Abstract
Abstract. A major challenge for in situ observations in mixed-phase clouds remains the phase discrimination and sizing of cloud hydrometeors. In this work, we present a new method for determining the phase of individual cloud hydrometeors based on their angular-light-scattering behavior employed by the PHIPS (Particle Habit Imaging and Polar Scattering) airborne cloud probe. The phase discrimination algorithm is based on the difference of distinct features in the angular-scattering function of spherical and aspherical particles. The algorithm is calibrated and evaluated using a large data set gathered during two in situ aircraft campaigns in the Arctic and Southern Ocean. Comparison of the algorithm with manually classified particles showed that we can confidently discriminate between spherical and aspherical particles with a 98 % accuracy. Furthermore, we present a method for deriving particle size distributions based on single-particle angular-scattering data for particles in a size range from 100 µm ≤ D ≤ 700 µm and 20 µm ≤ D ≤ 700 µm for droplets and ice particles, respectively. The functionality of these methods is demonstrated in three representative case studies.
Highlights
Mixed-phase clouds, consisting of both supercooled liquid droplets and ice particles, play a major role in the life cycle of clouds and the radiative balance of the earth (e.g., Korolev et al, 2017)
Phase discrimination of individual cloud particles larger than 200 μm is based on circularity analysis of ice particle images measured by optical array probes such as the 2D-S and 2D-C or CIP (Cloud Imaging Probe, DMT, Longmont, CO, USA)
We have shown that phase discrimination based on single-particle angular-light-scattering behavior is a robust method, which could be implemented in future cloud research instrumentation
Summary
Mixed-phase clouds, consisting of both supercooled liquid droplets and ice particles, play a major role in the life cycle of clouds and the radiative balance of the earth (e.g., Korolev et al, 2017). Phase discrimination of individual cloud particles larger than 200 μm is based on circularity analysis (e.g., diameter or area ratio, Cober et al, 2001) of ice particle images measured by optical array probes such as the 2D-S and 2D-C (two-dimensional stereo probe and twodimensional cloud probe, SPEC Inc., Boulder, CO, USA) or CIP (Cloud Imaging Probe, DMT, Longmont, CO, USA). The Particle Habit Imaging and Polar Scattering probe (PHIPS) is a unique instrument designed to investigate the microphysical and light-scattering properties of cloud particles. It produces microscopic stereo images whilst simultaneously measuring the corresponding angular-scattering function from 18 to 170◦ for single particles in a size range from 50 μm ≤ D ≤ 700 μm and 20 μm ≤ D ≤ 700 μm for droplets and ice particles, respectively. The results will be compared to measurements by other cloud particle probes during the same campaigns
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