Relationship between ice water content and equivalent radar reflectivity for clouds consisting of nonspherical ice particles

摘要

This study investigates the relationship between ice water content (IWC) and equivalent radar reflectivity (Z e ) at 94 GHz for clouds consisting of nonspherical ice particles with geometrical shapes of hexagonal solid and hollow columns, plates, 6-branch bullet rosettes, aggregates, and droxtals. The IWC is calculated from a set of 1119 ice particle size distributions (PSDs) measured during several field campaigns, which are discretized to 46 size bins based on particle maximum dimensions ranging from 2 to 10500 μm. The Z e at 94 GHz is calculated from the radar backscattering properties obtained by integrating over the PSD and chosen particle habit distributions. The influence of ice habit on the Z e -IWC relationship is investigated for ice clouds composed of individual ice particle habits and a habit mixture. The Z e -IWC relationship is found to be sensitive to cloud effective particle size and cloud temperature. For an ice cloud with a given IWC, the Z e tends to increase with increasing effective particle size. Similarly, the Z e generally increases with increasing cloud temperature, at least for clouds with IWC over 0.01 g/m3. These features are consistent with the observed relationship between effective particle sizes and cloud temperatures. The present investigation of the effect of temperature on the Z e -IWC relationship indicates that including temperature in the Z e -IWC relationship may not improve the estimates of IWC. However, the dependence of the Z e -IWC relationship on the effective particle size within a given temperature range is more pronounced, and may be potentially useful for inferring the cloud effective particle size from the Z e -IWC relationship.