Melting Layer Impact on the Radar Rainfall Estimation Using the Specific Attenuation

Radar quantitative precipitation estimation (QPE) using specific attenuation (RA) has demonstrated advantages of being immune to partial beam blockage, miscalibration and attenuation. Moreover, RA approach is less sensitive to the variability of drop size distribution than other radar-rainrate relations. However, the attenuation field is highly related to media dielectric constant and the RA approach can only be applied in areas where the radar beam is sampling pure liquid phase of precipitation. Therefore, an accurate identification of the melting layer bottom is important for a high quality RA QPE.

In this work, the impact of melting layer on RA based rainfall estimation is examined. Two methods of the melting layer bottom identification are tested. The first method uses a sounding at the radar site and a temperature threshold to determine the maximum range in a given tilt within which RA can be applied without potential contamination from the melting layer. The second method uses a 2-D freezing level height as a reference and determines the maximum ranges in a tilt radial by radial based on correlation coefficient and differential phase. The performance of RA QPE with different melting layer schemes is assessed with selected cases and results will be presented at the conference.