Comparing Precipitation Particle Sizes and Phases from the Surface to Aloft during the In-Cloud Icing and Large-Drop Experiment (ICICLE)

Precipitation sizes and types can vary significantly throughout an airport’s terminal airspace and pose a sig-nificant threat to aircraft safety. When an aircraft encounters supercooled drops, ice can accrete on the critical surfaces of the plane, resulting in decreased performance. This can be particularly problematic on takeoff and landing when it can limit a pilot’s options for escaping the hazard and/or removing ice buildup. By establishing relationships between hydrometeor sizes with height above ground, it may be possible to improve the diagnosis and forecasting of icing conditions within the terminal area knowing the ground-based observations of particle sizes. In this study, in situ and ground-based measurements of particle phase and size are compared to explore their horizontal and vertical variations within the terminal area. In situ microphysical data from five flights conducted during the In-Cloud Icing and Large-Drop Experiment (ICICLE) were used for this study. Ground-based in situ measurements of hydrometeor size and phase were also collected at stations collocated with airports in the region. In the stratiform cloud cases analyzed, the ground observations of precipitation aligned extremely well with the trends of the particle sizes observed aloft. In the convective cases, however, particle size at the surface differed by as much as 1.5 mm when compared to trends of particle sizes measured aloft. The type of cloud was found to be relevant to the spatial variations in particle size and phase. The challenges associated with using ground-based measurements to discern possible aircraft icing aloft are discussed.