A study of the relationship between the attenuation coefficient and radar reflectivity factor for spherical particles in clouds at millimeter wavelengths.

Because of millimeter wavelengths close to the scale of cloud particles, more and more millimeter radar systems are used to detect cloud and small precipitation particles. When using millimeter wavelength radars, the attenuation caused by cloud and precipitation particles’ scattering and absorption together with the water vapor and oxygen absorption at millimeter wavelength must be take into account. In order for the actual need of millimeter wavelengths cloud radar data processing, it is presumed that the cloud particles are sphere particles, and the cloud drop size spectra follow the K-M distribution and the rain drop size spectra follow the Gamma distribution by sampling them each for 1330 times, and by adopting the Mie scatter theory formula for computing scattering, absorbing and backscattering cross-sections, the attenuation coefficient k and radar reflectivity factor Z are calculated for 3.2 and 8.6 mm wavelengths and the k-Z relationship is obtained. The results show that the attenuation at the 3.2 mm is 5-10 times larger than that at 8.6 mm under the same conditions of drop size spectra. The k-Z relationship coefficients are available for attenuation correction of millimeter radars, and the formulas can be applied into correction for the 3.2 and 8.6 mm radar attenuation computations. 