The impact of the cascading structure of precipitation on reflectivity measurements

Reflectivity measurements rely on the assumption that hydrometeors are randomly distributed in space. However, the precipitating medium as been shown to possess a cascade-like structure over a large range of scales. It as also been advocated that due to inertia and sorting processes, this structure is destroyed at scales smaller than a few tens to hundreds of meters.

We examine if the cascading structure of the precipitating medium and the scale at which this structure is destroyed will impact on reflectivity measurements.

Simulations are performed from a modified fractal field representing a realistic number of rain drops in a radar resolution volume. It is found that a radar emitting a perfectly square pulse would be very sensitive to the amount of drops in the first and last few wavelength of a resolution volume because of constructive/destructive interference of the returns. Given a trapezoidal pulse rising/falling in a distance of a few wavelengths, reflectivity measurements become independent of the scales at which the structure break occurs.