Simultaneous radar and aircraft observations of mixed-phase cloud at the 100m scale

Abstract

Three UK C-130 aircraft flights performed in conjunction with the Chilbolton Advanced Meteorological Radar were carried out in mixed-phase clouds. The aircraft instrumentation included the Small Ice Detector (SID) and Nevzorov probe that are both capable of discriminating between liquid and ice phase. It was found that particle sphericity measured by the SID could be successfully used as a proxy for particle phase. Using a combination of the SID and other probes it is possible to determine whether a 100 m cloud segment is ice, liquid or mixed-phase. Regions as short as 100 m exhibited mixed-phase characteristics. There was generally good agreement between water phase indicated by the SID and Nevzorov probes, with any differences arising from the fact that the SID provides a number-weighted estimate of dominant phase, while the Nevzorov probe provides a mass-weighted estimate. The radar and aircraft observations show that when high values of differential reflectivity are observed the nearby presence of liquid water is indicated. When large ice crystals are present in deeper cloud they can suppress the differential reflectivity signal. Therefore the absence of a high differential reflectivity signal does not necessarily mean that liquid water is absent.