High resolution measurement of ice-supercooled water cloud interfaces

Cloud, as a mix of ice particles and supercooled droplets, provides an environment for ice phase precipitation, charge separation, secondary ice production, and for chemical reactions related to enhanced concentration of accreting, freezing, and evaporating cloud droplets. Measurement of such an environment by aircraft penetration requires high resolution instruments to differentiate between the relative concentrations of water and ice on a variety of scales.

Results from NCAR C-130 flights in winter time mixed-phase clouds near the Great Lakes show discontinuities down to 1 second data, equivalent to about 130 m, consistent with earlier measurements using replication techniques in convective clouds. Mixed phase regions, encountered along the flights, present constant variations from ice to water and vice versa, with sharp discontinuities characterizing transitions. From the analysis at different temperatures, it is concluded that the detail of the interface regions between all ice and all supercooled water cloud provides information on regions having monotonically varying ice/water content ratios over distances shorter than 100 m. Instrument response is different depending on ice particle density and size. Information about the nature of the mixed phase region may be derived from the comparison of the measurements of two T probes, different in shape and size, to discriminate between cloud particles, aided with Cloudscope video images.

Knowledge regarding the origin of such mixed phase regions provides basic underpinning for characterization of mixed phase cloud particle interaction leading to different processes within the cloud, particle interaction with aircraft, and particle measurement instrumentation.