Polarimetric Radar Relations for Quantification of Snow Based on Disdrometer Data.

Accurate measurements of snow amounts by radar are very difficult to achieve. The inherent uncertainty in radar snow estimates that are based on the radar reflectivity factor Z is caused by the variability of snow particle size distributions and snow particle density as well as the large diversity among snow growth habits. In this study, a novel method for snow quantification that is based on the joint use of radar reflectivity Z and specific differential phase KDP is introduced. An extensive dataset of 2D-video-disdrometer measurements of snow in central Oklahoma is used to derive polarimetric relations for liquid-equivalent snowfall rate S and ice water content IWC in the forms of bivariate power-law relations S = γ1Kγ1 DPZβ1and IWC5γ2Kγ2 DPZβ2, along with similar relations for the intercept N0s and slope Ls of the exponential snow size distribution. The physical basis of these relations is explained. Theirmultipliers are sensitive to variations in the width of the canting angle distribution and to a lesser extent the particles' aspect ratios and densities, whereas the exponents are practically invariant. This novel approach is tested against the S(Z) relation using snow disdrometermeasurements in three geographical regions (Oklahoma,Colorado, and Canada). Significant improvement in snowestimates relative to the traditional Z-based methods is demonstrated. [ABSTRACT FROM AUTHOR]