Estimations of aspect ratios of ice cloud particles with the WSR-88D radar

Knowing shapes of ice particles in clouds and precipitation is important for many practical applications including parameterization of cloud radiative effects in atmospheric models and remote sensing. The aspect ratio, which represents the ratio of particle minor to major dimensions, is the simplest parameter representing the overall shape of hydrometeors. Earlier studies have demonstrated that polarimetric radars capable of measuring depolarization ratio can be used for inferring mean aspect ratios of hydrometeors. Circular depolarization ratio (CDR) is especially useful because it does not depend on particle canting in the radar polarization plane. However, the polarization measurement scheme, which is now employed with most polarimetric radars, utilizes simultaneous transmission and reception (STAR) of radar signals. While CDR can potentially be reconstructed from STAR measurement variables, it requires the exact knowledge of phase shifts between horizontally and vertically polarized signals introduced by the radar hardware.

This study suggests the use of proxy CDR values, which can be directly inferred from STAR scheme measurements. Deriving proxy values makes some assumptions. The relation between CDR and its STAR measurement proxy is discussed. It is shown that the proxy values are dependent on propagation effects to lesser degree than CDR. The experimental data obtained with polarimetric WSR-88D in different meteorological environments are used to demonstrate derivations of CDR proxy values. Uncertainties of using these values for hydrometeor aspect ratio estimations are discussed.