Boundary layer clear-air radar echoes: origin of echoes and accuracy of derived winds

Radar reflectivity comparisons of clean-air echoes in Florida and Colorado were made at radar wavelengths of 3.5 and 10cm. These comparisons, when analyzed along with a theoretical backscattering model, indicate that the echoes result from both particulate and Bragg scattering with particulate scattering dominating in the well-mixed boundary layer. The return signal in this layer is highly horizontally polarized with differential reflectivity Z_DR values of 5-10 dB. This asymmetry causes the backscattering cross section to be considerably larger than one for a spherical water droplet of equal mass. It is concluded that insects are primarily responsible for the clear-air echo in the mixed boundary layer. -from Authors