduced from the computation of the variance of the mean Doppler velocity in a given time interval (typically about 30 seconds) and from an estimate of the horizontal wind obtained from model analysis. The main strength of this method is that it can be routinely implemented on a vertically pointing radar and gives a complete picture of the turbulence activity within clouds, whereas other techniques for estimating turbulent kinetic energy dissipation rate are generally obtained at a given level from aircraft data spectral analysis. Some sensitivity and validation studies will be presented as well as statistical analysis of the observed values.