Comparison of Aircraft Observations to Assess Cloud Phase Conditions during the BAIRS II Campaign

MIT Lincoln Laboratory partnered with the National Research Council (NRC) of Canada and Environment and Climate Change Canada (ECCC) to collect aircraft observations for five icing missions during the second Buffalo Area Icing and Radar Study (BAIRS II) conducted between January-March 2017. The in situ observations serve to identify the presence or absence of an icing hazard and provide a valuable verification data set to validate next-generation versions of the NEXRAD dual-polarimetric Icing Hazard Levels (IHL) detection product.

The Convair-580 aircraft used during these flights was outfitted with several microphysical and optical array probes (OAPs) which in isolation reveal an incomplete depiction of the cloud phase environment encountered. The aircraft and some of the probes used in BAIRS II were also used and analyzed by Cober et al. (2001) in earlier icing field experiments to document the observed instrument responses within liquid, glaciated, and mixed phase cloud conditions. Built upon that effort, an automated rule set approach was developed to assess and assign the cloud phase into six categories (glaciated, mixed, liquid below 0°C, liquid above 0°C, clear, and unknown) along each BAIRS II flight track. The primary sensors used to determine phase include temperature, liquid and total water content from the Nevzorov probes, particle concentration from the 3-46 µm Forward Scattering Spectrometer probe, and crystal habit classification frequencies of spheres-needles-dendrites-irregulars (SNDI) generated by the SNDI algorithm (Korolev and Isaac, 2000) and derived from the two-dimensional cloud (2D-C) and precipitation imaging probe (PIP) OAPs. A visual inspection of the particle imagery from multiple OAPs and a cloud particle imager (CPI) was performed as a final step to validate the assigned phase, re-categorize ‘unknown’ phase classifications, and identify supercooled large drop (SLD) environments when drop sizes exceeded 100 µm with few or no observed ice crystals. Details of the methodology used to determine cloud phase will be discussed, and example segments of the aircraft observations leading to some of the designated phase categories are highlighted.

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This material is based upon work supported by the Federal Aviation Administration under Air Force Contract No. FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Federal Aviation Administration.