Coherent Particle Scatter in Smoke and Cumulus Clouds

Recently, dual wavelength radar measurements of smoke and developing cumulus clouds have appeared in the literature which show a puzzling correlation between the measured radar returns. This correlation cannot easily be explained in terms of the conventional scattering mechanisms: coherent (Bragg) scattering from spatial fluctuations in clear-air refractive index and incoherent (Rayleigh) scattering from particles. In this paper, a possible explanation of the measurements is presented in terms of coherent scattering from the particles. It will also be argued that in clouds, Bragg scatter from fluctuations in water vapor content can be much smaller than from fluctuations in liquid water content, contrary to common belief.