Polarimetric signatures of ice crystals in clouds

Cloud ice crystals have important bearing on radiative transfer and associated temperature change of the atmosphere. Furthermore, some crystals grow to precipitation sized particles that replenish the Earth's water supply. Until the advent of radar polarimetry, remote measurements of crystals in clouds consisted of attempts to obtain the ice water content (IWC) from the reflectivity factor Z. Because of their low dielectric constant and small size, ice crystals backscatter considerably weaker signal than liquid hydrometeors of the same size and concentration. Nonetheless, there is a substantial range of reflectivities that is common to both ice crystals and small drops. Therefore, the radar reflectivity by itself could not serve for discrimination between these hydrometeors. Environment temperature or knowledge of the melting layer height have been used to delineate regions of ice from rainy regions. Remarkable changes are being made in remote sensing of ice crystals thanks to the advent of radar polarimetry. The authors describe crystal signatures in the fields of polarimetric variables and suggest possibilities for quantitative estimation of IWC.