Polarimetric Radar Detection of the Melting Layer using X- and S-band Frequencies

This research centers on the use of the Colorado State University-University of Chicago-Illinois State Water Survey (CSU-CHILL) Radar to detect melting layers within storms. The CSU-CHILL radar has the unique distinction of being able to make both dual-polarization and simultaneous dual-frequency (S- and X-band) measurements. Since different wavelength sizes occur between the S-band (larger) and X-band (smaller), hydrometeors will enter a Mie backscattering regime from a Rayleigh one at smaller diameters for the X-band than for the S-band. This change in backscattering causes changes in several different radar moments. By comparing these Mie backscattering influenced moments at the X-band against the typical Rayleigh backscattering at the S-band, one can detect where large hydrometeors may be present, such as large aggregates within the melting layer. This project examines archived radar data from the CHILL Radar as far back as 1995, as well as new data obtained throughout the research. Results found several bright band cases having lower ρ_hv values and higher standard deviation of ϕ_dp values in X-band when comparing to S-band. By comparing polarimetric radar variables between the two bands, melting layer categories have been developed based on how various polarimetric variables compared with each other in X- and S-band. Possible occurrences of Mie scattering are evident in S-band, while definite Mie scattering events were seen at X-band.