Polarimetric Radar Relations for Snow Estimation Based on Disdrometer Data

Accurate measurement of snow amounts by radar is very difficult to achieve. The inherent uncertainty in radar snow estimates based on the radar reflectivity factor Z is caused by the variability of snow particle size distributions and snow particle density as well as large diversity of snow growth habits.

In this study, a novel methodology for snow quantification based on the joint use of radar reflectivity Z and specific differential phase K_DP is introduced. An extensive dataset of 2D video disdrometer measurements of snow in central Oklahoma is used to derive polarimetric relations for snow water equivalent rate (S) and ice water content (IWC) in the forms of bivariate power-law relations S = a₁K_DP^b₁Z^c₁ and IWC = a₂K_DP^b₂Z^c₂, along with similar relations for the intercept N_0s and slope Λ_s of exponential snow size distribution. The polarimetric relations dramatically reduce the impact of the variability of snow particle size distributions on the S and IWC estimates. This novel approach is tested against the standard S(Z) relation using snow disdrometer measurements in three geographical regions (Oklahoma, Colorado, and Canada). It demonstrated significant improvement in snow estimates compared to the traditional Z-based methods.