Towards Understanding the Phase Composition of Mixed-Phase Clouds in High Latitudes using a Novel Airborne Technique for Discriminating Ice Crystals and Liquid Droplets
Final Report Abstract
Accurate identification of mixed-phase cloud phase composition is still a known challenge for the atmospheric measurement community. Especially, the current in-situ instrumentation are limited with their ability to detect the phase of the small (<100 µm) ice crystals, which are relevant to understand ice formation processes. Here we presented a new method to discriminate the phase of sub-700 µm cloud particles based on their angular light scattering behaviour. We used the Particle Habit Imaging and Polar Scattering (PHIPS) probe for simultaneous measurement of particle angular light scattering function and microscopic images and showed that the method can be used to reliably detect ice crystals even in conditions dominated by liquid droplets in number. The method was then applied in measurements of high-latitude mixed-phase clouds in two airborne campaigns in the Arctic and over the Souther Ocean. Ice crystal concentrations were derived down to 20 µm sizes and compared with model simulations. It was found that secondary ice processes are important over a wide temperature range in the summer time Southern Ocean clouds but not well captured by models. It should be also highlighted that the PHIPS probe is not originally designed for deployments in mixed-phase conditions and we found that a source of uncertainty in the derived ice crystal concentrations was present due to shattering of large ice crystals on the probe structures. It is suggested that an instrument re-design is conducted to reduce shattering artefacts for future deployments. The investigated phase discrimination method is well suitable to be applied in other single-particle instruments in the atmospheric measurement community or in other fields where sub-millimetre particles are generated or investigated.
Publications
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(2020). Structure of an atmospheric river over Australia and the Southern Ocean: II. Microphysical evolution. Journal of Geophysical Research: Atmospheres, 125(18), e2020JD032514
Finlon, J. A., Rauber, R. M., Wu, W., Zaremba, T. J., McFarquhar, G. M., Nesbitt, S. W., ... & DeMott, P. J.
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(2021). Observations and Modeling of Rime Splintering in Southern Ocean Cumuli. Journal of Geophysical Research: Atmospheres, 126(23), 1–18
Lasher-Trapp, S., Scott, E. L., Järvinen, E., Schnaiter, M., Waitz, F., DeMott, P. J., … Hill, T. C. J.
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(2021). Observations of clouds, aerosols, precipitation, and surface radiation over the southern ocean. Bulletin of the American Meteorological Society, 102(4), E894–E928
McFarquhar, G. M., Bretherton, C. S., Marchand, R., Protat, A., DeMott, P. J., Alexander, S. P., … McDonald, A.
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(2021). Phips-halo: The airborne particle habit imaging and polar scattering probe-part 3: Single-particle phase discrimination and particle size distribution based on the angular-scattering function. Atmospheric Measurement Techniques, 14(4), 3049–3070
Waitz, F., Schnaiter, M., Leisner, T., & Järvinen, E.
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In-situ Observation of Riming in Mixed- Phase Clouds using the PHIPS probe. Atmospheric Chemistry and Physics, 22, 7087–7103, 2022
Waitz, F., Schnaiter, M., Leisner, T., & Järvinen, E.
