In situ Icing Verification

By late 2013, the dual polarization upgrade will be complete for the entire NEXRAD network in the United States. The primary, functional upgrade is the ability to significantly improve estimates of the type of bulk scatterers contributing to the radar returns. To distinguish non-weather from rain, snow, and hail scatterers is especially valuable to the Federal Aviation Administration (FAA). MIT Lincoln Laboratory (LL) continues to develop and improve upon dual polarization based algorithm products for use in current and future FAA aviation weather systems.

A dual polarization radar network allows for development of an icing hazards detection algorithm provided the underlying dual polarization data and derived hydrometeor classifications are of high fidelity. With radar data volumes available as frequently as just over every four minutes, icing detection by radar adds a temporal and spatial resolution advantage to current methods used for aviation. In situ icing verification is the reference standard regarding the fidelity of radar-derived icing information. Pilot reports (PIREPs) of icing are available but have inherent uncertainty. The FAA NEXRAD Program Office sponsored a LL partnership with the Canadian National Research Council (CNRC) for four, directed icing missions within the radar range of dual pol NEXRADs (Cleveland and Buffalo) during February 2012 and 2013. The CNRC Convair 580 is fully equipped for icing missions with a full suite of thermodynamic, cloud microphysical, particle imaging, and on-board radar (W-band and X-band) sensors. Data from these sensors are used to determine the fidelity of the NEXRAD dual pol data and hydrometeor classifications.

A variety of winter weather events were encountered during more than 10 hours of direct measurements including fully glaciated clouds with various ice crystal types, mixed-phase, and clear icing conditions. This paper will discuss the coordination of the icing missions, the discoveries during the missions, and recommendations regarding further development and improvement of NEXRAD hydrometeor classification and icing hazard algorithms.

This work was sponsored by the Federal Aviation Administration under Air Force Contract No. FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government.