This data set contains particle size distributions of spherical and aspherical cloud particles between 5 and 45 microns with a 10-second time resolution calculated from the Small Ice Detector Mark 3 (SID-3). The SID-3 detects individual cloud particles passing a 532 nm laser beam using two nested trigger detectors. The trigger signal is recorded as a histogram with a maximum rate of 11 kHz that can be used to derive particle size distributions by using the procedure described in Vochezer et al. (2016), doi:10.5194/amt-9-159-2016. For a sub-set of triggered particles a two-dimensional (2-D) scattering pattern is recorded that can be analysed for particle sphericity by a specifically developed image analysis software. Occasionally, coincidence sampling in the camera field of view causes optical distortions of the 2-D scattering patterns of liquid droplets and, consequently, a misclassification of such scattering patterns to be aspherical by the classification software. For the subsequent identification and re-classification of coincidence scattering patterns a machine learning (ML) algorithm was developed.
From the numbers of observed spherical and aspherical 2-D scattering patterns the fractions of spherical and aspherical particles are derived. Multiplication of those number-based fractions with the total particle size distribution yields phase-specific particle size distribution. The uncertainty due to the fact that the imaged particles are a subset of all sampled particles can be estimated from the Clopper–Pearson confidence limits. The data was collected during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign, which was conducted northwest of Svalbard (Norway) between May 23 and June 6, 2017. The measurement area comprises an area north of Svalbard, approximately between 78 and 82°N. The SID-3 instrument was installed in the Polar-6 aircraft during the ACLOUD campaign. The data is in NetCDF format and contains the total number concentration, the total particle size distribution, the total number of aspherical particles, the aspherical particle size distribution, the total number of spherical particles, the spherical particle size distribution and the upper and lower limits for the total aspherical and spherical particles and aspherical and spherical particle size distributions calculated using Clopper–Pearson confidence limits.
