Characterising optical array particle imaging probes: implicationsfor small-ice-crystal observations

O'Shea, Sebastian; Crosier, Jonathan; Dorsey, James; Gallagher, Louis; Schledewitz, Waldemar; Bower, Keith; Schlenczek, Oliver; Borrmann, Stephan; Cotton, Richard; Westbrook, Christopher; Ulanowski, Zbigniew ORCID: https://orcid.org/0000-0003-4761-6980. 2021 Characterising optical array particle imaging probes: implicationsfor small-ice-crystal observations. Atmospheric Measurement Techniques, 14 (3). 1917-1939. https://doi.org/10.5194/amt-14-1917-2021

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Abstract/Summary

The cloud particle concentration, size, and shape data from optical array probes (OAPs) are routinely used to parameterise cloud properties and constrain remote sensing retrievals. This paper characterises the optical response of OAPs using a combination of modelling, laboratory, and field experiments. Significant uncertainties are found to exist with such probes for ice crystal measurements. We describe and test two independent methods to constrain a probe's sample volume that remove the most severely mis-sized particles: (1) greyscale image analysis and (2) co-location using stereoscopic imaging. These methods are tested using field measurements from three research flights in cirrus. For these cases, the new methodologies significantly improve agreement with a holographic imaging probe compared to conventional data-processing protocols, either removing or significantly reducing the concentration of small ice crystals (< 200 µm) in certain conditions. This work suggests that the observational evidence for a ubiquitous mode of small ice particles in ice clouds is likely due to a systematic instrument bias. Size distribution parameterisations based on OAP measurements need to be revisited using these improved methodologies.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.5194/amt-14-1917-2021
ISSN:	18671381
Date made live:	01 Sep 2020 08:01 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/528403

Item Type:

Publication - Article

Digital Object Identifier (DOI):

https://doi.org/10.5194/amt-14-1917-2021

ISSN:

18671381

Date made live:

01 Sep 2020 08:01 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/528403