The internal refractive index spectra of clouds from forward scatter radar observations

There are occasions when radar return from a volume of cloud is unexpectedly large if it is presumed to be caused by the classical mechanism of incoherent scatter from individual cloud droplets. Such a mechanism predicts the scattered power to be proportional to the inverse 4th power of the wavelength. The observed weaker wavelength dependence could result from Bragg-coherent scatter from the ensemble of droplets or it could result from an enhancement by the cloud of inhomogeneities in the dielectric constant of the gaseous medium within the cloud. Both mechanisms are discussed and compared with data acquired in a forward scatter mode by the WPL 3 cm radar system. Observed differences between the in-cloud and out-of-cloud refractive index spectra are discussed.