In-flight icing hazard detection with dual and single polarimetric moments from operational NEXRADs

The application of S-band weather radars to the detection of supercooled liquid aloft has historically not been an endeavor that shows significant skill. Returned power is heavily influenced by larger frozen particles and particle classification of supercooled liquid with gate-by-gate polarized moments tend to overlap with other particle species. NCAR has begun developing an algorithm for in-flight icing based on the detection with fuzzy logic of certain spatial patterns in the moment fields that had been previously noted in research flight campaign to be associated with the presence of supercooled liquid. The algorithm was first tested in 2011 with Colorado State University's frequently calibrated CHILL research radar and it was found that all of the 20 pilot reports of moderate or greater severity of in-flight icing collected during the field study had positive S-band icing warnings. In 2012, the algorithm was tested with operational NEXRAD input for 14 cases with moderate pilot-reported severity and 19 cases with no pilot-reported icing in the accompanying radar volume. The study found a two-fold increase in radar volume warned as containing no icing when in the presence of a pilot report of no icing, and a three-fold increase in radar volume warned as containing positive icing when in the presence of a pilot report of moderate icing severity. For this study, the existing S-band codebase was mirrored in two parallel streams; one based on the dual-polarization moment inputs and the other with all reliance on dual-polarization inputs stripped out. The purpose of this work was to examine the benefits to having dual-polarization in detecting in-flight icing hazard from S-band radar. Case studies from different icing weather scenarios were analyzed and quantified in order to evaluate improvements in icing diagnosis from dual-polarization and further establish the feasability of using operational NEXRAD for this purpose.