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The Small Ice Detector mark 2 (SID-2), which was built by the University of Hertfordshire, has been operated by the Met Office on the Facility for Atmospheric Airborne Research (FAAM) BAe-146 aircraft during a large number of flights. The flights covered a wide range of atmospheric conditions, including stratocumulus, altocumulus lenticularis, cirrus, and mixed-phase cumulus clouds, as well as clear-sky flights over the sea and over desert surfaces. SID-2 is a laser scattering device that provides in situ data on cloud particle concentration and size. SID-2 also provides the spatial light scattering data from individual particles to give some information on the particle shape. The advantage of SID-2 is that it can characterize the cloud particle shape for particle sizes less than the resolutions of the more usual commercially available ice crystal imaging probes. The particle shape characteristics enable, for example, small just-nucleated ice particles to be discriminated from supercooled water drops. SID-2 also has an open-path inlet that reduces shattering of large cloud particles compared to other probes that use a tube inlet.

The aim of this paper is to illustrate the capability of SID-2 to count, size, and determine cloud particle and aerosol shape. This is done by comparing the response of SID-2 to water drops, ice particles, and aerosols with that from other standard aircraft-based probes.