Vertical profiles of refractivity turbulence structure constant: Comparison of observations by the Sunset Radar with a new theoretical model

Vertical profiles of refractivity turbulence structure constant C2n (which is proportional to the radar volume reflectivity) from about 5 to 15 km are measured by the Sunset Radar every 50 seconds. The method of determining such profiles from the radar Doppler spectra is described. The C2n profiles for about an hour are averaged to form (C2n(radar)). The profiles of (C2n(radar)) are quite variable: on the average they decrease by about two orders of magnitude from about 5 to 15 km, and they often change by one order of magnitude from day to day at a given height. A theoretical model is developed that enables the calculation of C2n from routine rawinsonde profiles of wind, temperature, and humidity. This model is based on the assumption that the fluctuations of refractivity that scatter the radio waves are in equilibrium with homogeneous, isotropic, steady-state turbulence in the inertial subrange. An essential and new feature of this model is an estimate of the mean fraction of the radar-observed volume that is turbulent. The resulting profiles of (C2n(model)) agree well with the measured profiles of (C2n(radar)) in general shape, in changes from day to day, and in many details from kilometer to kilometer. This agreement implies that: (1) The vertical profile of C2n can be measured by Doppler radar. (2) The vertical profile of C2n can also be estimated by calculation from routine rawinsonde profiles, using our theoretical model.

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