Two Layers of Melting Ice Particles Within a Single Radar Bright Band : Interpretation and Implications

Abstract

Dual-frequency dual-polarization radar observations of the melting of two ice populations in a stratiform rainfall event are presented. The observed phenomenon occurs as a two-layer linear depolarization ratio (LDR) signature in a single radar bright band. Doppler spectra observations show that the upper LDR layer is caused by the melting of ice needles, potentially generated by the rime-splintering process, while the lower one is mainly due to the melting of background ice particles formed at the cloud top. The melting signal of small needles acts as a unique benchmark for detecting the onset of melting and is used to verify the current methods for the identification of melting layer boundaries. The radar-derived characteristics of the melting layer are found to be dependent on the radar variable and frequency used. The implications of the presented findings for radar-based studies of precipitation properties in and above the melting layer are also discussed.