Preprints
https://doi.org/10.5194/acp-2021-833
https://doi.org/10.5194/acp-2021-833

  05 Oct 2021

05 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

In-situ Observation of Riming in Mixed-Phase Clouds using the PHIPS probe

Fritz Waitz1, Martin Schnaiter1,2, Thomas Leisner1, and Emma Järvinen1 Fritz Waitz et al.
  • 1Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 2schnaiTEC GmbH, Bruchsal, Germany

Abstract. Mixed-phase clouds consist of both supercooled liquid water droplets and solid ice crystals. Despite having a significant impact on Earth‘s climate, mixed-phase clouds are poorly understood and not well represented in climate prediction models. One piece of the puzzle is understanding and parameterizing riming of mixed-phase cloud ice crystals, which is one of the main growth mechanisms of ice crystals via the accretion of small, supercooled droplets. Especially the extent of riming on ice crystals smaller than 500 μm is often overlooked in studies – mainly because observations are scarce. Here, we investigated riming in mixed-phase clouds during three airborne campaigns in the Arctic, the Southern Ocean and US east coast. Riming was observed from stereo-microscopic cloud particle images recorded with the Particle Habit Imaging and Polar Scattering (PHIPS) probe. We show that riming is most prevalent at temperatures around −7 °C, where, on average, 43 % of the investigated particles in a size range from 100 ≤ D ≤ 700 μm showed evidence of riming. We discuss the occurrence and properties of rimed ice particles and show correlation of the occurrence and the amount of riming with ambient meteorological parameters. We show that riming fraction increases with ice particle size (< 20 % for D ≤ 200 μm, 35–40 % for D ≥ 400 μm) and liquid water content (25 % for LWC ≤ 0.05 g m−3, up to 60 % for LWC = 0.5 g m−3). We investigate the ageing of rimed particles and the difference between "normal" and "epitaxial" riming based on a case study.

Fritz Waitz et al.

Status: open (until 16 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Fritz Waitz et al.

Fritz Waitz et al.

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Short summary
Riming i.e. the accretion of small droplets on the surface of ice particles via collision is one of the major uncertainties for the model prediction of mixed-phase clouds. We discuss the occurrence (up to 50 % of particles) and ageing of rimed ice particles and show correlation of the occurrence and the degree of riming with ambient meteorological parameters using data gathered by the Particle Habit Imaging and Polar Scattering (PHIPS) probe during three airborne in situ field campaigns.
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