Polarimetric radar observation of the melting layer during the pre-summer rainy season over South China

Abstract

ABSTRACT The geometric and polarimetric characteristics of the melting layer (ML) during the pre-summer rainy season over South China (PRSC) are investigated from 389 S-band polarimetric radar volume scans. The existing ML detection algorithm is slightly improved, in which the ML is automatically detected by using vertical gradients of radar reflectivity factor for horizontal polarizations (Z H), and co-polar cross-correlation coefficient (ρ HV) from quasi-vertical profiles. And these profiles are obtained by azimuthal averaging of polarimetric radar variables at antenna elevation 19.5°. The comparison between the detected ML top and the 0°C isotherm heights from ERA5 demonstrates that the detection algorithm has high accuracy with an offset of 158 m. Due to larger snowflakes, the average ML thickness in PRSC is thicker (i.e. 150 m) than that in other climatic regions. The ML is characterized by large Z H, large differential reflectivity (Z DR) and small ρ HV, with average values of 32 dBZ, 0.91 dB and 0.94. Furthermore, the peak values of Z H and Z DR in the ML are obviously larger than that from rain regions and snow regions, while the opposite is true for ρ HV distribution.